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In an attempt to find a non-corrosive stirrup as an alternative to steel stirrup in concrete structures under harsh environments, manual fabrication of fiber-reinforced polymer (FRP) strip stirrups is becoming increasingly popular to address premature failure in pultruded FRP stirrups in concrete beams. This study is the first to address the shear behavior of concrete beams with forta-ferro and handmade FRP strip stirrups. Here, the percentages of forta-ferro fibers added in the concrete mixes were 0.3 and 0.6% by total concrete volume, and the stirrups material was carbon FRP (CFRP). Six series of concrete beams were tested under a four-point bending load to examine the effect of adding fibers and stirrups on the shear behavior of concrete beams. It was found that incorporating forta-ferro fiber causes an increased ultimate load-bearing capacity, ultimate shear load, and deflections at the peak and failure points of concrete beams. An increased fiber content leads to an increase in these properties of concrete beams. The results also showed that, for a given fiber content, concrete beams with CFRP stirrups develop higher ultimate load-bearing capacity (10–33%), ultimate shear load (10–33%), and deflections at the peak (8–22%) and failure points (6–34%) compared to those without stirrups. It is also shown that the proposed model provides an accurate prediction of the shear capacity of fiber-reinforced concrete beams with stirrups. Positive effects of combining forta-ferro fiber and handmade CFRP stirrups in improving the shear resistance as well as the deformability of concrete beams were observed, which is promising. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The shear-carrying mechanism in reinforced concrete (RC) has long been uncertain, partly because previously available sensors were insufficient for capturing local behavior. In this study, three large RC beams with stirrups were instrumented with distributed fiber-optic sensors (DFOS) to measure the strain along the full length of the reinforcing bars, while digital image correlation (DIC) was used to measure distributed crack movement to calculate the forces that they transfer. The DFOS measurements along the stirrups showed that the total stirrup force along a shear crack was insufficient to resist the total applied shear. Free-body diagrams (FBD) were constructed along diagonal cracks using the sensor measurements and constitutive relations to investigate if the resulting summation of forces would be in equilibrium, and the results suggest that the main elements of shear resistance have been, at least approximately, identified for the first time with the aid of distributed sensing. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of South China University of Technology (Natural Science Edition) is the property of South China University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An experimental study was conducted to investigate the effects of stirrup corrosion, concrete strength and casting position on the behaviour of the bond between steel bars and concrete. Accelerated corrosion was applied to corrode the stirrups in concrete specimens under laboratory conditions. In total, 180 specimens were cast and tested in this experiment. The specimens had three nominal concrete strengths of C20, C40 and C50 with two deformed steel bars of 18 mm in diameter set in a 200 × 200 mm diagonal concrete prism with two stirrups of 8 mm in diameter to provide confinement. The steel bars were cast with different pouring positions, namely the upper and lower ends. Five corrosion levels were investigated, namely 0, 5, 10, 15 and 20%; 12 specimens were investigated for each corrosion level. A pull-out test was carried out to obtain the bond–slip curves. The test results indicate that the porosity of concrete has a great effect on bond degradation with the increase of the steel corrosion level. [ABSTRACT FROM AUTHOR]

In order to evaluate the influence of freeze–thaw action on the durability of concrete structures, this paper presented an experimental study to investigate the effects of freezing–thawing cycles and concrete strength on the bond behavior between steel bars and concrete confined with stirrups. Through freeze–thaw cycles and center pullout tests, the failure mode of pullout specimen, concrete strength, mass loss, dynamic elastic modulus, and bond–slip curves were analyzed. At last, the bond–slip constitutive model was proposed for specimens with stirrup confinement under freeze–thaw action. Main test results indicate that the failure mode and shape of bond–slip curves are affected by stirrups. The bond strength hasa certain increase after 100 freeze–thaw cycles owing to the constraining force from stirrups, whereas the splitting tensile strength significantly declines. After 100 freeze–thaw cycles, the splitting tensile strength of C20 and C40 decreased by 40.8% and 46.5%, respectively. The formula was provided to calculate the bond strength of constrained concrete after freeze–thaw cycles, and the damage coefficient and other related parameters in the formula were suggested. The predicted bond–slip curves are close to the experimental results, which could provide reference for the related research of bond performance after freeze–thaw action. [ABSTRACT FROM AUTHOR]

The present study aimed to introduce an accurate modeling strategy for the three‐dimensional (3D) nonlinear finite element analysis of reinforced concrete (RC) columns considering the effects of the stirrup confinement. For this purpose, concrete columns with different geometric characteristics and various reinforcement details whose experimental test data are available, were analyzed using the finite element method. The concrete damaged plasticity (CDP) was used to model the nonlinear behavior of the concrete material in the compression and the tension. The ideal elastic–plastic constitutive law was utilized for modeling the behavior of longitudinal and transverse rebars. Through comparing the experimental data and numerical results, the effect of various parameters, such as the type of stress–strain relationships used for modeling the behavior of confined concrete and the type of element used to model the stirrups, were evaluated. Additionally, the sensitivity of numerical results against the CDP model parameters (i.e., the viscosity parameter, the flow potential eccentricity, the dilation angle, the ratio of biaxial compressive strength to its uniaxial compressive strength, and the ratio of the second stress invariant on the tensile meridian) were investigated. The results show that the presence and modeling of stirrups in the RC columns alone are not enough for capturing the effects of concrete confinement. The use of beam elements instead of truss elements for modeling the stirrups as well as the use of Vallenas stress–strain relations for modeling the uniaxial behavior confined concrete, leads to numerical results that are more close to the experimental data. [ABSTRACT FROM AUTHOR]

