**************** Disclosure to Promote the Right To Information Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public. Mazdoor Kisan Shakti Sangathan "The Right to Information, The Right to Live" IS 4924-2 (1968) : Method of Test for Nail-jointed Timber Trusses, Part II: Proof Test [CED 13: Building Construction Practices including Painting, Varnishing and Allied Finishing] Jawaharlal Nehru 'Step Out From the Old to the New' a^v j i iw&*frgamsBP 2*S< W I *>S*V2^NK^ ^frcvvv^ Satyanarayan Gangaram Pitroda Invent a New India Using Knowledge Bhartrhari — Nitisatakam "Knowledge is such a treasure which cannot be stolen" .^^_ • BLANK PAGE *rt*2V^ PROTECTED BY COPYRIGHT IS: 4914 (Part II}- 1968 ( Reaffirmed 2000 ) Indian Standard METHOD OF TEST FOR NAIL-JOINTED TIMBER TRUSSES PART Jl PROOF TEST UDC 69 024*1; 620' 1 72 21 £) Copyright I960 INDIAN STANDARDS INSTITUTION MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG NbW DELHI I Price flj 2^? March 19 * 3 IS: 4924 (Part II) -1968 Indian Standard METHOD OF TEST FOR NAIL-JOINTED TIMBER TRUSSES PART II PROOF TEST Building Construction Practices Sectional Committee, BDC 13 Chairman Shri M. L. Nanda Members Additional Director Standards ( Architecture ) , RDSO Deputy Director Standards ( Architecture ), RDSO ( Alternate ) Shri B. D. Ahuja Shri P. C. Jain ( Alternate ) Shri B. V. Apte Shri K. J. Sapra ( Alternate ) Chief Architect Chief Engineer Chief Engineer ( B & R ) Executive Engineer ( Alternate Shri B. K. Choksi Shri J. Datt Shri Y. K. Mehta ( Alternate ) Shri V. S. Devdhar Prof Dinesh Mohan Director Shri C. M. Goveas Shri Harish Chandra Shri S. B. Joshi Shri R. N. Joshi ( Alternate ) Shri V. S. Kamat Shri Kewal Krishan Shri N. J. Masani Representing Central Public Works Department Railway Board ( Ministry of Railways ) National Buildings Organization ( Ministry of Works, Housing & Supply ) Builder's Association of India, Bombay Central Public Works Department ( Architectural Wing) National Buildings Construction Corporation Ltd, New Delhi Public Works Department, Government of Rajasthan ) In personal capacity ("Shrikunj", Near Prakash Housing Society, Athwa Lines, Surat 1 ) The Concrete Association of India, Bombay Institute of Surveyors, New Delhi Central Building Research Institute ( CSIR ), Roorkee Engineering Research Department, Government of Andhra Pradesh Atomic Energy Commission, Bombay Central Public Works Department M/s S. B. Joshi & Co Ltd, Bombay The Hindustan Construction Go Ltd, Bombay Public Works Department, Government of Punjab Forest Research Institute and Colleges, Dehra Dun ( Continued on page 2 ) INDIAN STANDARDS INSTITUTION MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG NEW DELHI 1 IS: 4924 (Part II) -1968 ( Continued from page 1 ) Members Shri T. R. Mehandru Col O. P. Narula Shri K. P. Ghosh ( Alternate ) Shri A. P. Paracer Shri D. J. Patel Senior Architect (B) I, Central Public Works Department Shri J. D. Shastri Shri T. N. Subbarao Shri P. M. Apte ( Alternate ) Superintending Engineer, Design and Marine Works Circle ExecutiveEngineer,B uilding Centre Division ( Alternate ) Shri R. Nagarajan, Director ( Civ Engg ) Representing Institution of Engineers ( India), Calcutta Engineer-in-Ghief ' s Branch, Army Headquarters Central Public Works Department Hindustan Housing Factory Ltd, New Delhi Indian Institute of Architects, Bombay Directorate General of Health Services, New Delhi Gammon India Ltd, Bombay Public Works Department, Government of Madras Director General, ISI ( Ex-officio Member ) Secretary Shri C. K. Bebarta Assistant Director ( Civ Engg ), ISI Timber Engineering Subcommittee, BDC 13:4 Convener Shri N.J. Masani Members Shri A. N. Bajaj ( Alternate to Shri N. J. Masani ) Shri P. M. Abdul Rahiman Dr S. M.K. Chetty Dr Joseph George ( Alternate ) Shri Daljit Singh Shri J. Durai Raj Shri K. G. Salvi ( Alternate ) Shri P. R. Rijhsinghani Senior Architect (I) Forest Research Institute and Colleges, Dehra Dun Structural Engineering Research Centre ( CSIR ), Roorkee Central Building Research Institute (CSIR), Roorkee Oriental Building and Furnishing Co Private Ltd, New Delhi Hindustan Housing Factory Ltd, New Delhi Engineer-in- Chief *s Branch, Army Headquarters Central Public Works Department (Architectural Wing) Shri P. C. Shah National Buildings Organization ( Ministry of Works, Housing & Supply ) Shri R. K. Bhartari ( Alternate ) Superintending Engineer (Delhi Central Public Works Department Central Circle IV ) Superintending Engineer Public Works Department, Government of ( Planning ) Madhya Pradesh Shri J. Vasudev Railway Board ( Ministry of Railways ) IS: 4924 (Part II) -1968 Indian Standard METHOD OF TEST FOR NAIL-JOINTED TIMBER TRUSSES PART II PROOF TEST 0. FOREWORD 0.1 This Indian Standard ( Part II ) was adopted by the Indian Standards Institution on 12 December 1968, after the draft finalized by the Building Construction Practices Sectional Committee had been approved by the Civil Engineering Division Council. 