Search

To improve the seismic performance of precast concrete reinforced frame structures which are widely used worldwide, and enable a certain repairable function for the precast structure after an earthquake, this paper proposes a new type of precast concrete frame joint using a full grouting sleeve connection with a disc spring device. The disc spring device was connected in series to the longitudinal reinforcement located in the plastic hinge zone at the beam end to provide a restoring force and protect the concrete. Six exterior beam-column joints consisting of one cast-in-situ beam-column joint and five precast concrete frame joints, using a fully grouted sleeve connection equipped with or without a disc spring device, were designed and fabricated. The failure process, hysteretic characteristics, and energy dissipation capacity of the joint specimens were analyzed based on reversed cyclic loading test. The results showed that the energy dissipation and seismic performance of the newly precast concrete joints equipped with the disc spring device were better than those of the precast concrete frame joints connected by ordinary grouting sleeves without a disc spring device. The disc spring device proposed in this study plays a similar role as a damper in the precast joint during loading and has the characteristics of concentrated damage as it transfers part of the damage in the joint core area to the built-in disc spring area at the beam end. Additionally, the deformation of the precast joints under a lateral seismic load was theoretically calculated, the calculated results were in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Beam-column joints' behavior is a key research focus due to their critical role in maintaining structural integrity and safety during earthquakes. While concentric joints have been extensively studied, eccentric joints, where beams' centerlines deviate from columns' centerlines, remain relatively unexplored. Beam-column joints exhibit more complex behavior, experiencing a significantly higher shear force (approximately six-fold that of a column), along with flexural moments and normal forces. The joint's eccentricity introduces a torsional moment that amplifies shear stress, and the beam is subjected to an out-of-plane moment (around one-sixth of the primary moment). The out-of-plane moment reduces the joint's resistance mechanism by reducing the confinement provided by beams. To examine the influence of beam eccentricity on the ductility, strength, and failure mechanism of beam-column joints, comprehensive nonlinear finite element (FE) analyses were conducted utilizing experimental eccentric beam-column joints, followed by meticulous validation of the developed model. The models employed incompatible mode mesh element and energy-based models for the concrete material behavior, utilizing an explicit solver. The models were used to examine the impact of various geometric parameters, boundary conditions, and axial load levels on behaviors (global and local) of the beam-column joint subassemblies. The examined geometric parameters encompass aspect ratios of joint and column for both joint types (exterior and interior). Joint behaviors were observed to be significantly influenced by the boundary conditions of the column. Furthermore, the aspect ratio of the joint, representing the beam-to-column depth ratio, played a predominant role in determining the joint failure mechanism by limiting their ability to develop beam hinges. Increasing the aspect ratio of the column had a modest effect on the joint's shear strength but improved the joint subassemblies' ductile behavior, despite increasing the joint's torsional moment. Higher column axial load levels increased the joint's shear strength and led to a shift in cracking patterns from diagonal to vertical. Interestingly, the study found that interior joints experienced higher out-of-plane moments. Exterior and interior joints maintained a level of approximately 62.5 % as a ratio between their shear strength across all models. Moreover, it was observed that yielding of joint stirrups correlated with a shear distortion angle of approximately 0.5 × 10 − 2 rad. Restrictions of ACI provisions on the aspect ratio of the joint seem to be conservative for eccentric interior joints. On the other side, the ACI provisions might overestimate eccentric exterior joint shear strengths as the aspect ratio exceeds unity. [ABSTRACT FROM AUTHOR]

This paper presents cyclic test results of nine beam-column joints, fabricated with Grades 60, 80, and 100 (Grades 420, 550, and 690) No. 11 (D36) headed bars in joints with matching concrete strengths. With the exception of the joint shear determination, each specimen was designed in accordance with ACI 318-14 provisions for special moment frame joints. The headed bar embedment length was determined using 1.0fy in accordance with ACI 318-14, rather than the ACI 318-19 requirement to use 1.25fy to calculate the development length. Test results demonstrate that the ACI 318-14 development length can be used for closely spaced high-strength No. 11 (D36) headed bars in joints with Code-conforming transverse reinforcement. This paper also aggregates the test data with prior research and compares the data with descriptive equations and breakout methodology for assessing the development length and anchorage strength of headed bars. The results support several design recommendations for the ACI 318 provisions. [ABSTRACT FROM AUTHOR]

One of the most critical aspects in the seismic behavior or reinforced concrete (RC) structures pertains to beam–column joints. Modern seismic design codes dictate that, if failure is to occur, then this should be the ductile yielding of the beam and not brittle shear failure of the joint, which can lead to sudden collapse and loss of human lives. To this end, it is imperative to be able to predict the failure mode of RC joints for a large number of structures in a building stock. In this research effort, various ensemble machine learning algorithms were employed to develop novel, robust classification models. A dataset comprising 486 measurements from real experiments was utilized. The performance of the employed classifiers was assessed using Precision, Recall, F1-Score, and overall Accuracy indices. N-fold cross-validation was employed to enhance generalization. Moreover, the obtained models were compared to the available engineering ones currently adopted by many international organizations and researchers. The novel ensemble models introduced in this research were proven to perform much better by improving the obtained accuracy by 12–18%. The obtained metrics also presented small variability among the examined failure modes, indicating unbiased models. Overall, the results indicate that the proposed methodologies can be confidently employed for the prediction of the failure mode of RC joints. [ABSTRACT FROM AUTHOR]

