Stirrup Ratio Research Articles

Analytical and experimental investigation of bond behavior of confined recycled brick-concrete aggregate concrete

Recycled aggregates made of building demolition waste containing concrete and bricks are called recycled brick-concrete aggregates (RBCA). This research experimentally and analytically studies the bond behavior between rebar and RBCA concrete through tests on twenty-two four-point supported beams made of RBCA. The experimental parameters are the replacement ratio of recycled brick aggregates (RBA), concrete strength, stirrup ratio, thickness of concrete shell, diameter of rebar, and anchorage length. The test results indicated that the replacement ratio of RBA had little, if any, influence on the bond failure mode of the specimens, while the bond strength tended to increase slightly along with the replacement ratio of RBA. The normalized bond strength of the specimens with 25% and 50% RBA replacement ratio increased by 7.7% and 11.6%. As the concrete strength, stirrup ratio, and thickness of concrete shell increased, the normalized bond strength of the rebars embedded in RBCA concrete increased. On other hand, the bond strength decreased as the anchorage length increased. The rebar embedded in RBCA concrete could exhibit as good bond behavior as that in recycled concrete aggregate (RCA) concrete, and fully developed its strength. Based on the test results, a bond-slip model is proposed for the rebar embedded in RBCA concrete. The proposed model taken account of the researched parameters is of practical significance for evaluating the bond behavior of rebar embedded in RBCA concrete components under composite stress. Good agreement is observed between the measured results and the calculated ones, implying sound accuracy of the proposed model.

Shear mechanism and bearing capacity calculation of steel fiber reinforced concrete beam-column joints

Based on the strut-and-tie model, the shear mechanism of steel fiber reinforced concrete (SFRC) beam-column joints is analyzed. In addition, based on the stress characteristics of SFRC beam-column joints, the influence of randomly distributed steel fibers at the cracks is equated to the effective bond stress of the steel fibers. Consequently, a formula for calculating the shear capacity of SFRC beam-column joints is proposed. Furthermore, a database of 132 SFRC beam-column joints is compiled. Based on the database, the proposed calculation method is optimized using statistical analysis method. Furthermore, the contributions of concrete, stirrups, and steel fibers to the shear bearing capacity are discussed. Finally, the proposed calculation method is compared with the existing calculation methods to validate the accuracy of the model. The results indicate that the shear bearing capacity provided by concrete can reach 90% of the total shear bearing capacity. The maximum shear bearing capacity provided by stirrups and steel fibers is 27% and 26% of the total shear bearing capacity respectively. When the stirrup ratio exceeds 1%, the enhancement of shear bearing capacity by the stirrups becomes more pronounced. Compared to straight steel fibers, hooked-end steel fibers can better enhance shear capacity. The proposed calculation method demonstrates higher accuracy compared to existing calculation methods, which can be used to predict the shear bearing capacity of SFRC beam-column joints.

Assessment of Ductility Indices in FRP-Strengthened RC Beams: A Statistical Analysis

The study aims to use statistical analyses to identify the optimal ductility indices that can characterize the behavior of FRP strengthened RC beams and assess the effects of the longitudinal reinforcements, expressed as total equivalent steel ratio (TESR%). The analyses are based on various techniques such as MANOVA, MANCOVA, and the Johnson-Neyman method. The results showed a significant relationship between TESR% and ductility indices at different levels of the moderator (stirrup ratio). The TESR% has a wide range of negligible regions on Naaman and Jeong's ductility index (0.74% to 1%) compared to Davies's and Oudah (0.72% to 0.87%) and El-Hacha's indexes (0.74% to 0.89%). Therefore, it appears that Naaman and Jeong's index may not provide an accurate assessment for RC beams strengthened by FRP material. The Oudah and El-Hacha index values are greater than those of other ductility indices due to the deformability ratio considered in the calculation. However, Davies's index was more sensible than the other two ductility indices due to its lower values.

