Search Results (295)

As a typical steel-concrete composite structure, Concrete-Filled Steel Tubular (CFST) structures utilize the synergistic mechanical advantages of steel and concrete, showing good performance in bearing capacity, ductility and fire resistance, and becoming important in modern buildings. However, CFST structures may suffer hazards like fire, which causes performance degradation affecting subsequent seismic behavior. To study seismic performance of fire-damaged CFST column-steel beam joints, low-cycle repeated loading experiments were carried out on 3 specimens: 2 exposed to different fire temperatures and 1 ambient temperature control. Tests examined hysteretic behavior, ductility, energy dissipation, bearing capacity and stiffness degradation under post-fire axial compression ratios. Results show fire-damaged specimens had similar ductile failure modes to the control. Despite high temperatures, they maintained relatively full hysteretic curves and strong energy dissipation, but with reduced bearing capacity, increased deformation, nonlinear ductility growth, and more significant degradation at higher temperatures. Full article

In this study, the impact resistance of WUF-B steel frame beam–column joints under fire was investigated using ABAQUS finite element software through a sequential thermal–mechanical coupling approach. By integrating a room-temperature impact model with a single-sided fire field applied to the lower flange of the steel beam, the multi-parameter influence mechanisms—including temperature (150–750 °C), fire area distribution, and impact momentum—were systematically analyzed. Results indicate that elevated temperatures significantly degrade structural impact resistance. At 750 °C, the peak impact force decreases by 73.3% compared to room temperature, while the mid-span bending moment increases by 63.3%. When the fire zone is near the impact point, localized thermal softening further reduces the peak impact force. Under constant impact energy, lower momentum (i.e., higher velocity) accelerates the rebound of the falling mass, revealing the role of momentum transfer efficiency in governing the transient response of high-temperature structures. Additionally, an analytical prediction model based on Timoshenko beam theory and thermo-mechanical stiffness degradation is developed. By introducing a segmented temperature reduction function, the model significantly enhances the accuracy of mid-span displacement predictions for steel structures under fire. Full article

In view of the adverse effect of the failure mode of the “strong beam and weak column” at the top-layer joint of subway stations on structural seismic performance under high axial compression ratio, a novel assembled steel–concrete composite (ASCC) beam–column joint for the top-layer is proposed in this paper, and its seismic performance is studied through cyclic loading tests and finite element analysis. The findings indicate that, in comparison to the reinforced concrete joint, the yield bearing capacity, ultimate bearing capacity, and ductility of the ASCC joint exhibit increases of approximately 46%, 13% and 40%, respectively, demonstrating superior seismic performance and a “strong column and weak beam” failure mode of the ASCC joint. The impact of parameters including the steel tube thickness, length of the lower steel tube, high axial compression ratio, and bolt quantity on the seismic performance of ASCC joints was further examined using a validated finite element model. Parametric investigations reveal that the ASCC joints with greater steel tube thickness, longer length of lower steel tube, and more bolts demonstrate significant improvements in load-bearing capacity, lateral displacement resistance, and energy dissipation capacity. A value of 0.80 can be recommended as the new high axial compression ratio upper limit of the current code. It is suggested that under the proposed new high axial compression ratio upper limit, the steel tube thickness should be 1–2% of the column diameter, while the length of the lower steel tube should be 1/3 of the length of the lower column, with more bolts restricting the deformation of the extended plates as the design and construction of joints better suit practical engineering applications. Full article