The existing Reinforced Concrete (RC) buildings stock is often characterized by a significant seismic vulnerability, due to the absence of capacity design principles, even in regions with high seismic hazard, such as Italy. Approximately 67% of existing RC buildings in Italy have been designed without considering seismic actions (GLD), resulting in very low transverse reinforcement amount in beams and, particularly, in columns. Additionally, beam-column joints typically totally lack stirrups. Consequently, shear failures under seismic actions are very likely for this pre-code building typology, often limiting their seismic capacity. However, the assessment of shear failures in beams/columns or joints varies significantly from code to code worldwide. The main goal of this work is to quantify the impact of different code-based brittle capacity models on the seismic capacity assessment and retrofit, focusing on GLD Italian pre-1970 RC buildings. This comparative analysis is carried out by first considering three current codes, emphasizing their, even significant, differences: European (EN 1998-3-1. 2005), Italian (D.M. 2018), and American (ASCE SEI/41 2017) standards. Then, shear capacity models prescribed by the current drafts of the next generation of Eurocodes are implemented and compared to the current models. The assessment includes: (i) a parametric comparison among models; (ii) the evaluation of case-study buildings capacity in their as-built condition and after shear strengthening interventions. The latter is performed on 3D "bare" models, due to the lack of practical guidance in most codes on modelling masonry infills. [ABSTRACT FROM AUTHOR]

The layout of the exterior retaining walls and external thermal insulation demands often introduce an eccentricity between the central axes of the beams and columns, leading to what is termed as an eccentric beam-column joint. Such the beam eccentricity is a key factor in shear failures within the joint region. This study addresses the negative impact of beam eccentricity on the shear capacity of reinforced concrete (RC) eccentric beam-column joints. Current research indicates that in the five prevailing shear capacity formulas of RC eccentric joints, adverse effects are primarily accommodated by either reducing the joint's effective width (b j) or implementing an eccentricity influence factor. The study challenges the validity of these approaches by dissecting the impact of singular and interactive factors, including. Eccentricity (2 e / b c), beam-to-column width ratio (b b/ b c), and the column's aspect ratio (h c/ b c). It was observed that while the influence of 2 e / b c is generally well-accounted for, the effects of b b/ b c and h c/ b c are not adequately considered in the Chinese code and ACI-318. Leveraging the softened strut-and-tie model and insights from these examinations, a refined formula for determining the shear capacity of eccentric joints is introduced. This formula incorporates the detrimental effects of beam eccentricity through a newly conceptualized eccentric influence factor, which is a function of both 2 e / b c and b b/ b c. Compared to existing models, this proposed formula also factors in the beam-to-column depth ratio and the longitudinal reinforcement in the middle of column section. Validation against experimental data from 26 eccentric joints demonstrates that the proposed formula yields predictions with the closest proximity to actual test results and the least variability compared to the five established formulas. This approach to considering the effects of e / b c and b b/ b c proves to be slightly more accurate than Zhou's model, making it a promising alternative for practical applications. [ABSTRACT FROM AUTHOR]

Beam-column (B-C) joints are recognized as critical regions in reinforced concrete (RC) moment-resisting frames when subjected to seismic loads. Furthermore, these joints may be subjected to high temperatures during their lifespan, which might cause severe structural damage. Accordingly, the seismic response of RC beam-column joints that were subjected to heat (i.e., 400 °C and 600 °C) was investigated in the present experimental work. The joint specimens were divided into three categories: Three joints were kept as is (i.e., reference joints; no strengthening is applied), whereas six joints were strengthened with one and two layers of stainless-steel expanded metal sheet mesh (SSEMSM) in order to improve their performance. To investigate the seismic performance of the joints, a quasi-static cyclic load was applied to the joints to simulate a seismic load. Results showed that the average maximum load for joints strengthened with one and two layers of SSEMSM, respectively, was increased by 11% and 21% at ambient temperature and by 2% and 9% at 400 °C, in comparison with the reference joint. In addition, using one and two layers of SSEMSM, respectively, led to achieving an average of 91% and 100% of the full capacity of the reference joint for B-C joints subjected to 600 °C. Furthermore, the experimental findings show a considerable improvement in the cyclic response of non-ductile RC joints that were strengthened with the SSEMSM strategy and subjected to high temperatures (i.e., higher load capacity, greater displacement, higher dissipated energy, higher ductility, and slower degradation in the secant stiffness). [ABSTRACT FROM AUTHOR]

This present research conducted an experimental study on the influence of different earthquake damages on the seismic performances of aged reinforced concrete (RC) beam-column joints retrofitted with basalt fiber-reinforced polymer (BFRP) sheets under cyclic loadings. Six beam-column joints included one benchmark specimen, one uncorroded specimen retrofitted with BFRP sheets, and four earthquake-damaged corroded specimens with the corrosion rates of 0% and 9% retrofitted with BFRP sheets. Test results demonstrated that the seismic performances of earthquake-damaged corroded specimens effectually improved after retrofitting with BFRP sheets, and the retrofitting effectiveness was significantly affected by the earthquake-damaged levels. The bucking of stirrups, spalling and crushing of concrete of retrofitted specimens were effectually postponed, while the ductility of corroded and uncorroded specimens under the earthquake damages increased after retrofitting with BFRP sheets. The total cumulative energy dissipation and final stiffness of retrofitted specimens considerably improved with the maximum increase of 22.3% and 14.3% comparing to those of benchmark specimen, respectively. Besides, the models for predicting the shear strength of RC beam-column joint cores considering the influences of earthquake damage, reinforcement corrosion, and FRP retrofitting were proposed. [ABSTRACT FROM AUTHOR]

