Axial Load Ratio Research Articles

Lateral load response of L-shaped steel–concrete composite shear walls using multi-partition steel tube

Behavior of L-shaped multi-partition steel–concrete composite shear walls (MP-SC-CSWs) subjected to the cyclic lateral load is experimentally and numerically evaluated. Such composite shear walls possess proper capacity, stiffness, and ductility, as the steel tube strengthened by inner steel plates considerably confines the infill concrete. Four large-scale L-shaped MP-SC-CSW specimens were designed, fabricated, and tested. The L-shaped specimens were exposed to lateral hysteretic loading and axial compression loading. The experimental parameters were axial load ratios and height-to-depth ratios (wall aspect ratios). The experimental results indicated that the L-shaped MP-SC-CSWs had high lateral capacities, energy dissipations, and good ductility. Based on the experimental observations, specimens failed in flexure mode. Increasing the axial load ratio enhances the capacity to dissipate energy but decreases the ductility. The tested specimens could meet the drift requirement of the specification even when subjected to a high design axial load ratio of 0.76. Additionally, the wall aspect ratios had little influence on the ductility. 3D nonlinear finite element models of tested specimens were established and verified with test results to conduct further numerical studies. A simplified method based on the plastic stress distribution was developed and confirmed by the experimental and finite element analysis to calculate the flexural capacities of MP-SC-CSWs.

Pile Group Effect Modeling and Parametric Sensitivity Analysis of Scoured Pile Group Bridge Foundations in Sandy Soils under Lateral Loads

Scour can increase the earthquake-induced damage in pile group foundations. Quantifying the parameter sensitivity of the seismic performance for scoured pile group foundations is essential for the optimal design and retrofit of bridges located in seismic-prone regions. Such quantification requires numerical models that are computationally efficient and accurate in describing the mechanical behavior associated with the complex soil–foundation–structure interaction of these systems. This study proposes an efficient finite-element model (FEM) of pile groups based on a beam on the nonlinear Winkler foundation approach. This FEM uses asymmetric p-multipliers to describe the different soil resistance exerted on leading and trailing piles when applying cyclic lateral loads. The proposed FEM is validated by comparing the numerical response with the experimental measurements taken from a quasi-static test available in the literature and is used to perform an extensive parametric sensitivity analysis to quantify the response sensitivity to 11 structural and soil parameters. Tornado diagrams are employed to identify an importance ranking of these parameters on the seismic performance of scoured pile groups. The obtained results indicate that the proposed FEM is able to capture both the global and local structural responses of pile group foundations. The parametric sensitivity analysis shows that pile group foundations have considerable ductility capacity. Pile diameter and axial load ratio of piles are the most important parameters for the seismic performance of pile groups. Increasing the pile diameter is the most efficient approach to improve the seismic performance of a pile group when considering scour effects. The seismic performance of a scoured pile group deteriorates with increasing piles’ axial load ratio. For a deep pile group foundation, seismic performance is very little sensitive to pile length and relative density of sand. Based on the results of the parametric analysis, recommendations are proposed for the seismic design of pile group foundations with scour effects.

NONLINEAR FINITE ELEMENT ANALYSIS OF REINFORCED CONCRETE SHEAR WALLS

Advanced computational modeling for the nonlinear analysis of reinforced concrete shear walls is presented. To this end, thirteen shear walls, with height-to-width ratios of 1.0 and 2.0, were analyzed and compared with the experimental data reported by Lefas and co-workers in 1990. These ratios were carefully chosen to enable the structural assessment of shear walls with realistic geometry under monotonic horizontal loading via computer simulations. In the analysis, the nonlinear behavior of concrete was represented by fracture-plastic constitutive models, implemented in the context of smeared crack approach and crush band method. From the results presented, it is shown that the modeling approach presented in this paper is capable of predicting the full response of the walls with good accuracy. This includes the post-cracking response, failure loads and crack patterns at various stages of loading, which are useful to characterize failure process. The influence of key parameters (height-to-width ratio, axial load ratio, web reinforcement ratio) on overall response is discussed.

