FRESCO | Fire Resistance Enhancements of Steel truss in COncrete beams

Project description

Composite Steel Truss in Concrete (CSTC) beams offer high structural efficiency within shallow floor systems and enable extensive prefabrication. However, their structural response under fire exposure has remained largely unexplored, and no specific design provisions currently exist in Eurocode standards. The research project sets out to establish reliable design methods for CSTC beams in fire conditions. The study combined full-scale fire tests, dedicated pull-out experiments, and advanced finite element simulations to investigate both bending and vertical shear resistance.

In the first part, two full-scale CSTC beams were tested under standard fire exposure, showing that adequate fire resistance can be achieved without additional protection when reinforcement bars are embedded in concrete. Complementary heat transfer analyses (HTA) and thermomechanical simulations supported the development of analytical expressions to predict reinforcement temperatures and the effective concrete section, leading to a comprehensive design methodology for determining bending resistance in fire for different resistance classes.

In addition, a separate pull-out test campaign using a special setup were conducted to examine the contribution of the steel diagonals to the vertical shear resistance at elevated temperatures. The experiments revealed that shear failure is governed by weld fracture of the diagonals, with the surrounding concrete contributing through compression struts. Based on these findings, an HTA-based analytical approach was developed to predict the shear resistance of CSTC beams in fire, calibrated through extensive numerical analyses.

The outcomes provide a comprehensive Eurocode-consistent design framework for evaluating CSTC beam performance in bending and shear under fire exposure, addressing a critical gap in current practice and supporting the safe and efficient use of shallow floor composite systems.