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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]

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]

The failure of the support system is one of the primary reasons for bridge failures during construction. Existing research on support system failures primarily focused on falsework, with less attention given to other components such as Bailey beams, transverse beams, and steel pipe piles. This study focused on an incident where the support system of a cast-in-situ box girder bridge experienced settlement due to the failure of Bailey beams, transverse beams, and steel pipe piles. To thoroughly analyze the accident's causes, a multiscale elastic–plastic finite-element model of the support system was developed based on the actual on-site layout. By combining the results of the finite-element model with comprehensive on-site data, it was found that the support system settlement accident was caused by a series of construction errors, including the incorrect placement of the Bailey beams, excessive vulnerability in the steel pipe piles' support positions, and inadequate welding strength between the transverse beams. To prevent similar accidents from recurring, the design, construction, and supervisory parties should collectively ensure the consistency between design and construction and increase their attention to potential stress concentrations in certain components of the support system. When the possibility of stress concentration exists, Bailey beams should be reinforced with vertical or diagonal struts depending on their actual support positions, while steel pipe piles should be reinforced with annular steel plates higher than 500 mm. This study focuses on an incident where the support system of a cast-in-situ box girder bridge experienced settlement due to the failure of Bailey beams, transverse beams, and steel pipe piles. These failures were primarily caused by inconsistencies between design and construction and a lack of attention to potential stress concentrations in certain components of the support system. In fact, the differences between design and construction are widespread and are one of the primary reasons for the failure of support systems during bridge construction. Therefore, the design, construction, and supervisory parties should work together to reduce the occurrence of such situations. Designers need to identify the most critical assumptions made during calculation and communicate these assumptions clearly to the construction team through a checklist. Construction and supervisory parties should implement these assumptions as much as possible and promptly report when they cannot be met. Furthermore, more attention should be given to potential stress concentrations in the support system. This requires designers to be aware of the limitations of beam element models when analyzing stresses at connection points. When stress concentrations are inevitable, the methods proposed in this study can be used to reinforce Bailey beams and steel pipe piles. [ABSTRACT FROM AUTHOR]

Experimental research was carried out regarding the flexural behavior of three full-scale external beam-column concrete joints cast with plain concrete in the presence of shear reinforcements in the joint regions constituted by horizontal and/or vertical stirrups and subjected to cyclic load reversals. Three specimens were designed to fail in the joint region. One had only one stirrup in the joint; another was confined with three horizontal stirrups in the joint; and one additional specimen had three horizontal and three vertical stirrups. The experimental results show that it is also possible to increase the shear strength of the joint regions and the bond strength of longitudinal bars of beams under cyclic reversal actions. From the analytical point of view, a simple model based on the limit state due to concrete crushing with horizontal and vertical transverse stirrups in both the elastic and plastic states was proposed with good prediction of experimental results and good results in comparison with other existing analytical expressions for shear strength prediction of joint regions. The original contribution of the research is to consider the concrete confinement of a strut member and its interaction with horizontal and vertical stirrups in the prediction of shear strength of a joint region. [ABSTRACT FROM AUTHOR]

In response to the increasing need for sustainable construction materials, numerous innovative timber-based structural systems have been developed in the past two decades. While timber-based shear-walls are popular, moment-resisting timber frames have received less attention in recent studies. However, with the availability of ductile and resilient beam-column joints (BCJs), timber frames can now be effectively used either independently or in combination with others. This study explores the feasibility of a dual system, consisting of cross-laminated timber (CLT) balloon shear-wall and glulam moment-resisting frame (CLTW-GMRF), and investigates the potential interaction between the two systems under seismic loading. The building features ductile and energy-dissipative BCJs and hold-downs. A seismic design procedure, based on a targeted moment proportion (MP) between the two systems, is presented and applied on a 10-story building. The building is assumed to be located in Vancouver, Canada, and its seismic performance is examined using 30 ground motion records in OpenSees. The system's efficiency with respect to engineering demand parameters is studied under different wall-to-frame MP values (50%–50% and 60%–40%) and ductility-related modification factors (2, 3, and 4). The study also investigates the system's performance with two BCJs and hold-down alternatives with bilinear hysteretic and self-centering energy-dissipative responses. Given the availability of resilient connections, the result highlights that the CLTW-GMRF coupled system is a viable alternative for high-rise hybrid timber construction. Moreover, the system's performance has significantly improved by using self-centering energy-dissipative systems. This paper unveils an innovative design approach and practical application for a CLTW-GMRF dual system. This innovative system incorporates energy-dissipative components that are designed and tested in existing literature: (1) the utilization of replaceable steel damper BCJs and buckling-restrained brace hold-downs, providing high ductility with large energy-dissipative capacity; and (2) the employment of hybrid BCJs made up of post-tensioned tendons and mild steel dissipators, along with hybrid brace hold-downs made up of pretensioned tendons and friction surfaces, which reduce residual deformations following seismic events. Utilizing these systems, the research introduces a versatile seismic design method congruent with existing codes and design standards, while offering flexibility through adjustable wall-to-frame moment proportions. The research also underlines the need for careful consideration of the interaction within the timber wall-frame systems. The implications are substantial amidst the growing trend of high-rise timber construction, aiming to fully exploit the potential of CLT and Glulam frames. Moreover, the research has the potential to serve as an essential resource for engineers aiming to optimize the sustainability and resilience of timber structures, particularly in seismic-prone regions. [ABSTRACT FROM AUTHOR]

This paper describes a component-based modeling approach for bare steel and composite beam-column joints subjected to quasi-static and impact loads under column removal scenarios. Two types of beam-column joints, viz. fin plate and welded unreinforced flange with bolted web, were simulated using the component-based modeling approach. The beam-column joints were discretized into individual springs consisting of various components. Material and geometry of the components were used to determine mechanical properties and failure criteria of the springs. After that, the springs were assembled together in a finite element package ABAQUS and component-based models were built. The joint models were validated against test results under quasi-static and impact loading scenarios. It was found that the component-based modeling approach performed well for both scenarios, with most of the relative errors less than 10%. Structural behavior of beam-column joints, including the development of load, axial force and bending moment for quasi-static loading scenario, as well as the development of displacement, axial force and bending moment for impact loading scenario could be captured by numerical simulations. The assumptions and limitations of the proposed modeling approach are presented as well. [ABSTRACT FROM AUTHOR]

Concrete and steel are typical rate-dependent materials. Therefore, the dynamic behavior of reinforced concrete (RC) members is inevitably affected by the loading rate. To study the effect of the loading rate on the behavior of RC beam–column joints (BCJs), a dynamic test was carried out on RC BCJs. Cyclic loading with various loading rates was applied to the column end of RC BCJs to simulate horizontal earthquake excitation. The final crack morphology and the first principal stress contour plots of BCJs indicate that dynamic loading can promote the shear effect in the core region of RC BCJs. The lower the shear span ratio is, the higher the loading rate and the more obvious the effect. Experimental results show that the yield strength and ultimate strength of BCJs are approximately linear with the logarithm of the loading rate. There is no obvious effect of the loading rate on the yield, ultimate, and failure displacements of the BCJ, but the shear angle of the core region is approximately linear with the logarithm of the loading rate. In addition, the effects of the loading rate on the stiffness degradation, ductility, and energy dissipation capacity are studied. [ABSTRACT FROM AUTHOR]

