Strength of Concrete-Filled Plastic Tube Stub Columns Using a Normalized Stiffness Approach

Abstract

The polymeric plastic tube can encase concrete and provide an external shell for confining and insulating concrete core from the impact of the surrounding environment. The effect of the tube and concrete strength on the concrete-filled plastic tubes (CFPT) stub columns specimens was investigated. Test results show that the tube provides passive confinement to the concrete core, which increases both the maximum peak load and the ultimate strain capacities. However, the tube has low stiffness, which affects its confinement capacity and hindrance its applications for structural use. To examine the role of tube stiffness and express the strength of a concrete-filled plastic tube, a previously proposed normalized stiffness approach for both active and passive confinement of FRP-confined concrete was adopted for the present study. From the perspective of stiffness and to better understand the behavior of CFPT specimens under uniaxial compression loads, a database of recent studies were assembled combined with the results of the present study. Several existing strength models for FRP-confined concrete were also used to predict the mechanical strength of CFPT. Two models were proposed with good predictions of the experimental results of the database.