Beam Longitudinal Reinforcement Research Articles

Numerical Study on the Retrofitting of Exterior RC Beam-column Joints with CFRP Composites Using the Grooving Method

Retrofitting seismically deficient beam-column joints (BCJs) in reinforced concrete (RC) structures is crucial to preventing collapse during high-intensity earthquakes. Fiber reinforced polymer (FRP) composites have proven effective for retrofitting these components, but debonding of the FRP from concrete surfaces remains a challenge. Recently, the grooving method (GM) has emerged as a promising solution to mitigate this issue, enhancing the bond between FRP and concrete. This paper presents a numerical investigation of BCJs retrofitted with FRP composites using the GM, focusing on various design parameters. The study utilized finite element models developed in ABAQUS, incorporating the concrete damage plasticity (CDP) model to simulate the nonlinear behavior of concrete. The interface between the concrete and FRP was modeled as a perfect bond, simulating the strong adhesion provided by the GM. The numerical results were validated against experimental data from two BCJ specimens, showing good agreement in terms of load-displacement behavior, peak loads, and failure modes. Key parameters studied include the beam longitudinal reinforcement ratio, column axial load ratio, and joint aspect ratio. The findings reveal that these parameters significantly affect the shear capacity of retrofitted joints, impacting the efficiency of the retrofitting.

Influence of joint forms on the seismic behavior of concrete-filled PVC-CFRP tubular column-RC beam joints connected with core steel tubes

To examine the effects of joint forms on the failure mode, hysteretic behavior, ductility and energy dissipation capacity of concrete-filled PVC-CFRP tubular column-RC beam connected with core steel tubes (“RC beam” for short), low-cycle reversed loading tests on 13 cross-joints and 11 T-joints were designed and conducted. The findings demonstrate that the core regions of both joint types experience normal shear failure. Less flexural cracking is present in the RC beams of T-joints, but the concrete crush failure is severer in the joint core area and mostly occurs on the ends of the cantilever beams. The seismic behaviors of both joint forms alter in the same pattern with an increase in the radius-thickness ratio of the core steel tube, the joint area stirrup ratio and the steel ratio. With a rise in the axial compression ratio, the ductility of the cross joints improves but the energy dissipation capacity shows no evident change, while both decrease for the T-joints. The cross joints show better energy dissipation capacity in the whole test. As the reinforcement ratio of the beam longitudinal reinforcement rises, the cross joints show a decrease in ductility and energy dissipation capacity, while T-joints have the exact opposite effect. The seismic behavior of core steel tube joints throughout the whole test is unaffected by CFRP strip spacing.

Assessment of the impact of column-to-beam strength ratio on seismic response of RC beam-column connections

Beam-column joints play an important role in the overall resistance of reinforced concrete frames during seismic events. The Earthquakes of Al Asnam on October 10, 1980, and Boumerdes on May 21, 2003 in Algeria, have highlighted the failure of beam-column joints as a cause of building collapse. 3D nonlinear finite element analysis with ANSYS software has been used in order to examine exterior RC beam-column joints under monotonic loading. The research has investigated the influence of the value of the column-to-beam strength ratio (CBSR) of these joints on shear strength and seismic performance of concrete structures by changing the height and longitudinal reinforcement of the beam while keeping column dimensions constant. It has been shown that the beam-column depth ratio and the beam longitudinal reinforcement ratio have a significant effect on the shear capacity and seismic behaviour of exterior beam-column joints. An appropriate value of the flexural strength ratio between the column and beam is crucial in order to establish a "strong column-weak beam" mechanism in reinforced concrete frames, because inadequate values can lead to premature failure or reduced shear capacity at the junction. The Algerian seismic code – RPA99/version2003 suggests a minimum value of column-to-beam strength ratio equal to 1.25 at joints for seismic design when building codes in other countries call for higher ratios. Nevertheless, this approach might not accurately represent the actual behaviour and could constrain the optimal performance of structures.

