Lateral Load Bearing Capacity Research Articles

Seismic Performance of Full-Scale Autoclaved Aerated Concrete Panel-Assembled Walls: Experimental Study and Numerical Modeling

Prefabricated panel-assembled wall systems, comprising a confining frame and infill lightweight panels of autoclaved aerated concrete (AAC), are widely employed in framed structures. Different from studies on a main frame with infill walls, this study aimed to explore the seismic performance of partition walls, which were fabricated with AAC panel-assembled walls and located outside of the main frames. Two full-scale specimens, one with a door opening and the other without, were constructed and cyclic loading tests were executed to examine the failure modes, hysteresis characteristics, envelope curves, ductility, strength and stiffness degradation, as well as energy dissipation capacity of the AAC panel-assembled walls. Additionally, a restoring-force model for the panel-assembled walls was developed and a method for predicting the lateral load-bearing capacity of the AAC panel-assembled walls was proposed. The findings indicated that the panels enhanced the system’s lateral resistance, energy dissipation capacity, and deformation capability. The door frame increased the initial stiffness, peak lateral load and energy dissipation capacity of the AAC panel-assembled wall compared to the wall without a door frame. Compared to the specimen without a door frame, the peak lateral load of the specimen with a door frame increased by 19.7–30.1%. The deformation capacity of the panel-assembled walls aligned with the requirements for concrete framed structures.

Experimental study on the seismic performance of GFRP-stiffened steel plate shear walls

This study conducted experimental investigations to evaluate the seismic performance of steel plate shear wall (SPSW) with infilled flat and corrugated steel plates stiffened by GFRP plates. Four half-scale specimens were subjected to cyclic quasi-static tests, comprising two specimens with ordinary flat and corrugated steel plates, and two specimens with flat and corrugated steel plates reinforced by GFRP plates. The objective of this study was to reveal how the form of steel plates (flat or corrugated) and the arrangement of GFRP plates influenced the seismic performance of SPSW. The research discussed the failure modes, lateral load-bearing mechanism, ultimate shear resistances, and energy-dissipating capacities of the different specimens. The experimental findings demonstrated that incorporating GFRP plates provided more effective reinforcement for corrugated SPSW compared to flat SPSW. According to the experimental data, the ultimate lateral load-bearing capacity, ductility, and energy-dissipating of the GFRP-stiffened corrugated steel plate shear wall have been increased by 9.3%, 46.4%, and 79.9% respectively compared with the unstiffened one, and the degree of stiffness degradation has been reduced by 10.2%. The findings of this study will provide important references for subsequent research on GFRP-stiffened steel plate shear walls.

Experimental and numerical analysis of assembled steel beam to CFDST column joint

A novel assembled joint between the concrete-filled double-skin steel tubular (CFDST) column and steel beams is developed in this paper. The joint is connected by extended endplates and high-strength bolts, and it is designed to facilitate post-disaster repairs. The pseudo-static test was performed on four 1:2 scaled joints, the endplate thickness, column form, and inner tube configuration were considered. The experimental results suggested excellent seismic performance of the joints, including plump hysteretic curves, high displacement ductility coefficients, and significant energy dissipation values. Then, accurate finite element (FE) models were established. Comparative results showed that the FE models better simulated the failure modes of endplate bending, weld tearing, local buckling of the flanges, and bolt fracture. In addition, there was a small deviation between the lateral load-bearing capacity obtained from tests and FE simulations. Next, stress analyses showed that the joint's yielding mode is from the flanges and endplates yielding to the outer tube web yielding. The stress on the inner tube was always lower than the yield stress, indicating that the CFDST column had a significant reserve of lateral load-bearing capacity. The main findings of numerous numerical analyses were that higher-strength endplates and steel beams with wider flanges substantially increased the lateral load-bearing capacity of the joint. Finally, a proposal was made to enhance the installation of ribs at beam ends. It improved the load-bearing capacity and initial stiffness and alleviated the stress concentration.

