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This paper describes a reduced-order modeling approach for thermal and structural analysis of fire effects on composite slabs with profiled steel decking. The reduced-order modeling approach, which uses alternating strips of layered shell elements to represent the thick and thin portions of the slab, allows both thermal and structural analyses to be performed using a single model. The modeling approach accounts for the trapezoidal profile of the concrete in the ribs; the structural resistance provided by the steel decking, including the webs of the decking; and the orthotropic behavior of the decking, which provides greater resistance along the ribs than transverse to the ribs. The modeling approach is validated against experimental data from one-way composite slabs tested under ambient-temperature, a one-way composite slab tested under fire conditions, and a two-way composite slab tested under fire conditions. Both implicit and explicit solution schemes are evaluated for the structural analysis, and the results show that it is feasible to scale down the hours-long fire duration to a simulation time of seconds in an explicit dynamic analysis, without adversely affecting the accuracy of the results. The steel decking contributes significantly to the structural resistance at ambient temperature, but as expected, its contribution is found to decrease rapidly under fire exposure. The modeling approach can account for the location of reinforcing bars (i.e., at a specified depth in either the thick or thin portion of the slab), and it is found that reinforcement location can have a significant effect on the structural response, because heat transfer in the composite slab results in higher temperatures in the thin portions of the slab between the ribs.

Although simple shear connections are typically idealized as perfectly pinned, the actual resistance of the gravity framing system to flexural and axial loads can be critical in evaluating the robustness and stability of steel buildings subjected to extreme loads such as earthquakes, fire, and column loss. There are several key reasons for including more realistic connection behaviors in the design and analysis of steel buildings for extreme loads: (i) the gravity connections may develop large localized deformations under combined flexural and axial loading, potentially precipitating their failure (e.g. due to local buckling, fracture of the bolts, etc.), (ii) the gravity connections provide critical lateral bracing to the columns, and failure of connections could lead to global instability (potentially resulting in disproportionate collapse), and (iii) accurately accounting for contributions from the gravity system in design could effectively reduce the demands on the lateral load-resisting system, thus reducing costs. In order to include contributions from the steel gravity frames in structural analysis and design, validated and computationally efficient analysis tools are needed. This paper describes a component-based model for single-plate shear connections that includes the effects of pre-tension and accommodates both standard and slotted holes, accounting for deformations associated with bolt slip, bolt bearing, and bolt shear. The model also accounts for load reversals and pinching effects associated with hysteresis, thus providing the capability to model the connections under arbitrary in-plane load histories. Validation cases show that the model is capable of simulating connection response under both earthquake and column removal loading.