Seismic performance of reinforced concrete beam-column joints with diagonal bars wrapped by steel tubes: experimental, numerical and analytical study

Diagonal bars can be used as joint reinforcement to address the congestion problem, yet a certain number of stirrups are still required for joint confinement. In this study, diagonal bars wrapped by steel tubes are proposed as joint reinforcement to fully replace the stirrups. Three interior beam-column joint specimens reinforced by conventional stirrups, debonded diagonal bars wrapped with plastic or steel tubes, are tested. The results indicate that replacing the plastic tubes with steel tubes can prevent shear failure in the joint without stirrups, increase the ductility, and reduce the joint distortion. However, it decreases the deformation capacity and increases the peak beam curvature. Compared to the stirrup-reinforced specimen, the specimen reinforced by the steel tube-wrapped diagonal bars has higher loading capacity and lower peak beam curvature without compromising the energy dissipation, stiffness, and joint distortion. Results from finite element analysis indicate that increasing the column axial load ratio to 0.4 leads to higher early stiffness and slower degradation of loading capacity. It should be noted that a sufficient area of steel tubes is required to avoid joint shear failure and sudden loss of loading capacity. The anchorage segments are recommended to be installed at the same depth as the beam longitudinal reinforcement to maximize their efficiency. Finally, an analytical model for predicting the failure mode and loading capacity is also developed, and a good agreement between predicted and tested results is obtained.

Shake table testing of out-of-plane response of repaired bridge subassembly with simplified ABC-inspired cast-in-place joints

Accelerated bridge construction (ABC) has been utilized in precast bridge structures because of its advantage to expedite on-site construction. In ABC, one of the main concerns is the joint connection as it needs to be well designed to maintain structural integrity. A recent study at the University of Nevada, Reno (UNR) was conducted to utilize ABC pocket connection concept in cast-in-place (CIP) cap beam-column bridge joint. The cap beam was constructed by having the cap beam longitudinal reinforcement bundled outside the pocket joint allowing the placement of the column reinforcement cage uninhibited. The specimen was tested in an inverted position at one of UNR’s shake tables and found to perform well under out-of-plane ground motion excitations, and the ductility of the column was confirmed through typical plastic hinge behavior. In this study, the specimen from the recent UNR test was further utilized by removing the damaged column in the cap beam through cutting and coring. A new column was constructed in the cap beam using the same reinforcement detailing from the original specimen. The repaired specimen was tested using the same loading protocol adopted from the 1994 Northridge earthquake as the original model. The objective of this study is to demonstrate that ABC-inspired CIP joints can provide a viable repair method after major earthquakes, where damaged columns can be replaced without affecting cap beam reinforcement. The repaired specimen performed well as the plastic hinge zone was developed in the column outside the joint, close to the interface of the cap beam, as desired and required by design. The cap beam remained essentially elastic, i.e. capacity-protected as required, throughout the test which is similar to the performance of the original model. High residual drift ratios were recorded at higher earthquake motions and were attributed to the slippage of the column in the joint. The paper also concludes with recommendations for the repair of CIP cap beam-column joints emulating ABC pocket connections.

Seismic behavior of reinforced concrete beam-column joints with unstressed steel strands fully or partially used for beam longitudinal reinforcement

Five beam-column joint specimens: three exterior and two interior specimens were subjected to cyclic loading to investigate the effectiveness of using unstressed Grade 1860 MPa steel strands as full/partial replacement for the conventional Grade 420 MPa deformed bars as beam longitudinal reinforcement. The study also developed a special hooked anchorage detail to anchor the steel strands in the joint region. The test specimens failed by beam plastic hinge formation near the column face as intended in design, with drift capacities between 5.12% and 7.57%. However, the full (100%) and partial (50%) replacement of deformed bars by strands led to a 58% and 28% decrease in average relative energy dissipation. Despite this, the full/partial replacement of deformed bars by strands as beam longitudinal reinforcement resulted in enhanced reentering capabilities. Fracture of longitudinal steel strands observed in the beam plastic hinge region at the end of the test indicated the effectiveness of the special hooked anchorage detail in allowing steel strands to develop their capacity. Further, the flexural strength of the beams of test specimens was evaluated through a detailed moment-curvature analysis, which predicted the beam flexural strength with high accuracy and less variation (mean = 1.01, standard deviation = 0.02). After that, beam flexural strengths were evaluated following the ACI 318–19 procedure modified to include the proposed bilinear strand model, which produced conservative estimates of beam flexural strength (mean = 1.15) suitable for design. Also, the procedure to estimate the beam's probable flexural strength is presented. Finally, required modifications to the conventional seismic design procedure were proposed to incorporate the use of strands as beam longitudinal reinforcement.