Joints in frame structures often fail before beams and columns in an earthquake and are a key part of reinforcement. In this study, to enhance the seismic performance of concrete frame structures, a steel-jacketed grouting composite reinforcement method is proposed by combining reinforcement technology, steel cladding technology, and eco-efficient materials from grouting technology. This method effectively utilizes the advantages of various materials, avoids major demolition and construction, and reduces waste and resource consumption. In order to verify the feasibility and effectiveness of the reinforcement method, one of the original joint specimens with a scale of 1:3 and one of the reinforced joint specimens were designed and tested. The experiments involved reversed cyclic testing of beam–column to measure its seismic behavior. The seismic performance indexes such as failure characteristics, hysteretic properties, and the energy dissipation capacity of the specimens were analyzed, and the corresponding finite element model was established. The influence of key parameters such as reinforcement range, steel plate thickness, and grout strength on its seismic performance was explored. The research shows that the method can effectively improve the seismic performance of the joints, and seismic performance indexes such as bearing capacity, ductility, and energy consumption of the specimens are significantly improved. The test results of the established finite element model are in good agreement. The variable parameter analysis of the finite element shows that the thickness of the steel plate has little influence on its bearing capacity. With the increase in the reinforcement range of the clad steel and the strength of the grouting material, the bearing capacity of the specimen increases. The research results can provide a reference for the reinforcement of frame structure joints. [ABSTRACT FROM AUTHOR]

This article presents a study of the wind-resistance and seismic behavior of steel frame elevator structures with square hollow section (SHS) members. The study was conducted by numerical analysis, it begins by examining the semi-rigid performance of SHS T-joints (beam-column joints) under in-plane bending moment, proposes a semi-rigid connection model for the joints, and then investigates the influence of semi-rigid joint effect on the performance of the steel elevators. Finite element (FE) results showed that the semi-rigid model can predict the moment-rotation response of the beam-column joints. The results also showed that the natural vibration period of the elevator with semi-rigid joints is 20% higher than that of an elevator with rigid joints. The semi-rigid joint effect causes the lateral drift of the elevator to increase by more than 47% under wind load, causing the maximum story drift of the elevator to exceed the limit specified in the current code. The semi-rigid joint effect causes the lateral displacement of the elevator to increase by approximately 15%-30% under the seismic waves of a rare earthquake. [ABSTRACT FROM AUTHOR]

The building industry requires the development of a ductile lateral force resisting system made of mass timber to help mass timber to continue to grow in popularity as the primary structural building material. The OpenSees framework was used to develop a numerical model of a single-story timber frame with a timber buckling-restrained brace, which was validated by the results of a previously completed series of quasistatic cyclic timber buckling-restrained brace (TBRB) component and subassembly tests. The experimental validation included a model developed for the hysteretic behavior of the TBRB and the rotational capacity of beam–column joints made with mass ply lam (MPL) panels, two slotted-in steel plates, and a number of steel dowels. The single-story model TBRB braced frame was then expanded to a numerical model of an eight-story mass timber buckling-restrained braced frame. The TBRB frame was analyzed with static pushover, quasistatic cyclic loads, and earthquake simulations. During the simulation of eleven design-level earthquake ground motions, the building experienced a peak interstory drift at of 2.54% at the first-floor level and a peak floor acceleration of 1.7g at the roof. The numerical model developed in this research of a timber buckling-restrained braced frame with TBRBs is novel and could be used to design timber buckling-restrained braced frames as a ductile lateral force resisting solution for mass timber buildings in seismic regions. [ABSTRACT FROM AUTHOR]

Due to its high effectiveness and low cost, viscoelastic damper (VED) is a commonly used type of passive energy dissipation device to reduce structural vibrations and responses against earthquakes and strong winds. Over the past decades, scholars have developed new types of VEDs to be installed at different structural locations. These VEDs offer better post-disaster recoverability and smarter behaviors for structures. Nonetheless, existing efforts of various VEDs and the technologies supporting VEDs were seldomly summarized. This article presents a critical state-of-art review of the existing research on VEDs, hybrid VED devices, and the design methods for structures installed with VEDs. First, the VEDs are classified based on the design locations in building structures, including VEDs used as coupling beams and damping walls, installed in braces and beam-column joints, and used to connect parallel structures. In addition to these classic VEDs, the study presents the high-performance VEDs and the corresponding techniques, such as the combined usage with other materials and/or devices. Furthermore, as an important contribution to the presented work, various design methods for structures enhanced by VEDs were systematically summarized. These methods considered different evaluation parameters aiming at different design targets. Finally, this article identifies and highlights research challenges in the existing studies. Possible improvements that could be made in the future were also provided. [ABSTRACT FROM AUTHOR]

The Clamped Split Pocket Mechanism (CSPM) prefabricated joint system was developed for a single-story steel instant house, designed to be compact and rapidly constructed without modifying the end of the beam and column element member. The CSPM bolted joint system was proposed as an optimal solution for post-disaster housing, especially after earthquakes. Despite its potential, the frictional tensile resistance behavior of the CSPM bolted joint system has not been previously studied, necessitating experimental investigation. This study examined the frictional tensile resistance behavior of the CSPM joint system by monitoring the effective friction coefficient under axial tension force. The experiments considered both the strong and weak axes of the joint and utilized two configuration types of specimens (L and T) with varying bolt pretensions of 2.5, 5, 7.5, and 10 kN. Results indicated that the effective friction coefficient of the CSPM bolted joint system ranged from 0.19 to 0.26, correlated to bolt pretension. Increased bolt pretension resulted in larger surface deformation of the split pocket, triggering a not uniform frictional tensile resistance across the steel surfaces of the split pocket joint. From this study, the achieved effective friction coefficients could guide the design of minimum pretension forces for clamps in prefabricated steel instant houses. [ABSTRACT FROM AUTHOR]

