THEORETICAL DEVELOPMENTS AND NUMERICAL VERIFICATION OF A DISPLACEMENT-BASED DESIGN PROCEDURE FOR STEEL BRACED STRUCTURES

摘要

The paper discusses concepts and presents procedures for the development of a displacement-based design (DBD) methodology for steel braced structures. One basic concept in DBD is the independence of yield deformations of structural members from their strength. This independence allows the yield deformation to be computed before selecting member cross section properties, i.e. at the starting phase of the design. Using appropriate sub-structuring techniques, yield displacements of the whole structure can also be computed independent of member strength. In addition, post-yield displacements can be computed before member cross sections have been completely detailed. This only requires that the ultimate limit state for the whole structure (e.g. the achievement of a limiting ductility in one or more members) is clearly identified. Once inelastic target displacements have been computed, earthquake engineering methods can be applied to compute the strength required in order that displacements are not exceeded under the design-level earthquake. The case of inverted V-bracing is taken as case study, because of specific features emphasizing problems that could be encountered in the application of the new methodology. Both static and dynamic inelastic response analyses under a set of selected acceleration records have been carried out, with reference to a 10-storey frame. Results are very encouraging about the potentialities of the novel methodology, showing that maximum displacements, drifts and ductility demand are within the limits imposed at the design stage.