Practical considerations on the design of concentrically-braced steel frames to Eurocode 8

Abstract

Conventional seismic design of steel buildings is typically conducted, at a preliminary stage, by resorting to idealisations of member joint behaviour (e.g. fully-articulated connections). After the main structural members are defined, one proceeds with the connection design process, whose actual behaviour may or may not deviate from the assumption initially made at the design stage. This research study assesses the implications of connection-related design assumptions for steel concentrically-braced frames (CBFs) designed to Eurocode 8. This goal is achieved through the use of a Python-OpenSees-based automated seismic analysis and design framework to define an extensive set of CBF archetypes. The effect of non-explicit consideration, at the design stage, of the diagonal-to-frame gusset connections is evaluated. Full compatibility of this assumption is shown to be unassured, particularly due to the combined effects of member length reduction and boundary condition flexibility on the member's normalized slenderness. Based on the extensive suite of frame and connection designs considered, a regression-based modified normalized slenderness factor is proposed to realistically estimate, at the design stage, the normalized brace slenderness.