The conventional reinforced concrete beam exhibits limitations in terms of bearing capacity, intricate construction procedures, and substantial labor requirements. In response to these challenges, a novel approach featuring an Angle Steel Skeleton (ASS) for concrete reinforcement has been proposed. In this study, four concrete beam specimens along with two beam-column joint specimens were meticulously prepared for static loading tests and low-cycle loading tests. The bending performance of the innovative structure, Angle Steel Skeleton-Reinforced Concrete Beam (ASSB), was comprehensively analyzed through static loading testing. Furthermore, formulations were developed to calculate the stiffness and bearing capacity of ASSB. Employing the finite element method, an examination was conducted to elucidate the influence of factors such as shear span ratio, concrete strength, and angle steel strength on the bearing capacity of concrete beams. Building upon the aforementioned investigations, the seismic performance and mechanical response of Angle Steel Skeleton-Concrete Beam-Column Joints (ASSJ) was investigated through low-cycle loading tests. An in-depth analysis was conducted to establish the correlation between the axial compression ratio and steel skeleton stress. Results from the research indicate that the adoption of ASS in lieu of steel cages results in a substantial enhancement in the ultimate bearing capacity of concrete beams, ranging from 29% to 36.6%. Additionally, there is a twofold increase in energy dissipation capacity, accompanied by a 14% increase in ductility. Notably, ASSJ specimens exhibit superior seismic performance, particularly in low-intensity seismic zones. [ABSTRACT FROM AUTHOR]

Steel fiber reinforced high-strength concrete (SFRHSC) is a composite material composed of cement, coarse aggregate, and randomly distributed short steel fibers. The excellent tensile strength of steel fiber can significantly improve the crack resistance and ductility of high-strength concrete (HSC). In this study, experimental and numerical investigations were performed to study the cyclic behavior of the HSC beam-column joint. Three SFRHSC and one HSC beam-column joint were prepared and tested under cyclic load. Two different volume ratios of steel fibers and three stirrups ratios in the joint core area were experimentally studied. After verification of the experimental results, numerical simulations were further carried out to investigate the influence of steel fibers volume ratio and stirrups ratio in the joint core area on the seismic performance. Evaluation of the hysteretic response, ductility, energy dissipation, stiffness, and strength degradation were the main aims of this study. Results indicate that the optimal volume fraction of steel fibers is 1.5%, and the optimal stirrups ratio in the joint core area is 0.9% in terms of the enhancement of the seismic performance of the SFRHSC beam-column joint. [ABSTRACT FROM AUTHOR]

Brittle shear failure of beam-column joints, especially during seismic events poses a significant threat to structural integrity. This study investigates the potential of steel fiber reinforced concrete (SFRC) in the joint core to enhance ductility and overcome construction challenges associated with traditional reinforcement. A non-linear finite element analysis (NLFEA) using ABAQUS software was conducted to simulate the behavior of SFRC beam-column joints subjected to cyclic loading. Ten simulated specimens were analyzed to discern the impact of varying steel fiber volume fraction and aspect ratio on joint performance. Key findings reveal that a 2% volume fraction of steel fibers in the joint core significantly improves post-cracking behavior by promoting ductile shear failure, thereby increasing joint toughness. While aspect ratio variations showed minimal impact on load capacity, long and thin steel fibers effectively bridge cracks, delaying their propagation. Furthermore, increasing steel fiber content resulted in higher peak-to-peak stiffness. This research suggests that strategically incorporating SFRC in the joint core can promote ductile shear failure, enhance joint toughness, and reduce construction complexities by eliminating the need for congested hoops. Overall, the developed NLFEA model proves to be a valuable tool for investigating design parameters in SFRC beam-column joints under cyclic loading. [ABSTRACT FROM AUTHOR]

In this research, the response of the RC Beam-Column Joint under the cyclic loads was analyzed with a FEM solver (Abaqus) by using various grades of Engineered Cementitious Composite (ECC) in the joint zone. The concrete damage plasticity model for concrete and ECC material under cyclic loading was proposed. Accordingly, the Finite Element Analysis (FEA) model was established with the consideration of different constitutive material models for concrete and Engineered Cementitious Composites. The accuracy of the proposed FEA model was validated with the experimental results. Failure mechanism, crack propagation, moment rotation relationship, and energy absorption under cyclic loading were investigated. Under controlled deformation, cyclic loads were applied to the samples at the end of the beam up to the failure point. It was found that the use of various grades of Engineered Cementitious Composites in the joint zone was effective in enhancing the ultimate moment capacity upto 38.50%, ductility upto 13.72%, and siffniness degradation upto 28.57% respectively of the joint up to the failure stage alongwith significant reduction in crack propagation. [ABSTRACT FROM AUTHOR]

The earthquake that occurred in the Cianjur area, West Java on Monday 21 November 2022 at 13.21 WIB resulted in 635 fatalities and 56,000 houses that were damaged. The results of the assessment found that many houses and public facility buildings still did not meet the requirements for earthquake-resistant buildings, especially in the use of concrete materials, main reinforcement, stirrups in columns, beams, foundations and beam-column joint, and did not have a strong column-weak beam planning concept. This can be seen from the inability of the column to withstand/carry the working load which causes the column to collapse and damage. Therefore, it is very necessary to pay attention to building planning in Disaster Prone Areas (DPA) in accordance with earthquake resistant building regulations SNI 1726:2019 and SNI 2847:2019. [ABSTRACT FROM AUTHOR]