0.2 Extensive investigations have been carried out in the Forest Research Institute, Dehra Dun on nail-jointed timber trusses fabricated from representative Indian species of timber, to find out relation between their long-term service behaviour and the observations made in short-term load tests. A method for conducting such long-term proof testing for these trusses systematically, so as to obtain dependable results, has now been evolved. To give necessary guidance to engineers, details of this method are eiven in this standard. The details of nail-iointed construction have Jbeen'covered in IS : 2366-1963*. 0.3 The main objectives of the tests shall be as detailed below: a) To simulate service conditions of loading on the truss, determining the stiffness of members and joints; b) To observe the joint slip ( instantaneous deformation ) and creep in timber roof trusses under prolonged loading, thus finding out the stiffness as a whole; c) To observe maximum deflection in the truss under long continued loading in order to provide initial camber in the bottom chord during fabrication stage; and d) To study the effect of humidity and temperature variation on timber roof frames with normal building openings. 0.4 In the formulation of this standard due weightage has been given to international co-ordination among the standards and practices prevailing in different countries in addition to relating it to the practices in the field in this country. 0.5 In reporting the results of a test or analysis, made in accordance with this standard, if the final value, observed or calculated, is to be rounded off, it shall be done in accordance with IS : 2-1960J. *Code of practice for nail-jointed timber construction. "("Rules for rounding off numerical values ( revised ) . IS: 4924 ( Part n>- 1968 1. SCOPE 1.1 This standard ( Part II ) covers the method of proof testing for the fabricated nail-jointed timber trusses to ascertain the actual behaviour of truss with regard to joint slip, deflection, etc, under service conditions and prolonged loading. 2. PROCEDURE OF TEST ( EXPERIMENTAL SET-UP ) 2.1 Support Conditions — The truss ( test specimen ) shall be supported either on timber column or masonry pillars and shall be fixed firmly. Sufficient clearance shall be made available under the bottom chord for observation as well as for hanging the weights. 2.2 Loading Arrangement — The arrangement for loading shall be as illustrated in Fig. 1. Loads shall be applied at the node points in top and bottom chords of the truss in the form of hanging platforms conforming to those actually applied in the field of construction. 2.3 Guiding Attachment for Lateral Stability — Guiding attachment shall be provided to keep the lateral stability of the unit under test. This may be done by keeping a similar truss unit placed at suitable distance to simulate rigidity in actual use brought by attachment of adjacent trusses through purlins, and linking both the units together with hinged timber purlins, so that the truss under test receives only lateral restraint without any restraint to the vertical deflection. 2.4 Deflection Measuring Equipment — One dial gauge at the centre of the bottom chord of the truss shall be fixed permanently for recording vertical deflection of the whole truss under test. 3. LOADING 3.1 Rate of Loading — Apply gradually a test load 1*25 times the design load at each of the node points in top and bottom chords. Note — It is assumed that this test load will produce the same effect as in long duration caused due to incidental and wind loads which generally produce impact on account of their speed, resulting in increased stresses. 