A simplified calculation model for maximum diagonal crack width of UHPC-NC composite beams

The study on precast UHPC-NC composite beams investigated the effects of shear span ratio, stirrup reinforcement ratio, and NC strength on cracking shear force and diagonal crack width. Tests on eight UHPC-NC beams and one RC beam revealed that increasing the shear span ratio reduced the cracking shear force and widened diagonal cracks. U-shaped UHPC formwork enhanced cracking shear force and delayed crack development. While stirrup ratio had minimal impact on cracking force, it helped delay crack growth. A proposed model accurately estimated cracking shear force and maximum diagonal crack width, offering valuable insights for engineering applications.

Experimental study on seismic performance of bridge pier with new HRB650E high-strength steel bar

To facilitate the application of high-strength steel in reinforced concrete bridge structures, this study explores the seismic performance of full-scale HRB650E high-strength reinforced concrete bridge piers. Initially, monotonic tensile tests were conducted on HRB400 and HRB650E steel rebars with the same slenderness ratio to analyze the differences in their mechanical properties. Subsequently, quasi-static cyclic tests were carried out on four square full-scale RC bridge piers to examine the influence of new high-strength rebars, stirrup ratios, and axial load ratios on the seismic performance. Based on the experimental results, a hysteresis model suitable for HRB650E reinforced concrete columns was developed. The findings indicate that the HRB650E steel bar exhibited lower uniform elongation and fracture elongation compared to HRB400 steel bar. The displacement at which HRB650E piers reached crack damage was 36 % higher than that of HRB400 piers, and they also showed lower residual displacements at all load levels. The maximum lateral load capacity and the ductility coefficient of HRB650E piers increased significantly compared to HRB400 piers. While the initial secant stiffness of both types was comparable, HRB650E piers exhibited a slower rate of stiffness degradation, resulting in higher secant stiffness at the ultimate state. They also demonstrated 35 % higher cumulative energy dissipation at the ultimate state. When the stirrup ratio of HRB650E piers was increased from 1.1 % to 1.7 %, there was a slight reduction in residual displacement, a small increase of the yield strength, and a minor improvement in the maximum lateral load capacity. Furthermore, a higher stirrup ratio was observed to improve energy dissipation levels at all loading stages. Increasing the axial load ratio of HRB650E piers from 0.1 to 0.2 allowed the piers to withstand greater deformations at the same repairable ultimate state, with significant increases in yield strength, maximum lateral load capacity, initial secant stiffness, and secant stiffness at the ultimate state, but a small increase in the cumulative energy dissipation. The hysteresis model for HRB650E RC columns, based on experimental data, exhibited good computational accuracy.

Seismic Performance of the Bridge Piers Reinforced with PP-ECC in the Plastic Hinge Region

Ductility deficiency in reinforced concrete (RC) piers is a substantial factor contributing to earthquake damage in bridge structures. In this study, the conventional concrete in the potential plastic hinge area was substituted with polypropylene fiber-reinforced engineered cementitious composite (PP-ECC), thereby leveraging its high ductility characteristics to explore the seismic performance of RC piers strengthened by PP-ECC. A finite element model was established to discuss the reinforced height, axial compression ratio, longitudinal reinforcement ratio and stirrup ratio on the hysteresis performance by referring to a published paper with a 1/5 scale test specimen. Based on the results of the parameter analysis, an ideal set of configuration parameters was proposed. Subsequently, a full-size simplified mechanical model was established with ideal reinforcement parameters. Time-history and pushover analysis were utilized to test the seismic response. The study indicates that the two analytical methods were largely consistent. The improvement in the displacement and shear force of the strengthened pier gradually decreased with the increase in acceleration amplitude. Time-history analysis reveals a decrease in the enhancement of displacement from 82.26% to 17.98% and a reduction at the bottom reaction from 12.2% to 1.5%. Under the pushover analysis method, the retrofitting level of the top displacement decreased from 77.22% to 11.53%, whereas the improvement level of the bottom shear decreased from 9.62% to 3.69%. These results provide a theoretical basis and reference standard for the application of PP-ECC.

