Study on retrofit techniques for ductile RC beams with severely damaged plastic hinge zones

The vulnerability of reinforced concrete buildings in Indonesia-especially in seismic regions like Padang-has been worsened by poor detailing and outdated codes. This study evaluates the seismic performance of a four-story office building designed initially under SNI 1726:2012 and SNI 2847:2013, considering the updated seismic demands in SNI 1726:2019. Linear analysis showed that several beams no longer met strength requirements, while columns remained adequate due to higher initial safety factors. The structure was then modeled with four confinement reinforcement scenarios, varying stirrup quantity and spacing, to reflect typical field practices. Shear strength validation was conducted beforehand to ensure plastic mechanisms could form without premature shear failure. Nonlinear pushover analysis using SAP2000, supported by moment-curvature results from XTRACT, focused on (1) base shear and drift capacity, (2) plastic hinge formation, and (3) energy dissipation capacity. While all models satisfied Life Safety (LS) criteria, Model D-with the widest stirrup spacing-showed early stiffness degradation, exceeded shear capacity in some columns, and recorded the lowest energy dissipation. These results confirm the key role of proper stirrup detailing in enhancing strength, ductility, and seismic resilience.

Abstract Concentrically and eccentrically brace frames are two types of steel bracing used as a lateral load resisting system to improve the stiffness of the frame against earthquakes. The primary difference lies in how their members connect and how they dissipate energy during a seismic event. In this study, two types of bracing systems, eccentrically inverted V-brace frames (EBFs) and concentrically inverted V-brace frames (CBFs) for steel buildings are analyzed using the ETABS program. Nonlinear static (pushover) analysis (NSP) were performed then developing fragility curves in terms of spectral displacements. Fragility curves used to quantify how these two different bracing systems affect a model’s vulnerability. In addition, was investigated the story drift and forming of plastic hinges for the two systems. From the results, it can be noticed that the eccentrically inverted V- brace frames (EBFs) more ductile than concentrically inverted V-brace frames (CBFs) and could withstand in seismic action design. For instance the probability of the complete damage state 50%, the spectral displacement of the EBFs is higher about 63 % as compared with the CBFs.

ABSTRACT The reinforced concrete coupled wall system is a prevalent lateral force‐resisting system for mid‐ to high‐rise buildings. To enhance the seismic performance of such systems, this study proposes a friction hybrid coupled wall (FHCW) system, which integrates friction steel truss coupling beams (FTCBs). The FHCW system is designed with explicit performance objectives across different earthquake levels: it remains elastic under service level earthquakes (SLEs); experiences first and second sliding of the FTCBs during design basis (DBE) and maximum considered earthquakes (MCE), respectively; and allows wall pier reinforcement to yield under very rare earthquakes (VREs). To validate the seismic performance of the proposed system, a large‐scale quasi‐static test was performed on a three‐story subassemblage extracted from a 24‐story prototype. Realistic boundary conditions were simulated by applying varying axial loads to the wall piers. Test results confirmed the predefined performance objectives. Up to the VRE level, wall piers remained elastic, with inelastic deformation concentrated in the replaceable friction dampers of FTCBs. The FTCBs exhibited full and stable hysteretic responses, contributing 67% of the total energy dissipation. Beyond VRE, plastic hinges formed at the wall bases, eventually leading to flexural failure. The FHCW specimen achieved a maximum roof drift of 0.02 rad, while FTCBs attained a chord rotation up to 0.045 rad, demonstrating excellent ductility and considerable safety redundancy. An elastic coupling ratio of 67% was measured, indicating reliable FTCB‐to‐wall‐pier connections and efficient coupling action. The results confirm that the FHCW system offers a promising alternative for the design of resilient building structures.