This paper investigates the effectiveness of local strengthening using textile reinforced mortar (TRM) jackets on the global response of reinforced concrete (RC) frames under gravity and lateral cyclic loadings. Finite element analysis (FEA) was employed to develop and validate an RC bare frame model against an experimental study in the literature. Consequently, four TRM strengthening configurations were applied considering the column's confinement and strengthening of joints and beams. With the aim to attain a ductile behavior of the frame, the selection of each configuration was based on the predicted failure of the preceding strengthening arrangement. A parametric study was performed to investigate the effect of the number of layers, length of TRM jackets, textile orientation, and distributed load values. Finally, the FEA models were compared with traditionally and noninteracting masonry infilled frames from the literature. By evaluating the local retrofitting influence on the global response of the frames, the strength and stiffness enhancements were marginal as compared to the control model. Local measures were more effective in the frame's post-peak response, hence, enhancing the ductility of RC frames. The TRM application to the beam-column joints resulted in substantially higher energy dissipation as compared to the model with no joint upgrading. When comparing the TRM local strengthening method to the global technique using infilled walls, the TRM retrofitted models showed similar energy dissipation to that of noninteracting masonry infilled specimen and lower values than those of the traditionally infilled frame. [ABSTRACT FROM AUTHOR]

This study aims to comprehensively investigate the reinforcement mechanism of the tunnel support structure and its supporting characteristics in layered and weak rock tunnels. Uniaxial compressive tests were carried out to study the mechanical and deformation characteristics of anchored rock with the system anchor bolt and the steel floral pipe. Besides, a three-point bending test of the steel–concrete composite beam was conducted to investigate the bending capacity of the grilles and I-beams. The experiment showed the following results: (1) The anchor bolt achieved the anchoring effect by improving the stress state and the strength of the surrounding rock. The improvement of the anchorage strength to the surrounding rock was reflected by the effect of the compression zone of preload, the healing effect of the anchorage agent on the surrounding rock, and the reinforcement effect of the anchor bolt on the density and strength of the anchor bolt. (2) By the CT scanning of the anchored samples after the experiment, it was found that the crack was blunted and arrested within the anchorage zone, and the crack-arresting effect was related to the range of the anchorage zone. The larger the anchorage zones, the better the crack-arresting effect. (3) The steel arch could effectively improve the ability of concrete antideformation. Compared with the lattice girder, the coordination ability of steel arch and concrete deformation was relatively weak. Its coordinate deformation stage was shorter than that of the lattice girder and earlier into the debonding stage. However, the stiffness of the steel arch and concrete was greater than that of the lattice girder after debonding and showed a strong bearing capacity. [ABSTRACT FROM AUTHOR]

Excessive residual displacements to the bridge structures were repeatedly observed after many previous major earthquakes, which may make the bridge structure lose its functionality and may have to be demolished and rebuilt. Reducing the residual deformation of bridge structures after a severe earthquake is a key research direction in earthquake engineering. Applying self-centering energy dissipation (SCED) braces to dissipate seismic energy and reduce the residual displacement is considered a good solution. Some research works have been carried out to investigate the seismic performance of double-column bridge piers equipped with SCED braces. However, these studies focused on the quasi-static behavior of the bridge piers only, and no previous study investigated their real dynamic response. This study investigates the seismic performance of reinforced concrete (RC) double-column bridge piers with SCED braces through shake table tests. Three 1/5 scaled bridge piers were designed, fabricated, and tested. In particular, the SCED brace was first designed based on the quasi-static performance of the bridge pier. The designed brace was then installed onto the bridge pier, and shake table tests were performed to explore the dynamic response of the bridge pier. For comparison, a bare bridge pier without a brace was also tested. The experimental results showed that the SCED brace could effectively protect the bridge pier from damage and minimize residual displacement. [ABSTRACT FROM AUTHOR]

Precast concrete (PC) and composite structures have been widely used in large industrial buildings for constructability and cost efficiency. The PC beams and composite columns are preferrable for use as long-span beams and large-sized columns, respectively, to realize efficient steel-concrete composite construction. The present study developed seismic details of the PC beam-to-composite column joint. A cyclic loading test was performed on the beam-column joints to investigate the seismic performance. For the test parameters, the connection details and the plastic hinge relocation were considered. The test results showed that the load-carrying capacity and deformation capacity of the specimens satisfied the requirements for intermediate moment frames specified in AISC 341-16. Further, the load-carrying capacities predicted using the plastic hinge relocation concept and the effective tension force of the bottom reinforcement at the PC beam section agreed with the test results. [ABSTRACT FROM AUTHOR]

A major disadvantage of the existing joint shear strength models is that they cannot consider the shear-resistance mechanisms and various uncertainties comprehensively. In order to overcome this limitation, a probabilistic shear strength model of reinforced concrete (RC) exterior beam-column joints was proposed. A simplified deterministic shear strength model for RC exterior beam-column joints was derived first by considering the contributions of the diagonal strut mechanism and truss mechanism. Then the probabilistic shear strength model for RC exterior beam-column joints was developed by taking into account both aleatory and epistemic uncertainties. Furthermore, the posterior distributions of probabilistic model parameters were updated by means of the Bayesian theory and the Markov chain Monte Carlo method. Finally, the proposed model was verified by comparison with 135 sets of experimental data and existing shear strength models. The results show that the proposed model has satisfactory prediction accuracy and low dispersion, which not only calibrates the influencing parameters on the prediction accuracy of the existing models, but also provides a probabilistic method to calibrate the confidence interval of the existing models. [ABSTRACT FROM AUTHOR]

In recent years, substantial efforts have been made to incorporate the nonlinear behavior of joints in frame analysis. In this regard, a well-established component-based model (CBM) is provided in EN 1993-1-8 to capture the nonlinear moment–rotation curve of steel beam-column joints. In this paper, to extend the design approach in EN 1993-1-8 to steel beam-to-reinforced concrete column (RCS) joints, a simple mechanical model is first developed to determine the moment resistance of RCS joints. The proposed model can predict two different failure modes of RCS joints and yields better accuracy and consistency compared to the current design method for such joints. After determining the joint moment resistance, an appropriate CBM is developed to simulate the nonlinear moment–rotation response of RCS joints. The proposed CBM can capture the moment–rotation behavior of RCS joints at elastic, transitional, and ultimate states. The initial rotational stiffness of RCS joints can be easily calculated based on the proposed CBM. This is particularly important in the frame analysis as the beam-column joint can be classified as a rigid, semirigid, or pinned joint based on the initial rotational stiffness. The derivations are discussed in detail, followed by verifications of the proposed CBM. Compared to the experimental results, the proposed CBM shows reasonable accuracy in predicting the moment–rotation behavior of RCS joints. Most importantly, the numerical procedure of the proposed CBM can be implemented by a spreadsheet method, which provides a simple and robust means for structural engineers to obtain the mechanical properties of RCS joints. [ABSTRACT FROM AUTHOR]

