10.36: Advanced numerical analysis of steel, concrete and composite structures under fire conditions

Abstract

High temperature in common fire causes changes in physical characteristics and mechanical strength of the materials used in the structures. In both steel and concrete, such characteristics deteriorate during the exposure to fire, and the structure load capacity and stiffness are reduced significantly with the increasing temperature. This work is on advanced analysis context of structures under fire, and it aims to develop a computational system for analysis of steel, concrete and composite structures in fire situation, based on the finite element method. The use of advanced analysis as a methodology of analysis/design of structures has various advantages. Among these advantages, there is the capture of strength limit and stability of a structural system and its members directly, without the need for separate verification of each member capacity. This provides a more realistic analysis and determine adequately the performance of a structure in a real fire. To achieve the objective, the CS-ASA (Computational System for Advanced Structural Analysis) is used and expanded to advanced analysis of structures in fire situation, taking advantage of existing features and adding new ones. Two new modules were created: CS-ASA/FA (Fire Analysis) and CS-ASA/FSA (Fire Structural Analysis). The first aims to determine the temperature field in the cross section of the structural elements by FE thermal analysis in permanent and transient regimes. The second was created to perform the inelastic second-order analysis of structures under fire considering the refined plastic hinge method coupled to strain compatibility method. The adopted numerical methodology is described and, for a more comprehensive validation of the implemented modules, various structural systems under fire are analyzed.

Advanced Numerical Study of Composite Steel‐Concrete Structures at High Temperature

“…computed beforehand, in order to accelerate the execution of the structural simulations. More details on the computation of interaction curves, the structural analysis, as well as the thermal structural problem, can be found in [12][13][14].…”

“…The following sections bring a summary of the FE formulation via RPHM, the SCM and how the bending moment-curvatures relationships are derived. Additional details of the structural solution strategy can be found in [13,14].…”

“…2), are adopted according to the normative prescription of EC 4 part 1-2 [15]. Further details of this computational module are available in [13,14]. In Figure 2, f p,Ts is the proportional limit; f y,Ts the effective yield strength of steel; • p,Ts the strain at the proportional limit; • y,Ts the yield strain; • t,Ts the limiting strain for yield strength; • u,Ts the ultimate strain; f c,Tc is the maximum compressive strength of concrete; • ci,Tc the strain corresponding to f c,Tc and; • cu,Tc the maximum compression strain of concrete.…”

Bifurcation Analysis of Columns of Composite Materials with Thermal Variation

“…To contextualize the present approach, a real reinforced concrete structure submitted to thermomechanical effects associated with gravitational loads was analyzed [5][6][7][8][9] . A 46 m high column, having 40 m of exposure to the environment, 6 m buried, with a slenderness rate greater than 400, was selected for the study.…”

Thermo-structural analysis of reinforced concrete beams

“…The first one, called CS-ASA/Fire Analysis (CS-ASA/FA) 12,13 is able to determine the temperature field in the cross-section of structural elements through thermal analysis via Finite Element Method (FEM) in permanent and transient regimes. The second module, CS-ASA/Fire Structural Analysis (CS-ASA/FSA), [14][15][16] was developed to perform a second order inelastic analysis of structures under high temperatures. Thus, a SCM-based approach is proposed for the evaluation of the cross-sectional strength, axial stiffness and flexural strength of reinforced concrete beams under high temperatures.…”