This study investigates the crashworthiness performance of double-walled cylindrical tubes reinforced with interior flat-ring circular ribs under axial compression. Finite element simulations were conducted to evaluate how ring number, thickness, and width influence energy absorption (EA), mean crush force (MCF), specific energy absorption (SEA), and deformation patterns. Increasing the number of rings enhances EA and SEA by hinge points for progressive folding, although excessive ring density leads to localized buckling and reduces efficiency. Optimal ring thickness improves EA by promoting progressive folding with minimal mass, whereas overly thick rings reduce the number of plastic hinges and slightly lower SEA. Increasing ring width restricts fold formation and, together with added weight, results in nearly constant SEA despite increasing MCF. These findings demonstrate the potential of interior flat rings as an effective and lightweight design strategy for improving the crashworthiness of thin‑walled energy-absorbing structures.

Plastic hinge line model of energy absorption estimation for thin-walled box beam under impact load

Rapid urban growth has increased the demand for multistorey reinforced concrete (RC) buildings in Indian seismic zones, where architectural requirements often introduce vertically irregular floor heights for parking or commercial podium levels. Floor-to-floor height directly governs lateral stiffness and mass distribution, so variations in storey height can create soft-storey mechanisms that amplify seismic demand compared with regular, uniform-height buildings. This review examines the effect of floor height variation on the seismic performance of RC frame buildings analysed using ETABS under IS 1893:2016 provisions. Published studies on uniform buildings and structures with increased ground-floor or podium heights are synthesised, focusing on changes in fundamental period, design base shear, storey drift profiles, and concentration of demand in flexible storeys. Results consistently show that soft-storey and podium configurations exhibit longer periods, reduced overall base shear, and significantly higher inter-storey drifts at the tall storey than comparable uniform-height frames, increasing the risk of plastic hinge formation and non-structural damage. The review highlights typical height ratios that trigger soft-storey behaviour, discusses code recommendations for vertical irregularity, and summarizes ETABS modelling practices for representing height variation in routine design. Research gaps are identified in performance-based evaluation and retrofitting strategies for existing soft-storey buildings. The paper provides practical guidance for designers to recognize unsafe height configurations early in planning and to adopt stiffness-balanced layouts or strengthening measures so that architectural floor-height demands remain compatible with seismic performance objectives for RC buildings in Indian conditions.

ABSTRACT ‘A single thread cannot be spun into a cord, and a single tree cannot create a forest’ – an ancient Chinese proverb highlighting the necessity of collective integration. This proverb captures the essence of fused deposition modeling (FDM) 3D printing, where multiple filaments merge into a solid structure. Diverging from this approach, we introduce lace 3D printing – an FDM-based approach that embodies the concept of ‘a single thread forming a cord, a single tree becoming a forest’. Using a continuous zig-zag filament path with tunable geometry, this approach enables direct and efficient fabrication of millimeter-scale deployable metamaterials that transform from a compact to a mechanically stable cellular state under uniaxial tension. Plastic hinge formation under uniaxial stretching drives structural deployment. We investigate how printing parameters and geometries affect fabrication quality, deployment behaviours, and mechanical responses, and develop a theoretical model to predict nonlinear deformation. Introducing spatial gradients enables programmable morphing, suggesting applications in aerospace engineering and biomedical devices. Finally, the mechanical performance of the deployed metamaterials is evaluated under various loading conditions, including compression, cyclic loading, bending, and impact, highlighting their potential as cellular materials for load-bearing and energy-absorbing applications.

Tall buildings are crucial in the modern urban era, providing a solution to accommodating the rising population density and addressing the land scarcity problem. Despite mitigating population density, constructing tall buildings is complex, as their structural safety under seismic loading remains a significant challenge, particularly in a seismically active region such as Nepal. Performance-Based Design (PBD) is an advanced structural engineering approach that prioritises the design of buildings based on their expected performance under various seismic loading scenarios. This study focuses on the seismic-resistant design of a 16-storey Reinforced Concrete (RC) shear-wall-framed tall building using a Performance-Based Design approach. The structure was modelled and analysed using ETABS software, in accordance with NBC 105:2020. Linear static and response spectrum analyses were performed, followed by a non-linear static pushover analysis for performance evaluation using FEMA 440 equivalent linearization. The results confirmed that all structural components met strength and serviceability criteria. The pushover analysis revealed that plastic hinges formed primarily in beams, indicating a ductile failure mode. The capacity curve and performance point were obtained, indicating that the overall performance level met the Life Safety criteria for the Design Basis Earthquake. The study concludes that the PBD approach effectively ensures seismic resilience and recommends its expanded use for essential structures in high-risk zones.

