Stirrup Strain Research Articles

Experimental Study on the Shear Strength of Dune Sand Concrete Beams

An experimental study was performed to investigate the shear strength of concrete beams made with dune sand (DS) from the Gurbantunggut Desert in the Chinese province of Xinjiang. The test consisted of 3 series of beams which explored the shear properties of dune sand concrete (DSC) beams. The failure mode, crack pattern, load deflection, and stirrup strain were investigated. Meanwhile, the effect of shear span‐to‐depth ratio (a/d), stirrup ratio, and dune sand replacement ratio on the shear strength of DSC beams was discussed. The results showed that the dune sand replacement ratio had insignificant influence on the failure mode of beams, so it was feasible to use DS to fabricate beams in regions of Xinjiang in China. Furthermore, the measured shear strengths of the DSC beams were compared with the calculated values of current design codes, and the results indicated that the shear strength of DSC beams was not precisely predicted by current design codes. Therefore, a modified formula was proposed to calculate the shear strength of DSC beams.

Interface shear transfer in reinforced engineered cementitious composites under push-off loads

Engineered cementitious composites (ECC) has been widely used for structural members and joints under various loading conditions. Nevertheless, the shear transfer mechanism at the interface of reinforced ECC needs further study due to the lack of experimental results. This paper investigates the interface shear transfer of reinforced ECC subjected to push-off loads. Experimental tests were carried out to quantify the shear resistance and to investigate the shear transfer mechanisms at different loading stages. The effects of ratio and type of stirrups were considered in the experimental programme. The peak and residual shear resistances of reinforced ECC were obtained and compared with the calculated values from existing design methods. The interface shear transfer mechanisms were determined by analysing the measured strains of stirrups and transverse dilatancy. A design equation was proposed based on experimental results. Finally, conclusions were drawn for the interface shear design of reinforced ECC.

Investigation on the shear behavior of steel reinforced NC/HDC continuous deep beam

Highly ductile fibres reinforced concrete (HDC) has the tensile strain-hardening behavior accompanied by multiple cracks. A steel reinforced HDC continuous deep beam (SRD-CDB) and a steel reinforced normal concrete continuous deep beam (SRC-CDB) were designed and tested to study their load-carrying capacities and deformability. Their failure patterns, load-deflection curves, stirrup strains, steel web strains and shear capacities were investigated. The load-carrying capacity and deformability of SRD-CDB were improved because HDC alleviated the damage and showed deformation compatibility with steel section and stirrups. Results calculated by direct strut-and-tie model are conservative for the design of SRC-CDB and SRD-CDB.

Field test and elastic dynamic response analysis of shallow-buried utility tunnel under explosion load

In order to study the load distribution rule, dynamic response and failure mechanism of the tunnel structure under explosion load, evaluate the protection potential of the tunnel project, and obtain the test data of the tunnel under explosion load, the anti-explosion test of the tunnel structure is designed. This paper mainly analyzes the dynamic response at the center of the roof under three working conditions of the proportional blasting depth of 2.000, 1.587 and 1.260 m/kg1/3. The test measures the size of the blasting pit, the time-history curves of the longitudinal bars and stirrup at the bottom of the roof center and the inner stirrup at the center of the side wall, acceleration time-history curve, reflection pressure time-history curve and displacement time-history curve. The test data show that the stirrup strain at the bottom of the roof center is much greater than that of the longitudinal bars, and the repeated displacement caused by the vibration of the tunnel is about the same. It is suggested that the tunnel should be symmetrical reinforcement and stirrup encryption, and ensure the compressive strength of concrete. The accuracy of the peak of reflected pressure is verified by the conventional weapon effect calculation software CONWEP, and the total pressure acting on the tunnel is further obtained and converted into uniform load. The maximum displacement of the roof center in the elastic response stage is calculated, which is in good agreement with the measured displacement.

Numerical modeling of size effect in shear strength of FRP-reinforced concrete beams

This study presents the numerical modeling of size effect in shear strength of FRP-reinforced concrete (RC) beams with and without stirrups by finite element analysis (FEA) model. The size effect was incorporated in the model by controlling the mesh size, softening tensile stress-strain response, and dilation angle. A new modification was suggested to represent the softening tensile strength of concrete for different size of beams. The calibrated FEA model for beams with and without stirrups showed great power and ability in simulating the experimental results in terms of ultimate shear capacity, ultimate deflection, flexural and stirrup strains, and crack patterns. Additionally, the calibrated model was then verified by thirteen experimental results from four different studies, as well as a parametric study was performed.

