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Under seismic loading, corroded reinforced concrete (RC) columns are prone to brittle shear failure, which poses a significant threat to existing structures. However, due to the mechanical defects and insufficient parameters included in the equations available in codes, the literature exhibits a lack of precision in predicting the shear strength of such columns. In this paper, a shear strength equation for the RC column was established based on the truss-arch model theory. On this basis, the effect of corrosion on key parameters such as the cross-sectional area of rebar, yield strength, compressive strength of concrete, and displacement ductility was fully considered to establish the shear strength equation of corroded RC columns. To assess the accuracy and applicability of the proposed equation, a database consisting of 215 specimen parameters was compiled. Comparative analyses were conducted with existing equations from the literature. The results indicate that the mean values and coefficient of variation for the ratio of calculated values to the tested values of the equation were 1.098 and 0.601, respectively, which proves the equation's high computational accuracy and low dispersion. Consequently, the proposed equation offers a more effective calculation method for predicting and assessing the shear strength of corroded RC columns. This method holds significant potential for enhancing the resilience of structures in seismic-prone regions. [ABSTRACT FROM AUTHOR]

Steel-reinforced concrete decks are prominently utilized in various civil structures such as bridges and railways, where they are susceptible to unforeseen impact forces during their operational lifespan. The precise identification of the impact events holds a pivotal role in the robust health monitoring of these structures. However, direct measurement is not usually possible due to structural limitations that restrict arbitrary sensor placement. To address this challenge, inverse identification emerges as a plausible solution, albeit afflicted by the issue of ill-posedness. In tackling such ill-conditioned challenges, the iterative regularization technique known as the Landweber method proves valuable. This technique leads to a more reliable and accurate solution compared with traditional direct regularization methods and it is, additionally, more suitable for large-scale problems due to the alleviated computation burden. This paper employs the Landweber method to perform a comprehensive impact force identification encompassing impact localization and impact time–history reconstruction. The incorporation of a low-pass filter within the Landweber-based identification procedure is proposed to augment the reconstruction process. Moreover, a standardized reconstruction error metric is presented, offering a more effective means of accuracy assessment. A detailed discussion on sensor placement and the optimal number of regularization iterations is presented. To automatedly localize the impact force, a Gaussian profile is proposed, against which reconstructed impact forces are compared. The efficacy of the proposed techniques is illustrated by utilizing the experimental data acquired from a bridge concrete deck reinforced with a steel beam. [ABSTRACT FROM AUTHOR]

Standard fire resistance tests and post-fire tests on residual mechanical properties were carried out on two four-edge simply supported reinforced truss concrete two-way composite slabs with wide seam splicing ("integral seam") and close seam splicing ("separated seam"), and the effects of the different splicing forms on the mechanical properties of the reinforced truss concrete composite slabs during and after exposure to high temperatures were explored. The results indicate that there are significant differences in terms of crack developments, moisture loss times on the slab surface, spalling characteristics of the bottom of the slab and cross-section temperature gradients of concrete and steel reinforcement along the thickness direction between the wide seam spliced reinforced truss concrete composite two-way slab (referred to as "S1 composite slab") and the close seam spliced reinforced truss concrete composite two-way slab (referred to as "S2 composite slab") in the fire test. This is mainly due to differences in the splicing forms and structural measures of the prefabricated base slabs at joints, which led to changes in the heat transfer path at the joints. As the temperature at the close seam can be released quickly, the stiffness recovery of the S2 composite slab is significantly greater than the stiffness weakening due to the thermal hysteresis of the concrete, so the deflection of the S2 composite slab recovers immediately after the fire stops. Overall, both the S1 and S2 composite slabs exhibit two-way high temperature deformation characteristics. The post-fire residual static load tests show that the static load-carrying capacity of the S1 composite slab is 12.08% higher than that of the S2 composite slab and the ultimate displacement is 8.74% lower than that of the S2 composite slab. It is appropriate to calculate the residual load capacities of the S1 and S2 composite slabs after the fire as a one-way slab. [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]

A probabilistic classification criterion was proposed to classify likely failure modes of reinforced concrete (RC) columns under seismic loading conditions. The accuracy and applicability of available flexure and shear strength models were scrutinized first to calculate the ratio of shear demand to shear strength (m). Then the probabilistic distribution characteristics of m, shear aspect ratio (λ), and transverse reinforcement ratio (ρsv) were examined to determine the probability of RC columns failing in different failure modes. Subsequently, a probabilistic classification criterion for likely failure modes of RC columns was suggested by considering the coupling effects of m, λ and ρsv. Finally, the classification accuracy of the proposed classification criterion was corroborated by comparing with existing classification criteria. Results reveal that the classification accuracy of the proposed probabilistic criterion is about 20% higher than those of existing classification criteria for RC columns failing in flexure, flexure-shear, and shear critical modes. The failure modes of RC columns progressively change from ductile flexure failure to flexure-shear, and then shear critical failure mode with the increase of m, and the decrease of λ and ρsv. [ABSTRACT FROM AUTHOR]