The article presents the optimization of high-pressure die casting process technology for equestrian stirrups with the application of computer simulation. In the initial stage, the output technology was analyzed, and on the basis of a series of virtual experiments the cause of defects in the casting was highlighted. The optimization process includes different designs of a gating system. Additionally, the casting application properties were evaluated in an exploitation simulation, taking into account predicted defects resulting from the casting and solidification process. Based on the conducted analyses, technological changes were made to the casting technology design allowing the defects occurring in the original technological concept to be removed. [ABSTRACT FROM AUTHOR]

Concrete beams reinforced in shear and flexure with linear elastic and brittle glass fiber–reinforced polymer (GFRP) bars show differences in behavior when compared with the traditional steel-reinforced concrete beams. The flexural design of these beams follows similar principles as the design of steel-reinforced concrete members, except that the cross section is over-reinforced to compensate for the lack of reinforcement ductility. GFRP-reinforced beams are designed in shear using semiempirical modifications to the design equations for steel-reinforced concrete. The modified equations have not been well studied for beams with high shear span to depth (a/d) ratios. The presented research program is composed of three-point bending tests of ten GFRP-reinforced concrete beams, with a/d slenderness ratios from 4.5 to 10.5 with constant flexural reinforcement and varied shear reinforcing. The observed mode of failure transitioned from shear to flexure-controlled with increasing specimen slenderness and increased shear reinforcing. All failures were controlled by concrete behavior, either in tension for beams without shear reinforcement or compression for beams with shear reinforcement. The inclusion of GFRP stirrups in the beams prevented brittle failures by providing confinement to concrete. Comparisons with the current design rules showed good agreement with experimental results. However, the relative contribution of concrete and reinforcement to shear-carrying capacities differed in the code predictions from results derived from measured strains. [ABSTRACT FROM AUTHOR]

To investigate the shear capacity and failure mechanism of RC beams after fire exposure, fourteen full-scale beams without stirrups were tested at ambient temperature and after fire exposure. Three parameters, including the loading ratio, shear span-to-depth ratio and longitudinal reinforcement ratio, were considered in static load tests. The deterioration mechanism of the shear bearing capacity at the diagonal section of RC beams without stirrups after fire exposure was experimentally, numerically and theoretically revealed, and a calculation formula for the shear capacity of post-fire beams without stirrups was proposed. The results show that the shear capacity and stiffness of the specimens decreased after fire exposure, and the shear strength loss of the beams increased with fire exposure time. The shear capacity and stiffness of fire-damaged specimens decreased as the shear span ratio λ increased, and the shear strength loss of the beams decreased with λ. Compared with the theoretical calculation and experimental results of beams without stirrups, the average of the absolute errors was 10.48%. Therefore, this formula can better calculate the residual shear capacity of beam without stirrups after fire exposure. [ABSTRACT FROM AUTHOR]

Self-Compacting Concrete (SCC) generally has lesser coarse aggregate contents and also the maximum size of aggregates is limited as compared to Normal Vibrating Concrete (NVC) for the same class of strength. This results in reduced aggregate interlock in Self-Compacting concrete as against NVC, which affects the shear strength of slender beams and thus, SCC might have lower shear strength. In this article, an experimental program that includes six slender beams of High-Strength Self Compacting Concrete (HSSCC) with compressive strength more of than 90 MPa and with different stirrup spacing is presented. Experimental test results of shear strength of HSSCC beams are compared with high strength NVC beams for different stirrups spacing. The results showed the ultimate shear stress of HSSCC beams is lower than NVC beams and an increase in transverse reinforcement index, ρw fy, in HSSCC beams decreases this difference. The results are also compared with different code provisions. Not much work has been done on beams with lower transverse reinforcement index (ρw fy) and in the present work, ρw fy ranges between 0.276 to 0.80.

This study aims to investigate the effects of the geometrical properties and volume content of steel fibers on the shear resistance of reinforced high-strength concrete (HSC) beams without stirrups. Hooked-end and twisted steel fibers with different aspect ratios ranging from 60 to 100 were used at volume fractions of 0.5%–1.0%. The shear strength of HSC beams without stirrups significantly increased due to the addition of steel fibers and by increasing their volume fraction by up to 1.0%, resulting in approximately 1.7 times higher shear resistance. A higher fiber aspect ratio was effective in improving the resistance to shear failure of HSC beams without stirrups and in enhancing beam deformability relative to the increase in shear strength. Using twisted steel fibers led to better shear resistance than hooked-end steel fibers, resulting in 1.11- and 3.34-times higher shear strength and ductility at the same fiber volume fraction on average. The shear strength of steel fiber-reinforced concrete (SFRC) beams was also predicted using eight different models. Narayanan's model most precisely predicted the shear strengths of reinforced SFRC beams without shear reinforcement, with an average v u , exp / v u , p r e d ratio of 1.16. The shear strength increased with the decrease in shear span-to-depth (a/d) ratio and the increase in the fiber factor. The contribution of steel fibers to shear strength was greater for deep beams than slender beams. The predicted shear strengths of deep beams and high-strength SFRC showed a significant deviation from the actual value and required careful consideration. [ABSTRACT FROM AUTHOR]

