Behavior and Limit States of Long-Span Composite Floor Beams with Simple Shear Connections subject to Compartment Fires: Experimental Evaluation.

This paper presents the results of compartment fire experiments on four 12.8 m long composite floor beams with various end support conditions. Specimens were constructed as partially-composite beams, consisting of W18×35 steel beams and 83 mm thick lightweight concrete slabs cast on top of 76 mm deep ribbed steel deck units. Test variables included two types of simple shear connections (shear-tab and welded-bolted double-angle connections) and the presence or absence of slab continuity over the girders. Each specimen was subjected to gravity loading using hydraulic actuators and 4000 kW compartment fires produced using natural gas-fueled burners. This study evaluated the characteristics of the fire loading and thermal and structural responses of the specimens. The test results indicated that there were significant effects of thermal restraints on the behavior and failure modes of the specimens with simple shear connections. The specimens resisted gravity loads at large vertical displacements near midspan (approximately a ratio of span length over 20) without collapse under fire loading. However, various limit states and vulnerabilities to fires were observed, including local buckling of steel beams near supports, flexural failure (yielding of steel beams and concrete fracture near restrained end supports), and connection failure (weld shear or bolt shear) during heating and cooling which could lead to partial or total collapse of the floor system.

Communication framework for Hybrid Fire Testing: developments and applications in virtual and real environments.

The response of structural systems to fire loads is typically assessed through performing 'standard' fire tests on individual members under constant mechanical boundary conditions. Full scale tests showed different behavior compared to the standard tests, but remain impractical. A promising approach to predict the behavior of full scale tests through testing individual structural members is Hybrid Fire Testing technique, where a subset of the structural system (Physical Substructure PS), is physically tested, while the remaining structure (Numerical Substructure NS), is simultaneously numerically analyzed. During the test, the mechanical boundary conditions on the PS and NS are continuously updated, and the updates are enabled by the communication framework. The communication framework is a key element for a successful hybrid fire testing and this paper will present the development of such communication in MATLAB. To validate the communication framework, first, a single degree of freedom linear system was analyzed, followed by a ten-story steel frame structure exposed to design fire. The analysis of the latter underlined the importance of considering the effect of the cold surrounding in assessing the fire behavior of structures under design fires. Sensitivity analysis showed the importance of several parameters (time step and substructures stiffness) in hybrid fire testing.

An Empirical Component-Based Model for High-Strength Bolts at Elevated Temperatures.

High-strength structural bolts are used in nearly every steel beam-to-column connection in typical steel building construction practice. Thus, accurately modeling the behavior of high-strength bolts at elevated temperatures is crucial for properly evaluating the connection capacity, and is also important in evaluating the strength and stability of steel buildings subjected to fires. This paper uses a component-based modeling approach to empirically derive the ultimate tensile strength and modulus of elasticity for grade A325 and A490 bolt materials based on data from double-shear testing of high-strength 25 mm (1 in) diameter bolts at elevated temperatures. Using these derived mechanical properties, the component-based model is then shown to accurately account for the temperature-dependent degradation of shear strength and stiffness for bolts of other diameters, while also providing the capability to model load reversal.