Development of a CFRP system to provide continuity in existing reinforced concrete buildings vulnerable to progressive collapse

Abstract

Reinforced concrete buildings may be vulnerable to progressive collapse due to a lack of continuous reinforcement. Progressive collapse is an extreme form of collapse that is disproportionate to the originating cause. Such collapses cause not only significant damage to buildings, but also greater loss of life and injuries. Carbon fiber reinforced polymer (CFRP) may be used to retrofit existing reinforced concrete beams and provide the missing continuity needed to resist progressive collapse. This research focuses on retrofitting the beams in a reinforced concrete building to provide sufficient continuity to reach catenary action. The catenary action may allow the beam to carry vertical loads at large displacements if a supporting column were removed. The CFRP can provide continuity through the negative moment reinforcement or through the positive moment reinforcement. The research was broken into three major components. Anchorage tests form the design basis of the CFRP retrofit and ensure that the capacity of the retrofit can be accurately predicted. Continuity tests determine if the CFRP retrofit is capable of providing continuity and if the retrofit will allow the beam to reach catenary action and sustain a load representing resistance to progressive collapse. The analysis model forms a set of equations for catenary action so the results can be applied to reinforced concrete beams in general. Forty anchorage tests, eight continuity tests, and one analysis model were constructed and evaluated. The anchorage tests found that carbon fiber anchors enabled improved utilization of the tensile capacity of a CFRP sheet and improved the efficiency of material usage in CFRP retrofits. The continuity tests found that beams without continuous reinforcement can reach catenary action (depending on design details) and a CFRP retrofit, if designed correctly (placed in locations that do not cause rebar fracture before catenary), may be able to reduce vulnerability to progressive collapse. The analysis model was able to accurately predict the load-deflection behavior of a reinforced concrete beam in catenary action. The overall conclusion is that a CFRP retrofit can reduce vulnerability to progressive collapse in reinforced concrete buildings.