Fibre-reinforced polymers (FRP) have emerged as viable substitutes for conventional steel materials because of their ability to avoid chloride-induced corrosion. However, the applicability and feasibility of FRP in concrete columns have yet to be fully elucidated. To overcome this research gap, this study incorporated carbon FRP mesh fabric (CFRP-MF) as stirrups and steel-FRP composite bar (SFCB) as longitudinal reinforcements. This study investigated the impact of the reinforcement type (steel, CFRP strips, and CFRP-MF), volume stirrup ratio, and concrete strength on the axial compression performance of concrete columns. The findings revealed that CFRP-MF enhanced the restraint capacity of the concrete core by approximately 11 % compared to conventional materials, improving the intensive restraining effect of CFRP-MF stirrups by weakening the concrete arching effect. Moreover, the load-carrying capacity of concrete column is directly proportional to stirrup volume ratio and concrete strength. Furthermore, the FRP partially constrained concrete calculation models were compared with FRP-MF, in terms of short-term life cycle impacts and structural performances. The results indicate that concrete columns with CFRP-MF stirrups and longitudinal SFCBs exhibit excellent properties, therefore establishing their potential for extensive utilization and enhanced durability in coastal environments. • A corrosion-resistant rebar combination is proposed to solve the issue of corrosion-prone rebars within structures. • Concrete columns with CFRP-MF stirrups have a higher load capacity and ultimate strain than RC columns. • The applicability of the FRP partial wrapping model to columns with CFRP-MF stirrups was evaluated and compared. • CFRP-MF stirrup columns offer lower weight, comparable carbon and resource consumption capabilities to RC structures. [ABSTRACT FROM AUTHOR]

Although fiber-reinforced polymer (FRP) reinforcements have become popular, the post-pultrusion bending leads to significant deficiency in bent portions of FRP hoops and spirals. This study adopts flexible carbon FRP (CFRP) grids as stirrups, and investigates the shear behavior of circular short columns reinforced with GFRP bars and CFRP grid stirrups. Six specimens with different shear reinforcement ratios, axial load ratios and types of stirrups (CFRP grids and steel hoops) were tested to shear failures. The failure modes, crack and strain developments, and shear load-horizontal displacement responses were presented for discussion. All specimens experienced shear-compression failures, and the critical diagonal crack widths increased approximately linearly with shear loads. The typical shear load-horizontal displacement curve consisted of three branches: a linear elastic branch, a cracking branch with progressive slope deteriorations, and an almost flat failure branch. Increasing CFRP grid stirrup ratio could not only enhance strength and ductility performance, but also alleviate the slope degradations, while increasing axial load ratios could enhance the initial cracking loads, restrain crack propagations, and reduce the lateral displacements. In terms of strength performance, steel hoops could be replaced by CFRP grid stirrups even with smaller stirrup ratio. Additionally, analytical investigations suggested that the effective stresses and strains of CFRP grid stirrups at failure may be lower than code limits. [ABSTRACT FROM AUTHOR]

Over the past few decades, numerous studies have explored the use of steel fiber (SF) as an alternative to transverse reinforcement rebars in reinforced concrete beams, either partially or completely replacing them. However, there are limited studies that have investigated the effect of fiber dosage and length on reinforced concrete beam performance under torsional loads without the use of transverse reinforcement rebars. In this study, experimental investigations were conducted to examine the performance of reinforced SF concrete beams subjected to torsional load, utilizing SFs as a complete substitution of transverse reinforcement rebars. Ten different concrete mixes with varying dosages of SFs, namely 0%, 0.5%, 1.0%, and 1.5%, were examined while maintaining the same aspect ratio for fiber length and diameter. The results revealed that the addition of SFs in the concrete mix had an impact on its properties, reducing workability but increasing flexural, tensile, and compressive strengths. By incorporating 1.0% of SFs in the concrete mix, the missing torsional strength resulting from the absence of stirrups was adequately compensated. Moreover, the presence of SFs significantly influenced the ductile behavior beyond the point of cracking in the tested beams. Hence, it is recommended that SFs are incorporated with dosages of 1.0% and 1.5% in the concrete mixture, particularly for beams subjected to torsion, as a viable substitute for stirrups.

This article studies two cases of technical diffusion: the origin and diffusion of stirrups in Eurasia and the diffusion of the Chinese postal system by the Mongols. These cases are linked to two major periods in the history of the Silk Roads, or Eurasian trade networks: the Islamic period and the Mongolian period, two periods that constitute, from the 8th to the 13th century, essential moments in the history of diffusion because of the establishment of new networks of economic exchange. In these networks, merchants and nomads have strongly contributed to the diffusion of all kinds of techniques on a very important scale.

Background How the modification of saddle fitting parameters in horse riding affects rider’s kinetics is very uncertain. The aim of this study is to describe how manipulating the two main adjustments that an end-user is likely to perform (saddle tilt and stirrup length) affects the biomechanics of a horse rider on a living horse. Methods Eleven showjumpers volunteered to take part in this study. Each participant performed a 120-strides standardization trial at trot and canter, with 0° saddle tilt and stirrup length that would position the rider’s knee at 90°. Following the standardization trial, four interventions were performed, which consisted of 60 strides with 60 mm shorter stirrups, 60 mm longer stirrups, 4° forward tilted saddle and 4° backward tilted saddle. Stirrup and rein tension forces were measured with tension loadcells. A symmetry index was calculated. Acceleration was measured with inertial measuring units at the helmet and back of the rider and shock attenuation was calculated. Results Shortening the stirrups and adjusting saddle tilt significantly enhanced shock attenuation at canter and increased force on the stirrups at trot and canter (p

