Search Results (106)

To investigate the influence of dry connection methods on the seismic behavior of assembled composite walls, four assembled composite walls were designed and tested. Various dry connection techniques were adopted for the horizontal interfaces, namely sleeve grouting connection, welding connection, box connection, and bolted connection. The failure process, failure mode, bearing capacity, rigidity, steel bar strain, and energy absorption performance of the specimens were investigated through quasi-static cyclic loading tests. The results indicate that all types of connectors can effectively transfer loads and satisfy the conceptual design principle of “strong joint and weak component”. The damage evolution of the specimens is essentially identical, and the limiting drift angles all exceed 1/90. In addition, the shear resistance of the specimens with different connection methods is preliminarily analyzed and estimated. Full article

Rectangular shield tunnels demonstrate significant advantages in underground space utilization due to their optimal cross-section efficiency and enhanced spatial functionality. Furthermore, their shallow overburden construction capability minimizes environmental impact and preserves subsurface resources. However, compared with circular shield tunnels, rectangular configurations exhibit greater susceptibility to longitudinal differential torsional deformation under asymmetric external loading. This deformation mechanism may induce excessive stresses in segments and connecting bolts, potentially causing joint offsets at tunnel rings that compromise structural integrity. This paper proposes a computational method for determining the longitudinal equivalent torsional stiffness of rectangular shield tunnels under combined compression–bending–torsion loading based on an equivalent continuum model. The proposed novel theoretical solutions were systematically validated against numerical simulations through comparative analysis. Parametric studies revealed that the effective ratio of longitudinal torsional stiffness increases proportionally with segment width-to-height ratio and bolt quantity while exhibiting inverse correlations with segment thickness and bolt equivalent shear length. The effective ratio of longitudinal torsional stiffness is directly correlated with compression–torsion ratios and bending–torsion ratios, with different load combinations significantly influencing torsional performance. Consequently, design optimizations incorporating increased bolt pre-tension forces or pre-stressed segment structures are proposed to improve torsional performance in rectangular shield tunneling systems. Full article

This study aims to enhance the damage controllability and overall seismic resilience of assembled underground structures under earthquake actions. To achieve this, three types of prefabricated roof–sidewall composite joints are proposed based on the design concepts of cogging for force transfer and local strengthening. These include the high-strength bolt–cogging–grouting sleeve joint (HCG), the prestressed steel strand–cogging–grouting sleeve joint (PCG), and the UHPC–cogging–grouting sleeve joint (UCG). Following the principle of positioning joints in regions of low structural stress, four 1/4-scale reinforced concrete (RC) specimens were designed and fabricated, including one cast-in-place (CIP) reference specimen and three precast RC specimens. Quasi-static tests were carried out to systematically evaluate the seismic behavior and internal force distribution of each specimen. Numerical validation was also performed using ABAQUS. The results show that both UHPC and a reasonable application of prestressing can effectively inhibit crack initiation and damage propagation at the joint seams. When the composite joints are positioned outside the plastic hinge region, they provide a reliable load transfer path for the reinforcement. The HCG and UCG joints significantly enhance the load-bearing capacity and energy dissipation capacity of the specimens. Their ductility and energy dissipation both achieve a seismic performance equivalent to that of the CIP specimen. Furthermore, damage in these specimens is predominantly confined to the designated plastic hinge region of the roof. This effectively mitigates shear damage in the roof–sidewall connection zone (RSC). Although the PCG joint improves the initial stiffness of the specimen, its energy dissipation capacity and ductility are reduced. It also causes damage to be transferred to the RSC. This leads to increased shear deformation and premature shear failure in this zone. Consequently, both UHPC and a reasonable application of prestressing can be used for the prefabrication of underground structures. Positioning the joints outside the roof plastic hinge zone can effectively achieve the seismic design goal of “strong joint, weak component”. Full article