This paper examines the influence of variable axial force on the seismic performance of flexural domain reinforced concrete (RC) columns through experimental testing of five full-scale specimens. The test results demonstrate that fluctuating axial force, when combined with simulated cyclic seismic loading, significantly impacts the flexural behavior of RC columns. The behavior of RC columns under fluctuating axial loads was markedly different from that of columns under constant axial loads. A notable observation was that the failure mode of the columns transitioned from ductile flexural failure to flexure-shear failure when comparing columns subjected to constant axial loads to those subjected to fluctuating axial loads that alternated between compression and tension. This study further demonstrated that the lateral load capacity of the columns, along with their deterioration, was significantly influenced by both the fluctuating pattern and intensity of the axial forces, as well as the displacement ductility. An empirical equation was proposed to estimate the residual lateral load capacity of flexural domain RC columns under varying axial forces, providing a practical tool for designers to assess the behavior of columns under different loading conditions. To corroborate the conclusions drawn from the experimental investigation and gain further insights into the influence of fluctuating axial force on the seismic behavior of flexural domain columns, this study additionally proposes a finite element (FE) model. According to the experimental and numerical results, an empirical equation to estimate the ultimate drift capacity of RC columns subjected to varying axial force is also proposed. • Experimental investigation on seismic performance of flexural reinforced concrete column subjected to varying axial forces. • Finite element model was proposed to corroborate the conclusions drawn from the experimental investigation. • Two empirical equations were proposed to estimate the residual lateral load capacity and ultimate drift capacity. [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]

An analytical model based on the strut-and-tie method for predicting the shear strength of reinforced concrete (RC) interior beam-column joints is introduced in this paper. Both contributions from truss and strut mechanisms are included in the analytical model. The contributions of concrete and transverse reinforcements based on EC2 [2004] are incorporated in the truss mechanism, whereas the strut mechanism is calculated based on the effective compressive strength of concrete. The deformation compatibility between the truss and strut mechanisms is also incorporated in the proposed model. The proposed model is validated by comparison with available experimental database. The validated results show a satisfactory correlation between the proposed model and available experimental database. The proposed model is also compared with the NZS 3101 [1998]; ACI 318 [2002]; and Hwang and Lee [2000]'s joint shear strength model and an improved performance is found. [ABSTRACT FROM AUTHOR]

Analytical investigations were carried out on high-strength concrete beam–column joints reinforced with high-strength steel rebars. The bond performance of test specimens was evaluated and compared with building code provisions. An analytical approach was obtained to study the influence of various patterns of column axial loading on the failure mechanism of beam–column joint subassemblies. In addition, a finite-element study was conducted to investigate the seismic behavior of reinforced concrete beam–column joints designed with high-strength materials. A novel recommendation for the joint depth to beam bar diameter ratio and the comparison between the proposed equations and those suggested by codes was presented. [ABSTRACT FROM AUTHOR]

Peak shear strength is a critical parameter in the evaluation of the seismic performance of structural walls. Different equations have been proposed to predict the peak shear strength of reinforced concrete squat walls in literature, which assume lateral loading is parallel to the web. In reality, however, seismic waves can reach structures from any direction, which necessitates the studies on the behavior of structural walls under various lateral loading directions. Unlike rectangular walls, non-rectangular walls naturally possess the capacity to resist lateral loads in both transverse and longitudinal directions. To explore the peak shear strength of such walls under different lateral loading directions, a widely used nonlinear finite element software Diana 9.4 was utilized in this article. Appropriate modeling approaches were first selected and further validated by simulating relevant experiments. Then a comprehensive parametric study was carried out to investigate the influence of lateral loading directions and other important parameters. [ABSTRACT FROM AUTHOR]

Considerable progress has been made on the research of non-rectangular reinforced concrete (RC) squat walls over the past decades. However, the experimental data of L-shaped RC squat walls remain limited, especially for their seismic behaviors under non-principal bending actions. This paper presents an experimental and numerical investigation on L-shaped RC squat structural walls with an emphasis on how varying the directions of lateral cyclic loading influences the seismic responses of these walls. Four L-shaped specimens are tested under lateral cyclic displacements and low levels of axial compression The variables are axial loads and lateral loading directions. The performance of specimens is discussed in terms of cracking patterns, failure mechanisms, hysteretic responses, deformation components and strain profiles. Furthermore, three-dimensional finite element models are developed to supplement the experimental results. The direction of lateral loading is found to have a significant effect on the peak shear strength of L-shaped RC squat walls. [ABSTRACT FROM AUTHOR]

A unique reinforced concrete column design method which aims to improve the ductile behavior of reinforced concrete columns by utilizing various steel grades for longitudinal reinforcements is evaluated in this article. Six large-scale reinforced concrete columns were tested, with the columns subjected to axial load and cyclic forces under reversed bending. The parameters varied in the test program including the axial loading level and the ratio and strength of longitudinal steel reinforcement. It was found from the test results that utilizing longitudinal high-strength steel reinforcement by the ratio of 30%, 50%, and 100% of the total longitudinal reinforcement in a column section will increase the lateral loading drift capacity by 18%, 26%, and 55% on average, respectively. Parametric studies via nonlinear finite-element approach were performed to study the influence of various design parameters on the ultimate drift capacity of reinforced concrete columns. The correlation between the ultimate drift capacity and the confinement level, the axial loading level, and the ratio and grade of longitudinal high-strength reinforcing bars was investigated. Design charts for various ultimate drift levels in terms of other design parameters were developed. [ABSTRACT FROM AUTHOR]

