This paper discusses the development of a publicly available database of composite steel beam-tocolumn connections under cyclic loading. The database is utilized to develop recommendations for the seismic design and nonlinear performance assessment of steel and composite-steel moment-resisting frames (MRFs). In particular, the sagging/hogging plastic flexural resistance as well as the effective slab width are assessed through a comparison of the European, American and Japanese design provisions. The database is also used to quantify the plastic rotation capacity of composite steel beams under sagging/hogging bending. It is found that the Eurocode 8-Part 3 provisions overestimate the plastic rotation capacities of composite beams by 50% regardless of their web slenderness ratio. Empirical relationships are developed to predict the plastic rotation capacity of composite steel beams as a function of their geometric and material properties. These relationships can facilitate the seismic performance assessment of new and existing steel and composite-steel MRFs through nonlinear static analysis. The collected data underscores that the beam-to-column web panel zone in composite steel beam-to-column connections experience higher shear demands than their non-composite counterparts. A relative panel zone-to-beam resistance ratio is proposed that allows for controlled panel zone inelastic deformation of up to 10 times the panel zone's shear yield distortion angle. Notably, when this criterion was imposed, there was no fracture in all the examined beam-to-column connections. Keywords Composite steel beam database・seismic performance assessment ・composite floors・Plastic rotation capacity・Panel zone shear resistance H.
This paper examines the influence of the framing action and slab continuity on the hysteretic behavior of composite-steel moment-resisting frames (MRFs) by means of high-fidelity continuum finite element (CFE) analyses of two-bay subsystems and typical cruciform subassemblies. The CFE model, which is made publicly available, is thoroughly validated with available full-scale experiments and considers variations in the beam depth and the imposed loading history. The simulation results suggest that beams in subsystems may experience up to 25% less flexural strength degradation than those in typical subassemblies. This is due to local buckling straightening from the slab continuity and framing action evident in subsystems. For the same reason, beam axial shortening due to local buckling progression is up to five times lower in subsystems than in subassemblies, which is consistent with field observations. While the hysteretic behavior of interior panel zone joints is symmetric, exterior joint panel zones in subsystems experience large asymmetric shear distortions regardless of the employed lateral loading history. From a design standpoint, it is found that the probable maximum moment in deep and slender beams (700mm) may be up to 25% higher than that predicted by current design provisions with direct implications to capacity design of steel MRFs. The 25% reduction in the shear stud capacity as proposed by current seismic provisions is not imperative for MRFs comprising intermediate to shallow beams and/or featuring a high degree of composite action (80%) as long as ductile shear connectors are employed.
This paper proposes a macro‐model for simulating the hysteretic behavior of composite‐steel beams as part of fully restrained beam‐to‐column connections in composite‐steel moment‐resisting frames (MRFs). Comparisons with experimental data suggest that the proposed model captures the asymmetric hysteretic response of composite‐steel beams including the cyclic deterioration in strength and stiffness. Moreover, the proposed model captures the primary slab‐column force transfer mechanisms and predicts the slip demands in beam‐slab connections under inelastic cyclic loading. The modeling approach is employed in a system‐level study to benchmark the seismic collapse risk of composite‐steel MRF buildings across Europe. Moreover, the beam‐slab slip demands are quantified through the development of beam‐slab slip hazard curves. The simulation studies suggest that the examined composite‐steel MRFs exhibit a system overstrength of about 4. This is attributed to the drift requirements in the current European seismic provisions.1 The annualized probability of collapse of the prototype buildings is well below 1% over a 50‐year building life expectancy regardless of the design site and the degree of composite action. Beam‐slab connections with a partial degree of composite action experience minimal damage for frequently occurring seismic events (i.e., 50% probability of exceedance over 50 years); and light cracking in the slab for a design basis earthquake. The above are important from a seismic repairability standpoint. Accordingly, it is recommended that the 25% reduction in the shear resistance of stud connectors is not imperative for seismic designs that feature steel beams with depths less than 500 mm.
Earthquake loss estimation in composite-steel moment resisting frames (MRFs) necessitates a proper estimation of the level of damage in steel beam-to-slab connections. These usually feature welded headed shear studs to ensure the composite action between the concrete slab and the steel beam. In partially composite steel beams, earthquake-induced damage in the shear studs and the surrounding concrete occurs due to shear stud slip demands. Within such a context, this paper proposes shear slip-based fragility functions to estimate the probability of being or exceeding four damage states in steel beam-slab connections. These damage states include cracking and crushing of the concrete slab in the vicinity of the shear studs, as well as damage in the shear studs themselves. The developed fragility functions are obtained from a gathered dataset of 42 cyclic push-out tests. They incorporate uncertainty associated with specimen-to-specimen variability, along with epistemic uncertainty arising from the finite number of available experimental results. An application of the proposed fragility functions is conducted on a six-story building with composite-steel MRFs. It is shown that steel beam-slab connections along the building height only exhibit light cracking (i.e., crack sizes of 0.3 mm or less) at design basis seismic events. At seismic intensities associated with a low probability of occurrence seismic event (i.e., return period of 2475 years) the nonlinear building simulations suggest that the 25% reduction of the shear stud resistance in steel beam-slab connections with beam depths of 500 mm or less is not imperative to maintain the integrity of the shear stud connectors.
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