1、| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BRITISH STANDARD BS 6446 : 1997 ICS 79.060
2、.01; 91.080.20 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Specification for Manufacture of glued structural components of timber and wood based panelsBS 6446 : 1997 This British Standard, having been prepared under the direction of the Sector Board for Building and Civil
3、Engineering, was published under the authority of the Standards Board and comes into effect on 15 June 1997 BSI 1997 The following BSI references relate to the work on this standard: Committee reference B/518/3 Draft for comment 95/107127 DC ISBN 0 580 26828 4 Amendments issued since publication Amd
4、. No. Date Text affected Committees responsible for this British Standard The preparation of this British Standard was entrusted by Technical Committee B/518, Structural timber, to Subcommittee B/518/3 Glued laminated timber, upon which the following bodies were represented: British Adhesives and Se
5、alants Association British Woodworking Federation Department of the Environment (Building Research Establishment) Glued Laminated Timber Association Institution of Civil Engineers Nordic Timber Council (UK) Timber Research and Development Association Timber Trade Federation Wood Panel Industries Fed
6、erationBS 6446 : 1997 BSI 1997 i Contents Page Committees responsible Inside front cover Foreword ii Introduction 1 Specification 1 Scope 1 2 Normative references 1 3 Definitions 1 4 Design parameters to be established prior to production 2 5 Materials 2 6 Joints 3 7 Preparation of timber and wood b
7、ased panel products 3 8 Permissible deviations on assembled component dimensions 4 9 Requirements for production facilities, manufacturing processes and production control 4 10 Storage 8 11 Testing of components 8 12 Marking 8 Annex A (normative) Determination of glue line shear strength 9 Tables 1
8、Selection of adhesive for service classes 3 2 Moisture content enhancement factors for wood based panels 3 3 Recommended limits of cupping when cramping pressure is used 4 4 Sizes and maximum spacings of nails for nail pressure on glue line 6 Figures 1 Examples of nail spacing 7 A.1 Shearing tool 10
9、 A.2 Dimensions of test specimens 11 List of references Inside back coverii BSI 1997 BS 6446 : 1997 Foreword This British Standard has been prepared by Subcommittee B/518/3, Glued laminated timber. It supersedes BS 6446 : 1984, which is withdrawn. This edition of BS 6446 has been revised to take acc
10、ount of the deletion of BS 1204 : Part 1, and its replacement by BS EN 301. This affects the scope, 6.3 and 7.1. The climate conditions given in the previous edition have been replaced by the corresponding service classes referred to in DD ENV 1995-1-1 and BS 5268 : Part 2 (see list of standards on
11、the inside back cover). Other minor revisions have been made to accommodate the revision or deletion of the standards referred to in this 1997 edition of this standard. The contents of the standard have in parts been re-arranged to reflect more closely component manufacturing processes, and annex A
12、has been re-written so that it is compatible with related European standards. When the original edition of this standard was prepared, the only woodbased panels for which design stresses were available (from BS 5268 : Part 2) were plywood and tempered hardboard. Both BS 5268 : Part 2 and DD ENV 1995
13、-1-1 now recognize design stresses for other types of woodbased panel, and this term has been substituted for plywood and/or tempered hardboard. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an in
14、side front cover, pages i and ii, pages 1 to 12, an inside back cover and a back cover. BSI 1997 1 BS 6446 : 1997 Specification Introduction There is a long history of structural components being successfully assembled from pieces of timber and plywood glued together, particularly in the aircraft in
15、dustry. The use in buildings of glued structural components (e.g. box beams, single web beams, stressed skin panels, gusseted trusses, etc.) made from timber, and wood based panels poses various problems with regard to the preparation of materials and the selection of adhesives because of the wide r
16、ange of environmental conditions that can be encountered in service. The gluing process is a sensitive operation. Changes in either environment of the production area or in the conditions of materials can have adverse effects upon the performance of the component in service. The work should be super
17、vised by skilled and experienced personnel and throughout the manufacturing operations strict control of quality should be maintained. Routine testing of glue line strength together with records of production are essential aspects of the quality assurance required by this standard. The handling, sto