Seismic performance of concrete-encased hexagonal CFST column base: Design method

This paper presents the parametric analysis and design method for the concrete-encased hexagonal concrete-filled steel tubular (CFST) column base under combined compression and biaxial bending. The corresponding experimental and numerical investigations on the seismic performance of the concrete-encased hexagonal CFST column base under combined compression and biaxial bending have been presented in the companion paper (Yang et al., 2023). The finite element model established in the companion paper is used to study the influence of key parameters on the load bearing capacity and the distribution of internal force. These parameters include those of the CFST column, the outer RC, the plate-anchor component, the axial load ratio and shear connectors. A total of six failure modes are identified, including three types of flexural failure and three types of shear failure. The ultimate capacity and ductility of the column base with flexural failure at the bottom or top of the plate are higher than that of other four failure modes, which are determined as the reasonable failure modes for practical application in the design and analysis of concrete-encased column bases. A novel design approach for the concrete-encased CFST column base is introduced. A simplified method is proposed to predict the flexural resistance of the concrete-encased CFST column base, following up with the shear strength calculation of outer RC to determine the stirrup arrangement. Some constructional recommendations are also proposed.

Lateral load resistance of reinforced concrete columns with brittle details

AbstractAnalytical models for shear strength and deformation capacity estimation of reinforced concrete members are essential for the practical implementation of performance‐based seismic evaluation of existing structures and form a key part of current seismic assessment codes (e.g., EN 1998‐3 (2005), (2022), ASCE/SEI 41‐17). Although these models have been derived from regression or calibration of large datasets collected from experimental literature, discrepancy persists between experimental and analytical estimates, especially in cases of members with old‐type detailing. The evident uncertainty about parametric dependencies of the underlying mechanistic problem motivated the present work, where a set of benchmark columns that represent older structural detailing are studied parametrically through advanced finite element simulation. Parameters considered were, the axial load ratio, transverse reinforcement amount and spacing, longitudinal reinforcement ratio, and anchorage/lap splice detailing; results were gauged in terms of the resulting drift ratio (deformation capacity) at the performance limit states and were compared with the Code estimates to evaluate their limits and conservatism. The simulation results were used to vet the assumptions that underlie the simple mechanistic models used in deriving seismic design expressions for yield and ultimate deformation capacities, shear strength, and the rate of its degradation with increasing ductility.

Seismic performance of concrete-encased hexagonal CFST column base: Experimental and numerical analysis

This paper presents the seismic behaviour of concrete-encased hexagonal concrete-filled steel tubular (CFST) column base under combined compression and biaxial bending. A total of 12 column base specimens are tested in terms of failure modes, load-displacement relationship, strain distribution, strength and stiffness degradation and energy dissipation capacity. The main parameters include the height of the outer reinforced concrete component, the loading angle of lateral load, the axial load ratio, the cross section of the CFST column and the base type. A finite element model is established, validated, and used to study the distribution of internal force. The effects of some key parameters on the internal force distribution of column base are studied, including the second-order torsion, the loading angle, the loading path of the lateral load and the sustained load. Three types of flexural failure modes are identified in both experimental and numerical investigations. The outer RC component as well as the axial load ratio have a significant influence on the failure mode of the column base. The concrete-encased column base tends to fail at the top section of the base plate with a higher axial load level. The outer reinforced concrete not only resists external load with the CFST column and plate-anchor component together, but also improves the strength and ductility of the CFST column.

Seismic performance of composite jacket-confined square high-strength concrete-filled steel tube columns

Adding external confining jackets in the potential plastic hinge regions is a practical approach to improving the deformation capacity of square concrete-filled steel tube (CFST) columns with high-strength concrete (HSC). To investigate the seismic behavior of composite jacket-confined square CFST columns with HSC, three jacket-confined CFST (JCCFST) columns and two CFST counterparts with concrete compressive strength of approximately 125 MPa were tested. The test variables included the jacket configuration and steel tube strength. The test results demonstrated that both the jacket-confined region and the adjacent unconfined region could be damaged when the jacket length was 1.25 times the steel tube width. Finite element analyses were also performed to comprehensively investigate the influence of the parameters on the column behavior. It was found that the ultimate drift ratio, θu, increased approximately in proportion to the effective jacket confinement index, λm, and the confinement index of the CFST section, ξs, and decreased rapidly as the axial load ratio, n, increased. The ratio of the moment capacity of a JCCFST column to that of the corresponding CFST column, Mju/M0u, increased as λm increased. The influence of n and ξs on Mju/M0u was not significant. Formulas for designing the confining jacket were also developed.

