Timber in construction Eurocode 5 Span tables and guidelines

Transcription

1 Standard Recommendation S.R. 71:2015 Timber in construction Eurocode 5 Span tables and guidelines NSAI 2015 No copying without NSAI permission except as permitted by copyright law.

2 I.S. xxx: Irish Standard national specification based on the consensus of an expert panel and subject to public consultation. S.R. xxx: Standard Recommendation - recommendation based on the consensus of an expert panel and subject to public consultation. SWiFT xxx: A rapidly developed recommendatory document based on the consensus of the participants of an NSAI workshop. SWiFT 6:2013 S.R. 71:2015 SWiFT 6:2013 This document was published under the authority of the NSAI and comes into effect on: 20 March, March, March, 2013 ICS number: Swift Square, Northwood, Santry Dublin 9 T F E standards@nsai.ie W T F W standards.ie Údarás um Chaighdeáin Náisiúnta na héireann

3 Contents Page Foreword Scope References Terms and definitions Symbols and abbreviated terms Strength class Span Other abbreviations Symbols Timber properties General Timber marking Timber durability Grading and strength class Other requirements Fire Environment Vibration Timber construction Construction details Notching and drilling General Notching Drilling Separation between notches and holes Construction tolerances Connections Support of water cisterns Design assumptions for span tables General Climatic action of the wind Site location conditions Fire resistance Ground floors Roof pitches Overhang at eaves and gable Gable ladders Design criteria Design loading Categories of use Design procedures Lateral stability of joists Lateral stability of rafters Intermediate purlin support Deflection Member sizes Purlins Joints Rules for members not included in the maximum span tables

4 Tiling battens Bridging and strutting Wall plates on masonry walls Finding the right table Load-span tables Floor span tables Ceiling span tables Flat roof span tables for SLC Roof rafter span tables for SLC Roof purlin span tables for SLC Flat roof span tables for SLC Roof rafter span tables for SLC Roof purlin span tables for SLC Wall studs General Design assumptions made for wall stud tables Design assumptions made for particular wall stud arrangements Single interior stud Single end stud Pair of interior studs End pair of studs Annex A (informative) Figures Annex B (informative) Additional design guidance and clarification B.1 General B.2 Method for use of span tables for conditions other than SLC 1 or SLC B.3 Further increase in maximum spans B.4 Permanent loading assumptions B.5 Vibration B.6 Purlins B.7 Calculation of maximum service load capacity of wall studs B.7.1 General B.7.2 Method of calculating the maximum service load capacity B.7.3 Example of calculation for maximum service load capacity Bibliography

5 Foreword This Standard Recommendation was developed by NSAI Timber Standards Consultative Committee, Working Group 2, Task Group 2 "Trussed rafters and timber in buildings". This Standard Recommendation, which replaces SWiFT 6:2013, relates to timber members commonly used in buildings constructed in Ireland and provides non-contradictory complementary information where those members are designed to I.S. EN and its National Annex. The drawings in this Standard Recommendation represent typical construction details. They are not prescriptive and alternative details may be appropriate. Attention is drawn to the acceptable constructional details published by the Department of the Environment, Community and Local Government which primarily show insulation and air tightness detailing. It is important for designers, specifiers and purchasers to understand the Construction Products Regulation (CPR), the meaning of the Declaration of Performance (DoP) and CE Marking of construction products. The appropriate specification and use of proper construction products plays a fundamental role in ensuring compliance with the Building Regulations. During all construction related activities account should be taken of the Safety, Health and Welfare at Work (Construction) Regulations. This Standard Recommendation does not purport to include all necessary provisions of a contract. Users are responsible for its correct application. Compliance with this Standard Recommendation does not of itself confer immunity from legal obligations. In line with international standards the decimal point is shown as a comma (,) throughout this Standard Recommendation. 3

