Search Results (470)

Preventing progressive collapse induced by accidental events poses a critical challenge in the design and construction of resilient structures. While substantial progress has been made in planar structures, the progressive collapse mechanisms of precast concrete spatial structures—particularly regarding the effects of precast slabs—remain inadequately explored. This study develops a refined finite element modeling approach to investigate progressive collapse mechanisms in fully bonded prestressed precast concrete (FB-PPC) spatial frames, both with and without precast slabs. The modeling approach was validated against available test data from related sub-assemblies, and applied to assess the collapse performance. A series of pushdown analyses were conducted on the spatial frames under various column removal scenarios. The load–displacement curves, slab contribution, and failure modes under different conditions were compared and analyzed. A simplified energy-based dynamic assessment was additionally employed to offer a rapid estimation of the dynamic collapse capacity. The results show that when interior or side columns fail, the progressive collapse process can be divided into the beam action stage and the catenary action (CA) stage. During the beam action stage, the compressive membrane action (CMA) of the slabs and the compressive arch action (CAA) of the beams work in coordination. Additionally, the tensile membrane action (TMA) of the slabs strengthens the CA in the beams. When the corner columns fail, the collapse stages comprise the beam action stage followed by the collapse stage. Due to insufficient lateral restraints around the failed column, the development of CA is limited. The membrane action of the slabs cannot be fully mobilized. The contribution of the slabs is significant, as it can substantially enhance the vertical resistance and restrain the lateral displacement of the columns. The energy-based dynamic assessment further reveals that FB-PPC spatial frames exhibit high ductility and residual strength following sudden column removal, with dynamic load–displacement curves showing sustained plateaus or gentle slopes across all scenarios. The inclusion of precast slabs consistently enhances both the peak load capacity and the residual resistance in dynamic collapse curves. Full article

RC piers in mountainous coastal or saline areas face the dual threats of rockfall impacts and chloride-induced steel corrosion, but their combined effects on dynamic response and residual bearing capacity remain unquantified. This study aims to investigate these combined effects over a 90-year service time and propose a damage assessment formula. A validated numerical model (relative error ≤14.7%) of corroded RC columns under impact is developed using ABAQUS, based on which the dynamic response and residual bearing capacity of an actual RC pier subjected to rockfall impacts during the service time of 90 years incorporating corrosion initiation (via Life-365 software 2.2) and propagation are analyzed, with the consideration of various impact energies (1–5 t mass, 5–15 m/s velocity). Results show that (1) increasing impact mass/velocity expands damage and increases displacement (e.g., the velocity of increases peak displacement by 33.41 mm in comparison to 5 m/s); (2) a 90-year service time leads to >50% severe surface damage and 47.1% residual capacity loss; and (3) the proposed and validated damage formula assessment formula for the residual bearing capacity enables lifecycle maintenance guidance. This work provides a validated framework for assessing combined corrosion-rockfall effects, aiding design and maintenance of structures. Full article

This study investigates the robustness of steel moment-resisting frames (MRFs) under column loss scenarios, both in undamaged and post-seismic conditions. In this context, robustness is defined as the ability of a damaged structure to prevent progressive collapse following an earthquake. A parametric investigation was conducted on 48 three-dimensional MRF configurations, varying key design and geometric parameters such as the number of storeys, span length, and design load combinations. Nonlinear dynamic analyses were performed using realistic ground motions and column loss scenarios defined by UFC guidelines. The effects of pre-existing seismic damage, façade claddings, and joint typologies were explicitly accounted for using validated component-based modelling approaches. The results indicate that long-span, low-rise frames are more vulnerable to collapse initiation due to higher plastic demands, while higher-rise frames benefit from load redistribution through their increased redundancy. In detail, long-span, low-rise frames experience roughly ten times higher displacement demands than their short-span counterparts, and post-seismic damage has limited influence, yielding rotational demands within 5–10% of the undamaged case. The Reserve Displacement Ductility (RDR) ranges from approximately 6.3 for low-rise, long-span frames to 21.5 for high-rise frames, highlighting the significant role of geometry in post-seismic robustness. The post-seismic damage was found to have a limited influence on the dynamic displacement and rotational demands, suggesting that the robustness of steel MRFs after a moderate earthquake is largely comparable to that of the initially undamaged structure. These findings support the development of more accurate design and retrofit provisions for seismic and multi-hazard scenarios. Full article

