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Previous studies have demonstrated that elevated temperatures exert a significant influence on the structural performance of reinforced concrete (RC) members. However, the residual shear performance of the RC beam under the combined effects of stirrup corrosion and fire has not been thoroughly explored. Therefore, this paper aims to investigate this aspect by prefabricating eight RC beams and employing experimental, numerical, and theoretical methods. The influence of varying stirrup corrosion degrees and fire exposure time on the residual shear capacity of these beams was examined. It was observed that corrosion-induced cracks had an impact on the distribution of the temperature field within the RC beams. Furthermore, the exposure to the corrosion–fire combination significantly affected the shear capacity of the RC beams. Notably, stirrup corrosion may lead to a more brittle failure after a fire. To assess the impact of corrosion degree and fire exposure time on the temperature field and residual shear properties of RC beams, a simplified finite element (FE) model considering the effect of concrete spalling was developed. The accuracy of this model was validated through a comparison with experimental results. Finally, three theoretical methods for predicting the residual shear capacity of postfire RC beams with corroded stirrups were proposed, based on Chinese, American, and European codes. A comparison between the calculated and test results revealed a good agreement. These methods can provide conservative predictions for practical engineering applications. [ABSTRACT FROM AUTHOR]

With the increasing utilization of reinforced concrete (RC) beams in eco‐friendly and fast‐paced construction practices, evaluating their impact performance becomes imperative. These beams are susceptible to unforeseen impact loads resulting from accidents or terrorist incidents throughout their service lifespan. Five groups of RC beams, each subjected to different curing periods, stirrup reinforcement, and drop hammer heights, were fabricated. Among these groups, one underwent static load testing, while the remaining groups were subjected to impact load testing utilizing the drop hammer test system. The failure modes, static response, dynamic response, and energy dissipation of RC beams were analyzed. Static tests revealed that RC beams exhibited a flexure‐governed failure mode with top surface concrete crushing, aligning with expectations. With increased stirrup reinforcement ratios, shear and flexural‐shear cracks during impact tests decreased, with high impact loads causing diagonal shear failure, severe concrete crushing, additional diagonal shear cracks, and a broader crack distribution. Higher drop hammer heights were found to increase overall energy dissipation, whereas increased stirrup reinforcement ratios resulted in moderate decrease. Specifically, the overall energy dissipation increased with higher drop hammer heights. Conversely, an increase in the stirrup reinforcement ratio was linked to a certain degree of decrease in overall energy dissipation. [ABSTRACT FROM AUTHOR]

To better understand how a flat slab responds to a punching effect with varying effective parameters, an experimental and numerical program was carried out in this study. The studied parameters included the flexural reinforcement (RFT) ratios, whether in tension or in compression, the concrete compressive strength (f cu) and using of stirrups. For this purpose, eighteen R.C flat slab were casted and tested in the R.C laboratory at Cairo University. All slabs had the same dimensions of (1100 ×1100) mm and the slabs thickness is 120 mm with a square column dimension equal to (150 ×150) mm at the center of slabs. The ratios of flexural RFT in tension and compression sides were (1.27, 1.76, and 2.25) % and (0.48, 0.75 and 1.09) % respectively. The tested slabs were casted with f cu (35 and 45) MPa. All the previous mentioned parameters were investigated in the presence and absence of stirrups. First cracking load, ultimate load capacity, crack pattern, load-deflection relationship, stiffness, energy absorption and RFT strain were analyzed and discussed to show the parameters' effects on all studied slabs. The results revealed that flexural tension RFT had a noticeable effect on the punching shear behavior compared to the compression one; which had a slight effect. Non-linear finite element 3-D models were verified with the experimental results and parametric study was conducted. Finally, the experimental results were compared and verified against different building design codes of practice (ACI 318, Eurocode 2 and ECP 203). The used codes were capable of estimating the shear capacity; but with conservative values. Eurocode 2 gave better prediction as it takes the flexural tension RFT into consideration. New equations were proposed to predict the punching shear strength considering flexural tension RFT ratio in case of presence and absence of stirrups. [ABSTRACT FROM AUTHOR]

