Postfire Strength of Channel-Type Shear Connectors

Abstract

The combined action of steel and concrete in composite beams is accomplished via shear connectors that prevent slip between the two materials. In a fire event, the performance of these shear connectors may be impacted, hence affecting the strength of composite beams during and after a fire. This paper investigates the residual strength of channel-type shear connectors exposed to elevated temperatures. Twenty-two push-out specimens were fabricated with normal-weight and lightweight concrete and channel heights of 60, 80, and 100 mm. The specimens were tested without any heat exposure or after experiencing maximum temperatures of 400, 600, or 750°C. Results showed that temperatures up to 400°C did not cause a noticeable change in the residual strength of shear connectors, but on average, normal-weight concrete specimens exposed to 600°C and 750°C showed 17 and 31 percent decrease in their residual strength, respectively. Relatively similar strength reduction was observed in lightweight concrete specimens. Equations used in AISC 360-22 and CSA-S16-19 specifications provided reasonably accurate estimates of the capacity of unheated specimens but were excessively conservative for heat-exposed specimens. Finite-element models of the specimens were developed and validated based on the measured load-slip behavior of the specimens in preheating and postheating conditions.