To address the issue of structural tilting caused by uneven foundation settlement in soft soil areas, this study combined a specific engineering case to conduct numerical simulations of the rectification process for an inclined reinforced concrete building using ABAQUS finite element software. Micropile-raft combined jacking technology was employed, applying staged jacking forces (2400 kN for Axis A, 2200 kN for Axis B, and 1700 kN for Axis C) with precise control through 20 incremental steps. The results demonstrate that this technology effectively halted structural tilting, reducing the maximum inclination rate from 0.51% to 0.05%, significantly below the standard limit. Post-rectification, the peak structural stress decreased by 42%, and displacements were markedly reduced. However, the jacking process led to a notable increase in the column axial forces and directional changes in beam bending moments, reflecting the dynamic redistribution of internal forces. The study confirms that micropile-raft combined jacking technology offers both controllability and safety, while optimized counterforce pile layouts enhance the long-term stability of the rectification system. Based on stress and displacement cloud analysis, a monitoring scheme is proposed, forming an integrated “rectification-monitoring-reinforcement” solution, which provides a technical framework for building rectification in soft soil regions. Full article

Rock slopes exhibiting anti-inclined interbedded strata have widespread distribution and complex deformation mechanisms. In this study, we used a physical model test with basal friction to replicate the evolution process of the slope deformation. Digital Image Correlation (DIC) and Particle Image Velocimetry (PIV) methods were used to capture the variation in slope velocity and displacement fields. The results show that the slope deformation is conducted by bending of soft rock layers and accumulated overturning of hard blocks along numerous cross joints. As the faces of the rock columns come back into contact, the motion of the slope can progressively stabilize. Destruction of the toe blocks triggers the formation of the landslides within the toppling zone. The toppling fracture zones form by tracing tensile fractures within soft rocks and cross joints within hard rocks, ultimately transforming into a failure surface which is located above the hinge surface of the toppling motion. The evolution of the slope deformation mainly undergoes four stages: the initial shearing, the free rotation, the creep, and the progressive failure stages. Full article

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

The use of both structural steel and reinforced concrete is common in civil and military infrastructure projects. Anchorage plays a crucial role in these systems, serving as the key element that connects structural components and secures attachments within complex composite structures. This research focuses on evaluating the performance of steel–concrete column connections under the combined effects of lateral loading and fire exposure. Additionally, the study investigates the use of carbon fiber-reinforced polymers (CFRP) for strengthening and repairing these connections. The research methodology combines experimental testing and finite-element modeling to achieve its objectives. First, experimental investigation was carried out to test two groups of steel-reinforced concrete column specimens, each group made of three specimens. The first group specimens were designed based on special moment frame (SMF) detailing, and the other group specimens were designed based on intermediate moment frame (IMF) detailing. These two types of design were selected based on seismic demands, with SMFs offering high ductility and resilience for severe earthquakes and IMFs providing a cost-effective solution for moderate seismic zones, both benefiting from ongoing innovations in connection detailing and design approaches. Then, finite-element analysis was conducted to model the test specimens. High-fidelity finite-element modeling was conducted using ANSYS program, which included three-dimensional coupled thermal-stress analyses for the six tested specimens and incorporated nonlinear temperature-dependent materials characteristics of each component and the interfaces. Both the experimental and numerical results of this study show that fire has a more noticeable effect on displacement compared to the peak capacities of both types of specimens. Fire exposure results in a larger reduction in the initial residual lateral stiffness of the SMF specimens when compared to IMF specimens. While the effect of CFRP wraps on initial residual lateral stiffness was consistent for all specimens, it caused more improvement for the IMF specimen in terms of post-fire ductility when compared to SMF specimens. This exploratory study confirms the need for further research on the effect of fire on the concrete–steel anchorage zones. Full article

This study established a numerical model for a foundation pit at the Zhongyilu Station of the Wuhan Metro Line 12, using Plaxis3D version 2021 finite element software to examine the horizontal displacement of the diaphragm wall, ground surface settlement, and differential settlement between the diaphragm wall and the lattice columns across various construction stages. A comparison with the cut-and-cover method prompted the adoption of a strategy that integrates segmental pouring of the main structure and the installation of internal supports to optimize the original scheme. The results indicated that as the foundation pit was excavated, both the horizontal displacement of diaphragm wall and the ground surface settlement gradually increased, while the differential settlement between the diaphragm wall and the lattice columns shows exhibited an initial decrease followed by an increase. In comparison to the cut-and-cover method, the cover-and-cut method demonstrated greater efficacy in controlling foundation pit deformation and minimizing disturbances to surrounding environment. As the number of segmental pouring layers and support levels increased, the overall deformation of the foundation pit showed a gradual decreasing trend, and the differential settlement between the diaphragm wall and the lattice columns continued to fluctuate. When each floor slab was poured in three layers with two supports placed in the middle, the maximum horizontal displacement of the diaphragm wall could be reduced by 22.47%, and the maximum ground surface settlement could be decreased by 19.01%. The findings in this research can provide valuable basis and reference for the design and construction of similar projects. Full article

