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This paper considers the time-varying behaviour of composite beams under sustained service loads. A non-linear method of analysis involving a Newton-Raphson solution procedure is developed and used to investigate the time-dependent response of composite cross-sections. The age-adjusted effective modulus method is used to model the constitutive relationship for concrete, while yielding and residual stresses in the steel joist are also accounted for. At typical service load levels, the effect of creep and shrinkage dominates the time-dependent reduction of stiffness, with the effect of residual stresses being only minor. M.A. Bradford and R.I. Gilbert
Mr A. C. G. Hayward (F) (Cass Hayward & Partners): The authors state that a design must take account of its erection or at least one possible sequence of construction. Unfortunately, the ‘accepted’ system in UK buildings, whereby the engineer designs only the members in a steel frame and requires the fabricator to proportion and detail the connections, is no encouragement, and problems occur. It has been known for fabricators to have been asked to design connections for a bending strength which exceeds that of the beams joined! Also the turnround demanded by ‘fasttrack’ construction means that a fabricator has insufficient time to design properly what are the most vital elements in the structure. Most structural failures or problems occur at connections.
Overcoming shape bias in timber laminates-and in rounding off errors in finite element shell programs! Mr P. Mawer, from Bude, remarks on a technique by which it is possible to overcome ‘wedging’ effects in the production of timber laminates, and draws an interesting analogy with a numerical device in computing: During manufacture of glued-laminated timber, a little trick is played by the planer operator.