Size effect modellings of axial compressive failure of RC columns at low temperatures

This paper applied a thermal-mechanical sequential coupled mesoscopic simulation method to explore the axial compression performance and the corresponding size effect of Reinforced Concrete Columns confined by Stirrups (i.e., RCCS) at low temperatures, with considering the interaction between concrete meso-components and steel bars as well as the low-temperature effect of mechanical parameters. Based on the heat conduction analysis, the axial compression mechanical failure behavior of RCCS with four structural sizes (i.e., 267 × 267 × 801, 400 × 400 × 1200, 600 × 600 × 1800 and 800 × 800 × 2400 mm) and two stirrup ratios (i.e., 1.26% and 2.89%) at different temperatures (i.e., T = 20, −30, −60 and −90°C) was subsequently simulated. The effects of temperature, structural size and volume stirrup ratio on axial compression properties were quantitatively discussed. The results showed that the peak strength of RCCS increased with the decreasing temperature, and the smaller-sized RCCS showed a stronger effect of low-temperature enhancement. Both the residual strength and displacement ductility coefficient decreased with the decreasing temperature. The peak strength, residual strength and displacement ductility coefficient of RCCS decreased with the increasing structural size, showing obvious size effects. The size effect on peak strength increased with the decreasing temperature, (the maximum increase was nearly 140%), but the size effect on displacement ductility coefficient decreased (the maximum decrease was nearly 70%). The peak strength, residual strength and ductility were enhanced with the increasing volume stirrup ratio, which was helpful to reduce the influence of size effect. Finally, an improved size effect theoretical model was proposed, which can effectively predict the axial compressive strength of RCCS with different structural sizes and stirrup ratios at room and low temperatures. The present research results can provide reference for the large-scale engineering application of RCCS in low-temperature environments.

Seismic performance of mortise-tenon joint in prefabricated platform canopy

To optimize the prefabricated canopy joints, improve the construction efficiency, and enhance the seismic performance of assembly joints, a novel mortise-tenon joint (MTJ) was proposed. To evaluate the seismic performance along the vertical and track directions, two 1:1.5 scaled specimens were tested under low-cycle reciprocated loading. The test results find the hysteretic curves in both directions exhibit the “pinch” effect especially in the vertical direction, indicating the feature of shear slippage. The displacement ductility coefficients were all above 5.0, and the ultimate drift ratios were 4.54 % and 5.88 % respectively, showing excellent deformation ability and ductility. The parameters, such as the sectional strength ratio, the stirrup ratio of the prefabricated beam, the reinforcement ratio and the cross-sectional area of the enlarged section, were analyzed by the validated finite element (FE) models. The analysis shows as the section strength ratio decreases and the stirrup ratio increased, the seismic bearing capacity improved, while the plastic hinge located on the prefabricated column varied to the prefabricated beam ends. Based on the results, it is recommended the number of longitudinal rebars through the prefabricated beam is 4, the stirrup diameter in the prefabricated beam is 10 mm and the the column cap is no less than 400 mm. Finally, based on the truss-diagonal strut model, a method for calculating the shear strength capacity of the novel joint was proposed. Compared with the test and FE results, the theoretical equations exhibit good computational accuracy.

Research on seismic performance and axial compression ratio of rectangular high-strength spiral stirrup confined concrete columns

Replacing traditional stirrups with high-strength rectangular spiral stirrups can improve the seismic performance of reinforced concrete columns. In order to study the seismic performance of high-strength spiral stirrup confined concrete columns, a validated finite element (FE) method was proposed to establish the FE model of reinforced concrete columns. Combined with the measured data of two existing specimens, parameter analysis was conducted on 19 specimens. The axial compression ratio, shear span ratio, stirrup spacing, and stirrup diameter were variable parameters. Based on a reliable model, internal stress analysis was conducted, and the influence of different variables on the seismic performance of reinforced concrete columns was revealed. The FE results suggest that, when the axial compression ratio is not greater than 0.6, the requirement of ductility greater than 3 in the Chinese Standard GB 50011-2010 can be met. The recommended shear span ratio for optimal ductility was around 4.5. The reinforcement ratio of high-strength spiral stirrups ranges from 1.0% to 2.2%. After completing the simulation of nearly 100 specimens (only calculating the ductility coefficient), a matching relationship between the axial compression ratio limit and the shear span ratio was proposed.