To effectively improve the anti-progressive collapse performance of steel frames, a novel reinforced joint, named the welded steel-frame joints strengthened by outer corrugated plates, was proposed. Firstly, the finite element model was validated according to previous test results. The anti-progressive collapse behavior of the novel reinforced joint was analyzed based on the validated modeling method. Effects of the central angle, corrugated plate thickness, corrugated plate width, length of circular arc, and welding angle on the anti-progressive collapse behavior of the reinforced joint were discussed. The design suggestions of the corrugated plates are presented. Finally, the effectiveness of the outer corrugated plates was further verified through one full-scale beam–column joint case and three plane frames. The results show that compared with the specimen strengthened by inner corrugated plates, the peak load and ultimate displacement of the joint strengthened by outer corrugated plates increased by 17.0% and 16.3%, respectively. Compared with the traditional full-scale beam–column joint, the load-bearing capacity and ultimate displacement of the joint strengthened by outer corrugated plates designed under reasonable suggestions significantly increased. Simply from the perspective of joints, the design suggestions were highly effective. Compared with the traditional plane steel-frame case with a total height of six floors, the bearing capacity and ultimate displacement of the plane steel-frame case strengthened by outer corrugated plates increased by 19.8% and 38.3%, respectively. The outer corrugated plates demonstrated a more pronounced effect in enhancing the collapse resistance for middle floors. Overall, the novel type of joint had a simple form and clear mechanical principles, which fully exerted the catenary capacity of the steel beams. The outer corrugated plates significantly improved the anti-progressive collapse performance of steel-frame structures. Full article

Compared to traditional connection joints, hybrid connection joints are more suitable for large-span frames, especially for prefabricated buildings. This study aims to investigate the seismic performance of novel hybrid connection joints using the proposed innovative finite element modeling method based on the cohesion zone model (referred to as the CZM method). The crack development mechanism of the beam–column interface and the bond–slip mechanism of mild steel were investigated in this work; the performances of self-centering and energy dissipation were also studied using the CZM method. It is demonstrated that the CZM method can be used to accurately and efficiently estimate the performance of hybrid connection joints. This study also shows that the damage of mild steel, post-tensioned steel (referred to as PT steel), and concrete of the innovative hybrid connection joint is slight, the residual deformation of the joint is small, and the equivalent viscous damping coefficient ${\xi }_{\mathrm{e}\mathrm{q}}$ is between 7.8% and 14.85%, which shows good self-resetting and energy dissipation performance. Full article

This study presents a high-performance external strengthening strategy for reinforced concrete (RC) beam–column joints, integrating near-surface mounted (NSM) Carbon Fiber Reinforced Polymer (C-FRP) ropes with externally bonded C-FRP sheets. The X-shaped ropes, anchored diagonally on both principal joint faces and complemented by vertical ropes at column corners, provide enhanced core confinement and shear reinforcement. C-FRP sheets applied to the beam’s plastic hinge region further increase flexural strength and delay localized failure. Three full-scale, shear-deficient RC joints were subjected to cyclic lateral loading. The unstrengthened specimen (JB0V) exhibited rapid stiffness deterioration, premature joint shear cracking, and unstable hysteretic behavior. In contrast, the specimen strengthened solely with X-shaped C-FRP ropes (JB0VF2X2c) displayed a markedly slower rate of stiffness degradation, delayed crack development, and improved energy dissipation stability. The fully retrofitted specimen (JB0VF2X2c + C-FRP) demonstrated the most pronounced gains, with peak load capacity increased by 65%, equivalent viscous damping enhanced by 55%, and joint shear deformations reduced by more than 40%. Even at 4% drift, it retained over 90% of its peak strength, while localizing damage away from the joint core—a performance unattainable by the unstrengthened configuration. These results clearly establish that the combined C-FRP rope–sheet system transforms the seismic response of deficient RC joints, offering a lightweight, non-invasive, and rapidly deployable retrofit solution. By simultaneously boosting shear resistance, ductility, and energy dissipation while controlling damage localization, the technique provides a robust pathway to extend service life and significantly enhance post-earthquake functionality in critical structural connections. Full article

