Risk-based Design of Regular Plane Frames Subject to Damage by Abnormal Events: a Conceptual Study

TL;DR

This paper introduces a risk-based approach for optimizing the design of regular plane frames to balance strengthening costs against the likelihood of progressive collapse due to abnormal events.

Contribution

It presents a novel risk-based formulation for the optimal design of plane frames considering element loss, threat probabilities, and failure modes.

Findings

Optimal trade-offs between strengthening costs and failure risks identified

Threat probabilities where strengthening is more cost-effective analyzed

Impacts of strengthening extent and cost on structural robustness studied

Abstract

Constructed facilities should be robust with respect to the loss of load-bearing elements due to abnormal events. Yet, strengthening structures to withstand such damage has a significant impact on construction costs. Strengthening costs should be justified by the threat and should result in smaller expected costs of progressive collapse. In regular frame structures, beams and columns compete for the strengthening budget. In this paper, we present a risk-based formulation to address the optimal design of regular plane frames under element loss conditions. We address the threat probabilities for which strengthening has better cost-benefit than usual design, for different frame configurations, and study the impacts of strengthening extent and cost. The risk-based optimization reveals optimum points of compromise between competing failure modes: local bending of beams, local crushing of columns, and global pancake collapse, for frames of different aspect ratios. The conceptual study is based on a simple analytical model for progressive collapse, but it provides relevant insight for the design and strengthening of real structures.