Enhanced Nonlinear Truss Model for Capturing Combined Earthquake and Fire Effects in RC Structures

Abstract

Post-earthquake fires can negatively affect the safety and collapse probability of Reinforced Concrete (RC) structures. At present, there has been no systematic effort to assess the performance of RC structures for combined earthquake and fire effects. Developing appropriate guidelines for this scenario requires simulation tools that can accurately capture material behavior during cyclic loading and at elevated temperatures. Ideally, simulation tools must also be conceptually simple and computationally efficient to allow extensive parametric analyses.

The goal of the present study is to enhance a previously established modeling approach so that it can describe the performance of RC structures for both cyclic loading and changes in material behavior due to elevated temperatures. The modeling approach is based on the nonlinear truss analogy and has been extensively validated for cyclic loading of RC shear walls and columns. The constitutive models for concrete and reinforcing steel are enhanced with the capability to account for the effect of elevated temperatures. The enhanced material models are validated using experimental data for concrete and steel at elevated temperatures. The capability of the proposed model to analyze structural-level behavior is verified and compared with experimental testing. The method is also endowed with the capability to describe the time-dependent heat conduction in a fire simulation. The use of the enhanced nonlinear truss model is more advantageous than refined finite element models because of its computational efficiency and conceptual simplicity.