Lateral impact behaviour of post-fire steel-reinforced concrete-filled steel tubular members: Experiment and evaluation method

Steel-reinforced concrete-filled steel tube (SRCFST), which exhibits superior mechanical behaviour and fire resistance than traditional concrete-filled steel tube (CFST), is widely used as a main load-carrying component in different structures. Structure might experience severe damage even collapse as a result of both impact and fire in extreme events. This study reports an experimental investigation on the responses of post-fire SRCFST members under lateral impact. Impact tests on 12 SRCFST specimens after fire were conducted, and the main parameters considered include the fire exposure time, impact height, axial load ratio, and section steel type. The temperature-time curves, failure modes, impact force, midspan deflection, axial force, plastic deformation, and energy absorption are investigated. The results show that post-fire SRCFST specimens under lateral impact experience global flexural failure. As the fire duration increases, the global deformation and local buckling of the specimen become more visible, and the plateau impact force decreases while the midspan deflection increases. In addition, based on the equivalent temperature of SRCFST members and the membrane force factor method, new simplified evaluation methods are proposed for calculating the dynamic flexural capacity and maximum deflection of SRCFST members subjected to lateral impact.

Seismic behavior of RC square columns strengthened with LRS FRP under high axial load ratio

A new type of fiber-reinforced polymer (FRP) with a tensile rupture strain of more than 5% was used for the seismic retrofitting of reinforced concrete (RC) square columns in this paper. A control column and 9 FRP-wrapped RC square columns were prepared with different number of FRP layers and FRP types. The seismic performance was comprehensively discussed and analyzed in terms of the failure modes, hysteretic behaviors, cumulative energy dissipation and FRP strain evolution. Experimental results showed that the ductility of specimens had a remarkable improvement as the confinement stiffness increased. Moreover, the buckling of longitudinal bars was restricted and postponed. Numerical analysis was conducted in OpenSees to further research the seismic performance of specimens based on an LRS FRP-confined concrete model and a reinforcing bar buckling model considering FRP confining effect. The simulated results were in close agreement with the experimental results. Parametric analysis was also conducted to investigate the influence of the FRP wrapping thickness, axial compression ratio and longitudinal reinforcement ratio on the seismic performance.

Experimental and theoretical study on seismic behavior of non-seismically designed shear walls with moderate shear span-to-length ratios

This study aims to examine the seismic performance of non-seismically designed shear wall with moderate shear span-to-length ratios (SLR) under relatively high axial loads. Four wall specimens with varying parameters, such as shear-to-flexure strength ratio, SLR, and axial load ratio (ALR) are fabricated and tested under cyclic loads. The experimental results, encompassing crack patterns, failure modes, hysteretic behavior, stiffness degradation, energy dissipation, and reinforcing bars strains, are presented and discussed. Digital Image Correlation (DIC) technology is employed for a comprehensive analysis of the crack patterns and deformation components of the tested specimens. The effective stiffness, including both effective flexural and shear stiffness is obtained through a deformation components analysis. These values are compared to the recommended values provided in FEMA 356 and ASCE 41–17. Moreover, the generalized force-deformation relationships in ASCE 41–17 are evaluated using the experimental results. Subsequently, a novel theoretical model for determining the force-deformation relationship of shear walls, incorporating stiffness degradation and flexural-shear interaction, is proposed and validated with test results. The results demonstrate that the proposed model effectively predicts the relationship between force and displacement.

