Column Axial Load Research Articles

Investigation of column axial load effect for bolted-end-plate type steel connections

Steel moment resisting frames (MRFs) experience not only lateral movements but also vertical ones during a seismic event. Particularly, the vertical deflections in the members of the structural system cause an increase in the possibility of high column axial compressive loads (CACLs) and correspondingly the bending moment value in the beam-to-column joints. Thus, the beam-to-column joint fails in an unanticipated form. Unfortunately, the available literature about this problem is limited and inconclusive. To help bridge the gap, this study examines the effects of the CACL on the structural behavior of bolted end-plate beam-to-column connections. In this context, this study has three purposes: verifying the experimental tests by the numerical models and evaluating the CACL effect both purely and depending on the variation of fundamental parameter values governing the joint components on the verified numerical models. The numerical analyses of the reference test specimens which are borrowed from the experimental tests in the literature are conducted utilizing a finite element (FE) model including material, geometry, and contact nonlinearities. It is concluded that a possible increase in CACL causes a deterioration in the structural behavior of the beam-to-column connection depending on the moment level transferred from the connection to the column and the shear stiffness of the panel zone.

Behavior of RC Columns with Different Internal Ties Configurations Subjected to Axial Load: Numerical Study

Reinforced concrete columns use a lot of ties, particularly inner cross-ties in large columns. The major goal of this work is to create new approaches for horizontal reinforcement in RC columns and evaluate their effect on column behaviour. The suggested V-ties as transverse reinforcement, which would replace the cross-ties features, are cost-effective. They make it possible to complete projects faster and spend less on labour and material. Numerical study is carried out. FE models for sixty (60) specimens were developed. Each specimen is modeled with different cross-sections (250*250 mm), (500*500 mm), (1000*1000 mm), (250*500 mm) and (250*1000 mm) at different values of spacing 50 mm, 100 mm, and 200 mm. It was discovered that adopting V-tie techniques instead of traditional ties might increase column axial load capacity, reduce early local buckling of longitudinal reinforcing bars, and enhance the concrete core confined to RC columns.

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.

Mechanics guided data-driven model for seismic shear strength of exterior beam-column joints

This study presents an enhanced predictive model for the seismic shear strength of exterior beam-column joints (BCJs). Initially, the principles of strut-and-tie mechanism and variable selection procedures were first utilized to identify the most influential parameters. Subsequently, an evolutionary algorithm, specifically multigene genetic programming (MGGP), was utilized to search for the near-optimal predictive model. The dataset used to develop, train, and test the proposed model was compiled from previously published tests, focusing specifically on cyclically loaded exterior BCJs that encountered shear and flexure -shear failures. The prediction performance of the developed model was assessed through various statistical measures, and then compared with that of other existing models. Additionally, sensitivity analyses were also performed to identify the influence and importance of each design parameter. The results demonstrated that the methodology employed in this study yielded an elegant model that adheres to the underlying mechanics and provides higher prediction accuracy compared to existing models. Furthermore, the sensitivity analyses showed that BCJ shear strength positively correlates with concrete compressive strength, beam reinforcement, joint transverse reinforcement, column intermediate vertical reinforcement, and axial load ratio, while it negatively correlates with the joint aspect ratio. Among these design parameters, beam reinforcement has the greatest influence on the model response, followed by concrete compressive strength. Conversely, column intermediate vertical reinforcement and axial load ratio have the least impact on the model response. The notable prediction capabilities and robustness demonstrated by the developed model render it an efficient design tool with promising potentials for adoption by practicing engineers and for consideration in design guidelines.

Unified machine learning approach for predicting CFST column axial load capacity

Unified machine learning approach for predicting CFST column axial load capacity

Performance-based seismic design of Ultra-High-Performance Concrete (UHPC) bridge columns with design example – Powered by explainable machine learning model