6 1 Scope TIMBER IN CONSTRUCTION EUROCODE 5 SPAN TABLES AND GUIDELINES The span tables in this Standard Recommendation give maximum spans for the following solid softwood structural members in buildings: Floor joists, including ground floor joists; Ceiling joists, including those supporting a standard water tank; Flat roof joists (0 to 5 ); Rafters (20 to 45 ); and Roof purlins. Roof slopes other than those listed above are not included in this Standard Recommendation. Load tables for 44 mm x 100 mm timber wall studs are also included. Maximum spans are given for members of a particular section size, spacing, strength class, and loading. For the tables, it has been assumed that the members are in service class 2 conditions (see I.S. EN ). Structural members properly selected using these span tables comply with the structural design requirements of I.S. EN and its corresponding National Annex. It is intended that members so selected can be used in timber building construction without further design. Designs to the Eurocodes, which are limit state standards, generally require higher factors of safety for stability and roof uplift than those that were required by the permissible stress standards previously used. Therefore, traditional connections and holding down details may not be adequate for designs using the Eurocodes and this Standard Recommendation and all connections should be designed. The loads on the members and the load combinations used for the preparation of the span tables comply with the requirements of the current editions of the following standards including their National Annexes: I.S. EN 1990; I.S. EN ; I.S. EN ; and I.S. EN Using these loading standards, wind uplift becomes a major design criterion for members and their connections. It is not feasible to provide span tables for all load cases and combinations. The loadings covered by the span tables in this Standard Recommendation are set out in Table 1. Structural design of members subjected to loads or load combinations outside those covered by the span tables should be designed by appropriately qualified and experienced engineers in compliance with 1.3 (2) in I.S. EN Flooring materials (e.g. T&G flooring boards, particle boards or plywood) are not covered in this Standard Recommendation. Dormers and hipped roofs are complex constructions and should not be designed using this Standard Recommendation. Instead their design should be referred to a competent timber designer; the load span tables should not be used in connection with these parts of a project. 4

7 When structural roof members are designed in accordance with the requirements of the current limit state design standard, IS EN , it will frequently be found that the strengths of connections required to resist uplift from wind forces are significantly greater than those required using former permissible stress design standards. Previously used traditional connections which were in common use may not have adequate strength. The design and detailing of connections for all members are not included in this Standard Recommendation and should be designed by appropriately qualified and experienced engineers in compliance with 1.3 (2) in I.S. EN References The following referenced documents are indispensable for the application of this Standard Recommendation. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. For referenced Eurocodes, the requirements of the corresponding National Annexes apply. I.C.P. 2, Slating and tiling I.S. 127, Structural timber Visual strength grading Sawn softwoods with rectangular cross-section S.R. 325, Recommendations for the design of masonry structures in Ireland to Eurocode 6 I.S. EN 335-1, Durability of wood and wood-based products Definition of use classes Part 1: General I.S. EN 335-2, Durability of wood and wood-based products Definition of use classes Part 2: Application to solid wood I.S. EN 335-3, Durability of wood and wood-based products Definition of use classes Part 3: Application to wood-based panels I.S. EN 336, Structural timber - Sizes, permitted deviations I.S. EN 338, Structural timber Strength classes I.S. EN 350-2, Durability of wood and wood based products - Natural durability of solid wood - Guide to natural durability and treatability of selected wood species of importance in Europe I.S. EN 351-1, Durability of wood and wood-based products - Preservative-treated solid wood - Part 1: Classification of preservative penetration and retention I.S. EN 460, Durability of wood and wood based products - Natural durability of solid wood - Guide to the durability requirements for wood to be used in hazard classes I.S. EN 1912, Structural timber - Strength classes - Assignment of visual grades and species I.S. EN 1990:2002, Eurocode - Basis of structural design I.S. EN , Eurocode 1: Actions on structures - Part 1-1: General actions - Densities, self-weight, imposed loads for buildings I.S. EN , Eurocode 1 Design of steel structures - Part 1-3: General actions Snow loads I.S. EN , Eurocode 1 Actions on structures - Part 1-4: General actions Wind actions I.S. EN :2004, Eurocode 5 Design of timber structures - Part 1-1: General - common rules and rules for buildings 5

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