The vertical load-bearing performance of slab–column joints is significantly affected by bottom reinforcement and concealed beams, but existing studies remain insufficient in analyzing their influence mechanisms. To address this, the effects of bottom reinforcement, concealed beam width, and punch-to-span ratio on the mechanical properties of joints are systematically investigated in this study through finite element analysis. Validating 2 experimental models and establishing 13 parametric models, the results shows that adding bottom reinforcement can enhance the late-stage bearing capacity and ductility of joints; increasing the ratio of top-to-bottom reinforcement improves bearing capacity but reduces ductility; a wider concealed beam leads to better bearing capacity and ductility performance of the joint; and under the same concealed beam width, a larger punching–span ratio reduces bearing capacity but improves ductility. This study reveals the critical role of bottom reinforcement and concealed beams in joint performance, providing a theoretical basis for optimizing design. Full article

A steel modular building is a highly prefabricated form of steel construction. It offers rapid assembly, a high degree of industrialization, and an environmentally friendly construction site. To promote the application of multi-story steel modular buildings in earthquake fortification zones, it is imperative to conduct in-depth research on their seismic behavior. In this study, a seven-story modular steel building is investigated using shaking table tests. Three seismic waves (artificial ground motion, Tohoku wave, and Tianjin wave) are selected and scaled to four intensity levels (PGA = 0.035 g, 0.1 g, 0.22 g, 0.31 g). It is found that no residual deformation of the structure is observed after tests, and its stiffness degradation ratio is 7.65%. The largest strains observed during the tests are 540 × 10⁻⁶ in beams, 1538 × 10⁻⁶ in columns, and 669 × 10⁻⁶ in joint regions, all remaining below a threshold value of 1690 × 10⁻⁶. Amplitudes and frequency characteristics of the acceleration responses are significantly affected by the characteristics of the seismic waves. However, the acceleration responses at higher floors are predominantly governed by the structure’s low-order modes (first-mode and second-mode), with the corresponding spectra containing only a single peak. When the predominant frequency of the input ground motion is close to the fundamental natural frequency of the modular steel structure, the acceleration responses will be significantly amplified. Overall, the structure demonstrates favorable seismic resistance. Full article

The performance of reinforced concrete (RC) frame structures will gradually decrease over time, posing a threat to the safety of buildings. Although the performance of some buildings may still meet the safety requirements, they cannot meet new usage requirements. Therefore, this paper proposes a new-type joint to promote the development of research on the reinforcement and renovation of RC frame structures in response to this situation. The RC beams and columns of the joints are connected by embedded horizontal steel plate (a single plate with dimension of 150 mm × 200 mm × 5 mm), and the beams and columns are individually wrapped in steel. Through conducting low cyclic loading tests, this paper analyzes the influence of carrying out wrapped steel treatment and the thickness of wrapped steel of the beam and connector on mechanical performance indicators such as hysteresis curve, skeleton curve, stiffness, ductility, and energy dissipation. The experimental results indicate that the reinforcement using steel plate can significantly improve the dynamic performance of the joint. The effect of changing the thickness of the connector on the dynamic performance of the specimen is not significant, while increasing the thickness of wrapped steel of beam can effectively improve the overall strength of joint. The research results of this paper will help promote the application of reinforcement and renovation technology for existing buildings, and improve the quality of human living. Full article

The design of steel connections presents considerable complexity due to their inherently nonlinear behavior, cost constraints, and the necessity to comply with structural design codes. These factors highlight the need for advanced computational algorithms to identify optimal solutions. In this study, a comprehensive computational framework is presented in which the finite element method (FEM) is integrated with a genetic algorithm (GA) to optimize material usage in bolted steel end-plate joints, while structural safety is ensured based on multiple performance criteria. By incorporating both material and geometric nonlinearities, the mechanical response of the connections is accurately captured. The proposed approach is applied to a representative beam-to-column assembly, with numerical results verified against experimental data. By employing the framework, an optimized layout is obtained, yielding a $10.4\%$ improvement in the overall performance objective compared to the best-performing validated model and a $39.3\%$ reduction in material volume relative to the most efficient feasible alternative. Furthermore, a $53.6\%$ decrease in equivalent plastic strain is achieved compared to the configuration exhibiting the highest level of inelastic deformation. These findings demonstrate that the developed method is capable of enhancing design efficiency and precision, underscoring the potential of advanced computational tools in structural engineering applications. Full article