Self-consolidating concrete (SCC) can be characterised by its flowability, stability and passing ability. Although SCC tends to have a more uniform microstructure in the concrete–reinforcement interfacial transition zone, the reduction of the nominal size and coarse aggregate content in the concrete mix may adversely affect its shear strength. Therefore, the aim of this research was to evaluate the shear strength of SCC by means of push-off tests of 45 specimens, produced with one conventional concrete and two SCC mixtures, with two different coarse aggregate contents (reference and reduced by 30%). The transverse reinforcement ratio ranged from 0.46% to 2.28%, using closed stirrups crossing the shear plane. The increase of reinforcement ratio resulted in improvements in shear strength for specimens with one, two and three stirrups, while specimens with four and five stirrups had a premature failure owing to concrete crushing near the notch. No significant difference in shear strength was identified owing to concrete type or coarse aggregate. The experimental results were also compared with codes estimates, and Eurocode 2 presented the best fit to experimental results when compared with the American code ACI 318 and the Canadian standard CSA A23.3. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete (UHPC) has the advantages of high compressive and tensile strength, high bending strength, good durability, remarkable corrosion resistance, and low self-weight. In this study, ten UHPC specimens were designed based on three fundamental parameters, including the ratio of the gross supporting area Ab to the bearing plate area Al (local area aspect ratio Ab/Al), the ratio of core area Acor to the bearing plate area Al (core area aspect ratio Acor/Al,), and the reinforcement ratio pv, to investigate mechanical behaviors and bearing capacity. Failure modes, cracking load, crack propagation, wedge features, the relationship between local compression and deformation, and the local bearing capacity was investigated. Finite element models (FEMs) were built to simulate and validate the observed behavior of the anchorage zone under compressive loading. The experiment results demonstrate that the pv significantly increases the bearing capacity. When the reinforcement ratio increased from 4.5% to 3.7%, the bearing capacity increased by 23%, and the effect of Acor/Al was not obvious. In addition, decreasing the Ab/Al from 11.1 to 6.3 increases the bearing capacity to 19%. Furthermore, a model was proposed to predict the bearing capacity of the UHPC specimens reinforced with stirrups. The calculated values, numerical predictions, and experiment results showed good agreement. [ABSTRACT FROM AUTHOR]

Conventional pultruded fiber-reinforced polymer (FRP) rod stirrups are susceptible to premature bent corner rupture and bond slip failure of overlapping legs. This research proposed a new type FRP shear reinforcement, closed-type winding GFRP (CW-GFRP) stirrups, featuring a fully closed rectangular cross-section. CW-GFRP stirrups completely avoided slip and significantly improved the strength of bent portion of stirrups. To investigate the feasibility of using CW-GFRP stirrups as shear reinforcement, shear test of 8 concrete beams reinforced with conventional pultruded stirrups and CW-GFRP stirrups was conducted. The beams were 300 mm deep and 150 mm wide, and their shear span ratio were 2.07. The effect of the material of stirrups, the spacing of stirrups, and the width of CW-GFRP stirrups were investigated. The test results showed that pultruded stirrups exhibited bond slip failure, in contrast, CW-GFRP stirrups reinforced beams prevented this failure and showed enhanced stiffness, narrower shear crack width and 1.09–1.12 times higher shear capacity. The splitting failure typical of CW-GFRP stirrups was reported, and a smaller stirrups width is expected to avoid splitting and generate greater strain at ultimate. It can be concluded that the new type of CW-GFRP stirrups is an optimized form of FRP shear reinforcement to supersede conventional pultruded stirrups. Strut-and-tie models based on ACI 318-19 and CSA S806-14 were used to predict the shear strength and produced a safe but relatively accurate prediction. [ABSTRACT FROM AUTHOR]

Copyright of Guangdong Architecture Civil Engineering is the property of Guangdong Architecture Civil Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Architecture & Civil Engineering is the property of Chang'an Daxue Zazhishe and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The compressive capacity of the column is one of the key parameters in the design. The importance of such structural members and their performance under load conditions are very effective in the overall behavior of the structure, and its failure can lead to the collapse of the entire structure. Therefore, determining the capacity of columns is considered an important issue in structural problems. Thus, this article presents an applicable computational framework to predict the compression capacity of stirrups-confined concrete. A machine learning model based on neuro-fuzzy systems was considered to formulate the proposed model. For this purpose, some experimental datasets were gathered from the literature to tune the unknown parameters of the model and evaluate its accuracy. The target, the ratio of the ultimate axial capacity to bearing area, was predicted with consideration of the column properties, including the compressive strength of concrete, stirrups section area, dimension of the stirrups, and the column section. The results showed that the proposed framework could be used as an applicable technique to determine the compressive capacity of the stirrups-confined concrete columns. [ABSTRACT FROM AUTHOR]

This paper presents a new method for calculating the area of shear stirrups of steel-reinforced concrete frame joints based on inverse reliability theory. The method can calculate the shear stirrup area of steel-reinforced concrete frame joints by using inverse reliability analysis theory on the premise that the target reliability index and the randomness of structural parameters are given. The method is used to calculate the shear stirrup area of a steel-reinforced concrete frame joint, and the sensitivity of the parameters is analyzed. The rationality of the area of the shear stirrup is also discussed. The results show that the randomness of parameters has a great influence on the area of shear stirrups of steel-reinforced concrete frame joints. Ignoring the randomness of parameters will affect the shear safety of steel-reinforced concrete frame joints. [ABSTRACT FROM AUTHOR]