Size effect on the shear failure of high-strength concrete beams reinforced with basalt FRP bars and stirrups

Abstract Six large-scale high-strength concrete beams reinforced with basalt fiber reinforced polymer (BFRP) bars and stirrups and three corresponding beams without stirrups were constructed and tested for shear failure under four-point bending. The main parameters considered were the beam effective depth (300, 500, and 700 mm) and the stirrup spacing. The test results indicated that the size effect on shear failure could not be eliminated completely, as the initial shear crack, shear crack width, shear resistant components analysis, strain in the BFRP stirrups, and normalized shear strength were still related to the beam depth. The ACI 440-15 strain limit of 4000 µs could be relaxed with the condition that the serviceability requirement is satisfied. Furthermore, based on a collected database from the literature, an accurate and conservative equation was proposed to predict the FRP stirrup strain limit. The proposed equation includes the effects of all influencing parameters, which is more reasonable than the constant strain limit used by most design codes.

Experimental Study on Shear Behavior of Steel Fiber Reinforced Concrete Beams with High-Strength Reinforcement.

Many researchers have performed experimental and theoretical studies on the shear behavior of steel fiber reinforced concrete (SFRC) beams with conventional reinforcement; few studies involve the shear behavior of SFRC beams with high-strength reinforcement. In this paper, the shear test of eleven beams with high-strength reinforcement was carried out, including eight SFRC beams and three reinforced concrete (RC) beams. The load-deflection curve, concrete strain, stirrup strain, diagonal crack width, failure mode and shear bearing capacity of the beams were investigated. The test results show that steel fiber increases the stiffness, ultimate load and failure deformation of the beams, but the increase effect of steel fiber decreases with the increase of stirrup ratio. After the diagonal crack appears, steel fiber reduces the concrete strains of the diagonal section, stirrup strains and diagonal crack width. In addition, steel fiber reduces crack height and increases crack number. Finally, the experimental values of the shear capacities were compared with the values calculated by CECS38:2004 and ACI544.4R, and the equation of shear capacity in CECS38:2004 was modified to effectively predict the shear capacities of SFRC beams with high-strength reinforcement.

Experimental and Analytical Studies of U-Shaped Thin-Walled RC Beams Under Combined Actions of Torsion, Flexure and Shear

U-shaped thin-walled concrete bridge beams usually suffer the combined actions of flexure, shear and torsion, but no research about the behavior of U-shaped thin-walled RC beams under combined actions has been reported in literature. Three large specimens of U-shaped thin-walled RC beams were tested under different torque–bending moment ratios (T–M ratios) of 1:5, 1:1 and 1:0 to investigate the mechanical responses such as crack patterns, reinforcement strains, failure modes and ductility. The testing results showed that ductile flexural failures occurred for all three of the U-shaped thin-walled beam specimens, although the combined shear effect of circulatory torque, warping torque and shear force increased as the T–M ratio increased from 1:5 via 1:1 to 1:0, reflected by diagonal cracks and stirrup strains. More specifically, basically symmetrical flexural failure was dominated by the bending moment when the T–M ratio was 1:5; flexural failure of the loaded half of the U-shaped thin-walled section was dominated by the combined action of the bending moment and warping moment, while there were only a few cracks on the other half of the U-shaped section when the T–M ratio was 1:1; and anti-symmetrical flexural failure was dominated by the warping moment when the T–M ratio was 1:0 (pure torsion). A simple method to calculate the ultimate load of such U-shaped thin-walled RC beams under different T–M ratios was suggested, and the calculating results were corresponding well with the experimental results.