Cyclic performance of T-Shaped CFST column to steel beam joint with vertical stiffener

This paper proposes experimental and analytical research on T-shaped concrete-filled steel tubular (CFST) columns to steel beam joints in residential buildings. A novel vertical stiffener joint was advised in this paper. Six joints of 1/3 scale were performed low-cyclic loading tests, to study the seismic performance of the joints. Test parameters contain axial load ratio and vertical stiffener size. Test results indicated that the steel beam exhibited buckling failure, making all hysteretic curves present spindle-shaped. All joints demonstrated sufficient energy dissipation capacity. The peak and ultimate load decreased with increased axial load ratio. The failure mode, hysteresis curves, and skeleton curves achieved from the finite element method (FEM) are consistent with the test results. Finally, a mechanical model based on experimental and FEM results is proposed to evaluate the moment bearing capacity of the specimens.

Cyclic loading test for lightly reinforced exterior wall with openings

Recently, slender and lightly reinforced exterior walls with large openings have been frequently used in high-rise residential buildings for economical construction. Although the exterior walls can be severely damaged by moderate earthquakes, minimum reinforcement is used, and the seismic details are not used in the current design practice because it is assumed that the seismic performance of the exterior walls is not significant in the entire structure. To investigate the strength and damage mode of the exterior walls, four exterior wall specimens with openings were tested under cyclic lateral loading. The main test parameters were the type of the openings (i.e., small, horizontal slot, vertical slot), and the reinforcement ratio in the horizontal components (horizontally 0.42–1.29%, and vertically 0.28–0.89%). The test results indicated that the peak strengths of the exterior walls with large depth of the horizontal components reached the nominal flexural strengths calculated by assuming solid walls and neglecting the opening effect. However, due to the premature tensile fracture of the vertical rebars, the lateral stiffness was significantly degraded, and the energy dissipation was limited. Further, the maximum crack width was affected by opening type and reinforcement ratio. A parametric study was conducted using a finite element (FE) model to investigate the effects of the design parameters. Based on the test and analysis results, a design recommendation for exterior walls with openings was provided. The exterior walls can be designed as solid walls under the following limited conditions: the total opening areas are less than 10% of the wall area in elevation, the relative flexural stiffness of the horizontal components is greater than the lateral stiffness of the walls, and the axial load ratio is less than 10%. Further, the allowable lateral drift ratio for permissible crack damage was suggested to be 0.10%.

Stability bearing capacity of concrete filled steel tubular columns subjected to long-term load

Concrete-filled steel tube (CFST) are commonly used in modern building and bridge applications. Despite their popularity, studies on the investigation of the influence of long-term load on the stability bearing capacity of such elements are scarce. This study investigates how the key parameters including slenderness ratio (λ), axial load ratio (m), and eccentricity ratio (e/r) affect the stability bearing capacity of a CFST column under sustained load. Twenty three CFST columns were fabricated to investigate the effect of long-term load on the stability bearing capacity. Fourteen specimens were subjected to constant compressive loading for 462 days and then tested for failure. The remaining 9 were companion load-free specimens. A three-stage finite element method was used to predict the stability bearing capacity after creep. The results indicate that the stability bearing capacity of CFST columns decrease after being subjected to long-term load. Both the experimental and numerical results indicated that the load of steel tube for long-term load specimens reaching up to the elastic–plastic and plastic process was lower than that of the load-free specimens. Moreover, the corresponding strain of the creep specimens was greater than that of the load-free specimens when the member reached the maximum load. Benchmarking analyses have shown that the creep reduction coefficient (kcr) proposed for CFST columns can be used to predict the reduction of stability bearing capacity after creep. Furthermore, a collected database comprising 49 CFST specimens subjected to long-term load was used to investigate the proposed formulae for kcr. The results show that the formulae were consistent with the experiment results.