Given that the biaxial hysteretic model of shear-critical reinforced concrete columns is usually developed by incorporating with the single-degree-of-freedom system to write its expression in differential equation of motion control, it is unfeasible to match with the experimental data of the biaxial quasi-static testing in terms of force-displacement relationship. Therefore, a simple and effective biaxial hysteretic model is proposed in this study based on the Bouc–Wen–Baber–Noori model for characterizing the biaxial quasi-static testing of shear-critical reinforced concrete columns. An incremental numerical algorithm is then proposed to solve the pair of coupled differential equations based on the backward Euler discretization method and Newton–Raphson iteration scheme. Moreover, the influence of critical model parameters affecting the typical hysteretic characteristics of shear-critical reinforced concrete columns, such as strength deterioration, stiffness degradation, pinching phenomena, and biaxial coupling effect, is investigated, respectively, to demonstrate the capability of the biaxial hysteretic model developed. Finally, a parameter calibration procedure using the differential evolution algorithm is introduced to calibrate the magnitude of involved model parameters by comparing with the experimental data of the biaxial quasi-static testing. According to the investigation, it is found that the developed biaxial hysteretic model can reasonably describe the typical hysteretic characteristics of shear-critical reinforced concrete columns under biaxial quasi-static excitation. Following the proposed parameter calibration procedure, the biaxial hysteretic model developed produces the biaxial hysteretic loops of shear-critical reinforced concrete columns, which is in good agreement with the experimental data once the magnitude of involved model parameters is calibrated. [ABSTRACT FROM AUTHOR]

The effective stiffness of a structural wall is an important property in design, which many design codes estimate by the moment inertia of the wall section with a reduction factor. The reduction factor is typically estimated by empirical equations based on configurations of the wall. The existing methods for the reduction factor were proposed based on investigations on rectangular reinforced concrete (RC) walls. The effective stiffness of non-rectangular RC walls can be more complex than that of rectangular RC walls. As such, more research investigations are required. Based on finite element models, the effective stiffness of U-shaped and T-shaped RC walls was investigated in this paper. The numerical results were further adopted to develop methods for calculating the effective stiffness of non-rectangular wall in different loading directions. The proposed method was afterward compared with the experimental data. [ABSTRACT FROM AUTHOR]

The shear lag effect is a commonly reported observation in tests on flanged reinforced concrete (RC) structural walls. This effect is conventionally ignored but more evidence has shown that calculation and analyses ignoring this effect could significantly overestimate flexure strength and stiffness. Existing research indicates that well distributed diagonal cracks exist in the flange of the flanged RC walls with the shear lag effect and the effect should be calculated based on shear stiffness of the cracked concrete. A truss model was proposed but the model can only consider the effect at the bottom sections of cantilever flanged walls loaded at the top which therefore precludes its application in the design of flanged RC structural walls. This paper presents an improved truss analogy for calculating the shear lag effect for flanged section at any height of RC walls with any lateral load distributions. Predictions of the proposed method are compared with available experimental data and finite element (FE) results. The method is then applied to improve the fibre beam-column element models to generate a new prediction model which was found to predict to be able to accurately predict the flexure stiffness of RC walls. [ABSTRACT FROM AUTHOR]

With the increasingly real threat of terrorism around the world, many iconic and important buildings may become targets of terrorist attack. This can lead to severe casualties and economic losses as such extreme loading events are not considered in conventional building design. However, experience from past events has shown that most well designed structures will not completely collapse immediately upon the loss of one or more columns as in cases of sabotage. As such, the residual load resisting capacity is crucial in post damage situations where engineers have to make a decision of whether to rehabilitate or rebuild the damaged building. To better understand the behavior of such damaged structures, a series of tests are conducted in this present study. The dynamic response of the specimens is assessed through dynamic tests. Following dynamic tests, the specimens, which have suffered different degrees of damage, are re-tested by push-down loading regimes to capture their residual behavior. The experimental and analytical results indicated that the damage caused by the dynamic response will significantly degrade the initial stiffness and detriment the efficiency of compressive arch action and compressive membrane action even if the specimens actually only experience elastically dynamic response. However, when the specimens undergo a considerable plastically dynamic response, no compressive arch action and compressive membrane action are able to develop. The load resisting capacity would derive mainly from tensile membrane action and catenary action in large deformation stage. [ABSTRACT FROM AUTHOR]