Experimental investigation of high-cycle fatigue behavior for prestressed concrete box-girders

An experimental study is proposed to investigate the high-cycle fatigue behavior of prestressed concrete box-girders. Special focus is on the shear diagonal cracks in the webs of girders, which is rarely investigated in the open literature. Laboratory fatigue tests were designed and conducted to study the propagation of shear diagonal crack of PC box-girder specimens under cyclic loadings. The development of stirrup strain, propagation characteristics of diagonal crack and the related factors are discussed in detail. A finite element (FE) model for concrete damage of PC box girder under high-cycle fatigue loading is established to investigate the crack propagation behavior. Following this, a model for the calculation of diagonal crack widths of PC box-girder under fatigue loading is proposed based on the experimental observations. The calculation results are compared with experimental data for validation. It is observed that the maximum stirrup strain in crack zone increases 67.9% based on this investigation. The ratio of displacement during the last cycle and that during initial loading can research 40.3% in the current investigation. Finally, several conclusions are drawn based on the proposed study.

Behavior of RC beams strengthened in shear with FRP and FRCM composites

This paper presents the results of an experimental campaign carried out to investigate the behavior of reinforced concrete (RC) beams strengthened in shear with externally bonded composites. Two different types of composites were studied: Fiber Reinforced Polymer (FRP) and Fiber Reinforced Cementitious Matrix (FRCM) composites. In addition, different types of fiber (carbon and steel) were employed, and the influence of internal transverse steel reinforcement ratio and the presence of composite anchors were investigated. Internal-external shear reinforcement interaction, i.e. reduction of the stirrup strain due to the presence of the composite, was observed for both FRP and FRCM strengthened beams, but the interaction was less pronounced for those with FRCM composites. The anchors employed in this study did not affect the shear strength of the beams, but changes in the concrete crack pattern, mid-span displacement, and failure mode were observed. For FRCM strengthened beams, strains measured in the fibers showed higher exploitation ratios, i.e. the ratio between the maximum measured fiber strain and the rupture strain, for beams with carbon FRCM than those with steel FRCM. Effective strains computed using available models were considerably lower than the maximum measured fiber strains.

Analysis of FRP Shear Strengthening Solutions for Reinforced Concrete Beams Considering Debonding Failure

AbstractIn this paper, a fiber beam model previously developed by the authors for the nonlinear analysis of strengthened elements, including the effects of shear, is used to predict the response of reinforced concrete (RC) beams strengthened in shear with fiber reinforced polymers (FRP) sheets. In the previous version of the model, debonding failure of FRP was not included; hence, its application was limited to the simulation of wrapped configurations. The model is now extended to account for debonding failure in order to allow for its application to beams strengthened with U-shaped and side-bonded configurations. Existing experimental tests on RC beams strengthened in shear by FRP sheets in both wrapped and U-shaped configurations were numerically simulated. The model reproduces, with reasonable accuracy, the experimental failure loads, the load-deflection behavior, and the strains in FRP and stirrups with increasing load. The advantages of this proposal are related with the simplicity and straightforwar...

Experiments and calculation of U-shaped thin-walled RC members under pure torsion

U-shaped thin-walled RC (Reinforced Concrete) members have been widely applied in construction projects of urban rail viaduct in China. Researches about the torsional response of this kind of structures are extremely limited. Four large U-shaped thin-walled RC beams with both ends restrained were tested to investigate the pure torsional response. The detailed information includes torque–rotation curves, crack patterns, failure mode and steel bar strains. Typical flexural failures at support and mid-span where the warping moment predominates were observed in all four test specimens. And at quarter span, stirrups strain caused by circulatory torsion reached nearly 80% of total stirrup strains at failure stage, due to variable proportion between circulatory torsion and warping torsion after yielding of longitudinal steel bars. Finally, a simple method to calculate ultimate torque of such structures was proposed here. And it agrees well with tested results.