18、rage and protection of components after manufacture, including transportation to site, erection and any protection that may be required until the building is completed, are of equal importance to the manufacturing requirements given in this standard. Due regard should be given in this respect to the
19、 recommendations of BS 5268 : Part 2. The requirements of this standard are the minimum to achieve sound glued joints and consequently an adequate performance in service. 1 Scope This British Standard specifies the requirements for the manufacture of structural components which have been designed us
20、ing either: a) design or load testing data from BS 5268 : Part 2; b) properties established from European Technical Approvals; c) information derived from prototype testing according to BS 5268 : Part 2. In such components (e.g. box beams, single web beams, stressed skin panels, gusseted trusses) ma
21、de from separate pieces of timber, plywood or other wood based panels that are glued together, the continued integrity of the glue line is essential for satisfactory performance in service. Requirements are specified for production facilities, materials, types of joint, production, production contro
22、l, the use of preservative and flame retardant treated materials and storage. Glued laminated timber structural members and finger joints in structural softwood are specified in accordance with BS EN 386 and BS EN 385 respectively. NOTE. Components manufactured in accordance with this British Standa
23、rd may not be suitable for use in service class 3 of DD ENV 1995-1-1 and BS 5268 : Part 2 where they are exposed directly to the weather, e.g. marine structures. 2 Normative references This British Standard incorporates, by dated or undated reference, provisions from other publications. These normat
24、ive references are made at the appropriate places in the text and the cited publications are listed on the inside back cover. For dated references, only the edition cited applies; any subsequent amendments to or revisions of the cited publication apply to this British Standard only when incorporated
25、 in the reference by amendment or revision. For undated references, the latest edition of the cited publication applies, together with any amendments. 3 Definitions For the purposes of this British Standard the definitions given in BS 6100 : Part 4 and BS 6138 apply together with the following: 3.1
26、adhesive spread Amount of adhesive applied to the surfaces to be bonded. In a single spreading this amount is applied to one surface, in double spreading it is divided between the two surfaces to be joined. 3.2 closed assembly A number of pieces spread with adhesive and assembled in a component prio
27、r to the application of pressure. 3.3 open assembly A number of pieces spread with adhesive prior to closed assembly. 3.4 clenching Method of securing the point side of a protruding nail by driving it sideways thereby forming a right angled bend. 3.5 cold-setting adhesive Adhesive that can be applie
28、d and will set at a temperature of 23 C or lower.2 BSI 1997 BS 6446 : 1997 3.6 curing time Curing time is that time interval between mixing the adhesive and the attainment of full bond strength. NOTE. Full water resistance may not be attained for considerably longer. The glue lines of components sho
29、uld therefore be protected from wetting (e.g. due to weather or by water-based finishes and preservative treatment) for at least 7 days after assembly. 3.7 cramping pressure Force applied to the contact faces of glued pieces divided by the area of the glued surface over which the force is deemed to
30、act. 3.8 glue line (bond-line) The adhesive layer in a bonded joint. NOTE. The term glue line is deprecated in BS 6138; the preferred term is bond-line. glue line has been used throughout this document, however, as it is the term most widely used and understood in the woodworking industry. 3.9 harde
31、ner Curing agent for use with resins that yield rigid (hard) products. NOTE. It may be supplied in either liquid or powder form, or may be incorporated in the adhesive by the manufacturer. It is an essential part of the adhesive, the properties of which depend on using the constituent parts of the a
32、dhesive as directed. 3.10 jigs Formers that are used at the time of manufacture to give the member its finished shape. 3.11 pot life Period during which the adhesive can be used after mixing the constituents. NOTE. This varies with the volume and temperature of the mixed adhesives and the ambient te
33、mperature. 3.12 run off Reduction of a finished cross-sectional dimension at the end of a piece of timber that occurs during a machining operation. 3.13 setting temperature Temperature of the adhesive during the setting process. 3.14 setting time Time interval between the commencement of the setting
34、 process, e.g. the application of heat and/or pressure to an assembled joint, and the attainment of sufficient bond strength to enable the components to be handled. 3.15 storage life (shelf life) The time of storage under stated conditions during which an adhesive may be expected to retain its worki