Lateral strength evaluation of innovative and traditional composite shear wall systems

This paper proposes formulations for predicting lateral load-bearing capacity of two types of composite shear wall (CSW) systems, which consist of a steel frame and a reinforced concrete (RC) plate attached to one side using bolts. Due to the high out-of-plane stiffness of the RC plate, it can effectively provide out-of-plane constraint to prevent out-of-plane deformation of the steel plate in CSW systems. However, in traditional CSW systems, direct contact between the RC plate and the frame often results in crushing at the former under seismic loading, thereby providing insufficient restraint against out-of-plane deformation of the steel plate. In contrast, the innovative CSW system with a gap maintained at the steel frame and RC plate exhibited superior seismic behavior than its traditional counterpart. While previous studies have investigated cyclic behavior and parameter effects of CSW systems, there remains a gap in evaluating their lateral strength. The proposed formulations show a mean distinction among theoretically determined and actual lateral load-bearing capacity less than three percent.

Research on Lateral Load Bearing Characteristics of Deepwater Drilling Conductor Suction Pile

The vast reserves of natural gas hydrates in offshore areas present significant challenges to development. Surface well construction technology is crucial for the extraction of deepwater natural gas hydrates. To ensure the safety of the subsea wellhead during the drilling process for deepwater natural gas hydrates, a novel conductor suction pile device has been designed, comprising a combination of suction piles and surface conductors. And research has been conducted to investigate the lateral stability characteristics of the conductor suction pile. Drawing upon the pile foundation load-bearing theory and the equilibrium of the differential element, a theoretical analysis model and corresponding governing equations of the conductor suction pile system are established. A solution for a multi-point boundary value problem by simplifying the conductor suction pile system into a two-end free beam is proposed. The governing equations are then converted into a first-order differential equation system, and the four-stage Lobatto IIIa collocation method program for the multi-point boundary value problem is developed and resolved using MATLAB 2023a. Furthermore, a case study of a well in the South China Sea elucidates the effects of wellhead load and seabed soil properties on the lateral load-bearing capacity of the conductor suction pile system, verifying the collocation method’s validity against the results from the finite difference method. After conducting a comparative analysis of the lateral load-bearing performance between conductor suction piles and traditional surface conductors, it is observed that conductor suction piles exhibit lower horizontal displacement and bending moments compared to surface conductors. Therefore, conductor suction piles demonstrate a substantial safety margin. The research findings provide a theoretical basis for the lateral stability of conductor suction piles during deepwater natural gas hydrate drilling. This offers a safe and efficient method for surface well construction in the extraction of natural gas hydrates.

Experimental Study on Seismic Performance of Prefabricated Monolithic Concrete–Polystyrene Panel Composite Wall Panels

A normal composite wall panel is a structural component composed of polystyrene insulation boards and concrete surface layers reinforced with steel wire mesh. It can be entirely prefabricated in a factory or constructed with the concrete surface layers cast on-site. A novel prefabricated monolithic concrete–polystyrene panel composite wall panel (CPC wall panel) is proposed in this study. The CPC panel features a middle part that is prefabricated in the factory while the reinforced concrete regions at its two side ends are cast on-site. To evaluate the seismic performance of the wall panel, 18 CPC specimens were designed, manufactured, and quasi-statically tested, through which the structural behaviors, failure mode, and load-bearing capacity were studied. In addition, the influences of the height-to-width ratio and the vertical compressive stress level on the seismic performance of the CPC panels were also investigated. The test results showed that the connectors spaced at 400 mm × 500 mm could ensure the concrete layers on both sides of the polystyrene board worked collectively under seismic conditions. When subjected to lateral loads, the interface between the newly poured concrete and the existing concrete exhibited good bonding. Moreover, the failure mode of the CPC wall panel was largely correlated to the height-to-width ratio that, for specimens having four steel bars of 12 mm diameter and a height-to-width ratio greater than 1, the flexural failure was initially developed, followed by diagonal shear failure. In specimens with a height-to-width ratio of 1, flexural and diagonal shear failures occurred almost simultaneously. For specimens with a height-to-width ratio of less than 1, the final diagonal shear failure was predominant. The longitudinal reinforcing bars at the two ends of the CPC panels could effectively improve their lateral load-bearing capacity, with the enhancement influenced by the height-to-width ratio, the vertical load applied to the wall panel, and the cross-sectional area of the steel bars. In practice, the lateral load-bearing capacity of the CPC panel can be conservatively evaluated using the calculation method of the reinforced concrete shear walls. Finally, the ductility of the CPC specimens was affected by the height-to-width ratio and the axial compressive stress level, such that the specimens with a larger height-to-width ratio and lower axial compressive stress exhibited better ductility.

