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Concise Eurocodes: Design of Timber Structures

This is a sample chapter from Concise Eurocodes: Design of Timber Structures. To read more and buy, visit http://shop.bsigroup.com/bip2198 © BSI British Standards Institution

This book is one of a series of books which currently comprises the following: Concise Eurocodes: Loadings On Structures BS EN 1991: Eurocodes 1 (BSI ref BIP ref 2199) Concise Eurocodes: Design of Timber Structures: BS EN 1995: Eurocodes 5 (BSI ref BIP ref 2198) Concise Eurocodes: Geotechnics BS EN 1997: Eurocodes 7 (BSI ref BIP ref 2205)


Concise Eurocodes: Design of Timber Structures

BS EN 1995: Eurocode 5 Julian Marcroft


First published in the UK in 2011 by BSI 389 Chiswick High Road London W4 4AL

© British Standards Institution 2011 All rights reserved. Except as permitted under the Copyright, Designs and Patents Act 1988, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means – electronic, photocopying, recording or otherwise – without prior permission in writing from the publisher. Whilst every care has been taken in developing and compiling this publication, BSI accepts no liability for any loss or damage caused, arising directly or indirectly in connection with reliance on its contents except to the extent that such liability may not be excluded in law. The right of Julian Marcroft to be identified as the author of this Work has been asserted by him in accordance with sections 77 and 78 of the Copyright, Designs and Patents Act 1988.

Typeset in Frutiger by Monolith – http://www.monolith.uk.com Printed in Great Britain by Berforts Group. www.berforts.com British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library

ISBN 978 0 580 69452 3


Contents Foreword BS EN 1995-1-1: Eurocode 1 Section 1 Wind loading

vii 1

1.1 Scope

1

1.2 Normative references

1

1.3 Terms and definitions

3

1.4 Symbols

4

BS EN 1995-1-1: Eurocode 1 Section 2 Basis of design

10

2.1 Basic requirements

10

2.2 Principles of limit state design

10

2.3 Design values

11

2.4 Ultimate limit states

12

2.5 Serviceability limit states

15

2.6 Basic variables

16

2.7 Partial factors for material properties and resistances

18

2.8 System strength

19

BS EN 1995-1-1: Eurocode 1 Section 3 Material properties

20

3.1 Strength modification factors for service classes and load-duration classes

20

3.2 Deformation modification factors for service classes

21

3.3 Solid timber

21

3.4 Glued laminated timber

22

3.5 Laminated veneer lumber (LVL)

22

3.6 Wood-based panels

23

3.7 Adhesives

23

3.8 Metal fasteners

24

BS EN 1995-1-1: Eurocode 1 Section 4 Durability

25

4.1 Resistance to biological organisms

25

4.2 Resistance to corrosion

25

BS EN 1995-1-1: Eurocode 1 Section 5 Basis of structural analysis

26

5.1 General

26

5.2 Effective cross-section at a joint

26

5.3 Trusses

26

BS EN 1995-1-1: Eurocode 1 Section 6 Ultimate limit states 6.1 Design of cross-sections subjected to stress in one principal direction

Concise Eurocodes: Design of Timber Structures This is a sample chapter from Concise Eurocodes: Design of Timber Structures. To read more and buy, visit http://shop.bsigroup.com/bip2198 © BSI British Standards Institution

28 28

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Contents

6.2 Design of cross-sections subjected to combined stresses

33

6.3 Members with notches and holes

36

BS EN 1995-1-1: Eurocode 1 Section 7 Serviceability limit states

39

7.1 Limiting values for deflections of beams

39

7.2 Vibrations in residential floors

40

BS EN 1995-1-1: Eurocode 1 Section 8 Connections with metal fasteners and connectors

