Search Results (320)

The study proposes and investigates a seismic retrofitting strategy based on an external reinforced concrete exoskeleton, grounded in the analysis of the actual force transfer mechanisms between the existing structure and the added system. The three-dimensional numerical model was developed in ETABS, employing linear response spectrum analysis in accordance with EN 1998-1 and P100-1/2013. The internal forces transmitted at the structural interface were determined using the Section Cut method, enabling the identification of integrated resultants and the prioritization of critical connections. Three types of connections are examined—slab-to-slab, column-to-wall, and beam-to-joint—while the distribution of stresses within the anchor groups is assessed based on an elastic model under combined axial force and bending action. The results indicate that the global structural response is governed by diaphragm coupling, whereas the vertical interfaces ensure kinematic compatibility and the redistribution of axial and bending effects. The proposed methodology provides a coherent framework for the rational design of interface connections in retrofit interventions carried out without interrupting building operation. Full article

The construction of single-story industrial halls in high-seismicity regions requires reliable beam-to-column connections to ensure adequate structural stiffness and strength. This paper investigates the emulative performance of a rigid precast beam–column connection utilizing threaded couplers and grouted corrugated steel sleeves. An experimental pro-gram was conducted on five scaled specimens—one monolithic reference and four pre-cast—subjected to quasi-static cyclic loading. The objective was to verify if the precast system achieved emulative behavior. Experimental results confirm this goal was fully achieved: the precast specimen exhibited a maximum recorded force nearly identical to the value recorded for the monolithic reference. Furthermore, the total dissipated energy for the precast joint had only a marginal 2.6% difference from the monolithic reference. Results demonstrate that the proposed solution provides emulative behavior consistent with monolithic casting. Specifically, the specimens achieved plastic deformation capacities exceeding 3%, surpassing current seismic design code requirements. While smaller diameter rebars (D14) experienced tensile failure at approximately 3% to 4% drift due to strain localization, specimen with larger D25 bars reached 4% drift without major damage. This paper concludes that the connection is suitable for seismic applications provided large diameter rebars (≥20 mm) are used. Full article

The seismic retrofit of existing reinforced concrete (RC) buildings equipped with dissipative bracing systems requires not only a global performance-based assessment, but also a rigorous verification of the local behavior of critical structural connections. In this context, the present study focuses on the numerical seismic performance of a beam–column connection extracted from a retrofitted RC hospital building located in Italy. The investigated joint represents a central node where two orthogonal steel bracing systems converge and transfer seismic forces to an RC column strengthened with heavy steel jacketing and anchorage devices. A detailed three-dimensional finite element model of the connection is developed using solid elements for concrete and steel components, explicit modeling of reinforcement bars, bolts, and anchor rods, and advanced nonlinear constitutive laws for both materials. Two modeling strategies are considered, including the explicit simulation of contact interfaces between steel components, in order to capture local stress redistribution and potential interaction effects. The connection is subject to seismic demand derived from the global structural analysis, corresponding to different values of the behavior factor, thus ensuring consistency between global design assumptions and local verification. The results highlight the progressive activation of nonlinear mechanisms within the steel components, the development of cracking and compression damage in the concrete core, and the preservation of a clear hierarchy of resistances under design-level seismic actions. The numerical outcomes allow a critical discussion on the role of local connection behavior in supporting the global dissipative strategy and provide quantitative insights into the evaluation of the behavior factor from a local-response perspective. The study emphasizes the importance of detailed connection-level analyses in the seismic retrofit of strategic facilities and supports a more consistent integration between global performance objectives and local structural design. Full article

Concrete building systems require decisions at both the member and the building level, because locally efficient cross sections do not necessarily lead to a favorable whole-building response. This study presents a two-level comparative framework comprising (i) a member-level parametric assessment of nine reinforced-concrete and composite cross-section families across six concrete grades (54 scenarios) and (ii) a building-level ETABS assessment of seven structural configurations (Models A–G) derived from a residential reinforced-concrete frame benchmark. At the member level, the alternatives were evaluated based on axial resistance, along with simplified screening-level CO₂ and cost proxies. At the member level, axial resistance increased with concrete grade, although the marginal benefit diminished at higher grades for steel-dominant layouts. Balanced composite sections showed the most favorable normalized strength-to-material-proxy trends, whereas steel-heavy alternatives provided high absolute resistance but lower overall efficiency. The comparison between the member-level hybrid-section screening and the building-level composite configuration further showed that promising local section behavior does not automatically translate into superior whole-building performance. At the building level, the compared configurations were assessed through vertical base reactions, modal properties, and top-level lateral displacement response. Replacing solid beams and columns with hollow members of identical outer dimensions reduced the self-weight-related base reaction from 9591 to 8832 kN (7.9%) but slightly increased the top-level displacement response, indicating a mass–stiffness trade-off. Larger improvements were obtained when the global lateral-force-resisting mechanism was modified directly: the braced configuration produced the shortest fundamental period ($T_1=0.433$ s) and the lowest displacement response, while the core-wall configuration also reduced both period and displacement substantially. By contrast, the height-extended configuration produced the most flexible response among Models A–F. An additional exploratory variant with semi-rigid beam-to-column connections (Model G) confirmed that connection-level flexibility produces a measurable but moderate increase in period and displacement relative to the reference frame, without altering the global load-resisting mechanism. Overall, the results confirm that member-level and building-level assessments should be treated as complementary decision levels in early-stage structural design. Full article

