Abstract
The design of composite joints for connecting concrete-filled double-skin tubular (CFDST) columns to steel beams supporting reinforced concrete (RC) slabs is presented in this paper. Five half-scale specimens were designed, including four composite joints with RC slab and one bare steel beam joint, and were tested under a constant axially compressive force and lateral cyclic loading at the top end of the column to evaluate their seismic behavior. The main experimental parameters were the construction of the joint and the type of the column. The seismic behaviors, including the failure modes, hysteresis curves, ductility, strength and stiffness degradation, and energy dissipation, were investigated. The failure modes of the composite joints depended on the joint construction and on the stiffness ratio of beams to columns. Joints of stiffening type had significantly higher load-bearing and deformation capacities than joints of nonstiffening type. Compared with the bare steel beam joint, the bearing capacities of the composite joints with RC slabs were markedly increased. The composite action was remarkable under sagging moments, resulting in larger deformation on the bottom flanges of the beams. Overall, most specimens exhibited full hysteresis loops, and the equivalent viscous damping coefficients were 0.282∼0.311. The interstory drift ratios satisfied the requirements specified by technical regulations. Composite connections of this type exhibit excellent ductility and favorable energy dissipation and can be effectively utilized in superhigh-rise buildings erected in earthquake zones.
Highlights
A concrete-filled double-skin tubular (CFDST) column is composed of an outer tube and an inner tube that is fully or partly filled with concrete. e mechanical behaviors of CFDST columns have been studied by many researchers in recent years. e results indicate that CFDST columns exhibit higher bearing capacities, ductility, and energy consumption with smaller sections compared with traditional concrete-filled steel tubular (CFST) columns, increasing space utilization in buildings [1, 2]
A series of cyclic loading experiments performed on steelbeam-to-CFDST-column joints with reinforced concrete (RC) slabs were reported in this paper. e conclusions obtained based on these discussions are summarized as follows: (1) e composite joints proposed in this paper for connecting CFDST columns to steel beams supporting concrete slabs exhibit better performance in terms of loading capacity, lateral stiffness, ductility, and energy dissipation in comparison with bare steel joints
With the use of stiffening-type web anchorage plates, the joint strength was increased by 30% and 19% in the positive and negative directions, respectively, and the ultimate displacement was increased by 25% and 14%. ese findings indicate that it is necessary to strength the bottom flanges of the steel beams in the proposed composite joints
Summary
A CFDST column is composed of an outer tube and an inner tube that is fully or partly filled with concrete. e mechanical behaviors of CFDST columns have been studied by many researchers in recent years. e results indicate that CFDST columns exhibit higher bearing capacities, ductility, and energy consumption with smaller sections compared with traditional concrete-filled steel tubular (CFST) columns, increasing space utilization in buildings [1, 2]. Liao et al [9] studied the effects of RC slabs on the seismic behavior of composite joints with concrete-encased CFST columns under cyclic loading. Han and Li [10] analyzed the seismic performance of joints connecting CFST columns to steel beams with RC slabs through experiments. E specific purpose of the study was to investigate the composite effects on seismic performance, including the failure modes, hysteresis curves, bearing capacity, ductility, energy dissipation, and strength and stiffness degradation, due to the presence of an RC slab. Some useful conclusions and suggestions are proposed for the seismic design of steel-beam-to-CFDST-column joints based on the results, which have significance for the application of CFDST columns in composite structures
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