Quasi-Static Test and Lateral Load-Bearing Capacity of a New Grid Pile Foundation for Long-Span Bridges

This study proposes a new form of underground diaphragm wall foundation with hexagonal sections, called the grid pile foundation (GPF), which is used for long-span bridges. To investigate the lateral bearing capacity characteristics of the integrated pile foundation, the quasi-static test as well as numerical simulations were conducted. Firstly, the quasi-static test was conducted to obtain the lateral load–displacement curve, the soil pressure distribution, and the deformation and stress distribution of the pile foundation and the surrounding soil. Then, the finite element model of the proposed GPF foundation was built, which was verified and calibrated based on the test data. Finally, the parametric analysis was performed to investigate the effects of soil friction angle, pile foundation Young’s modulus, and pile length on the lateral bearing capacity characteristics of the proposed GPF. It is concluded that the GPF would transition from the stiffness stage to the plastic strain stage under lateral load, and deformation occurred simultaneously. The stress in the soil around the pile foundation is high in the upper portion and low in the lower portion, and the active and passive failure zones of the soil are formed under the action of the GPF. Both experimental and numerical simulations indicate that the GPF has a good lateral load capacity, and the lateral load capacity is most affected by the length of the piles. The GPF is expected to provide a new solution to the construction of large-span bridges with diaphragm wall foundations.

Experimental and numerical research on the lateral behaviour of glued timber frame structures with and without X-type diagonal bracing

The advanced processing technology of glued wood can provide strong support for the construction and application of the modern timber structures. The modern timber structure can meet the requirements of low-carbon development goals and natural living standards, but there still exist some technical difficulties to research, such as seismic performance and design code problems. Hence, this paper presents the lateral behaviour of glued timber frame structures with and without X-type diagonal bracing by experimental and numerical research methods based on these problems. Two single-layer single-span bare glued-laminated timber (GLT) frame specimens and two GLT frames infilled with X-type diagonal bracing specimens with a 1:1.5 scale were designed to investigate the lateral behaviours under the cyclic loading tests. Three types of beam-column joint connectors (the exposed type with infilled steel plate, the coated type with infilled steel plate and the extended coated type with infilled steel plate) were designed to guarantee the effective connection between components. The failure mode, hysteretic characteristics, lateral load-bearing capacity, stiffness degradation, deformation and the lateral load resistance cooperative working mechanism between X-type diagonal bracing and GLT frame of specimens were analyzed. The test results present that the lateral behaviour of the GLT frame is significantly improved after being infilled with the X-shaped diagonal bracing, and the yield lateral load-bearing capacity and the elastic stiffness of the coated type beam-column joint connection in the GLT frame were 1.876 and 1.36 times than that of the specimen with exposed type beam-column joint connection, respectively. The beam-column joint of the bare GLT frame specimen is failure before the column-base joint. The diagonal bracing joints of the GLT frame specimen infilled with the X-shaped bracing were failures first, and then the beam-column and the column-base joints of the GLT frame were damaged. For the specimen infilled with the X-type diagonal bracing, the lateral resistance load was borne by the GLT frame and diagonal bracing, in which the percentage of the lateral load borne by the diagonal brace gradually decreases, while the percentage of the lateral load borne by the GLT frame gradually increases. In addition, the load-deformation relationships of the specimen joints were derived. Based on these relationships, the numerical analysis of the specimen was carried out to study the influences of GLT frame span-depth ratio, the slenderness ratio of GLT diagonal bracing and the wall thickness of steel tube diagonal bracing on the lateral resistance of this structural system.

Effect of axial-load ratio and shear-span ratio on seismic behavior of the prefabricated structures for cast-in-place RC boundary elements confined uniform hollow panels