To address the issue of easy shearing damage of Carbon Fiber Reinforced Polymer (CFRP) in enhancing the axial compressive performance of CFRP and Ultra‐High‐Performance Concrete (UHPC) strengthened concrete columns, two methods, prestressed CFRP and UHPC with spiral stirrups, were employed for composite strengthening of reinforced concrete (RC) columns. A total of one unstrengthened column and eight strengthened columns were designed and fabricated to validate the effectiveness of the proposed methods. The axial compressive performance and bearing capacity of each specimen were analyzed by considering parameters such as single or composite strengthening method, presence of spiral stirrups in UHPC, and application of pre‐stressed CFRP. The results show that, compared with any single strengthened specimen, the ultimate bearing capacity of the composite strengthened specimen is greater than the sum of the corresponding single strengthened specimens, and the bearing capacity of the prestressed CFRP with spiral stirrup UHPC composite strengthened specimen is the most significant, reaching 235.63%. By incorporating spiral stirrups in the UHPC jacket, the phenomenon of uneven fragmentation during the failure of the strengthened column is improved. This helps prevent premature shearing damage of CFRP and enhances the fracture strain and effective utilization of CFRP. Additionally, prestressed CFRP effectively restrains the lateral deformation and crack development of the core concrete in the UHPC jacket, fully utilizing the high compressive strength of UHPC. This further enhances the ultimate bearing capacity and ductility of the specimens. Based on the experimental phenomena and strain of each material, the failure mechanism of prestressed CFRP‐spiral reinforced UHPC composite‐strengthened columns is proposed. Finally, a unified bearing capacity calculation formula for single and composite strengthened columns is established, based on the theory of confined concrete strength and the assumption of strength increment superposition. The formula is validated with experimental results from relevant literature, showing small errors in the calculated results and indicating good applicability of the formula. [ABSTRACT FROM AUTHOR]

In this paper, steel–polyethylene hybrid fiber-reinforced strain-hardening cementitious composites (HECC) are applied in beam–column external joint core region to form a novel HECC/reinforced concrete (RC) composite beam–column joint with reduced anchorage length of beam longitudinal rebar and eliminated transverse rebar, and thus to alleviate rebar congestion and simplify the construction process efficiently especially for precast RC frame structures. Five external beam–column joint specimens are constructed and tested under cyclic loading to illustrate the influences of the anchorage length of beam longitudinal rebar and longitudinal rebar ratio on the seismic performance of beam–column joint. The effects of design parameters on seismic performance, including hysteresis behavior, degradation of strength, energy dissipation capacity, and cracking patterns are discussed in detail. Experimental results indicate that the replacement of normal concrete with HECC in beam–column joint core region could apparently reduce the amount of stirrups in the joint core area while maintaining reliable seismic behavior. Remarkably, specimen with no stirrups in the core area exhibits nearly equivalent seismic behavior to that of the control RC specimen. Furthermore, the application of HECC in joint core area allows for a substantial reduction of the required anchorage length for the beam longitudinal rebar to 9d, which further simplifies the construction process considerably. [ABSTRACT FROM AUTHOR]

To better understand how a flat slab responds to a punching effect with varying effective parameters, an experimental and numerical program was carried out in this study. The studied parameters included the flexural reinforcement (RFT) ratios, whether in tension or in compression, the concrete compressive strength (fcu) and using of stirrups. For this purpose, eighteen R.C flat slab were casted and tested in the R.C laboratory at Cairo University. All slabs had the same dimensions of (1100 ×1100) mm and the slabs thickness is 120 mm with a square column dimension equal to (150 ×150) mm at the center of slabs. The ratios of flexural RFT in tension and compression sides were (1.27, 1.76, and 2.25) % and (0.48, 0.75 and 1.09) % respectively. The tested slabs were casted with fcu (35 and 45) MPa. All the previous mentioned parameters were investigated in the presence and absence of stirrups. First cracking load, ultimate load capacity, crack pattern, load-deflection relationship, stiffness, energy absorption and RFT strain were analyzed and discussed to show the parameters’ effects on all studied slabs. The results revealed that flexural tension RFT had a noticeable effect on the punching shear behavior compared to the compression one; which had a slight effect. Non-linear finite element 3-D models were verified with the experimental results and parametric study was conducted. Finally, the experimental results were compared and verified against different building design codes of practice (ACI 318, Eurocode 2 and ECP 203). The used codes were capable of estimating the shear capacity; but with conservative values. Eurocode 2 gave better prediction as it takes the flexural tension RFT into consideration. New equations were proposed to predict the punching shear strength considering flexural tension RFT ratio in case of presence and absence of stirrups.