Steel–concrete composite components exhibit significant advantages, including reliable mechanical performance, rapid construction, cost efficiency, and low environmental impact. Existing studies on their seismic behavior have mainly focused on developing novel connection forms and enhancing joint zone strength, while systematic investigations into the post-earthquake axial compression behavior and failure mechanisms of composite joints remain limited. To address this gap, this study investigates the mechanical performance of steel–concrete composite components under strong seismic and post-earthquake conditions. Seismic damage characteristics are first analyzed based on representative case studies of conventional steel–concrete columns. Subsequently, low-cycle reversed loading tests followed by post-earthquake axial compression tests are conducted on seven beam–column joints with varying damage levels, and the damage evolution and seismic performance of joint zones under different structural configurations are systematically evaluated. In addition, the seismic performance of steel–concrete composite shear walls is further validated. The results provide a scientific basis for the seismic design, post-earthquake assessment, and repair of steel–concrete composite structures. Full article

This study proposes a design method for a novel bolted endplate rigid connection between circular concrete-filled steel tube (CCFT) columns and wide-flange (WF) steel beams, with particular emphasis on the parametric behavior governing joint performance. Based on the preliminary quasi-static tests, finite element simulations are conducted to evaluate the flexural behavior and failure mechanisms under beam-end maximum moment, followed by an extensive parametric study examining the effects of square tube dimensions, high-strength grout, and column axial load. The numerical results show that the wall thickness of the square steel tube significantly affects grout indentation. A 60% reduction in wall thickness led to a 503% increase in indentation. In contrast, variations in tube dimensions, grout strength, and column axial load within the studied range caused less than a 16% change and did not influence the flexural performance. These results indicate that the constraints on tube dimensions and axial load may be relaxed. The proposed connection effectively overcomes the limitations of conventional CCFT-to-beam joints, including unfavorable stress transfer, complex detailing, and construction inefficiency, by modifying the load-transfer mechanism and reducing the demand on tensile-critical welds, thereby enhancing ductility. Based on the parametric findings, a design method is established, and theoretical analysis confirms that the proposed connection satisfies the stiffness requirements for fully rigid connections. Future quasi-static tests with different member sizes are recommended to validate these findings. Full article

This study investigates the influence of out-of-plane beam skew on the cyclic performance of column-tree steel moment connections. Utilizing validated finite element (FE) models against experimental data, the cyclic responses of various configurations were evaluated under the AISC cyclic loading protocol up to a story drift ratio of 0.05 rad. Skew angles of 0°, 10°, 20°, and 30° were examined across three representative beam depths. The results demonstrate that all configurations satisfy the AISC 341 acceptance criteria for Special Moment Frames (SMFs), maintaining at least 80% of the plastic moment capacity (0.8 M_p) up to a 0.04 rad story drift ratio. However, the introduction of beam skew resulted in a gradual reduction in energy dissipation capacity, with the total dissipated energy decreasing by 2.9–8.9% at a 30° skew. Notably, the inelastic energy component was more sensitive to the skew than the frictional components, exhibiting a maximum reduction of 15.4%. While out-of-plane skew disrupted the symmetry of stress triaxiality and plastic strain at the beam-to-column interface, the overall fracture susceptibility was not significantly exacerbated up to 30°. Furthermore, column twisting remained within a negligible range (below 0.5°), and its impact on global stability was limited. Despite the general stability, a premature bolted splice failure was observed in deep beam configurations at a 30° skew during the 0.05 rad drift cycles. Based on these findings, it is concluded that column-tree connections with an out-of-plane skew up to 30° are viable; however, a design limit of 20° is recommended for deep beam configurations to ensure structural integrity under extreme cyclic demands. Full article