Size effect in uncracked and pre-cracked reinforced concrete beams shear-strengthened with composite jackets

The paper deals with the size effect on shear behaviour of reinforced concrete beams strengthened with fiber reinforced polymer jackets. Continuous U-jackets were made of glass or carbon fiber fabrics and epoxy composite materials. Twelve uncracked or pre-cracked strengthened reinforced concrete beams and six beams without strengthening, all of them in 6 different sizes, were tested. The results indicate that fabric-epoxy continuous U-jackets have reduced the brittleness of the shear failure of beams, tensile strains in stirrups, and, in a significant way, also the width of shear cracks at the failure state. Although similar strengthening was used for both, uncracked and pre-cracked beams, activation of jackets significantly differed. While jacket strains and their strengthening effectiveness were affected by the sizes of uncracked, retrofitted beams, they remained almost constant in pre-cracked, repaired beams of varying sizes. In contrast to repaired beams, stirrups in retrofitted beams did not yield at failure. Degree of strengthening, defined as the ratio of strengthened-to-unstrengthened beam shear capacities, was studied. It was found out that consideration of the degree of strengthening would provide relations reflecting real behaviour of reinforced concrete beams strengthened with fiber reinforced polymer U-jackets or U-jacketed strips.

Parametric Analysis of Seismic Performance of RC Columns Strengthened with Steel Wire Mesh

By establishing a finite element (FE) model of reinforced concrete (RC) columns strengthened with steel wire mesh, the mechanical properties under low-cyclic loading are analyzed, and the correctness of the FE model is verified. Hysteretic curves, skeleton curves, strain curves, and changes in stiffness and ductility of the strengthened RC columns under various strengthening conditions are calculated in this study by using the FE model to examine the effects of axial compression ratio, longitudinal reinforcement ratio, concrete strength, steel wire quantity, and eccentric compression on the seismic behavior of the strengthened columns. The results show that an increase in axial compression ratio results in an improvement in the ultimate bearing capacity of the strengthened columns by 9%-17% and a reduction in ductility by 9%-15%. In addition, increases in the stirrup ratio, longitudinal reinforcement ratio, concrete strength, and steel wire quantity result in improvement in ultimate bearing capacity, and ductility of the strengthened columns can be improved by 2%-28%. Moreover, an increase in vertical pressure results in rapid development of eccentric, stirrup, and steel wire strains in the strengthened columns, which causes reductions in ultimate bearing capacity in the columns by 2%-13%, energy consumption by 35%, and additional reductions in stiffness and ductility.

Experimental and analytical behavior of strengthened reinforced concrete columns with steel angles and strips

The need of strengthening reinforced concrete columns, due to loss of strength and/or stiffness, is an essential requirement due to variation of the loads and environmental conditions applied on these columns. Steel jackets around the reinforced concrete (RC) columns are usually made by means of steel plates covering all over the column surface area. For the value of engineering purposes, another technique was developed using steel angles at the corners of the RC columns connected with discrete steel strips. In this paper, an experimental program is designed to evaluate the improvement in load-carrying capacity, stiffness and ductility of strengthened RC columns, concomitant with steel angles and strips. Despite of prevailing a substantially increased loading capacity and strength a pronounced enhancement in ductility and stiffness has been reported. A need for experimental test results with low value of concrete strength to mimic the local old-age structures condition that required strengthening in local countries. Seven columns specimens are tested to evaluate the strength improvement provided by steel strengthening of columns. The method of strengthened steel angles with strips is compared with another strengthening technique. This technique includes connected and unconnected steel-casing specimens. The observed experimental results describe load-shortening curves, horizontal strains in stirrups and steel strips, as well as description of failure mode. The extra-confinement pressure, due to existence of steel cage, of the strengthened RC column can be also observed from experimental results. The code provisions that predict the load-carrying capacity of the strengthened RC composite column has a discrepancy in the results. For this reason, an analytical model is developed in this paper to compare the code limit with experimental observed results. The proposed model accounts for the composite action for concrete confinement and enhancement of the local buckling of steel elements. This adopted model is simplified and applicable to practical design field. In this respect, the experimental results and those of the analytical model showed a good agreement.

The Strain Change Rules of Full-Scale High Strength Concrete Frame Columns with High Axial Compression Rations

Based on experimental study of 9 full-scale high-strength concrete(HSC) rectangular frame columns with high axial compression ratios, high-strength longitudinal reinforcements and transverse reinforcements and rectangular interlocking ties, their strain change rules of longitudinal reinforcement, stirrups and concrete were discussed and analyzed. The main results indicate as follows. The maximum tensile strain of longitudinal reinforcement decrease and the tensile strain of concrete increase quickly as the axial compression ratios and the strength grades of concrete are higher; the strains of outer stirrups are all the time greater than those of inner stirrups; the single brace stirrups have the same action with the closed stirrups.

