Search Results (66)

Ensuring the structural integrity of reinforced concrete (RC) components in nuclear facilities exposed to extreme conditions is essential for safe decommissioning. This study investigates the impact of high-temperature exposure on RC pedestal structures supported by steel ring-shaped shear connectors—critical elements for maintaining vertical and lateral load paths in containment systems. Scaled-down cyclic loading tests were performed on pedestal specimens with and without prior thermal exposure, simulating post-accident conditions observed at a damaged nuclear power plant. Experimental results show that thermal degradation significantly reduces lateral stiffness, with failure mechanisms concentrating at the interface between the concrete and the embedded steel skirt. Complementary finite element analyses, incorporating temperature-dependent material degradation, highlight the crucial role of load redistribution to steel components when concrete strength is compromised. Parametric studies reveal that while geometric variations in the inner skirt have limited influence, thermal history is the dominant factor affecting vertical capacity. Notably, even with substantial section loss in the concrete, the steel inner skirt maintained considerable load-bearing capacity. This study establishes a validated analytical framework for assessing structural performance under extreme conditions, offering critical insights for risk evaluation and retrofit strategies in the context of nuclear facility decommissioning. Full article

Current research on the stress mechanisms of composite connectors within steel–concrete structures of bridge towers is sparse, and there is a lack of established experimental methods and finite element modeling techniques for studying these mechanisms. This study focuses on a specific type of composite shear connector within the steel–concrete section of the Shunde Bridge tower. By employing proposed experimental methods and finite element model analysis, this research examines the load–slip curves and stress distribution of these shear connectors. It aims to elucidate the stress mechanisms and mechanical relationships between the composite connectors and the individual perforated plate connectors and shear stud connectors that comprise them. The results demonstrate that the proposed experimental methods and finite element modeling approaches effectively analyze the stress mechanisms of composite connectors, revealing that the ultimate load-bearing capacity and elastic stiffness of the composite connectors are approximately the sum of those of the individual connectors configured in parallel; The mechanical performance of the composite connectors in the steel–concrete section of the bridge tower is approximately the additive sum of the mechanical performances of the individual connectors comprising them. By comparing the experimentally measured load–slip curves with those calculated from the finite element models, it validates the modeling approach of the finite element model, and the material parameters established through material characteristic tests and literature review are reasonable. Full article

The use of steel-concrete composite slim-floor beams with dowel shear connectors is uncommon, and the design rules provided in Eurocode 4 for composite construction are not directly applicable to the slim-floor composite beam. In this paper, a finite element model is developed, followed by a parametric study that examines the effects of various shear connector parameters on the structural behaviour of composite beams. The comparison and analysis show that the load-bearing capacity increases with a bigger concrete dowel, as long as the shear connection degree is less than 100% and the dowel diameter is not greater than 80 mm; the load-bearing capacity goes up about 5–10% for every 10 N/mm² increase in concrete strength and about 2% for every 4 mm increase in rebar diameter in the dowel; also, the dowel central spacing has a big impact on the structural behaviour. The composite beams showed great flexibility, with the end slip at the highest load being more than 6 mm and the maximum load declining by less than 15% when the midspan deflection reached L/30. The proposed calculation method for bending moment resistance is more than 90% accurate for composite beams that have a shear connection degree greater than 40%. The findings from this research provided more profound insights into the behaviour of this type of slim-floor composite beam. Full article