Ultra-high-performance concrete (UHPC) has rapidly become a material of choice in modern construction owing to its favorable properties, such as superior strength, toughness, and durability. Yet, accurate quantification of damage states using appropriate engineering demand parameters (EDPs) remains a significant challenge in the performance-based seismic design (PBSD) of UHPC columns. This gap is especially evident in the scarcity of research focused on the PBSD of UHPC columns. Therefore, this study aims to develop an explainable machine learning (ML) powered predictive model for the drift ratio limit states of UHPC bridge columns across four damage states. To achieve this, a fiber-based numerical model was developed and then validated against large-scale experimental results of UHPC columns tested under reverse cyclic loading. The Latin hypercube sampling method is employed to generate a comprehensive database of UHPC bridge columns (10,000 UHPC columns), considering uncertainties across a spectrum of design factors, including column geometry, material characteristics, reinforcement ratio, and axial load ratio. The drift ratios at the initiation of four damage states are determined using the numerical model. Subsequently, the power of the ML algorithm is leveraged to introduce drift ratio limit states for UHPC columns that capture the onset of four different damage states. The efficacy of the developed model is assessed using a range of statistical metrics, including the composite fitness score, DX% metrics, coefficient of determination, root mean squared error (RMSE), normalized RMSE, and mean absolute error, which demonstrated high predictive accuracy of the drift ratio limit states on both the training and unseen or test datasets. Furthermore, a model-agnostic Shapley Additive exPlanation (SHAP) is used to explain the output of the model and examine the influence of various design factors on drift ratio across the damage states. Notably, the axial load ratio and aspect ratio are found to be major factors in determining the drift ratios across the damage states. The developed model is deployed into a software tool in order to enable its practical application. Additionally, the implementation of the developed model in the context of PBSD is illustrated through a design example. Furthermore, the study proposed capacity uncertainty parameters to aid the fragility assessment of UHPC columns. Finally, the proposed model, along with capacity uncertainty parameters, is used for the fragility assessment of UHPC columns reinforced with varying steel bar grades. The results demonstrate the less vulnerability of UHPC columns reinforced with higher bar grade, yet the effect of bar grade lessens at severe damage levels.

Effect of vertical stiffeners on the seismic performance of T‐shaped CFST column to steel beam joint

SummarySpecial‐shaped concrete‐filled steel tubular (SCFST) columns have recently been developed for efficient steel‐concrete composite construction. In this study, a novel vertical stiffener joint for the SCFST column and steel beam frame structure is proposed. Five SCFST columns with H‐section beam joints were investigated under cycling loading. The test parameters mainly consider the column stiffening form, vertical stiffener type, and the column axial load. The failure pattern, hysteretic curves, and strain development of specimens are analyzed. Experimental results demonstrate the proposed joint with vertical stiffeners can develop the steel beam's full plastic flexural capacity and exhibit favorable seismic performance. In addition, a finite element (FE) model is developed to explore the effects of the following parameters on the hysteretic performance: vertical stiffener sizes, width‐to‐thickness ratio of column steel tube, and the column axial load. Based on the experimental and FE analyses, a stress and deformation model of the joint steel tube was established. To facilitate the practical applications, a calculation formula for joint strength was also put forward, considering the contribution of vertical stiffener, and front and side steel plates of the joint steel tube.

Cyclic behavior and shear strength of exterior reinforced concrete beam-column joints with inclined columns

The adoption of inclined columns results in inclined beam-column joints (BCJs). Although the behavior of regular BCJs have been widely investigated, researches on the cyclic behavior and shear strength of inclined BCJs are limited, and further investigations are required to ensure seismic safety of the frames adopting inclined columns. In this work, cyclic behavior of inclined BCJs was first experimentally studied by testing 3 exterior BCJ specimens. After that, a finite element model was developed and validated by the experimental results. The model was subsequently used for parametric study to reveal the effects of key parameters on the joint shear strength. In the end, a theoretical model based on the softened strut and tie model was proposed to estimate the joint shear strength of inclined BCJs. Results showed that the inclination caused an initial joint shear force under column axial load, leading to different joint behavior in positive and negative loading directions. The joint shear strength was increased in the inclination direction but declined in the other direction, while the ductility showed an opposite trend. Meanwhile, regardless of the inclination direction, energy dissipation and equivalent viscous damping of BCJs were reduced and stiffness degradation was slowed. The parametric study revealed that the inclination effect was amplified with higher inclinations. The overall joint shear strength can be effectively enhanced by adopting higher concrete strength and column axial load. Increasing the joint stirrup ratio was also beneficial for the shear strength, but its efficiency was relatively lower. Based on the comparison of the predicted joint shear strengths and those from experimental and numerical programs, it was proved that the modified strut and tie model was advantageous over the formulas in GB 50010 in capturing the shear strengths. This work contributes to understanding the cyclic behavior and shear strength of inclined BCJs to improve seismic safety of frames adopting inclined columns.