The seldom investigation of variable length of damage region prevents the estimation of probabilistic drift limits of reinforced concrete columns at different performance levels for the performance-based seismic design. However, if using the numerical approach to predict the variability of damage region within the framework of force-based beam-column element, the current force-based beam-column element is unable to model the spreading of damage region. Therefore, a new numerical simulation method is proposed to compute the emergence, propagation and termination of damage region of reinforced concrete columns. Then, based on the developed numerical simulation method, the measured response of experimental testing is calibrated. From the calibration, it can be observed that there is a rapid increase on the variable length of damage region with the increasing of lateral displacement and then followed by a stable stage. The propagation of the longitudinal reinforcement yielding and concrete tensile cracking mainly occurs in the ascending branch of the load–displacement response. Then, based on the growth characteristic of the damage region from the numerical simulation, an empirical equation is proposed to describe the variable length of damage region by using the least-square regression analysis to fit the computed responses for its simplicity to use in engineering practices. Finally, the stable length of damage region is reinvestigated by carrying out a parametric study with the developed numerical simulation method, indicating that two critical design parameters, specifically the axial load ratio and the shear span ratio, have considerable influences on this quantity of interest. [ABSTRACT FROM PUBLISHER]

A new method for considering the shear lag effect in the flange of reinforced concrete (RC) walls with flanged sections is proposed. The method is developed based on the truss analogy for the cracked flange segment in tension. Comparisons with the experimental data reveal that the proposed method can predict the influence of the shear lag effect in the tested RC structural walls with flanged sections with greater accuracy as compared to the conventional method of effective flange width. Furthermore, parametric studies were performed based on nonlinear finite element models for further investigation of the shear lag effect and accuracy of the proposed method. The parametric studies show that the influences of the height and the length of the wall and the distribution of longitudinal reinforcement were reasonably captured by the proposed method when the maximum tensile strain in the flange was close to the yielding strain of the longitudinal reinforcing bars. [ABSTRACT FROM AUTHOR]

In order to reconcile the larger scatter and avoid the biased estimate from deterministic predictions for the shear strength of reinforced concrete (RC) squat structural walls, a probabilistic shear strength model is developed in this paper based on the strut-and-tie model and the generalized likelihood uncertainty estimation (GLUE) method. The strut-and-tie model is used to derive an appropriate function form for the probabilistic shear strength model, where four unknown model parameters (e.g. k1, k2, k3 and k4) are defined carefully to guarantee them having a clear physical-based meaning so that the corresponding prior distribution ranges can be specified reasonably. Then, the GLUE method is adopted to estimate the posterior cumulative distribution of k1, k2, k3 and k4 with an available experimental database. Furthermore, to demonstrate the stability of the estimated posterior cumulative distribution, the sensitivity of three major aspects in GLUE method is investigated. Finally, based on the estimated cumulative distribution of k1, k2, k3 and k4, the developed probabilistic shear strength model is simplified as a mean prediction model and a standard deviation prediction model for facilitate using in engineering practice. Therefore, with the developed probabilistic shear strength model, not only can the squat structural walls be designed in confidence, but the accuracy of those deterministic predictions can be evaluated in a probabilistic manner. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Two series of experimental tests on reinforced concrete (RC) squat walls with irregular openings were analysed. The experimental evidence indicated that flanges significantly affect the failure modes, initial stiffness, ultimate strength and deformation capacity. Given the complexity of the stress distribution in walls with irregular openings, strut-and-tie models are generally used in design and analysis to explicitly demonstrate the shear force transfer and load distribution paths. A comparison of experimental data with analytical results from the existing strut-and-tie model indicated that the latter may underestimate the ultimate strength by 51%. Although the strut-and-tie model is a lower-bound solution, the underestimation of 51% is still very large and may lead to unfavourable shear failure. An improved strut-and-tie model was thus developed, based on test observations. The improved strut-and-tie model can provide a more accurate prediction for the ultimate strength of walls with irregular openings. Based on the model, design recommendations and suggestions for reinforcement details in RC walls with irregular openings are also presented. [ABSTRACT FROM AUTHOR]

T-shaped slender reinforced concrete (RC) structural walls are commonly used in medium-rise and high-rise buildings as part of lateral force resisting system. Compared to its popularity, experimental results on seismic performance of these walls are relatively sparse, especially for data regarding these walls in the non-principal bending directions. This article aims at providing additional experimental evidence on seismic performance of T-shaped RC structural walls. Experimental results of six T-shaped RC walls were presented. These walls resemble the structural walls found in existing buildings in Singapore and possess slightly inferior details compared to the requirements of modern design codes. The test variables were the loading direction and the axial load ratio. The experimental results were discussed in terms of the failure mechanisms, cracking patterns, hysteretic responses, curvature distributions, displacement components, and strain profiles. In addition, the experimental results were compared with methods commonly adopted in current design practice including the nonlinear section analyses, shear strength models and effective width of the tension flange. The experimental data illustrate that the shear lag effect not only was not accurately accounted for by the effective width method but also significantly affected the strength and stiffness of the tested specimens. [ABSTRACT FROM PUBLISHER]

