valhalla · • a point load of 1.5kn applied in a 300mm square area. • a design gust speed of...

Gotham Farm, Chiselhampton, Oxford, OX44 7XGTel: +44 2039 410327

email: [email protected] web: www.kayam.com _______________________________________________________________________________

VALHALLA

1. INDEX2. STRUCTURAL SUMMARY27. METHOD STATEMENT53. STAKES AND ANCHORS

_______________________________________________________________________________Atticbest Limited, Company Reg No: 02894293 - VAT No: 765 0221 50

Tensile 1

STRUCTURAL SUMMARY

The following is extracted from the Tensile 1 Operations manual from thesection titled Tensile 1 Basis of Design and Operation by Stuart C Holdsworth at

Cameron Holdsworth Associates

Newton House, 3 The Avenue

Braintree, Essex

CM7 3HY

Tel: +44 (0) 1376 328961

Fax: +44 (0) 1376 553468

“ TENSILE 1” and “VALHALLA” are trading names referring to the same structure.

Tensile 1 Safety Manual:Part 1 MANAGEMENT MANUALGearhouse Structures +44 (0) 1932 570343

2Gearhouse Structure Edition 1 1999

1. FABRIC SPECIFICATION FOR ROOF

VALMEX 900 PVC coated fabric.

• Base fabric of high tenacity polyester.• PVC-coated on both sides.• Surface - high gloss lacquer.• Dirt repellent.• Easy to clean.• Dimensionally stable.• Resistant to cold.• Flame retardant.• Mildew inhibited.Technical data:Weight .................. .... approx. 900 g/sq. m (DIN 53352)Tensile strength ........... approx. 4000/4000 N/5cm (DIN 53354)Tear strength .............. approx. 600/600 N (DIN 53363)Adhesion ................... >100 N/5cmFlame retardancy ....... DIN 4102 B1

CSE-RF-1/75 Category 1 NFP 92507 M2

BS 5438 part 2a and 2bCold crack ............. -30 degrees Celsius (DIN 53361)Flexing strength ....... no cracking after at least 100,000 flexes (DIN 53359)Widths: (cm) .......... 1500The above data are averages from production. Product descriptions and suggestedand uses are general and subject to trial for the intended end use. Production issubject to change.



2. FABRIC SPECIFICATION FOR WALLS

VALMEX 700 PVC coated fabric.

• . Base fabric of high tenacity polyester.• PVC-coated on both sides.• Surface - high gloss lacquer.• . Dirt repellent.• Easy to clean.• Dimensionally stable.• Resistant to cold.• Flame retardant.• Mildew inhibited.Technical date:

Weight ................. approx 690 g/sq.m.Tensile strength ....... approx 320/300 dan/5cm (DIN 53354)Tear strength .......... approx 35/30 Dan (DIN 53363)Adhesion ............... approx 10 dan/5cmFlame retardancy ....... BS5867 TYPE B, ITALIAN CLASS 2

CLASSMENT M 2, DIN 4102 B1NFPA 701 small and large scale

Cold crack ............. -40 degrees Celsius (DIN 53361)Flexing strength ....... no cracking after at least100,000 flexes (DIN 53359)Widths: (cm) .......... various

The above data are averages from production. Product descriptions and suggestedand uses are general and subject to trial for the intended end use. Production issubject to change.



3. MEMBRANE STRUCTURES:

1.1.1 INTRODUCTION:

There are no British Standards1, written for Engineers, giving the requirements andbasis for the design of membrane structures. This is partially a reflection of the sizeand scale of the industry, its relative youth, and specialism. Relatively fewpermanent structures rely solely upon a membrane as the primary or sole means, ofproviding a structural covering. Conventional structures rely on internal rigidity tocarry loads and achieve the required stability. Membranes must rely upon their form,and prestress, to achieve the same balances in the absence of bending and shearstiffness.The following document is a synthesis of experience and best practice. It is notintended to be a final statement on best design practice, but a snap shot at thecurrent position in the evolution of this branch of design. The safe operation,maintenance and inspection procedures remain the province of the tent-master. Thefollowing document is meant as an aid to the certification process, and givesguidance as to the safe operating parameters.Definitions: a glossary of the more commonly used terms, and a description ofsome of the terms used to describe the various parameters, and parts of amembrane structure is appended at the rear of this section.

1.1.2 FUNDAMENTAL REQUIREMENTS.

The structure, including foundations and all components necessary to support thestructure, should be designed and constructed such that:

• They safely sustain all forces imposed upon them during erection and theperiod of intended use;

• Perform adequately in normal use throughout the design life;

• Use materials that have adequate durability; with regard to the erectionand dismantling, the intended use of the structure i.e. abrasion, etc., fireresistance i.e. will not readily support combustion, biological and chemicalattack and weathering.

• Have appropriate levels of safety with regard to the consequence offailure;

• Give occupants adequate means of escape, and, or incorporateparameters and an advanced warning and operating system sufficient toensure that those occupying or using the structure are not placed at unduerisk of injury;

1 DIN and ASTM codes are further developed than the current BSI codes in this regard.



• Incorporate a robust maintenance and inspection system on all thoseelements of the structure resisting loads during erection, use, dismantlingand transit so as to ensure they are safe to use.

1.1.3 DESIGN DOCUMENTATION.

The following list outlines the documentation required and included to validate thestructure.

• A general description of the characteristics of the structure, loadingpatterns and derivation, design life, operating parameters, including largedeflection behaviour and anisotropic material behaviour.

• Information on, and fundamentals of the methodology of shapefinding, theanalysis, computer programs and how to read the input and outputs fromthe programs used.

• Reports on fire testing and material properties.

• Shapefinding and analysis outputs.

• Calculations for cables, webbing, and supporting structure.

• Drawings showing the layout of the fabric panels, typical seams, interfaceswith cables, webbing and the supporting structure, typical clamping platedetails, foundation and staking requirements, and pretensioningrequirements.

1.1.4 OTHER DOCUMENTATION.

• Designers Risk Assessment for the erection and dismantling and typicaluse of the structure.

• Operator’s specific risk assessment and H&S policy plus public safetyrequirements and documentation specific to the venue.

The following will remain in the domain of the supplier and design team.• Detail fabrication drawings, fabric compensation, patterns, individual

fabrication drawings and clamping plates, cable and webbing patterns etc.and copyright.



4. DESIGN PARAMETERS, REQUIREMENTS ANDCHARACTERISTICS OF TENSILE 1.

1.1.5 DESIGN REQUIREMENTS.

The following is a synopsis of the design requirements of Tensile 1.• Design wind gust speed 50m/s upon permanent or special foundations.• Flexible layout configurations ranging from 45m x 45m to 75m x 150m in

15m increments for internal dimensions. External boundaries for the fabricare 5 metres offset from these dimensions, the guys being offset 12.5m.

• Provide a mounting for 30m truss carrying 20 tonnes of equipmentuniformly distributed.

• To be used for short periods at temporary venues, be readily erected anddismantled and transported or stored prior to use at other venues.

• Not to be used at venues at which snow or other large distributed (<0.2kN/m2) vertical loads can be expected.

• Utilise British standards as appropriate and design to UK operatingrequirements.

• Minimum basic foundation loads of 150kN/m2 as a working load, with theuse of appropriate spreaders where this performance requirement isexceeded or the soil conditions prove incapable of this loading.

• Design life. With effective maintenance, and a willingness to repair orreplace parts of the system as required, there is no need for a set limit asa design life. The maintenance requirements include the need to inspectthe structure whenever it is erected or dismantled and replace all itemseither damaged or seen to be failing. Temporary structures, althoughmore prone to damage arising from the handling, transit and erectionphases, are easily maintained at workshop level.

• Base design specified as an enclosed fabric walled structure.

1.1.6 LOADS.

The following loads have been utilised in assessing the performance of the structure.• BS 6399 Parts 1-3 for loads. Adapt for temporary use and short venue

times, i.e. Up to 14 days on a site.• Assume the internal operating temperature does not go below 12.5

degrees Celsius and that snow loads can be ignored as per BS 6661.• A maximum uniform loading of 0.2kN/m2 can be applied to the structure.

This will allow limited access for the purposes of repairing the structure.• A point load of 1.5kN applied in a 300mm square area.• A design gust speed of 50m/sec for the purposes of deriving the design

wind loads.



• Membrane dead loads are less than 50N/m2 and can be ignored2 for thepurposes of the design.

• Seismic loads can be readily resisted by membrane structures, as the lowmass of the membranes ensures that seismic resistance is an inherentcharacteristic of that form of structure.

• The curvature and pretension of the membrane are sufficient to preventponding.

1.1.7 THE APPLICATION OF WIND DESIGN CODES TO MEMBRANESTRUCTURES, OVERVIEW AND SUMMARY.

Commentary on British standard wind codes, etc.

Currently there are two wind codes in common use within the UK (1998). These areBS CP3 ChV Pt2 and BS6399 Part 2. This latter code is the current code and hasbeen published and cited to replace BS CP3.The two codes are notable for the difference in the design philosophy andcomplexity. The topic to which they address themselves is also complex, involvingbluff body aerodynamics, atmospheric energy transfer systems, equations of motionand frictional and turbulence effects to name but a few of the complexities.The approach is, as always, an amalgam of science and statistics. As the scienceand statistical base have moved on since the advent of CP3, BS 6399 reflects thisimprovement. The basic wind maps have changed, CP3 relying upon a 3 sec gustas the defining start point, BS 6399 the 1 hourly mean wind speed. Both have 50year observation modes.The codes noted above show an increase in accuracy, the newer code being moreaccurate than the former as it does allow for aeroelastic dynamic effects by checkingthat the structural design is valid, dynamic structures being outside of the scope ofthe code. Neither code was entirely designed with fabric structures in mind.Fabric structures locally may act aeroelastically . This is shown by the billowing orfluttering of small areas of fabric as it takes a new shape to gain local equilibriumwith the wind pressures to which it is exposed. This action lies outside of all currentwind codes and can only be accounted for in part by the analysis of the system usingcomputational modelling. As a small local phenon it has no effect on the overallstructure.The approach must therefore be to establish a site, or design wind speed and allowthe analysis to take care of the latter actions, knowing that the global behaviour ofthe structure is quasi-static and within the parameters set by the codes.Traditionally a global wind load and pressure has been used on fabric structures, thelocal pressure differences being considered to be redistributed by flutter. Thisapproach also required less computation, and is in part another reason for the highfactors of safety used.Tensile 1 was designed with reference to local pressure variation. An end sectionincorporating two middle sections was utilised as the basis for the model. The roofdesign was not compromised by only utilising a part model as all wind directions 2 BS6661 Design, construction and maintenance of single-skin air supported structures, and ASTMcodes



were considered, and coherency and accuracy tests were performed utilising themodel for the Kayam, comparing results for part and whole system models. Nodiscernible differences were noted from this exercise.Consideration has been given to erection loads, and failure modes or configurationsthat my lead to wind stagnation within the tent. A wind of 25m/sec giving a pressurecoefficient of approximately1.5 to 2 will not exceed the design loads for the specifiedsystem.