Premature shear failure in reinforced concrete (RC) beam–column joints (BCJs) or at the top of columns can significantly compromise a building's seismic response, leading to major damage or global collapse, as observed in the aftermath of recent seismic events. Local strengthening solutions based on the employment of fiber-reinforced polymers (FRPs) are effective at increasing shear strength and preventing the failure of BCJs, and are also quick and easy to apply. This has led to their increased use in recent postearthquake reconstruction processes. However, large-scale plans to mitigate seismic risk require strengthening solutions that produce a minimum level of disruption and do not prevent the use of buildings. This can be achieved only by conducting work from a structure's exterior. This paper, therefore, proposes a novel FRP strengthening layout for exterior RC BCJs that combines the use of quadriaxial fabric and mechanical FRP spike anchors. In order to validate the proposed solution and quantify the effects of the number of layers and anchors, four full-scale BCJs are tested under a constant axial load and reversed cyclic displacement. The results are presented and discussed in relation to: global subassembly and local joint-panel response, energy dissipation, and the strain demand on the FRP fibers. A comparison with current available design formulations for anchored-FRP fabrics is made to produce preliminary design criteria. [ABSTRACT FROM AUTHOR]

One of the common deficiencies of pre-70s reinforced concrete (RC) moment frames is the shear failure of beam–column (BC) joints. In addition to that, joints with high tension demand have limited shear capacity to resist seismic actions, according to the New Zealand (NZ) seismic assessment guidelines. Fiber-reinforced polymers (FRP) have been widely used in research and practice for seismic retrofitting of BC joints prone to shear failure. However, in many cases, the tests were conducted on two-dimensional BC joints, which does not necessarily represent the limitations structural engineers face in practice, such as the presence of the diaphragm slab, transverse beams, and access limitations to the joint panel. The American Concrete Institute guidelines for FRP strengthening only mention that strengthening joints is possible but do not provide design guidance. The European fib Bulletin 90 provides design guidance but assumes that the joint panel is always available to install FRP, which is rarely the case in real structures. We have proposed a design method for shear strengthening of beam–column joints using FRP sheets and FRP anchors based on the adaptation of aforementioned design documents, published research, and first principles of engineering. The intention is for this case study to inspire other engineers who face the same issue and to encourage further research in this area. [ABSTRACT FROM AUTHOR]

This paper introduces a modular, assembled steel beam-column flange connection joint that efficiently connects prefabricated beams and columns using high-strength bolts. It enables the rapid repair of damaged joints after earthquakes by replacing flange connectors and high-strength bolt groups. Four joint specimens with varying thicknesses and lengths of the inner flange sleeve, scaled at a 1:2 ratio, were fabricated to evaluate performance. These specimens were subjected to low circumferential reciprocal loads to investigate damage modes, hysteresis curves, skeleton curves, ductility performance, energy dissipation capacity, and seismic performance, including stiffness degradation. The test and analysis results reveal that the primary failure mode is characterized by bulging of the flange jacket cover, with damage concentrated in the plastic hinge zone at the beam end. The flange connection joint exhibits excellent load-bearing, rotational, and energy dissipation capacities. The 'secondary strengthening' feature significantly enhances joint load-bearing capacity, ductility performance, and energy dissipation, increasing overall safety redundancy. Increasing the thickness and length of the flange connector substantially improves seismic performance and enlarges the plastic development area. [ABSTRACT FROM AUTHOR]

In this paper, seven half‐scale specimens are used to investigate the effects of the beam–column width ratio, concrete strength, and axial load on the seismic performance of wide exterior beam–column joints. The test results show that all the specimens undergo bending damage at the beam end. The concrete damage in the core column is not significant, meeting the seismic requirements of strong column–weak beams and strong joint–weak members. For specimens with small beam widths, the increase in axial load can effectively reduce the damage to the concrete in the outer joint and increase the strength of the specimen. Increasing the beam width and concrete strength reduces the ductility of the specimen while increasing the strength of the specimen. The bonding performance of the longitudinal bars anchored outside the core column is poor, as bond–slip with the concrete is observed during the test. In addition, compared with ACI 318‐19, GB 50011‐2010 is more conservative for calculating the shear strength of exterior wide beam–column joints. Finally, a corresponding finite element model is established by MSC Marc and verified based on the experimental results. [ABSTRACT FROM AUTHOR]

In this paper, steel–polyethylene hybrid fiber-reinforced strain-hardening cementitious composites (HECC) are applied in beam–column external joint core region to form a novel HECC/reinforced concrete (RC) composite beam–column joint with reduced anchorage length of beam longitudinal rebar and eliminated transverse rebar, and thus to alleviate rebar congestion and simplify the construction process efficiently especially for precast RC frame structures. Five external beam–column joint specimens are constructed and tested under cyclic loading to illustrate the influences of the anchorage length of beam longitudinal rebar and longitudinal rebar ratio on the seismic performance of beam–column joint. The effects of design parameters on seismic performance, including hysteresis behavior, degradation of strength, energy dissipation capacity, and cracking patterns are discussed in detail. Experimental results indicate that the replacement of normal concrete with HECC in beam–column joint core region could apparently reduce the amount of stirrups in the joint core area while maintaining reliable seismic behavior. Remarkably, specimen with no stirrups in the core area exhibits nearly equivalent seismic behavior to that of the control RC specimen. Furthermore, the application of HECC in joint core area allows for a substantial reduction of the required anchorage length for the beam longitudinal rebar to 9d, which further simplifies the construction process considerably. [ABSTRACT FROM AUTHOR]