Ductile structures have demonstrated the ability to withstand increased seismic intensity levels. Additionally, these structures can be restored to their operational state promptly following the replacement of damaged components post-earthquake. This capability has been a subject of considerable interest and focus in recent years. The study presented in this paper introduces an innovative beam-column connection that incorporates V-shaped steel as the replaceable energy-dissipating component. It delineates the structural configuration and design principles of this joint. Furthermore, the paper conducts a detailed analysis of the joint’s failure mode, stress distribution, and strain patterns using ABAQUS 2022 finite element software, thereby elucidating the failure mechanisms, load transfer pathways, and energy dissipation characteristics of the joint. In addition, the study investigates the impact of critical design parameters, including the strength, thickness, and weakening dimensions of the dog-bone energy-dissipating section, as well as the strength and thickness of the V-shaped plate, on the seismic behavior of the beam-column joint. The outcomes demonstrate that the incorporation of V-shaped steel with a configurable replaceable energy-dissipating component into the traditional dog-bone replaceable joint significantly improves the out-of-plane stability. Concurrently, the V-shaped steel undergoes a process of gradual flattening under load, which allows for a larger degree of deformation. In conclusion, the innovative joint design exhibits superior ductility and load-bearing capacity when contrasted with the conventional replaceable dog-bone energy-dissipating section joint. The joint’s equivalent viscous damping coefficient, ranging between 0.252 and 0.331, demonstrates its robust energy dissipation properties. The parametric analysis results indicate that the LY160 and Q235 steel grades are recommended for the dog-bone connector and V-shaped steel connector, respectively. The optimal thickness ranges are 6–10 mm for the dog-bone connector and 2–4 mm for the V-shaped steel connector, while the weakened dimension should preferably be selected within 15–20 mm. Full article

The effectiveness of an innovative retrofit scheme using near-surface-mounted (NSM) X-shaped CFRP ropes for the strengthening of substandard RC beam–column joints was investigated experimentally. Three large-scale beam–column joint subassemblages were constructed with poor reinforcement details. One specimen was subjected to cyclic lateral loading, exhibited shear failure of the joint region and was used as the control specimen. The other specimens were retrofitted and subsequently subjected to the same history of incremental lateral displacement amplitudes with the control subassemblage. The retrofitting was characterized by low labor demands and included wrapping of NSM CFPR-ropes in the two diagonal directions on both lateral sides of the joint as shear reinforcement. Single or double wrapping of the joint was performed, while weights were suspended to prevent the loose placement of the ropes in the grooves. A significant improvement in the seismic performance of the retrofitted specimens was observed with respect to the control specimen, regarding strength and ductility. The proposed innovative scheme effectively prevented shear failure of the joint by shifting the damage in the beam, and the retrofitted specimens showed a more dissipating hysteresis behavior without significant loss of lateral strength and axial load-bearing capacity. The cumulative energy dissipation capacity of the strengthened specimens increased by 105.38% and 122.23% with respect to the control specimen. Full article