This paper presents the proposed indeterminate strut and tie (IST) method to analyze fiber-reinforced polymer (FRP)-reinforced concrete deep beams with stirrups. The solution of the IST method does not require the assumption of reinforcement yielding and is capable of reflecting the material nonlinearity of concrete. The essential features of the IST methodology for glass FRP-reinforced deep beams are discussed and then analyzed in detail. These features include modeling concrete compressive response, softening concrete compression behavior in struts, and obtaining the depth of compression nodes. For each of these features, several approaches are discussed. The proposed IST methodology is validated by comparing the analysis results with the experimental results, and recommendations for the most suitable modeling methods are proposed. [ABSTRACT FROM AUTHOR]

In this paper, three concrete‐filled L‐shaped steel tube (CFLST) stub columns subjected to axial compression were tested, with one normal CFLST stub column and two stirrup‐confined specimens. The investigation focused on the effect of the equivalent stirrup ratio on ultimate bearing capacity, axial compression stiffness, ductility factor, and strain ratio of the columns. 3D finite element (FE) models of the specimens were constructed and verified against the tests results and data from literature Parametric analysis was carried out to analyze the influence of different section length–width ratios, steel ratios, material strength grades, and equivalent stirrup ratios on the ultimate bearing capacity. Additionally, the confinement effect of stirrups on the core concrete was analyzed. By generalizing the stress nephogram of the core concrete at the ultimate state and considering the equilibrium of forces, a formula was proposed for calculating the ultimate bearing capacity of the stirrup‐confined CFLST stub column under axial compression using the superposition method. The accuracy of the proposed formula was demonstrated by comparing its results with experimental results, FE model results, and those proposed by other scholars. [ABSTRACT FROM AUTHOR]

Many researchers have studied how modifying conventional shear reinforcement into spiral and truss systems improves the behavior of RC beams. However, there is a scarcity of studies investigating the influence of spiral reinforcement, and limited research is available on the flexural capacity of beams utilizing truss reinforcement systems. Additionally, recent designs focused only on the rectangular spiral and rectangular truss systems, underscoring the necessity of incorporating a new design of modifications in the stirrup configurations. These gaps must be addressed to identify the most effective design for achieving the desired flexural capacities. As a result, the present study conducts a simulation and experimentation on RC beams utilizing modified stirrups through the Abaqus software to describe the load-deflection relationship, determine the flexural capacity and ductility, and analyze the failure mode and crack patterns. The present study simulated seventeen finite element models, including one control beam as BN and four various designs that used rectangular spiral (BR-S), rectangular truss system (BT-R), and a new modification, namely vertical X-shaped stirrups (BV-X), and X-shaped truss system (BT-X) with four spacings of 150mm, 125mm, 100mm, and 75mm. The findings reveal that the most effective enhancement in RC beam behavior was observed within the BT-R group, particularly with BT-R 100, which demonstrated a remarkable 6.551% increase in flexural capacity compared to BN. Moreover, stirrup spacing and inclination considerably impact the beam's performance, depending on the various modifications of stirrups in RC beams. Furthermore, uniform failure modes have been observed across all models and specimens, including BN, demonstrating that modified stirrups improve RC beam performance. The present study compared and verified the finite element simulation results through an actual experiment from BN and BT-R 150 models and specimens. [ABSTRACT FROM AUTHOR]