3.2 Period of Loading — Test load shall be kept constant until a perma- nent set in the dial gauge reading is reached, subject to a maximum period of one year. 4. OBSERVATION 4.1 Record of Deflection — Deflection reading shall be recorded, at the centre of the bottom chord, daily. IS: 4924 (Part II) -1968 LOAD LOAD LOAD LOAD POSITION OF DIAL GAUGE IA Type of Truss to be Used for Three, Four and Five Metres Spans LOAD LOAD LOAD POSITION OF DIAL GAUGE LOAD IB Type of Truss to be Used for Six Metres Span Fig. 1 Loading Arrangement for Standard Short Span Timber Trusses IS: 4924 (Part II) -1968 4.2 Climatic Variations — Major climatic variations and their effects on deflection shall also be noted. 5. INTERPRETATION AND UTILIZATION OF DATA 5.1 Time-slip curve shall be plotted to a convenient scale showing complete observation for the whole year. A specimen of such curve is shown in Fig. 2. 5.2 Instantaneous deflection shown by the graph after 24 hours may be taken as due to slip of joints. 5.3 Initial camber shall be provided at the bottom chord of the truss. This shall be equal to 9nn of the span or double of the maximum deforma- tion observed during proof test, whichever is more. 6. GENERAL GUIDANCE 6.1 Details are given below: a) Nail-jointed timber trusses shall be designed conforming to IS: 883-1966*; b) The two ends of the truss shall be considered fixed at their supports; c) Split-chord construction shall be preferred as it allows the use of higher value of nail strength being in multiple shear; d) Timber splice plates, if used, shall be provided in such a way that the grain of the plates coincides with the direction of load to be transmitted; e) The individual thickness of a timber splice plate shall not be kept less than 2 cm as it is liable to split due to atmospheric variations. It is recommended that the total thickness of the side members (or two splice plates) shall be kept 1*5 times the thickness of main member for better behaviour of structural units; f) The thickness of main member in monochord construction shall not be kept less than 3 cm; g) The individual thickness of spaced members in split-chord construction shall not be kept less than 2*0 cm in case of web members and 2*5 cm in case of chord members; h) The space between two spaced members shall be restricted to a maximum of 3 times the individual thickness of the member; *Code of practice for design of structural timber in building ( second revision). MAXIMUM DEFORMATION OBSERVED — TEST IS CONTINUED SUBJECT TO A MAXIMUM PERIOD OF ONE YEAR INSTANTANEOUS DEFORMATION } DUE TO SLIP OF JOINTS NOTED AFTER 24 HOURS 30 60 i i i i i i -i_i i i_ 90 120 150 180 210 ' ' 240 ' ' 270 ' ' 300 ' ' 330 ' ' 3^0 TIME, DAYS Fig. 2 Specimen Curve in Long-Term Proof Testing of Nail-Jointed Timber Trusses I IS: 4924 (Part II) -1968 j) Care shall be taken that serious knots, shakes and checks ( which are strength-reducing defects ) do not occupy places where joints are provided; k) For nail-jointed construction only seasoned timber is recom- mended. The timber is to be seasoned to an optimum average moisture content which it is liable to experience while in service, so that the effect of atmospheric variation is minimized; m) Timber distance pieces shall be inserted in the spaced compres- sion member, at a distance of 30 d> where d is the thickness of individual member, with a minimum of one piece at the centre between two node points. In the spaced tension members one spacer piece at the centre is sufficient to keep the integrity and safety of the truss during and after fabrication stages; n) Better pieces ( with lesser strength-reducing defects ) shall be used for longer tension members or longer compression members; p) As far as possible, the nails at the joints shall be arranged in such a way that the line of force in the members passes through the centroid of the group of nails transmitting load to it. Where it is not practicable, suitable allowance shall be made for any eccentricity in computing the maximum force in the member; q) A minimum of two nails at a node point and four nails at a lengthening joint shall be provided for the rigidity of a joint; r) In order to avoid splitting of the members recommended prebore for a particular gauge of nail shall be provided; and s) Nailing of joints shall be done from both the faces. Protruding nail shall either be cut flush or may be clenched across the grains of timber.