Flat slab structures are extensively utilized in modern construction owing to their efficient load transfer mechanisms and optimized space utilization. Nevertheless, the persistent issue of brittle punching shear failure at connection zones continues to pose significant engineering challenges. This study proposes an innovative cross-shaped steel-reinforced concrete (SRC) column–slab connection. Through combining test and numerical analyses, the failure mechanisms and performance control principles are systematically analyzed. A refined finite element model incorporating material nonlinearity, geometric characteristics, and interface effects is developed, demonstrating less than 3% error upon test validation. Using the validated model, the influence of key parameters—including concrete strength (C30–C60), reinforcement ratio (ρ = 0.65–1.77%), shear span–depth ratio (λ = 3–6), and limb height-to-thickness ratio (c₁/c₂ = 2–4)—on the punching shear behavior is thoroughly investigated. The results demonstrate that increasing concrete strength synergistically improves both punching shear capacity (by up to 49%) and ductility (by 33%). A critical reinforcement ratio threshold (0.8–1.2%) is identified. When exceeding this range, the punching shear capacity increases by 12%, but reduces ductility by 34%. Additionally, adjusting the shear span–depth ratio enables controlled failure mode transitions and a 24% reduction in punching shear capacity, as well as a 133% increase in displacement capacity. These results offer theoretical support for the design and promotion of this novel structural system. Full article

The present research aims to the evaluation of the deformation capacity of existing reinforced concrete shear walls designed with past non-conforming seismic regulations. A refined analytical model (referred to as the Proposed Model) is presented for generating Load–displacement (P-d) curves for RC shear walls. The model is applicable to medium-rise walls designed with or without modern seismic provisions and incorporates shear effects in both deformation and strength capacity. The application of the Proposed Model is assessed through comparison with numerical models implemented in the widely accepted OpenSees platform. Specifically, two types of elements are examined: the widely used flexural element Force-Based Beam-Column Element (FBE) and the Flexure-Shear Interaction Displacement-Based Beam-Column Element (FSI), which accounts for the interaction between flexure and shear. The results of both analytical and numerical approaches are compared with experimental data from four RC shear wall specimens reported in previous studies. Full article

Understanding the structural behaviour of flat plate systems during fire exposure is critical for ensuring the safety of occupants and emergency personnel. Flat slabs, a widely used structural system, undergo significant thermal deformations in fire, which increase demands on supporting columns and reduce the stiffness and strength of concrete and steel. While experimental fire tests have provided valuable data to understand the behaviour of isolated components of flat slabs, numerical analysis is the only route to comprehending the structural behaviour of full-scale flat plate structures during fire exposure. ABAQUS is commonly used for modelling reinforced concrete (RC) structures under fire, with two prevailing techniques: (1) solid element modelling for concrete and truss reinforcement and (2) shell element modelling with embedded steel layers and line-column elements. However, uncertainties remain regarding the influence of modelling parameters such as dilation angle and concrete tensile stress, and the impact of surface fire exposure has not been comprehensively studied. This study presents a novel contribution by conducting a detailed numerical investigation of a full-scale flat plate structure exposed to fire using both modelling approaches. The shell-element model was validated against experimental data and used to evaluate the effect of dilation angle and tensile strength assumptions. A unique aspect of this work is the assessment of fire exposure on different slab surfaces, including bottom, top, and both, which provides insights into slab deflections and column displacements under different surface fire exposure scenarios. The structure was then modelled using solid elements to systematically compare modelling techniques. The results highlight key differences between approaches and guide for selecting the most suitable modelling strategies for fire-exposed flat plate systems. Full article