Two types of hoop layouts, double-perimeter hoops (DPH) and continuous-stirrup hoops (CSH), were examined in this research for beams of special moment frames. Compared to conventional hoops (CH), the DPH and CSH have the advantage of better constructability. Full-scale beam specimens--specimen CH as a control specimen and specimens DPH and CSH as test specimens--were tested using lateral cyclic loading to examine their seismic performance. Test results showed that although specimen DPH violated the Code requirement for the number and spacing of laterally supported longitudinal bars, the specimen still exhibited seismic performance sufficient for beams of special moment frames. Specimen CSH showed better seismic performance than the control specimen (CH). The better performance of CSH was mainly attributed to the better concrete confinement and reinforcing bar buckling restraint ability of the intermediate hoops of the CSH than the intermediate stirrups of the CH. [ABSTRACT FROM AUTHOR]

The reinforced concrete corbel is widely used in assembled concrete structures as a convenient cantilever support member. In this paper, eight double-corbel specimens with the same design load capacity were obtained according to the strut-and-tie method (STM) in ACI 318-19. Corbels with different dimensional parameters were produced by varying the concrete compressive strength or shear span separately. The differences in actual bearing capacity and mechanical performance among the corbels were then compared to assess the accuracy and safety of the STM under the two variables. In addition, as the horizontal stirrups are not taken into consideration in the nominal design capacity of the STM, three non-stirrup corbel specimens were designed to investigate the effect of stirrups on the load-bearing capacity under different shear spandepth ratios. The results show that changing the concrete strength or shear span significantly affects the actual bearing capacity of the corbels, despite the design load capacity remaining constant. Increased compressive strength of the concrete or decreased shear span at the design stage results in a higher level of safety for the STM. The larger the shear span-depth ratio, the greater the strengthening effect of the stirrups on the corbels' bearing capacity. [ABSTRACT FROM AUTHOR]

The behavior of steel fiber reinforced concrete (SFRC) is highly dependent on mix design, where the properties of its components, such as cementitious matrix and fibers, impact the physical and mechanical properties of the composite. Incorporating steel fibers into concrete modifies its physical properties, potentially leading to fiber segregation and resulting in a nonuniform distribution of the fibers within the material. In experimental studies, an increase in fiber volume has been found to change the failure mode of SFRC beams from shear to flexure, and numerical investigations have shown that randomness in fiber distribution can significantly influence the behavior of the composite. Therefore, this study aims to develop a numerical model that considers variations in material properties to simulate the change in the failure mode of SFRC beams due to variations in fiber volume. The failure and yielding parameters were initially established and integrated into the concrete damaged plasticity (CDP). Subsequently, the response of both steel and concrete to tension or compression stresses was ascertained. Finally, the appropriate meshes and finite elements were chosen for the simulation. In the final approach, two methods were employed to introduce randomness into the beam. One divided the beam into different vertical segments: 30, 45, and 90, and the other combined vertical and horizontal segments: 30 vertical with 4 horizontal, 45 vertical with 5 horizontal, and 90 vertical with 10 horizontal. A script was developed in Python to automatically insert the properties. The numerical model successfully captured the change in failure mode from shear to flexure resulting from fiber volume increase. Vertical and horizontal segments increased toughness due to crack deviation, better predicting cracking pattern and loading capacity for the highest fiber contents. [ABSTRACT FROM AUTHOR]