Steel fibres provide ductility to concrete structures. This, in turn, gives possibility to replace or reduce conventional reinforcement in structural elements. In this study, the focus is on structural walls and the fibres as potential replacements for horizontal reinforcement in areas where vertical rebars are needed. An experimental study was conducted, in which prismatic specimens with longitudinal rebars were subjected to centric loading. Ten samples with 12 specimens in each were tested. The parameters considered were: fibre content, concrete cover for the longitudinal bars, and presence of stirrups. Self-compacting concrete with 30 and 60 kg/m 3 steel fibres was used. Relative and normalised values of the test results were calculated; correlation and analysis of variance was used to estimate the effect of fibres. The results show that the fibres eliminated brittle collapse and spalling of concrete at failure. A strong negative correlation (−0.72 to −0.92) between amount of fibres and load-bearing capacity was found. On average, the reduction of the capacity was 8% to 16% if compared to the specimens with no fibres. However, a positive effect of the fibres on the ductility was observed. Specimens with 30 kg/m 3 fibres showed the same post-peak behaviour as specimens with minimum horizontal reinforcement required by Eurocode 2. The study suggests that combination of steel fibres and conventional rebars can lead to less qualitative compactness of the self-compacting concrete, which in turn may reduce load-bearing capacity and stiffness of the structure. Special attention on concrete cover and distance between rebars should be paid if self-compacting concrete structures with steel fibres are designed. [ABSTRACT FROM AUTHOR]

The aim of this study is to improve the shear behavior of reinforced concrete (RC) beams with stirrups by using highly ductile fiber-reinforced concrete (HDC), which is a fiber-reinforced cement-based composite material with tensile-strain-hardening properties. Twelve reinforced HDC (RHDC) beams and three RC beams with stirrups were tested under a concentrated load. The experimental parameters involved the shear span to effective depth ratio, stirrup ratio, and longitudinal reinforcement ratio. The results revealed that the mode of failure of RHDC beams, which exhibited better ductility than RC beams, included diagonal compression, shear compression, diagonal tension, and flexural shear failure. RHDC beams exhibited stable multiple crack propagation behavior and satisfactory integrity, thus showing that HDC effectively restricted the development of shear cracks and improved the damage resistance of beams. Compared with RC beams, the shear strength, displacement ductility factor, and deflection-clear span ratios corresponding to the peak load and ultimate deflection increased by up to 30.5%, 44.9%, 150.0%, and 148.0%, respectively. RHDC beams exhibited higher residual strength and deformation capacity than RC beams, thus indicating that HDC significantly improved the brittle shear failure mode. Specimens H-1 and H-2 exhibited the largest improvement in shear strength and displacement ductility factor, respectively, compared with RC beams. The shear strength of RHDC beams increased as the shear span to effective depth ratio decreased. For RHDC beams with the same shear span to effective depth ratio, the shear strength increased with the increase in the longitudinal reinforcement ratio and stirrup ratio under shear compression failure. [ABSTRACT FROM AUTHOR]

This research discusses the performance of engineered cementitious composite (ECC) beams with and without transverse reinforcements using thorough analytical and finite element (FE) approaches under shear. The overall goal of this investigation was to assess the impact of various design characteristics, such as (i) shear span-to-effective depth ratio, (ii) transverse reinforcement ratio, etc., on the shear behavior of ECC beams. Nonlinear three-dimensional (3-D) FE analysis was performed with the commercial software ABAQUS to simulate the shear performance of ECC beams by employing the material properties obtained from the damage plasticity model. The correctness of the proposed FE model was validated with the benchmark experiments available in the literature. The developed FE model accurately computed the ECC beam's overall load–deflection behavior and failure modes. In addition, the provision available in the Architectural Institute of Japan (AIJ) A-method was successfully employed to assess the shear load-carrying capacity of ECC beams. Furthermore, the effects of transverse reinforcement (pw) and shear span-to-depth ratio (a/d) on the behavior of ECC beams were also investigated. From a detailed parametric study, it was understood that a decreased a/d ratio exhibits enhanced load-carrying capacity for beams with and without stirrups for a particular cross-section. It was also observed that for the entire a/d ratio, the amount of stirrups had no substantial effect on the load-carrying capability of ECC beams. [ABSTRACT FROM AUTHOR]

Under earthquake load, as the inelastic deformation increases, the shear strength of reinforced concrete coupling beams is degraded by diagonal cracking. In the present study, for the performance- based design of short coupling beams (l/h ≤ 2.5), a shear strength degradation model based on diagonal strut and truss mechanisms was developed, addressing the effects of the target chord rotation, longitudinal reinforcing bar ratio, length-to-height ratio, ratio and details of transverse reinforcement, distributed longitudinal web bars, and diagonal bars. Based on the proposed method, a simplified moment-rotation relationship of plastic hinges was developed for the nonlinear numerical analysis of coupling beams. For verification, the proposed method was applied to existing coupling beam specimens with a conventional reinforcing bar layout, distributed longitudinal web bars, and/or diagonal reinforcement. The predicted moment-rotation relationships generally agreed with the test results. Thus, the proposed plastic hinge model is applicable to the nonlinear analysis of short coupling beams to describe the shear strength degradation after flexural yielding. Design recommendations for the practical application of the proposed method were discussed. The proposed model revealed that the use of distributed longitudinal reinforcement and diagonal reinforcement is effective for high ductility. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Three-point bending tests were carried out on nineteen Reinforced Concrete (RC) beams strengthened with FRP in the form of completely wrapping. The strip width to spacing ratios, FRP type, shear span to effective depth ratios, the number of FRP layers in shear, and the effect of stirrups spacing were the parameters investigated in the experimental study. The FRP contribution to strength on beams having the same strip width to spacing ratios could be affected by the shear span to effective depth ratios and stirrups spacing. The FRP contributions to strength were less on beams with stirrups in comparison to the tested beams without stirrups. Strengthening RC beams using FRP could change the failure modes of the beams compared to the reference beam. In addition to the experimental study, a number of equations used to predict the FRP contribution to the shear strength of the strengthened RC beams were assessed by using a limited number of beams available in the literature. The effective FRP strain is predicted by using test results, and this prediction is used to calculate the FRP contribution to shear strength in ACI 440.2R (2017) equation. Based on the statistical values of the data, the proposed equation has the lowest coefficient of variation (COV) value than the other equations. [ABSTRACT FROM AUTHOR]