The rapid development of multimegawatt wind turbines presents greater demands on the structural safety and stability of tower structures. In response, this study investigates the axial compressive behavior of steel–concrete–steel (SCS) composite towers with a low steel ratio and enhanced shear connection. The two steel plates are integrated by bolt connectors to ensure overall stiffness and effective composite action. Axial compression tests are conducted on curved tower wall members representing a 1/16 segment of the tower cross-section. Previous experimental results indicate that failure is dominated by local buckling of steel plates between adjacent connectors, highlighting the critical role of connector-induced confinement in controlling instability. Numerical models of curved composite walls are established and validated against previously published experimental results, showing good agreement in both failure modes and bearing capacity. Parametric analysis indicates that increasing the bolt diameter from 16 mm to 20 mm and 24 mm enhances the ultimate load by 3.09% and 6.58%, respectively. For the full-section tower model, reducing bolt spacing to 500 mm, 300 mm, and 250 mm increases the ultimate load by 16.33%, 20.05%, and 21.79%, respectively, compared to the bolt-free model. These results confirm that reducing connector spacing substantially enhances bearing capacity through improved confinement and delayed local buckling. A calculation method for evaluating the axial bearing capacity of SCS composite towers incorporating confinement effects is proposed, showing good consistency with both experimental and numerical data. Full article

This study investigates the cyclic behaviour of demountable steel–concrete composite extended end-plate reduced web section (RWS) connections for the first time, aiming to facilitate post-seismic beam replacement. A validated high-fidelity finite element (FE) model was developed to analyse 285 FE models, evaluating response characteristics based on the Ibarra–Medina–Krawinkler model. Key parameters, including the influence of composite action over the web opening, web opening diameter, and end-distance, were considered. Findings indicate that RWS connections with medium to large web openings experience cyclic strength degradation while remaining compliant with American and European seismic standards. Additionally, bolted shear studs yielded a more stable and predictable contribution to the connection’s strength up to 5%, outperforming traditional welded studs in consistency. This research emphasises the importance of aligning web opening size and location with capacity design ratios between connection components for acceptable seismic performance, proposing specific web opening sizes and locations to enhance structural resilience. Full article

The Innovative Lightweight Cold-Formed Steel–Concrete Composite Floor System (LWT-FLOOR) addresses key challenges faced by the construction industry related to the efficiency, adaptability, and life-cycle usability of structural elements. Within this context, the present study investigated the behaviour of demountable bolted shear connections in a composite system combining built-up cold-formed steel (CFS) girders and concrete slabs. An experimental programme comprising 18 push-out tests was conducted on two composite configurations: built-up back-to-back CFS sections and built-up sections incorporating a corrugated web. The influence of key parameters, including the bolt diameter, CFS thickness, steel grade, and connector spacing, was evaluated. The results show that increasing the bolt diameter enhanced the shear resistance and initial stiffness while reducing ductility, whereas reducing the CFS thickness led to a moderate decrease in resistance accompanied by a pronounced increase in ductility. The incorporation of a corrugated web increased the ultimate shear resistance by approximately 30–40%. The existing analytical models from current standards were found to be inadequate; however, the introduction of a spacing-dependent correction factor into the prEN 1994-1-1 model significantly improved the prediction accuracy, reducing the coefficient of variation from 16% to 4.36%. The findings provide a quantitative basis for improving the design of demountable shear connections in lightweight composite CFS-concrete systems. Full article

Top-and-seat angle connections (TSACs) exhibit inherently asymmetric and nonlinear moment–rotation behavior, which can significantly influence the global response of steel frames subjected to combined gravity and lateral loading. In this study, a three-dimensional finite element model of an unstiffened TSAC is developed and validated against experimental moment–rotation data from the literature under monotonic loading conditions. The validated model is then used to investigate the influence of key geometric parameters, including top angle thickness, bolt diameter, and beam depth, on the connection’s moment–rotation response in both positive and negative bending directions. Subsequently, the monotonic connection behavior is incorporated into nonlinear static analyses of steel portal frames to examine the effects of asymmetric connection response and moment reversal on frame-level stiffness degradation and capacity. A practical SAP2000 modeling workflow is proposed in which the finite element-derived monotonic moment–rotation curves are implemented using zero-length rotational link elements, allowing combined consideration of material, geometric, and connection nonlinearities at the structural level. The comparisons between Abaqus and SAP2000 results demonstrate consistent frame-level responses when identical monotonic connection characteristics are employed, highlighting the ability of the proposed workflow to reproduce detailed finite element predictions at the structural analysis level. The results indicate that increasing top angle thickness, bolt diameter, and beam depth enhances the lateral stiffness and base shear resistance of steel frames. Positive and negative bending directions are defined consistently with the applied gravity-plus-lateral loading sequence. Full article