42

8.1 Connections made with metal dowel-type fasteners

42

8.2 Connections made with split-ring or shear-plate connectors

58

BS EN 1995-1-1: Eurocode 1 Section 9 Components and assemblies

63

9.1 Glued thin-webbed beams

63

9.2 Trusses

63

9.3 Roof and floor diaphragms

64

9.4 Wall diaphragms

65

9.5 Bracing

72

BS EN 1995-1-1: Eurocode 1 Section 10 Structural detailing and control

75

10.1 General

75

10.2 Materials

75

10.3 Glued joints

75

10.4 Connections with mechanical fasteners

76

10.5 Assembly

77

10.6 Transportation and erection

77

10.7 Control

77

10.8 Special rules for diaphragm structures

78

Annex A: Characteristic strengths and moduli for timber and wood-based materials

80

Annex B: Methods, in accordance with BS EN 1991-1-7 (and its National Annex), for designing platform timber-frame buildings to sustain an extent of localised damage from an unspecified cause without disproportionate collapse

87

Annex C: Cross-referencing between Concise Eurocode 5 clauses and the associated clauses in BS EN 1995-1-1, NA to BS EN 1995-1-1, 91 BS EN 1990, NA to BS EN 1990, BS EN 1991-1-1 and PD 6693-1-1

vi


Foreword For consulting engineers the transition in structural design procedures from a British Standard to the replacement Eurocode constitutes a major programme of work for any construction material. In the case of timber this transition is made more problematic by the proliferation of BS EN documentation required by a designer as well as because for many consulting engineers timber is a minority-use structural material at a time when the switch to Eurocodes is being made simultaneously for all construction materials. Concise Eurocode 5 is intended to assist consulting engineers by providing a briefer and more accessible presentation of the design procedures associated with BS EN 1995-1-1: Eurocode 5: Design of Timber Structures encompassing the following features: a)

It is laid out in the same Code format as the Eurocodes and maintains the same 10 sections as BS EN 1995-1-1 albeit with most sections being reduced in length. b) Unlike BS EN 1995-1-1 it does not cover the less frequently used components (e.g. tapered or curved glued laminated beams) or fasteners (e.g. staples) as well as not addressing the more complex analytical techniques (e.g. second-order effects). c) It directly incorporates the Nationally Determined Parameters of the National Annex to BS EN 1995-1-1 as well as some of the more important non-contradictory complementary information (NCCI) of PD 6693-1-1. d) Its section 2 ‘Basis of design’ has been extended to include the essential requirements (e.g. load combination rules) of BS EN 1990 (and its National Annex). e) The characteristic values of the structural properties of the more commonly used wood-based materials, currently found in BS EN product standards, have been included in its Annex A. f) Concise Eurocode 5 is broadly half the length of BS EN 1995-1-1. Concise Eurocode 5 in Annex C cross-references its clauses to the associated clauses in BS EN 1995-1-1 (or its National Annex), BS EN 1990 (or its National Annex) or PD 6693-1-1. The raison d’être for Concise Eurocode 5 is intended to be accessibility to the design procedures pertaining to BS EN 1995-1-1 rather than explanation of the design procedures of BS EN 1995-1-1. However, notwithstanding this, in Annex D, two design examples are presented covering design aspects where BS EN 1995-1-1 is markedly different from BS 5268. NOTE This book provides informative commentary on BS EN 1995. However, compliance with the Eurocodes can only be ensured by careful use of the complete version of the official Eurocodes and associated documentation.


vii


Source reference

BS EN 1995-1-1: Eurocode 1 Section 1 Wind loading 1.1 Scope EC 5-1-1, 1.1.1(1)

(1) Concise Eurocode 5 applies to the design of buildings in timber (solid timber, sawn or planed, glued laminated timber or wood-based structural products, e.g. LVL) or wood-based panels jointed together with adhesives or metal fasteners. It complies with the principles and requirements for the safety and serviceability of structures and the basis of design and verification given in BS EN 1990.

EC 5-1-1, 1.1.1(2)

(2) Concise Eurocode 5 is only concerned with requirements for structural resistance, serviceability and durability.