This paper proposes the double-endplates replaceable beam-column joint (DEBJ) based on the seismic design concept of replaceable beam. Compared to the common extended endplate bolted joint (CEBJ), the DEBJ is easy to be connected and replaced after earthquakes, and it can achieve plastic hinge outward movement in steel frame. Due to double endplates and different failure modes, the current moment-rotation models for CEBJ cannot be used for DEBJ. Therefore, based on the classical model used for traditional endplate joints, a theoretical moment-rotation model for DEBJ is developed, and the calculation methods on ultimate bending moment and initial rotational stiffness are deduced. A parametric study is performed for DEBJ based on a test-validated finite element (FE) model developed in this paper. The predicted moment-rotation curves calculated from proposed theoretical model is validated by the experimental results on endplate joints and FE results on DEBJ. The results show that the established theoretical model proposed in this paper can predict the moment-rotation relation curves of DEBJ and the common extended endplate bolted joint (CEBJ) accurately, the predicted results by established theoretical model are in good agreement with experimental and FE results according to the comparison. It is revealed that the established model has universality to some extent. [ABSTRACT FROM AUTHOR]

Ensuring resilience through rapid buildings recovery in seismic zones has been placed at the forefront of recent studies. However, studies that compare the relative resilience of buildings constructed with different materials are lacking. This paper focuses on a comparative resilience analysis of concrete moment frames where beam-column connections are made with varying types of concrete mixtures. The connections are made with normal strength concrete (NSC), rubberized concrete (RbC), steel fiber rubberized concrete (STFRC), synthetic fiber rubberized concrete (SYFRC), and high strength concrete (HSC). Nonlinear static pushover and incremental dynamic analysis (IDA) are utilized to understand system response and the level of damage sustained following an earthquake. Subsequently, seismic fragility functions are constructed for the five considered frame types. The frames are subjected to different seismic scenarios, and the corresponding losses, recovery time, and resilience are quantified. A comparison between the five frame types is carried out to examine the optimal concrete mixture to be used to reduce damage probabilities, total direct losses, and recovery time and subsequently enhance resilience. The results show that rubberized concrete strengthened with steel and synthetic fibers can reduce economic losses by up to 19% and increase building resilience by up to 37% compared with the frames constructed with normal strength concrete. [ABSTRACT FROM AUTHOR]

Building code implementation in developing countries is a serious concern due to poorly regulated construction practices. Deficiencies in terms of material strength and structural detailing are found the most in reinforced concrete frames in Pakistan. This paper presents the results of quasi-static cyclic tests performed on reduced-scale RC frames with and without beam-column joint detailing and considering normal and low-strength concrete respectively. Fragility functions and loss curves for the standard/sub-standard frames were derived using an experimentally validated numerical model. Furthermore, the existing RC frames building stock was rehabilitated with various configurations of steel bracing i.e. one way diagonal, one way eccentric, two way diagonal, two way eccentric and concentric. The developed fragility and loss curves for the rehabilitated frames confirmed that the two way diagonal steel bracing system outclasses the other types. Moreover, inter-story drift limits for as-built and rehabilitated frames were proposed under design base earthquakes and maximum considered earthquakes. Maximum considered earthquakes pushed the ductile as-built frame further than the moderate damage state, thus rehabilitation after such an event will be required for the structure. The presented results will help in seismic risk assessment, decision-making and public awareness. [ABSTRACT FROM AUTHOR]

This study investigates the behavior of hybrid beam-column connections with numerous detailing methods to be incorporated into precast concrete moment-resisting frames under simulated reversed cyclic loading, and ultimately develops a design procedure. Seismic performance of moment-resisting precast concrete beam-column connections was investigated through simulated reversed cyclic load tests. In addition, nonlinear finite element analysis (FEA) of typical monolithic and precast concrete connections was carried out using a modified concrete damage plasticity model. Good agreement was achieved between experimental and numerical results, which indicates that the FEA model is capable of capturing failure modes of the investigated precast concrete connections. Simple detailing modifications resulted in major improvements in the performance of connections in terms of load-displacement curves, stiffness, and energy dissipation. Finally, a design procedure was developed for the investigated connections based on failure modes and investigated limit states. [ABSTRACT FROM AUTHOR]

This study investigates the behavior of beam–column (B-C) joints made of ultra-high performance concrete (UHPC) under constant axial force and increasing bi-directional bending. Third-scale corner B-C specimens, comprising a UHPC joint, two column segments, and two beams at right angle, were fabricated and tested to failure. The studied parameters were joint type, evaluating two materials UHPC and normal strength concrete (NSC), and spacing of transverse reinforcement in beams and columns. Test results indicated that utilizing UHPC in the joint region instead of conventional NSC results in increasing the ultimate capacity of the joint by 47%, changing the failure mode from brittle shear within the joint to a ductile beam flexure, increasing the joint ductility by 35–70%, and increasing the initial and secant stiffnesses by 27–50% and 57–74%, respectively. Leveraging the results from the study such as utilizing only half the transverse reinforcements required in national codes and removing transverse reinforcement in the joint, UHPC seems a viable option to solving the construction problems associated with NSC joints such as reinforcement congestion and concrete segregation. An analytical investigation is also included and showed the ACI-ASCE 352 code to significantly overpredict the joint shear capacity. [ABSTRACT FROM AUTHOR]