Steel and prestressed concrete traction poles can be fixed to reinforced concrete pile foundations using typical bolted connections. The stainless steel fastening screw is connected to the ordinary steel foundation pile reinforcement by friction welding under specific friction welding process parameters. From the perspective of the structural strength of the connection between the traction pole and the foundation pile, regarding the transfer of tensile and shear forces through a single anchor bolt, the yield strength of stainless steel bolts should be R_e,min ≥ 345 MPa for M30 anchors, R_e,min ≥ 310 MPa for M36 anchors and R_e,min ≥ 300 MPa for M42 anchors. This requirement is reliably met by martensitic stainless steels, while other stainless steels have yield strengths below the required minimum. What truly determines the foundation pile’s load capacity is not the satisfactory mechanical strength of the stainless steel (here, the parameters are met), but the quality of the friction-welded end connection between the reinforcement and the threaded bars. Incorrect selection of the type of prestressing steel in the analyzed connection can have enormous consequences for foundation pile manufacturers. Annual production of foundation piles amounts to thousands of units, and an incorrect decision made by the pile designer at the design stage can result in significant financial losses and a high risk to human life. This article presents the results of studies on friction-welded connections of M30, M36, and M42 threaded bars made of austenitic 1.4301 (AISI 304) and martensitic 1.4021 (AISI 420) stainless steel with B500SP reinforcement bars. The tests yielded negative results for 1.4021 (AISI 420) steel, despite its yield strength exceeding R_e ≥ 360 MPa. Full article

Laminated bamboo (LB) has shown enough exceptional performance to be used in constructions, but the performance of the bolted connections remains to be explored. To meet the criteria of low-carbon construction and fill the research gap in LB dowel embedment performance, this study examined the longitudinal dowel embedment behavior of LB. Failure modes, load–displacement curves, embedment strength, and elastic foundation parameters were examined after four sets of half-hole specimens with dowel diameters (6, 8, 10, and 12 mm) were tested in accordance with ISO 10984-2. The majority of the data was confirmed to follow a normal distribution by the Kolmogorov–Smirnov test. Interlaminar shear failure (dominant in 10 and 12 mm groups) and local crushing (dominant in 6 and 8 mm groups) were the primary failure modes. There were clear linear and nonlinear phases in the load–displacement curves (excellent ductility). The average elastic foundation modulus was 3565.55 MPa (0.39 times the compressive modulus); meanwhile, the average proportional limit, yield, and ultimate strengths were 35.48, 63.08, and 74.44 MPa (0.59, 1.06, and 1.25 times the parallel-to-grain compressive strength). The ultimate strength varied from 72.64 MPa to 76.71 MPa as the diameter rose; however, the elastic foundation beam coefficient dropped significantly. A novel calculation based on LB’s parallel-to-grain compressive strength accorded well with test results, while the existing code formulae (GB 50005, NDS, and CSA O86) overestimated LB embedment strength. The design of LB bolted connections is guided by this study, which also explains LB embedment criteria and offers design parameters and a prediction method. Full article