A numerical investigation is presented in this study to describe the effect of inclined stirrups on the shear behavior for reinforced concrete deep beams. This study was exceeded by two steps as a part of verification and parametric study. In the first step, three beams were analyzed with different arrangements of their stirrups. Two beams are reinforced with vertical and inclined stirrups when there are no stirrups in the third beam. The numerically load-deflection curves, cracking patterns, and load-maximum crack opening curves were presented for all analyzed beams. These numerical results were verified by the experimental study of Teng, Ma [1] showing an excellent agreement between them. In second step, another 16 beams within 4 groups were analyzed to show the parametric influence of using inclined stirrups. This parametric study presented the effect of main reinforcement ratio, shear span-to-depth ratio, space between stirrups, and bar cross-sectional are of stirrups on the deep beams reinforced with vertical and inclined stirrups. The deep beam reinforced with inclined stirrups leads to a significant increasing in the shear strength due to the contribution of these stirrups to restrict the opening of diagonal shear crack. [ABSTRACT FROM AUTHOR]

This research work presents experimental and numerical findings of continuous rectangular spiral shear reinforcement of beam-column connections subjected to seismic type loading. A total of four exterior beam-column subassemblies with continuous, spirally bound, rectangular reinforcements and conventional stirrups as closed manner control specimens were considered. For the spirally strengthened specimens, three different stirrups angle inclines (75°, 80°, 85°) were adopted, and their performances were compared in terms of hysteresis pattern, failure behavior, skeleton curve, stiffness degradation, and energy dissipation. Specimens with stirrups inclination angles of 75°, 80°, and 85° exhibited 14%, 28%, and 19% improvements in terms of load-carrying capability over the referred specimen, respectively. In addition to that, a numerical investigation was also carried out using ATENA version 5.3.4 finite element software to validate the experimental result. The developed numerical model shows good correlation with the experimental result and can be used in the design of spiral-strengthened reinforced concrete (RC) members. [ABSTRACT FROM AUTHOR]

Corrosion of longitudinal reinforcement and stirrup in reinforced and prestressed concrete beams is very common for structures and infrastructures, which is one of the main reasons for the decrease in stiffness and durability of structure. In order to evaluate the influence of corrosion of different types of stirrups on the bearing capacity of the prestressed concrete beam, the method of using electricity to accelerate corrosion was adopted. Load experiment on 4 corroded prestressed concrete beams with different corrosion rates and different stirrup types was carried out. In this paper, reduced scale model beams were designed based on the 5 × 50 m simple-continuous box girder of the Donghai Bridge. The results show that for prestressed concrete beams with different corrosion rates and stirrup types, the load-deflection curve can be divided into an elastic stage and a plastic stage. The corrosion of longitudinal bars and stirrups will reduce the flexural capacity, but the overall decline is not obvious. When the corrosion rate is 10%, the bearing capacity of the ordinary stirrup specimen decreases by 6.1%; epoxy-coated stirrup specimen decreases by 4.9%; stainless stirrup specimen has nearly no change. The influence of different types of stirrups on cracking load, deflection, and bond-slip behavior is discussed. [ABSTRACT FROM AUTHOR]

Under the background of climate change, the steel industry is considered one of the least eco-friendly industries. Flax fiber-reinforced polymer (FFRP) is an emerging sustainable alternative to steel reinforcement bar; however, its application is much restricted due to its interior material properties. This paper proposed a novel way to form closed-shape stirrups with FFRP, which is suitable for replacing steel stirrups. A multi-disciplinary investigation was conducted concerning the structural and environmental performance of FFRP stirrups in reinforced concrete (RC) beams. Seven specimens were tested under a three-point bending load. The FFRP stirrups substantially increased the shear capacity and ultimate vertical displacement by 77% and 74%, respectively, and shifted brittle failure to ductile failure. The closed-shape stirrups avoided the stress concentration and increased the utilization of FFRP tensile capacity to over 80%. Decreasing the spacing of FFRP stirrups effectively increased the shear capacity and ductility; increasing the width or layer of FFRP stirrups improved ductility only. A life cycle assessment (LCA) was later performed to evaluate and compare the environmental performance of steel, FFRP, and carbon FRP stirrups. As compared to carbon FRP and steel ones, FFRP stirrups substantially decreased the global warming and fossil depletion potential by over 60%. The main contributors to the environmental impacts of FFRP stirrups were the heavy metal released into the water and terrestrial environment during the cultivation process. [ABSTRACT FROM AUTHOR]