Development of fragility functions is a pertinent stage in seismic performance assessment of structures. A database of lightly Reinforced Concrete (RC) walls under simulated seismic loading is compiled from the literature to establish the drift-based seismic fragility functions. To classify the damage states experienced by RC walls, the Park-Ang Damage model is amended in this research. Then, the modified Bouc-Wen-Baber-Noori hysteresis model is implemented in ABAQUS to predict the hysteresis behavior of RC walls. Thereafter, the proposed hysteresis model is employed to develop the seismic fragility curves of low to mid-rise RC walls in Singapore using incremental dynamic analysis approach. [ABSTRACT FROM PUBLISHER]

An efficient and simplified plane beam-column joint model that can describe the strength deterioration, stiffness degradation, and pinching effect was developed for the nonlinear analysis of non-seismically detailed reinforced concrete frames. The proposed beam-column joint model is a super-element consisting of eight spring components and one panel zone component, representing the bond-slip mechanism of the longitudinal reinforcement and the shear deformation mechanism of the joint concrete core region, respectively. In order to represent the dynamic response at the system level, the elastic constitutive law is applied to the eight connector springs, while the Bouc-Wen-Baber-Noori (BWBN) model is adopted to describe the hysteretic behavior of the panel zone component. For the implementation of the finite element analysis, the algorithmically consistent tangent of the BWBN model is derived as a uni-axial constitutive model, while the initial stiffness of the panel zone component is determined by the concrete compression strut assumption. The accuracy and efficiency of the proposed beam-column joint model were calibrated at both the component and structural levels by comparing the simulated results with the experimental data for non-seismically detailed joint sub-assemblages and a reinforced concrete plane frame. [ABSTRACT FROM PUBLISHER]

A series of six one-third scaled reinforced concrete (RC) structural walls with irregular or regular openings were tested to investigate the effects of size, arrangement, and irregularities of the openings on the seismic behaviour of RC walls. The crack pattern development, failure mechanism, and hysteretic responses of tested specimens are presented. The stiffness deterioration and equivalent hysteretic damping (energy absorption capacity) of tested specimens are compared and discussed. Another series of six rectangular walls with openings, which are tested by Yanez et al., are also introduced for quantification of the flange effects on seismic behaviour of RC walls with openings. It is found that flanges could significantly increase ultimate strength but reduce deformation capacities. Moreover, flanges may change the failure mode of rectangular walls from ductile flexural failure to brittle sliding shear failure. Flanges may aggravate the concrete crushing, spalling as well as buckling and fracture of vertical reinforcements. However, concrete crushing and rebar fracture is mainly concentrated in the flanges. [ABSTRACT FROM AUTHOR]

The behaviour of reinforced concrete (RC) beams under single or repetitive drop-weight impact loading has come under increasing attention within the engineering community in the past decades. However, until now, little effort has been sought towards examining the residual resistance of RC beams after impact damage. To contribute towards a better understanding in this area, both experimental and numerical investigations were carried out. The beams were first tested under drop-weight impact loading. Subsequently, quasi-static bending tests were conducted on the same specimens to obtain the residual behaviour. Thereafter, one beam from each series without any prior damage was tested under monotonic static loading to compare its behaviour with impact-damaged specimens. Furthermore, to investigate the structural response in detail, a numerical procedure was developed in an explicit finite-element program. Upon successful validation of the numerical results with the experimental outcomes, numerical case studies were carried out to quantify the variation of residual resistance index in terms of various parameters. [ABSTRACT FROM AUTHOR]

For reinforced concrete flat slab structures, column failure due to unexpected extreme loading may significantly increase the moment and shear force at adjacent slab-column connections, which can trigger punching shear failure at these connections and result in progressive collapse of flat slab structures. To determine the possible load-resisting mechanisms developed in flat slab structures in resisting progressive collapse, three multi-panel flat slab substructures are tested in this study. A flat slab substructure is tested as a control specimen. The remaining two specimens are strengthened by adding drop panels or post-installed shear bolts. Punching shear failure is observed in the control specimen and the specimen with post-installed shear bolts after reaching their yield loads. However, even the control specimen without any strengthening exhibited considerable post-failure resistance and deformation capacity mainly due to sufficient integrity reinforcement, which had been installed in the bottom of the slab. Test results indicated that drop panels not only increase the flexural resistance but also raise the punching shear resistance of the connections significantly. Thus, no obvious punching shear failure is observed in the specimen with drop panels. However, post-installed shear bolts can only increase the punching shear resistance. For post-failure behaviour, this is not very effective. The test results demonstrated that flexural failure dominates the performance of test specimens, as relatively low slab reinforcement ratio but high span/thickness ratio was designed. [ABSTRACT FROM AUTHOR]

This article describes an experimental study carried out on of reinforced concrete (RC) walls of less confining reinforcement than that recommended by ACI 318. A total of eight RC walls with boundary elements comprising of five walls with aspect ratio of 1.125 and three walls with aspect ratio of 1.625 were tested by subjecting them to low levels of axial compression loading and simulated seismic loading, to examine the structural performance of the walls with limited transverse reinforcement. Conclusions are reached concerning the failure mode, drift capacity, strength capacity, components of top deformation, and energy dissipation characteristics of walls on the seismic behavior with limited transverse reinforcement. The influences of axial loading, transverse reinforcement in the wall boundary elements, and the presence of construction joints at the wall base on the seismic behavior of walls are also studied in this paper. Lastly, reasonable strut-and-tie models are developed to help in understanding the force transfer mechanism in the walls tested. [ABSTRACT FROM PUBLISHER]