The seismic performance of a proposed bolted angle connector beam-to-column joint with a stiffener (hereinafter referred to as a BACS joint) was investigated utilizing quasi-static tests on six specimens with H-shaped steel members. The failure modes, hysteretic curves, skeleton curves, stiffness degradation, and energy dissipation capacity were analyzed. The test results indicated that the BACS joint exhibited a 28.1% higher moment resistance and a 12.6% greater equivalent viscous damping coefficient compared to a welded connection with the same specifications. Furthermore, when compared to a short-beam spliced connection with comparable steel consumption, the BACS joint demonstrated advantages in both the load-bearing capacity and the energy dissipation. The numerical analysis results based on ABAQUS software demonstrated that increasing the stiffener height could not only enhance the bending capacity and stiffness of the connection, but also promote the relocation of the plastic hinge towards the beam end, thereby improving the failure mode. The increase in the stiffener thickness led to a minor improvement in the bending capacity of the connection, yet the influence of the stiffener thickness on the connection stiffness was limited. Furthermore, the use of steel with a higher strength grade could substantially increase the bending capacity of the BACS joint, while the enhancement in stiffness was relatively modest. Therefore, economic considerations should be integrated into the engineering design process.

The supporting system of super-large cooling towers is crucial for the structural safety of nuclear power plants. The X-shaped reinforced concrete column has emerged as a promising solution due to its superior stability. However, the performance of the cast-in-place base joint, which is a key force-transfer component, requires thorough investigation. This study experimentally investigates the mechanical performance of the joints under ultimate vertical compressive and tensile loads. The loads represent gravity-dominated and extreme wind uplift scenarios, respectively. A comprehensive testing program monitored load–displacement responses, strain distributions, crack propagation, and failure modes. The compression specimen failed in a ductile flexural compression manner with plastic hinge formation above the column base. In contrast, the tension specimen exhibited a tension-controlled failure pattern. Crucially, the joint remained stable after column yielding in both loading scenarios. The result validates the “strong connection–weak member” design principle. The findings confirm that the proposed cast-in-place joint possesses excellent load-bearing capacity and ductility. Therefore, the study provides a reliable design basis for the supporting structures of super-large cooling towers.

This research has focused on Chang Qing concrete-filled steel tube (CFST) truss arch bridge, addressing potential elastoplastic dynamic instability issues due to the replacement of hangers and deck system during maintenance. An energy conversion criterion was first proposed based on discrete Lyapunov functional. The vibration responses, energy conversion patterns, and plastic deformation characteristics of truss arch bridges under different load-release conditions (1/4 g, 1/2 g, and 1 g) were studied through finite element analysis. The obtained results indicated that under a load release of 1/4 g, the system presented stable periodic energy conversion (alternating decay of kinetic and strain energy), with the absolute Lyapunov exponent value of less than 1, proving the dynamic stability of the structure. With the increase of load release to 1/2 g, energy conversion process exhibited abrupt changes, with plastic hinges forming in arch ribs and diagonal braces, which resulted in asymmetric degradation of structural stiffness. Lyapunov exponent diverged and the system entered a nonlinear dynamic instability state. Complete release of gravity load resulted in asymmetric distribution of plastic hinges along both sides of the truss arches, compete interruption of energy conversion, and significant vibration amplitudes of Poincaré section, giving rise to loss of load-bearing capacity. This research revealed the effectiveness of discrete Lyapunov function in exploring dynamic stability, providing a theoretical basis for safety control in the engineering of bridge maintenance.