EC 5-1-1, 1.1.2(2)

(3) The following subjects are dealt with in Concise Eurocode 5: Section 1: Section 2: Section 3: Section 4: Section 5: Section 6: Section 7: Section 8: Section 9: Section 10:

EC 5-1-1, 1.2

General Basis of design Material properties Durability Basis of structural analysis Ultimate limit states Serviceability limit states Connections with metal fasteners and connectors Components and assemblies Structural detailing and control

1.2 Normative references BS EN 300 BS EN 301

BS EN 312 BS EN 335-1 BS EN 335-2

Oriented Strand Board (OSB) – Definition, classification and specifications Adhesives, phenolic and aminoplastic for load-bearing timber structures; classification and performance requirements Particleboards – Specifications Durability of wood and wood-based products – definition of hazard classes of biological attack. Part 1: General Durability of wood and wood-based products – definition of hazard classes of biological attack. Part 2: Application to solid wood


1

Section 1 Wind loading

Source reference

BS EN 335-3

BS EN 350-2

BS EN 351-1

BS EN 385 BS EN 409 BS EN 460

BS EN 594 BS EN 636 BS EN 912 BS EN 1382 BS EN 1383 BS EN 1990 BS EN 1991-1-1 BS EN 1991-1-3 BS EN 1991-1-4 BS EN 1991-1-7 BS EN 10147

BS EN 13986 BS EN 14080

2

Durability of wood and wood-based products – Definition of hazard classes of biological attack. Part 3: Application to wood-based panels Durability of wood and wood-based products – Natural durability of solid wood. Part 2: Guide to natural durability and treatability of selected wood species of importance in Europe Durability of wood and wood-based products – Preservative treated solid wood. Part 1: Classification of preservative penetration and retention Finger jointed structural timber. Performance requirements and minimum production requirements Timber structures – Test methods. Determination of the yield moment of dowel-type fasteners – Nails Durability of wood and wood-based products – Natural durability of solid wood – Guide of the durability requirements for wood to be used in hazard classes Timber structures – Test methods – Racking strength and stiffness of timber frame wall panels Plywood – Specifications Timber fasteners – Specifications for connectors for timber Timber structures – Test methods – Withdrawal capacity of timber fasteners Timber structures – Test methods – Pull through testing of timber fasteners Eurocode – Basis of structural design Eurocode 1: Actions on structures – Part 1-1: General actions – Densities, self-weight and imposed loads Eurocode 1: Actions on structures – Part 1-3: General actions – Snow loads Eurocode 1: Actions on structures – Part 1-4: General actions – Wind actions Eurocode 1: Actions on structures – Part 1-7: General actions – Accidental actions Specification for continuously hot-dip zinc-coated structural steel sheet and strip – Technical delivery conditions Wood-based panels for use in construction – Characteristics, evaluation of conformity and marking Timber structures – Glued laminated timber – Requirements



Source reference

BS EN 14081-1

BS EN 14374 BS EN 14545 BS EN 14592 BS EN 15425

BS EN ISO 1461

EC 5-1-1, 1.5

Timber structures – Strength graded structural timber with rectangular cross-section – Part 1, General requirements Timber structures – Structural laminated veneer lumber – Requirements Timber structures – Connectors – Requirements Timber structures – Fasteners – Requirements Adhesives, one component polyurethane, for load bearing timber structures – Classification and performance requirements Hot dip galvanized coatings on fabricated iron and steel articles – Specifications and test methods

1.3 Terms and definitions 1.3.1 Characteristic value Refer to Annex A.

1.3.2 Equilibrium moisture content The moisture content at which wood neither gains nor loses moisture to the surrounding air.

1.3.3 Fibre saturation point Moisture content at which the wood cells are completely saturated.

1.3.4 Moisture content The mass of water in wood expressed as a proportion of its oven-dry mass.

1.3.5 Racking Effect caused by horizontal actions in the plane of a wall.

1.3.6 Racking discontinuities Racking discontinuities in a wall are either door openings or large window openings whose dimensions exceed stipulated limits.


3


Source reference

1.3.7 Racking wall A racking wall is a sheathed timber-frame wall located in a direction parallel to the wind (or other form of horizontal) load, commonly extending between return walls. A racking wall may comprise a single wall diaphragm or, if it contains racking discontinuities, may comprise more than one wall diaphragm.

1.3.8 Slip modulus A property used in the calculation of the deformation between two members of a structure.

1.3.9 Wall diaphragm A wall diaphragm is a length of racking wall between racking discontinuities. It may contain no window openings or alternatively may contain fully framed window openings of dimensions less than stipulated limits. A wall diaphragm may comprise a single wall panel or alternatively may contain more than one wall panel, provided that the connection between adjacent wall panels has been designed to provide adequate vertical shear resistance.