Reinforced concrete slabs can be exposed to explosive and impact loads, prompting extensive research into their behavior under various static and dynamic loading conditions. Researchers have explored numerous techniques to enhance the structural integrity of these slabs when subjected to impact loads, but certain knowledge gaps persist. Particularly, the application of shear reinforcement, such as conventional stirrup shear reinforcement, to strengthen slabs against impact remains relatively uncommon. This study aimed to investigate the impact of conventional stirrup shear reinforcement on the dynamic response and failure modes of reinforced concrete slabs when subjected to low-velocity impact loading. The first phase involved experimental evaluation, focusing on the influence of vertical conventional stirrups as shear reinforcement in two-way, fully fixed RC slabs. Portable drop weight testing equipment was used to subject six (800 × 800 × 90 mm) RC slabs, to impact testing. Three slabs were strengthened with stirrups in two directions orthogonally configuration, while three control slabs received no additional reinforcement. Various parameters, including vertical displacement, strain at multiple points on the stirrups, main steel, and concrete, as well as acceleration at a specific point on the slab, were measured. Additionally, the failure modes were closely monitored. In the second phase, finite element models of the slab study samples were created using ABAQUS software. The numerical model results aligned with the experimental findings, indicating that the proposed finite element model can effectively assess the structural behavior of reinforced concrete slabs subjected to low-velocity impact loads. The third part of the research involved a parametric study to investigate the effects of bar diameter and drop position on the structural response of the slabs. The outcomes of this study highlight the significant positive impact of shear reinforcement, particularly in the form of conventional stirrups, on the load-bearing capacity of reinforced concrete slabs. Slabs with stirrups exhibited noteworthy improvements in strength, stiffness, and ductility compared to control specimens without shear reinforcement. Specifically, the presence of conventional vertical stirrup shear reinforcement increased the slab's capacity by 29.5% under the total impact energy until complete failure. [ABSTRACT FROM AUTHOR]

The shear behavior of basalt fiber–reinforced polymer-reinforced seawater–sea sand concrete (BFRP-SSC) beams was investigated experimentally. The effects of several factors, including stirrup diameters (8, 10, and 12 mm), stirrup spacings (100, 125, and 150 mm), and shear span-to-depth ratios (1.55, 1.95, and 2.35), were considered. The results demonstrated that the shear mechanism of the diagonal section of BFRP-SSC beams could be explained using the arch truss model. Moreover, the shear span-to-depth ratio significantly influences the shear capacity, bending stiffness, diagonal crack width, and shear failure mode of beams, with diagonal compression failure occurring in beams with a ratio of 1.55 and shear compression failure occurring in beams with a ratio between 1.95 and 2.35. In addition, the actual shear capacities of 72 BFRP-reinforced concrete (BFRP-RC) beams were compared to the results obtained by five design provisions. Correction coefficient of shear span-to-depth ratio, modification to stirrup spacing, correction equation of stirrup strain, and shear contribution coefficient of stirrups were proposed to modify the shear equation in ACI 440.1R-15. The results of the modified shear equation showed a good agreement with the actual shear capacities of beams. The findings of this research have theoretical significance for the design and practical application of BFRP-SSC beams in marine construction. [ABSTRACT FROM AUTHOR]

Scaled-down-reinforced concrete beams with rectangular staggered continuous spiral stirrups are experimentally investigated. Scale-down RC beams were considered in the current research due to ease of construction and economic feasibility. As the brittle shear failure should be avoided, continuous research trials have been conducted to find an effective technique to improve shear failure mechanism. Twenty-two beams were investigated for shear behavior under 4-point static push-over load considering the normal stirrups and compared with continuous staggered spiral ones. Stirrup spacing, shear arm ratio a/d, and shear reinforcement configurations are the main variables. All beams were designed and scaled down to be one-eighth of the full-scale beams. To minimize the size effect of using small-scale models, mortar was used instead of conventional concrete. The focus in this study was related to improved shear capacity, dissipated energy, and shear cracks propagation. It was found that using spiral reinforcement instead of normal one leads to a significant enhancement in shear capacity and dissipated energy by 33% and 45%, respectively. Therefore, the prototype RC model expected capacities were detailed calculated considering the scale-down factor used by authors. The experimental results were compared by calculated values according to international standard and specifications. [ABSTRACT FROM AUTHOR]

With the aim of studying the cracking behavior of anchorage zones of post‐tensioning tendons, an experimental research has been performed. The experimental program included eight prismatic specimens with 265 mm × 265 mm × 580 mm and 300 mm × 300 mm × 600 mm, reinforced with combinations of spirals and stirrups. The studied variables included the cross‐section dimensions and the amount of confining stirrups. In this study special anchorage devices were used in all specimens, which are commonly used in everyday practice. To be able to fulfill the loading protocol, concrete strains were measured. These values were also used to study the cracking loads and crack widths, and to assess the influence of the different studied variables, as well as the failure loads. Models from the literature were used to estimate the expected values for cracking loads. These values were compared with the experimental ones to verify their adequacy for the tested specimens. From the experimental tests, it can be concluded that the increase of the stirrup diameter leads to lower cracking loads. The increase of the cross‐section dimensions results in an increase in the cracking load. Available theories for estimating the cracking load do not provide satisfactory predictions of the expected cracking load. [ABSTRACT FROM AUTHOR]