Steel frame structures have been increasingly widely used in high-rise and multi-story building design. However, traditional rigid welded beam–column joints exhibit poor ductility and high residual stress, which are key reasons for their susceptibility to brittle failure under strong earthquake actions. This study proposes a new type of beam–column joint for steel frames: the corrugated web beam–column joint. In this new joint, the web of the I-beam near the beam flange is partially replaced with a corrugated web that exhibits a folding effect—this modification weakens the plastic bending capacity of the I-beam and promotes the outward movement of plastic hinges. Low-cycle reciprocating loading tests were conducted to verify the performance of two specimens, namely one with the traditional beam–column joint and the other with the corrugated web beam–column joint. Through experimental comparison, it was found that plastic hinges in the new corrugated web joint are generated at the corrugated web, while no damage occurs at the beam-end welds. This indicates that the corrugated web beam–column joint can stably achieve the outward movement of plastic hinges and avoid the location of the beam-end welds, thereby providing theoretical and experimental foundations for the structural design of new ductile steel frames.

In the elastic–plastic analysis of structures, the deformation problem of cantilever beams is a classical problem, in which it is usually assumed that the material constituting the beam has an identical elastic modulus and identical yield strength when it is tensioned and compressed. These characteristics are manifested graphically as the symmetry of tension and compression. In this work, we will give up the general assumption and consider that the material has the property of tension–compression asymmetry, that is, the material presents different moduli in tension and compression and different yield strengths in tension and compression. First, the elastic–plastic response of the cantilever beam with a concentrated force acting at the fixed end in the loading stage is theoretically analyzed. When the plastic hinge appears at the fixed end, the maximum deflection at the free end is derived, and in the unloading stage the residual deflection at the free end is also given. At the same time, the theoretical solution obtained is validated by the numerical simulation. The results indicate that when considering the tension–compression asymmetry of materials, the plastic zone length from the fixed end no longer keeps the classical value of 1/3 and will become bigger; the tension–compression asymmetry will enlarge the displacement during the elastic–plastic response; and the ultimate deflection in loading and the residual deflection in unloading are both greater than the counterparts in the classical problem. The research results provide a theoretical reference for the fine analysis and optimal design of cantilever beams.

Currently, concrete wall panels have gained widespread attention from the global academic community, but there is relatively little research on concrete sandwich exterior-hanging walls. Based on relevant research by domestic and international scholars on multilayer walls, a novel exterior-hanging green self-insulating wall (EHGSW) has been proposed. Three full-scale frame specimens were constructed: one pure frame, one exterior-hanging wall frame without windows, and one exterior-hanging wall frame with windows. A sliding connection joint was placed between the upper end of the walls, while two load-bearing connection joints were placed at the lower end of the walls. The slotted hole of the sliding connections joint was limited to be 25 mm. Through low cyclic loading tests, the failure modes and seismic performance of reinforced concrete (RC) frame structure with the EHGSW were studied, focusing on seismic behaviors such as hysteresis curves, envelope curves, ductility, stiffness degradation, and energy dissipation capacity. The results indicated that the specimens exhibited flexural-shear failure at the low-ends of the RC columns and the both ends of the RC beams, leading to the development of plastic hinges. When the relative drift between the wall panel and the frame reached the limit of the slotted hole, the stiffness increased sharply. After the failure of the upper sliding connection joint, the hysteresis curves of specimens K2 and K3 were remained consistent with those of specimen K1. The strength degradation factor of the specimens ranged from 0.88 to 0.94. The ductility index of specimens K2 and K3 were between 4.51 and 6.78, it has been improved compared with the pure frame specimen K1 (ductility index of 2.89). The energy dissipation factor of the specimens varied within the range from 0.07 to 0.181.

ABSTRACT After an earthquake, the ductile reinforced concrete (RC) beam members in an RC building structure with seismic design may develop moderately damaged plastic hinges, and then the repair should be conducted to recover its functionality. Therefore, to investigate the seismic capacity of a ductile RC beam member with the damaged plastic hinge zone (DPHZ) after the repair is necessary. In this work, six ductile RC beam specimens are designed to obtain the seismic capacity for the repaired specimens. To let the specimens with the specified damaged levels in the plastic hinge zones, the dynamic loading test is conducted. Then, the repair methods, including surface treatment, epoxy low‐pressure injection, and epoxy resin mortar coating, are applied according to the different damage levels of each specimen. Finally, the test results related to strength, stiffness, and energy dissipation are used to quantify the pre‐ and post‐earthquake seismic capacity of a ductile RC beam with the repaired DPHZ, that is, the reduction factors. Additionally, this work also investigates the application of the prediction models suggested in ASCE/SEC 41 for the force–deformation curve on the ductile RC beams with the repaired DPHZ.