1.3.10 Wall panel A wall panel consists of timber framing connected on one or both faces to wood-based sheathing sheets. Within the length of a wall panel adjacent sheathing sheets should be connected to the same wall stud.

EC 5-1-1, 1.6

1.4 Symbols For the purpose of Concise Eurocode 5, the following symbols apply.

Latin upper case letters Ad Aef C Cd E0.05 Ed Ed,dst Ed,stb (EI )b

4

Design value of accidental action Effective contact area in compression perpendicular to grain Minimum spring stiffness at bracing support Limiting design value of a serviceability criterion Fifth percentile value of modulus of elasticity parallel to grain Design value of effect of action; Design value of the effect of destabilizing actions Design value of the effect of stabilizing actions Floor flexural rigidity perpendicular to the joists



Source reference

(EI )joist (EI )ℓ F90,Rd F90,Rk Fc,90,d Fd Fd,b Ff,Rd Fi,v,Rd Fk Ft,d Fv,0,Rk Fv,α,Rk Fv,Ed Fv,ef,Rk Fv,Rd Fv,Rk Gk,j H Ki,w Kopening Kser L Lt Lef Md Mhole,d Mstb Mstb,lim My,Rk Nd Qk,i Rd Rk Vd Vhole,d

Bending stiffness of a floor joist Longitudinal floor bending stiffness Design splitting capacity Characteristic splitting capacity Design compressive load perpendicular to grain Design value of action Design stabilizing force at each bracing support Design lateral capacity of an individual wall sheathing fastener Design racking strength of a wall diaphragm Characteristic value of action Minimum resistance in any direction of a joint in a truss Characteristic load-carrying capacity of the connector for a force parallel to grain Characteristic load-carrying capacity of the connector for a force at angle α to grain Design shear force on side of connection Effective characteristic load-carrying capacity for one row of fasteners Design racking strength of a racking wall Characteristic load-carrying capacity per shear plane per fastener Characteristic values of permanent actions Height of wall diaphragm Modification factor for wall length, vertical load and holding-down arrangements; Modification factor taking into account the effect of fully-framed window openings Slip modulus per shear plane per fastener Length of wall diaphragm Overall length of truss Effective length of beam Maximum design moment acting on beam Design moment acting on the beam at the hole centre Stabilizing moment for the wall diaphragm from net dead load Limiting value of stabilizing moment for the wall diaphragm from net dead load Characteristic fastener yield moment Mean compressive force in element requiring bracing Characteristic values of variable actions Design value of load-carrying capacity or material strength property Characteristic value of load-carrying capacity or material strength property Design shear force Design shear force acting on the beam at the hole centre


5


Source reference

Latin lower case letters a a1 a2 a3,t a3,c a4,t a4,c ab ad b bd bef d d1 dc dh dhole dit f1 fax,k fc,0,d fc,0,k fc,90,d fc,α,d fhead,k fh,k fm,k fm,y,d fm,z,d fp ft,0,d ft,0,k ft,90,d fu,k fv,d h he hef hemb k1 – k4

6

Limit for unit point load deflection Spacing of fasteners within one row parallel to grain Spacing of fasteners within one row perpendicular to grain Distance between fastener and loaded end Distance between fastener and unloaded end Distance between fastener and loaded edge Distance between fastener and unloaded edge Bay length between bracing supports Design value of geometric data (e.g. span, member dimension) Member width Diaphragm width Effective width of member taking into account the influence of cracks Fastener diameter Diameter of centre hole of connector Connector diameter Nail head diameter Diameter of hole Screw inner thread diameter Fundamental frequency Characteristic pointside withdrawal strength Design compressive strength parallel to grain Characteristic compressive strength parallel grain Design compressive strength perpendicular to grain Design compressive strength at an angle α to grain Characteristic headside pull-through strength Characteristic embedment strength Characteristic bending strength Design bending strength about the (strong) y-axis Design bending strength about the (weak) z-axis Design shear capacity per unit length of perimeter sheathing fasteners Design tensile strength parallel to grain Characteristic tensile strength parallel grain Design tensile strength perpendicular to grain Characteristic tensile strength of the fastener Design shear strength Member depth Loaded edge distance to the centre of the most distant fastener Effective (reduced) depth in notched beams Embedment depth of the connector Modification factors for split-ring or shear plate connectors