Enhancing shear behaviour of the exterior beam-column joint using sufficient reinforcement details or ultra-high-performance fiber-reinforced concrete

This study aims to improve the low shear strength of an exterior beam-column joint (BCJ) by using a different reinforcement pattern or ultra-high performance fiber-reinforced concrete (UHPFRC) in the beam-column joint. The main studied parameters were the transverse reinforcement ratio, anchorage of the longitudinal beam reinforcement, beam-column depth ratio, and utilizing UHPFRC. Five specimens with a one-third scale were experimentally tested under one-direction cyclic loading. All the samples were compared to the control sample in terms of crack pattern, mode of failure, hysteresis and envelope behavior, ductility factor, energy dissipation, normalized shear strength, percentage of beam flexural capacity, and stiffness degradation. Compared to the control specimen, the joint shear strength increases by 13%, 25%, 9%, and 38% for specimens that were made better by increasing the transverse reinforcement ratio, increasing the beam anchorage bar length in the joint, lowering the beam-column depth ratio to 0.80, and using UHPFRC instead of normal concrete in the beam-column joint. The UHPFRC in BCJ can be used instead of increasing the anchorage of the beam bars or the transverse reinforcement within the joint to get the same or better shear strength performance.

Finite element model of reinforced concrete interior beamcolumn joints subjected to cyclic loading

This paper presents the finite elements of beam-column joints subjected to cyclic loads. This study aims to numerically obtain the beam-column joints' capacity without shear reinforcement in the joints. The variable used in the specimen is the beam's longitudinal reinforcement ratio. While the analytical study was carried out using ATENA 2D software, a computer program based on the non-linear finite element method. In this analytical study, the beam-column joints are loaded cyclically to obtain the envelope curve of the hysterical response. The results of this numerical analysis are then compared with the test results. The comparison results show that the model used in ATENA 2D can approach the test results well. In addition, the crack pattern obtained from the analysis shows a pattern close to the test results.

Experimental Analysis of the Effectiveness of Pre-Stressed Steel Strips for the Strengthening of Beam-Column Joints in Existing RC Buildings

Beam-column joints in existing Reinforced Concrete (RC) buildings are usually characterized by the absence of transverse reinforcement. The observation of post-earthquake damage, as well as several numerical and experimental studies, have soundly demonstrated the possible impact of the response of unreinforced joints on the damage – up to collapse – of existing RC buildings under seismic action. In this study, a possible strengthening approach for these elements, based on CAM® technology, is investigated through experimental tests. The results of these tests are reported, along with the results of a previous experimental campaign carried out on the same topic. Full-scale external beam-column joint specimens are tested, with and without strengthening, and with different characteristics in terms of amount of beam longitudinal reinforcement and concrete compressive strength. Different failure modes are observed for the as-built specimens (joint failure without (J) or after (BJ) beam flexural yielding). The effectiveness of the adopted strengthening approach is demonstrated, observing an increase in joint shear strength and subassemblage ductility and – unless a joint failure in compression occurs – a possible modification of the failure mode into a ductile, flexure-controlled response of the subassemblage, as for code-compliant beam-column joints.

