Figure 1.7: Load distribution in building

1.7.1 PERMANENT ACTIONS, G, gPermanent actions or dead loads consist of the permanentconstruction material loads comprising the roof, floor, wall, andfoundation systems, including claddings, finishes, and fixedequipment. The load type can vary greafly depending on the type ofconstruction and the interior finishes. Dead loads of structuralelements cannot be readily determined because weight dependson size which in turn depends on weight to be supported (initiallyweight must be assumed to make a preliminary calculation, andthen actual weight can be used for checking the calculation).Permanent actions are a constant over the life of the structure.

12-1

Figure 1.8: Permanent loads effects on structure

Table

iB:l-l Htlh'&il..r}!}i|it !*turl&ilrttf llll. l-l fhlrao thig. OEd tlr.d.r

---

1.5

ltr eildrfr fi?m t?r

Ir.a. 2,,6lll t?,l$ rt{a9,us rnltr tt? 'r0 tt,16 l&trs ru't,

r?il ,r,xttn r.f

t.t

.tyd..tu:{{flrGd*rmfia{rffil&dnq

Otrtt t ,&edr{.QanHG,S{a fimerrsc*, rdrrcft.d cii*Lr

Cmcqdrlirndrmellt,etory.ett*i'c{tild,er, ho!3od'rl.prtl 16HmI.e'*{!tdldw14ry{arli.lofind *d&nrffi(3Mr&i&rrtE4'e$r'fhfto(kel hsfitxlqf$e

/t'tt6

UA,t,tJt,o

LN0.tl

0.D

0"11

0.s

Otrt

ent03

OIE0lr

I

3

&ffilkncldtmndrrerieh&tw q*t*rtgrAil.a* *kirtiblxd {ll r,tgl)r@r, {Seo{*tr {,$lx 16;ilstadfi.d& lz

weo(MlI t4t{ n{ogi;Itrcrrdmo*h &

fbm fl{(bddsmm&ra'defunrl 9{fi!mmr,phinptirn'{m} tSlooi oonft, is'iiid[lee] ll

&^&sed&eidIb$rs&,qqr*5*laxsmqiuip

ehsrt

s.dE!

t0 '0.{t10utt 0t

dfi?hm rfialrlG!.t .6$bc r.

13-1

1.7.2 Variable Actions, Q, qVariable actions or live loads are produced by the use andoccupancy of a building. Actions include those from human

, occupants, furnlshings, non-fixed equipment, storage, andconstruction and maintenance activities. Variable Ioads areestablished by code for different occupancies.The loads are assumed for purposes of design shall be the greatestloads that probably will be produced by the intended uses andoccupancies, provided that the minimum live loads to beconsidered as uniformly distributed.ln the design of floors, probable concentrated loads shall beconsidered. Where such loads may occur, the supporting beams,girders and slabs shall be designed to carry either the concentratedloads.

Figure 1.9: Variable loads effects on structure.

variable actions can be leading or non leading. The combinationfactors as shown below are the characters of variable actions isdiscussed in detail in 1.8;

Q*

VoQrVrOrVzQt

Characteristics value, U = 1.0Combine valueFrequent value

Quasi-permanent value

14-1

Figure 1.20: Real variable actions are idealized as uniform distributionactions

Table 1.6

Catagory Exanrpla qt (kN/mi tA1 All arcac within scli contcr'ned singfc family dwall;ngs or nredu]ar

studenl acccrnrrotlaticnCornrnuntl areas linclLding kitclrens) in blocks of flats thst arenc rnore than 2 storeys and orlv 4 Cweilirrgs per flonr areaccessiblc frorn a ling{e rtaircasc.Eedrcorns anel dorrnit,Jries except those in A1 arid A3Eedrcoms in holls snd ma-te]s; hspata, wa{ds; toiler ereasGeneral oi{ice use olher than in B2O{fiee ereas at or below ground fioor levelCorridors, hallways, aisles which are not subjected to crowds orwheeled vehiclas and enmmlnai areas in blccks nf flals natcovered by AlAreas strsceptible ro lar0F crowrisStagcs in .g,ublic oecembly *reas {ctre Ncte 6}Areas in general retail shops alrd cfepartment Etores