This paper introduces an equation developed based on the strut-and-tie analogy to predict the shear strength of reinforced concrete columns with low transverse reinforcement ratios. The validity and applicability of the proposed equation are evaluated by comparison with available experimental data. The proposed equation includes the contributions from concrete and transverse reinforcement through the truss action, and axial load through the strut action. A reinforced concrete column with a low transverse reinforcement ratio, commonly found in existing structures in Singapore and other parts of the world was tested to validate the assumptions made during the development of the proposed equation. The column specimen was tested to failure under the combination of a constant axial load of 0.30 f'cAg and quasi-static cyclic loadings to simulate earthquake actions. The analytical results revealed that the proposed equation is capable of predicting the shear strength of reinforced concrete columns with low transverse reinforcement ratios subjected to reversed cyclic loadings to a satisfactory level of accuracy [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) structural walls with coupling beams are widely used as the primary lateral-load-bearing elements in high-rise building structures. Many researches have shown that there is uncertainty in the estimation of the effective stiffness of RC coupling beams. In an attempt to develop rational approaches regarding the stiffness of these structural components, this paper presents the analytical approaches, considering the influence of flexural and shear deformations, to determine the effective stiffness of RC coupling beams. A comprehensive parametric study, including 144 combinations for the conventionally reinforced concrete coupling beam (CCB) and 48 combinations for the diagonally reinforced concrete coupling beam (DCB), is carried out and two equations to estimate the effective stiffness of RC coupling beams are proposed each as a function of aspect ratio, transverse reinforcement ratio, longitudinal reinforcement ratio, diagonal reinforcement ratio and concrete compressive strength, on the basis of these parametric case studies. The proposed analytical approaches and the equations for assessing the effective stiffness of CCBs and DCBs are then verified by comparison with experimental results obtained from literature. [ABSTRACT FROM AUTHOR]

Fragility functions play an essential role in evaluating the seismic vulnerability of structures. To establish the seismic fragility functions of lightly Reinforced Concrete (RC) beam-column joints, the Park-Ang Damage model has been amended to quantify the damage states and the modified Bouc-Wen-Baber-Noori model has been employed and implemented in ABAQUS to predict the structural hysteresis behavior. Following successful calibration of the numerical results of a RC test frame from literature, the proposed model has been utilized to assess the seismic fragility curves of low to mid-rise RC frames in Singapore for 30 scaled ground motions using incremental dynamic analysis approach. [ABSTRACT FROM AUTHOR]

Highlights: [•] Quantitative analysis of shear deformation, considering the effect of tension stiffening after diagonal cracking. [•] Calculating the minimum inclined crack angle using the minimum energy principles. [•] Formula for calculating the effective shear stiffness. [Copyright &y& Elsevier]

This paper presents the results from Finite Element (FE) simulation on six Reinforced Concrete (RC) beam-column jointsand experimental study. The joints investigate dhave additional, vertically distributed reinforcement along the beams and lateral cyclic loading is applied, with constant axial force. Experimental results provide insight into the joint behaviour under conventional and unconventional displacement histories in terms of hysteresis loop, crack pattern and joint shear stress. The FE numerical models are validated by comparing the numerical results with experimental results obtained from six tested specimens and two specimens from previous studies. Parametric studies are performed to investigate the complex behaviour of the joints under the influence of axial loads as well as the numbers of vertically distributed reinforcement layers. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) structures when subjected to sudden destruction of a column by blast pressure, experience dynamic effects in its response. Hence, reliability assessment of the damaged ductile frame against progressive collapse under dynamic loading conditions is conducted in this research. This paper aims at establishing three performance functions, two of which will consider structural collapse due to lack of strength and deformation capacity respectively while the third will incorporate the shear response of structural components for the weakest collapse mechanism. Since any of the performance functions may lead to structural collapse, a global performance function of the damaged structure is developed by considering the minimum of the functions. The results are then used in conjunction with Monte Carlo Simulation (MCS) to estimate the reliability of the damaged structure. A numerical example of a four storey RC frame is presented to address the applicability of the proposed approach and the effects of different structural parameters on its reliability against progressive collapse after the sudden column loss are investigated thereafter. [ABSTRACT FROM AUTHOR]

Previous studies indicated that RC flat slabs, especially without drop panels, are of high vulnerability to progressive collapse because no beams could assist in redistributing the axial force previously carried by the lost columns. In order to reduce the likelihood of progressive collapse, necessary strengthening schemes should be applied. Six specimens of similar dimensions and reinforcement details were prepared, two of which were unstrengthened and served as control specimens, while the remaining four were strengthened with two different schemes: orthogonally (Scheme 1) or diagonally (Scheme 2) bonded carbon-fiber-reinforced polymer (CFRP) laminates on the top surface of the slab. The progressive collapse performance of the strengthened specimens was studied in terms of their load-displacement relationships, first peak strength, initial stiffness, and energy dissipation capacities. The dynamic ultimate strength and corresponding dynamic effects of flat slabs after the sudden removal of a corner column was also discussed due to the dynamic nature of progressive collapse. Test results indicated that both schemes were effective in improving the performance of RC flat slabs in resisting progressive collapse. [ABSTRACT FROM AUTHOR]

