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Gusset rotation would cause adverse influence on the buckling-restrained brace (BRB) end zone and even lead to premature buckling of the BRB end zone. However, limited studies to date referred to the gusset rotation response. To evaluate the cyclic behavior and gusset rotation response, five 1/2-scaled buckling-restrained braced frame (BRBF) subassemblages with various gusset connections, i.e., pinned gusset connection, bolted gusset connection, welded gusset connection, pinned-welded gusset connection, and pinned-bolted gusset connection, were conducted under horizontal cyclic loading. The effects of gusset connection type on the failure modes, horizontal initial stiffness, energy dissipation and rotation response of specimens were analyzed in detail. It showed that all specimens performed plump and stable hysteresis behavior. The upper gusset rotation of the specimen with pinned gusset connection was larger than that of bolted gusset connection, followed by welded connection. Meanwhile, the finite element (FE) models were established and validated by test results. Furthermore, the standard FE model of a full-scale one-story one-bay steel moment BRBF with a single diagonal BRB was developed and then extended to a large number of models to investigate the contribution of various parameters on the upper gusset rotation. Finally, the gusset rotational formulae for predicting its response, as the steel moment BRBF reached to either 2.0% or 3.0% drift, were proposed on the basis of the results of the extensive parametric analysis. It could be used to determine the rotation of the BRB end zone, and the flexural moment acting on the BRB end zone and corresponding practical design procedure can be finally derived to avoid the potential premature failure of the BRB end zone.

U-shaped steel–concrete composite girder has higher flexural resistance, more excellent fire resistance and better sound insulation due to the infilled concrete in U-shaped steel girder, compared with traditional composite beams. The existing researches indicated that U-shaped composite beams with shear connectors of headed studs and steel angles all exhibited good flexural performance. However, limited studies were conducted on shear resistance of angle-shaped connectors in U-shaped composite beams and then it is difficult to choose the more suitable shear connector for U-shaped composite beams. Therefore, push-out tests of different configuration of shear connectors were performed to determine their effectiveness in developing composite action in term of strength and load-slip behavior. In the tests, several options of shear connectors were examined including steel angle welded to webs, steel angles welded to flanges, headed studs, steel angle welded to webs working together with headed studs, and two separated steel plates welded to webs. The experimental results showed angle connectors welded to the webs of U-shaped girder possess higher shear resistance, larger slip capacity among all shear connectors. Combining with avoiding the congestion between shear connectors and longitudinal reinforcements, steel angles welded to the webs are recommended as shear connectors for U-shaped composite beams. At last, analytical formulas were proposed to describe the load-slip curves of different shear connectors and the design parameters obtained by regression analysis agreed well with the test results.

The welded steel tube and high-strength cementitious grout jacketing is a hybrid strengthening method for deficient reinforced concrete (RC) column without enlarging its entire cross-sectional area. This paper presents an experimental study on the performance of the welded steel tube and cementitious grout jacketing retrofitted RC (STGRRC) stub column under axial compression to figure out its strengthening effect. A total of eight STGRRC stub columns and one high-strength cementitious grout jacketing strengthened RC stub column are designed and analysed to investigate the effects of various parameters including the aspect ratio, the concrete cross-sectional area ratio (Ac/A) and the concrete strength. To better acknowledge the strengthening feature of the type of composite column, detailed discussions on the crucial indexes in terms of the confinement effect, the strength enhancement and the damage failure analysis are presented. The result reveals that the strength, stiffness and ductility of the original RC column could be highly improved by using this strengthening method. The axial compressive resistance of STGRRC stub column decreases with the increasing of aspect ratio and concrete cross-sectional area ratio. The ductility index value reduces with varying the aspect ratio and concrete strength in ascending order as well as the decreasing of concrete cross-sectional area ratio. To provide a basis for the future design and application, a simplified analysis method is proposed to predict the axial compressive resistance of the STGRRC stub column based on the limit equilibrium theory and verified well with experimental results.

