Mitigation of Progressive Collapse by the Activation of the Elasto-Plastic Catenary Behaviour of R.C. Slab Structures

Fabrizio Palmisano

doi:10.2174/1874836801408010122

Abstract

Mitigation of progressive collapse was highlighted in 1968 with the collapse of the Ronan Point building in the United Kingdom. Technical standards followed suit with increased requirements and recommendations to encourage the design and construction of more robust buildings. The intent has been to establish a design process that recognizes and considers the potential that buildings could experience abnormal and extreme loads or events that seriously compromise one or more critical load-carrying elements. This article aims to show that if the main goal of the design is to protect human lives in these extreme conditions, even sacrificing the building functionality, simple measures such as the activation of the elasto-plastic catenary behaviour of the slab reinforcement, could be very effective to increase the building robustness without substantially increasing the cost of a structural system.

Highlights

The 1968 Ronan Point collapse (Fig. 1) has been instrumental [1] in making engineers aware of the possibility of a chain reaction or progressive collapse
In R.C. buildings, the estimated final damage caused by a progressive collapse phenomenon is proportional to the original damage extension
The loads, in every deviation nodes, give horizontal thrusts to the structure. This scenario demonstrates that a column collapse creates, in the floors, forces similar to those generated by an earthquake

Summary

INTRODUCTION

The 1968 Ronan Point collapse (Fig. 1) has been instrumental [1] in making engineers aware of the possibility of a chain reaction or progressive collapse. This direct method requires that, for any structural element over which the building cannot bridge, the element must be designed as a ‘key’ or ‘protected’ element, capable of carrying a static pressure loading of 34 kPa. The approach of the Eurocodes is more articulated. In R.C. buildings, the estimated final damage caused by a progressive collapse phenomenon is proportional to the original damage extension The larger this extension becomes, the lower the probability to activate alternate load paths becomes, because a large bypass of the damaged area needs a large strain energy investment that can be achieved only by large building deformations. The loads, in every deviation nodes, give horizontal thrusts to the structure This scenario demonstrates that a column collapse creates, in the floors, forces similar to those generated by an earthquake. The consequence is an extensive failure commonly referred as ‘domino effect’: every local rupture has effects disproportionate to the original cause

THE TENSILE MEMBRANE BEHAVIOUR OF FLOOR SLABS

K qULS lT2

The Elasto-Plastic Behaviour

H Ey A r

CONCLUSION