This study evaluated the seismic performance of a clamped split pocket mechanism (CSPM) as a beam-column joint system for a prefabricated instant steel house. The CSPM utilizes a plug-and-play connection system with preloaded bolts, eliminating the need for on-site welding during assembly. Two full-scale CSPM specimens were examined for their stiffness, hysteretic behavior, skeleton curves, ductility, and failure modes using cyclic loading tests. The results indicated that the CSPM specimens exhibited a hysteretic response shape that appeared as a reverse S-shaped curve with pinching in the middle. Plastic deformation was formed through inelastic local buckling in the split pocket, which was crucial in absorbing seismic energy, effectively preventing brittle failure, and thereby reducing damage to the joint system. According to the criteria of AISC 341-16, the CSPM specimens were classified as partially restrained (PR) and ordinary moment frames (OMF) as their moment capacity did not surpass 0.8Mmax at a rotation angle of 0.02 rad despite exhibiting adequate and stable lateral resistance in positive and negative loading directions up to 0.04 rad. This objective can be achieved with the condition that the beams and columns remain undamaged. Finally, the CSPM proved to be a reliable prefabricated beam-column joint system for a one-story instant steel house. [ABSTRACT FROM AUTHOR]

This paper introduces a novel type of prefabricated semi-rigid concrete beam–column joint, aiming to examine its load-carrying capacity and seismic performance in comparison with a traditional cast-in-place joint. This study utilized the ABAQUS 2020 software to establish finite element models for both types of joints and conducted finite element analysis under low circumferential reciprocating displacement loads. When comparing the energy dissipation capacity, ductility, ultimate load-carrying capacity, stress mechanism, and damage mode, a comprehensive evaluation of the two types of joints was performed. Furthermore, this study investigated the impacts of various factors such as the axial compression ratio, concrete strength, reinforcement strength, and connector strength on the ultimate load-carrying capacity, ductility, and energy dissipation performance of the joints. Based on the findings, the newly combined joint exhibited a substantial 31.7% increase in its ultimate load-carrying capacity, along with a notable 7.23% enhancement in ductility and an improved energy dissipation capacity when compared with the cast-in-place joint. As a result, it can be concluded that the seismic performance of the new joint surpasses that of cast-in-place joints. Additionally, this study examined the impact of modifying relevant parameters on the seismic performance of the new prefabricated semi-rigid concrete beam–column joint. [ABSTRACT FROM AUTHOR]

On the shear load‐bearing capacity of thin‐walled box girders with unreinforced joints in the webs As part of the LT bridge construction method (L: Longitudinal, T: Transversal), which is being developed at TU Wien, thin‐walled hollow concrete box girders are used longitudinally and are combined with deck slab elements and in‐situ concrete. Due to the construction process, unreinforced joints remain in the webs of these box girders, while the bottom and deck slabs can be continuously reinforced due to the in‐situ concrete layers. The question arose as to how this joint configuration affects the shear load‐bearing capacity of the box girders. In order to gain a fundamental understanding, two large‐format test specimens, one with joints in the webs and one without, were investigated experimentally. The shear force capacity of the girder with joints corresponded approximately to the one of the girder without joints, showing that it was possible to transfer significant shear forces despite the joints. The joint opening proved to be characteristic for the shear load‐bearing behaviour, as the stirrups adjacent to the joint act like a suspension reinforcement. A local increase in the stirrup reinforcement in this area is therefore recommended. Non‐linear finite element analyses were carried out to analyze the effects of post‐tensioning, as used in the LT method, on the load‐bearing behavior. It was shown that the load‐bearing behavior of the post‐tensioned girder with joints largely corresponds to the one without joints. [ABSTRACT FROM AUTHOR]

Strength enhancement of non-seismic concrete beam–column joints (NSCBCJs) via carbon fiber-reinforced polymer composites (CFRPCs) integration has become a viable strategy. However, the implementation of these NSCBCJs without transverse reinforcement shows poor performance during earthquakes in seismic locations. Thus, strengthening the anti-seismic performance of NSCBCJs to meet the acceptance criteria of ACI 374.1-05 is fundamentally significant. Yet, in addition to limited experimental results, only a few numerical studies based on the finite element model have been performed to determine the anti-seismic behavior of NSCBCJs. Consequently, the stress contribution of CFRPCs to NSCBCJs is not clearly understood. Therefore, we used a finite element model to examine the strength contribution of CFRPCs to NSCBCJs. The performance of the proposed finite element model was validated using the experimental results, demonstrating a good agreement between them. It was shown that the strength of NSCBCJs was improved due to CFRPC incorporation, thereby achieving compliance with the seismic requirements of ACI 374.1-05. In addition, CFRPCs presence could enhance the confinement, reduce the deformation of the NSCBCJs and, thus, decrease their stiffness and strength degradation, while simultaneously improving the energy dissipation. [ABSTRACT FROM AUTHOR]

A 3D-finite element analysis within the numerical program ABAQUS is adopted in order to simulate the seismic behavior of reinforced concrete beam-column joints and beam-column joints strengthened with CFRP ropes. The suitability of the adopted approach is investigated herein. For this purpose, experimental and numerical cyclic tests were performed. The experiments include four reinforced concrete (RC) joints with the same ratio of shear closed-stirrup reinforcement and two different volumetric ratios of longitudinal steel reinforcing bars. Two joints were tested as-built, and the other two were strengthened with CFRP ropes. The ropes were applied as Near Surface Mounted (NSM) reinforcement, forming an X-shape around the joint body and further as flexural reinforcement at the top and bottom of the beam. The purpose of the externally mounted CFRP ropes is to allow the development of higher values of concrete principal stresses inside the joint core, compared with the specimens without ropes, and also to reduce the developing shear deformation in the joint. From the results, it is concluded that X-shaped ropes reduced the shear deformation in the joint body remarkably, especially in high drifts. Further, as a result of the comparisons between the yielded outcome from the attempted nonlinear analysis and the observed response from the tests, it is deduced that the adopted method sufficiently describes the whole behavior of the RC beam-column connections. In particular, comparisons between experimental and numerical results of principal stresses developing in the joint body of all examined specimens, along with similar comparisons of force displacement envelopes and shear deformations of the joint body, confirmed the adequacy of the applied finite element approach for the investigation of the use of CFRP-ropes as an efficient and easy-to-apply strengthening technique. The findings also reveal that the connections that have been strengthened with the FRP ropes demonstrated improved performance, and the crack system preserved its load capacity during the reversal loading tests. [ABSTRACT FROM AUTHOR]