Following the 2010/2011 Canterbury and 2016 Kaikoura earthquakes, a number of reinforced concrete (RC) beams in high-rise structures developed a single primary crack at the beam-column interface without the formation of distributed secondary cracks along the beam length. Detailed assessments showed that these beams have conforming longitudinal steel ratios and the single-crack mechanism may be due to design and/or construction practices for beam-column joints in the 1980s. In order to investigate the seismic behavior of reinforced concrete beams with detailing that inhibited the spread of flexural yielding, an experimental program was carried out on RC beam specimens, having similar reinforcement detailing to that of beams that developed a single crack at their ends during the Kaikoura earthquake to understand their seismic behavior, postearthquake repairability, and residual low-cycle fatigue life. Experimental results showed that the beams were able to undergo significant inelastic drift demands without loss of lateral resistance and have sufficient residual drift capacity following moderate and large earthquake demands. The response of the beam specimens was dominated by hinge rotation via the bond-slip mechanism. Comparisons showed that the measured drift capacities of the beams exceeded the predicted drift capacities computed using state-of-the-practice procedures. [ABSTRACT FROM AUTHOR]

It is widely accepted that the seismic retrofitting of nonseismically detailed reinforced concrete beam-column joints (BCJs) in reinforced concrete (RC) frame buildings is an urgent necessity due to its high vulnerability and potential consequences in seismic events. As a result, considerable effort has already been put into developing efficient and practical retrofitting solutions for such BCJs. Most of the existing techniques, however, are based on either passive confinement techniques, for example, fiber reinforced polymer (FRP) wrappings, or involve a considerable joint enlargement, which, in many cases, is undesirable. In this study a new technique of retrofitting BCJs is proposed by employing a more effective method of confinement (i.e., active confinement), utilizing the shape recovery feature of shape memory alloys (SMAs). To evaluate the performance of the proposed retrofitting scheme, experimental tests were conducted on full-scale BCJ specimens. The efficacy of the proposed retrofitting scheme is evaluated in terms of enhancement in strength, ductility, energy dissipation capacity, damage reduction in the specimens, and ease of application. The results from this study suggest that the proposed retrofitting scheme could be effectively used in achieving the full capacity of the joints corresponding to beam yielding and consequently enhances the energy dissipation capacity of the system significantly. The test results demonstrated that the proposed retrofitting scheme performs excellently in reducing the joint shear strain (core damage) (to almost zero or negligible) and also in retaining the full axial load carrying capacity of the column, even at very large drift values. The proposed retrofitted scheme could also be conveniently used in cases where the capacity ratio of column-to-beam needs to be improved. This paper presents a novel retrofitting technique for beam-column joints of a reinforced concrete frame buildings. Beam-column joints that are either falling short of the minimum recommended strength to withstand medium to strong earthquakes or requiring an upgrade due to a change in use or class could be retrofitted using this technique. This proposed retrofitting scheme consists of two main components: (1) precast concrete attachments that are first attached to the column section near the joint region, and (2) shape memory alloy wire that is wound over the precast concrete attachment. The proposed scheme employs the unique material property of shape memory alloy wire. Shape memory alloy wire is a class of smart materials that have several unique material properties, including the shape memory effect used in this technique. The process requires heating of shape memory alloy wires to about 200–300°C. Heating shape memory alloy wires causes them to shorten due to shape memory effect and thus results in an inward pressure in the confined region. The inward pressure applied by the shape memory alloy wire spiral together with the supplementary stiffness provided by the precast concrete attachment makes the overall joint considerably stronger and ductile. The proposed technique could be easily used in retrofitting the external beam-column joints—the most critical ones. Moreover, it has a potential to be used in conjunction with other conventional materials, such as steel or fiber reinforced polymer, to reduce the overall cost of the retrofitting. [ABSTRACT FROM AUTHOR]

The grouted splice sleeve (GSS) connection is considered to be an effective bending moment–resisting connection between precast RC members. This connection type has been used extensively in nonseismic regions. The application of such a connection type in moderate or high seismic regions has been investigated and considered for multistory moment frame buildings and highway bridges. A computational modeling strategy is proposed at local and global levels for developing an appropriate computational model for such a connection type using a recessed GSS connection with intentional debonding. A computational model capable of predicting the structural response under cyclic loading was developed using established material models and a forced-based beam-column element considering low-cycle fatigue of reinforcing bars, bar-slip, intentional debonding of reinforcing bars, and plastic hinge length. The proposed model for recessed GSS connections with intentional debonding was experimentally validated. The proposed model was subsequently used to obtain the seismic response of a three-column bridge bent to near- and far-field earthquakes in terms of the overall maximum drift ratio and the drift ratio at the maximum seismic force. [ABSTRACT FROM AUTHOR]

Construction nonconformity assessment of buildings is critical to ensure the anticipated quality and living safety for their future occupants. Previous studies have paid less attention to identifying and analyzing building construction nonconformities (BCNs) in the design and construction (D&C) phases. They considered expert judgments in nonconformity assessment, which are critiqued for human bias, uncertainty, and imprecision. In a BCN assessment, previous studies also did not consider the specific time frame to detect construction nonconformities. This study aims to prioritize nonconformities in the D&C phases, addressing the limitations of expert judgment by applying the fuzzy group decision-making approach (FGDMA). The FGDMA computes the defuzzified scores of the nonconformities to prioritize and identify critical nonconformities. The defuzzified scores are explained further by associating them with the corresponding fuzzy numbers to address the limitations involved in expert judgments. The study also identifies the detection time of BCNs and analyzes 15 different Bangladeshi project scenarios to understand their context better. The critical nonconformities identified include premature stressing on concrete, inaccurate water-cement ratios, insufficient concrete compaction, lack of full-time site supervision, and the absence of stirrups in beam-column joints. Critical nonconformities are mostly identified during construction, and residential, commercial, and multipurpose buildings, regardless of ownership (i.e., public or private) and size, have experienced poor quality construction. This study will assist major stakeholders (owner, contractor, consultant, and regulatory authorities) to fully understand the critical nonconformities in different building projects from their preconstruction to construction phases for better quality assurance in providing a safe living and working environment for their future occupants. The study identifies critical nonconformities and their frequency, severity, and detection times in different construction projects, including residential, commercial, and multipurpose buildings and mosques. It also studies 15 different project scenarios for analyzing the nonconformities of government and privately funded/owned buildings. The most common nonconformities are premature stressing on concrete (loading to concrete members before gaining their design strength), inaccurate water-cement ratios, insufficient concrete compaction, and the absence of stirrups in beam-column joints. These nonconformities all occur due to lack of full-time site supervision and poor workmanship during construction. The dominating detection time for identifying the critical nonconformities is "during construction." Thus, it is possible to control many by careful supervision and improved workmanship during construction. The project scenario analysis shows that residential, commercial, and multipurpose buildings, regardless of ownership (i.e., public or private), experience poor quality construction. These findings will assist stakeholders with different engagement levels in managing their roles in building projects to deliver a better quality of construction, and hence a sustainable and safe living and working environment. [ABSTRACT FROM AUTHOR]