Behaviour and design of composite walls under lateral loading and combined loading

This study aims to investigate the behaviour of concrete filled composite walls (CF-CWs) without any boundary elements under lateral loading and combined axial and lateral loading. Under this objective, an experimental programme was set covering both compact and slender CF-CWs utilising different connector types and arrangements. Specimens were designed with the aspect ratio (height to width ratio) of 1.9 so that the in-plane flexural behaviour dominated the failure modes. Meanwhile, for the combined loading, different axial load ratios (n) were applied to the specimens in order to investigate the effects of axial load and the relative lateral load-displacement responses. An extensive numerical study was conducted following the experiments with over one hundred three-dimensional finite element models. The simulations involved S690 high-strength steel together with high-strength concrete C100. The accuracy of the models was validated with the experimental results. The experimental and numerical outcomes were presented, analysed and discussed in detail. In addition, design provisions were proposed to calculate the in-plane flexural capacity of CF-CWs without boundary elements with different aspect ratios. The design recommendations can be applied to the CF-CWs with mild steel as well as high-strength steel up to S690. The validity of the recommendations was examined by this study and the available data from the previous literature.

Axial-flexural strength of steel-concrete composite shear walls

A predictive equation is proposed for the axial-flexural strength of rectangular and flanged Composite Plate Shear Walls-Concrete Filled (C-PSW/CF), with and without endplates and boundary elements. The proposed equation is based on plastic stress distribution, adjusted by coefficients to account for influential design parameters. The adjustment coefficients are established by a regression analysis performed on the data developed using an extensive numerical parametric study. The continuum-based finite element model used for the simulations is first validated using the available test data. The effects of various design variables, including the aspect ratio, slenderness ratio, reinforcement ratio, axial load ratio, infill concrete compressive strength, and yielding strength of the steel faceplates on axial-moment are then numerically examined. Four cross-sections, including double skin plate, double skin plate with endplates, double skin plate with boundary elements, and double skin plate with flanges, are considered. The results are used to develop a new predictive equation to obtain the flexural strength of C-PSW/CFs in presence of axial loading. The proposed equation is finally validated using the experimental test data and its accuracy is evaluated by comparing it to available predictive equations and the method proposed by the 2016 AISC Seismic Provisions. The results show that the proposed design equation can well predict the flexural moment capacity of C-PSW/CFs with various cross-sections in presence of axial loading.

Behavior of circular concrete-filled steel tabular columns under monotonic and cyclic torsions

This paper studied the behavior of circular concrete-filled steel tabular (CFST) columns under monotonic and cyclic torsional loading. Experiments were performed on 16 CFST columns, followed by analyses. Each column was axially loaded by a constant axial load with ratios of 0–0.7 and monotonically or cyclically twisted until failure. Experimental results showed that the failure modes of CFSTs under monotonic and cyclic loading were similar and torsional buckling of steel tubes was absent due to the mutually beneficial interaction between the steel tube and concrete. An axial load ratio ≥ 0.5 resulted in the descending branch, reducing the ductility by up to 17.8%. The axial load ratio marginally affected the yield torsional moment capacity of CFSTs but considerably affected the elastic rotational stiffness. The yield rotational stiffness increased and the yield rotation decreased as the ratio of the axial load increased to ∼0.3. Further increase in the axial load ratio had an inverse effect. Cyclic loading reduced the yield and ultimate torsional moments by 6.4% and 11.1%, respectively; however, it did not induce a stiffness degradation. Further, it reduced the yield and ultimate rotations by 10% and 30.7%, respectively. A model to predict the torsional yield moment capacity was proposed based on the concept of decoupling the resistances resulting from cyclic loading. The proposed model is simple and accurate, and will be useful for engineers in practice.

Experimental and numerical investigation on hysteretic behavior of posttensioned precast segmental Concrete-filled double skin steel tubular piers