Investigation on the progressive collapse resistance of three-dimensional concrete frame structures reinforced by steel-FRP composite bar

Compared with conventional steel bars, steel-FRP (fiber reinforced polymer) composite bars (SFCBs) have distinctive post-yield stiffness, and the high efficiency of SFCBs in enhancing the progressive collapse resistance of concrete frames has been confirmed by recent quasi-static experimental studies on SFCB beam–column subassemblages. However, the realistic progressive collapse of structures is a dynamic process, and the three-dimensional (3D) effects are essentially important for determining the collapse response. In this study, numerical models are built to explore the progressive collapse behavior of 3D frame structures reinforced by SFCBs. The static and dynamic capacities of five SFCB frames and one reinforced concrete (RC) frame are compared under different column–removal cases. Results show that by virtue of the post-yield stiffness, the static load factors of SFCB frames are much larger than those of RC frames at the same deformation, proving that SFCB frames have better robustness against collapse failure than RC frames. After the dynamic removal of columns, all RC frames are subjected to progressive collapse failure, while SFCB frames can successfully complete the dynamic load redistributions and quickly reach a steady state. Further, the dynamic increase factor (DIF) of SFCB frames is proposed based on the ratio of maximum dynamic flexural responses to static flexural responses of beam joint sections under the same gravity loads (1.2 times dead load plus 0.5 times live load), and the conservative DIFs of 1.55 and 1.3 are recommended for a corner column–removal case and the other single column–removal cases, respectively. Finally, parametric analyses are conducted to reveal the effect of beam longitudinal reinforcement ratio, beam span-to-depth ratio, and dynamic duration for the column removal on the progressive collapse resistance of SFCB frames. The results lay a foundation for the progressive collapse design of 3D SFCB frame structures.

Behavior of RC Beam–Column Joints Strengthened with Modified Reinforcement Techniques

Using a significant number of transverse hoops in the joint’s core is one recognized way for achieving the requirements of strength, stiffness, and ductility under dynamic loading in a column joint. The shear capacity of a joint is influenced by the concrete’s compressive strength, the anchoring of longitudinal beam reinforcement, the number of stirrups in the joint, and the junction’s aspect ratio. Seismic motion on the beam may produce shear capacity and bond breaking in the joint, causing the joint to fracture. Furthermore, due to inadequate joint design and details, the entire structure is jeopardized. In this study, the specimens were divided into two groups for corner and interior beam–column joints based on the joint reinforcement detailing. The controlled specimen has joint detailing as per IS 456:2000, and the strengthened specimen has additional diagonal cross bars (modified reinforcement technique) at the joints detailed as per IS 456:200. The displacement time history curve, load-displacement response curves, load-displacement hysteretic curve, and load cycle vs. shear stress were used to compare the results of the controlled and strengthened specimens. The findings show that adding diagonal cross bars (modified reinforcing techniques) to beam–column joints exposed to cyclic loads enhances their performance. The inclusion of a diagonal cross bar increased the stiffness of the joint by giving an additional mechanism for shear transfer and ductility, as well as greater strength with minimum cracks.

Neural network prediction of joint shear strength of exterior beam-column joint

Beam-Column joints are the critical locations in the reinforced concrete structures as they experience a massive amount of deformations under earthquake. The shear failure of the beam column joint should be avoided for the safety of the structure. In the present study, prediction of joint shear capacity of exterior Beam-column joint is proposed using artificial neural network (ANN). Experimental investigations performed by different authors have been examined and used to prepare the data sets for training, testing and validating the neural network. Parameters responsible for the shear strength of the exterior Beam-Column Joints are identified and the artificial neural network model is proposed to predict the joint shear strength. Input parameters for the ANN model are width and depth of the joint, concrete compressive strength, length of beam, top and bottom longitudinal reinforcement in the beam, yield strength of longitudinal reinforcement in beam, ratio of beam to column depth, joint Shear reinforcement index, beam bar index and column load index. The performance of the neural network model is evaluated by the statistical relations like Coefficient of correlation, Root mean square error and Scatter index. The proposed model is compared with an empirical formula and different equations suggested by the design codes. The results show that the proposed neural network model can effectively predict the joint shear strength of the Exterior Beam-Column joint.