Other codes.

Equivalent static gust method, quasi-static assessment, time domain:Examples: UK, BS CP3 ChV Pt2, France NV65:1976, Australia AS

1170:1983Admittance method: quasi-static assessment, frequency domain:

Examples: Canada NRCC 17724:1980, Australia AS1170:1983, USAANSI A58.1:1982

Some wind data comparisons:

Location Sheffield.

Hourly-mean wind speed not exceeded for more than 50% of the time fromany direction. 4m/sAs above, but not exceeded 1% of the time 12m/s.Hourly-mean wind speed maximum 5o year return period, 23m/sMaximum gust speed not likely to be exceeded in a 50 year period 46m/s

1.1.8 WIND LOADS AND THE PERFORMANCE CHARACTERISTICS OFTENSILE 1.

The membrane design for Tensile 1 is designed for a very high gust speed of 50m/sec. The structure is characterised by the use of a hyperboloid3 support systemaround the Kingpoles, divided by some large areas incorporating flattish anticlastic4

panels. This shape is a function of the constraints placed upon the structure in orderthat it may be transported and erected readily, meeting the required layout criterionset by the client. The principals of this system have been proven in a series ofsmaller tents made prior to Tensile 1 5 such as the Kayam.Wind is the predominant loading on the membrane as designed. To resist the windloads, without excessive flutter, the membrane must have adequate curvature andpretension. These curving streamlined forms make the adoption of the wind codesloading formulae and requirements a problem. Wind tunnel testing can help definethe loads more accurately, but are incapable of modelling the large deformations,which off load the structure through a combination of shape changes and thealteration of the internal pressure caused by relatively large volumetric changes.The code clauses are a basis for design, but must be treated with caution and laced

3 Conic shapes.4 Saddle shapes.5 Kayam, this has a 15m module and has been built to 130m x 40m internal dimension. Fabricexternal boundaries are 5m outside of this.



with judgement derived from experience of the membrane and system underconsideration.At the design wind speed the membrane of Tensile 1 is exhibiting relatively largedeformations as modelled. These deformations have the effect of significantlychanging the gradient of the anticlastic surfaces, from those liable to cause a localsuction to those capable of causing a positive pressure. Clearly the system will findan equilibrium position between the two extremes, or potentially flutter betweenthem. The Kayam when modelled in the same program exhibits similar tendenciesto large deformations with the ability to change the pressure force vectors. Neitherthese deformations, nor flutter, have been visible when operating in strong winds.The loads for the Tensile 1 structure have been derived from the guidance given inBS 6399 Part 3. A simple model and a more complex load pattern have beenderived, assuming the load system is static and in equilibrium at the commencementof the gust striking the structure. No attempt has therefore been made to modelload vector changes resulting from the windflow altering with the geometric shapechange of the membrane.The non-linear response and changes in the load path are reflected in the model.This is liable to give a conservative estimate of the forces within the system, whichtend to be self-compensating in actual use. Traditionally a global wind force iscalculated and this is modified by a form factor C f, usually approximating to 0.7 orthat order. This is then applied to the whole structure and effectively allows for thisability to compensate and redistribute loads.Although membrane structures are for the most part excluded from the provisions ofthe code by their dynamic characteristics, the provisions of the code have beenproven to give conservative results in practice and have therefore been adopted as abasis for the design.

1.1.9 OTHER LOADS, INCLUDING IMPOSED LOADS, SNOW LOAD,EQUIPMENT LOADS.

The system is required to carry an imposed load of 0.2kN/m2. This load reflects abasic requirement for robustness, to ensure the system has sufficient capacity todeal with unforeseen climatic conditions, allow limited access in the event of, or needfor inspection or repair, and ensure that the design pretension is sufficient to cater forthese eventualities.This load is not the maximum the system is capable of resisting, but is a reasonablecompromise on the likely everyday loads the structure is liable to be exposed towhilst fulfilling its design function.Temporary structures, which are designed to be portable and easily erected, areoften limited by their ability to derive the required support from the stakes andanchors securing them. In many instances this practical limitation will set theeveryday operating parameters for the structure, long before the fabric or membersreach their limits. Special foundations and prepared sites will be required to achievethe higher specifications and structural limits.The structure has been checked to ensure that a concentrated load of 1.5kN iscapable of support. This simulates the action of a person walking on the tent.The structure has not been designed to resist snow loads. This reflects the realitiesof the hire market within which the tent is to be used. It is not a reflection on the



membrane’s ability to carry this load if required, although the Kingpoles are limited to0.2kN/m2 when carrying 20 tonne loads from equipment suspended from flyingtrusses on the balerings. With these loads removed there is a considerable ability tocarry higher vertical loads on the membranes. In reality many areas of themembrane are capable of shedding snow loads because of the smoothness of thematerial and the local gradient. Additionally the Tent master, responsible for the safeoperation and deployment of the structure, will clear the structure of snowaccumulations in the event of accidental exposure to snowloads, or dismantle thestructure when snow is forecast.Gearhouse Structures has specified equipment loads equivalent to a 20 tonne loadon a truss. These loads will be applied rarely, and can be considered as an extremecondition. This loading will not be a regular feature of the operation of the structure.

1.1.10 OBTAINING COHERENT FACTOR OF SAFETIES FOR THE STRUCTURE.

Tensile 1 is an amalgam of many parts, many of which have been fabricated ormanufactured to a British or Continental standard. Each set of standards has a setof safety factors built in. These safety factors may be made up in a variety of ways,but each global safety factor is met to incorporate the variables to which the systemor component is exposed.Examples of these variables are:

• Loads and load systems• Manufacturing tolerances• Material variations

• Accuracy of the analysis• Accuracy of installation, wear and tear, and the use to which the

component is exposed, etc.The present fashion, utilised by the recent British Standards and Eurocodes is to usepartial safety factors, each theoretically derived from a statistical probability analysis,to access the risk associated with each stage of the processes outlined above.Some of the older codes are not transparent, and the derivation of the FOS is notimmediately apparent, and may reflect use and custom rather than a detailed riskassessment. Additionally the use to which the component or material is exposed inthe operation of Tensile 1 may not reflect that for which it was originally designed.These requirements require factoring in if a coherent FOS is to be achieved in whichthe likely hood of the failure of a component is equal, and the public is guarded fromrisk of injury to the required standard.An additional complication to be added to the adjustment and formulae, is the natureof Tensile 1 and the requirements set by Gearhouse Structures for the design,namely portability and a very high design wind speedAn example of how the FOS may vary with correction for use can be illustrated byconsidering the load path from the anchors to the webbing belts and fabric.

• Anchor system, minimum testing FOS=2• Shackle FOS=5

• Cable FOS=7



• Chains FOS=5• Steel clamping plate and connection FOS�1.5

• Webbing FOS=7• Fabric FOS=6.

As considered by the National standards these theoretically, although not actuallyhave an equal probability of failing under the worst condition on which the standardconsiders them appropriate to use, a use for which they are not likely to be exposedin service on Tensile 1.Consider also that be replacing the shackle by a fabricated steel plate system theFOS could be reduced legitimately to around 1.5 and the need for appropriateadjustments becomes apparent. The adjustments are listed below in the followingsection.The public should not be exposed, or indeed the work force during much of theerection of the tent. Equally it would be inappropriate to allow public on the sitewhen winds were gusting above 20-25m/s as this is considered a dangerous level forhuman exposure. At 25m/s the FOS of wind loads become 4 times greater than at50m/s as the wind force is a function of the square of the wind speed. Thisrequirement when factored in sets an appropriate additional factor at times of publicuse.It is important that Tensile 1 is correctly and securely erected. Should large areas offabric be slack, maintenance poor, anchors insufficient, etc. then the marginsallowed as factors of safety will be severely eroded.

1.1.11 FACTOR OF SAFETY (FOS), MATERIALS AND LOADS.

The following series of tables gives the factors used in deriving ultimate loads or theFOS appropriate to a system or material. γm is the material partial safety factor: γl

loading partial safety factor. The combined factor γmγl is quoted below.• Steel structural members: γmγl as BS5950.6

Dead +Pretension

1.4DP

Imposed 1.6IDead &Pretension +imposed

1.4DP+1.6I

Wind 1.4WDead &Pretension +wind

1.4+1.4

Dead &Pretension +Imposed + wind

1.2DP+1.2I+ 1.2W

• Static Steel cables and other static cable and anchor systems: γmγl as below.Breaking strength ≥ 6 Except side poles.



Dead +Pretension

2.2DP

Dead &Pretension +Imposed thegreater of

1.6DP+2.7I or2.2DP+2.2I

Dead &Pretension +imposed + wind

2DP+2I+2W

Erection anddismantling

2 Min with nopersonnelexposed todanger5 otherwise.

Dead &Pretension +wind

2DP+2W

Shackles loadedcentrally and inaccordance withcode, static cablesystems

2DP+2W or Minof 2 on otherconditions.

• Webbing and polyester ropes, permanently fitted: γmγl as below.Breaking strength ≥.

Dead +Pretension

2.5DP

Dead &Pretension +Imposed thegreater of

1.6DP+2.7Ior2.5DP+2.5I

Dead &Pretension +imposed + wind

2.5DP+2.5I+ 2.5W


2E

Dead &Pretension +wind

2.5DP+2.5W



• Fabric and webbing reinforcement: γmγl as below.Breaking strength (Based upon mean uniaxial breaking strength). ≥.

Self weight +Pretension

4DP

SW + Pretension+ Imposed0.2kN/m2

4

SW + Pretension+ Wind 50m/sec

3


4

SW + Pretension+ 1.5kN pointloads

5

• Moving ropes and cables: γmγl

Breaking strength ≥.Erection only 5EAny static loadsystem

2.0 asreplaceablecables

Erection +pretensioning

2.2

• Webbing belt lines, detachable: γmγl

Breaking strength ≥.Erection only 5EOther loadsystems,minimum of

2.0 asreplaceablecables

Erection +pretensioning

2.2



1.1.12 LOAD PATTERNS.

The largest loads operating on a membrane structure usually originate from windinduced forces. The Tensile 1 structure is no exception. Positive pressure existsonly on the steeper sides of the cones, or hyperboloid surfaces. In these locationsuniformly distributed climatic loads will not remain on the surface. In other areas thewind induces suction forces which will remove any previous climatic system loadlikely to occur when the structure is utilised within the specified design parameters.On the basis of the above parameters the structure has been designed for thefollowing load combinations, and the worst combination taken for the purposes of thedesign.