In this paper, a modified three-dimensional element is introduced for limit analysis of RC structures, which considers more aspects of structural behaviour. Using the introduced element, the influence of stirrup confinement on the shear and moment resistance of RC beams is evaluated by lower bound limit analysis. To analyse and solve the relevant optimization problem, the semidefinite programming method, SDP, is employed. The modified Mohr–Coulomb yield criterion is utilized to constrain the concrete stress state. Beams with a constant amount of shear reinforcement per unit length, with different values of stirrup spacing, are studied. It means that they only differed in the effect of confinement induced by stirrup reinforcements. The performance of the proposed element is verified by comparing the results of numerical limit analyses with experimental results. This comparison revealed the efficiency and accuracy of the proposed model and the capability of the introduced element to take the effect of stirrup-induced confinements into account. After modelling and investigating the effect of stirrup confinement in load bearing of RC beams, a simplified equation for the design and practical purposes is proposed. Using this equation, the shear resistance of the beams could be modified for different stirrup space choices. The results obtained from this simplified equation are compared with numerical limit analysis and experimental results. The comparisons indicate the reasonable accuracy of the proposed equation. [ABSTRACT FROM AUTHOR]

Attributed to its extraordinary strength and durability, the future of reinforcing and prestressing material in reinforced cement concrete (RCC) structures most likely belongs to carbon fiber reinforced polymer (CFRP). However, CFRPs are rarely employed in real structures till now, since the technology to manufacture CFRP rebars and stirrups is still evolving. This is especially applicable for manufacturing of rebars with surface profiles (ribs) and bent sections for stirrups. Unlike thermoset polymers, thermoplastic polymers are highly viscous prior to curing and can be melted and cured again. This creates possibilities for the production technology as well as recyclability. In this paper, new thermoplastic CFRP rebars and stirrups are introduced, which are manufactured in a novel way. The rips are engraved directly after pultrusion and the stirrups are thermoformed out of a straight and already profiled bar. A holistic approach is applied, which enables to evaluate the mechanical overall performance and to compare it with existing products in a reasonable way. This requires the introduction of new parameters, for example the fiber utilization rate. The novel CFRP reinforcement is investigated through tensile tests on bars and stirrups as well as bond tests. The bond performance is quite similar to existing products. Especially while considering how efficient the fibers are utilized in the CFRP bar, the tensile performance and the quality of the stirrups is excellent. [ABSTRACT FROM AUTHOR]

Wide beams are commonly used in reinforced concrete (RC) structures for architectural considerations such as facilitating the placement of services and providing adequate clear height. However, behaviour of these beams is not as efficient as normal width beams due to the small structural depth. Motivated by the lack of guidelines for wide RC beams with spiral reinforcement, this paper investigates their shear behaviour using innovative lateral reinforcement configurations. A comprehensive experimental program was conducted by testing nine beams under four-point loading. The effect of different parameters on the behaviour of such beams was investigated. These parameters included number, dimensions, and configurations of spirals. The experimental program also included testing of 18 standard cylinders spirally reinforced under compression to study the performance of confined concrete in the compression zone of wide beams. The results showed that the spiral lateral reinforcement is an efficient alternative for traditional closed stirrups for shear resistance in wide beams. Compared to regular closed stirrups, using spiral reinforcement or inclined links with regular closed stirrups can greatly improve the shear capacity and deformation. Also, reduction in the amount of lateral reinforcement can be achieved if the proposed lateral reinforcement is adopted instead of traditional stirrups. Based on the test results and the ACI 318–19 code, an equation is proposed and validated to estimate the shear strength of wide beams with regular/spiral lateral reinforcement. [ABSTRACT FROM AUTHOR]

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In order to improve the fragile nature of concrete, and its low tensile strength, and with a view to giving it the desired properties, which serve to build more durable structures at less cost, the association of a self-consolidating concrete with fiber, is considered a wise combination. However, given the limited amount of research on the response of SFSCC structures, designers and engineers do not use this material with confidence. In the present work, an experimental companion was conducted, in the interest of examining, the combined effect of fibers and stirrups include low and high rate of steel fiber, on the behavior of SFSCC beams. This choice allowed working on economically viable SFSCC. Beams were made also with ordinary concrete and others with self-consolidating. Thirty-six beams were of identical cross-section 10x20cm and length of 120cm; carried out with or without longitudinal and transverse reinforcement. Before proceeding with the main part of the research program, the concrete mixtures were characterized first in the fresh state by the following tests: Slump Flow, Time Flow T500; J-Ring, L-Box, V-Funnel and Sieve stability, and then in the hardened state: compressive and tensile strengths. In the light of the results obtained, it was found that adding steel fibers to fresh self-consolidating concrete decreased its workability and fluidity, but improved its hardening properties. Subsequently, the addition of the steel fibers increased the flexural capacity of the beams significantly, and improved their ductility. Also, an addition of the steel fibers in an adequate percentage, in this case at 0.9%, made it possible to replace the shear reinforcements, and can lead to changing the mode of failure from a collapse by brittle shear, to a mechanism of ruin in ductile bending.