Owing to the absence of robust analytical theoretical analysis methods, the elastic-plastic ultimate bearing capacity of angle steel section components in transmission tower is usually addressed by finite element simulation and experiments. In this work, the elastic stiffness matrix that accounts for the deformation of the element was derived using fifth-order interpolation function. The dual nonlinear static analysis method was proposed by combining the material nonlinear plastic stiffness matrix and geometrical nonlinear stiffness matrix. The material nonlinear plastic stiffness matrix of beam element with angle section was derived through the yield surface and the concentrated plastic hinge models, and the geometrical nonlinear stiffness matrix of angle section was derived by the rigid-body criterion. The accuracy and effectiveness of the analysis method proposed in this work were verified through various examples, and the research results can provide theoretical references for the analysis and calibration of the mechanical properties of transmission tower.

The interaction between soil and structure, which merges geotechnical and structural engineering, plays a crucial role in seismic regions. Traditional structural design often assumes that buildings are fixed at their foundations, neglecting the influence of local soil conditions. However, accounting for soil–structure interaction (SSI) indicates greater structural flexibility, modified dynamic behaviour, and variations in the intensity and distribution of earthquake forces. These influences are especially notable in soft or moderately stiff soils, where foundation flexibility may cause increases or decreases in seismic demand. To account for these influences, American pre-codes provide detailed guidelines for incorporating SSI into structural analyses. In this study, these guidelines were applied in both nonlinear static (push-over) and nonlinear dynamic (time-history) analyses of a six-storey reinforced concrete frame structure. The analyses considered two different soil types, B and C, which were classified according to Eurocode 8, to evaluate the effect of different soil rigidity on structural behaviour. The findings, with a focus on kinematic interaction, highlighted how foundation embedment influences seismic behaviour. The results showed notable deformations in storey displacements and inter-storey drifts, as well as the formation of plastic hinges, indicating nonlinear response mechanisms. Reduced capacity curves under lower seismic forces confirmed the influence of SSI. This study underscores the necessity of incorporating SSI effects to improve seismic design accuracy and enhance the prediction of structural behaviour during earthquakes.

Advancing multifunctional mechanical metamaterials requires harmonizing auxetic behavior (negative Poisson's ratio, NPR) with high‐energy absorption (EA) capabilities. This study presents a snowflake‐perforated honeycomb metamaterial where radial buckling activates NPR‐driven EA enhancement. Plastic hinges at 45° ligaments initiate auxetic contraction, while NPR‐induced transverse compression forces hierarchical folding, delaying densification and amplifying energy dissipation. Geometric parameters ( a/b , d ) tune this cooperative mechanism within an optimal design window, enabling NPR to intrinsically reinforce EA. Integrated experiments and simulations confirm that NPR actively elevates EA through biaxial strain constraints and extended folding sequences. Parametric studies establish aspect ratio ( a/b ) as the primary regulator of NPR‐EA synergy, while inscribed diameter ( d ) governs structural stability. A gradient design strategy further leverages NPR‐induced compaction through spatially coordinated parameters, maximizing multifunctional performance. This work pioneers a tunable metamaterial paradigm where NPR fundamentally fortifies impact protection.

Abstract Usually, pinned ends are assumed to calculate the compression capacity of closely spaced double‐angle members. In reality, the joints used in practice provide additional rotational restraints at the member's ends, which significantly influence the compression member capacity of such built‐up sections. The current study systematically investigates this effect. This is realized through a numerical parametric study using finite element models. The varied parameters are: i) member length, ii) type and dimension of the individual angle sections, iii) number of interconnections, iv) dimensions of the gusset plates at the member's ends (i.e. thickness, width and depth). Finally, a design model is introduced which is based on second order theory calculation of an eccentrically loaded column with rotational end restraints. Furthermore, appropriate stiffness functions for these rotational end restraints are presented, also including cases with plastic hinges in the gusset plate. It is shown that this new design model can accurately predict the ultimate compression capacity of closely spaced double‐angle members.