Search Results (470)

Prefabricated H-section steel composite wall columns (PHSWCs) are crucial for advancing modular steel construction, yet their elastic buckling performance lacks a universally accurate predictive model due to the complex interplay between section interaction and semi-rigid bolted connections. To address this, a comprehensive theoretical framework for elastic buckling analysis is developed in this study. The model integrates Euler–Bernoulli beam theory for the H-sections, a three-dimensional spring system to represent the stiffness of bolted connections, and the Green strain tensor to account for geometric nonlinearity. Validation against ABAQUS (2020) and ANSYS (2021 R1) shows high accuracy (average errors: 1.0% and 1.2%, respectively). Furthermore, a unified formula for the normalized slenderness ratio is derived via stepwise regression, which elegantly degenerates to the classical Euler solution under limiting conditions. The main conclusion is that this framework enables rapid and precise buckling analysis, reducing parametric study time by 95% compared to detailed finite element modeling. It establishes a bolt density coefficient threshold of η = 0.5 that separates composite from independent section behavior, with an optimal design range of η = 0.2 to 0.25, thereby offering a robust theoretical basis for PHSWC design. Full article

Despite tremendously valuable work on the T-stub, its safety and reliability in post-fire conditions remain a major concern. It is well known that steel is sensitive to high temperatures. Material degradation at high temperatures is likely to cause the T-stub to yield or gradually collapse, potentially leading to the failure of the entire structure. Recent studies have shown that steel joints exhibit a significant change in moment-rotational response post-fire, as the joint’s load–displacement behavior and failure modes change with increasing exposed temperature. However, studies on T-stubs at high post-fire temperatures are very limited. In this study, the aim is to investigate the post-fire load–displacement curves, ductility, plastic, and ultimate capacities of the unstiffened T-stub connected to a rigid base as a function of the exposed temperature. Of the 36 unstiffened T-stubs tested, 30 were subjected to high temperatures. The selected temperature values were 400 °C, 600 °C, 800 °C, 1000 °C, and 1200 °C. A thin plate of 10 mm was selected for the flange of the T-stub in order to obtain mode 1 behavior. Bolts of M16 and M24 were utilized in order to investigate the effects of bolt diameter on the behavior due to the change in distance of plastic hinges. Furthermore, the distances from a T-stub stem to bolt row (p_f) of 40 mm, 60 mm, and 80 mm were selected. As p_f values decrease, the plastic capacity increases, while the ultimate displacement capacity and the ductility decrease. A direct relation between p_f and yield displacement, and between pf and ultimate capacity, was not detected. As the applied temperature increases, the yield displacement increases and the ductility decreases. No significant change in either the plastic or ultimate capacity was observed up to 400 °C. At higher exposed temperatures, the plastic and ultimate capacity decrease as the applied elevated temperature increases. A significant reduction in the plastic and ultimate capacity was especially observed after post-fire exposure to 1000 °C and 1200 °C. The effects of elevated temperature are more pronounced for the plastic capacity of materials. Reduction factors for both plastic and ultimate capacities were proposed to account for the post-fire effects. The proposed reduction factors can predict the effects of a post-fire environment with high accuracy. The results were compared with AISC 358 and Eurocode 3, and it was revealed that the current standards underestimate the actual capacities. A modified calculation, including a reduction factor, is proposed to obtain more accurate results of unstiffened T-stubs for post-fire conditions. Full article

High-strength S690 steel is becoming increasingly popular in Hong Kong because of its numerous advantages in terms of mechanical properties and cost-effectiveness. Compared to normal-strength steel, the welding parameters such as preheat temperature, inter-pass temperature, and heat input energy of high-strength S690 steel should be controlled more strictly; additional post-weld heat treatment should be carried out for hydrogen diffusion in some situations. These strict requirements pose challenges to welding operations at construction sites. In Hong Kong, all field connections of high-strength S690 steel components are made using bolted connections, and there are currently no precedents for welded connections on site. To verify the reliability of on-site welding and optimize the welding process to facilitate operation, on-site welding tests of high-strength S690 steel with various welding procedures were conducted. These welding tests were first performed on the steel plates, followed by tests on the H-section steel components, to examine the mechanical reliability of the welding connections under tension and compression. The effects of heat input energy, welding joints, post-weld heat treatment, and wind blocking measures on welding quality and welding efficiency were studied. Full article