1.7,3 Wind Actions

This actions is variable and beyond human control. Wind loads arethe positive or negative pressures exerted on a buiiding when itobstructs the flow of moving air. Wind loads generally actperpendicular to the surfaces of the house. The wind loading

1.6

A3B1

6L

c31

(,ll Ic52D

1.57.O4i,

3.C3.0

507.64.0

1 5-1

pressures, direction and timing are constanily changing. Forpurpose of calculation however wind is considered a static force.Statistical approach adopted to quantify the magnitude anddirection of related design loads.** wind, earthquake or snow loads are not considered live toads but transientloads b/c so variable and are determined by consulting codes

Figure 1.21: Wind load effect on building

1.7.4 Accidental Actions, A

Accidental actions such as impact from construction vehicres,cranes or building equipment (e.9. skip of fresh concrete), localfailure of final or temporary supports, etc., which might result in(progressive) collapse of load bearing structural elements, shail bechecked for the relevant limit states.

1.8 Basic of structural design

ln common with most other modern design standards, the Eurocodeshave adopted the 'limit state design' method. The object is to ensurethat the probability of operating conditions reaching failure conditionsis so low as to be negligible. This is done by factoring the appliedloads upwards so that a 'design load' which represents a probablemaximum load is estimated; likewise a 'design resistance' whichrepresents a probable minimum resistance is also estimated byfactoring resistances downwards.

16-1

A Iimit state is a state beyond which the structure no longer satisfiesthe design requirements. Ultimate limit states (ULS) includeexcessive deformation, rupture, instability and equilibrium loss; thisstage related to structural collapse or endangering human safety.serviceability limit states (sLS) include excessive defrection orvibration. This state related to conditions which are regarded asbeing unacceptable in everyday use but which do not actuallyendanger the structure or its occupants.

The term 'design value' is used for factored loading and resistances.The loads are obtained by multiplying the characteristics value by theappropriate partial safety factors. The design resistances areobtained by dividing the characteristics resistances by theappropriate safety factors. Safety factors needed for ultimate limitstate and serviceability limit state can be refer to BS EN 1990. Thesafety factors can be classified as partial safety factors andcombination factors from Table l and Table 2 in BS EN 1gg0respectively. From Clause 6.3 BS EN 1990, Design Value of anAction, F6 csh be expressed as;

Fa = Tf Fr"p

Fr"p = QF*

(6.7a)

(6.Lb)withwhere

Fk

Fr"o

T7

4,

ls the characteristics value of the actionIs the relevant representative value of the actionls a partial factor for the action which takes account ofthe possibility unfavorable deviations of the actionvalues from the representative valuesls either 1.0 or Qo,{t or {z

17-1

1.8.1 Combinations of actions

The different loads discussed in the previous subsections do notoccur alone but in combinations. The designer must determinewhich combination is the most critical for the structure. Fundamentalcombinations of actions may be determined from EN 1990 using either of:o Equation 6.10o Less favorable of Equation 6.10a and 6.10b

2r",, Grc,i * ypP + yq1Qr't* I yq,i!)o,tQx,i. (6.10)

2t",, Gr,,i * yeP + Te,rtpo,iQrt *\ro,,tlto,i.Qr,,i (6.10a)

\F,rr,, Gx,i * ypP + TqrQt ,t +lro,ttlto,tQr,1 (6.L0b)

"" f; it 0.925 from NA 2.2.3.2

substitute factors from Tables 1 and 2 into the equation and check for arange of different loading combinations and choose the least favorableresult.

Table 1.7 and rable 1 .8 show combination factors, r.f extracts from Table3.1 NA ,A1.1 and partial factor for actions, )21 rspectively.

18-1

Table 1.7: Recommended values for r[ factors for building

More information is extracted from Eurocode as shown in Figure 1.22

Actiou W v4 tl4fuipora$ b.cds iu hriMfurgs, rareeon, {seeE\ r$9r-1-tiC ntegory A : iloilEsric. residenml areas('ategoryB:offrcearrarCategtrRr C : comgrrgatriorr nreasCategoqr D : sirq4:utg area:Categolt E::toftrt tueilsCategtrry F ; trattrc area.

rdricle v;eight { J0k\iCateuory G : nathr ilre;1.

