chapter 1 introduction - manual for the design of timber building

7/28/2019 Chapter 1 Introduction - Manual for the Design of Timber Building

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ISucE/trada Manual for the design of timber building structures to Eurocode 5

Inoucion

. aims of he Manua l

This Manual and the accompanying CD provides qualified Structural Engineers with guidanceon the structural design of single-storey and medium-rise multi-storey buildings using common

forms of structural timberwork. Structures designed in accordance with theManual will normally

comply with BS EN 1995-1-1: Eurocode 5: Design of timber structures Part 1-1: General:

Common rules and rules for buildings (EC5), together with its supporting codes and standards.

The Manual is primarily intended for carrying out simple calculations, and is not necessarily

relevant to the design of complex buildings requiring more sophisticated analysis. However it is good

practice to check the output of complex analyses using simplified methods such as those provided.

For simplicity reference to clauses in BS EN 1995-1-1 will be in the form EC5 4.2(1)

Reference to clauses in theManual will be by section, e.g. Section 2.1.1.

.2 the Euocoe sysem

1.2.1 Origin and purpose

The structural Eurocodes are produced by the European Committee for Standardisation (CEN), its

members being the national standards bodies of the EU and EFTA countries, e.g. BSI.

1.2.2 List of Eurocodes

The complete set of Eurocodes consists of the following:

BS EN 1990: Eurocode: Basis of structural design (EC0)

BS EN 1991: Eurocode 1: Actions on structures (EC1)

Part 1-1: General actions Densities, self-weight and imposed loads

Part 1-2: General actions on structures exposed to fire

Part 1-3: General actions Snow loads

Part 1-4: General actions Wind loads

Part 1-5: General actions Thermal actions

Part 1-6: Actions during execution

Part 1-7: Accidental actions from impact and explosions

Part 2: Traffic loads on bridges

Part 3: Actions induced by cranes and machinery

Part 4: Actions in silos and tanks

BS EN 1992: Eurocode 2: Design of concrete structures (EC2)

BS EN 1993: Eurocode 3: Design of steel structures (EC3)

BS EN 1994: Eurocode 4: Design of composite steel and concrete structures (EC4)

BS EN 1995: Eurocode 5: Design of timber structures

Part 1-1: General Common rules and rules for building (EC5)

Part 1-2: General Structural fire design (EC5-1-2)

Part 2: Bridges (EC5-2)


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BS EN 1996: Eurocode 6: Design of masonry structures

BS EN 1997: Eurocode 7: Geotechnical design

BS EN 1998: Eurocode 8: Design of structures for earthquake resistance

BS EN 1999: Eurocode 9: Design of aluminium structures

Eurocodes 1 to 9 all comprise several parts, but only EC1 and EC5 have been listed in full.

1.2.3 Principles and Application Rules

All the Eurocodes contain Principles and Application Rules.

Principles are general statements, definitions, design rules or analytical models for which

no alternative is permitted, for example EC5 8.2.3(2)P The strength of the steel plate shall be

checked. Clauses which comprise a principle are identified by the letter P.

Application Rules are generally recognised rules which comply with and satisfy the

Principles. Alternative design rules may be used instead, provided that they can be demonstrated

to comply with the Principles and to produce similar levels of safety, serviceability and durabilityto the Application Rules.

1.2.4 Nationa l Annexes

Every National Standards body may produce its own National Annex (NA) for each part of each

Eurocode. An NA provides values or decisions related to Nationally Determined Parameters

(NDPs) which allow for differences in such matters as climatic conditions, standards of

workmanship, and perceptions of acceptability in deflections. UK NDPs are identified by

bold type in theManual.

1.2.5 Non contradictory complementary information

The Eurocode system also permits reference in NAs to sources of non contradictory

complementary information (NCCI) which help designers to use the associated Eurocodes. In

the UK the principal source for EC5 is BS PD 66932.

ThisManual includes a number of NCCI items which will not be found in EC5 itself.

1.2.6 Eurocode design basis

The Eurocode common basis of design for all structural materials is based on limit states and

partial safety factors. For structural timber design in the UK this represents a major change from

BS 5268-23, in which all the safety factors are incorporated in the permissible stresses. A limit

state is simply a state beyond which a structure no longer satisfies its performance requirements.