The beam–column connection is an important element in frame construction. Despite numerous studies, there is still no uniform procedure for shear force design across countries. We continue to witness serious problems and even collapse of buildings under seismic activity caused by failures in the beam–column connection of the frame. During the last 60 decades, a large number of experimental studies have been carried out on frame assemblies, where various parameters and their compatibility under cyclic activities have been investigated. What remains misunderstood is the magnitude and distribution of the forces passing through the joint and their involvement in the magnitude of the shear force. Here, the creation of a new mathematical model for the beam and column contributes significantly to our understanding of the flow of forces in the frame connection. For this purpose, the full dimensions of the beam and its material properties are taken into account. All investigations were carried out before crack initiation and after crack propagation along the face of the column, where it separates from the beam. In the present work, the beam is subjected to two symmetrical, transverse, uniformly distributed loads. Expressions are derived to determine the magnitudes of the support reactions from the beam, as a function of the height of its lateral edge. The load positions corresponding to the extreme values of the support reactions are determined. Numerical results are presented for the effect over the magnitudes of the support reactions from different strengths of concrete and steel on the beam. The results are compared with those given in the Eurocode for shear force calculation. It is found that the shear force determined by the proposed new model exceeds the force calculated by Eurocode by 4–62.5%, depending on the crack development stage and the beam materials. Full article

We designed detachable steel sleeves to reinforce wooden joints and improve their integrity under earthquake action and investigated their mechanical properties. Monotonic bending tests were performed on a half-tenon pure wooden joint and a joint strengthened by a detachable steel sleeve. More obvious tenon pulling-out failure was observed in the pure wood joint; in comparison, only slight extrusion fracture of wooden beams and extrusion deformation of steel sleeves occurred in the wood joint reinforced by a detachable steel sleeve. Our test results showed that the initial rotational stiffness of the strengthened joint, JG1, was increased by 495.4% compared with that of the unstrengthened joint, JG0. The yield bending moment increased by 425.9%, and the ultimate bending moment increased by 627.5%, which indicated that the mechanical performance was significantly improved when the joint was reinforced by a detachable steel sleeve. Numerical simulations of different components were performed with finite element analysis software to analyze the mechanical performance of the reinforced joint. It was found that the stiffness and ultimate flexural performance of the joint could be increased by setting stiffeners on the steel sleeve and connecting the wooden column with self-tapping screws. The results of the tests were compared with those obtained through finite element analysis, and a high degree of accuracy was achieved, which could provide a theoretical basis for the reinforcement of timber structural buildings. Full article

Under the impetus of achieving global sustainable development goals, the civil construction industry is accelerating its transition towards high-quality, green, and low-carbon practices. Prefabricated, modular building technology has become a key tool due to its advantages in energy conservation, emission reduction, and shortened construction periods. However, existing research on the seismic performance of prefabricated, modular, reinforced concrete column–beam (RCS) composite structures often focuses on the construction form of beam–column joints, paying less attention to the impact of floor slabs on the seismic performance of joints during earthquakes. This may make joints a weak link in structural systems’ seismic performance. To address this issue, this paper designs a prefabricated, modular RCS composite joint considering the effect of floor slabs and uses the finite element software ABAQUS 2023 to perform a quasi-static analysis of the joint. The reliability of the method is verified through comparisons with the experimental data. This study examines various aspects, including the joint design and the material’s constitutive relationship settings, focusing on the influence of parameters, such as the axial compression ratio and floor slab concrete strength, on the joint seismic performance. It concludes that the seismic performance of the prefabricated, modular RCS composite joints considering the effect of floor slabs is significantly improved. Considering the composite effect of the slabs, the yield loads in the positive and negative directions for node FJD-0 increased by 78.9% and 70.0%, respectively, compared to that of the slab-free node RCSJ3. The ultimate bearing capacities improved by 13.2% and 9.98%, respectively, and the energy dissipation capacity increased by 23%. Additionally, the variation in the axial load ratio has multiple effects on the seismic performance of the joints. Increasing the slab thickness significantly enhances the seismic performance of the joints under positive loading. The bolt pre-tensioning force has a crucial impact on improving the bearing capacity and overall stiffness of the joints. The reinforcement ratio of the slabs has a notable effect on the seismic performance of the joints under negative loading, while the concrete strength of the slabs has a relatively minor impact on the seismic performance of the joints. Therefore, the reasonable design of these parameters can optimize the seismic performance of joints, providing a theoretical basis and recommendations for engineering application and optimization. Full article