Due to a lack of test data on large-diameter headed bars, design provisions limit the bar diameter of headed bars to 36 mm or less. In exterior beam–column joints with two-layer headed bars as beam bars, if the layer-to-layer spacing of the headed bars is narrow, the side-face blowout area of an individual headed bar is overlapped. Existing design provisions do not consider the effects of layer-to-layer spacing. In this study, 34 simulated exterior beam–column joints were tested to examine the effects of bar diameters over the limitation of existing design provisions using large-diameter (41- and 51-mm) headed bars. The side-face blowout strengths of the two-layer headed bars were experimentally investigated through simulated exterior beam–column joints with layer-to-layer spacing of 2db (two times the bar diameter). The test results showed that the side-face blowout strengths had the same characteristics for bar diameters from 22 to 51 mm. For the two-layer headed bars, crack propagation and failure mode were the same as those for single-layer headed bars, but due to the overlap of the blowout area, the strength of the individual headed bar was reduced. A new model was proposed to predict the side-face blowout strengths of large-diameter high-strength headed bars in both a single layer and in two layers by incorporating a spacing factor for an individual headed bar into a model from the literature. A total of 173 test results from this study and previous studies were compared with predictions from the proposed model, and the average and coefficient of variation (COV) of test-to-prediction ratios were 1.08 and 17.4 %, respectively. [ABSTRACT FROM AUTHOR]

This paper presents a new strut-and-tie model (STM) based on provisions of ACI 318-19 and ACI 440.2R-17 for estimating the shear strength of fiber-reinforced polymer (FRP)-strengthened exterior joints. Beam–column joints are vulnerable elements in reinforced-concrete structures subjected to seismic loadings and similar extreme demands. The FRP strengthening technique offers numerous advantages for retrofitting joints in existing structures with inadequate reinforcement or confinement. The design of FRP-strengthened joints requires the development of reliable procedures, including equations to predict the shear strength of the joint. Existing literature and research on STM warrant the development of simple, reliable, and practical specifications applied to a wide range of design criteria. The proposed method involves an STM model containing horizontal and vertical mechanisms. The methodology compares predicted joint shear strength results with existing experimental results to obtain a reliable design approach. This comparison, along with verification of alternative analytical results, indicates the appropriateness of the presented model for predicting the shear strength of FRP-strengthened joints. Results contribute to the enhancement and efficiency of the practical design of these joints. [ABSTRACT FROM AUTHOR]

The architectural beauty of curved structures is recognized worldwide. Owing to their balanced form, vaults, domes, and arches were largely adopted over the last centuries. Currently, the erection of new curved masonry structures is dramatically reduced. However, strengthening existing arches is often required to prevent their collapse under static or seismic force. Present limitations regarding such constructions include the antiquated and expensive erection technique employed for curved members. Moreover, the assembly of provisional supporting structures (scaffolding) is generally time- and cost-consuming. Accordingly, the following research provides an innovative construction method that focuses on overcoming the drawbacks of the scaffolding-based approach. A fast lift-up technique was developed to reduce the time and costs of traditional construction techniques. Specifically, the required number of blocks that constitute the arch in this study was aligned side by side on the floor and then connected using a bonded strip of composite material (i.e., FRP—fiber-reinforced polymer). The middle block was then lifted. Thus, each corresponding block could be rotated around the contact point with the adjacent block. When all blocks left the floor, an arch shape was achieved. To validate the proposed method in terms of mechanical performance, an experiment was conducted, as reported herein. A traditional masonry arch built using scaffolding was tested for comparison, and two types of reinforced arches were tested until failure. The first was traditionally built and then reinforced, whereas the second was built using the proposed innovative technique. The specimens were instrumented and tested under a centered or eccentric vertical point load. In all cases, the composite application prevented failure of the hinged joints, as is typical of unreinforced arches, resulting in significantly increased loadbearing capacity, which registered scatters of |11|% and |28|% for the centered and eccentric loads, respectively, when comparing the traditional reinforced arch with the innovative solution. [ABSTRACT FROM AUTHOR]

High-performance fiber-reinforced cement-based composite (HPFRCC) is a class of construction materials that exhibit pseudo-strain hardening behavior under tension after first cracking and gradual softening behavior under compression after crushing. Compared to conventional concrete, the enhanced tension and compression performance make HPFRCC promising for earthquake-resistant structures. Extensive studies have explored the seismic performance of reinforced HPFRCC with different material designs and in different structural forms, while real-world applications are emerging. This paper is intended to summarize the collective knowledge that the research community has gained and to identify future research needs. We review (1) HPFRCC cyclic performance on the material level, (2) seismic performance of reinforced HPFRCC flexural members, including beams and columns, (3) shear-dominant members, covering coupling beams and structural walls, and (4) the behavior and design of HPFRCC beam-column joints. We conclude with key challenges and opportunities for the research and professional community. [ABSTRACT FROM AUTHOR]

By installing unsymmetrical chamfers on the soffits of beams, it has been proved in the earlier studies to be effective for strengthening nonseismically designed beam-column joints (BCJs). To generalize this, this study aims to extend the strengthening strategy to BCJs having upper and lower columns of different sizes. Such column eccentricity is not uncommon in gravity-load designed structures. In this study, experimental studies were conducted on six 2/3 scale specimens designed for joint shear failure, including three interior and three exterior specimens. The performance of specimens with nonseismic detailing was compared with that of having joint shear reinforcements or strengthened with chamfers. All specimens were under constant axial load and were subjected to cyclic displacements until failure. Response of chamfer under cyclic horizontal displacement was studied by analyzing the strains in chamfer. First and foremost, column eccentricity has both positive and negative influences on BCJs when subjected to cyclic displacements. Chamfer contributes to joint shear capacity when it is in compression. This leads to formation of an additional strut within the chamfer. For exterior joints, this phenomenon becomes obvious, and performance is improved when displacement is applied in one loading direction only. Lastly, width of additional strut formed in chamfer is associated with chamfer size. [ABSTRACT FROM AUTHOR]

This paper presents the study of the behavior of a precast continuous beam-column joint that bases its structural work on the friction by wedge effect. It was used in an industrialized social buildings system with excellent performance and is intended to extend its use to architectural programs for residential buildings, which requires the study of the behavior of the beam-column joint. A computational model calibrated against full-scale test results, based on finite element method (FEM) implemented in the software Abaqus, is used. The present paper aims to evaluate the influence of the geometrical and physical-mechanical parameters on the deformational state of the joint. The geometrical parameters are inclination of the column faces and beam ribs that shape the wedge, and the number of slots on these faces, which contribute to the transmission of bending moments of the joint. The physical-mechanical parameters are the axial load on the column and the compressive strength of the concrete of the wedge that joins the beam and the column. To evaluate this influence, the absolute and relative vertical displacements between the beam and the wedge and the lateral displacement experienced by the wedge are determined, and the statistical analysis of the results are included. The influence of the inclination of the column depression, beam rib faces, and the number of slots on these faces in the development of the wedge effect of the joint is demonstrated. The results also demonstrate the positive influence of the increase in axial load on the development of the wedge effect as well as the need not to use a concrete with a compressive strength greater than 20 MPa in the wedge. [ABSTRACT FROM AUTHOR]