Experimental Study on the Seismic Performance of Brick Walls Strengthened by Small-Spaced Reinforced-Concrete–Masonry Composite Columns

Through low-cycle reciprocating tests on 11 masonry wall specimens strengthened using reinforced-concrete–masonry composite columns, the effects of the position of the composite column, height-to-width ratio, column reinforcement ratio, and axial load ratio on their load-carrying capacity, stiffness, ductility, and energy dissipation capacity were investigated. It was experimentally found that, by strengthening brick walls with RC–masonry composite columns, the concrete and masonry parts can work together effectively, the failure mode shifts from shear to flexural failure, and the strengthened walls exhibit improved bearing capacity, ductility, and energy dissipation performance compared to unstrengthened masonry walls. It is suggested the composite columns can be placed at the ends of the wall if a strengthening measure is required. For walls with height-to-width ratios greater than 1, placing composite columns in the middle of a wall has little effect on the bearing capacity and stiffness of the wall but can improve the ductility of the wall. The height-to-width ratio is a primary factor influencing the structural performance of masonry walls strengthened using composite columns. A smaller height-to-width ratio leads to higher load-carrying capacity and stiffness but may result in reduced ductility. In comparison, the impact of the column reinforcement ratio and axial load ratio is relatively weaker. The flexural capacity of the masonry wall after strengthening can be obtained using the calculation method for concrete members subjected to a combined action of flexure and compression, in which the compressive strength of the masonry is considered.

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.

Hybrid simulation framework with mixed displacement and force control for fully compatible displacements

AbstractA novel framework for hybrid simulation of the seismic response of structures is presented that employs a mixed displacement and force control strategy. A key feature of this framework is a controller‐based displacement‐to‐force transformation that enables compatible displacements between the numerical and experimental model for force‐controlled degrees of freedom. The framework can be applied within conventional displacement‐based time‐integration algorithms allowing for implementation across a variety of software and hardware architectures; it is demonstrated here using OpenSees software with detailed nonlinear numerical models. This study includes numerical verification of the proposed force control strategy and actual implementation in a hybrid simulation of special moment frames with full‐scale beam‐column subassemblies. In the hybrid tests, the experimental column axial load is applied in force control due to the large stiffness and when combined with lateral seismic loads, results in column local buckling with significant axial shortening. The hybrid simulation results verify that the proposed mixed displacement and force control strategy effectively enforces displacement compatibility and force equilibrium between the numerical and experimental structures at the boundary degrees of freedom.

Shear strength formula for interior beam-column joints with plain bars in existing buildings

Beam-column joint behavior in Reinforced Concrete (RC) structures is a key issue for earthquake engineering, because, under seismic loads, these elements are subjected to high stresses, which could lead to unexpected collapses, due to the development of brittle failure mechanisms. In Italy, many existing RC buildings constructed before the mid-1970's present structural deficiencies, as they were designed in the absence of the prescriptions of modern seismic codes. In particular, the use of plain reinforcing bars, inappropriate anchorage solutions and the lack of joint horizontal hoops are rather widespread.This paper presents an in-depth overview on seismic behavior of interior beam-column joints reinforced with plain bars, under cyclic loads, based on experimental results available in the literature. The inadequacies of certain reinforcement arrangements and details of tested joints are highlighted. A critical discussion of the damages and failure mechanisms developed in the joints, in relation to the reinforcement details and to the effects of the main influencing parameters, is provided. These parameters are the mechanical properties of materials, the geometry of the joint and the converging elements, and the column axial load. A formula to predict shear strength of joints with plain bars is proposed.Due to the lack of similar papers in the literature, the present analysis constitutes the basis for a comprehensive understanding of behavior of interior joints with plain bars under seismic actions. Moreover, due to the absence in the main current Codes of design formulas for the shear strength assessment of existing beam-column joints with plain bars, a design formula is also proposed. This formula is a valuable tool to design the retrofit intervention of existing buildings reinforced with plain bars, constituting a not negligible part of the built heritage.

