Vertical shear resistance of Composite Steel Truss in Concrete (CSTC) beams in fire: Pull-out tests and numerical analyses

The present study introduces a special experimental setup for investigating the anchorage resistance of the diagonal of Composite Steel Truss and Concrete (CSTC) beams at elevated temperatures involved in the vertical shear resistance. The experimental campaign comprised four pull-out tests wherein each specimen was subjected to standard ISO 834–1 fire conditions and a constant load on the diagonal web bar. The observed failure mode in the tests indicated that the pulling resistance is limited by the fracture of the bar occurring near the bottom weld seam, resulting from the heat-degraded mechanical properties of the material. To further expand the experimental findings, finite element (FE) models were developed and validated against the test results via heat transfer and thermomechanical analyses in terms of temperature measurements and steel-concrete slip displacements. The numerical model was subsequently used to establish a benchmark data pool for verifying the suitability of the proposed method to predict the anchorage resistance of the diagonal web bar of CSTC beams in fire. This approach calculates a reference temperature defined at the expected fracture surface via heat transfer analyses. The resulting temperature-dependent yield strength is ultimately considered for the steel component of the vertical shear resistance, which cannot exceed the resistance of the diagonal concrete strut, in accordance with the strut-and-tie model. • Four pull-out tests on CSTC beams in fire were carried out. • Specimens exhibited steel fracture near the top of the bottom seam. • Validated numerical models were used to enlarge the test database. • A thermal analysis-based approach was proposed for determining the fire resistance. • A methodology for determining the vertical shear resistance was derived.