FEATURES
Certified laminated timber beams are manufactured under controlled conditions and processes , and have to be marked with certain information , such as the stress grade , certification mark of the certifying body , trade name and application class . Image : RSB Beams
Firstly , proper drying , grading / selection and machining of the timber to be used are very important considerations . The finger joints in boards to be used in laminated beams must also comply with the requirements set out in SANS 10096 , which governs the manufacture of finger-joints in structural timber .
In addition , the adhesive used to bind the wood together must be selected for the appropriate application class for which the laminated timber beam will be used . Adhesive systems are specially designed for use in these specific application classes , which range from exposed exterior to interior dry .
“ A structural beam manufactured with adhesive designed for interior dry use will not last long if used in an exterior application . Proper manufacturing process control is vital , as the use of the correct adhesive and timber will prove worthless if not correctly applied ,” Stears remarks . He adds , “ Important factors and conditions , such as timber moisture content and adhesive manufacturer requirements , like press time , pot life and spread rate , are vital to ensure a quality end product .” Once the manufacturing process is complete , grade compliance needs to be established or verified . This is achieved by means of a proof load test , which records the relevant data to determine compliance with the grade requirements on strength and MOE . Once this has been completed , adhesive bond integrity tests are performed on small samples to determine compliance in the total manufacturing process .
CERTIFICATION OF STRUCTURAL LAMINATED TIMBER
“ It is important to note that all timber used for structural purposes in South Africa must meet the strength requirements for stress grade 5 as a minimum , which means that any timber , including laminated timber units , that does not meet the relevant grade requirements is not
appropriate or safe for use as structural timber ,” says Stears . “ Only a few laminated timber manufacturers in South Africa are certified by an accredited product certification body , like SATAS and the South African Bureau of Standards ( SABS ), for the manufacture of laminated beams to the requirements of SANS 1460 for laminated timber .”
Note : Both SATAS and the SABS are the only two bodies accredited by the South African National Accreditation Systems ( SANAS ) to carry out certification on structural laminated timber .
Certified laminated timber beams are manufactured under controlled conditions and processes , and have to be marked with certain information , such as the stress grade , certification mark of the certifying body , trade name ( of the manufacturer ) and application class ( interior or exterior ).
According to Stears , “ The manufacture of structural laminated beams in compliance with SANS 1460 is a costly process , which is why some unscrupulous contractors may make use of inferior imported or ‘ backyard ’ products that do not meet the required standards for strength or quality for structural applications . The knock-on effects of this are potentially devastating .”
“ If a cheaper alternative product is used , failures could result , but these would more than likely only occur a few years after construction , and in most instances responsibility of repair and related costs would befall the unsuspecting owner ,” he says .
“ Laminated timber is a viable resource and an intelligent choice for structural construction applications , but the use thereof without traceability and product certification is a recipe for disaster ,” Stears affirms . “ While the informed homeowner or project developer can aid in the demand for above-board product , it is ultimately the responsibility of architects , designers and engineers to insist on certified laminated timber beams for use in structural applications ,” he concludes .
58 FEB / MARCH 2017 //