The present study is focused on the retrofitting solution and its verification through experimental investigation for the two most common catastrophic modes of failure in reinforced concrete (RC) frame buildings, namely, buckling of reinforcing bars in the plastic hinge region of columns and shear failure of beam–column joints. The first mode of failure is retrofitted with interlinked coupler-box assemblies, while the second mode is repaired with external carbon fiber–reinforced polymer (CFRP) wrapping. The efficiency of the proposed retrofitting technique is evaluated by the hysteresis behavior, failure mechanism, and performance index parameters of the re-established frame, which are compared with the results of the initially tested bare frame. The recommended mechanism restricts the restored frame section against any possible movement or rotation and helps by a subsequent shift in yield location. The prime advantage of the proposed technique is that it prevents the possible slip of rebar from the sleeve, which is intercepted by the interlinking process, and eliminates the formation of inclined shear cracks at beam–column joints restricted by externally wrapped CFRP composites. The synergic effect of coupler-box and CFRP enhances the overall performance of the re-established frame by keeping the frame sections intact even after a lateral drift of 6%, which is relatively higher than the collapse prevention drift level, i.e., 4% as per FEMA guidelines. The obtained test results reveal the capability of CFRP and coupler-box assemblage as a possible futuristic approach for retrofitting outmoded RC building frames, in which buckling in longitudinal rebars of columns at their respective plastic hinge locations is inevitable. [ABSTRACT FROM AUTHOR]

This research work presents experimental and numerical findings of continuous rectangular spiral shear reinforcement of beam-column connections subjected to seismic type loading. A total of four exterior beam-column subassemblies with continuous, spirally bound, rectangular reinforcements and conventional stirrups as closed manner control specimens were considered. For the spirally strengthened specimens, three different stirrups angle inclines (75°, 80°, 85°) were adopted, and their performances were compared in terms of hysteresis pattern, failure behavior, skeleton curve, stiffness degradation, and energy dissipation. Specimens with stirrups inclination angles of 75°, 80°, and 85° exhibited 14%, 28%, and 19% improvements in terms of load-carrying capability over the referred specimen, respectively. In addition to that, a numerical investigation was also carried out using ATENA version 5.3.4 finite element software to validate the experimental result. The developed numerical model shows good correlation with the experimental result and can be used in the design of spiral-strengthened reinforced concrete (RC) members. [ABSTRACT FROM AUTHOR]

Beam–column joints in concrete buildings are critical for structural integrity under earthquake loading. Thus, accurate beam–column joint nonlinear models are important in seismic assessment and design of buildings. Most joint models in the literature are deterministic; the majority of which either are based on a small data set or do not distinguish failure modes and types of joints. This paper presents a data-driven probabilistic nonlinear model for concrete beam–column joints with transverse reinforcement. The model is based on multilinear regression using a newly developed database of 395 reinforced (confined) joints. Based on this database, current US seismic assessment provisions for beam–column joints were found to be conservative and have inconsistent levels of probability of exceedance for various nonlinear modeling parameters. The proposed probabilistic model unifies the level of probability of exceedance at 50%, a level that is consistent with the recently updated nonlinear beam and column provisions to avoid the bias in nonlinear assessment procedures. The proposed model exhibited good correlation with the test database, validation data sets, and cyclic backbones curves. Improved performance-based seismic design accuracy and economy for ductile concrete frames may result if current seismic assessment standards are updated based on the proposed model. [ABSTRACT FROM AUTHOR]

The seismic behavior of fiber-reinforced polymer-reinforced concrete (FRP-RC) columns is far from being fully explored. Therefore, numerical and analytical studies were performed to address the effects of different parameters and evaluate the current design provisions for confinement reinforcement under seismic loading. Using a commercially available software package, a three-dimensional nonlinear finite-element model (FEM) was constructed and validated against the experimental results of full-scale glass FRP (GFRP)-RC circular columns previously tested by the authors. The validated FEM was, then, used to conduct an extensive parametric study investigating the effect of concrete compressive strength, spiral pitch, axial load level, and column aspect ratio (i.e., shear span-to-depth ratio). It was found that increasing the concrete strength caused an increase in lateral load capacity and initial stiffness, whereas the drift capacity decreased. The latter property was also significantly affected by the variation of spiral pitch and axial load level. On the other hand, the aspect ratio had a marginal effect on moment or drift capacities. Using the results of the FEMs, two new design models were proposed. The proposed models showed remarkably better predictions than the equation adopted by the Canadian standard for the design of FRP-RC structures. [ABSTRACT FROM AUTHOR]

This paper introduces a novel technique called arched steel haunches with rib element (ASHR) for seismic retrofitting of RC frames. In this approach, the arched haunch is equipped with a steel ring or link, as the rib element (RE). A simplified physical model was proposed to approximate their behavioral curves. To evaluate the model's accuracy, a series of cyclic load tests on arched steel haunches, with and without RE, were conducted. The experimental responses showed that by increasing the RE stiffness, the maximum damping ratio decreased conversely, while the strength, plastic stiffness, and even dissipated energy increased. Accordingly, the tensile and compressive strength increased up to 1.5 and 1.35 times, respectively. However, the elastic stiffness did not vary compared to the reference specimens; the tensile plastic stiffness increased up to three times and, the ultimate secant stiffness in tension and compression enhanced up to 1.56 and 3.9 times, respectively. Moreover, the total energy dissipation upgraded up to 1.39 times with the fusing of the rib elements. It should be noted that the results of this pilot study will be used in future research on the experimental behavior of the reinforced concrete beam-column joints. [ABSTRACT FROM AUTHOR]

Reliable and robust numerical modeling of RC columns under lateral load is commonly performed using one-dimensional elements. Although the strain is assumed to vary linearly through the section, bond-slip and buckling of reinforcing bars at the joints/connections contribute substantially to the column response. This paper presents a three-dimensional (3-D) fiber-based model with explicit representation of the bond-slip that occurs at the column-footing interface for cast-in-place columns and at the interface between bars and mechanical couplers for precast columns with grouted sleeve (GS) connections. The model contains beam elements with fiber sections for concrete, beam elements for longitudinal steel bars and sleeves, and spring elements for interfacial bond-slip behavior. The novelty is that the model can be achieved using existing software implementations, retains the efficiency of fiber-based elements under cyclic loading, and parameters are calibrated based on component-level testing, unlike other resultant or hybrid models that require arbitrary backbone and cyclic property specification. An extensive experimental program was conducted to investigate the behavior of GS couplers and calibrate the bond-slip models. Four large-scale RC columns were then used to verify the proposed model by comparing the measured load-displacement, energy dissipation, curvature, and failure mode with the numerical responses. [ABSTRACT FROM AUTHOR]