To reduce the cast in place work of concrete and realize the industrial production of a bamboo–concrete composite (BCC), innovative connection systems composed of an assembled bamboo–lightweight concrete composite (ABLCC) structure featuring perforated steel plate connectors are presented for use in engineering structures. This study examined the shear performance of connection systems composed of an assembled BCC structure featuring perforated steel plate connectors based on the design and fabrication of three groups of shear connectors with nine different parameters using bamboo scrimber, lightweight concrete, perforated steel plates, and grout. Push-out tests were conducted on these shear connectors. A linear variable differential transformer (LVDT) and digital image correlation (DIC) were utilized for measurements. The test parameters comprised fabrication techniques (assembled and cast-in-place/CIP) and connector size (steel plate thickness). This study investigated mechanical performance indicators, including the failure mode, load–slip relationship, shear stiffness, and shear capacity of the shear connectors. The experimental results showed that the shear connector failure modes involved concrete spalling near the connectors and deformation of the perforated steel plates. The load–slip curves generally included three stages: high slope linear increase, low slope nonlinear increase, and rapid decrease. The shear capacity and stiffness of the assembled shear connectors were 0.84 times and 2.46 times those of the CIP connectors, respectively. The stiffness of the 4 mm steel plate connectors increased by 42% compared to the 2 mm steel plate connectors. Analysis showed that the shear capacity of the BBC primarily consisted of four aspects: the end bearing force of the steel plate, contact friction, and forces due to the influence of tenon columns and the reinforcing impact of through-rebars. This study proposes a simple and suitable formula for obtaining the shear capacity of perforated steel plate connectors in the BCC structure, with the analytical values being in good agreement with the test results. Full article

Additional steel supporting joists (ASSJs) can effectively enhance the anti-overturning capacity of the existing solo-column concrete pier (SCP) bridges. Although the interface consists of bolt connections between steel and concrete is the crucial load-transmitting portion, the design of the interface between the ASSJ and SCP still mainly relies on practical experiences. In an actual bridge rehabilitation project with ASSJs in China, a novel connection comprising large-diameter bolts and an epoxy resin layer was adopted to overcome the shortcomings of the initial design. In this study, connections composited with large-diameter bolts and different interfacial treatments were investigated. Four push-out tests on the interfacial shear performance of steel–concrete connections were carried out. The experimental parameters encompassed the interface treatment method (barely roughened surface, smearing epoxy resin, and filling epoxy mortar) and the number of bolts (single row and double rows). The failure modes were unveiled. According to the experimental results, the interfacial treatment method with filling epoxy mortar could uniformly transfer stress between concrete and steel and improve the shear stiffness and shear resistance of the steel–concrete connections. Compared with specimens with barely roughened interfaces, epoxy mortar and epoxy resin employed at the steel–concrete interface can increase the shear-bearing capacity of connections by approximately 47.71% and 43.46%, respectively. However, the interfacial treatment method with smearing epoxy resin resulted in excessive stiffness of the shear members and brittle failure mode. As the number of the bolts increased from a single row to a double row, the shear-bearing capacity of a single bolt in the specimen exhibited approximately an 8% reduction. In addition, by comparing several theoretical formulae with experimental results, the accurate formula for predicting the shear-bearing capacity of bolts was recommended. Furthermore, the load-bearing capacity of an ASSJ in the actual engineering rehabilitation was verified by the recommended formula GB50017-2017, which was found to accurately predict the shear-bearing capacity of large-diameter bolt connectors with an epoxy mortar layer. Full article

This paper proposes a hybrid steel plate–bolt dry and wet jointing method, where the dry jointing part is a steel plate–bolt connector joint and the wet jointing part is a cast-in-place concrete. The novel precast concrete shear wall (PCW) combines the advantages of both dry and wet connections. A steel plate–bolt dry–wet hybrid connection shear wall model was developed using the finite element method, and a low circumferential reciprocating load was applied to the PCW. By analyzing the force and deformation characteristics of the wall, the results showed that the failure mode of novel PCWs was bending-shear failure. Compared to the concrete wall (CW), the yield load, peak load, and ductile displacement coefficient were 6.55%, 7.56%, and 21.49% higher, respectively, demonstrating excellent seismic performance. By extending the wall parameters, it was found that the increased strength of the novel PCW concrete slightly improved the load-bearing capacity, and the ductility coefficient was greatly reduced. As the axial compression ratio increased from 0.3 to 0.4, the wall ductility decreased by 22.85%. Increasing the reinforcement rate of edge-concealed columns resulted in a severe reduction in ultimate displacement and ductility. By extending the connector parameters, it was found that there was an increased number of steel joints, a severe reduction in ductility, enlarged distribution spacing, weld hole plugging and bolt yielding, reduced anchorage performance, and weakening of the steel plate section, which reduced the load-bearing capacity and initial stiffness of the wall, with little effect on ductility. Full article

