Extreme response of reinforced concrete buildings through fiber force-based finite element analysis

• A fiber-based model for progressive collapse resistance assessment was developed.
• A special purpose routine was prepared for sudden column loss simulation in MRFs.
• Explicit and implicit dynamic analyses reproduced the response of 2D and 3D MRFs.
• Demand-to-capacity ratio of the secondary beams controls the behavior of 3D MRFs.
• Structural redundancy enables a safe rationally-controlled alternative load path.

Recent events showed that buildings designed according to conventional codes are not necessarily able to resist man-made extreme events such as impact or explosions. In the past, safety against disproportionate collapse of key elements has been increased by non-structural protective measures such as barriers, sacrificial elements and limitation or control of public access. Codified procedures emerged in the last decade asking for resistant structural design methodologies to inhibit failure incidents acting on structural components performance.This paper presents an open access procedure using a fiber-based model in order to reproduce the progressive collapse of reinforced concrete (RC) buildings subjected to blast loading in an urban environment that leads to the loss of one or more bearing elements. Member removal in this fashion represents an event that happens when extreme situations or abnormal loads destroy the member itself. Two- and three-dimensional models of frame structures have been created and compared using three different numerical tools: an open source program such as OpenSees and two different commercial codes, SeismoStruct and Ls-Dyna. The first two are more classical fiber-based software, while the last one is a well-established general purpose finite element (FE) package. Removal of critical elements is assumed to occur in the building studied and a special purpose routine has been developed, within OpenSees and SeismoStruct, to create a fiber model capable of simulating overall structural response due to their failure. In this computational routine, one or more vertical members are instantaneously removed from the model and the ability of the building to successfully absorb member loss is investigated. The results obtained have been compared and validated by using the transient dynamic FE program Ls-Dyna.The numerical and modeling outcome of this research on progressive collapse behavior of RC buildings may be immediately applied to the design, vulnerability assessment and strengthening of different structural typologies ranging from residential frames to strategic and military facilities.