Inventory-Constrained Structural Design: New Objectives and Optimization Techniques

Increasing pressure to reduce the life-cycle impact and material consumption of new structures is driving interest in the use of minimally processed or second-hand structural materials in new construction. Conventional structural design methods, however, assume supply chains which can deliver effectively infinite supplies of structural elements in a wide range of dimensions. The use of minimally-processed or reused structural materials requires a new design approach which is tolerant of highly constrained inventories, in which elements exist in strictly finite quantities and are of predetermined dimensions. There is little literature or industry experience concerning this kind of inventory-constrained design. This paper presents theoretical contributions which are intended to provide a groundwork for future researchers and designers to develop and evaluate methods for inventory-constrained structural design. The concept of an “assignment” of inventory elements to structural elements is introduced. An integer program for the optimization of assignments of bar-type inventory elements to a statically determinate pin-jointed truss is formulated. New objectives for the optimization of assignments are introduced. Finally, analytical and numerical techniques for computing the “Offcut Ratio” objective are presented which may help designers to significantly reduce material consumption and waste, particularly for repetitive truss-like structures such as roof trusses, utility towers, and truss bridges.