35、ng properties. 3.16 synthetic resin adhesive Adhesive substantially composed of a synthetic resin or resins, including any hardener or modifier that may have been added by the manufacturer or that may be required to be added before use according to the adhesive manufacturers instructions. 4 Design p
36、arameters to be established prior to production 4.1 Service conditions The manufacturer shall obtain details of the anticipated service conditions and moisture content prior to production. 4.2 Manufacturing specification Those elements of the specification which can affect manufacture shall be estab
37、lished before commencing production. The following are examples of such elements: a) the types of material (see clause 5); b) preservative and flame retardant treatments (see 4.3); c) the moisture content of the component in service; d) the dimensions of individual pieces and the component; e) the l
38、ocation of joints and splices; f) the camber; g) the surface finishes. 4.3 Preservative and flame retardant treatments The manufacturer of the structural components shall obtain and follow advice from the manufacturer of the preservative or flame retardant and from the adhesive manufacturer on the c
39、ompatibility of materials, both where treatment of individual pieces is to take place before gluing and where treatment of a component is to take place after gluing. This shall be done at the earliest possible opportunity. 5 Materials 5.1 Timber and wood based materials The species or type and stren
40、gth class of timber, and wood based panels shall be those specified in the design of the component and shall be selected either from those for which mechanical properties are given in BS 5268 : Part 2 or for which there is a European Technical Approval. NOTE. Other materials may be used which have b
41、een established as suitable by prototype testing. 5.2 Mechanical fasteners Unless otherwise specified by the designer the following mechanical fasteners shall be used to apply glue line pressure (see the note in 7.1.3): a) nails; b) woodscrews; c) staples. BSI 1997 3 BS 6446 : 1997 5.3 Adhesives Adh
42、esives shall conform to either type I or type II of BS EN 301. The choice of type I or type II shall be determined by the service class intended for the finished component as given in table 1. Table 1. Selection of adhesive for service classes Service class 1) BS EN 301 Adhesive type 1I I 2I 1) As d
43、efined in DD ENV 1995-1-1 and BS 5268 : Part 2. The types of components defined in this standard may not be suitable for use in service class 3. 6 Joints 6.1 General The type of materials shall be chosen from those specified in 5.1 and shall have the appropriate moisture content determined in accord
44、ance with 9.3.1. NOTE 1. The materials specified in 5.1 are the basis for the construction of a wide range of structural components. NOTE 2. When there are differing changes of moisture content in the pieces forming a joint, distortion occurs and stresses are induced in the glue line. Limits are the
45、refore placed on the maximum change of moisture content in a piece between the time of manufacture and when in service, as well as the maximum difference of moisture content between adjacent pieces at the time of manufacture. Unless the limits given are observed there could be failure of the joint.
46、6.2 Component thickness The maximum material thickness should relate to its stiffness and to the method of cramping to ensure that correct pressure is transmitted to all parts of the glue line (see 7.1.3). 6.3 Moisture content At the time of manufacture the moisture content of timber shall be within
47、 5 % moisture content of the anticipated equilibrium value (see 4.1) of the timber in service. The maximum difference between the moisture contents of adjacent pieces of the timber at the time of manufacture shall be 4 % moisture content. The equilibrium moisture content of wood based panels is less
48、 than that of solid timber. This should be allowed for when calculating the differential moisture content at the time of bonding (see table 2). Table 2. Moisture content enhancement factors for wood based panels Material Multiplication factor Solid wood 1.00 Tempered hardboard 1.67 Particle board 1.
49、42 Plywood 1.25 7 Preparation of timber and wood based panel products 7.1 Timber 7.1.1 Moisture content The moisture content of the timber, at the time of machining the gluing surfaces, shall be in accordance with 6.1. 7.1.2 Gluing surface 7.1.2.1 The gluing surfaces shall be machined not more than 24 h before assembly. The surfaces shall be cleanly and accurately cut with no compression or damage of the fibres, hit and miss planing, or run off at the ends. The depth of cutter marks shall not exceed 0.5 mm. NOTE. For non-rectangular cross-sections, special care should b