To meet the requirements of seismic safety, energy efficiency, and convenient transport, while achieving efficient construction of low or multi-story building structures. A prefabricated structure was developed with uniform hollow panels as the main force elements and cast-in-place RC provides restraint. The safety of the connection between the elements was verified by a low cyclic loading experiment and numerical analysis. In addition, the influence of the axial-load ratio and the shear-span ratio on the seismic performance of the structure was investigated, and the damage characteristics of progressive failure were revealed. The study found that as the axial-load ratio increased from 0.15 to 0.30, the cracking of the uniform hollow panels progressed, but the cracking of the columns was delayed, and the tendency of the edge member to separate from the uniform hollow panel increased. The ultimate lateral load capacity increased by 9.96 %, but the deformation capacity decreased, and the ductility coefficient decreased from 3.19 to 2.45. As the shear-span ratio decreased from 1.35 to 0.95, the uniform hollow panel and the structural columns cracked earlier and later, respectively, and the ultimate lateral load-bearing capacity increased by 25.03 %. However, the cracks at the base of the column increased, the deformation capacity decreased, and the ductility coefficient decreased from 3.19 to 2.15. Meanwhile, it is observed that the structure exhibits a three-stage progressive failure characteristic, i.e., the joint working stage, transformation transition stage, and weak frame stage. This greatly improved the deformation and energy dissipation capacity of the structure, which maintained good stability even when the inter-story displacement angle reached 1/50. This paper also established the calculation method for the lateral load resistance of this prefabricated structure, which showed accurate and reliable results. In general, the results of this research can provide an important reference for building design code and the application of this structure.

Seismic performance of GFRP-rubberized concrete-steel hybrid solid columns

The application of structured rubberized concrete offers an effective solution for recycling rubber tires. This paper proposes a novel GFRP-rubberized concrete-steel hybrid solid columns (GRSRC), which combines rubberized concrete with circular FRP-concrete-steel double-skin tubular columns (DSTCs). Quasi-static tests were carried out on 7 GRSRC specimens to investigate the influence of rubber contents, steel tube diameters, and axial load ratios on their seismic performance. The test results indicate that the GRSRC has excellent ductility, lateral displacement capacity, and energy dissipation capacity. The GRSRC exhibits slow strength degradation at large lateral displacements due to the double-tube confinement effect. Using rubberized concrete with a rubber content of 20% as a replacement for ordinary concrete has little impact on the seismic performance of the specimens. When the rubber content reaches 40%, the seismic performance decreases significantly. Furthermore, its lateral load-bearing capacity, energy dissipation capacity, and deformation capacity are also reduced with the decreasing diameter of the steel tube, resulting in brittle damage. Increasing the axial load ratio enhances the stiffness, lateral load-bearing capacity, and energy dissipation capacity but may reduce ductility, deformation capacity, and hysteretic performance. Finally, a simplified model of GRSRC restoring force is established and validated, providing a theoretical basis for practical engineering applications.

Experimental and numerical investigations on seismic behavior of spiral stirrup-confined square concrete-filled steel tubular columns

To investigate the seismic behavior of spiral stirrup-confined square concrete-filled steel tubular (SS-CFST) columns, ten square CFST columns, including eight SS-CFST columns and two ordinary CFST columns were experimentally studied through the cyclic loading tests. The critical test variables included the axial load ratio, spiral pitch, and longitudinal reinforcement ratio. First, the seismic behavior of the SS-CFST columns was herein discussed and clarified based on the failure modes, hysteretic response, skeleton curves, load-bearing capacity, strength and stiffness degradation, ductility and energy dissipation. Then, a total of 53 full-scale finite element (FE) models were established for parameter analysis of SS-CFST columns. The experimental and numerical results showed that the expansion deformation, necking and fracture of spiral stirrup were not formed when the SS-CFST columns were damaged, but the confinement effect effectively reduced the concrete fragmentation, alleviated the buckling of steel tube and longitudinal rebar, and limited the expansion of internal cracks. In the range of n=0.20–0.50, the ductility of SS-CFST columns significantly decreased with an increase in the axial load ratio, despite the stable bearing capacity and good energy dissipation of the columns. Moreover, unlike SS-CFST columns with high axial load ratio, spiral stirrup can only slightly improve the load-bearing capacity of SS-CFST columns with small axial load ratio (nt≤0.35). Compared with ordinary CFST columns, the strength degradation, ductility, collapse resistance, and energy dissipation of SS-CFST columns were significantly improved except for lateral stiffness, and the ultimate drift ratio of all SS-CFST columns in the test was greater than 3.00%. Furthermore, for SS-CFST columns, increasing the longitudinal reinforcement ratio can improve the lateral load-bearing capacity and stiffness. Finally, the formulas established in this paper can be adopted to assess the lateral load-bearing capacity of SS-CFST columns.