Dead + PretensionDead + Pretension + Imposed truss loadsDead + Pretension + wind parallelDead + Pretension + wind orthogonalDead & Pretension + wind parallel + trussloadsDead & Pretension + wind orthogonal +truss loads

The membrane loads and system point loads were obtained by analysis in Easy7

with no additional factoring. All loads were factored utilising the appropriatecombinations identified from section 6 to achieve the relevant ultimate, loads orappropriate design factors of safety.Other load patterns investigated include point loads of 1.5kN to simulate accessrequirements in the field and investigations of loads occurring during the erectionand dismantling procedures.

1.1.13 OPERATING PARAMETERS.

There are two principal constraints on the operation of the Tensile 1 structure. Thefirst of these arises as a consequence of the chosen design parameters andspecification; the other as a consequence of the mobility of the structure. The firstconstraint is that arising from snow, or similar predominantly uniform gravitationalclimatic loads. As designed the structure is not to be utilised when these loads areto be expected. The system has a capability to carry these loads with certainrestrictions on the use of the internal truss system. However further analysis wouldbe required to verify the capabilities of the structure and derive the forces andanchoring requirements.

The second constraint arises from use of temporary foundations and stakes asanchoring systems. These will limit the capabilities of the system to below thedesign and material limits for the structure. To achieve the higher limits a permanentfoundation system is probably required.Summary of the operational constraints for Tensile 1.

7 Easy: - the membrane analysis software. See the section on analysis.



Vertical Imposed loads,still air conditions,uniformly distributed

Not greater than0.2kN/m2 i.e. 20kg/m2.

Snow loads None.

Public use or hire,maximum operationalwind speed.8

25 m/sec (50mph)

Maximum predictedsurvivable windspeed.Ideal conditions 9.

50m/sec (108mph)

Note: wind speed is that arising from the strongest gust. The survivable wind speedis based upon a need to utilise the structure after a severe storm. The truss systemshould be dropped close to the ground, and the membrane protected from damagearising from flying debris. The above quoted figures relate to the designated designsystem with sidewalls, double guys on sidewall poles, etc.

1.1.14 SIDE POLES.

The side poles of Tensile 1 are not a safety critical item for the tent. Failure of thepoles should not jeopardise the safety of the structure; providing it is being operatedwithin the prescribed design limits and the tent has been properly maintained anderected.The side poles have been designed on a modified basis to that which accords withthe principles of BS5950. Traditionally the poles are interwoven with the sidewallsof the tent. Every second pole then acts in bending from the applied wind loads.In the basic configuration Tensile 1 has side poles of between 6 to 8 metres inheight, spaced at 2.25m centres. Wind acting on the membrane off-loads thesidepoles, and would put them into direct tension if they are anchored downsufficiently well.Designing the poles for the wind induced bending moments would make the erectionof the tent and poles beyond the capabilities of a single person, and would requirethe use of machinery. As the poles are only functioning when the tent is subjectedto an applied down force; the design has been verified on that basis only.

8 A method of accurately forecasting and measuring site wind speed should be arranged.9 Ideal conditions, i.e. Un-damaged fabric, properly erected, guyed to stiff foundations and anchorscapable of taking the loads, and all of the structure in as new condition.



When subjected to wind loads the poles are assumed to fail. By placing the polesoutside of the sidewall on the windward side this failure mode would be averted. This

would be an option for the tent-master under more extreme wind conditions.For the axial loaded conditions the sidepoles comply with BS5950 in all regards withthe exception of slenderness.There are guys and storm guys on the line of the sidewalls at 1.125 metre centres.The number of potential side pole locations can be doubled if necessary. This facilitywill also enable the Tent-master to move internal side poles outside when required,or place additional external side poles on the windward side. By doubling thenumber of sidepoles the ability of the tent to resist vertical loads is enhanced.

1.1.15 MATERIAL PROPERTIES, ANISOTROPIC BEHAVIOUR

The material supplied for the membrane has been obtained with the manufacturerstest certificates and performance data. Additional tests have been undertaken toverify the manufacturer’s data, and to obtain information on the relevant data to usefor the purposes of setting the stiffness characteristics of the fabric in the computermodel, and also the stretch and compensation required during patterning. Furtherinformation on testing and the manufacturer’s test date follows in the section ontesting and the Appendix.The anisotropic material behaviour is illustrated in the following data.Typical valuesfor uniaxial test results for the Mehler material give mean warp strength of 80kN/m-width warp strength and 60kN/m width on the weft. Biaxial strengths of 67% of thesevalues could be expected. The steepest slope and highest peak value represent thewarp strength and stiffness, and the others in ascending order represent the resultsfor the warp and bias.



The material is said to exhibit anisotropy because it behaves differently across thetwo orthogonal axis, and yet differently again when strained across the bias. Thisbehaviour is a function of the fibre used to make the material, the yarn into which it isspun, and the manner in which it is woven. For typical membrane fabrics there aretwo common weaves. The first of these types include two different weaves; a plainweave in which the fabric is loosely woven to form a scrim, or a tighter weave whichthe yarns touch and form a cloth. Alternatively a fabric can be made in which theyarn is directly laid over the top of each other. The advantages and disadvantagesof the differing types of fabric can be summarised as follows:The reasons for the differing behaviour of the material across the warp and weft, theanisotropic behaviour, will now become more apparent, but first we need tounderstand some of the basic characteristics of fabrics and the manufacturingprocesses in which they are made.The long straight yarns of the plain weave are the warp yarns, the yarns interwovenbetween the warp yarns are the weft yarns 10. The warp yarns are usually placedunder considerable tension during the weaving process by the action of stretchingthem within the loom. The weft is crimped around the warp, adding to the thicknessof the material.

10 Some times called the fill yarns.



Type Advantages Disadvantages

Loosely wovenplain scrims:

High mechanical adhesion.High tear strength

Low tensile strength.Coating between the yarnopenings will be subjected toexcessive wear

Tightly wovenfabrics with plainweave.

High tensile strength.Easy to coat with liquid systems.

Only chemical adhesion is made.There is no mechanicaladhesion.Low tear strength.Three layer thickness.High filling strength.

Plain weave. Laidcloths.

Two layer thickness.Very high tear strengths.Excellent balance of tear and tensileproperties.Balance of mechanical andChemical adhesion.

Low elongation in both warp andfill.Poor interaction between warpand fill fabrics.

When tested under a uniaxial load parallel with the yarn, the predominantly straightand partially pretensioned warp yarns stretch. The weft has to firstly straighten out,or flatten, by attempting to crimp the warp. This straightening of the fibres before fulltensioning of the weft ensures that woven weft strains further under any given load.When tested across the bias the fabric coating predominantly takes the loads. Thisis not a recognised test, but can give some useful correlating data for estimating thecorrection of deflections when comparing cable net computer models with realmembrane fabric behaviour.When tested under biaxial loads the woven plain cloths will not reach the breakingloads that are achieved when tested uniaxially. The act of crimping by the weftagainst the warp causes cutting of the yarn fibres and damage to both the weft andwarp yarns. This then limits their strength by comparison with a uniaxial loading.Typically the strength is 67% of that obtained by testing the weft and warp strengthsuniaxially. A laid up fabric will behave differently to a woven fabric under biaxialloading. The crimping effect does no occur, and it is possible to balance the strengthin both directions of the cloth lay-up.Pretensioning before coating, varying the characteristics of the warp and weftmaterial, and altering the tightness of the weave can also be used to further modifythe material characteristics. It is also possible to alter the angle between warp andweft, or the lay-up of the plain weaves. It is not necessary to encompass thebehaviour of fabrics with these additional characteristics in this document.

1.1.16 MODELLING ANIOSTROPIC BEHAVIOUR.

The anisotropic behaviour of the fabric is modelled by giving the computer-input filesvalues for the angle between warp and weft, and also stiffness values for the warpand weft. The stiffness values were obtained from manufacturer’s data for thematerial, and by a series of tests on material samples that were used to calibrate thevalues used in the programme with those obtained by testing. Further samples wereused to verify the manufacturers testing data. The manufacturer supplied test datarelevant to the material that is in the appendix or included in the section on testing.



Additional tests were used to confirm the design requirements with regard topatterning and compensation.The graphs that are appended, and shown in the section on testing, summarise thecalibration exercise and prove the mean values for strength used in the design. Theimportant characteristics of the graphs include:

• The stiffness; or extension modulus of the fabric. This corresponds in effectto the Young’s modulus, or modulus of elasticity of the material.

• The manner in which the computer generated stiffness tracks the graph forthe tested material. Where the material has been repeatedly strained and ahysterisis has occurred after the initial set, it can be seen that the line derivedby analysis closely correlates to this condition. A mobile structure isconstantly erected and dismantled, and it is also subjected to cyclic climaticand environmental loading. Thus it will be subjected to repeated strainingand the material will stiffen as a consequence. The membrane has beenmodelled with this stiffening effect allowed for. Any permanent set can betaken out by adjusting the guys and by compensation allowances whenpatterning the fabric.

1.1.17 FIBRES AND COATINGS USED FOR TENSION FABRICS.

A Type number usually classifies architectural fabrics or materials used fortensioned fabric structures. Most fabrics are in the range of 1 to 4, the higherstrength material being given the higher number.Materials : Tensioned fabric structures can be constructed from yarns made from anumber of different materials. These include nylon, polyester, glass and aramids,with fibreglass and polyester being the most commonly used materials. Eachmaterial is characterised by different behaviour.

• Nylon: higher strength than polyester but lower extension modulus.Unstable when exposed to moisture. Degraded by exposure to Ultravioletlight.

• Polyester: Degraded by Ultraviolet light, lower tensile strength than nylon,but greater stiffness by virtue of a higher extension modulus. Can be morereadily protected from UV light than nylon by blocking coatings.

• Glass: high modulus of extension and tensile strength. Intolerant ofrepeated flexure by virtue of the relative brittleness of the fibres. Glassdoes not degrade when exposed to UV light. Unsuitable for temporarystructures. Needs handling with care.

• Aramids: Kevlar is the well-known example of an aramid fibre. Aramidsare an organic material that may have a very high tensile strength. Theyare more resistant than glass to repeated flexure, but not as good aspolyester. Aramids also degrade when exposed to UV light.

Coatings: The commonly used coatings for architectural fabrics are:• Polyvinylchloride: (PVC). Commonly used with nylon and polyester fabrics

PVC can be given most colours, is UV light resistant and pliable.• Polytetrafluoroethylene: (PTFE). This compound is chemically inert, stable

in normal environments, resistant to most forms of deterioration. It has



high strength and is flame resistant. PTFE is available in a white colouronly.

• Silicone: This has excellent UV resistance, flame resistance, high tensilestrength and modulus of elasticity. As with PTFE it is most commonlyused with glass fabrics to give long lasting and dimensionally stablefabrics.

Toppings: These are added onto the surface of a fabric to resist atmosphericpollutants, UV light and add give an additional ability to self-clean. The followingmaterials are commonly used for toppings.

• Polyvinylflouride (PVF): commonly used with bot PVC and PTFE coatingson polyester.