In order to improve the seismic performance of traditional precast lightweight walls, a new precast concrete wall with beam connection and embedded steel support is proposed in this study. Six 2/3-scale specimens were designed for a quasi-static cyclic loading test, and a numerical study was carried out. Key variables include shear span ratio (0.8–1.6), wall thickness (120–200 mm), concrete strength (C25–C40), and concealed column configuration. The experimental results reveal three distinct failure modes, specifically, brace buckling, weld fracture at the lower joints, and bolt shear failure. The system shows excellent ductility (displacement ductility coefficient μ = 3.2–4.1) and energy dissipation capacity (equivalent viscous damping ratio ξ = 0.28–0.35), and its performance is 30–40% higher than that of traditional reinforced concrete walls and close to that of steel plate shear walls. The shear span ratio is reduced by 50%, the shear bearing capacity is increased by 16%, but the peak displacement is halved, and the peak load of concealed column is increased by 57%. The finite element analysis verified the experimental trends and emphasized that the shear capacity can be increased by 12–18% by widening the steel brace (relative to thickening) under the condition of constant steel volume. The results demonstrate that BIM-driven design is very important for solving connection conflicts and ensuring constructability. Parameter research shows that when the concrete strength is greater than C30, the yield load increases by 15–20%, but the influence on the ultimate bearing capacity is minimal. These findings provide an operational guide for the implementation of high-performance prefabricated walls in earthquake-resistant steel structures, and balance the details of constructability through support, connection, and BIM. Full article

Steel angles connected by bolts have been commonly used in transmission towers. Due to the limited length of steel angles, double-shear splice connections are generally adopted to connect steel angles in main members. The stability of this type of members remains unclear as a result of the presence of discontinuity and is difficult to evaluate using existing design methods. This study presents numerical simulations of steel angles with double-shear splice connections under axial compression. Numerical models are established for discontinuous steel angles and validated against published experimental results. Parameters including splice steel ratio, discontinuity location, slenderness ratio, and width-to-thickness ratio on the axial compression load capacity of steel angles are evaluated. A design equation is proposed based on numerical results to quantify the axial load capacity of discontinuous steel angles. Comparisons with experimental data and values calculated using Chinese design code demonstrate that the proposed equation can predict the ultimate load capacity of discontinuity steel angles with better accuracy than the design method in the Chinese code. Finally, a design equation is further simplified by eliminating the effect of parameters with limited influence on ultimate load under axial compression. Full article

Fiber-reinforced polymer (FRP) composites, particularly glass fiber-reinforced polymer (GFRP), are increasingly utilized in civil engineering due to their high strength-to-weight ratio, corrosion resistance, and environmental sustainability compared to steel. Shear connectors in FRP–concrete hybrid beams are critical for effective load transfer, yet their behavior under static loads remains underexplored. This study aims to investigate the shear strength, stiffness, and failure modes of GFRP, CFRP, AFRP, and stainless-steel shear connectors in FRP–concrete hybrid beams through a comprehensive parametric analysis, addressing gaps in material optimization, bolt configuration, and design guidelines. A validated finite element model in Abaqus was employed to simulate push-out tests based on experimental data. The parameters analyzed included shear connector material (GFRP, CFRP, AFRP, and stainless steel), bolt diameter (16–30 mm), number of bolts (1–6), longitudinal spacing (60–120 mm), embedment length (40–70 mm), and concrete compressive strength (30–70 MPa). Shear load–slip (P-S) curves, ultimate shear load (P), secant stiffness (K₁), and failure modes were evaluated. CFRP bolts exhibited the highest shear capacity, 26.50% greater than stainless steel, with failure dominated by flange bearing, like AFRP and stainless steel, while GFRP bolts failed by shear failure of bolt shanks. Shear capacity increased by 90.60%, with bolt diameter from 16 mm to 30 mm, shifting failure from bolt shank to concrete splitting. Multi-bolt configurations reduced per-bolt shear capacity by up to 15.00% due to uneven load distribution. Larger bolt spacing improved per-bolt shear capacity by 9.48% from 60 mm (3d) to 120 mm (6d). However, in beams, larger spacing reduced the total number of bolts, decreasing overall shear resistance and the degree of shear connection. Higher embedment lengths (he/d ≥ 3.0) mitigated pry-out failure, with shear capacity increasing by 33.59% from 40 mm to 70 mm embedment. Increasing concrete strength from 30 MPa to 70 MPa enhanced shear capacity by 22.07%, shifting the failure mode from concrete splitting to bolt shank shear. The study highlights the critical influence of bolt material, diameter, number, spacing, embedment length, and concrete strength on shear behavior. These findings support the development of FRP-specific design models, enhancing the reliability and sustainability of FRP–concrete hybrid systems. Full article