Experimental and numerical study on reinforced concrete beam-column joints with diagonal bars: Effects of bonding condition and diameter

Diagonal bars anchored in beams have been proven to be an effective reinforcement detail for reinforced concrete interior beam-column joints (BCJs) in mitigating the congestion of conventional stirrups without compromising their seismic performance. This paper investigates the effects of bonding condition and diameter of diagonal bars on the seismic performance of interior BCJs. Four interior BCJ specimens, including one control specimen reinforced with conventional stirrups and three others reinforced with diagonal bars, were fabricated and tested under cyclic loading. The results show that the control specimen fails with plastic hinges formed at the beam-joint interfaces, while all other specimens fail with relocated plastic hinges on the beams. The two BCJ specimens reinforced with bonded and debonded diagonal bars show similar improvement over the control specimen in terms of joint damage level, loading capacity, energy dissipation, stiffness degradation, and bonding condition of beam longitudinal reinforcement. For instance, the BCJ specimens reinforced with bonded and debonded diagonal bars possess 9% and 12% higher loading capacity, and 13% and 7% higher energy dissipation than the control specimen. Debonding the diagonal bars can slightly reduce joint cracks but has marginal effect on the overall performance of BCJs. In addition, the debonding treatment weakens the contribution of the diagonal bars to joint shear resistance, as evidenced by the increased strain in joint stirrups. Furthermore, increasing the diameter of debonded diagonal bars enhances the ductility and energy dissipation of the BCJ specimens since this improves their buckling resistance after concrete spalling. In addition, finite element models for BCJs were developed and validated for parametric study. The simulation results indicate that insufficient diagonal bars can lead to unsuccessful relocation of plastic hinges in BCJs, which decreases the loading capacity and accelerates the load degradation. With similar total sectional area, reducing the number of diagonal bars deteriorates their anchorage in beams. This consequently weakens the flexural capacity at beam ends, leading to unsuccessful plastic hinge relocation and poor seismic performance of BCJs.

Investigation of the Structural Behaviour of RC Beam-Column Sub-frame Subjected to Progressive Collapse

The aim of this study is to investigate the effects of varying design variables on the structural behaviour of reinforced concrete (RC) sub-frames under progressive collapse. A finite element modelling approach is presented and validated against the experimental results concerning a 2D frame (3 columns and 2 beams) and a 3D frame (4 columns and 3 beams). The performance of the RC sub-frame is discussed by choosing the scenarios of the exterior, interior, and multiple column loss, respectively, and by increasing the number of stories and bays. Further studies are conducted based on the numerical method to reveal the effect of beam longitudinal reinforcement ratio (BLRR), beam section depth (BSD), and concrete compression strength (CCS). The results show that both BLRR, CCS and BSD have a significant influence on the compressive arch action (CAA) capacity of the structure under progressive collapse, and the load-carrying capacity of the RC sub-frame increases with an increasing number of stories.

Relocating plastic hinges in reinforced concrete beam-column joints by mechanically anchored diagonal bars

The implementation of strong column-weak beam concept in reinforced concrete (RC) moment-resisting frames results in the formation of plastic hinges at the beam ends, which could lead to the strain penetration of beam longitudinal reinforcement into beam-column joint (BCJ) cores. This causes high shear forces inside joint cores, bonding deterioration of longitudinal reinforcement and consequently jeopardizes the seismic behaviour of BCJs. Plastic hinge relocation by mechanically anchored diagonal bars has been proposed to mitigate such potential damage to BCJ cores. This paper investigates the effect of relocating distance of plastic hinge on the seismic performance of BCJs with mechanically anchored diagonal bars. Five interior BCJ specimens including one control specimen reinforced with conventional stirrups and four others reinforced with mechanically anchored diagonal bars were tested under cyclic load. Test results indicate that the plastic hinges can be generally relocated by different distances to the anchorage ends of diagonal bars. Increasing the relocating distance can enhance the loading capacity and stiffness of BCJs, but also increase the potential of joint shear failure. The ductility, energy dissipation and joint shear deformation of BCJs are first improved then reduced as the relocating distance increases. Although the strain penetration of beam longitudinal reinforcement into the joint cores can be gradually alleviated as the plastic hinges are moved farther away from the joints, the induced bending moments at the beam ends are amplified and subsequently increase the joint shear forces. Moreover, increasing the length of anchorage segments increases the forces sustained by the mechanically anchored diagonal bars. Therefore, a lower bound of the relocating distance of plastic hinges is recommended to take advantage of the benefits from reduced strain penetration, while an upper limit needs to be specified to avoid joint shear failure. In addition, an analytical model is developed to predict the failure modes and loading capacities of BCJs with the plastic hinges relocated by different distances. A satisfactory agreement between the prediction and the experimental results is obtained.