• Polyvinyl deneflouride (PVDF): used with polyester fabrics.• Urethane, again used with polyester based fabrics.• Acrylics: again used with polyester based fabrics



5. TESTING.

It can be seen from the foregoing that fabrics can have varying characteristicsaccording to their composition and weave or lay-up. Manufacturing processes canadd another level of variability. There are several test standards for materials. In theUK BS EN 22286 and BS 3424 are applicable. Parts of the test procedures in thisBritish Standard also conform to ISO 2286. The Mehler fabric also has DIN testingcertificates and ASTM ratings, which are given here.Mehler the manufacturer of the Tensile 1 membrane material supplied the followinginformation for the Type 2 material Valmex 900. The full size copies are appendedfor this and the Type 1 material Valmex 700.Testing to correlate the computer modelled behaviour against that of the realmaterial gave the simulations that are graphically outputted after the manufacturersdata. It will be noted that once the material has stiffened the relative stiffness of themodel and tested fabric relate closely in all but the direction of the bias, i.e. acrossthe warp and weft. As the fabric can load in this direction by combining actions in warp and weft,without lozenging as much as much as stated by the simulation at working fabricloads this offers a partial explanation as to difference between the predicted andactual behaviour of the tent in the field. The background information for this comesfrom visual observations on the Kayam when erected during winds that were gustingup to 90mph, (45m/s.) The following graphs, appended at A4 size, show thecalculated material behaviour versus that obtained by testing.



6. PATTERNING.

Patterning is the process by which the calculated surface geometry, stretch andprestress are integrated to give a manufactured membrane fabric form that acts asdesigned, and has the prescribed shape, stiffness, strength and prestress.Patterning also encompasses other elements such as the connecting members,webbing and cabling that need integration with the membrane to ensure that the totalsystem acts in the prescribed manner.Patterning is accomplished by breaking the three-dimensional surface geometry intoa series of strips that are related to the shape, cloth width and the orientation of theyarn. The individual elements form 2D surfaces that when placed together form a 3Dapproximation to the defined surface geometry.Allowances must be made for the stretch in the fabric, the formation of joints and thecut-outs required for clamps and cables and webbing.The patterns for Tensile 1 were developed on in-house software11.

11 Patterner by Bruno Postle in conjunction with RE design.



7. WEATHER AND OTHER ENVIRONMENTAL ACTIONS

1.1.18 RAINFALL:

A storm with an intensity of 50mm per hour of rain will deposit approximately 1.2m3

of water on the fabric of the 20-pole version of the tent in a minute. The water willrun-off from the valleys of the tent and will quickly cause local flooding, and affect theperformance of the stakes. Water running of from a height of several metres at agood velocity also has the ability to seriously erode loose soil. If a rainwater kit is notused then precautions should be taken to ensure that the run-off does not erode thesoil, and that it is discharged away from the tent and anchors through a temporarydrainage system.

1.1.19 SITE CLIMATOLOGY:

There may be a need to make a more accurate assessment of the local macro-climatic conditions to suit ventilation or more particularly a simplified erection system.Most countries have a design wind code from which an assessment of the tentperformance could be made. These are available through the BSI with an Englishtranslation. A series of graphical outputs from the analysis with loads from the keysystem points for differing wind speeds and directions would help with determiningthe correct configuration.Snow loads: the effect of these loads as against any revised design criterion willhave to be evaluated.Topographical features, structures or other influenecs liable to affect the windsimpinging on the structure of Tensile 1 should be assessed whenever possible. Sitewhere these features are likely to severly distabilise or accelereate the wind shouldbe avoided.

1.1.20 OPEN SIDED TENT WITHOUT SIDEPOLES AND SIDEWALLS, ETC;

It is probable that other configurations, other than those assumed in the initial designfor the tent, will be required. Should a structure or display be mounted within theTensile 1 tent, when erected in an open sided configuration, this may well cause acomplete change in the wind-loads that the tent is exposed to. It will then benecessary to:

• Re-access the tent wind loads• Re-run the membrane analysis, and re-evaluate the anchorage’s and

maximum wind exposure levels for the structure.

In particular the possibility of any internal structures acting as wind obstructions;shedding wind into the membrane needs to be considered.



1.1.21 UNUSUAL WEATHER.

The following weather systems or patterns are examples of weather systems thatmay be problematical.

• Ice accretion and snow systems particularly where the ice or snowsticks or adheres to the membrane.

• Micro-bursts and other severe wind turbulence with potential forhigh vertical wind components.

• Tornado’s, hurricanes, cyclones, typhoons and other strongcyclonic wind systems

• Thunderstorms and other severe storm cells.

1.1.22 SEISMIC DESIGN, AREAS OF VOLCANIC ACTIVITY, EARTHQUAKESETC;

There are many areas of the world where seismic and volcanic activity are a threat.Dust and storms associated with volcanic activity would mean that areas wherecurrent active volcanoes exist would need to be avoided. An active volcano isdefined in this case as a volcano likely, or liable to, deposit ash, noxious gases,pyroclastic flows, or floodwaters, etc., on the tent’s location.Membrane structures are inherently resistant to seismic activity because of the lowmass of the membrane and the ability resist dynamic loads. However the Kingpoleand truss system would need evaluating for this loading system.Seismic design for the tent under different configurations and seismic events couldbe undertaken either to the American or European codes.The load events would need to be evaluated according to location, or alternatively aunique set of data, similar to the 50m/sec. wind event, could be checked



1.1.23 ONE HOUR MEAN WIND SPEEDS EUROPE 50YR RETURN PERIOD

Tensile 1

Method Statement




Braintree, Essex

CM7 3HY

Tel: +44 (0) 1376 328961

Fax: +44 (0) 1376 553468


Tensile 1 Safety Manual:

Part 2 ERECTION MANUAL

Gearhouse Structures +44 (0) 1932 570343


1. ERECTION METHOD

2.1.1 Anchors and setting out:

In most cases all anchors and the correct setting out and marking will have beenundertaken prior to the arrival of the components to the site. This work will beundertaken by the setting out team (T1Prelim). For completeness the methods forsetting out have been added to this document.

2.1.2 Erection Procedure

The following section covers the erection of Tensile1. A previous version may bereferred to in the Tensile 1 Design and Operations Manual which was written byMr Rudi Enos.

There are seven major areas of concerns for those responsible for the erection ofTensile 1. . These are:

• The safety and welfare of all those working on the erection. Those notrequired, or who have no immediate need to be present, should not bewithin the safety zone, and those within the area should be trained,competent personnel who clearly understand the risks and dangers thatare involved. The safety zone should be clearly established, and markedon the ground. Only those authorised should be within this zone, and thisauthorisation should be clearly labelled by the displaying of a photographicpass appended to the clothing. PPE’s, as identified by the risk analysis,should be worn at all times.

• The use of the correct rigging equipment and procedures with correctlyrated and maintained equipment with valid certification.

• Ensuring that the system does not become overloaded and that all of themajor components are erected correctly and the loads remain within thestated design limits.

• The anchorage and stakes are correctly rated for the fitting and loads thatare liable to occur.

• When the roof is being raised, there is a period when the structure is not infull control, so high winds may require delays in hoisting.

• When the “A-frames” are being raised, the roof may be overloaded along ageodesic surface that has insufficient capacity and will tear.

• Pretension the membrane to ensure that the correct surface shape andprofile are obtained. This may require the use of the side poles to definethe membrane edge shape.





2. PROCEDURE AND CHECKS.

The following safety procedures should be followed during the erection of Tensile1.These procedures are based upon the usual green field site venue and may requireadaptation for special sites or the use of permanent foundations.

Pre-Erection Check. It is absolutely essential that this following check isundertaken prior to commencing erection and the placement of the anchor andstaking systems.

§ Has the site been investigated and all hazards reported and marked. Isthe site cleared for the safe use and erection of Tensile 1. Is all of therelevant paper work in place and hazards marked, enclosed by barriers orthe correct warning signs.

§ Weather information check for significant risks from winds etc. Do notconsider erecting the fabric when winds in excess of 10m/s are forecast.Met Office http://www.met-office.gov.uk , 0336 411 211 international info,0374 555 876 or 0374 555 828 for UK info.

The erection of Tensile 1 cannot take place until the Operations Manager has thisinformation and the Erection Manager has sighted this documentation and signed tostate that he is familiar and appraised of all of the risks associated with the chosenlocation. The wind speed should be constantly monitored using portable and siteanemometers.

Erection. Stage 1 kingpoles, headtrees and electrical assemblies. ResponsibleOfficers are the Operations Manager and the Erection Manager

Significant risks:

The following are considered significant risks:

§ Unauthorised personnel within the safety zone.

§ Unqualified or inexperienced staff and personnel.

§ Incorrectly rated rigging or incorrectly rigged assemblies.

§ The use of damaged or derated equipment.

§ Anchors or stakes incapable of carrying the correct loads.

§ Anchors or stakes coming loose.

§ Rigging and running lines failing or becoming trapped.

§ Lifting Motors failing or the brakes failing.

§ Falling rigging and kingpoles.

§ Electrical short-circuits or shocks to personnel.





§ Weather changes, or changes in the ground stratum caused by changes inthe weather.

§ Accidents involving mechanical plant.

These risks are covered by risk analysis statements. Personnel working within thesafety zone should be fully briefed on the risks and the control methods.

Plant required;

The following plant are required:

§ All terrain forklift.

§ Screw Anchor Driving plant

§ Stake driving plant.

§ Anchor testing plant.

§ Tirfors, pulllifts, electrical winches.

§ Hammers

§ All terrain lifts.

The following outlines the procedures for the erection of Tensile 1kingpoles.

Item Description Checkedby/time date

1 Establish and cordon of the safety zone. Check and identifythe credentials of all the personnel involved and issue thecorrect permits, ID’s and PPE’s. Allocate roles andresponsibilities to the relevant personnel and ensure that allpersonnel are familiar with the chain of command, procedures,facilities and layout of the site, and any hazards of risksparticular to the site.

2 § Identify the marking out, and load the correct equipmentinto the areas.

3 § Place and position stakes and anchors as required for thelocation and the site.






4 § Place the kingpole bases and balerings, plus the kingpoleunits into location and attach to the adjoining sections.Stake the bases into location. Connect the rigging. A set oftemporary diagonal guys will be needed to support each setof poles until the final set are raised. Undertake a thoroughinspection of the components and layout1. Check that the80 metre lifting cable is connected to the 28 metreconnecting cable.

5 § Place and connect the Headtree as per the drawing,ensuring that the rigging and motors are correctly supportedand placed.

6 § Recheck the rigging for snagging and then identify andcheck that all the correctly rated rigging is in the requiredlocation. Check that spacers are in place as required onthe shackles.

7 § Place all of the required electrical equipment andaccessories after all of the traffic and tracking by plant inthe area has been completed.

8 § Place the lifting frames onto the kingpoles and rig as perthe assembly drawings

9 § Recheck the anchorages and electrical accessories.Obtain the permission of the responsible Electrician that allis in order to proceed with the lift.