This research explores how RC columns respond to blast-induced dynamic effects, with a novel focus on partially submerged scenarios, bridging a gap between air blast and underwater explosion (UNDEX) research. Using advanced finite element modeling in LS-DYNA, the study captures the unique behavior of RC columns under mixed-media conditions, where shockwaves propagate through water and air interfaces. Comprehensive parametric analyses explore the influence of charge size, blast stand-off, and depth of water, revealing distinct dampening mechanisms and structural responses. Key findings include a measurable reduction in peak displacement of partially submerged explosions compared to fully submerged explosions, attributed to the moderating effects of the water–air interface. A total of 60 simulation cases were conducted to systematically analyze partially submerged scenarios, providing robust insights into energy transmission and damage mechanisms. The numerical models, validated against published experimental data by others, demonstrate the accuracy of computational modeling in simulating damage profiles, displacement histories, and energy dissipation trends. This research offers practical implications for designing resilient RC structures in coastal and maritime environments. The results contribute significantly to the field of blast mechanics, advancing our understanding of mixed-media shockwave dynamics and their impact on critical infrastructure. Full article

Single-column hybrid-reinforced self-centering segmental assembled bridges (SHR-SCSAB) exhibit vertical stiffness discontinuities, significantly impacting the refinement of their seismic design methodology. In this study, we investigate SHR-SCSAB by employing the finite strip method to calculate the maximum transverse bearing capability of segmental assembled piers, and the corresponding horizontal displacement at the pier top. By leveraging the mechanical properties of hybrid reinforcement materials, we further derive an analytical expression for the equivalent elastic stiffness of SHR-SCSAB as an integrated system. OpenSees software was used to establish a finite element model of the SHR-SCSAB, and the agreement between numerical simulations and analytical solutions validates the accuracy of the derived equivalent elastic stiffness expression. Additionally, this study evaluates the seismic performance of single-column SHR-SCSAB and examines the influence of key parameters on its behavior. The results demonstrate that hybrid reinforcement effectively addresses the low energy dissipation capacity inherent in self-centering bridges while preserving their advantage of minimal residual displacement. These findings significantly advance the refinement of seismic design methods for SHR-SCSAB. Full article

Reinforced concrete columns constructed prior to the 1970s often exhibit deficient lap splices at the base, characterized by insufficient splice lengths. In response to the urgent need for an efficient seismic assessment of these vulnerable structural elements, this study proposed a modelling method for lap-spliced columns. Typically, numerical simulations of columns with lap splices require the cross-sections of the lap-spliced and non-lap-spliced zones to be established, a process that is complex and time-consuming. This paper proposes an equivalent distribution of curvature along the height of the column to represent the effect of lap splice defects on the mechanical behavior of columns, thereby reducing the modelling complexity of such components. Four large-scale column specimens with varying lap splice lengths were subjected to monotonic pushover loading to investigate the effect of splice length on failure modes, strain distribution, and displacement ductility. An active strengthening method was employed to improve the performance of columns with deficient lap splices. Applying lateral prestress to the strengthening devices improves the mechanical behavior of columns. The experimental results revealed that insufficient splice lengths lead to reduced ductility and stress-transfer capacity. The strengthened specimen demonstrated significantly improved ductility and enhanced stress-transfer efficiency, indicating a marked improvement in mechanical performance. The proposed equivalent plastic hinge model was established in OpenSees. A database was created to verify the accuracy of the model. The results showed the modelling method to be accurate. Full article

The increasing demand for sustainable and resilient construction solutions calls for the integration of innovative, non-conventional materials in structural retrofitting. This study investigates the use of basalt fiber-based engineered geopolymer composites (BFEGC) as a retrofitting material for fire-damaged reinforced concrete (RC) short columns. A total of 14 columns (150 mm × 150 mm × 650 mm) were cast. Two columns were used as control specimens. The remaining 12 columns were exposed to various fire conditions: 300 °C for 30 min, 600 °C for 20 min, and 900 °C for 15 min, followed by gradual (GC) or rapid cooling (RC). Among the columns, six were left unwrapped (GC-NW, RC-NW), while six others were retrofitted with BFEGC (GC-W, RC-W) and subjected to axial loading until failure. The results showed that BFEGC wrapping improved the mechanical performance of fire-damaged columns, especially at 600 °C. The 600RC-W columns exhibited 1.85 times higher ultimate load, 1.56 times greater displacement ductility, and 2.99 times higher energy ductility compared to unwrapped columns. The strength index and confinement coefficient of the 600RC-W columns increased by 2.31 times and 40.2%, respectively. Microstructural analysis confirmed the formation of salient hydration products under elevated temperatures. BFEGC shows significant reduction in carbon emissions and embodied energy, compared to conventional cement-based binders for fiber-reinforced polymer systems. Full article