This paper presents an experimental study and nonlinear finite element analysis (NLFEA) using the FE ANSYS© code modelling the composite effect of stirrups and steel fibres on the shear behaviour of reinforcedconcrete beams. To achieve this objective, fifty-eight (58) steel-fibre-reinforced concrete (SFRC) beams made of normal-strength concrete (NSC) and high-strength concrete (HSC) with and without stirrups were tested under bending and subjected to two concentrated and symmetrical loads using digital image correlation (DIC). The main test variables were concrete compressive strength (C30 and C60 MPa), stirrup aspect ratio (0 % and 0.56 %), steel fibre volume fraction (0 %, 0.5 %, 1 %, 2 % and 3 %) and steel fibre aspect ratio (l f /d f of 65 and 80). The experimental results show that the shear capacity of SFRC beams increases significantly as the percentage of steel fibres increases. The combination of stirrups and steel fibres can change the failure mode of the beams from brittle by shear to ductile by bending. The shear behaviour of SFRC beams without stirrups is similar to, and sometimes better than, that of SFRC beams with stirrups, suggesting the possibility of replacing stirrups with steel fibres in sufficient quantities. The measured shear strength is compared with the theoretical values obtained from the models available in the literature, and the correlation is satisfactory. Acceptable agreement was also found between the experimental and NLFEA results for the first diagonal crack load and ultimate load. The predicted FE values for the steel-fibre orientation factor of 0.45 are in agreement with the experimental values. • The addition of steel fibres does not improve the compressive strength of high strength concrete (HSC), but it does improve the ductility of this material. • The failure mode of HSC changes from sudden and explosive to ductile behaviour. • The addition of steel fibres improves the tensile strength of normal strength concrete (NSC) and HSC, especially when the steel fibres have a higher aspect ratio. The improvement in this mechanical property is not proportional to the volume fraction of steel fibres added. • The failure mode of the tested beams changes from shear to flexion in the series of beams with stirrups and with steel fibres, and in the series of beams without stirrups and with sufficient amounts of steel fibres (ρ f > 1 %), and the ultimate load is improved. • The shear behaviour of the steel fibres reinforced concrete (SFRC) beams without stirrups is similar to that of SFRC with stirrups, and sometimes better, when the steel fibres are used in higher quantities (ρ f > 1 %), which shows that the replacement of stirrups by steel fibres in the RC beams does not have a negative effect on the shear behaviour. • The experimental results for the ultimate shear strength of the fibres reinforced HSC beams without stirrups (FHB-S0) are similar to the theoretical values predicted by the different models used to estimate the contribution of the concrete and the steel fibres to the shear capacity of the beams. • The contribution of the stirrups is overestimated by the model proposed in Eq. (6) because it is based on the yielding of the stirrups, which is not observed in the failure of the tested beams. • The numerical FEA presented in this study is able to reproduce the flexural response of the RC beams (with or without stirrups) observed experimentally, with all types of concrete, with an acceptable degree of accuracy. It is also found that the numerical models based on the FEA approach produce higher values than the experimental models. Furthermore, when the value of the steel fibre orientation factor is 0.45, close agreement is obtained between the measured experimental data and the FEA prediction of the first diagonal crack load and ultimate load results. [ABSTRACT FROM AUTHOR]

The article discusses the relevance of developing techniques for confined elements with FRP reinforcement. The method for calculating centrally confined concrete columns with non-metallic GFRP reinforcement (without regard to its compression work) is proposed for the first time in the Russian Federation. The strength model was developed based on the well-known theoretical model of confined concrete. The article considers the effect of strengthening the concrete core of the columns, which is obtained due to the more frequent placement of both transverse and longitudinal reinforcement. The dependence of the bearing capacity of concrete columns on the strength of the transverse reinforcement material is shown. It was proved that with a decrease in the spacing of the longitudinal reinforcement, the area of ​​the effectively confined concrete core inside the reinforcement cage increases. It was shown that, due to the low compressive modulus of elasticity of the FRP reinforcement, the stress in it will be comparable to the concrete stress. Therefore, the compressive strength of the FRP reinforcement can be neglected in the case of determining the bearing capacity of centrally confined concrete elements. As a result, a strength model for calculating confined concrete elements with FRP reinforcement was proposed, considering the spacing of transverse reinforcement, the longitudinal and transverse reinforcement ratio, and the strength of the material of transverse reinforcement. The developed strength model can be applied not only for square, but also for columns of round and rectangular sections.

This paper investigates the shear performance of HDC beams reinforced with stirrups. The use of HDC led to limited crack propagation, multiple micro diagonal cracks between the load and support points, and ductile shear failure mode with significant nonlinear response, compared to reference specimens. The contribution of longitudinal reinforcement for shear strength of HCD specimens were larger than RC specimens. An average increment in shear strength of about 19% and a maximum value up to 40% was obtained. A modified formula for evaluating the shear capacity of HDC beam was proposed, and assessed with experimental results.

Despite the existence of numerous code requirements and heuristic equations concerning the shear capacity of slender beams reinforced with steel fiber without stirrup, engineers specializing in structural retrofitting and analysis frequently encounter difficulties in identifying a suitable equation. This paper presents a soft computing study designed to predict the shear capacity of slender steel fiber-reinforced concrete (SFRC) beams without stirrup. It introduces a novel equation based on the multivariable adaptive regression splines (MARS) method, supported by an extensive dataset comprising 488 experimental observations sourced from existing literature. Besides a series of existing equations proposed by researchers was introduced to assess the accuracy and capability of the MARS equation against other existing ones. The study rigorously compares the accuracy and capability of the proposed MARS equation with pre-existing equations, demonstrating its superiority and effectiveness in estimating the shear capacity of slender SFRC beams without stirrup, thus contributing significantly to the field of civil engineering. [ABSTRACT FROM AUTHOR]