10 § Recheck the anchorages and electrical accessories.Obtain the permission of the responsible Electrician that allis in order to proceed with the lift.

11 § Tension the system, check all fittings and running lines.

12 Lift the kingpole clear of the ground and place on the support.

13 § Dress the top of the kingpole with the flag-staff and thefabric covering system.

1 Drawings 278 and 281






14 § Do a final check on the rigging and running lines prior tolifting to the kingpoles of the supports. Place a man on everyback anchor position to check for movement. When all isready continue the lift. When the poles are nearly verticalincrementally inch to the plumb vertical position. The poles areliable to sway until the securing guys are tensioned and need to be watchedclosely. Poles may be lifted as a synchronised set, or in short lifts as pairs,maintaining a balance in the connecting guys.

15 § As soon as the King Poles have been hinged vertically theyshould be checked for 'plumb' in both planes and then madesecure to avoid any possible danger.

16 § Remove the lifting frame.

17 § Utilising the anchored kingpoles as the lifting frame, repeatthe relevant procedure for the remaining kingpoles on theopposite side of the tent. When almost vertical, lateral instability atthe head will also occur with these kingpoles and again care isneeded until tensioned guys secure them.

18 § Check that the rigging and anchors are all secure, makingfast with the chains and shorteners.

19 § Place and connect the balerings.2 Check all lifting fittingsare free to move as required and correctly attached withspacers as required.

20 § Clear the centre of the structure within the area of the roofof any tools, materials or items that may damage or puncturethe fabric.

Erection Stage 2, the roof fabric stage. Responsible officers the OperationsManager and the Erection Manager.

Significant risks:






2 Drawing 276







§ Rigging and running lines failing or becoming trapped.

§ Lifting Motors failing or the brakes failing.

§ Falling rigging and kingpoles.

§ Electrical short-circuits or shocks to personnel.

§ Weather changes, particularly wind increases that will endanger thepartially erected structure, or changes in the ground stratum caused bychanges in the weather. Obtain a three day forecast from the Met OfficeWeather Centre

§ Damage to hands from handling the sheeting, particularly when soaked.


§ Personnel climbing the kingpoles or fabric and falling.


The following outlines the procedures for the erection of Tensile 1roof fabric. Themethod is written assuming a level site. Adjustment in the levels and angles givenwill be required to allow for sites with undulating or sloping surfaces. It is usual onan evenly sloping surface for the tent to be erected at right angles to the surface(assuming slope angles less than 10 degrees). For undulating surfaces a commonlevel is given for the top of the kingpoles and all other items referenced to this.






21 Layout and place the “A Frames” into the correct locations 3.The lifting points are to face in towards the centre of the tentand be placed upon a stand to avoid damaging the fabric.Attach lifting lines to the top of the “A Frames” and attach to theanchors with tirfors or winches.

22 Ensure that all side guy anchors are in place as per drawing313.

23 Place the sheet pallets into the correct locations and unloadthe sheets4.

24 Attach sheets to the neighbour using the correct pins.

25 Attach belts to balering, and sheets to belts and balering withcorrect pins and fittings.

26 Attach the webbing and fabric as required to the “A Frames”.This operation may wait until the fabric has been initially liftedby the balering if necessary.

• Attach the rainflaps and waterproofing system.

27 It is essential that the roof is secured to the King Poles at thelifting points with the fastenings provided.

28 Attach side guys to anchors and belting lines to anchors.

29 Before raising the roof all lifting gear must be checked toensure that it is in a sound condition and securelyattached. If it is excessively windy or there are problemswith soft ground conditions then the erection of the unitshould not be attempted.

3 See drawing 275, 281 and 3134 Drawing 281






30 § Before any attempt is made to lift the structure checkthat all of the main guy’s, pins and stakes are secure.

§ No-one should stand beneath the roof until the liftinggear and the main structure has been secured

§ During lifting, the roof must be kept fairly level at alltimes, and regular checks should be made to ensurethat nothing is caught or snagging.

§ Additional brace webbing’s must be used during windyconditions.

§ Update the weather information for the next 72 hours

§ Use the side guys to control the membrane in a breeze.

31 Commence the lifting of the fabric roof by lifting the balerings toa level approximately 4 metres above the base of the kingpole.Note that when lifting the tent roof on the balerings, thebalerings must be maintained close to level at all times.

32 Starting on two opposite corners and working anti-clockwisecommence pulling the “A Frames” towards the vertical. Theinitial “A Frame” to be lifted approximately to a 60 degree angleto the horizontal initially, facing the centre of the tent. Watchfor geodesic lines running from the “A frame head” through thematerial and stop lifting when this occurs. Move onto to thenext frame in the anti clockwise direction and repeat, limitingthe lift when the geodesic line appears in the fabric.

33 In this manner both teams work around the tent until all of the “A Frames” have been lifted to the initial position set by theformation of a geodesic line through the fabric.

34 The teams then continue pulling the “A Frames” pass thevertical and into the final position at an angle approximately 70degrees to the horizontal.

35 Lift the centre fabric of the roof to a level approximately 14-16metres above the base of the kingpoles.

36 Adjust all of the “A Frames” and side-pole guys and ratchetthem into the required final position approximately 60 degreesto the vertical, facing away from the centre of the tent.






38 Lift the centre of the tent on the balerings to the final height ofapproximately 22metres above the base of the kingpoles.Dress out and tension the structure by pulling out the guys andadjusting the balering positions.

39 Clear the site of tools, check dressing out and adjust asnecessary.

40 Dead anchor the balering to the kingpoles to suit the dressingout.

Erection Stage 3, the walling stage. Responsible officers the Operations Managerand the Erection Manager.

Significant risks:








§ Side poles coming loose and dropping.

§ Tools falling.

§ Weather changes, particularly wind increases that will endanger thepartially erected structure, or changes in the ground stratum caused bychanges in the weather. Update the weather report.

§ Damage to hands from handling the sheeting, particularly when soaked.



The following outlines the procedures for the erection of Tensile 1wall fabric. Themethod is written assuming a level site. Adjustment in the levels and angles givenwill be required to allow for sites with undulating or sloping surfaces.






41 Place any trussing system within the confines of the tent anderect in accordance with the requisite method statement.

42 Identify and load out the side poles, organise this be area andset the required teams to work.

43 Using the teams erect the sidepoles from the lifting platformand stake at the base. Adjustable height sidepoles will berequired for undulating surfaces, or alternatively the sidepoleswill need to be angled to suit the variations in surface level.

Ensure that the head of the side poles is correctly fitted.

44 Adjust the dressing out of the tent and reset the kingploebalering dead anchors.

45 Identify and locate the correct locations for door, emergencyexits and sidewall panel locations.

46 Starting on the windward side, place the wall, door and side-panels into location, working from the lift as required. Thiswork may be split into sections with teams as previously noted.

47 Ensure that the base of the walls and head are correctlyanchored, and that adjoining sheets are fitted correctly.

48 Check that all is in order, the Erection Manager can sign thetent over to the Production manger and T1 Safety Crew.

This assumes that any flying truss members that are requiredare in situ as required and tested as necessary.





3. ADDITIONAL ERECTION INFORMATION

2.1.3 Section one - Marking out

The marking out for tensile one will usually be undertaken prior to the arrival of theerection team on site. The marking out team of two will usually require the site plan,position of the tent and orientation.

The team will usually set out the structure from a co-ordinated grid system utilising adifferential GPS system, marking out the various structural units with spray paint.

Once the position and orientation is established, this setting out and marking can beachieved by two men working a 12 hour day for two days. 32 large cans of paint, in 4colours are required and 40 ranging rods for a 16 poler.

Sidepole positions and guys are not usually marked, and have been excluded fromthis time analysis. However Sidepole corner locations, and the line running throughthe guy positions is, defined again by corner positions, is included in this.

The kingpole and “A Frame” base positions and orientations are marked with anoutline pattern,

Anchor locations are marked with a star centred on the required driving point.

A marking out grid will usually be given to the Erection Manager with the grid andreference points.

2.1.4 Anchors and stakes;

The anchor positions are marked on the ground utilising the ranging rods as a guideto the angle at which the anchors are to be driven (Chance Screw anchors).

An advance team will usually drive the anchors and principle stakes before the mainerection team arrives. Their work may overlap with the Erection Team at times.

All stakes through base plates will be driven after the arrival of the Erection Teamduring the setting up and assembly of the components. This work will commenceimmediately the baseplates are correctly installed into position.

PLEASE SEE SEPARATE DOCUMENT ”STAKES & ANCHORS”

2.1.5 Checking anchors guys and stakes

Never think that as you have checked the guys and that they are safe and do notneed checking again. Time taken to check and rechecking the guys and anchors isnever wasted.





A regular checking and recording system is required. It is recommended that this beundertaken by the T1 (Safety) staff and recorded in the site diary. The Operationsmanager is to implement the scheme and monitor the effectiveness.





4. ADDITIONAL INFORMATION (ERECTION).

2.1.6 Bearing pressures:

The following bearing pressure can be expected on the base plates as a result of theloading required.

Kingpoles;

Without staging and trussing the load will not exceed 40kN/m25 in normal serviceunless the membrane pretension is increased or a vertical load is applied to themembrane. (E.g. A uniform membrane load 0.2kN/m2 gives a baseplate pressure of320kN/m2)

A frames.

The “A Frames” only load as a consequence of the applied pretension. Therecommended pretension is 23.5kN. Base plate loads of the order of 10kN/m2 areprobable.

General Note on baseplate pressures.

Transient loads during the erection sequence may exceed these quoted figures.Sidepoles can carry up to 22.3kN6 under a uniform load of 0.2kN/m2 (13kN usualmax)

2.1.7 Connecting Kingpoles for Tensile 1.

Significant risks directly related to kingpole unit assembly:



§ The use of damaged slings when lifting, this will allow the kingpoles to fallif they should fail.

§ Trapped fingers, or damage sustained to hands by hitting them with thehammer whilst drifting in the pins.



Required plant and tools:

5 limit set by motor assemby used and recommended pretension as mid 1999.6 At webbing belt locations.





All terrain forklift.2 tonne SWL Slings2lb hammerLump hammer20mm rod to help with alignmentPinch barsSledge hammer

PPE’s

Safety or Rigger boots with steel caps, goggles, ear defenders, hard hat, Riggersgloves, tool pouch with tools on lanyards

The kingpoles consist of 4 principal components, and usually arrive partiallyassembled, as a top pole, bottom pole and adjustable base, and a baseplate.

The baseplates are placed and aligned on the prescribed spot, with the hinge lineparallel with the long axis of the tent (4 poles and above), and at right angles to theopposite kingpole in the tent. The kingpole units are then placed facing out from thecentre in the correct alignment.

The kingpole assemblies require joining at midheight at 4 separate locations. Thejoinis by means of a pin assembly. The kingpoles need to be laid out so that the axisof the holes is parallel to the ground. The kingpoles my require packing to adjust toheight and level, and a forklift to facilitate lifting.