The configuration of beam–column joints in precast concrete (PC) building structures varies widely, and different connection methods significantly affect the progressive collapse resistance of the structure. This study investigates the progressive collapse resistance of an innovative beam–column connection node frame. Finite element models of four-story, two-span space frame structures made of reinforced concrete (RC) and PC were developed using ANSYS 14.0/LS-DYNA R5.x software, employing nonlinear dynamic and static analysis to examine structural collapse behavior under bottom middle or corner column damage. Numerical results indicate that following the failure of the middle or corner column due to explosion loading, the vertical displacement and collapse rate of the PC structure with the novel connection method are less than those of the RC structure during collapse progression. Furthermore, upon removal of the middle or corner column, the residual load-carrying capacity of the PC structure with the innovative connection increased by 7% and 3.7%, respectively, compared to the RC structure. This suggests that PC structures with this type of connection demonstrate superior performance in resisting progressive collapse, offering valuable insights for future engineering applications. [ABSTRACT FROM AUTHOR]

Four exterior reinforced concrete beam–column joint subassemblages with poor reinforcement details and low-quality materials were constructed and subjected to cyclic lateral deformations under constant axial loading of the columns. The longitudinal rebars at the top of the beams were well-anchored in the joint region with a 90° hook and transversely welded to prevent premature slippage. The same was true for the longitudinal rebars at the bottom of the beam of the first specimen. Contrarily, the anchorage of the rebars at the bottom of the beam of the other three subassemblages was straight and of insufficient length. One of these specimens (the second) also had deficient lap splices of the column reinforcement, while the other three specimens had continuous column rebars. The third and the fourth subassemblage were designed with different joint aspect ratio and beam shear span/depth ratio values. The overall seismic performance of the specimens was evaluated and compared. The failure mode of the subassemblages was accurately predicted by the proposed analytical model. It was clearly demonstrated that the anchorage of the rebars, the length of the lap splices, the joint aspect ratio and the shear span/depth of the beam ratio value crucially affect the cyclic response of beam–column joints and, hence, may cause a severe detrimental impact to the overall structural integrity. [ABSTRACT FROM AUTHOR]

Structures subjected to severe loads, such as earthquakes, often develop cracks at the beam-column joints, underscoring the significance of these regions in design. This study focuses on a comparative analysis of beam-column joints constructed with Ultra-High-Performance Concrete (UHPC) and Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) using the Finite Element Method (FEM) within the Abaqus software, contrasting with Low-Strength Concrete (LSC) and Normal-Strength Concrete (NSC). The results underscore the superiority of UHPFRC in compressive and tensile strength, coupled with enhanced ductility. Furthermore, distinct failure mechanism are observed in the concretes, captured by concrete damaged plasticity (CDP), leading to a deeper understanding of the behavior of these high-strength materials. These findings carry significant implications for enhancing structural safety and performance, particularly in situations involving seismic or other severe loads

This paper evaluates the effectiveness of a novel capacity-design based retrofit for improving both the local and global behaviour of existing reinforced concrete buildings using fibre-reinforced polymers. The approach was previously tested on beam-column joints and is here extended to the building level. A new fibre-element model for the global retrofit is proposed and validated against full-scale experiments. Non-linear push-over analyses confirm the adequacy of the retrofit and fragility analyses are used to compare it to a simpler local retrofit. Finally, cost-benefit analyses for three levels of seismicity highlight the cost-effectiveness of the global retrofit for moderate to high seismicity. [ABSTRACT FROM AUTHOR]

Long-term stability of the protective coal pillars in coal mines can ensure normal and safe use of roadways; in turn, the integrity of the roadway plays an important role in safe and efficient mining in coal mines. The initial damage and rheological damage caused by coal-seam excavation disturbance have important influences on the selection of reasonable widths of the protective coal pillars. Based on damage mechanics and the theory of elastic foundation beams, a coupled damage constitutive relationship of rock-like materials is proposed in this work by considering the influence of threshold and residual strength to establish the mechanical model of the elastic damage foundation beam. By theoretical analysis and numerical calculation, the differential equation of the deflection curve of the beam is solved, the influence range of the advance abutment pressure under the condition of coupling damage is obtained, and the width of the protective coal pillar is determined. The results show that compared with the elastic foundation beam model, after considering the coupling damage of coal, the influence range of the advance abutment pressure increases with time over a certain duration. At the end of this duration, the influence range of the advance abutment pressure remains almost unchanged. For the case considered in this paper, the long-term stability of the roadway is guaranteed when the width of the coal pillar is 120 m. The potential interference or change related to the specific situation of the site can be studied by changing the relevant parameters in the model to study different working conditions, or the damage of the roof rock beam during the mining process of the working face can be considered, which will be the subject of further research in the future. [ABSTRACT FROM AUTHOR]