Numerical investigation on a precast bridge using GPC and BFRP reinforcements subjected to cross-fault rupture and fling step excitation

This study investigates the seismic performances of a precast bridge made of geopolymer concrete (GPC) with fibre-reinforced polymer (FRP) reinforcements subjected to cross-fault ground motions. A numerical model was developed and verified against experimental results from a previous study and then used to evaluate the bridge's performances under earthquake excitations. The study found that a simplified model was able to reliably capture the failure pattern and displacement response of the bridge, reducing simulation time significantly. Additionally, the numerical results indicated the combination of torsional and flexural cracks was the primarily damage mode of the columns, which was not observed in the experimental test. This study also revealed that while the performances of the bridge using ordinary Portland cement (OPC) and GPC were similar under low ground excitations, GPC columns were more susceptible to brittle failure under higher ground excitations due to their brittleness. The use of FRP reinforcements led to similar displacement response as steel reinforcements under low ground displacement excitation, although severe flexural and shear damages on the column of Bent 2 were observed due to the lower elastic modulus and shear resistance of Basalt FRP material than steel. To address the disadvantages of brittle GPC and low-modulus of basalt FRP reinforcements, it is suggested to reinforce GPC with fibres and/or increase stirrup ratios if green GPC and corrosion-resistant basalt FRP reinforcements are used to construct bridges for seismic resistance.

Experimental study on the shear behaviors of inverted castellated T-steel reinforced UHPC (ICTSRU) beams with hollow section

To reduce the production costs of steel reinforced UHPC composite beams and fully utilize the material strength of steel, this paper introduced an innovative prefabricated composite beam comprising a reinforced ultra-high performance concrete beam and an internal castellated inverted T-steel, forming an inverted castellated T-steel reinforced UHPC (ICTSRU) composite beam. Investigating the shear behavior of ICTSRU beams is the primary objective of this research. Seven composite beams were loaded under simply supported four-point loading conditions, and the effects of key parameters such as the shear span-depth ratio, steel fiber volume fraction, and stirrup ratio were studied. The findings from the test indicated that the ICTSRU beams demonstrated superior deformation ability and significant residual shear strength after the peak load. The shear span-to-depth ratio significantly influenced the failure modes and carrying capacity of the ITSRU beams. As the span-to-depth ratio increased from 1.1 to 1.6 and 2.1, the failure mode developed from shear failure to flexural failure and the shear resistance decreased by 19 % and 48 %, respectively. Enhancing the steel fiber volume fraction and the stirrup ratio can mitigate the initiation and propagation of diagonal cracks, thereby augmenting the shear strength and ductility of ICTSRU beams. Following a comprehensive analysis of the experimental results, a predictive model for the shear strength of the ICTSRU beam is proposed. This model posits that the shear capacity of the ICTSRU beam comprises the shear resistance contributions from the UHPC matrix, stirrups, steel web, and steel fibers. A comparative analysis of the computed values and the test results showed that the proposed calculation method has a high accuracy in predicting the ultimate shear strength of ICTSRU beams.

Shear performance and capacity of FRP reinforced concrete beams: Comprehensive review and design evaluation

To enhance the durability of concrete structures in harsh environments, replacing steel bars with FRP bars is judged a feasible method. The low elastic modulus and transverse strength of FRP bars result in the weak shear capacity of concrete beams reinforced with FRP bars. Reviewing and summarizing existing literature are important for addressing this challenge. The research progress on the shear behaviour of concrete beams reinforced with FRP bars was systematically described from two aspects in this paper. In the aspect of literature review, shear mechanisms and main influencing factors of concrete and FRP stirrups were summarized. In addition, achievements and shortcomings of existing literature were summarized, and potential research directions were pointed out. In the aspect of design method evaluation, a database containing 525 samples was established and calculation models of shear capacity of concrete beams reinforced with FRP bars in seven codes were evaluated. Evaluation parameters mainly included shear span ratio, effective height, and maximum strain of FRP stirrups. Based on the calculation model in Italian code CNR DT203-06, an optimized model was proposed to improve the accuracy in predicting concrete shear contribution. The review and evaluation in this paper had important reference significance for improving the design level of concrete structures reinforced with FRP bars and promoting the engineering application of FRP bars.