To facilitate joining the units the kingpoles must be placed into alignment, and thenthe pins drifted gently through on one side so as to make a hinge assembly. Oncethis hinge has been made, the unit may be lifted utilising a forklift or levers so thatthe other pins can be gently drifted through to complete the connection.

The baseplate unit is aligned with the adjustable foot, and the securing pin andspacers, etc. drifted in using a sledgehammer as required. The complete unit ispinned together, and utilising the forklift placed in the correct final location over theprescribed baseplate point. The securing pins are then driven through thebaseplate.

Dress the kingpole with the required fittings, cables, dead anchors, etc.

2.1.8 Balering assembly

Significant risks directly related to the balering assembly:



§ The use of damaged slings when lifting, this will allow the balering units tofall if they should fail..





§ Trapped fingers, or damage sustained to hands by hitting them with thehammer whilst aligning the units.




All terrain forklift.2 tonne SWL Slings2lb hammer20mm rod to help with alignmentPinch bars

PPE’s


The balering is assembled in two halves around the base of the kingpole. The unitsshould be placed in location using the forklift. The pins through the base obstructaccess to the base area and make assembly difficult if they are insufficientlyembedded.

Place the units in contact and lever the units over each other so that the projectingtongues overlap in the required alignment. When aligned place the correct boltthrough the top plate, and repeat on the opposite side. Utilising the services of theforklift and slings as required lift the balering and support as necessary so as enablethe placing and tightening of the bottom bolts safely.

Tighten the top bolts and check the assembly. Dress the balering with the requiredshackles and fittings.

2.1.9 “A Frame” assembly

Significant risks directly related to the “A Frame” assembly:



§ The use of damaged slings and shackles when lifting, this will allow theunits to fall if the slings should fail..

§ Trapped fingers, or damage sustained to hands by hitting them with thehammer whilst drifting in the pins and bolts.








All terrain forklift.2 tonne SWL Slings2lb hammerLump hammer20mm rod to help with alignmentPinch bars

PPE’s


The “A Frames” are assembled from 3 main components. The base units (2#), areplaced in the prescribed location and in alignment with the tent

The forklift is then used to bring the leg units to the location and lay them on theground facing the centre of the tent and centred at right angles to a line through thebase units.

The legs are then parted until they are placed at the correct angle to allowconnection to the baseplates. Remove the baseplate pins, and adjust to allow thepins to be driven through the legs and baseplate to connect the units. Repeat for thesecond leg.

Realign the baseplate and frame into the correct location and pin to the groundutilising the 50mm pins driven through the baseplate holes formed for that purpose.

Dress with guys and shackles as required and lift onto the legs supports to allow thepositioning of the roof fabric.

2.1.10 Assembling and raising the truss sections.

Significant risks directly related to the “A Frame” assembly:



§ The use of damaged slings and shackles when lifting, this will allow theunits to fall if the slings should fail..

§ Trapped fingers, or damage sustained to hands by hitting them with thehammer whilst drifting in the pins and bolts.








All terrain forklift.2 tonne SWL Slings2lb hammerLump hammer20mm rod to help with alignmentPinch bars

PPE’s


SWL 20 tonnes evenly distributed, with a maximum node load of 1 tonne.

The truss units comprise of three primary units that unfold and pin together.

The units are laid flat in sequence and in the correct alignment. Utilising woodenpackers; to lift the units clear from the ground, and slinging the units from the forklift,pull the sections apart and connect utilising the attached members, to form theindividual sections.

When completed, align these sections and connect to the centre section, utilising thepin sections.

Hang from the lifting slings and align between the kingpoles.

Cross brace between the centre sections and ends of the truss, and tighten tomaintain the correct alignment.

Lift into location and dead anchor.

2.1.11 Section Seven - Dressing Out

The Tensile1 can now be 'dressed out' (pretensioned). A simple visual check is allthat is needed to ensure that the roof is pulled out in a regular manner. To check ifthe roof is 'regular', stand on looking along one axis (long or short), and look carefullydown the tent. The joins of the tent should be in line from one end of the tent to theother. With no wrinkling in the roof, or pulls or creases, (effectively, the roof is pulledout 'flat'), and the main seams are in line, the tent is correctly shaped. To achievethis balance it is necessary for the balering's on different king poles to be lifted to thesame height in respect of the roof membrane and each other.





2.1.12 Section Eight - Pretension

The roof can be correctly dressed but be insufficiently tensioned! It is necessary topretension the roof, prior to it being tensioned by wind loads. Unless the structure isnew and requires stretching, the roof should sit in it's intended shape without toomuch tension in the plane of the roof; therefore tension radially as well as down theseams. The rim must be taut, and this is achieved by adjusting the sideguys andadding a “radially tension” around the surface of the roof. To obtain the correctbalance of forces within the tent, and shape, it is possible that some adjustment ofthe balering positions will be required. The aggregate load on the balering resultingfrom the tensioning process is approximately 4.5tonnes.

2.1.13 Section Nine - Signing Off

Upon completion of the erection, and when the Erection Manager has completed allthe final inspections, Gearhouse Structures Ltd. Require the manager to sign thestructure off. Signatures should be appended on all of the required completionchecks. Upon receipt of the Production managers counter signature, the ErectionManager will hand over the day to day responsibility to the Production Manager andthe T1 Safety crew.

2.1.14 Dismantling the Tent:

Dismantling the tent is effectively a reverse of the erection process. The risksassociated with dismantling the tent are those associated with erection, and shouldbe referred to when briefing staff.

Summary;

• Remove truss and stage systems• Check inside for obstructions and debris, clear as necessary.

• Check the wind speeds and predicted weather for day• Dismantle sidewalls and doors and associated stakes• Check inside for obstructions and debris, clear as necessary.• Disconnect dead anchors on kingpoles• Lower balerings to approximately 16m above datum (Approximately 6m)• Remove tension from leeside sidewall guys, and remove every second guy

• Move leeward “A Frames” to vertical position by allowing them to pull back• Reduce tension on windward side side poles and “A Frames” as previously

noted. Only remove every second sidewall guy if the conditions permit this.• Lower balerings to approximately 12m above the ground.• Lower the A Frames into the centre of the tent in a reversal of the erection

sequence, taking care to avoid overstressing the fabric and fittings alonggeodesic lines as previously stated in the erection sequence.

• Lower balerings to ground.





• Remove guys to sidepoles, and all anchors liable to foul the fabric.• Remove the “A Frames” and fittings• Disconnect the fabric and roll this up.• Place the boxes into location and load.• Remove the kingpoles in a reversed operation to that of erection.• Remove all remaining anchors

• Check all equipment and pack for transport and storage.





5. ACTION IN HIGH WINDS AND OTHER ADVERSE CONDITIONS.

The following advise in given as an assistance to the Operations Manager andErection Manager. The experience of these two key personnel, and the crewresponsible to them, is crucial when dealing with these difficult conditions.

2.1.15 High Winds during erection and dismantling:

Maximum advised wind speed <10m/s (20mph) during erection anddismantling.

Tensile 1 should never be erected or dismantled in high winds. Long range (5 day),and 24hr weather forecasts should be accessed to ensure this does not occur.Should the erection team find themselves in the difficult position of erecting ordismantling the tent when high winds strike then the current advise is as follows.

Before starting any work ensure the team are aware of all current risks assessmentsfor the actions they will be undertaking.

Rule #1-never endanger life. Keep a cool head. Be aware!

There is likely to be more happening than can be easily assimilated. It is thereforeessential that the actions and processes necessary have been thought throughpreviously.

Before erecting kingpoles:

All groundwork can be completed in any comfortable wind environment. Where theitem has a large wind area, the comfortable handling of that item will set the limit.The anticipated limits are 20-24m/s and 14m/s respectively.

Whilst erecting kingpoles;

The current limits for erecting the kingpoles are 10m/s for side wind conditions, andfor winds acting along the length of the kingpole 20m/s. As the wind direction canvary quickly it is advised that the lower limit be adhered to. The side wind conditionis set in recognition of the sensitivity of the kingpole whist vertical and prior totensioning and adjusting guys.

In the event of wind speed exceeding these limits during erection the kingpolesshould be lowered if it is safe to do so. Otherwise stop the lift and guy tight intoposition.





Erecting the roof

The fabric roof should not be lifted in winds gusting above 10m/s. In the event thatthese conditions are exceeded whilst lifting, the roof should be immediately lowered,and the side pole guys utilised to stake the fabric tight if required. If the tent is almosterected, and is in the process of dressing out, then if safe to do so, finish theoperation and make tight, completing the operation of final dressing out when safe todo so.

Erecting sidewalls.

Sidewall placement is difficult when the wind speed exceeds 10m/s. It is importantthat the tent is fully configured with all sidewalls if the wind speed is likely to exceed30m/s. A partially configured tent may be a significant risk as the wind may stallunder the membrane and exceed the design loads.

If this condition occurs it is best to allow the side walls to stream in the wind andallow the clear passage of the wind.

2.1.16 High winds when erected

Tensile 1 has the following design and operating advisory limits:

Design wind Speed 50m/s

Limit for public use 25m/s

Survivable wind speed >35m/s

The term survivable wind speed has been used because it is the point at which thewind environment becomes very hostile for personnel. Wind born debris, fallingtrees and other hazards will become a significant risk. Personnel will have greatdifficulty in standing and functioning properly.

Tornado’s, micro bursts and vertical wind shears, katabatic winds and turbulentvortices are outside of the performance envelope of Tensile 1 and will causepremature failure of the structure. Areas in which these winds will occur should beavoided, or alternatively special precautions put in place which are outside of theserecommendations.

A properly anchored, fully maintained, correctly constructed Tensile 1will withstand a50m/sec-wind speed under absolutely ideal conditions. In practice the structure willrarely function at these levels of efficiency. The wind environment will not be clean,as there will be large amounts of wind blown debris in evidence. This debris willdamage and weaken the fabric such that it will fail long before the design limit hasbeen reached.