This study investigates the shear-bending performance of GFRP (Glass Fiber Reinforced Polymer) connectors in sandwich insulation composite wall panels following tension–compression fatigue damage. A total of 24 specimens, divided into 11 groups, were prepared for experimental analysis. Three distinct load amplitudes (5.4 kN, 4.0 kN, 2.7 kN) and three fatigue loading cycles (30,000, 50,000, 80,000) were established as loading conditions. The experimental protocol included out-of-plane tension–compression fatigue tests followed by post-fatigue shear-bending tests. The influence of varying load amplitudes and fatigue loading cycles on failure modes, load–displacement relationships, and bearing capacity alterations was systematically examined. A two-factor analysis of variance (ANOVA) was utilized to evaluate the statistical significance of these factors. The findings reveal that the predominant shear-bending failure modes post-fatigue damage are connector fracture and concrete crushing in the anchorage zone. Specifically, under a load amplitude of 2.7 kN and 30,000 cycles, the shear-bending capacity of the specimens exhibited a minimal reduction of 1.82% compared to the ultimate capacity of undamaged specimens. Conversely, at a load amplitude of 5.4 kN and 80,000 cycles, the shear-bending capacity experienced a substantial decline of 37.11%. Both load amplitude and fatigue loading cycles were found to significantly impact the shear-bending capacity, with fatigue loading cycles demonstrating a more pronounced effect. This research provides critical insights for the design and assessment of sandwich insulation composite wall panels, particularly in the context of long-term fatigue damage and its implications on structural performance, thereby contributing valuable theoretical and practical knowledge to the field. Full article

To improve both the composite performance of precast thermal insulation wall panels and the environmental sustainability of the structure, this study employs recycled concrete, and introduces an innovative four-footstool Glass Fiber Reinforced Plastic (GFRP) connector to join the inner and outer panels of precast thermal insulation wall systems. The experimental program included pull-out, shear, and bending tests to compare the performance of wall panels equipped with traditional Thermomass MS connectors and the novel GFRP connectors, using both conventional and fully recycled concrete. The results indicate that, when paired with recycled concrete, the GFRP connectors exhibited a 14.8% higher pull-out bearing capacity than the traditional connectors. Additionally, shear tests demonstrated that the GFRP connectors offered a 20.6% improvement in shear resistance compared to the Thermomass MS connectors. The bending strength of panels with GFRP connectors also showed an enhancement, with a 16.5% increase in flexural strength relative to those using traditional connectors. Notably, the GFRP connectors contributed to a more uniform crack distribution under loading, thereby improving the overall structural integrity. A reduction factor γ for the GFRP four-footstool connector was proposed based on a fully composite model, and the analysis of the composite degree calculation showed that the recycled concrete sample using the new GFRP connector had the highest composite degree. Full article

Recent research indicates that high-strength bolts could be more effectively and efficiently used to connect steel girders and fabricated decks or retrofit existing composite girders than headed studs. To reduce the number of bolt shear connectors and, thus, further accelerate the construction of composite girders, high-strength large bolts could be an excellent alternative, resulting in greater concrete stress below the bolt. Also, hybrid fiber-reinforced concrete (HFRC) has better tensile ductility and strength than that of ordinary concrete (OC). Therefore, this study tried to design eighteen push-out test specimens, including different configurations of bolt shear connectors, to investigate the static properties of post-installed, high-strength, large-bolt shear connectors with fabricated HFRC/OC slabs. The experimental results indicated that the capacity and initial stiffness of a high-strength large through-bolt shear connector was the smallest. The fiber might enhance the capacity and initial stiffness of bolt shear connectors. Increasing the bolt diameter can significantly enhance the initial stiffness and load-bearing capacity, while the clearance of the bolt hole had a great influence on the capacity, initial stiffness, and slippage of the post-installed high-strength large-bolt shear connector. Finally, the capacity equation and slip behavior of post-installed, high-strength, large-bolt shear connector with fabricated HFRC deck were obtained using the regression method, which could provide the reference for their design. Full article