A finite element dynamic modeling method considering the bolt non-uniform connection effect for the vibration characteristics of the disk–drum–shaft coupled structure is proposed. This structure consists of disks, drums, and hollow shafts, with significant differences in their geometric structures, which poses a challenge to modeling efficiency. A universal element with four nodes and 60 degrees of freedom is created in this paper. Based solely on the universal element and first-order shear theory, a universal expression for the stiffness matrix and mass matrix applicable to disk, drum, and shaft structures is derived to improve modeling efficiency. A dynamic model of the coupled structure is established by simulating the non-uniform connection effect of bolts and boundary conditions through the construction of an eight-degree-of-freedom spring-damping element. The effectiveness of the modeling method is verified through experiments, and the results showed good consistency between the natural frequency and vibration response of the simulation and those of the experiment. Finally, the influence of changes in bolt pre-tightening torque on the vibration characteristics of coupled structures is studied. Full article

Nuclear power plant (NPP) shear walls are typically ultra-thick and heavily reinforced, posing significant challenges for conventional cast-in-place (CIP) construction. To overcome these issues, this study proposes a precast concrete shear wall (PCSW) system with bolted connections. Owing to orthogonal wall layouts dictated by functional requirements, these structures are subjected to significant out-of-plane seismic demands, making their performance under such loading a critical design concern. Therefore, this paper investigates the out-of-plane seismic performance of scaled (1:2) models of PCSWs (300 mm thick) under an axial pressure ratio of 0.2 and without axial pressure through low-cycle repeated load tests, and compares them with corresponding CIP shear walls. All specimens exhibited flexural failure, while damage in PCSWs was relatively minor and concentrated within the grouting layer. Compared with CIP specimens, the precast specimens showed more pinching and smaller residual deformation, with cumulative energy dissipation reaching 70–80% of CIP specimens. The flexural load-bearing capacity of the precast specimens was close to that of the CIP specimens, with differences within 5%. The ductility of the precast specimens under axial pressure ratios of 0 and 0.2 was 4.54 and 2.68, respectively, differing from the CIP specimens by 16% and −10%. The stiffness degradation trends of both systems were essentially consistent. Overall, the results demonstrate that the out-of-plane seismic performance of PCSWs with bolted connections is broadly equivalent to that of CIP counterparts, confirming their feasibility for application in NPPs. Full article

The introduction of functional elements is essential for many industrial components which rely on elements such as bolts, screws, nuts, or clips that are integrated into the workpieces. In the field of cold joining technologies, double-sided self-pierce riveting (DS-SPR) presents itself as a proper alternative to produce the mechanical connection of those elements into sheet panels. For the purpose of this investigation, a tubular rivet with a machined thread to replicate a hollow bolt was joined to a sheet panel. Since this application will be subjected to torsion loads when a nut or other elements are fastened, tubular rivets with different numbers of semi-longitudinal rectangular openings at their ends (0, 2, 4, and 8) were investigated to identify the optimal design that ensures proper performance during its service life. The results show that rivets with four openings achieved a torsional resistance of more than 40 N·m, which is over double that of the original rivet without openings, while maintaining comparable shear strength (~10 kN). A functional hollow bolt with an outer thread was successfully produced, achieving a torque capacity of 35 N·m, equivalent to an M8 solid bolt, but with reduced weight. These findings highlight DS-SPR as a viable technology for manufacturing functional riveted elements that combine the permanent joints between sheets and removable connections with secondary components, offering both structural performance and lightweight advantages. Full article