Providing all openings are secure, the sidewalls in place, and the tent properlydressed and anchored, the tent will withstand extreme winds. The practicable limitfor the safety of personnel must be around 35m/sec. Flying debris may well place a





actual limit well below this. Therefore the recommended method for dealing withforecast high winds, to ensure crew safety, and in absence of further data must beas follows:

v Whenever possible, lower the tent and strap down the fabric so that thewind will pass over the fabric.

v In all cases the Operations Manager is to appoint a Safety Officer responsiblefor deciding the safe limit for crew operations. (The Operations Manager(T1OM) or Erection Manager (T1EM) may act as the Safety Officer, or appointanother competent person as required )

v Have an agreed place of safety for crew.

v Have an agreed communication signal and method that can be heard or seenby the crew and will inform them of the immediate need to recover to theplace of safety.

v Evacuate all members of the public, and advise other Event functions downwind of any potential dangers.

v Check for upwind hazards and monitor as necessary.v Have members with radio communications call regularly and advise the

Safety officer of the local conditions.v Secure the tent and anchors and make the structure as weather tight as

practicable.

v Monitor the performance of the structure as the wind speeds increase. Logwind speeds and video the performance of the structure if possible.

v Whilst safe to do so, supplement anchors and repair damage.v Avoid placing the crew in danger. Do not work on the membrane or inside

when the structure starts to load significantly, flutter or behave in an unsafemanner.

v Ensure the Safety Officer is aware of all crew actions and clears them beforecommencing the work.

v NEVER RISK LIVES, LIMBS, OR THE SAFETY OF THE CREW OR THEPUBLIC.

v IF SAFETY IS IN DOUBT, DO NOT ATTEMPT THE COURSE OF ACTIONTHAT WILL IMPERIL THE INDIVIDUAL OR CREW.

v Ensure that the crew roster is available to check that all crew members aresafe.

v Where and when the structure of Tensile1 poses a risk to others at an Event,the Safety Officer is to keep them fully informed and appraised of the risks sothat they may act accordingly and ensure the safety of their own personnel.

v Keep contemporary records, record all actions, times and warnings in theHazard log and diary.

The dangers to be aware of are:

• Anchors and fittings pulling because of the movement of the fabric.





• Debris flying into a damaging the fabric. This may lead to a total failure of asheet. Sheet failure may cause a large increase in the internal pressure asthe wind “stalls” within the tent. This in turn may lead to total failure.

It is probable that the Tensile 1may be used as a shelter without side walls. On itsown the units can in all probability resist loads of up to 35m/s, although this has notbeen confirmed structurally.

However, event units within the membrane diverting or stalling the wind willsignificantly reduce this figure. This configuration should therefore only be used invery sheltered locations where winds below 15m/s can be expected at ground level.

2.1.17 Snow, Rain and other loads.

Minimum internal temperature 12.5°°C in freezing or snow conditions .

The membrane has not been designed to withstand snow loads. Properlyconfigured, a uniform membrane load of 0.2kn/m2 can be resisted. This is roughlyequivalent to 200mm of fresh uncompacted snow. Snow must never be allowed toaccumulate on the membrane, either by ensuring that the membrane is heated orcleared manually where this does not expose the operatives to risk.

Rain is unlikely to overload the tent unless this is allowed to pond. Ponding can onlyoccur when the fabric is loose, or misshapen, and subjected to a heavy deluge.

The only other significant vertical load likely to affect the membrane is wind blownsands or volcanic ashes. These should be immediately cleared if safe to do so.

Always evacuate the tent if any of the conditions described is or is liable to occur.Only send personnel onto the roof if it is safe to do so, when panels are notliable to rip or fittings fail, and when no other course of action is possible. Tryclearing the membrane with hot air pumped inside, or jetted water in the case of dustloads.

The Operations Manager is to appoint a Safety officer and implement therecommendations above for as for high winds.

Do not endanger life, failure of the tent is preferable.2.1.18 Maintenance requirements and the affect upon performance

Basic maintenance should include a wash down with warm soapy water to keep thestructure clean. The fabric should then be stored when dry.

Inspection, when ever the structure is erected or dismantled should include checkson the fabric for tears and holes, fraying of webbing systems, pulled or damagedbolts, pins and fittings, checks on wire rope assemblies, mechanical parts and thecertification of the same.

Premature failure of any one component will jeopardise the performance of thestructure. The exact change in performance will vary with the type of failure and can





not be readily predicted. An unexpected failure will always pose a major threat to thesafety and wellbeing of those working or utilising the tent.

The tear strength of a damaged fabric is a fraction (<20% typical) of the intact fabric.The actual consequence of a hole or tear will vary with the position and likely loadingof the fabric. Many areas are more highly stressed than others and can be shown ona stress diagram. The tent is also heavily reinforced with webbing systems, and ifthese are fully bonded to the fabric substrate these will reduce the effects of anydamage by limiting the run of the tear and carrying the load.

Repairing large tears or rips by sending personnel onto the erected fabric isnot safe. The structure should be lowered and repaired.

2.1.19 Difficult Sites and non-standard configurations.

Difficult sites and non-standard erection configurations will be dealt with by referral tothe design team and specialists. This work will be controlled through the office of theOperations Manager.

The results of the studies will be disseminated by the operations Manager to therequisite field managers and a thorough briefing document prepared with therequired risk analysis and data.





6. GLOSSARY

neck or necks Tapered top part of a tent section

section The large fabric assemblies that form a tent

panels The individual pieces of fabric that when seamed, form asection

bale ring The lifting ring(s) used to hoist the fabric of a tent. After thering used to hoist sails on ships.

Guy Tie back or mast stabilising rope, cable or webbing.

king pole The main or central poles or a tent or membrane.

horseshoe The 'U' shaped brackets used to fasten the fabric to the bale.

Tensile 1

STAKES & ANCHORS.




Braintree, Essex

CM7 3HY

Tel: +44 (0) 1376 328961

Fax: +44 (0) 1376 553468




1. STAKES AND ANCHORS

The tent is totally dependent upon the stakes and ground anchors for stability.Therefore the stakes and anchors capabilities should always be proven using sitetests, or from the tent-masters previous knowledge of the soil and site conditions.

There are many types of stakes and ground anchors available. In addition,manufacturers such as A. B. Chance make systems for this type of temporarystructure1. The following data and information has been compiled using data andresearch undertaken by Ovesen and Stromann (1972) for computing the ultimateresistance of ground anchors in sand; and by Mackenzie (1955) and Tschebotarioff(1973) in cohesive materials. For comparison, other work by Broms (1964) has beenincluded at the rear of this section.

Position SWL Degreesto Horiz.

Side pole (webbing belt) 105kN 45°Side pole (normal) 23.0kN 45°Side pole guy (webbing belt) 148.0kN 45°Side pole guy (normal) 27.5kN 45°End Outer Tie downs 107.0kN 43°Mid Outer Tie downs 308.0kN 62°End Inner Tie downs 135.5kN 46°A frames 123.5kN 45°

Anchor loads at 50m/s wind speed

Two types of stake have been considered in this guide, and one pullout anchor. Thestakes are a pin of 50mm nominal diameter with an embedded length of 1.37m, anda 175mm wide beam of 3 metres embedment. These are similar to the systemscurrently used on the Kayam, and have been used successfully for a number ofyears. The values given below in the graphs represent an anchor loaded at thecentre of area in the ground. For stakes loaded at the top, parallel with the groundsurface, these loads should be halved (1/2) where the soil acts plastically as itdeforms, or if failure occurs at the point the soil mass reaches the elastic criticalstress, by one third (1/3). As the load on the stakes is usually inclined from theground contour to give a vertical component the later value of 1/3 is probably moreappropriate

1 See manual 2 for further information on these types of anchor.



Location of points described in the text.



20

40

60

15 17

15 17

20

40

60

φ=45°φ=40°φ=35°φ=30°φ=25°

SWL KN for50mm stake embedded1370mm in thesoil.Dry soil conditions.

Soil Density γ dense angulargravelly silty sand.

DensesandLoose sand

Above is the output graph for a nominal 50mm width stake embedded1370mm in drygranular material.

For a material with a dry density of 16.5 kN/m3 (γ) and an angle of shearingresistance (φ) of 35 degrees a SWL (Safe working load) of 28kN can be estimatedfrom the graph. This value corresponds to the SWL for the stake loaded at thecentre of soil area. To allow for the load being applied to the top of the stake thisSWL should be further reduced to between 14 and 10kN. The choice is dependentupon the soil characteristics, the angle to the ground contour line at which the stakeis placed, and the line in which the load action occurs. For most applications thelower value is appropriate.

The largest concentrated load at a system point on Tensile 1 is of the order of 300kNwhen using guyed sidewalls. Using a system of stakes based upon the 175mm wideunits embedded in a soil with the same characteristics as the previous example, andassuming the spacing was sufficient to prevent them interacting, then each stakewould give a SWL of 305kN/3=102kN. For a 300kN load a system of 3 stakeswould be required.

Staking in saturated granular material is not to be recommended. Using formulaedeveloped from the previous estimates the graphs in the appendices give anestimate of the SWL that can be expected. Alternatively a known value for γsat andφsat can be used to look up values on the graphs for a dry material to gain anestimate of the SWL. For most cases no reasonable capacity can be expected.Only extremely dense material with a high angle of friction gives a consistent, butlow, pullout load. Permanent or tested foundations must be used where theseconditions are liable to occur.



To estimate φ for granular soils the following table proposed by Terzaghi and Peckmay be used.

Round grainsuniform.

Angular grainswell graded.

Silty sands. Sandy gravels. Inorganic silts.

Loose 27.5 33 27-33 35 27-30

Dense 34 45 30-34 50 30-35

When saturated the angle of φ should be reduced by 2 degrees from the abovefigures.

The following graph relates the SPT (standard penetration values) on the vertical

0

20

40

60

30 35 40

30 35 40very denseDenseMedium denseLooseVery

Loose

scale, to the angle of shearing resistance φ for granular soils.

SPT versus angle of shearing resistance φφ .



The following table after Das et al gives typical moisture contents and dry-unitweights for some soils.

Type of soil

Void ratioe

Naturalmoisture

content insaturatedcondition

(%)

Dry unitweightkN/m3

γγd

SaturatedweightkN/m3

γγsat

Loose uniform sand 0.8 30 14.5 Down to 9

Dense uniform sand 0.45 16 18 9 to 12

Loose angular-grained silty sand 0.65 25 16 9 to 12.5

Dense angular grained silty sand 0.4 15 19 10-13

Stiff clay 0.6 21 17 9 to 13.5

Soft clay 0.9-1.4 30-50 11.5-14.5 6.5 to 9.5

Loess 0.9 25 13.5 6 to 9

Soft organic clay 2.5-3.2 90-120 6-8 0.5 to 4

Glacial till 0.3 10 21 10 to 13.5



2. STAKES AND ANCHORS IN CLAY SOILS:

The following table gives the values for undrained shear strength for some commonUK clays with their description. The clays found at or near the surface

DescriptionUndrainedshear2

strength(kN/m2)

Hard boulder clays, hard fissured clays (e.g. deeper London and GaultClays)

>300

Very stiff boulder clay, very stiff “blue” London Clay 150-300Stiff fissured clays (e.g. stiff “blue” and brown London Clay), weatheredboulder clay.

75-150

Firm normally consolidated clays (at depth), fluvio-glacial and lake clays,upper weathered “brown” London Clay.

40-75

Soft normally consolidated alluvial clays (e.g. marine, river and estuarineclays.)

20-40

Guy loads and tie-downs @ wind speed of 50m/sec (unfactored kN).

