The axial compressive performance of novel L‐shaped and T‐shaped concrete‐filled square steel tube (L/T‐CFSST) column was assessed in this study. Ten L/T‐CFSST columns were tested to failure under axial load. The experimental data were used to determine various failure modes, bearing capacities, and load‐displacement curves. The test parameters included the section form, steel tube thickness, steel yield strength, and slenderness ratio. The axial compressive performance of the L/T‐CFSST column proved favorable, and each square steel tube showed strong cooperative performance. The failure mode of the stub column specimen (H/D ≤ 3) was strength failure caused by local buckling of the steel tube and that of the medium‐long column member (H/D > 3) was instability failure caused by overall bending of the specimen. A finite element analysis (FEA) model was established and successfully validated by comparison against the test results. Based on the FEA model, parametric analyses were conducted to investigate the effects of steel tube thickness, concrete strength, steel yield strength, and slenderness ratio. The ultimate loads obtained from the experiments and FEA were compared to the results calculated by the available design codes. A formula was established to calculate the axial compressive strength and stability bearing capacity of the L/T‐CFSST column accordingly. The calculation results are in close agreement with the FEA and experimental results, and the proposed formula may provide a workable reference for practicing engineers.

The prefabricated semi-rigid concentrically braced steel frame has always been the main form of residential steel structures, much work so far has focused on the earthquake-resistance performance of such structures. However, little attention has been devoted to systematic model testing, further effort is still required to explore the structural performance with experimental studies. Two semi-rigid concentrically braced steel frames were designed and tested to failure under reversed low-cyclic loading. The hysteretic curves, bearing capacity, energy dissipation capacity, ductility and stiffness degradation performance were studied in detail. Then the performance was compared to analyze the advantages and disadvantages of the two frames. The tests showed that the plastic deformation and damage were primarily concentrated at the braces, and the columns and semi-rigid connections exhibited hardly any plastic deformation. The specimens went through the elastic stage, elastic-plastic stage and failure stage during the tests. The results indicated the specimen with chevron braces has better seismic performance. The structure presents the characteristic of ductile failure on the whole. The steel frame and braces of the specimens cooperatively perform together so that the structure has two seismic fortification lines. The structure with chevron braces possesses an excellent bearing capacity, a high lateral stiffness, a reliable lateral-resistance performance and a strong energy dissipation capacity. In contrast, because of the premature fracture of the cross joints, the structure with X-shaped braces has a lower material utilization efficiency, which leads to a dramatic decrease in the bearing capacity and stiffness, as well as low ductility and a poor energy dissipation capacity.

In order to study the mechanical behavior of bolted beam‐column connections, the accuracy and applicability of the finite element model were firstly validated according to the published experiments on end‐plate connections using ABAQUS. Then, in order to discuss the mechanical behavior of connections, three semirigid connections which are convenient for prefabricated construction, including top‐and‐seat angle connections with web and ear plate, extended end‐plate connection, and T‐stub connection, were examined using numerical simulation analysis to study and compare their capacity, hysteretic behavior, ductility, and degradation characteristics in detail. The results showed that the finite element models that were built could effectively simulate the load bearing behavior of bolted connections under both single‐direction loading and cyclic loading. The three connections showed good load bearing capacity. The connectors significantly affected the energy dissipation capacity under load. The extended end‐plate connection demonstrated the best performance in both mechanical behavior and manufacture and installation, so it would therefore be the preferred option.

Special T-shaped composite columns with concrete-filled square steel tubulars have good restraint on internal concrete, are convenient to process, have a high bearing capacity and good mechanical properties, and can increase the aesthetics of the building and the utilization rate of indoor space. Theoretical analysis, experimental study, and numerical simulation of the eccentric compression performance of the special-shaped column are carried out. Taking the specimen length, eccentric distance, and eccentric direction as test parameters, nine specimens with different slenderness ratios were designed to carry out eccentric compression tests. The eccentric compression performance was numerically simulated and analyzed by the general finite element software ABAQUS. The results show that the short column mainly suffers section strength failure, while the middle and long columns mainly suffer bending instability failure without torsional deformation. The degree of influence of the test parameters decreases in turn according to the eccentric distance, eccentric direction, and length of the specimen; there is no weld cracking phenomenon, and the square steel pipes can work together. The finite element calculation results are in good agreement with the experimental and theoretical values.

This study presents the mechanical behavior of L-shaped concrete-filled square steel tube (L-CFSST) composite columns under uniaxial eccentric compression. Nine specimens were tested and the effects of eccentricity, steel tube thickness, steel yield strength, and slenderness ratio were investigated regarding failure modes, ultimate load, load-lateral displacement curves, and load-strain curves. Test results showed that, under uniaxial eccentric load, these columns showed favorable mechanical properties and steel tubes showed strong cooperative working performance. There were two types of failure modes for these columns: local buckling of the steel tube or overall bending of the specimen. ABAQUS was used to simulate the loading process and the accuracy of the numerical simulation results was verified by comparing failure characteristics, load-displacement curves, and ultimate bearing capacity with the test results. The N/N_u-M/M_u curves of the columns under uniaxial eccentric load with different parameters were simulated by the finite element method. A simplified formula for predicting the N/N_u-M/M_u relationship was established based on the finite element analysis results, which might be a workable approach for designing L-CFSST composite columns in engineering practice.

Three semirigid connections which are convenient for prefabrication have been proposed in this paper. Based on them, the quasi‐static test was conducted on three prefabricated semirigid steel frames with X‐shaped braces in order to investigate their hysteresis behavior, bearing capacity, energy dissipation capacity, and failure mechanism. A comparative analysis of the semirigid connections was made to analyze their advantages and disadvantages. Then, a numerical simulation was carried out via using ABAQUS to verify the test results, and the causes of the errors were analyzed. The results showed that the prefabricated semirigid steel frames with X‐shaped braces had good seismic behavior, the braces cooperated well with the steel frame in resisting lateral load, and the braces failed before the steel frame, which meant the structure had two seismic fortification lines. The results of the numerical simulation tallied with the test results, which means the finite element model could accurately simulate the structure’s mechanical behavior under cyclic loading. The structure had a better bearing capacity and ductility when using extended end‐plate bolted connections.