The posttensioned precast segmental concrete-filled double skin steel tubular (CFDST) piers proposed in this study combines the advantages of posttensioned precast segmental piers and composite CFDST piers, in such way to reduce on-site construction burdens, increase section modulus, and reduce self-weight. To investigate the hysteretic behavior of this new type of bridge pier, one posttensioned precast segmental CFDST pier was designed and tested under cyclic lateral loading, with one cast-in-place CFDST pier as reference. Test results show that the proposed posttensioned precast segmental pier performs well with good ductility, satisfactory energy dissipation, and small residual displacement. The damage to precast segments is effectively avoided by using CFDST members. Moreover, a numerical study was also conducted to investigate the influences of different design parameters on the hysteretic behavior of posttensioned precast segmental CFDST piers. The design parameters studied in this paper included the pier aspect ratio, amount of energy-dissipating (ED) bars, axial load ratio due to gravity, axial load ratio due to prestressing force, initial stress level in prestressing strands and CFDST cross-sectional parameters. It has been found that the amount of ED bars, axial load ratio due to gravity and axial load ratio due to prestressing force are the more important factors on energy dissipation and self-centering capacities. The pier aspect ratio being greater than 7 has a negative effect on residual drift ratio of posttensioned precast segmental CFDST piers due to P-Δ effect. The initial stress level in prestressing strands has little effect on energy dissipation and self-centering capacity, but influences the failure mode and deformation capacity.

Experimental and numerical study on seismic performance of precast concrete hollow shear walls

Precast hollow shear wall structure is a new type of prefabricated shear wall structure. The wall of the structure is composed of precast hollow panels, cast-in-place boundary elements and cast-in-place vertical splice joints. The precast hollow panel is provided with vertical and horizontal holes, and concrete is poured at the construction site to form solid wall. Horizontally inserted reinforcement bars are arranged in the horizontal holes of the hollow panels, which are indirectly overlapped with the horizontally distributed reinforcement bars in the hollow panels to realize the connection of horizontal reinforced bars of adjacent hollow panels in the same story. In order to study the seismic performance of precast hollow shear wall, quasi-static tests were conducted on five hollow shear wall specimens with aspect ratio of 1.61 to 2.07. The experimental results showed that the specimens failed due to flexure-compression, which achieved the expected design target of “strong shear and weak bending”, and horizontal reinforcement indirectly connected by horizontal inserts could effectively resist horizontal shear force. The ultimate drift ratios of specimens ranged from 1.4% to 2.6%. The load-carrying capacity of the hollow shear wall could be calculated according to the formula for cast-in-place shear wall provided by the GB 50010–2010. Two kinds of connection between the hollow panels (direct splicing connection and cast-in-place vertical splicing connection) could make the hollow panels become a whole. The seismic performance of the hollow shear wall with precast boundary elements also met the requirements of the GB 50011–2010. Finally, the finite element model of shear wall specimen was established and verified using MSC.MARC software. On this basis, the impact of key parameters on the seismic performance of the precast hollow shear wall was studied. The results show that the axial load ratio and boundary longitudinal reinforcement ratio had great influence on the seismic performance, while the diameter of the steel bar inserted horizontally had little effect on the seismic performance of the precast hollow shear wall with higher aspect ratio.

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.

Parametric Studies on Seismic Performance of New Precast Braced Concrete Shear Walls under Cyclic Loading

A new precast concrete (PC) shear wall system with diagonal-shaped or cross-shaped concealed bracing was developed and experimentally validated, owning sufficient energy-dissipation capacity, in a previous study. Given that the seismic performance of such precast braced concrete shear (PBCS) walls is not comprehensively understood, this paper numerically investigates the influences of axial load ratio (ALR) and various reinforcement ratios (RRs) on the mechanical behavior of PBCS walls under cyclic loading. For this purpose, the numerical models based on the layered-shell element are developed to analyze the PBCS walls and validated regarding the deformation capacity of experimental results. A total of 156 PBCS wall models with different ALRs, longitudinal RRs of the boundary columns and bracing, and horizontal and vertical web RRs are established and tested under cyclic loading. It is concluded that the effects of bracing RR and horizontal web RR on the hysteretic responses are negligible and thus can be designed as the minimum suggested by the codes. However, the ALR, boundary column RR, and vertical web RR can significantly affect the lateral bearing capacity and displacement ductility of PBCS walls. In addition, the ALR limits for both types of PBCS walls are presented to satisfy the ductility requirements. Moreover, the simplified formulations regarding the bearing capacity and ductility of PBCS walls are proposed, respectively, which show good agreement with the numerical results. The outcomes of this research not only provide an in-depth understanding on the seismic behavior of the PBCS walls, but also promote the design code expansion and potential engineering application of such new types of PC shear walls.