Mahmud Dwaikat

High-Temperature Properties of Steel for Fire Resistance Modeling of Structures

Fire is one of the most severe conditions to which structures can be subjected, and hence, the provision of appropriate fire safety measures for structural members is an important aspect of design. The recent introduction of performance-based codes has increased the use of computer-based models for fire resistance assessment. For evaluating the fire resistance of steel structures, high-temperature properties of steel are to be specified as input data. This paper reviews high-temperature constitutive relationships for steel currently available in American and European standards, and highlights the variation between these relationships through comparison with published experimental results. The effect of various constitutive models on overall fire resistance predictions is illustrated through case studies. It is also shown that high-temperature creep, which is not often included in constitutive models, has a significant influence on the fire response of steel structures. Results from the case studies are used to draw recommendations on the use of appropriate constitutive models for fire resistance assessment.

High-Temperature Properties of Concrete for Fire Resistance Modeling of Structures

Fire is one of the most severe conditions to which structures can be subjected, and hence, the provision of appropriate fire safety measures for structural members is an important aspect of design. The recent introduction of performance-based codes has increased the use of computer-based models for fire resistance assessment. For evaluating the fire resistance of steel structures, high- temperature properties of steel are to be specified as input data. This paper reviews high-temperature constitutive relationships for steel currently available in American and European standards, and highlights the variation between these relationships through comparison with published experimental results. The effect of various constitutive models on overall fire resistance predictions is illustrated through case studies. It is also shown that high-temperature creep, which is not often included in constitutive models, has a significant influence on the fire response of steel structures. Results from the case studies are used to draw recommendations on the use of appropriate constitutive models for fire resistance assessment. DOI: 10.1061/ASCEMT.1943-5533.0000041 CE Database subject headings: Constitutive relations; Fire resistance; Temperature effects; Steel structures. Author keywords: Performance-based design; Fire resistance; Constitutive relationships; High-temperature properties; Structural steel.

Evaluating Fire Resistance of Steel Girders in Bridges

In current practice, no special measures are applied for enhancing structural fire safety of steel bridge girders. Further, there is very limited information and research data in the literature on the fire resistance of structural members in bridges. In this paper, the fire response of a steel bridge girder under different conditions is evaluated using the FEM computer program ANSYS. In the analysis, the critical factors that influence fire resistance, namely, fire scenario, fire insulation, and composite action arising from steel-concrete interaction, are accounted for. Results from numerical studies show that the composite action arising from steel-girder-concrete-slab interaction significantly enhances the structuralperformance(and fireresistance)ofasteelbridgegirderunder fireconditions.Othersignificantfactorsthatinfluence fireresistanceof steel bridge girders are fire insulation and type of fire scenario. DOI: 10.1061/(ASCE)BE.1943-5592.0000412.

Modeling Fracture and Delamination of Spray-Applied Fire-Resisting Materials under Static and Impact Loads

A specially developed two-dimensional cohesive zone finite element (CZFE) scheme is applied to simulate the fracture and delamination phenomena that occur in spray-applied fire-resisting material (SFRM) on steel structures. A cohesive zone material model for the SFRM is introduced and utilized to model both the internal cohesion in SFRM and the interfacial adhesion at the steel-SFRM interface. The CZFE model is validated by comparing predictions from the model with results from an adhesion test conducted at ambient temperature. The validated model is successfully applied to simulate the spontaneous initiation and propagation of cracks in the SFRM under static and impact loads. Results from the numerical studies indicate that the proposed model is capable of predicting the initiation and propagation of cracks within the insulation material and at the interface. The results show that the development of transverse cracks in the insulation layer help prevent further delamination of the SFRM. Also, it was foun...

Engineering approach for predicting fire response of restrained steel beams

Predicting the response of restrained beams under fire conditions is complex owing to the development of fire-induced forces and requires finite-element or finite-differences analysis. In this paper, a simplified approach is proposed for predicting the fire-induced forces and deflections of restrained steel beams. The method applies equilibrium equations for obtaining critical fire-induced forces and then utilizes compatibility principles for obtaining temperature-deflection history of the beam. Effect of end restraints, thermal gradient, location of axial restraint force, span length, and load intensity are accounted for in the proposed approach. The validation of the approach is established by comparing the predictions from the proposed approach with results obtained from rigorous finite-element analysis. The applicability of the proposed approach to practical design situations is illustrated through a numerical example.

Effect of restraint force location on the response of steel beams exposed to fire

Restrained steel beams, when exposed to fire, can develop significant fire-induced restraint force. In most previous studies, the location of the fire induced restraint force was always assumed to be situated at the center of gravity of the beam cross section. In practice, the location of axial restraint force can vary depending on many parameters, including the configuration of the connection at the supports of the beam. A set of numerical studies is presented to illustrate the response of unprotected steel beam-columns under realistic fire, load, and restraint scenarios. Results from the parametric studies indicate that fire scenario, beam span, and restraint conditions have significant influence on the behavior of restrained beams under fire. High intensity fires produce high axial forces at early stages of fire exposure, whereas in mild fires, significant axial force develops only at later stages of fire exposure. Presence of axial and rotational restraint enhances the fire resistance of beams due to the development of tensile catenary action. Overall, the fire response of restrained beams generally improves when the axial restraint is located in the bottom flange.