-l0kl\ { rehicle neiehr ( l60kNdiateeo$ H : lo*fs

!.:Lr..

0,1rj.:1.0

0,:

il.70

0.50.50.:tt.0.9

0.'

0"5

0

0.30.30.60.60.8

0.6

0.3il

Snorr load.s on hriltlines {se e E}- I 8! 1- I.ii'rFinland- L'elalri" .l.-011\'il'. SrxedenReurafuder ol'CET \{eurber Srates- lorlocatecl at al[fide H r" I0m r:n a.s.l"Reurairuler of CEli \Ie$rber $tfites- torl+cated at alrrnrete H f ](]IJtl rn a.s,l.

irler

ilTerft.10fi_70

fi.50

0.i0r't.50

0.:0

fr.:trrl.l0

0

\lutd lmdron l.rrdlrtttrgt llee EN l99l.t-,{l [.fi (lr ITen$a.rnu'e umn-fire1 fu truddforgs (ree ENI99l-I-5'!

tl.h 0.5 0

litlTT Ttrn yr values ura1. he ier tr,r' tl-le )'ialiomai arulex* Fnr eomrtri* no[ rnerfioueel lx]o*'. see rel*l'a*r kcal ar*riilitns,

Table 1.8: Partial factor for actionsPermanent Aotlons

lsJLeadlng or Main AooompanyingVadebls Aodon Varlable Aotlon

/qt lq.rUltlmate Llmit

State

OU

Unfavourabletl

1.35

Favourablo

0.9t.0

151.5

1.6

1.6!ate: V{heu uariable actions are fevoursble f,r Shqlld lrc takeru as zsr+

19-1

6.:1.3 C:ornbinafion of actions (frtigue relificafious extlutled)6.1.3.1 General

(1)F Fot eaclt ctitical load case. the clesign r.alues of the etlects sf actions (E.1) shall bedetemunerl bv combining the values of actious 1trrat are cr-rnsitlererl to occr-u srunrlTaneously.

(1) Each crnnbitaliou of actious should iLrclutle :-

a Ieaclilg rlariable ftctio1t, or-

an accidental actiou.

(i) The corubiltrtious of actiors slrotLl

1.8.2 Unfavourable and favourable loading

Loads may be considered as 'favourable' or unfavourable' in anyload combination, depending on whether they increase or reducethe effects such as bending moment, axial force ect. in thestructural members.

Unfavourable permanent loads I y, I t.SSfavourable permanent loads I y, I t.OOUnfavourable variable loads I yo I t Sfavourable variable loads I vn I O

1.8.3 Leading variable actions Qr,r

The leading variable action is the one that leads to the mostunfavourable effect (i.e. the critical combination). ln Equation 6.10,the full value of the leading variable action is applied TerQw (.e.1.5 x characteristic imposed load)ln order to generate the various load combinations, each variableaction should be considered in turn as the leasing one. Theconsideration should also be given to whether loading is favourableor unfavourable.

Example 1.1

A roof has the following loads applied;Permanent load, Grc: 7.0 kN /mzVariable actions, 0r = 0.5 kN /m2Wind load;

wupttft = 1.25 kN /m2wd.owntoad. = 0.4 kN /m2S : 0.4 kN /m2

Determine the most critical combination load.

Snow

21-1

Solution:Partial factors

From Table NA ,A1.1Actions

Category H: roofsSnow : sites up to 1000 mWind

i. Equation 6.10

EY*,tGw * * /e,r Qnr f E]/c,itno,r Qr,i

lto0.7

0.5

0.5

(6.10)

Load CombinationlPermanent and imposed (leading)

1.35Gk + 1.5Qk = 1.35 x 1.0 + 1.5 x 0.5 = 2.1.0 kN /m2

Load Combination2Permanent and snow (leading)

1,.35Gk + L.SQ|: 1,35 x 1.0 * 1.5 x 0.6 : 2.25 kN /m2

Load Combination3Permanent, snow (leading) and wind (download)

1.35Gk + 1.5S * 1.5 x 0.5 x w4: 1.35 x 1.0 * 1.5 x 0.6 * 1_.5 x 0.5 x 0.4:2.55 kN /m2