A critical component of performance-based design (PBD) is the quantification of damage states in terms of engineering demand parameters (EDPs). One of the most widely used EDPs to define damage states of reinforced concrete bridge columns is the drift ratio. Here, a fiber-based numerical model was validated by comparing its damage predictions against experimental results for large-scale tests of reinforced concrete columns subjected to reversed cyclic loading. The Monte Carlo sampling technique was adopted to generate 1,000 well-confined and flexure-dominated concrete columns, each having a unique combination of aspect ratio, axial-load ratio, longitudinal and spiral reinforcement ratios, and concrete and reinforcing steel yield strengths. The columns were analyzed numerically under static pushover loading, and the drift ratios corresponding to various strain limits were recorded. The resulting data were fit to mathematical expressions through machine learning–based symbolic regression. The proposed simplified expressions well predicted the drift ratios obtained from the numerical analysis with a minimum square of the correlation coefficient of 0.88. Also, the predicted drift ratios from the proposed expressions were comparable to those measured experimentally at key damage states, such as concrete cover spalling, concrete core crushing, and bar buckling. In particular, the predictions of the proposed expression at rebar buckling, which was based on a reinforcing steel tensile strain of 0.05, were more accurate than two widely used expressions found in the literature. Finally, the application of the proposed expressions within the context of PBD was demonstrated by a numerical example. The proposed simplified expressions are not intended to replace pushover or nonlinear time history analyses as part of the PBD, but rather provide approximate predictions of the limit states, which would significantly facilitate the development of appropriate preliminary designs, especially at early design stages. In addition, since the predictions of the proposed expressions were validated using previous experimental data, they can serve as a benchmark for the bridge engineering community when determining the limit states of reinforced concrete columns through numerical analyses. [ABSTRACT FROM AUTHOR]

The extreme multihazardous event involving a truck collision and an air blast is a low-probability, high-consequence event for bridge piers. This study aimed to numerically investigate the performance and failure modes of multicolumn piers under a medium-sized truck collision combined with an air blast. Full-scale, finite-element models of multicolumn piers with three configurations were developed using LS-DYNA software with a soil domain restraining the foundations. The accuracy of modeling approaches was verified by comparing tested and simulated results. The collisions were simulated using a single-unit truck (SUT) at velocities ranging from 65 km/h to 120 km/h and combined with air blasts at different scaled distances. Analyses were completed to examine damage propagation and dynamic response during the extreme multihazards. The results showed that after the SUT collision compromised pier capacity, further deterioration occurred from the subsequent air blast, resulting in severe damage and even failure of the pier. In addition, parametric studies were conducted to assess the effects of several load and design parameters on pier performance and identify the controlling parameters. Representative failure modes of multicolumn piers under truck collisions combined with air blasts were assessed. The findings from this study provided a comprehensive understanding of multicolumn pier response to the extreme multihazards and developed recommendations for the practical design and analysis of the multicolumn pier. [ABSTRACT FROM AUTHOR]

This study presented an experimental and analytical investigation on the seismic behavior of a reinforced concrete (RC) interior joint with corroded reinforcements. A total of eight RC interior joints with similar reinforcing detailing were tested and subjected to lateral cyclic loading. The variables studied in this research were the corrosion level of reinforcements in terms of mass loss and the column axial force ratio. The cyclic performance of all the joints including crack pattern, lateral loading capacity, energy dissipation, and lateral displacement decomposition were examined. The corroded joint constitutive model was calibrated and validated using the finite-element method. An analytical strut-and-tie model (STM) was developed for explaining the internal force flow and further parametric investigations. Results indicated that corrosion of reinforcements had a substantial effect on the strength and lateral drift capacity of the joints. In addition, based on the STM model, the axial force ratio exceeding 0.3 and longitudinal reinforcement corrosion level around 6–10% were detrimental toward joint behavior and can contribute to joint shear failure. [ABSTRACT FROM AUTHOR]

This paper presents an analytical approach to predicting the shear strength of exterior beam-column joints without transverse reinforcement using a strut-and-tie model (STM). The proposed model contains a single diagonal strut with varied angle and width for modeling the shear behavior. Modeling analyses involve three approaches to determine the width and angle of the diagonal strut for the best prediction of experimental shear strength values. An experimental database of 25 exterior beam-column joints without transverse reinforcement and without confining out-of-plane members was developed to verify the accuracy of the model predictions. The presented analyses reveal that existing models may overestimate the shear strength of referenced joints and, therefore, highlight the need for a better fitting model. The discussions include a comparison of predicted joint shear strength values with existing experimental results using three different formulations. Moreover, the discussions examine existing code requirements and the reliability of the presented STM in comparison with code regulations. Concluding remarks supported by statistical measures highlight the fitness of the STM to safely predict the shear strength and identify the optimum approach to determining the model geometry. [ABSTRACT FROM AUTHOR]

Experimental research was carried out regarding the flexural behavior under cyclic reversal loading of six full-scale external beam-column concrete joints cast with plain concrete in the presence of shear reinforcements in the joint regions. The types of shear reinforcements adopted in the joint region were horizontal stirrups and inclined bars. All specimens were designed to fail in the joint region. One had only one stirrup in the joint, another had five stirrups in the joint, and three joints had a fix through diagonal bars of diameters 10, 12, and 14 mm subsequently inserted in inclined holes of diameter 20 mm created in the joint region of the existing reinforced concrete (RC) frames, and the holes were filled with epoxy resin. The experimental results indicate that it is possible to increase the shear strength of joint regions with inclined bars. The increase in shear strength was proportional to the increase in the amount of the steel area of the inclined bars, and the overall performances were comparable in terms of strength to that of well-confined joints. From the analytical point of view, a simple model based on the limit state of concrete crushing with transverse stirrups and inclined bars in both the elastic and the yielded states was developed and verified against the experimental results. [ABSTRACT FROM AUTHOR]

