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Quality of timber construction - Guidance document for buildings and load bearing structures

Quality of timber construction - Guidance document for buildings and load bearing structures. A printed RIL report published at the end of 2006 The work in the QA working group has been actively industry driven Jouni Hakkarainen, Metsäliitto Osuuskunta/Puutuoteteollisuus, pj.

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Quality of timber construction - Guidance document for buildings and load bearing structures

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  1. Quality of timber construction - Guidance document for buildings and load bearing structures • A printed RIL report published at the end of 2006 • The work in the QA working group has been actively industry driven Jouni Hakkarainen, Metsäliitto Osuuskunta/Puutuoteteollisuus, pj. Juha Elomaa, Ramboll Oy Unto Hyytiä, Versowood Oy Antero Järvenpää, Late-Rakenteet Oy Ari Kevarinmäki, VTT Veijo Lehtonen, Late-Rakenteet Oy Mikko Mäkinen, SPU Systems Oy Alpo Ranta-Maunus, VTT Gunnar Åstrom, RIL Tomi Toratti, VTT, siht. • 15 working group meetings in 2 years • Has been well received by the building designers • The city of Helsinki mentioned they will be using the proposed quality ensurance practices

  2. Definition of building quality A. The process quality is made up of the design and building processes as well as the communication and co-operation between these parties B. The quality of the end-product on the other hand may be divided to visual, functionality, ecological and technical quality. The service-life perspective is an essential part of the end-product quality

  3. A. Indicators of a good quality process are: • The objectives of the building project are well defined and clear • The schedule is realistic • The staging and decision making processes function • The responsibilities and tasks of the building partners as well as the related scheduling is agreed • The competences of the persons involved is adequate • The building partners form a positive atmosphere and a desire to cooperate • Sufficient resources are allocated to the design and building processes • The security measures are taken care of • The critical stages are identified and these are emphasized

  4. B. End-product quality • Visual quality is composed of the appearance of the visible structures, the rooms and building volumes, the environment and the combinations of the above. • The functionality quality is determined on how the building performs its intended functions, eg. logistics and ergonomics or in other ways efficiently and comfortably. • The technical quality is made up of durability, strength, safety and healthiness. • The ecological quality is first effected when the building materials are chosen in the initial stages of the project, however the major part is determined on the building use. The main issues are the energy efficiency of the building, long service life, good maintenance procedures and modifiability of the building.

  5. Considering timber the following should receive special attention • Handling of information and communication between the building project partners • Bracing of load bearing structures • Considerations on performance of connections and how these are effected by variable humidity conditions • Swelling and shrinking of timber elements • Cracks caused by shrinkage of moist wood • Orthotropic strength of wood • Fire safety

  6. The scope of this report is on the quality assurance of the end-product quality, which is achieved by a functional cooperation among the project partners, sufficient coverage and quality of design and on the documentation to be produced in a building project. This report describes the following means for quality assurance: • Building process – Moisture control plan, assembly plan, tolerances • Design – initial risk analysis, design process, following the design in the site, information and feedback flow between engineer and building site • Fabrication of elements - Approved methods for design, fabrication and quality control (templates given) • Maintenance – Contents of the maintenance manual

  7. Documentation needed for decisions on quality and information transfer among building project partners • Project description template : a) all technical information on project b) all decisions recorded c) a tabulated form is provided, when and what decisions should be done • Moisture control plan template: a) moisture of wood through the building process from factory to ready building. b) moisture protection levels. • Assembly plan template • Tolerances in timber construction a) Fabrication tolerances for materials (CEN standards) b) Assembly tolerances (Finnish building codes) c) Tolerances for connections

  8. Preface 3 1Introduction 4 1.1Scope 4 1.2Partners in a building project 4 2Plans and documents 6 3Project description 7 3.1Introduction 7 3.2The content of the project description 8 4Quality assurance of the structural design13 4.1Introduction 13 4.2Main requirements of the structural design13 4.3Documents to be drafted 14 4.4Quality control 14 4.5Following the structural design during construction work 15 4.6Structural risk analysis 15 4.7Information transfer and control of updates on the plans 16 5Materials 17 5.1Wood materials and product standards 17 5.2Durability of wood 19 5.3Corrosion of fasteners 19 6Industrially fabricated elements and building components and quality control 21 6.1Introduction 21 6.2The control of the process 21 6.3Storage and transportation 21 6.4Connection techniques 22 6.5Specific guidelines 23 7Quality assurance of the building process24 7.1General requirements 24 7.2Supervision on building site 25 7.3Moisture control plan 25 7.4Assembly plan 28 7.5Inspections, testing and repair 29 7.6Tolerances 29 8Stability of structures 35 8.1Introduction 35 8.2Design and execution 35 8.3Responsibilities for stabilization 35 8.4Stability of a building and bracing 35 8.5Stability of the whole building 35 8.6Bracing 36 9Special Risks 37 10Maintenance Manual 37 11References 39 Appendix A. Durability of wood Introduction Mould and rot in wood Structural protection Chemical protection Appendix B. Checklist for the structural design Appendix C. Checklist for the assembly plan Appendix D. Example of a project description Table of contents

  9. Tasks for the building developer Decision on project Counselling and supervision of construction Bidding and negotiation of contracts Organisation of design Initial project plan, Organisation of construction Main phases Prep. Of design Prep. of construction Construction Building use Project plan. Draft plan Construction design Assess. Of needs Main documents Project descriptiondraft Project description version II Project descriptionversion III Initial risk analysis Construction design External inspection Moisture control plan Assembly plan Maintenance manual

  10. Table 3.1 The content of the project description, where a recommendation of the partner responsible to deliver the content is given using the following abbreviations: Building developer (or representative): BD, Main designer: MD, Architectural designer: AD, Structural designer: SD

  11. Moisture protection levels Protection level 0, ST0, no protection- moisture content depends on the climate and may not be assigned, to be used only in winter climates and in short durations Protection level 1, ST1, plastic covering- moisture content below 20 % Protection level 2, ST2, sheltered- moisture content below 20%, more reliable than ST1 Protection level 3, ST3, internal conditions or a tent with heating- moisture content below 15 %

  12. Table 7.3 Assembly tolerance on timber structures (main reference: Finnish general construction quality requirements RYL 2000 ).

  13. 1) In the direction of grain, the nails have to be at least d out of line from each other, if a1 < 14d. 2) Drilling once through all members or using one drilled member as a template 3) When wood members have 1 mm oversize holes and metal parts have 1,5..2 mm oversized holes. 4) In both surfaces of all wood members 5) In the grain direction, the row may be out of line max. 5 mm from each other 6) When in wood-metal connections have 1 mm oversized holes in metal parts 7)t is the design smooth length in a wood member 8) Gap between wood surface and metal plate, where tt is the metal plate thickness 9) For example the distance of a supporting L-plate from the wood-wood contact surface

  14. Table 7.5 The tolerance of holes for connectors, if no other information is given in the structural design. D is the hole diameter, d is the connector nominal diameter, Lp is the depth of the hole measured from the designed connector head location and L is the nominal length of the connector. Wood here signifies all wood and wood-based panel products.

  15. Further ideas for the future • The guideline should be made into European level • Production of a CEN standard • Performing a risk analysis on a demanding building project

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