A new energy-dissipating RBS connection with double-nut-bolts: Seismic performance assessment and design methodology

This article investigates analytically the seismic performance of a new RBS beam-column connection system with Double Nut Bolts (RBS-DNB) and double shear tabs. The bolts in the proposed RBS-DNB connection are used to: i) increase the strength of the beam’s reduced section, ii) increase the energy dissipating capacity of the connection, and iii) delay damage of the beam in the plastic hinge zone. A reference RBS connection from the literature is first modeled and calibrated in Abaqus® software. A set of RBS-DNB connections are then designed (according to a new proposed method) and subsequently modeled in Abaqus®. The analytical results from the reference RBS connection and RBS-DNB connections are then compared in terms of cyclic response, beam strength, dissipated energy, beam hinge deformation and damage. The results show that, compared to the reference RBS connection, the proposed RBS-DNB connection system can increase the strength of the beam’s reduced section and dissipate more energy by up to 16 % and 12 %, respectively. Moreover, a damage assessment shows that RBS-DNB connections can efficiently delay the initiation of beam hinging, and reduce buckling deformation and damage to the beam hinge compared to the reference RBS connection. The new proposed design method ensured the safe load-carrying mechanism of RBS-DNB connections, and it also predicted well the potential damage at the components of the RBS-DNB connections. Finally, the results of pushover analyses on typical 4-storey buildings with RBS-DNB connections demonstrated their higher lateral load bearing capacity compared to those with conventional RBS connections. This study contributes towards developing more robust energy-dissipating connections for steel buildings located in seismic areas.

Frequency- and intensity-dependent impedance functions of laterally loaded pile groups in cohesionless soil

The frequency-dependent horizontal impedance functions of a model floating 2 × 2 pile group, embedded in cohesionless sand under a 1g condition, were investigated experimentally. The tests were conducted using large amplitude loads inducing soil yielding. The soil-pile system was housed in a laminar shear box fastened to the top of a unidirectional shaking table. Quasi-static and dynamic loads were applied in a lateral direction under the fixed pile-head condition to evaluate the force–displacement relationship and the horizontal impedance functions, respectively. The results of the quasi-static loading exhibited rate-dependent behavior for the lateral load-bearing capacity of the piles. Notably, the analysis of the soil surface near the piles, using a stereo-PIV calibration, demonstrated a consistent failure pattern despite the significant variation in velocity. Furthermore, an important observation was the convergence of the horizontal dynamic impedance functions towards the secant static stiffness as the amplitude of dynamic loading increased.

Seismic performance of steel-reinforced reactive powder concrete columns

The seismic performance of the innovative steel-reinforced reactive powder concrete (SRRPC) composite columns was evaluated via the cyclic experiments considering the steel shape ratio, axial compression ratio and the stirrup ratio. The SRRPC columns generally exhibited appreciable seismic behavior, great crack-resistance and excellent anti-spalling property. It was found that increasing the steel shape ratio from 4.20% to 5.35% can significantly enhance the ductility and the energy dissipation capacity. As the axial compression ratio increased from 0.1 to 0.3, the peak lateral load increased but the ductility significantly decreased. Increasing the stirrup ratio from 1.57% to 2.52% was not helpful for seismic performance in the pre-peak zone but was beneficial to the strength and ductility in the post-peak zone. Moreover, the average strength loss of the SRRPC columns with low axial compression ratio at the 4.5% drift ratio was less than 12.5%, satisfying the modern seismic drift criteria. Two coefficients, βtu and k, for predicting the equivalent tensile strength were identified and compared to the suggested values from the specifications JGJ/T 465-2019 and T/CCPA 35-2022, respectively. An analytical model was successfully developed to predict the lateral load-bearing capacity. Good agreements were found between the experimental and analytical results.

Structural Performance of Energy Efficient Geopolymer Concrete Confined Masonry: An Approach towards Decarbonization

Geopolymer concrete is preferred over OPC due to its use of energy waste such as fly ash, making it more sustainable and energy-efficient. However, limited research has been done on its seismic characterization in confined masonry, highlighting a gap in sustainable earthquake-resistant structures. Our study compares the performance of alkali-activated fly-ash-based geopolymer concrete bare frame and confined masonry wall panels with conventional concrete. Experimental results showed that geopolymer concrete bare frame has 3.5% higher initial stiffness and 1.0% higher lateral load-bearing capacity compared to conventional concrete. Geopolymer concrete confined masonry exhibited 45.2% higher initial stiffness and 4.1% higher ultimate seismic capacity than traditional concrete. The experimental results were verified using a numerical simulation technique with ANSYS-APDL, showing good correlation. Comparison with previously tested masonry walls revealed that GPC confined masonry has similar structural behavior to cement concrete masonry. This study demonstrates that geopolymer concrete made from waste energy such as fly ash is a sustainable and low-energy substitute for OPC concrete, particularly in highly seismic-prone areas, for a cleaner environment.