Behavior and analysis of inverted T-shaped RC beams under shear and torsion

The 1998 ASCE-ACI Committee 445 on shear and torsion identified researching combined shear and torsion as well as giving physical significance for torsion design as an upcoming challenge (ASCE-ACI Committee 445 on shear and torsion, 1998). Most of the previous experimental studies were focused on reinforced (RC) beams under flexure, shear or torsion. The behavior of inverted T-shaped beams with both web and flange closed stirrups are not fully explored. In this research paper, an innovative test setup capable of simulating the behavior of inverted T-shaped beams under combined shear and torsion was developed and implemented. The behavior of three inverted T-shaped beams tested under different values for the ratios of the applied torque to the applied shear force is discussed. The value of the torque to shear ratio significantly affects the behavior of the inverted T-shaped beams in terms of cracking pattern; failure mode; strut angle of inclination; cracking and ultimate torque; post-cracking torsional rigidity; cracking and ultimate shear; flange and web stirrup strain. The flange stirrup is more efficient in resisting torsion moment over shear forces. A model capable of predicting the behavior of flanged beams under combined actions was developed and implemented. The model showed good agreement with the experimental results from three different experimental studies.

Exploring GFRP bars as reinforcement for rectangular and L-shaped beams subjected to significant torsion: An experimental study

Steel corrosion related problems have been a heavy burden on countries economically and socially for many decades. Therefore, the inevitable quest to find an alternative for steel reinforcements is long overdue. On the other hand, fiber reinforced polymer (FRP) bars have non-corrosive nature and could be the solution for this problem. In this study, the objective is exploring the usage of glass fiber polymer (GFRP) bars as torsion reinforcement for L-shaped beams. New adhesively bonded GFRP stirrups are presented and implemented. Five beams were constructed and tested under significant torsion. The bonded GFRP stirrups were more effective as transversal reinforcement compared with the bent steel stirrups and the bent GFRP stirrups. It improved the ultimate torsional strength and increased the corresponding unit angle of twist and the maximum stirrup strain as well as the major concrete crack width. In addition, the increase in the GFRP transversal reinforcement percentage improved the ultimate torsional strength, the toughness, and the deformability. Moreover, the usage of a stirrup strain value of 0.4% resulted in overly conservative predictions for the ultimate torsional resistance; however, it provided adequate torsional deformability index and toughness.

The Analysis of Relationship between Stirrup and Longitudinal Reinforcement with Regression Analysis

Regional confined concrete is a method which can strengthen constraint in the most needed position, it can make concrete, longitudinal reinforcement and transverse stirrup to form a more effective binding, and provide a stronger restraint in required regional giving full play the role of constraints. In the result analysis of the regional confined column specimen load test, we found that longitudinal reinforcement and stirrup strains have certain relationship. This article analyses the relationship between the two from the stirrup and longitudinal reinforcements strains in the contingency load, references are provided for the further development of regional confined concrete theory. Taking the two specimens as examples, the regression analysis was carried on between longitudinal reinforcement and stirrup strain, the relationship equation was obtained

Combined Shear and Bending Behavior of Joints in Precast Concrete Segmental Beams with External Tendons

Precast concrete segmental bridges with external tendons are becoming widely constructed all over the world. The main objective of this study is to obtain a further understanding of the behavior of joints when they are subjected to combined shear and bending. Nine specimens of precast concrete segmental beams (PCSBs) with external tendons were match cast and tested: six of the specimens were tested under combined shear and bending; two specimens were tested under pure bending; and one specimen was tested under direct shear. Failure processes and modes, joint resistance, and strains of stirrups and prestressing tendons were recorded in the tests. Based on the results of the experiment, the study analyzed the mechanism of combined shear and bending resistance for dry and epoxied joints when loads were located in the immediate vicinity of the joint. Additionally, simplified failure modes of dry and epoxied joints subjected to combined shear and bending were presented in this paper. On the basis of the simplified failure modes, formulas were deduced for evaluating the resistance of joints when failure occurred in a joint section with loads applied in the immediate vicinity of the joints. The formulas provided a rational prediction of the joint resistance under combined shear and bending, which in turn verified the rationality of the proposed failure modes.