Short columns with deficiencies of low-strength concrete and large spacing of transverse reinforcement are quite common in construction practice in many developing countries in seismically active regions. Therefore, it is important to retrofit this type of column to avoid negative consequences in the case of severe damage. External fiber–reinforced polymer (FRP) jacketing is one of the most practical methods to retrofit reinforced concrete (RC) frame members against shear actions. However, knowledge of the seismic behavior of FRP-retrofitted RC short columns is still limited. Thus, the aim of this study was to investigate the seismic response of FRP-retrofitted low-strength RC short columns with and without predamage through the testing of 11 short column specimens representing old and deficient RC buildings. Accordingly, the results of a research program on the seismic behavior of such columns and on their repair and FRP retrofitting, covering experimental and analytical phases, are presented. In the experimental phase, test results obtained for short columns, FRP-retrofitted short columns, and repaired and retrofitted short columns are documented. Test results provide important knowledge about the effects of extremely low-strength concrete, and of different levels of predamage on the behavior of FRP-retrofitted substandard short columns. In the analytical phase, the performance of relevant design documents in predicting the shear strength of such columns retrofitted with FRP jacketing was tested through the comparison of predicted and experimental results. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the seismic performance of a steel frame with an external diaphragm joint between a concrete-filled steel tube (CFST) column and H-shaped steel beam through experiments and finite-element (FE) analysis. A quasistatic test was conducted on five steel frame specimens. The parameters involved in the test were joint stiffness, beam-to-column stiffness ratio and concrete strength. Based on the experimental results, failure mode, lateral load versus displacement hysteretic curve, skeleton curve, strength and stiffness degradation effects, ductility, and energy dissipation capacity were analyzed. The experimental results show the hysteretic curves have a plump shuttle shape; the strength degradation effect and stiffness degradation effect are relatively feeble; and the ductility and energy dissipation capacity are excellent. Therefore, the tested specimens have good seismic performance. Also, this suggests that larger joint stiffness brings about superior seismic performance; a stronger column leads to higher bearing capacity as well as inferior ductility and energy dissipation capacity; and a CFST frame performs better than a hollow steel tube column frame under cyclic loads. On the basis of the experimental results, the ABAQUS software version 6.14 was adopted to establish the FE models. The applicability and accuracy of FE simulation were first verified by experimental results. Then, quantitative parametric analysis was carried out to study the effects of different parameters on seismic performance of the CFST frame with an external diaphragm joint. [ABSTRACT FROM AUTHOR]

In reinforced concrete (RC) moment frames, the performance of the whole structure to provide a suitable strength against lateral loads depends on the behavior of each structural element. Therefore, the capacity of such members plays a vital role in the final response of RC buildings. However, the nonlinear nature of complex materials like concrete and its combination with other parameters makes the calculation of capacity more difficult. An estimation of the strength is a critical challenge in civil engineering with many applications, especially for damage detection, retrofitting, and strengthening programs. In this article, new computational frameworks are evaluated to introduce innovative approaches with the aim of determining the structural capacity of beams, columns, and joints in RC frames using soft computing (SC) techniques. Neuro-fuzzy models, group method of data handling (GMDH), and, also, three different structures of neural networks are presented and discussed. To this end, three collections of experimental datasets are gathered to assess the models. Moreover, mathematical equations are extracted from the considered systems for practical usages. Finally, the best predictive model for each structural element is proposed in detail. A comparison study between the results obtained from the presented methods and the laboratory values indicates that the proposed models can estimate the capacity of the elements with high accuracy and can be used as a powerful tool for evaluating the capacity of the structural members of RC frames. [ABSTRACT FROM AUTHOR]

Beam-column (BC) joints play an important role in the seismic performance of moment-resisting RC frame structures. Several techniques have been suggested to improve the seismic efficiency of BC joints, but these techniques have been criticized for being labor-intensive and/or vulnerable to premature debonding. To overcome these deficiencies, a novel stochastic lattice structure is proposed in this work to improve the shear-deficient RC BC joints. The optimization procedure was carried out for different shapes of stochastic lattice structures that give the maximum shear capacity, and the shear capacity is compared with the designed exterior standard beam-column joint. The expression for shear capacity of the stochastic lattice structure was formulated by considering a unit cell of 10 mm length. The maximum shear capacities of the triangle, hexagon, and pentagon shapes were obtained by varying the cell angle and length. The results of different cell shapes were compared with the allowable shear stress of designed beam-column joints. In addition to the optimization procedure, three-dimensional (3D) finite-element (FE) models were developed to study the behavior of the joints using the optimized stochastic lattice in the joint core. Compared with the control specimen, the beam-column joints with the proposed lattice give much better performance in terms of cumulative energy dissipation, lateral stiffness, joint shear deformation, and angle of beam rotation. [ABSTRACT FROM AUTHOR]

With the recent increased use of precast concrete (PC) structures, their progressive collapse resistance under hazardous conditions, such as explosion and fire, has become a great concern for the structural engineering community. In this study, static push-down tests were performed on eight PC beam-column substructures, in a column removal scenario due to fire, to investigate their progressive collapse resistance. The test specimens were classified into four groups, and static loading was applied to them under and after fire in a specially designed hybrid heating furnace. The test parameters were the wet-connection details in PC beam-column joints and the timing of high temperature. Structural performance and failure modes were evaluated, including thermal responses, load-displacement relationships, temperature–axial force relationships, and beam moment–axial force relationships. The test results showed that in the joint specimens using a lap splice connection and/or at high temperature, insufficient compressive arch action (CAA) and catenary action (CTA) developed. [ABSTRACT FROM AUTHOR]

Precast concrete frames have been widely used, though little is known about their fragility under the combined influence of seismic excitation and corrosion. In this study, one four-story precast concrete frame with different corrosion levels is taken as an example, which is simulated by using a multiscale finite-element model consisting of solid elements for corroded beam-column joints and beam elements for beams and columns, respectively. A fiber model is proposed to simulate the hysteretic behavior of corroded steel bars by employing the user-defined material subroutine in Abaqus. The proposed multiscale finite-element model is validated through existing experiments, so that a balance between accuracy and computational costs is obtained. Based on the proposed finite-element model, the influence of corrosion on seismic fragility of the frames is investigated through incremental dynamic analysis. Four limit states regarding the maximum interstory drift ratio are defined to evaluate seismic fragility. The analysis results show that structural responses are highly random under different ground motions and corrosion levels. Meanwhile, the seismic fragility of the frame is significantly influenced by corrosion ratios, and the probabilities of exceedance show exponential growth with the increase of corrosion level for all four limit states. [ABSTRACT FROM AUTHOR]

For performance-based design of reinforced concrete moment frames, the inelastic load-displacement relationship including strength degradation of beam-column joints should be accurately defined. In this study, a simplified design equation for joint shear strength was developed, addressing the effects of the target story drift ratio, beam rebar detail, joint configuration ratio, and joint hoops. Using the proposed method, a plastic hinge element was developed for nonlinear numerical analysis of beam-column connections. The proposed model was applied to existing interior and exterior beam-column joint specimens with or without joint hoops. The predicted lateral load-drift ratio relationships were compared with the test results and current design models. An existing cyclic behavior model was also implemented in the proposed plastic hinge model for time history analysis. [ABSTRACT FROM AUTHOR]

This paper presents experimental and analytical investigations carried out on RC beam–column joints incorporating engineered cementitious composite (ECC) material in the beam–column joint region. Six interior and exterior beam–column joints with different reinforcing detailing in the joint cores were designed and tested. Representative column axial loading and quasi-static lateral cyclic loadings were applied. Hysteresis behavior, crack patterns, joint shear stress, energy dissipation capacity, and strain profiles of reinforcements were examined. Results demonstrated ductile failure with flexural plastic hinges generated in the adjacent beams, which indicated an improvement of the joint shear capacity with the application of ECC. An analytical truss model for ECC joints was developed to investigate the joint shear force transfer mechanism. The predicted internal force flow of the ECC joints under seismic action yielded a reasonable correlation with the crack pattern. The effect of the joint transverse reinforcement also was studied based on the analytical model. A parametric study was performed via a validated finite-element analysis. Results indicated that higher column axial loading was detrimental to the performance of the joints, especially above an axial load ratio of 0.3 for joints incorporated with higher strength ECC. In addition, joint transverse reinforcements still needed to be added in some cases to avoid joint shear failure. [ABSTRACT FROM AUTHOR]