Research and Modification on the Park-Ang Damage Index for Railway Rectangular Piers

ABSTRACT This study addressed the issue of distortion in evaluating the seismic damage state of railway bridge piers using the original Park-Ang damage index. By constructing a parameterized co-simulation program with two finite element models, OpenSees and Abaqus, five sets of flexural failure and five sets of flexural-shear failure rectangular pier quasi-static test results were selected to validate the rationality of the calculation program. Four hundred and eighty parameterized calculations were conducted using this program. The combination coefficient β and critical damage index DI within the Park-Ang damage index were modified using nonlinear regression algorithm and convolutional neural network algorithm. The adaptability of the damage index calculation was ultimately verified through an engineering case study of a simply supported beam bridge. The research findings are as follows: 1) The main factor influencing β is the longitudinal reinforcement ratio, while the axial compression ratio, shear span ratio, volumetric stirrup ratio, aspect ratio, concrete strength, and steel strength are secondary parameters influencing β. 2) Compared to the nonlinear regression algorithm, the convolutional neural network algorithm can better establish a calculation model between pier structural parameters and β, clarifying their relationship. 3) It is recommended to use critical values of 0.11, 0.29, 0.49, and 1.00 for assessing pier damage as no, slight, moderate, severe, and collapse damage when using the damage index calculation model. 4) The Park-Ang index corrected by convolutional neural networks demonstrates improved accuracy and computational stability, making it suitable for practical assessment of seismic damage in bridge structures.

Strut‐and‐tie model for column‐to‐drilled shaft connections in reinforced concrete bridge columns subjected to lateral loads

AbstractDrilled shafts with a larger diameter than columns are frequently adopted as the foundation of highway bridge columns due to their superior economic efficiency and lower impact on existing facilities in the urban built‐up area. Different section dimensions lead to a socket connection between the column and the oversized shaft and a noncontact lap splice of their longitudinal bars. The force‐transfer mechanism and failure process of column‐to‐drilled shaft connections were deeply revealed in this study. Detailed FE models were developed at the Diana platform and validated against previous experimental results. Subsequently, a parametric study investigated the effect of the shear span‐to‐depth ratio, diameter ratio of shaft‐to‐column, column embedment depth, and shaft stirrup ratio. Finally, a modified strut‐and‐tie model (STM) was proposed to design stirrups of the transition region efficiently considering the experimental failure mechanism. Results indicate that the numerical models built in the Diana platform can precisely simulate the mechanical behavior of column‐to‐drilled shaft connections. The failure mechanism of column‐to‐drilled shaft connections is shaft stirrups yield at the compressive side induced by extrusion between the embedded column and shaft. The lateral loading capacity of column‐to‐drilled shaft connections increases with the increase of shear span‐to‐depth ratio, diameter ratio of shaft‐to‐column, column embedment depth, and shaft stirrup ratio. The modified STM is able to reveal the variation tendency of shaft transverse reinforcement demand with the various design parameters and give an average stirrup stress ratio of 1.20 and a coefficient of variation of only 8.31%.