In this paper, the shear behavior of concrete beams reinforced with FRP stirrups is studied. The shear performances of six concrete beams with a size of 150 mm × 300 mm × 3000 mm under four-point loading up to failure were experimentally analyzed. The critical parameters included the shear span to depth ratio (λ) and stirrup spacing (S). The test results revealed that as λ increased from 1 to 2, 3, and 4, the ultimate shear capacity of the beam decreases by 50.5%, 67.7%, and 69.2%, respectively. Meanwhile, as S increased from 100 mm to 150 mm and 200 mm, the ultimate shear capacity decreased by 16.1% and 44.6%, respectively. A new shear capacity calculation model of concrete beam reinforced with FRP stirrups was also proposed, which further considered the shear capacity of the FRP stirrups on the basis of the shear capacity of an RC beam without stirrups using the strut-and-tie model. Finally, the experiment and calculation results of 56 beam specimens reinforced with FRP stirrups extracted from this paper and previous studies were compared using the calculation models proposed in this paper, in order to evaluate the accuracy of these calculation models. [ABSTRACT FROM AUTHOR]

This study investigates the impact of varying glass fiber-reinforced polymer (GFRP) stirrup spacing on the performance of doubly GFRP-reinforced concrete beams. The research focuses on assessing the behavior of GFRP-reinforced concrete beams, including load-carrying capacity, cracking, and deformability. It explores the feasibility and effectiveness of GFRP bars as an alternative to traditional steel reinforcement in concrete structures. Six concrete beams with a cross-section of 300 mm (wide) × 250 mm (deep), simply supported on a 2100 mm span, were tested. The beams underwent four-point bending with two concentrated loads applied symmetrically at one-third of the span length, resulting in a shear span (a)- to-depth (h) ratio of 2.8. The experimental findings reveal that altering the GFRP stirrup spacing along the longitudinal axis of the beams, from 200 mm (equivalent to the effective depth (d)) to 50 mm (equal to (d⁄4)), altered the mode of failure from flexure-shear to flexure-compression. However, when the spacing was equal to or less than (d⁄3), there was no significant improvement in load-carrying capacity, as the contribution of GFRP bars in resisting shear loads was limited. Under service loads, the GFRP-reinforced beams exhibited wider cracks, but reducing the stirrup spacing helped restrain crack widening. Incorporating GFRP bars in the compression zone had a positive effect on reducing crack width in the tension zone. Additionally, using GFRP stirrups with spacing varying between (d) and (d⁄2) in the pure bending region increased the deflection ductility indexes. To enhance the ductility of GFRP-reinforced concrete beams, it is recommended to use GFRP stirrups in the pure bending region with spacing greater than the spacing between GFRP stirrups in the shear spans. The study highlights that the current ACI code overestimates the shear capacity provided by GFRP stirrups, particularly when the spacing is less than or equal to (d⁄3). [ABSTRACT FROM AUTHOR]

Using carbon fiber-reinforced composite (CFRP) grid stirrups to replace traditional steel stirrups in reinforced concrete (RC) beams can effectively improve the corrosion resistance of structures in marine environments. In this study, the durability of RC beams with CFRP grid stirrups under the coupled effects of sustained loads and immersion in seawater was studied. The sustained loads were set at 24% and 48% of the ultimate bearing capacity of the RC beam, and the specimens were immersed in artificial seawater at room temperature for 90 days, 180 days, and 360 days, respectively. The crack load and shear capacity of the beam were measured at the scheduled time. The initial stiffness of the beam decreased as the immersion time increased, and the higher the sustained load was, the lower the initial stiffness of the conditioned beam. The contribution of the CFRP grid stirrup to the shear load capacity after the cracking load was reached was more significant than that before. The effects of the 48% sustained load on the ultimate tensile strain of the CFRP stirrup were more significant than those for the 24% sustained load. Both immersion and sustained loading improved the cracking load and shear capacity of the beam, and the contribution of sustained loading to the shear capacity decreased as the immersion time and the sustained load level increased. Equations were proposed for predicting the shear strength of RC beams with CFRP grid stirrups under sustained loading and seawater immersion. [ABSTRACT FROM AUTHOR]