EFFCT OF HOOPS AND COLUMN AXIAL LOAD ON SHEAR STRENGTH OF HIGH-STRENGTH FIBER REINFORCED BEAM-COLUMN JOINTS

A reinforced concrete frame is referred as "RIGID FRAMES". However, researches indicate that the Beam-Column joint (BCJ) is definitely not rigid. In addition, extensive research shows that failure may occur at the joint instead of in the beam or the column. Joint failure is known to be a catastrophic type which is difficult to repair. This study was carried out to investigate the effect of hoops and column axial load on the shear strength of high-strength fiber reinforced Beam-Column Joints by using a numerical model based on finite element method using computer program ANSYS (Version 11.0). The variables are: diameter of hoops and magnitude of column axial load. The theoretical results obtained from ANSYS program are in a good agreement with previous experimental results.

The shear strength of existing non-seismic RC beam-column joints strengthened with CFRP Sheets: Numerical and analytical study

A key part of RC structure seismic performance is the effective distribution of earthquake forces across all resistance elements through reinforced concrete (RC) beam-column (B-C) joints. By virtue of their ease of implementation and convenient material properties, Carbon-Fiber-Reinforced Polymers (CFRP) are highly utilized for strengthening existing structures with inadequate reinforcement or insufficient confinement. Previous experimental research revealed that debonding failure widely occurs on CFRP shear-strengthened B-C joints. The experimental research as well showed the value of column axial load makes a great contribution to such joint’s failure mode. Using CFRP U-jacketing to strengthen non-seismically B-C joints, this article presents a non-linear, two-dimensional FE model for investigating shear behavior. The developed FE model considered the adhesive layer between CFRP sheets and concrete to capture the debonding and a bond-slip model was implemented between concrete-to-CFRP sheets using connector elements. The FE results were verified versus experimental works from literature to prove the proposed FE model's accuracy with appreciate to load-deformation relation and failure modes. Depending on the verified FE model, a parametric study on shear-strengthened RC B-C joints with CFRP U-jacketing with free and fixed ends was performed below monotonic loading. In the existing study, several parameters, including column-to-beam flexural strength ratio (over strength ratio), concrete strength, and value of column axial load, were investigated on the structure's strength and ductility. Using the developed strut-and-tie model (STM), new design equations were proposed to calculate strengthened RC B-C joint's shear strength using CFRP. The proposed equations incorporate the interfacial bond among concrete and CFRP effect, as well CFRP sheet end boundary (free or fixed). The developed design equation’s ability to estimate shear strengths of strengthened B-C joints with CFRP was verified through experimental works and FE results. It was evident from verification results that the produced design equations were compatible with experimental and FE model results.

Post-blast capacity evaluation of concrete-filled steel tubular (CFST) column based on machine learning technique

In the present study, the post-blast axial load-bearing capacity of the CFST column under the close-in explosion is investigated. Dynamic response and residual axial load capacity (RALBC) of 1599 circular CFST columns are numerically studied using a validated finite element model. The effects of column dimensions, material properties, blast loading, and axial load ratio are discussed. Based on the huge database, prediction models of RALBC are developed using three commonly used machine learning techniques including Extreme Gradient Boosting (known as XGBoost), Artificial Neutral Network (ANN), and Support Vector Regression (SVR). Comparison results show that the prediction model generated by the XGBoost performs the best among the three methods followed by the ANN and SVR methods. The RALBC of the CFST columns can be estimated rapidly and accurately with the prediction model developed in the present study. Finally, the feature importance of the input variables is analyzed using the additive feature attribution method SHAP (Shapley Additive ExPlanation). The results show that geometric parameters are the main factors impacting the RALBC of the CFST columns under close-in explosion.

Effect of column flexural capacities and axial loads on bond behavior of interior beam-column joints

The bond behavior of longitudinal beam bars passing through the joint zone is affected by the column flexural capacity, while there is a paucity of research results; in addition, the bond behavior can be improved by the axial compressive load, while the upper limit of the axial load was still not clear due to lack of experimental researches with high axial load ratios (larger than 0.6). In this investigation, the hysteretic behavior of 8 interior joints with 600 MPa high-strength longitudinal beam reinforcing bars was compared and analyzed in detail. Four joints adopted the concrete-filled steel tubular column with continuous steel tube, namely CFSTJ specimens; and the other four joints, i.e., their counterparts, adopted the concrete-filled steel tubular column with discontinuous steel tube, namely TRCJ specimens. The discontinuous column steel tube led to different column flexural capacities and axial load ratios. The test results showed that all specimens exhibited good hysteretic behavior before 5% drift, and the bond behavior of CFSTJ specimens was better than that of their counterpart TRCJ specimens. Combining these observations with available test data of reinforced concrete (RC) interior joints in the literature, the effect of column flexural capacities and axial loads on the bond behavior was then further analyzed and quantified. Finally, based on provisions in NZS 3101 and EN 1998–1, more accurate design equations were proposed by considering the depth of column compression zone and limiting the axial load ratio.