22-1

Load Combination4Permanent, snow and wind (download) (leading)

1.35Gk* 1.5 x 0.5 xS * 1..5wa= 1.35 x 1.0 * 1.5 x 0.4 * 1.5 x 0.5 x 0.6

,, : 2.40 kN /m2

Load Combination5Permanent and wind (uplift) (leading)

-0.88 kN /m2

ii. Equation 6.10a The negative sign tndlcates that thewind load acts i11 the opposite sense totlre permanent load

Zyc,iGu,i t yeP + Tqdto,iQq -lEyq,irPojQk,r

=E=

(6.10a)

Load CombinationlPermanent and imposed (leading)

1.35Gk * 1.5 x 0.7 x Qp = 1.35 x 1.0 * 1.5 x 0.7 x 0.5 = 7.BBkN /m2

Load Combination2Permanent and snow (leading)

1.35Gk* 1.5 x 0.5S = 1.35 x 1.0 + 1.5 x 0.5 x 0.6 = 1.8 kN/m2

Load Gombination3Permanent, snow (leading) and wind (download)

1..35Gk* 1.5 x 0.5 x S * 1.5 x 0.5 xwa

= 1,35 x 1.0 * 1.5 x 0.5 x 0.6 + 0.75 x 0.4 = 2.1OkN/m2Load Combination4Permanent, snow and wind (download) (leading)

1.35Gk* 1.5 x 0.5 x S * 1.5 x 0.5 xw7: 1.35 x 1.0 * 1.5 x 0.5 x 0.4 + 1.5 x 0.5 x 0.6: 2.1.0 kN /m2

23-1

Z{;Yc,i Guj t YpP + Yq1Q4 *Zyej{o,iQp,t

=@

Load Combination5Permanent and wind (uplift) (leading)

1.0Gk + 1.5 x 0.5 vwu= 1.0 x 1.0 -0.75x1.ZS: -0.06 kNlmz

,iii. Equation 6.10b

(6.Lob)

Load CombinationlPermanent and imposed (leading)

(0.925x1.35)Gp+1..5Qk:0.925 x 1.35 x 1.0 * 1.5 x 0.5 :2kN/m2

Load Gombination2Permanent and snow (leading)

(0.925 x 1.35)G;, + 1.5S = 0.925x 1.35 x 1.0 * 1.5 x 0.6 : 2.15kN /m2

Load Combination3Permanent, snow (leading) and wind (download)

(0.925 x 1.35)G4 + 1,5S * 1.5 x 0.5w7: 0.925x 1.35 x 1.0 * 1.5 x 0.6 * 1.5 x 0.5 x 0.4= 2.45 kN /m2

Load Gombination4Permanent, snow and wind (download) (leading)

(0.925 x 1.35)G4 * 1.5 x 0.5 x S t LSwa= 0.925x 1.35 x 1.0 * 1.5 x 0.5 x 0.4 * 0.75 x 0.6: 2.00 kN /mz

24-1

Load Gombination5Permanent and wind (uplift) (leading)

0.925 x 1.0 x Gp * 7.5wu: 0.925 x

Results

Load Combination

1.0 -

1.5 x 7.25: -0.95 kN /m2

6.10 6.10a 6.10b1. Permanent and imposed (leading)

2. Permanent and snow (leading)

4. Permanent, snow and wind (download)(leading)

2.10

2.25

1.88 2.001.80 2.15

2.40 2.10 2.00

5. Permanent and wind (uplift) (leading) -0.88 -0.06 -0.95

1.9 ANALYSIS OF STEEL STRUCTURES

The design process requires a knowledge of the stiffness and strength ofthe structure under load. The basic for this process is a knowledge of thematerial behaviour.The methods of structural analysis are treated in many textbooks. ln mostmethods, the distribution of forces and moments throughtout the structureis determined by using the conditions of static equiribrium and ofgeometric compatibility between the members at the joints. The way inwhich this is done depends on whether a structure is statically determinateor is statically indeterminate.

3. Permanent, snow (leading) and wind 2.55 2.10 2.45(download)

The criticalconibination load case

25-1