Source reference

k90 ka1 ka2 kamp kc,90 kcr kcrit kc,y , kc,z kd kdef kdist kf kh kl kℓ km kmod kn krope kshape kstrut ksys kv ky , k z l ℓ ℓb ℓd ℓeq ℓthr m mt n nef

Embedment strength modification factor for all angles to grain other than 0° Reduction factor for the minimum spacing a1 parallel to grain; Reduction factor for the minimum spacing a2 perpendicular to grain Amplification factor to account for shear or slip deflections Modification factor for compression strength perpendicular to grain Factor to take account of effect of cracks on shear strength Factor which takes into account reduced bending strength due to lateral buckling Factors taking account of reduced compression strength due to lateral buckling Modification factor for screw diameter Deformation factor taking into account duration of load and moisture content Proportion of load acting on a single joist Bracing modification factor Depth factor for bending and tensile strength Length factor for LVL tensile strength Bracing length modification factor Bi-axial bending factor Modification factor for the effect of duration of load and moisture content Material constant for evaluation of shear strength in notched beams Rope effect modification factor Factor accounting for effect of shape of the cross-section on torsional strength Factor to account for stiffness contribution of floor strutting System strength factor Reduction factor for shear strength of notched beams Factors for evaluation of reduced compression strength due to lateral buckling Member length (for LVL) Span or length of cantilever Overall span of the stabilizing system Floor or roof diaphragm span Equivalent floor span Length of the threaded part in the pointside member Mass of floor corresponding to permanent actions only Threshold mass of floor for fundamental frequency calculation Number of fasteners/connectors in the row Effective number of fasteners/connectors in a row


7


Source reference

np p qd s sj sn t t1 t2 tpen ucreep ufin ufin,G ufin,Q uinst uinst,G uinst,Q x

Number of parallel members Proportion of wall diaphragm occupied by window openings Design internal stability load per unit length Size effect exponent for LVL Floor joist spacing Wall sheathing perimeter fastener spacing Thickness of OSB or particleboard (embedment strength calculations) Headside member thickness Central member thickness for double shear connections or pointside penetration for single shear connections Pointside penetration or the length of the threaded part in the pointside member Creep deformation Final deformation Final deformation for permanent action Final deformation for variable action Instantaneous deformation; Instantaneous deformation for permanent action Instantaneous deformation for variable action Distance from the line of action of the support reaction to the corner of the notch

Greek letters a an b bc cF cG cM cQ krel,m krel,y krel,z ky kz n qk

8

Angle of stress or load to grain Ratio of effective member depth to member depth in notched beams Ratio of pointside-to-headside embedment strengths Material constant for evaluation of lateral buckling modification factor Partial factor for the action Partial safety factor for permanent actions Partial factor for a material property Partial safety factor for variable actions Relative slenderness under bending Relative slenderness ratio corresponding to bending about the y-axis Relative slenderness ratio corresponding to bending about the z-axis Slenderness ratio corresponding to bending about the y-axis Slenderness ratio corresponding to bending about the z-axis Material constant for evaluation of lateral torsional buckling modification factor Characteristic density of the wood-based material



Source reference

qm rc,0,d rc,90,d rc,α,d rm,y,d rm,z,d rt,0,d rt,90,d sd stor,d w0 w1 w2

Mean density of timber or wood-based material Design compressive stress parallel to grain Design compressive stress in the effective contact area perpendicular to grain Design compressive stress at an angle α to grain Design bending stress about the (strong) y-axis Design bending stress about the (weak) z-axis Design tensile stress parallel to grain Design tensile stress perpendicular to the grain at the hole location Design shear stress Design torsional stress Factor for combination value of a variable action Factor for frequent value of a variable action Factor for quasi-permanent value of a variable action


9