This study proposes a novel type of demountable steel–concrete composite beam (the slab is connected to the steel beam by T-shaped shear connectors, TCBs) to address the limitations of traditional composite beams, including difficulties in disassembly and challenges in resource recycling. Finite element analysis was conducted to compare a TCB’s mechanical performance and failure modes with those of traditional bolt-connected steel–concrete composite beams (BCBs). The results show that, while the TCB exhibits reduced initial stiffness, it enhances mid-span deformation capacity, demonstrating superior ductility and a more uniform damage distribution. Furthermore, the influence of parameters such as concrete strength, bolt diameter, steel beam strength, and flange thickness on the flexural performance of the TCB was investigated. When the bolt diameter increases from 16 mm to 24 mm, the flexural capacity increases by 45.26% and the ductility increases by 63.3%. Enhanced steel beam strength led to a 55.17% increase in bearing capacity, while an increase in flange thickness by 3 mm contributed to a 24.8% improvement in load-bearing capacity. Additionally, the ultimate flexural moment resistance was calculated and verified based on the shear-resisting connection theory, with the computed results showing good agreement with the finite element analysis results. The average ratio of these values was 0.97, with a standard deviation of 0.06. The findings provide a theoretical basis for designing and engineering applications of demountable composite beams. Full article

Sandwich panels, consisting of two concrete wythes that encase an insulating core, are designed to improve energy efficiency and reduce the weight of construction applications. This research examines the thermal and flexural properties of a novel sandwich panel that incorporates ultra-high-performance fiber-reinforced concrete (UHPFRC) and cellular lightweight concrete (CLC) as its core material. Seven sandwich panel specimens were tested for their thermo-flexural performance using four-point bending tests. The experimental parameters included variations in UHPFRC thickness (20 mm and 30 mm) and different shear connector types (shear keys, steel bars, and post-tension steel bars). The study also assessed the effects of adding steel mesh reinforcement to the UHPFRC layer and evaluated the performance of UHPFRC box sections without a CLC core. The analysis concentrated on several critical factors, such as initial, ultimate, and serviceability loads, load–deflection relationships, load–end slip, load–strain relationships, composite action ratios, crack patterns, and failure modes. The thermal properties of the UHPFRC and CLC were evaluated using a transient plane source technique. The results demonstrated that panels using post-tension steel bars as shear connectors achieved flexural performance, and the most favorable composite action ratios reached 68.8%. Conversely, the box section exhibited a brittle failure mode when compared to the other sandwich panels tested. To effectively evaluate mechanical and thermal properties, it is important to design panels that have adequate load-bearing capacity while maintaining low thermal conductivity. This study introduced a thermo-mechanical performance coefficient to evaluate both the thermal and mechanical performance of the panels. The findings indicated that sandwich panels with post-tension steel bars achieved the highest thermo-mechanical performance, while those with steel connectors had the lowest performance. Full article

High-strength bolt connectors, known for their robust strength and ease of disassembly, are suitable not only for the construction of new steel–concrete composite beams but also for reinforcing existing composite or steel beams. Static push-out tests were performed on nine specimens to examine their shear behavior. The primary failure mode was observed at the steel–concrete interface, characterized by the tensile–shear failure of the bolt and localized crushing of the concrete beneath the bolt. The preload had no significant influence on the ultimate bearing capacity and ultimate slip displacement, while it had a substantial impact on the initial slip load. The failure process was divided into static friction at the interface, sliding at the interface, elastic deformation of the bolt, and plastic deformation of the bolt. The parametric analysis using the finite element method was performed to assess the impact of concrete strength, reserved hole diameter, interface friction coefficient, and bolt diameter and strength. It revealed that the ultimate bearing capacity is composed of interfacial friction and bolt shear capacity, which are not independent of each other. To decouple these components, a novel calculation method for determining the ultimate bearing capacity of high-strength bolt connectors was developed and validated using existing test data. Full article