Effect of infilled CLT shear walls on the lateral performance of glued-laminated timber frames: Experimental and numerical analysis

A new timber structural system about the combination of cross-laminated timber (CLT) and glued-laminated timber (GLT) aiming to improve the timber lateral performance and satisfy the seismic demands has recently been proposed, highlighting the important influence on the design of timber frame-shear walls structure. This paper presents the lateral behaviour and seismic performance of GLT frame infilled with CLT shear walls by experimental and finite element numerical analysis. Four specimens of 1:1.5 scale including one bare GLT frame and three GLT frames infilled with CLT shear walls were designed to research the lateral performance under the cyclic loading tests. The mechanical characteristics of these specimens were effectively evaluated in the form of theoretical derivation under the lateral load, and the theoretical models of the beam-column joint and the column-base joint were established. Based on the theoretical calculation methods, the finite element models of four specimens were established and analyzed by Abaqus software to research the lateral performance of the influence of CLT shear walls on the GLT frame. The results indicate that the lateral deformation of the bare GLT frame is obvious, the shear cracks emerge in the joints, and the damage degree of the beam end of the beam-column joint is significantly greater than that of the column-base joint. The lateral load-bearing capacity of the GLT frame is improved after being infilled with CLT shear walls, and the damage degree of GLT frame joints is significantly improved. The elastic lateral stiffness of GLT frame infilled CLT shear walls with the opening can reach 9.66–13.1 times higher than that of bare GLT frame according to the test results. From the beginning of loading to the failure stage, the lateral load of specimens provided by the CLT shear wall is more than 50 %, and the contribution of the CLT shear wall to the lateral performance of the structure is significant in collaborative work. The numerical analysis based on the FE models of GLT frame infilled with CLT shear wall shows that the opening type, size and thickness height ratio of the CLT wall are obvious effects on the lateral resistance of the structure. The lateral load-bearing capacity increase by about 95.06–127.5 % when the thickness of the CLT shear wall of three-layers wood panels increases from 30 mm to 105 mm. The lateral resistance increases by 49.29–72.29 %, and the lateral stiffness increases by 48.26 % when the thickness of the CLT shear wall of five-layers wood panels increases from 50 mm to 150 mm. The research shows that CLT can increase the lateral load-bearing capacity and stiffness of structures, which can satisfy the demands of better lateral performance and sustainable buildings with a low carbon cycle.

Static and Dynamic Behavior of Circularized Reinforced Concrete Columns Strengthened with Hybrid CFRP

In this study, three strengthening techniques, near-surface mounted NSM-CRFP, NSM-CFRP with externally bonding EB-CFRP, and hybrid CFRP with circularization were studied to increase the seismic performance of existing RC slender columns under lateral loads. Experimentally, 1:3 scale RC models were studied and subjected to both lateral static load and seismic excitation. In the dynamic test, a model was subjected to El Centro 1940 NS earthquake excitation by using a shaking table. According to the test results, the strengthening techniques showed a significant increase in load carrying capacity, of about 86.6%, and 46.6%, for circularization and NSM-CFRP respectively, of the reference unstrengthened columns. On the other hand, columns strengthened with hybrid NSM-CFRP and EB-CFRP showed a different failure mode. Dynamically, the lateral drift was decreased by about 75%, 47%, and 49% for earthquake amplitudes of 0.05g, 0.15g, and 0.32g respectively. Finally, it was concluded, depending on the static and dynamic analyses, that the circularization process showed a significant increase in lateral load-bearing capacity.