Shear behavior of reinforced concrete beams with high-strength reinforcements after high temperatures

This paper investigates the effect of steel reinforcement configured with different strengths after different high temperatures on the shear performance of the test beams, a total of 20 reinforced concrete (RC) beams, through experiments, numerical analyses and theoretical studies, in order to understand the key factors affecting the shear performance of the beams. The test revealed that the mechanical properties of concrete and steel reinforcement showed a trend of increasing and then decreasing after high temperatures. Increasing the stirrup ratio and stirrup strength can significantly improve the crack resistance and shear capacity of the beams, as well as the deformation performance of the beams. The residual shear strengths of test beams with high-strength stirrups after exposure to high temperatures are significantly greater than those of ordinary reinforced concrete beams. Specifically, the shear capacity of beams with high-strength stirrups after exposure to 800°C increased by 23.7 % compared to ordinary beams, and the mid-span deflection performance increased by 28.7 %. The stresses in the shear span region of the test beams after high temperature were more concentrated at the diagonal and the number of cracks was significantly reduced. In this paper, a simplified formula for calculating the residual shear capacity of RC beams after room and high temperatures is proposed, which can well predict the test results.

Experimental and numerical investigation on shear behavior of concrete beams reinforced with CFRP grid shear reinforcements

This research investigated the shear behavior of concrete beams reinforced with Carbon Fiber Reinforced Polymer (CFRP) bars and grids as longitudinal reinforcements and stirrups, in experiment and finite element (FE) methods. Five concrete beams were tested under a monotonical load and experienced shear failure as expected. The test variables including stirrup ratio and grid dimension were considered to investigate the interaction between grid and concrete, and the influence between the horizontal and vertical fibers of the grid. It found that reducing the grid dimension with the constant stirrup ratio could effectively improve the stress distribution of the grid and the shear capacity of the beam. The grid dimension greatly determined the shear capacity of specimens when the stirrup ratio changed in a small range. The horizontal fibers of the grid had anchoring effects on the vertical fibers and directly carried the tensile stress from concrete at the top and bottom of the beam. In FE analysis, the fiber composite layer was adopted to simulate the CFRP grid. The load-midspan deflection of specimens and strain development of the grid in the FE model showed good agreement with the tests. In parameter analysis, the grid configuration with the horizontal fiber arranged in the middle or upper part of the section was recommended.

Nonlinear Analysis of Prestressed Steel-Reinforced Concrete Beams Based on Bond–Slip Theory

In this study, a static load test of prestressed steel-reinforced concrete simply supported beams was carried out utilizing three test beams to investigate the bond–slip effect between the section steel and concrete in prestressed steel-reinforced concrete beams. Finite element models of three beams considering two different bond–slip constitutive relations and without considering bond–slip performance were developed in ABAQUS. The influence of shear bolt nails on the bond slip between the section steel and concrete was analyzed, and the load–slip curves of the three test beams were also computed. Generally, the results showed that the finite element calculations considering the bond–slip effect are more consistent with the experimental calculations, and the bond–slip constitutive relationship proposed by Yang Yong is more suitable for the numerical simulation of prestressed steel-reinforced concrete beams. When the effective prestress is increased from 222.15 KN to 279.61 KN, the ultimate bearing capacity increases by 14.8%. When the concrete strength is increased from 37.21 MPa to 47.97 MPa, the ultimate bearing capacity increases by 15.2%. When the stirrup ratio is 0.50%, compared with 0.25%, the ultimate bearing capacity increases by 7.8%. When the steel content is 5.41%, compared with 3.37%, the ultimate bearing capacity increases by 9.1%. The results of this study can provide a reference for future research and engineering applications of bond slip between section steel and concrete in prestressed steel-reinforced concrete beams in the future.

Experimental Investigation on Pure Torsion Behavior of Concrete Beams Reinforced with Glass Fiber-Reinforced Polymer Bars