Precast reinforced concrete (RC) structures offer advantages in terms of construction efficiency and quality control; however, their seismic performance is governed by the behavior of the beam–column connections. This study presents an experimental investigation of the cyclic response of precast RC beam–column joints that include a composite steel connection, designed to enhance strength, stiffness, and damage control in critical regions. A composite joint specimen was tested under displacement-controlled cyclic loading, and its behavior was compared with that of a corresponding pure RC connection. Experimental results showed that the composite configuration effectively prevented premature failure at the beam–column interface, relocated plastic hinges away from the joint core, and significantly improved the load-carrying capacity, stiffness, and energy dissipation. To interpret the experimental observations and examine the internal stress transfer and evolution of damage, a three-dimensional nonlinear finite-element model was developed. The simulations reproduced the observed modes of failure, shapes of deformation, hysteretic responses, and moment distribution trends, particularly in the post-yield and strain-hardening ranges. Although the pinching effects observed experimentally were not fully captured numerically, the overall levels of agreement in the ultimate strength and plastic hinge locations were satisfactory. The combined results indicate that composite steel-reinforced precast beam–column joints represent a promising solution for improving seismic performance. Full article

This paper proposes a novel prefabricated beam-to-column joint to increase the seismic performance and post-earthquake recoverability of steel frames, which use the shape memory alloy (SMA) bolts and replaceable steel ring dampers. The comparative analysis of the seismic behavior was conducted for three beam-to-column connection types using finite element models. The three connection types include those installed using internal SMA bolts, external SMA bolts, and external SMA bolts with novel ring dampers. In addition, the novel ring damper was analyzed separately. These analysis results indicate that the connection type installed using external SMA bolts is superior to that by internal SMA bolts for the seismic performance of beam-to-column joints. The beam-to-column joints have the best seismic performance among the three joints when equipped with the additional steel ring damper, which can be easily replaced. This ring damper can increase the energy dissipation by approximately 11% and effectively reduce the stress of SMA bolts, which can delay their failure. The increasing preload of SMA bolts and high-strength bolts has a certain positive effect on the improvement of the seismic performance. All of the three joints exhibit excellent self-centering characteristics, with residual displacements nearly at zero. The gap of replaceable ring dampers can keep the re-centering capacity and improve the energy dissipation of joints. However, the changes in the steel strength of dampers have little impact on the seismic performance. This study verifies the improvement of the replaceable ring dampers on the seismic performance and post-earthquake recoverability, providing a reference for the seismic design of resilient structures. Full article

Beam-to-column connections govern both seismic performance and post-earthquake repairability of steel moment-resisting frames. Yet direct, apples-to-apples comparisons among welded, bolted, and repair-oriented replaceable-fuse moment connections are still scarce, which hinders rational selection for resilient construction. This study conducts a unified finite-element comparison of three representative joint archetypes—W-RBS, Bolted, and Prefab-web-fuse—under monotonic and cyclic loading. Consistent moment-rotation definitions are adopted, and normalized indices are introduced to compare hysteresis shape, degradation, and energy dissipation across joint concepts with different strength scales. Component-wise plastic dissipation is also extracted to quantify damage localization and assess main-frame protection and replaceability. Results reveal clear trade-offs: W-RBS provides the highest strength and dissipation but degrades most in stiffness; the bolted joint shows pinching due to interface compliance; and the web-fuse concept concentrates inelastic demand in a replaceable segment, supporting repairability-oriented design. The proposed framework offers mechanism-based guidance for selecting steel moment connections toward resilient and repairable frames. Full article

In the modular construction of liquefied natural gas (LNG) plants and receiving terminals, transport beams are critical components that enable modular mobility. However, these beams are susceptible to large deformations due to complex loads during land and sea transportation. Traditional monitoring methods (i.e., strain gauge and deflection meters) often suffer from low efficiency and poor accuracy and may disrupt operational continuity in real-time monitoring systems. This paper presents a non-contact, real-time deformation detection system for LNG modular transport beams based on digital image technology, which integrates a high-resolution camera with a real-time software framework to remotely monitor structural integrity. An experiment was conducted on a full-scale support column-transport beam frame with specialized connection joints designed for rapid assembly. Five digital image correlation (DIC) detection regions (5 cm × 5 cm) were established on box-shaped beam sleeves, column sleeves, and the end plates of the beam–column joints. In addition, displacement gauges were installed at the same DIC locations. The experimental results demonstrate that the DIC measurements show good agreement with traditional measurement methods, verifying the applicability of the proposed system for large-scale LNG engineering structures. Full article