To investigate the design principles and simplified calculation model of large-size PBL-stiffened steel–concrete joints, this study uses a Y-shaped rigid frame-tied arch composite bridge as an engineering background. Based on deformation coordination theory, a combination of theoretical analysis and numerical simulation was employed to derive a simplified calculation model that accounts for boundary conditions such as the stiffness of steel beam end restraints and the local bearing effect of the bearing plate. Parametric analysis of the steel–concrete joint was conducted. The results indicate that the derived simplified calculation model exhibits good accuracy and is suitable for calculating force transfer in various components of the steel–concrete joint under different boundary conditions. Using the simplified model, the effects of parameters such as steel–concrete joint length, connector stiffness, and structural axial stiffness on the axial force transfer in primary force-bearing components (connectors and bearing plates) were studied. The findings reveal that an excessively long steel–concrete joint does not effectively reduce maximum shear force; variations in connector stiffness primarily affect connectors farther from the bearing plate without changing the shear force distribution. Increasing the axial stiffness of the steel structure within a certain range can improve the maximum shear force in connectors, whereas increasing the axial stiffness of the concrete structure has the opposite effect. Full article

To study the lateral performance of a cold-formed steel–concrete insulation sandwich panel composite wall, two full-scale specimens with different arrangements were designed. The specimens underwent cyclic loading tests to examine the failure characteristics of the composite wall, and lateral performance aspects such as the experimental hysteresis curve, skeleton curve, and characteristic value of the whole loading process were acquired. The experimental results indicate that the failure of the composite wall system was primarily caused by the failure of the connection; the overall lateral performance of composite walls with one wall panel at the bottom and two wall panels at the top (W1) was superior to that of composite walls with two wall panels at the bottom and one wall panel at the top (W2). When loaded to an inter-story drift ratio of 1/300, the composite wall did not exhibit any significant damage. A finite element (FE) model was developed and validated by the experiments. Factors affecting the shear bearing capacity were analyzed based on the FE model, including the yield strength of diagonal braces, the thickness of the diagonal braces, the arrangement pattern of the wall panels, the dimensions of the wall panels, and the strength of the connection of the L-shaped connector and the flat connector. The FE results show that all these factors can influence the lateral performance of the composite wall. Full article

Combining steel with wood has been practised for many years. The issue is related to two main areas, i.e., bonding steel elements with wood so that they serve as connectors facilitating the assembly of wood elements and bonding steel elements to wood beams to improve their load-bearing capacity. In the first case, the adhesives used may be relatively expensive and more difficult to apply, whereas in the second one, especially when steel elements are glued inside the glulam (GL) beams, it is better if the adhesives used are more accessible to apply and cheaper. As it seems rational to reinforce wood with high-modulus ties, research has been carried out to compare the connection quality of commercially available adhesives that can be used for this purpose. Moreover, thermosetting adhesives have been applied as an alternative and cheaper solution. Thermostat adhesives also have a high pH of the bond, which prevents the steel from rusting. The research shows that the load-bearing capacity of the bond depends on whether the bars are ribbed or sheet metal. Moreover, among thermosetting adhesives, the most favourable load-bearing values were obtained using a mixture of PF/pMDI (phenol formaldehyde resin/polymeric diphenylmethane diisocyanate) and powder from recycled tyres. The shear strength of these joints was 1.63 N/mm² and 3.14 N/mm² for flat specimens and specimens with ribbed bars, respectively. Full article