Experimental study on concrete beams without web reinforcement based on fractal theory

Based on the development and distribution of cracks, we explored the shear performance of concrete beams without web reinforcement under different shear span ratios and longitudinal reinforcement ratios. Nine groups of concrete beams without web reinforcement with shear-span ratios of 1.5, 2, 2.5 and longitudinal reinforcement ratios of 1.28%, 1.62%, and 1.99% were used for four-point loading shear tests. The cracks on the surface of the test beam were analyzed by applying fractal geometry theory, and the box counting method was used to calculate the fractal dimension of the cracks on the surface of the beam under the effect of the graded load and the ultimate load. The relationship among the fractal dimension of the beam surface, the ultimate load, the graded load and the span was discussed. The results show that the shear-span ratio is inversely proportional to the ultimate load and cracking load, while the longitudinal reinforcement ratio is directly proportional to the ultimate load and exhibit a small influence on the cracking load. Concrete beams without web reinforcement have obvious fractal characteristics under the effect of graded loading or ultimate load. The fractal dimension under the effect of graded load is 0.964–1.449, and the fractal dimension under the effect of ultimate load is around 1.33. The graded load, mid-span deflection and fractal dimension show a good logarithmic relationship. The change curve of graded load and fractal dimension is affected by the shear-span ratio and the beam longitudinal reinforcement ratio. The intermediate deflection is less affected by the shear-span ratio. Under the effect of the longitudinal reinforcement ratio, the curvature of the curve shows a trend of first increasing and then decreasing, but the relationship between the ultimate load and the fractal dimension has certain differences. The ultimate load first increases and then decreases with the increase of the shear span ratio, and the difference is greater with the increase of the longitudinal reinforcement ratio.

Seismic performance of exterior reinforced concrete beam-column joint with corroded reinforcement

Corrosive environment adversely affects the durability of existing reinforced concrete (RC) structures as well as its performance under seismic loading. In this paper, the seismic behaviour of corroded reinforced concrete (RC) exterior joint was experimentally evaluated. Eight similar RC exterior joints with various corrosion level of reinforcements were tested under two levels of representative column axial force ratio. Lateral loading resisting, ductility, energy dissipation and stiffness of corroded specimens were examined and compared with uncorroded control specimens. Joint shear stress and the development length of beam longitudinal reinforcement were investigated and compared with available design code. In addition, the joint internal force flow of corroded joint was investigated analytically based on modified strut-and-tie model (STM). Experimental results indicate that corrosion of reinforcements have significant adverse effect on the strength and lateral drift capacity of the joints as well as other mechanical properties. Based on the STM model and parametric study, it is further found that the effect of corrosion level on joint stress level is more significant at higher axial force ratio. In addition, an axial force ratio above 0.2 is detrimental to the joint.