Progressive collapse is characterized by disproportionate structural failure triggered by localized damage, such as column loss under extreme loading conditions. The objective of this study is to develop a simplified analytical model that is applicable in engineering practice without the need for high-fidelity nonlinear finite element analysis. Although current design guidelines (GSA and DoD) provide analytical procedures and acceptance criteria, they do not explicitly address the tensile resistance of girders after the acceptance criteria are satisfied, particularly under large deformation and connection failure. To address this limitation, this study proposes a simplified theoretical load–displacement model for a fixed-end girder subjected to three concentrated loads, considering the effects of secondary beams and focusing on the local girder response under a column-removal scenario. The proposed model incorporates moment–axial force interactions at plastic sections in the large-deformation range. Based on one-dimensional finite element analysis results, an early-developed axial force of 0.15F_p at the onset of the transition stage and a residual bending moment of 0.3M_p during the catenary action stage are explicitly introduced to better represent actual structural behavior. The girder response is idealized using five characteristic points: yielding (Y), full plasticity (P), transition initiation (T), pure catenary action initiation (C), and collapse governed by connection failure (F_conn). Stress distributions at plastic sections are analyzed using three-dimensional finite element models to establish stress-based formulations and a rational procedure for estimating axial force at collapse. The validity of the proposed model is verified through comparisons with finite element analysis results for girders with different span-to-depth ratios. The results demonstrate reasonable agreement in terms of collapse load and displacement, particularly for slender girders, confirming the applicability of the proposed model for progressive collapse assessment. Full article

Wind turbines are subjected to complex stochastic loadings generated by various environmental sources, including wind, waves, and earthquakes. Efficient mitigation of the resulting vibrations in the structural components, such as the tower and monopile, leads to more cost-effective designs and longer operational life by reducing fatigue accumulation. Conventional vibration control systems have primarily relied on tuned mass dampers. However, alternative and non-conflicting strategies that modify the connection between the tower and the foundation at the transition piece level have recently gained attention. This study investigates the hourglass transition piece (HGTP), a novel concept that utilises the Reduced Column Section approach. The hourglass geometry enables fine-tuning of the wind turbine’s fundamental period and introduces controlled rotational motion, both contributing to a reduction in structural stresses and improved dynamic performance. To assess the efficacy of the HGTP as a vibration control system, an analytical model of a simplified wind turbine is developed. The formulation employs frequency-dependent solutions of prismatic and tapered beam elements, assembled to capture the dynamic behaviour of the turbine equipped with the HGTP. Exact dynamic stiffness matrices are derived and assembled into a stochastic framework suitable for uniformly modulated non-stationary random processes. Modal and dynamic responses are evaluated for different reductions of the hourglass central section. A case study based on the IEA 15 MW Reference Wind Turbine demonstrates that the HGTP can mitigate stochastic mean peak bending moments induced by wind and earthquake excitations by up to 50%, confirming its potential as an effective vibration control solution. Full article

The study of the mechanical response and crack propagation behaviour of H-shaped beam-column specimens is of great significance for ensuring the safety and stability of buildings. As a connection structure that has gained ubiquity in modern shopping malls and high-rise buildings, an in-depth exploration of the failure mechanisms of H-shaped beam-column components will facilitate more accurate technical support for building maintenance and service life prediction. The present study employs a combination of drop-weight impact tests and the caustic method to systematically investigate the dynamic fracture characteristics of H-shaped beam-column joints under various prefabricated crack configurations. The results demonstrate that the number and location of cracks in H-shaped beam-column specimens have a significant impact on the propagation path and velocity. Specifically, beam-end cracks are prone to bifurcation, while column-end cracks predominantly initiate from the beam-column intersection. This phenomenon is particularly evident in specimens with prefabricated cracks at both the beam ends and column ends. The propagation of cracks at the beam ends is arrested due to the presence of compressive stress when they reach the beam-column intersection. During this period, the stress intensity of the column-end cracks increases significantly, with a growth rate of 33%. Full article

To address complex connections in prefabricated concrete structures, a novel joint connecting a prefabricated concrete-filled steel tubular column and a composite beam is proposed. Pseudo-static tests on six scaled specimens and ABAQUS finite element analyses were conducted to investigate seismic mechanisms, focusing on slab effects and beam-bottom configurations. Experimental results show the joints exhibit plump hysteretic curves. The composite beams displayed distinct shear-dominated failure, while the stiffened column remained intact. With an average ductility coefficient of 2.84 and an ultimate equivalent viscous damping coefficient of 0.207, the specimens demonstrated excellent deformation and energy dissipation capabilities. The slab’s flange effect significantly enhanced negative bearing capacity, causing mechanical asymmetry. Comparatively, the steel plate beam bottom configuration offered superior stiffness and stability over the reinforcement beam bottom configuration. Sensitivity analysis revealed that bearing capacity is highly sensitive to beam parameters (e.g., longitudinal rebar strength, connector length) but less sensitive to column parameters. Notably, the bearing capacity of the beam bottom configuration using reinforcement increases significantly with concrete strength and reinforcement ratio, whereas the beam bottom configuration using a steel plate shows marked insensitivity to these factors. These findings clarify the load transfer mechanism and support the seismic design of prefabricated structures. Full article