Due to the rapidly increasing urbanisation in China, the energy consumption of buildings and infrastructures has increased; this has resulted in environmental problems such as excessive carbon emissions. Increasing the strength of steel rebars enables manufacturers to use less steel and save more energy. The micro-alloyed 635 MPa hot-rolled ribbed high strength rebars (HRHSR) offer the advantages of high strength, good ductility, and low costs, compared to ordinary rebars. Bond anchorage is one of the key problems that limits the promotion and application of 635 MPa HRHSRs in practice. In this study, the bond properties of 635 MPa HRHSRs embedded in concrete subjected to monotonic loads were investigated. A total of 120 specimens, which consisted of 60 simple-anchored and 60 hooked-anchored specimens, were subjected to direct pull-out tests to evaluate the effects of anchorage length, hoop ratio, concrete cover, rebar diameter, concrete strength, and anchorage types on the anchorage feature. Meanwhile, the mechanical properties and failure modes of 635 MPa HRHSRs were also analysed. The results demonstrated that the concrete compressive strength, cover size, anchorage length, and stirrups ratio had a positive influence on the ultimate bond strength, whereas the bar size had a negative influence on the ultimate bond strength. Furthermore, four typical failure modes were analysed, including rebar yielding, concrete splitting, concrete crushing, and rebar rupturing, which occurred during the pull-out tests. Thereafter, a modified equation for calculating the ultimate bond strength of 635 MPa HRHSRs in concrete was derived based on the mechanical model and further verified using the test data. This study is expected to be beneficial in promoting the widespread application of 635 MPa HRHSRs and enabling resource savings in the future.

Cold-formed steel (CFS) shear walls filled with lightweight polymer material (LPM) is an efficient structural system which can provide high lateral stiffness and strength to resist lateral loads. Despite the significant advantages, the nonlinear behavior of the CFS shear wall filled with LPM is not fully understood. In this study, a total of seven full-scale CFS shear walls filled with LPM were tested under cyclic loads. The test parameters included different LPM types, X-shaped bracing configurations, sheathing types and wall openings. The failure modes hysteresis curves, envelope curves, feature values, ductility ratio, stiffness and energy dissipation of CFS shear wall with and without filling LPM were systematically compared. The experimental data reveled that this type of shear wall showed higher load carrying and energy dissipation capacities than CFS framing wall without LPM. To assist with the design of CFS shear walls filled with LPM, a modified strut-and-tie model was proposed. The modified strut-and-tie model was validated using the experimental data. The result demonstrates that the proposed model can be utilized to accurately estimate the load carrying capacity of CFS shear walls filled with LPM. The presented experimental and analytical results can be used by engineers to design CFS shear walls filled with LPM for earthquake engineering applications.

Concrete encased CFST (CECFST) column is a composite member consisted of outer encased concrete and inner CFST. Currently, a cast-in-place connection between a CECFST column and a reinforcement concrete beam is generally employed in engineering practice due to the outer encased concrete hinders the application of assembled connection, and the steel beam is usually connected to the CECFST column by on-site welding. In this paper, a novel on-site assembled connection between a CECFST column and a steel beam was proposed. In considering various material models and complex contacts, a FE model for this type of joint was established and verified. Further, parametric analyses of the assembled connections to concrete encased CFST columns were conducted to analyze the structural behavior. More importantly, an extended component model was developed to cover the feature of CECFST column focusing on the initial stiffness and moment resistance of the assembled connection. The load transfer mechanism for bolt in tension and beam flange in compression were considered in the modelling for evaluating the stiffness and strength of column wall in tension and in compression, respectively. The numerical results from the parametric analyses coincided well with the predicted results. The numerical and analytical results declared that this novel assembled connection between the CECFST column and steel beam performed favorable structural behavior and could be employed in assembled structures with CECFST columns.

To investigate seismic behavior and failure modes of blind bolted concrete-filled steel tubular (CFST) frames with semi-rigid connections, an experimental study on two specimens of two-layer single-span blind bolted end plate CFST frames was conducted under low-cyclic loading. Both the end plate type and the loading type were taken into consideration in this paper. The seismic behavior of the overall composite structures was analyzed and evaluated in terms of the hysteretic behavior, failure modes, stiffness and strength degradation, ductility, and energy dissipation capacities. Some simplified models were proposed in this paper to predict initial stiffness and moment capacity for blind bolted end plate joints to CFST columns. It was concluded that the blind bolted CFST frames with semi-rigid connections exhibited large hysteretic loops, good ductility, and excellent energy dissipation capacity. These studies enable improvement in the practical design and application of semi-rigid CFST frames in seismic regions.