Fingerplate expansion joints are commonly used in bridges to accommodate large movements in bridge decks, often due to thermal expansion or contraction. Although these joints are designed to last the bridge’s lifetime, they have experienced premature degradation under high-volume vehicular loads. Damage to these joints can compromise structural integrity and endanger public safety. To address this, a series of experimental fatigue tests were conducted to simulate cyclic vehicular loading, with the goal of identifying the controlling failure modes and refining design practices for fingerplate expansion joints. The study involved constructing fingerplate joint specimens based on standard Missouri Department of Transportation (MoDOT) designs, incorporating three design variables: fingerplate thickness, flange stiffeners, and concrete embedment. Additionally, two optimized designs were developed and tested under both fatigue and static loading conditions. Two distinct failure types were observed in the specimens. Specimens with flange stiffeners experienced fatigue failure, characterized by crack propagation through the back weld of the fingerplate to the supporting beam. In contrast, specimens without flange stiffeners failed due to serviceability issues, as they could not sustain the required load before reaching the maximum allowable deformation, leading to buckling of the supporting beam’s top flange. The optimized designs showed no fatigue degradation and exhibited increased ultimate strengths compared to the standard MoDOT designs. Overall, a thicker fingerplate improved the stiffness and fatigue performance of the expansion joint, while bolted connections effectively eliminated the crack propagation fatigue failure observed in many specimens and in the field. Full article

Fire hazard presents a critical challenge to the structural reliability of underground modular infrastructure. This study examines the fire resistance performance of prefabricated monolithic utility tunnels featuring longitudinal threaded connections. A series of fire exposure tests was conducted on assembled utility tunnel specimens using different bolt materials and thermal conditions, enabling evaluation of fire behavior, deformation behavior, and residual capacity. The observed thermal properties revealed significant temperature gradients across tunnel sections, with the peak internal–external differential reaching 536.8 °C. Post-fire mechanical degradation was evident in reduced stiffness and ductility, and the residual load-bearing capacity declined by up to 12.28% compared to unexposed specimens. Specimens using high-strength threaded bolts demonstrated superior performance compared to stainless steel bolt specimens, exhibiting a 4.67% higher residual capacity and 13.87% less residual deformation. A sequential thermal–mechanical finite element model was developed and calibrated based on experimental results, offering a reliable simulation framework for investigating fire-induced damage and residual strength in modular utility tunnel systems. These findings provide a quantitative basis for fire safety assessment. 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

This research addresses the critical gap in accurately modelling pultruded fibre-reinforced polymer (FRP) beam-to-column joints, where previous studies largely ignored progressive damage mechanisms. A novel finite element framework is developed in ABAQUS, integrating Hashin’s failure criterion with fracture energy-based damage evolution to simulate delamination and brittle failure in FRP cleats. The model is rigorously validated against full-scale experimental data, achieving close agreement in moment–rotation response, initial stiffness (within 5%), and ultimate moment capacity (variation < 10%). Quantitative results confirm that delamination at the fillet radius governs failure, while qualitative analysis reveals the sensitivity of stiffness to cleat geometry and bolt characteristics. A parametric study demonstrates that increasing cleat thickness and bolt diameter enhances stiffness up to 15%, whereas bolt–hole clearance introduces slip without significantly affecting strength. The validated FEM reduces reliance on costly physical testing and provides a robust tool for optimising FRP joint design, supporting the future development of design guidelines for pultruded FRP structures. Full article

Modular barges are increasingly applied in inland and nearshore operations for their transportability and flexible assembly, yet the reliability of their connections remains insufficiently studied. This study presents a finite element analysis of a 15-ton-class modular barge in service, focusing on bolted and interlocking joints under still-water and wave-induced loads. A detailed three-dimensional model with explicit contacts was developed, and four load cases combined hydrostatic and deck loads with longitudinal and transverse crest/trough scenarios. Results showed that the highest stresses occurred in central stiffeners and lower interlocking joints, but all were below allowable limits, ensuring adequate safety margins. Bolted joints exhibited low stress, confirming their robustness and redundancy within the hybrid system. By analyzing an operating barge under realistic conditions, this study demonstrates the structural adequacy of the modular concept and provides a basis for future guidelines and larger modular floating platforms. Full article