Abstract: Research on reinforced concrete (RC) deep beams has seen considerable headway over the past three decades; however, information on the dynamic shear strength and behavior of RC deep beams under varying rates of loads remains limited. This paper describes the experimental results of 24 RC deep beams with and without shear reinforcements under varying rates of concentrated loading. Results obtained serve as useful data on shear resistance, failure patterns and strain rates corresponding to varying loading rates. An analytical truss model approach proves its efficacy in predicting the dynamic shear resistance under varying loading rates. Furthermore, three-dimensional nonlinear finite element (FE) model is described and the simulation results are verified with the experimental results. A parametric study is then conducted to investigate the influence of longitudinal reinforcement ratio, transverse reinforcement ratio and shear span to effective depth ratio on shear behavior. Subsequently, two empirical equations were proposed by integrating the various parameters to assess the dynamic increase factor (DIF) of maximum resistance under varying rates of concentrated loading. [Copyright &y& Elsevier]

The vulnerability of conventional RC structures to structural failure caused by the loss of corner columns has been emphasized over the past years. However, the lack of experimental tests has led to a gap in the knowledge for the design of RC building structures to mitigate the likelihood of progressive collapse caused by losing a ground corner column. Seven one-third scale RC beam-column substructures were tested to investigate their performance. The variables selected for the test specimens included beam transverse reinforcement ratios, type of design detailing (nonseismic or seismic), and beam span aspect ratios. Shear failure was observed to have occurred in the corner joint, and a plastic hinge was formed at the beam end near the fixed support in the nonseismic detailed specimens. However, plastic hinges were also formed in the beam end near to the corner joint for the seismically detailed specimen. Vierendeel action was identified as the major load redistribution mechanism before severe failure occurred in the corner joint, but a cantilever beam redistribution mechanism dominated after the corner joint suffered severe damage. The test results were compared with the Department of Defense design guidelines to highlight the deficiencies of the recently updated guidelines. [ABSTRACT FROM AUTHOR]

Experimental observations on 11 RC columns tested at Nanyang Technological University and existing experimental data of 79 shear-critical RC columns are presented. Significant arch action is found in columns with a small shear span-to-depth ratio and high axial-load ratio under shear force. Using the sectional method for shear strength of these types of columns, which does not consider arch action, would give a more conservative prediction. On the basis of the truss-arch model, an expression to predict the shear strength of shear-critical RC columns is presented, which considers both the contributions of concrete and transverse reinforcement to shear strength in the truss model, as well as the contribution of arch action through compatibility of deformation. The proposed model is compared with other shear strength models using the available column test data consisting of 90 shear-critical RC columns, and the results show that the proposed model can improve the accuracy of shear strength predictions for shear-critical RC columns. [ABSTRACT FROM AUTHOR]

This paper seeks to examine the concrete contribution to shear strength and determine the inclination of the compressive strut within the variable truss model for slender RC shear-critical beams with stirrups. Using the modified compression field theory in place of the conventional statistical regression of experimental data, the expression for the concrete contribution to shear strength was derived, and the inclination of compressive struts was determined. A simplified explicit expression for shear strength was then provided, with which shear strength can be calculated without extensive iterative computations. This method was then verified using the available experimental data of 209 RC rectangular beams with stirrups and compared with the current methods from the American Concrete Institute and the Canadian Standards Association. The theoretical results are shown to be consistent with the experimentally observed behavior of shear-critical RC beams. [ABSTRACT FROM AUTHOR]

The majority of research studies on the behavior of reinforced concrete members with externally bonded fiber reinforced polymer (FRP) sheets have been focused on beams, columns, and beam-column joints. However, limited experimental studies have been conducted to investigate the performance of structural walls retrofitted by wrapping FRP strips or sheets, especially on structural walls with openings. The validated retrofitting schemes for strengthening damaged walls without openings may not be suitable for walls with openings. Therefore, a series of experimental studies were carried out at Nanyang Technological University, Singapore, to study the effectiveness of the proposed repair and strengthening schemes in recovering the seismic performance of the damaged walls with irregular or regularly distributed openings. The strut-and-tie approach was utilized to design the repair schemes. The repaired walls managed to recover their strength, dissipated energy, and stiffness reasonably, indicating that the strut-and-tie approach can be a good design tool for FRP-strengthening of structural walls with openings. Moreover, the shear and sliding capacities of repaired walls were enhanced by using fiber anchors. The repaired walls failed primarily because of debonding of the fiber reinforced polymer at the base of the walls. [ABSTRACT FROM AUTHOR]