The failure of beam-column joints in RC frame buildings induced by a strong earthquake can lead to the collapse of buildings. Therefore, numerous experimental studies have been carried out on beam-column joints made with natural aggregate concrete (NAC). However, only a few experimental tests have been conducted on recycled aggregate concrete (RAC) beam-column joints. This paper presents an experimental investigation of the seismic behavior of various types of RAC beam-column joints. A series of five RAC beam-column joint specimens, including three interior joints and two exterior joints, were tested under quasi-static cyclic loading and their behaviors were evaluated in terms of strength, stiffness, cumulative energy dissipation, damping ratio, and damage indexes at different load steps. The influence of joint type, column axial compression level, stirrup ratio in the joint panel, and longitudinal reinforcement ratio on the seismic performance of RAC joints was evaluated. The validity of RC joint shear strength models proposed by different building codes to predict RAC joint shear strength were examined by comparing the experimental shear strength values with analytical results. [ABSTRACT FROM AUTHOR]

This study presents the experimental and analytical investigations carried out on high-strength concrete beam-column joints with Grade 700 longitudinal bars in beams and columns. Seven full-scale interior RC beam-column joints with various reinforcement detailing were designed according to the specific seismic provisions of current building codes. Test specimen variables included concrete compressive strength, reinforcement yield strength, and axial compression loading level. The test specimens were subjected to constant column axial loading and quasi-static lateral load reversals. The performance of each test assembly was examined in terms of cracking patterns, lateral loading capacity, reinforcement strain profiles, secant stiffness, energy dissipation capacity, joint shear strength, and bond performance. All specimens displayed ductile failure mode and it is concluded that the use of high-strength concrete and applied axial compression loading can improve specimen bond conditions. Parametric studies via finite-element analysis were performed to examine the influence of various parameters on the strength, bond condition, and energy dissipation capacity of the specimens. In addition, a backbone curve model for the shear behavior of the joints is proposed. An explanation for the observed cracking pattern and further analytical investigation on the joint shear capacity of the specimens is presented. [ABSTRACT FROM AUTHOR]

A three-dimensional surrogate model is presented for the seismic performance assessment of cylindrical atmospheric liquid storage tanks. The proposed model consists of a concentrated fluid mass attached to a single vertical beam-column element that rests on rigid beam-spokes with edge springs. The model is suitable for rapid static and dynamic seismic performance assessment. Contrary to other simplified models for tanks, its properties are determined through a simple structural analysis that can be performed in any nonlinear analysis software, without the need for complex finite-element models. The results compare favorably to those of three-dimensional finiteelement models on three tanks of varying aspect ratios. A step-by-step example of the modeling procedure is presented for a squat unanchored tank, and a sensitivity analysis is conducted in order to investigate the effect of various modeling parameters on the seismic response of the proposed tank model. [ABSTRACT FROM AUTHOR]

Welding defects and fatigue cracks in full-penetration welded beam-column connections, resulting in partial-penetration welds, are found in existing steel moment-resisting frame bridge piers. The welding defects may have an unfavorable effect on the seismic performance of a large number of existing piers, most of which have been in operation for over 50 years. This study aims to clarify the effects of the weld profile, e.g., weld leg length, penetration depth, and incomplete penetration depth, on seismic performance of the beam- column connections in existing piers with welded box sections. The effect of gusset stiffeners (termed fillets in this paper) at the beam-web-to-column-web joint on the improvement of seismic performance is also studied. In this study, experiments on 10 specimens with different incomplete penetration depths and fillet radii are performed under quasi-static cyclic large displacement loading. Based on the test results, cracks may initiate either at the beam end or at the weld of the beam-flange-to-column-flange joint, and the sum of the external and internal total weld leg lengths is a dominant parameter that affects crack propagation at the joint. In addition, the fillet at the beam-web-to-columnweb joint can delay the decrease in the load-carrying capacity. [ABSTRACT FROM AUTHOR]

The nonobjective disadvantages of the force-based frame element, such as the nonobjective curvature prediction, have been discussed by many researchers. The trial-and-error method is commonly used to determine element size, but it could cost tremendous computational efforts. This paper proposes and analytically studies the optimal element size for reinforced-concrete piles for bridges when using forcebased beam elements. In this study, the relationship between the optimum element size and integration point number is investigated, and the equivalent plastic hinge length is used and correlated to the optimal element size, on the basis of which the moment-curvature and forcedisplacement responses are objective and the soil effects on the pile response could be simulated sufficiently as required. The results of a case study show that both the local and global responses can be very well predicted, and the nonobjective disadvantage of the force-based element could be eliminated using the proposed optimal element size. Additionally, the optimal element size with more than two integration points is suggested for modeling the plastic hinge in the pile above the ground. [ABSTRACT FROM AUTHOR]

The demand for sustainable concrete structures with longer service life and lower maintenance cost has been driving the use of glass fiber-reinforced polymer (GFRP) reinforcement in new concrete structures. The behavior of GFRP bars under seismic loading in reinforced concrete (RC) frame structures has not been widely investigated. Furthermore, the ability of FRP-RC frame structures to dissipate energy in seismic events is still questionable due to the elastic-linear behavior of the FRP reinforcement. Very few studies have been conducted on the seismic behavior of GFRP-RC exterior beam-column joints, and none studied the shear capacity of joints. Therefore, this study attempts to partially fill this gap by investigating the shear capacity of beam-column joints reinforced with GFRP bars and stirrups. Six fullscale exterior beam-column joint prototypes (T-shaped) were constructed and tested under simulated seismic load conditions. Test parameters in this study included the concrete strength and the shear stress level in the joint. Diagonal shear failure in the joint exhibited in some specimens showed the significance of evaluating the shear capacity in the joint. [ABSTRACT FROM AUTHOR]

The presented studies have been conducted on the scope and magnitude of damages inflicted by earthquakes over the years. Many RC buildings, designed and constructed in the 1960s and 1970s, have serious structural deficiencies, especially in their beam-column joints. Such deficiencies result from inadequate joint shear strength or confinement of column reinforcement. The joints require elaborate retrofit measures to ensure the performances comparable to those of new designed structures. In this research, a new seismic retrofitting method is presented for beam-column joints based on the two-dimensional enlargement of the joint by using steel plate, angles, and posttensioning rods. The seismic adequacy of deficient RC beam-column joints, and the efficacy of steel plates and posttensioning rods, have been investigated for retrofitted joints through experimental and numerical analyses. According to the results obtained through investigations, this new rehabilitation scheme is effective, simple to install, and nondisruptive to the function of the building. The behavior of the experimental results has also been successfully predicted by a finite-element model. [ABSTRACT FROM AUTHOR]