2 Can be used as value for cohesion c. where φ=0, (s=c+σtanφ)



0

50

100

150

200

25 50 75 100

25 50 75 100

0

50

100

150

200SWl kN for 175mm widestake embedded 3 met resloaded atcentreof area incohesive materials.

stif f claysFirm claysShear st rength kN/m2.Soft clays

The following graph gives the equivalent resistance for a 175mm wide stakeembedded in a cohesive soil 3 metres with �=0. The following is an example of itsuse. To resist a 300kN load, when the load is applied at the top of the stake, in afirm clay c=100kN/m2 will require 300x3/180 stakes: i.e. Load to be resisted x factorfor loading at top (Between 2 and 3)/ value from graph at c=100kN/m2, i.e. 5 stakes.When dealing with soils that exhibit cohesion and an angle of shearing resistance,the so-called c φφ soils, in the absence of test results, the SWL may be estimated fromthe values for granular soils.The following table gives a field test as to the consistency of clays. It is given as aguide only and may need to be reassessed for individual sites.

Consistency Field test

Undrainedshear

strengthrange.KN/m2

ApproximateEquivalent

N value

Very Soft Exudes between the fingers whensqueezed in the hand

Under 20 Under 2

Soft(Soft to firm)

Moulded by light finger pressure 20 to 40(40 to 50)

2 to 4

Firm(Firm to stiff)

Can be moulded by strong finger pressure. 50 to 75(75 to 100)

4 to 8

Stiff Cannot be moulded by fingers. Can beindented by thumb.

100-150 8-15

Very stiff or hard Can be indented by thumb nail Over 150 Over 15



3. OTHER FACTORS AFFECTING STAKES AND ANCHORS.

1.1.1 GROUNDWATER.

The proximity or presence of ground water can greatly affect the performance of astake or anchor. The water content of clays also greatly affects the amount ofcohesion that can be obtained. The natural water table needs to be at least half theanchor depth below the embedded length of the anchor in a granular soil if thepredicted SWL’s are to be achieved. The point and angle at which a stake is loaded,the amount of superficial crust covering the main bearing stratum, and the bendingstrength and head restraint avaible in the stake are other variables that affectperformance. A site investigation, or trial, should be undertaken to prove theperformance of the stakes or anchors.

1.1.2 RAINFALL.

Heavy rainfall can modify the behaviour of the soil greatly. Sands, gravels and othergranular soils are usually free draining. Whilst the soil remains unsaturated theperformance of the stakes will remain virtually unmodified from that of the originalplacement. Should the drainage prove insufficient then the ability of the stakes toresist load is modified dramatically downwards It is important that a functioningrainwater catchement system is in place, and that extra stakes are driven whenthese conditions are anticipated.



4. GROUND IMPROVEMENTS.

By locally improving the density of a granular soil in the staking zone the capabilitiesof the stakes can be much improved. This improvement can be bought about byvibrating the unsaturated material above the free water table. This vibration can bemade at the time of driving the stake if a hydraulic vibrator is placed on the stake asit is driven. As an indication of the improvement in φ and γ that can be obtained thefollowing graph is appended. It can be seen that by improving the material from theloose condition, to the very dense alters γ and φ considerably. Relative density isdefined as Dr=(γn-γmin/γmax—γmin) x (γmax/γn) where γn is the condition of the soilsample.

25

30

35

40

45

50

0 20 40 60 80 100

0 20 40 60 80 100

25

30

35

40

45

50

Uniform gravel, well graded gravel-sand-s iltUniform coarse sand, well graded medium sand.Uniform medium sand, well graded f ine sand. Uniform f ine sand

y = +0.0800x1 + 38.0, m ax de v:0.00

rela tive density %

φ ef fect ive angl e ofshearing re sistance.

So il t yp e in asending order top to b ottom.

y = +0 .0800x1 +38.0, m ax dev:0 .00

y = +0.0960x1 + 34.8, m ax d ev:0.00

y = +0.112x1 +31.6 , max dev:0.00

y = +0.140x1 +28.0 , max dev:0.00



5. ESTIMATIONS OF SOIL STRENGTH.

By using these tables and the extracts from table 6 of BS5930 on the following page,an estimate of the soil capabilities of a site may be made. This assessment can bemade in advance of any tests in-order that the correct stake combinations and typescan be selected. It is assumed that prior knowledge of the soil conditions has beenobtained either from a site investigation or previous use of the site.This knowledge is essential in order to assess bearing capacities under thekingpoles, staking requirements and drainage. The site investigation andassessment also needs to look at the local seasonal wind conditions so as to ensurethe correct placement of the tent. These actions remain the responsibility of theoperator and the tent-master and are essential if the tent is to be operated safely andreliably.

Rock: where this exists directly under the site it is assumed that proprietary anchorswill be used and tested in accordance with the manufacturer’s requirements.

The kingpole loads up to 400kN at the base plate when subjected to the full trussloads of 200kN a uniform membrane loading of 0.2kN/m2, and a pretensionof 80kN.The base-plate is sized at 1024mm square to give a underside unfactored bearingpressure of 400kN/m2. This is above the capacity of most soils and thereforespreaders in the form of concrete pads, steel plates, matting, or railway sleepers willbe required when these loads are expected.

The following table gives guidance as to the allowable bearing pressures on certainsoil types and the size of spreader required. Extracted from BS 8004.

Type of soil

Allowable bearingpressure

(kN/m2)

Spreader plate size

(maximum req. for this bearing pressure)

Loose sand 90 2.1m’s square (i.e.2.1x2.1metres)

Medium densesand

100 2m’s squares

Firm clay 75 2.31m’s square

Stiff clay 150 1.65m’s square



6. SOIL TYPES: GUIDE TO IDENTIFICATION

Compactness/strengthBasic Soiltype

Particle sizemm

Visual identification Composite soil types. (Mixtures ofbasic soil types.)

Term Field test

BOULDERS

>200 Only seen in pits or exposures Scale of secondary constituentswith coarse soils.

Loose By inspection of voidsand particle packing.

COBBLES <200 but>60

Often difficult to recover fromboreholes.

Term % ofclay orsilt.

Dense

Coarse20 to 60

Slightly clayey, slightlysilty GRAVEL OR SAND

5

Medium6 to 20

Clayey or silty GRAVELOR SAND

5 to 15 loose Can be excavated witha spade; 50mm woodedpeg can be easily driven

GRAVELS

Fine2 to 6

Easily visible to the naked eye;particle shape and grading can bedescribed.Well graded, wide range of grainsizes, well distributed. Poorlygraded: not well graded. May beuniform: size of most particles liesbetween narrow limits; or gapgraded: an intermediate size ofparticle is markedly absent or underrepresented.

Very clayey or very siltyGRAVEL OR SAND

15 to 35 Dense Requires pick forexcavation: 50mmwooden peg hard todrive.

Coarse0.6 to 2

Sandy GRAVELor gravely SAND

Sand or graveland importantsecondconstituent ofthe coarsefraction.

Slightlycement-ed

Visual examination; pickremoves soil in lumpswhich can be abraded.

Medium0.2 to 0.6

SANDS

Fine0.06 to 0.2

Visible to the naked eye; very little orno cohesion when dry; grading canbe described.Well graded, wide range of grainsizes, well distributed. Poorlygraded: not well graded. May beuniform: size of most particles liesbetween narrow limits; or gapgraded: an intermediate size ofparticle is markedly absent or underrepresented.

For composite types described as:Clayey: fines are plastic, cohesive.Silty: fines are not plastic or havelow plasticity.

Coarse0.02 to 0.06

Scale of secondary constituentswith fine soils.

Soft orloose

Easily moulded orcrushed in the fingers.

Medium0.006 to0.02

Term % ofsand orgravel

Firm ordense

Can be moulded orcrushed by strongpressure in the fingers.

SILTS

Fine0.002 to0.006

Only coarse silt is barely visible tothe naked eye; exhibits littleplasticity but marked dilatancy;slightly granular or silky to the touch.Disintegrates in water; lumps dryquickly; possess cohesion but canbe powdered easily between thefingers.

Sandy or gravely CLAYOR SILT

35 to 65 Very soft Exudes between thefingers when squeezedin the fingers.

CLAY:SILT Under35

Soft Moulded by light fingerpressure

Firm Can be moulded bystrong finger pressure

stiff Can only be dented withthe thumb

CLAYSDry lumps can be broken but notpowdered between the fingers; theyalso disintegrates under water butmuch more slowly than silt; smoothto the touch; exhibits plasticity but nodilatancy; sticks to the fingers whenwet and dries slowly; shrinksappreciably on drying and usuallycracks. INTERMEDIATE AND HIGHPLASTICITY CLAYS show theseproperties to a moderate and higherdegree respectively.

Very stiff Can only be indented bythe thumb nail.

Firm Fibres alreadycompressed together

Spongy Very compressible andopen structure

PEATSvariesPredominantly plant remains, usually dark brown orblack in colour, often has distinctive smell. Low bulkdensity

Plastic Can be moulded in thehand and will smearfingers.



7. METHOD FOR ESTIMATING STAKE LOADS BROMS (1964)

1.1.3 COHESIVE SOILS



8. AFTER BROMS (1964)

1.1.4 NON -COHESIVE SOILS

The previous graphs may be used to estimate the load carrying capacity of a stake,accounting for the bending behaviour and capacity of the stake with an allowance forthe eccentricity of loading. Use of this graph requires structural knowledge of thesection properties and is best carried out by a structural engineer. However in itssimplest form it may be evaluated by use of the length depth ratio. For example:



Take a 90x90RSA of 2500mm embedded length placed into the soil such thatthe diagonal face is at right angles to the direction of pull. The soil has acohesion of 50kN/m2.

From the above data the d iagona l d itance can be est imated at 90√ 2=128mm, bu t the b

oook va lue from Br it ish stee l is 145mm which we wi l l use.

L/D=2500/145= 17 .24 , a n d e/D=0

from graph t i t led 18. 10.2 short p i les in cohes ive so i ls we can read of the corresponding

va l ue for Hu/CuD2 = 5 0i .e Hu=50CuD 2 =50x50x0 . 145 2 =52 .5kN

SWL 52 .5/2=26 .3kN

the Brit ish steel sect ion book a lso states that the u lt imate moment of resistance of the

sect i on i s 7.64kNm

from the graph g iv i ng data on l ong p i les i n cohes ive so i ls we ca lcu late the va lue Mu/CuD3

=7 .64/50x0 . 145 3 =50. 1 .Aga i n e/D=0 and H u=20x50x0. 1452=21kN a nd SWL=21/2=10.5kN o r u nde r

ha lf the or ig ina l va lue. As the fa i l ure mode is re lated to a property of the stee l and

occurs under wind load a lower safety factor of 1 .4 wou ld be approp iate wh ich g ives a

s l ight l y h igher va l ue of a SWL=15kN

The corresponding value for the first calculation using the previous charts would givea SWL of 27.8kN. These values should be now proven by testing up to 20% of theanchors as per BS 8081 Code of Practice for Ground Anchors.

valhalla · • a point load of 1.5kn applied in a 300mm square area. • a design gust speed of...

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