The failure mechanism of torsional concrete beams with fiber-reinforced polymer (FRP) bars is essential for developing the design method. However, limited experimental research has been conducted on the torsion behavior of concrete beams with FRP bars. Therefore, the pure torsion test of four large-scale FRP-RC beams (2800 mm × 400 mm × 200 mm) was conducted to investigate the influence of the stirrup ratio (0, 0.49%, and 0.98%) and longitudinal reinforcement ratio (3.01%, 4.25%) on torsion behavior. The test results indicated that three typical failure patterns, including concrete cracking failure, stirrup rupturing failure, and concrete crushing failure, were observed in specimens without stirrups (stirrup ratio 0), partially over-reinforced specimens (stirrup ratio 0.49%), and over-reinforced specimens (stirrup ratio 0.98%), respectively. The tangent angle of spiral cracks at the midpoint of the long side of the cross-section was approximately 45° initially for all specimens. The torque–twist angle curves exhibited a linear and bilinear behavior for specimens without stirrups and specimens with stirrups, respectively. As the stirrup ratio increased from 0 to 0.98%, torsion capacity increased from 24.9 kN∙m to 27.8 kN∙m, increased by 12%, ultimate twist angle increased from 0.0018 rad/m to 0.0403 rad/m. As the longitudinal reinforcement ratio increased from 3.01% to 4.25%, the torsion capacity increased from 27.8 kN∙m to 28.3 kN∙m, and the ultimate twist angle decreased from 0.0403 rad/m to 0.0244 rad/m. Based on test results, the stirrup strain limit of 5200 με and spiral crack angle of 45° was suggested for torsion capacity calculation. In addition, based on the database of torsion tests, the performance of torsion capacity provisions was assessed.

Experimental and theoretical study on the shear behaviors of an innovative precast UHPC composite beams reinforced with inverted T-shaped steel

The innovative precast composite beam consisted of reinforced UHPC beam and inner inverted T-steel shape (forming ITSRU composite beam) is proposed for the marine structures serviced in harsh environment and subjected to complicated loading conditions. The novel composite beam possesses the advantages of lightweight, high strength and ductility, enhanced durability. To study the shear behaviors of ITSRU beams, a shear test program consisted of seven composite beams were conducted to study the effects of shear span-to-depth ratio, steel fiber volume fraction, stirrup ratio and inverted T-steel web thickness. UHPC used in this paper possess compressive strength more than 125 MPa, ultimate tensile strength more than 8.9 MPa and ultimate tensile strain more than 2256με. The inverted T-steel and steel rebar used in this paper have grades of Q355 and HRB400, respectively. A segmented loading control method was used in the shear test, in which a forced-controlled with a rate of 20 kN/min was used before the beam yield and the displacement control was implemented at a rate of 0.5 mm/min after reaching the yield load. The test results revealed that the ITSRU beams exhibited admirable deformation capacity and considerable residual shear capacity even for the composite beam with shear span-to-depth ratio of 1.0. The increasing of stirrup ratio, steel fiber volume fraction and inverted T-steel web thickness could improve the shear resistance and the ductility as well as suppress the appearance of the diagonal shear critical cracks. Based on the test results, an analytical shear model considering the contributions of UHPC in shear compression region, stirrups, steel fibers and inverted steel web was developed to predicted the shear resistance of ITSRU beams. The interaction mechanism of the different components in the ITSRU beams was considered in the analytical shear model. The accuracy of the developed calculation method was verified by the test results.

Experimental and Numerical Investigations on the Seismic Performance of High-Strength Exterior Beam-Column Joints with Steel Fibers.

Steel fiber reinforced high-strength concrete (SFRHSC) is a composite material composed of cement, coarse aggregate, and randomly distributed short steel fibers. The excellent tensile strength of steel fiber can significantly improve the crack resistance and ductility of high-strength concrete (HSC). In this study, experimental and numerical investigations were performed to study the cyclic behavior of the HSC beam-column joint. Three SFRHSC and one HSC beam-column joint were prepared and tested under cyclic load. Two different volume ratios of steel fibers and three stirrups ratios in the joint core area were experimentally studied. After verification of the experimental results, numerical simulations were further carried out to investigate the influence of steel fibers volume ratio and stirrups ratio in the joint core area on the seismic performance. Evaluation of the hysteretic response, ductility, energy dissipation, stiffness, and strength degradation were the main aims of this study. Results indicate that the optimal volume fraction of steel fibers is 1.5%, and the optimal stirrups ratio in the joint core area is 0.9% in terms of the enhancement of the seismic performance of the SFRHSC beam-column joint.