Finite Element Analysis of Key Influence Parameters in Reinforced Concrete Exterior Beam Column Connection subjected to Lateral Loading

Beam column connection is the most critical zone in a reinforced concrete frame. The strength of connection affects the overall behavior and performance of RC framed structures subjected to lateral load and axial loads. The study of critical parameters that affects the overall joint performances and response of the structure is important. Recent developments in computer technology have made possible the use of Finite element method for 3D modeling and analysis of reinforced concrete structures. Nonlinear finite element analysis of reinforced concrete exterior beam column connection subjected to lateral loading was performed in order to investigate joint shear failure mode in terms of joint shear capacity, deformations and cracking pattern using ABAQUS software. A 3D solid shape model using 3D stress hexahedral element type (C3D8R) was implemented to simulate concrete behavior. Wire shape model with truss shape elements (T3D2) was used to simulate reinforcement’s behavior. The concrete and reinforcement bars were coupled using the embedded modeling technique. In order to define nonlinear behavior of concrete material, the concrete damage plasticity (CDP) was applied to the numerical model as a distributed plasticity over the whole geometry. The study was to investigate the most influential parameters affecting joint shear failure due to column axial load, beam longitudinal reinforcement ratio, joint panel geometry and concrete compressive strength. The Finite Element Model (FEM) was verified against experimental test of exterior RC beam column connection subjected to lateral loading. The model showed good comparison with test results in terms of load-displacement relation, cracking pattern and joint shear failure modes. The FEA clarified that the main influential parameter for predicting joint shear failure was concrete compressive strength.

Finite Element Analysis of Key Influence Parameters in Reinforced Concrete Exterior Beam Column Connection subjected to Lateral Loading

Beam column connection is the most critical zone in a reinforced concrete frame. The strength of connection affects the overall behavior and performance of RC framed structures subjected to lateral load and axial loads. The study of critical parameters that affects the overall joint performances and response of the structure is important. Recent developments in computer technology have made possible the use of Finite element method for 3D modeling and analysis of reinforced concrete structures. Nonlinear finite element analysis of reinforced concrete exterior beam column connection subjected to lateral loading was performed in order to investigate joint shear failure mode in terms of joint shear capacity, deformations and cracking pattern using ABAQUS software. A 3D solid shape model using 3D stress hexahedral element type (C3D8R) was implemented to simulate concrete behavior. Wire shape model with truss shape elements (T3D2) was used to simulate reinforcement’s behavior. The concrete and reinforcement bars were coupled using the embedded modeling technique. In order to define nonlinear behavior of concrete material, the concrete damage plasticity (CDP) was applied to the numerical model as a distributed plasticity over the whole geometry. The study was to investigate the most influential parameters affecting joint shear failure due to column axial load, beam longitudinal reinforcement ratio, joint panel geometry and concrete compressive strength. The Finite Element Model (FEM) was verified against experimental test of exterior RC beam column connection subjected to lateral loading. The model showed good comparison with test results in terms of load-displacement relation, cracking pattern and joint shear failure modes. The FEA clarified that the main influential parameter for predicting joint shear failure was concrete compressive strength.

Prediction model for compressive arch action capacity of RC frame structures under column removal scenario using gene expression programming

Compressive arch action (CAA) is one of the important resistance mechanisms against progressive collapse in reinforced concrete (RC) frame buildings at small deformations. In this study, the distinguishing features of Gene Expression Programming (GEP) are utilized in order to establish a prediction model for the CAA capacity of RC beam-column substructures. The proposed equation correlates CAA capacity with six input parameters, i.e., compressive strength of concrete (fꞌc), double-beam span-to-depth ratio (Ld), width of beam (b), top and bottom longitudinal reinforcement ratio at the joints (ρt &ρb, respectively), and the ratio of axial restraints stiffness to the axial stiffness of beam (α). The data for the above-mentioned variables is collected from different studies to develop the proposed model and subsequently implemented for the verification purpose. Different statistical and external validations criteria recommended in literature are carried out to assess the performance of the developed model. Furthermore, sensitivity and parametric analyses are also performed using criteria available in literature. The performance of the genetically developed GEP model was checked and compared with models developed by using regression techniques. The GEP model demonstrated superior performance to linear and non-linear regression methods. The results show that the developed model is successfully capable of evaluating the CAA capacity of RC beam-column substructures and is incredibly imperative for prediction rationales.