Ultimate limit states are associated with collapse or similar forms of structural failure that may

endanger the safety of people, and generally involve the consideration of strength and stability.

Serviceability limit states are associated with user discomfort or dissatisfaction or a lack of

functionality, and generally involve the consideration of deformation (i.e. the deflections of

members or slip in connections). Partial safety factors are used to increase the values of loads and

to decrease the material strength values (also to adjust stiffness properties for second order linear

elastic analysis see EC5 2.2.2(1) Note 2). In each case the values of the factors are specified


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and are applied to the characteristic values of the loads or material properties, so the approach to

safety is known and transparent.

.3 Scope of he Manua l

1.3.1 Nationa l scope

TheManual is intended primarily for the design of buildings within the United Kingdom. Wherevalues and design methods specified in UK National Annexes are quoted the information given

may not be applicable elsewhere.

1.3.2 Struc tures covered

For the majority of design situations and materials involving timber the information required has

been provided in thisManual or in the accompanying CD.

Two principal types of timber structure are covered:

open frame buildings, i.e.

statically determinate beams and columns stabilised by bracing and/or verticaland horizontal diaphragms

frameworks with rigid joints such as portal frames

a combination of the above

timber platform frame buildings with a maximum height of 18 metres to the finished floor

level of the top storey.

1.3.3 Principal subjects covered

roofs, floors and walls

flexural, tension and compression members

diaphragms, flitch beams

mechanically fastened and glued connections

load duration, service class, creep, durability and fire resistance.

1.3.4 Subjects not covered

foundations and geotechnical design (see BS EN 1997:Eurocode 7: Geotechnical design

(EC7)4)

seismic design (see BS EN 1998: Eurocode 8: Design of structures for earthquake

resistance (EC8)5)

the following detailed design issues:

analysis of frame structures EC5 5.4.2

analysis of trusses with punched metal plate fasteners EC5 5.4.3

glued thin-webbed beams EC5 9.1.1

glued thin-flanged beams EC5 9.1.2

mechanically jointed beams EC5 9.1.3

mechanically jointed and glued columns EC5 9.1.4

trusses EC5 9.2.1 and 9.2.2.


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Amendments May 2008

1.3.5 Additional information contained in the CD

material properties of solid timber, glulam, wood-based panel products and structural

timber composites

nail, screw, bolt and dowel connection spreadsheets

links to manufacturers web sites.

For a more detailed list see the Contents.

1.3.6 Sources of additional information

For timber-related subjects which are not covered by theManual, EC5 or its supporting standards

should be consulted.

Other useful publications are:

STEP Timber Engineering , Volumes 1 and 26

TRADAs EC5 Guidance Documents and EC5 Design Examples 7

TRADAs Software Toolbox

8

(includes the design of connections to EC5 and will includedomestic timber members in the near future)

Panel Guide Partnerships PanelGuide9

Building Research Establishment published material.

It is also intended to publish other manuals in this series on EC0 and EC1. Further sources of

information are given in the References.

1.4 Conens of he Manua l

TheManual is set out in the sequence normally followed in design.Sections 2, 3 Principles of structural timber design

Section 4 Initial building design process

Sections 5, 6 Design of individual members and connections

Sections 7-10 Design of roofs, floors and two principal types of building

There are two additional sections.

Section 11 Checking and specification guidance

Section 12 Workmanship, installation, control and maintenance

1.5 definiions

1.5.1 Technical terms

In order to rationalise the meanings of various technical terms for easy translation, some of the

terms used in the past have been redefined more precisely in the Eurocodes. Those of particular

importance are listed, together with other timber related terms which may not be familiar to

engineers who are more accustomed to other materials, in the glossary.


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1.5.2 Axis nomenclature

The use of traditional axis nomenclature in the UK has been altered to match a consistent

European approach throughout the Eurocodes, as shown in Figure 1.1. Thex-x axis lies along the

length of the member,y-y is the principal or major axis, andz -z is the minor axis.

Fig . Nomenclature of axes

.6 Noion

The Latin and Greek characters that apply to designs to EC5 are listed under Notation in the

preliminary pages of thisManual.

z

y

y

z

x x