Thermal and Structural Behavior of Fire-Exposed Beam–Column Connections Consisting of Corbels Cast with Columns and Continuity Bars

Abstract

Beam–column connections with corbels supporting the beams and continuity reinforcement protruding from the columns, also known as composite connections, are often used in construction as an alternative to monolithic cast-in-place connections. Since they are halfway between fully rigid and pin connections, these semirigid composite systems require more in-depth investigation, especially concerning their behavior at high temperatures and in fire. Compared with fully rigid connections, the primary advantage of semirigid systems is that they allow the use of precast beams. Unlike pin connections, semirigid systems allow a certain degree of fixity at beam ends after the in-place casting of the top of the beams. This study focused on the designs of two full-size specimens representing the region of the connection comprising the column stub, corbel, and beam extremity cast and tested in ambient conditions and under standard fire exposure to compare their performance with two monolithic specimens tested under the same conditions. The study also develops a numerical model of the connection using a finite-element discretization (ANSYS software) to conduct a sequential analysis of the thermal and static behavior of the connection. The numerical results are shown to satisfactorily fit the deflection curves, crack patterns, and actual conditions of the specimen after failure. The semirigid connection is stiff at ambient and medium temperatures but behaves as a pin connection at high temperatures. Further, the moment redistribution with a decreasing hogging moment at the beam ends and higher sagging moment at the midspan shows that semirigid beam–column connections are more vulnerable at high temperatures than monolithic connections.