Accurate identification of modal properties in a steel cantilever beam is crucial for enhancing numerical models and supporting structural health monitoring, particularly when numerical and experimental data are combined. This study investigates the modal system identification of a steel cantilever beam using finite element method (FEM) simulations, which are validated by experimental testing. The beam was bolted to a reinforced concrete block and subjected to dynamic testing, where natural frequencies and mode shapes were extracted through Frequency Domain Decomposition (FDD). The experimental outcomes were compared with FEM predictions from SAP2000, and discrepancies were analysed using the Modal Assurance Criterion (MAC). A model updating procedure was applied, refining boundary conditions and considering sensor mass effects, which improved model accuracy. The updated FEM achieved closer agreement with frequency deviations reduced to less than 4% and MAC values above 0.9 for the first three modes. Beyond validation, the research links the updated FEM results with a Building Information Modelling (BIM) framework to enable the development of a digital twin of the beam. A workflow was designed to connect vibration monitoring data with BIM, providing visualisation of structural performance through colour-coded alerts. The findings confirm the effectiveness of FEM updating in generating reliable modal representations and demonstrate the potential of BIM-based digital twins for advancing structural condition assessment, maintenance planning and decision-making in civil engineering practice. Full article

To investigate the initial rotational stiffness and ultimate moment of fully bolted connections in panelized steel modular structures, a finite element analysis was carried out on 20 joint models. High-fidelity models were developed using ABAQUS, and their accuracy was confirmed through comparison with experimental tests. A parametric study was performed to systematically evaluate the effects of the column wall thickness in the core zone, internal diaphragm configurations, angle steel thickness, and stiffener layouts on the joint stiffness and ultimate strength, leading to practical optimization suggestions. Additionally, a mechanical model and a corresponding formula for predicting the initial rotational stiffness of the joints were proposed based on the component method in Eurocode EC3. The model was validated against the finite element results, showing good reliability. Three failure modes were identified as follows: buckling deformation of the beam flange, buckling deformation of the column flange, and deformation of the joint panel zone. In joints with a weak core zone, both the use of internal diaphragms and increased column wall thickness effectively improved the initial rotational stiffness and ultimate bearing capacity. For joints with weak angle steel connections, adding stiffeners or increasing the limb thickness significantly enhanced both the stiffness and capacity. The diameter of bolts in the endplate-to-column flange connection was found to have a considerable effect on the initial rotational stiffness, but minimal impact on the ultimate strength. This study offers a theoretical foundation for the engineering application of panelized steel modular structural joints. Full article

Due to structural characteristics and connection dimensions, the dynamic characteristics of dual metal rubber clamps (DMRCs) show significant differences in bolt connection direction and opening direction. Accurately identifying the dynamic parameters of DMRC in different directions is of great significance for analyzing the dynamic characteristics and vibration control of aero-engine piping systems. This paper takes a DMRC-double straight pipe structure as the research object and establishes a dynamic model of this structure based on the finite element method as the mechanical parameter identification model of DMRCs. A refined simulation mechanism is adopted in the model to reflect the dynamic characteristics of the DMRC. The DMRC is simplified into four concentrated mass blocks and four spring-damping groups to simulate its mass, stiffness, and damping effects. Each spring-damping group consists of a linear spring, a rotational spring, and a damper. The four groups of springs are further divided into two directional groups to simulate the stiffness and damping effects in the opening direction and bolt connection direction, respectively. Four concentrated mass blocks are applied to the four nodes of the pipe to simulate the mass effect of DMRCs. Based on the dynamic model of the pipeline structure mentioned above, the synchronous identification algorithms and procedures for multiple mechanical parameters of DMRCs are proposed, aiming to minimize the deviation of natural characteristic indicators (natural frequency and peak of frequency response function) obtained through testing and model simulation. This method can synchronously identify linear stiffness, rotational stiffness, and damping in different directions. Finally, the effectiveness of the identification method is verified through experiments. 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

The structural integrity of transmission towers, as the backbone of power grids, is critical to overall grid safety, relying heavily on the reliability of bolted connections. Dynamic loads such as wind-induced vibrations can cause bolt loosening, potentially leading to structural deformation, cascading failures, and large-scale blackouts. Traditional manual inspection methods are inefficient, subjective, and hazardous. Existing automated approaches are often limited by environmental noise sensitivity, high computational complexity, sensor placement dependency, or the need for extensive labeled data. To address these challenges, this paper proposes a portable acoustic detection system based on Variational Mode Decomposition (VMD) and an Adversarial Multilayer Perceptual Network (AT-MLP). The VMD method effectively processes non-stationary and nonlinear acoustic signals to suppress noise and extract robust time–frequency features. The AT-MLP model then performs state identification, incorporating adversarial training to mitigate distribution discrepancies between training and testing data, thereby significantly improving generalization and noise robustness. Comparison results and analysis demonstrate that the proposed VMD and AT-MLP framework effectively mitigates structural variability and environmental interference, providing a reliable solution for bolt loosening detection. The proposed method bridges structural mechanics, acoustic signal processing, and lightweight intelligence, offering a scalable solution for condition assessment and risk-aware maintenance of transmission towers. Full article