Design Aspects of Pitched and Tapered Glued Laminated Beams

Abstract

The current AITC recommended procedure for the design of pitch and tapered curved (PTC) glulam beams is an iterative one that requires initial approximation of certain parameters. Trial designs are checked for compliance with the design criteria (i.e., allowable stresses, deflections, and dimensional limits), and revisions are made as necessary. The resulting design is structurally satisfactory, but generally the procedure does not converge to the most efficient design based on material usage. In the present study the design of a PTC glulam beam is formulated as a structural optimization problem. Minimization of material volume is the design objective. Solutions are obtained for representative values of top slope, span length, superimposed loads, and allowable stresses. The results are intended to: (1) Evaluate certain AITC recommendations regarding trial values of parameters; (2) suggest better approximations where necessary; and (3) identify the design constraints controlling the optimum solution. In addition, several shortcomings of the current procedure are identified, and recommendations are made for correcting them.