This article presents the analytical and experimental investigations carried out on reinforced concrete (RC) columns with light transverse reinforcement. A semi-empirical model is developed to estimate the ultimate displacement (displacement at axial failure) of RC columns with light transverse reinforcement subjected to simulated seismic loading. The developed model is calibrated using the collected data of RC columns tested to the point of axial failure. A series of experiments is conducted on five RC columns with light transverse reinforcement to validate the applicability and accuracy of the developed model. It is concluded from the study that the mean ratios of the experimental to predicted ultimate displacement and its coefficient of variation are 1.077 and 0.194, respectively, showing a good correlation between the developed model and the experimental data. [ABSTRACT FROM AUTHOR]

Abstract: An analytical approach based on modified Bouc–Wen–Baber–Noori model has been proposed in this paper for predicting the hysteresis behavior of reinforced concrete beam–column joints with limited transverse reinforcement. The analytical model presented in this research is able to capture the characteristics of non-seismic detailed beam–column joints such as stiffness and strength degradation and pinching. Livermore Solver for Ordinary Differential Equations (LSODE) and Genetic Algorithm (GA) have been employed to solve the differential equations and to execute systematic estimation of the parameters associated with the model respectively. The analytical model has been calibrated with the experimental results of old fashioned interior and exterior beam–column joints obtained from the literature. In a bid to examine the influence of variation of each analytical parameter on the model, sensitivity analysis has been performed. Thereafter, an extensive parametric study has been conducted to relate the physical parameters of beam–column joints to the analytical model parameters. The upper and lower bounds of the magnitude of the analytical model parameters have been proposed subsequently with a method to identify the parameters for a specific beam–column joint depending on its physical parameters. [Copyright &y& Elsevier]

Prevention of structures against progressive collapse has become a concern of increasing significance and the alternative load path method (ALPM) is the extensively acknowledged approach in this area of research. With the basis of ALPM and by amalgamation of the Monte Carlo simulation method and an iterative algorithm, a new approach is developed in this paper to assess the reliability of ductile RC frame structures when subjected to one column failure. This paper focuses on the construction and solution of the performance function of the damaged structure under static service loadings. With this intention, three types of critical zones are identified and an optimum model is presented to determine the possible failure modes for each zone. By employing the virtual work principle and critical collapse mechanism criterion, the performance function is established in terms of minimum internal virtual work and external virtual work done by service loadings. Three equations containing the interaction between the axial forces and bending strength of structural members are evolved to calculate this function, and by solving these equations from the top floor to the floor of the failed column the performance of the damaged structure can be appraised. [ABSTRACT FROM AUTHOR]

Experimental and analytical studies carried out on a RC moment-resisting frame after it is subjected to the loss of its ground-story exterior column is presented in this paper. Four full-scale interior beam-column subassemblages with varying degrees of nonseismic detailing were subjected to a monotonic loading regime to simulate the effects of redistributed gravity loads on the subassemblage after the loss of an exterior ground column. The variables in the test specimens include the beam longitudinal reinforcement ratios and the spacing of the transverse reinforcement within the beams, columns, and joints. The load-displacement relationships, crack development patterns, and failure mechanism obtained from the tests are also discussed. The finite-element models are validated by comparing the results with the experimentally obtained data. Parametric studies are then performed to study the influence factors, such as the beam transverse reinforcement ratio and the incorporation of an additional exterior beam-column element and slab on the global behavior of the subassemblages. [ABSTRACT FROM AUTHOR]

This paper presents the experimental results of four lightly Reinforced Concrete (RC) exterior beam-column joints with and without beam stubs under cyclic loading with constant column axial force applied at the top of the column. The parameter investigated was the type of reinforcement used in the beam, i.e. plain and deformed bars. Test results showed that when the hooks anchored down in the column increased the tensile stress in the diagonal concrete strut in the joint core, this led to diagonal crack of the concrete and a decrease in the joint shear strength. The seismic performance of the exterior RC joints without beam stub was also observed to be much improved when the hook tail of beam reinforcements was bent inside the joint core. The strut-and-tie model based on the recorded strain in the joint transverse reinforcement could be used to determine the force flow in the joint core. [ABSTRACT FROM AUTHOR]

Two specimen series [limited seismic (LS) and nonseismic (NS)] were subjected to quasistatic loadings to evaluate the residual axial capacity of blast-damaged reinforced concrete (RC) columns. A validated numerical model was used to predict the residual lateral deflection of RC columns subjected to an explosive attack. Three hydraulic actuators were installed horizontally to reproduce the target residual lateral deflection as predicted through this numerical model. Another two hydraulic actuators were installed vertically to apply the axial load and measure the residual axial capacity of the damaged columns. The effects of parameters such as axial loading and the transverse reinforcement ratio are investigated through this study. The results obtained from the experimental study showed the improved performance that LS detailing provided to RC columns to resist blast or lateral loads. This subsequently led columns detailed with a higher transverse reinforcement ratio to have an increased residual axial capacity when laterally damaged, as compared with the NS detailed specimens. Axial load (service load) on the columns was also found to affect the residual deflection profile and residual axial capacity of the columns after the specified blast event. The validity range of a previously published function to determine blast-damaged residual axial capacity of RC columns is refined through the results obtained. [ABSTRACT FROM AUTHOR]