Seismic behavior of RC columns strengthened with near-surface-mounted aluminum alloy bars and CFRP wraps

This paper proposed a near-surface-mounted (NSM) strengthening technique by using aluminum alloy (AA) bars and carbon fiber-reinforced polymer (CFRP) wraps to improve the seismic behavior of square reinforced concrete (RC) columns. Eight strengthened concrete columns with square cross sections of 250 mm × 250 mm and 1600 mm shear span were tested under axial compression and reversal cyclic loading to investigate the effects of NSM reinforcement ratios (0.36–1.29%), layers of CFRP wraps (0 and 3), and axial compression ratios (0.1 and 0.4) on the seismic behavior. The failure mode, hysteretic response, load-bearing capacity, ductility, stiffness degradation, and energy dissipation capacity of those column specimens were analyzed. Results indicated that the lateral load-bearing capacity, stiffness, and cumulative energy dissipation capacity increased with the increase of the NSM reinforcement ratio. The CFRP wraps in the NSM technique can provide hoop confinement to avoid the buckling failure of NSM AA bars, and improve the seismic behavior by mitigating spalling of concrete. When increasing the axial compression ratio from 0.1 to 0.4, the lateral load-bearing capacity and cumulative energy dissipation capacity increased significantly, while the stiffness degradation became obvious. In addition, three-dimensional (3D) finite element (FE) models were developed and verified by comparisons in the deformation and lateral loads at characteristic points, as well as the strain distribution along NSM AA bars. The verified FE models can be used to analyze the damage of concrete and the stress distribution at the interface between epoxy and concrete.

Experimental and numerical evaluation of steel fibres RC patterns influence on the seismic behaviour of the exterior concrete beam-column connections

Exterior concrete beam-column connections are one of the important parts of the concrete structural frames that play an important role in controlling the seismic behaviour of structures during an earthquake. Providing sufficient ductility for beam-column connections helps to dissipate more energy during a cyclic load and improves the performance of structures. In this study, the cyclic behaviour of exterior concrete beam-column connection was studied experimentally and numerically. To improve the cyclic performance of the connections, steel fibres (SF) were used. A total of 20 exterior concrete beam-column connections were produced and tested under a cyclic load. SF were added at 1% in terms of volume. SF-reinforced concrete was used in four different patterns. In addition, the influence of bent angles for longitudinal reinforcement bar in the connection region was studied: 90° and 135°. Furthermore, the effect of transverse reinforcement on the cyclic behaviour of the connection was studied by providing different spacings in the column: 150 mm and 100 mm. Formerly, a finite element method software, ABAQUS, was used to study the effect of compressive strength of concrete (normal and high-strength), longitudinal rebars ratio and transverse reinforcement spacing in the beam on the behaviour of exterior concrete beam-column connection produced by different SF-reinforced concrete patterns. Evaluation of the maximum lateral load-bearing capacity, drift ratio, maximum displacement, ductility, efficiency and energy absorption of connections were the main aims of this study. The results showed that using SF-reinforced concrete in the connection zone was the best pattern in terms of maximum lateral resistance and deformation of the connections, especially when a 135° bent angle was provided for the longitudinal rebars. In addition, using high-strength concrete led to reducing the ductility and efficiency of connections, particularly when a 90° bent angle were performed for the longitudinal rebar in the connection region.

Hysteresis behavior of 3D RC exterior beam-column joints strengthened with CFRP sheets and spike anchors

Full-scale 3D exterior beam-column joints lacking shear reinforcement but externally shear-strengthened with carbon fiber reinforced polymer (CFRP) sheets were investigated with respect to their behavior under both gravity and lateral cyclic loadings. For this purpose, three such joints including one control and two experimental ones (strengthened either with CFRP sheets or with both CFRP sheets and spike anchors) were subjected to relevant tests. Prior to CFRP installation, all the externally strengthened specimens were subjected to surface preparation and grooving in order to prevent possible CFRP debonding. The flexural capacity of both the non-strengthened and strengthened joints were estimated using a specially-developed analytical method. Comparisons of the lateral load–displacement hysteresis curves and in the test results revealed that, compared to the control, the externally strengthened joints showed enhancements of 30, 222, and 200% in lateral load-bearing capacity, energy dissipation, and secant stiffness, respectively. It was further found that despite the efficacy of the shear retrofit design proposed for 3D exterior connections, those strengthened with the combined CFRP sheets and spike anchors outperformed the ones solely strengthened with CFRP sheets. The sectional analysis results also revealed that the simple method proposed in this study is well capable of estimating bearing capacity in both the control and strengthened connections with reasonable accuracy.