Behaviour and design of monotonically loaded reinforced concrete external beam-column joints

This paper describes an experimental investigation into the influence of beam reinforcement detailing, column axial load and shear reinforcement on the joint shear strength of reinforced concrete external beam-column connections. A series of twelve external beam-column joint specimens were tested in three groups of four specimens. Series 1 investigated the influence of beam reinforcement anchorage type and bend radius. Series 2 studied the influence of column axial load on joint shear strength while series 3 studied the influence of intermediate column bars and joint shear reinforcement. The paper presents the experimental results and describes the influence of the considered variables on joint shear strength. Three existing empirical design equations for external beam-column are evaluated using data from this program and previously tested beam-column joint specimens. Finally, design recommendations are made.

Live load effects in hammer-head piers of continuous highway bridges and design equations based on numerical simulations verified by field tests

In this study, design equations are proposed to calculate the internal forces in hammer-head bridge pier components under the effect of live loads. For this purpose, first, the finite element model (FEM) of an existing bridge is built and the modeling approach is verified against field test results. Next, a four-span benchmark bridge representative of the bridges in the US is selected. FEM of the benchmark bridge is built, and sensitivity analyses are performed on the bridge model to identify the bridge parameters affecting the magnitude and distribution of the girder live load support reactions and hence the internal forces in the hammer-head pier components. The sensitivity analyses revealed that the number of girders, girder spacing, girder type, slab thickness and the overhang distance significantly affect the magnitude and distribution of the girder live load support reactions and hence the forces in hammer-head pier components. Then, parametric analyses of bridges are performed based on the sensitivity analyses results where each parameter is assigned a wide range of values. Subsequently, minimum least squares regression analyses of more than 50,000 data are performed to obtain equations to estimate the maximum cap beam moment and shear force, the maximum column moment and accompanying axial load as well as the maximum column axial load and accompanying moment. The hammer-head pier forces calculated using the design equations are shown to be in reasonably good agreement with FEM analyses results.

Structural Performance Comparison of Structural Systems Using LIRA and ETABS

This paper investigates a comparison of structural systems of high rise (96m of 30 stories) buildings subjected to gravity load and wind load of speed 90mph. Three structural systems, Moment frame system, Shear wall system, and Tube-in-Tube system of identical base area and loadings are structurally designed, in ETABS and LIRA software. Linear wind response analysis was carried out as per ASCE 7-05. Parameters like fundamental time period, Maximum story displacement, Maximum column axial load and Vertical floor displacement are considered in this study. As per the findings, the maximum story displacement is found to be within the allowable limiting value. Tube-in-Tube system shows a better performance from the other systems for minimizing the story displacement. The modal time period, vertical displacement and Maximum column axial load values are also minimum in Tube -in-tube system.

Finite element analysis to predict the cyclic performance of GFRP-RC exterior joints with diagonal bars

This paper presents a finite element modeling (FEM) approach to predict the cyclic response of glass fiber-reinforced polymer (GFRP) reinforced concrete (RC) exterior beam-column joints with different joint details. Four GFRP-RC exterior beam-column joints detailed with U or L-shaped anchorages at the end of the longitudinal bars of the beam, horizontal stirrups and additional diagonal bars (Z or U-shaped) at the joint region were modeled and analyzed under reversed cyclic loading. The FEM cyclic behavior in terms of load-drift ratio, cracking patterns, joint shear stress and strain evolutions were compared with the experimental behaviors. The FEM predicted load-drift ratio response, cracking patterns and dissipated energy showed good correlations with the experimental results. A parametric study was conducted to evaluate the influence of compressive strength of concrete, column axial load ratio and size of the additional diagonal bar on the performance of the GFRP-RC joints. It was found that an increase in the column axial load significantly degraded the performance in terms of strength, maximum joint shear stress and ductility of the GFRP-RC joints. Also, GFRP-RC joints with additional U-bars were able to resist higher joint shear stress and drift ratio than GFRP-RC joints with additional Z-bars, respectively.