Arch action in deep reinforced concrete (RC) members has a beneficial effect on shear capacity. The Strut-and-Tie Method (STM) is one of the proposed methods for the design of steel reinforced deep beams (DBs). However, some iterations may require to obtain the optimum solution. This paper investigates the shear capacity of fiber reinforced polymer (FRP)-reinforced DBs using STM and sectional methods of Canadian Standard Association (CSA) and American Concrete Institute (ACI) design provisions. To this end, 106 FRP-reinforced DBs were compiled from the literature. It has been found that current sectional methods do not adequately account for the effects of arch. action on DBs. From this investigation, modifications were proposed in the current sectional methods to calculate the shear capacity of FRP-reinforced DBs. The proposed modifications were found to significantly improve the prediction accuracy. The sectional methods proposed by CSA and ACI were found to be better than the CSA-STM method in predicting the shear capacity of FRP-reinforced DBs.. The mean, standard deviation and coefficient of variation for the proposed CSA sectional method are 1.00, 0.28 and 28.2% and for the proposed ACI sectional method are 1.01, 0.26 and 25.6, respectively. The same for the CSA-STM method are 2.20, 0.76 and 34.4%, respectively. The proposed methods can be used to predict the shear capacity of FRP reinforced deep members. [ABSTRACT FROM AUTHOR]

Analytical and computational calibrations and subsequent parametric analyses were performed on the four UHPFRC beams under flexure to estimate their actual shear strength. The computational models were calibrated using different values for the CDP parameters, and a finite element mesh sensitivity study was conducted. These models predicted the experimental behavior satisfactorily, and the analytical model was also able to find the beams' failure loads and proved to be a simple tool to estimate their behavior. The parametric analysis showed that the current beams did not require stirrups once the UHPFRC had high shear strength, and the maximum shear capacity was accurately determined. [ABSTRACT FROM AUTHOR]

Influence of transverse reinforcement on load bearing behaviour of reinforced concrete columns To ensure the integrity of an entire structure, reinforced concrete columns should still have a defined residual load‐bearing capacity or robustness after reaching their ultimate load. A robust post‐peak behaviour can be achieved e. g. by a suitable detailing. In this context, the influence of the stirrup locks is often underestimated and subordinated to practical construction concerns. In this paper, this aspect is investigated experimentally. Column tests demonstrate in detail that the design of stirrup locks has a significant influence on the post‐peak behaviour of reinforced concrete columns and that the regulations of EC2 and the recommendations of the commentary version do not sufficiently address this issue. [ABSTRACT FROM AUTHOR]

Punching shear resistance of flat slabs with combined reinforcement utilising steel fibres and stirrups To reinforce areas subject to punching shear, punching shear reinforcement systems such as stirrups or double‐headed anchors are commonly used. An alternative is to utilise steel fibre reinforced concrete (SFRC), which can achieve a similar increase in load‐bearing capacity as stirrups. In the current German codes, a combined utilisation of SFRC and punching shear reinforcement is excluded due to a lack of experimental data to validate a design approach. On the other hand, both Model Code 2010 and Annex L of the next generation of Eurocode 2 already contain design principles that consider steel fibres and punching shear reinforcement additively. However, the suitability in terms of reliability/safety and economic efficiency has not yet been sufficiently validated due to missing experimental results. In order to close the existing gap, a total of eight large‐scale punching shear tests with combined reinforcement (stirrups, steel fibres) were carried out by the Chair of Concrete and Masonry Structures at the Technical University of Munich (TUM) following initial positive findings from preliminary tests. This paper describes and discusses in detail the setup, testing procedure and main results and findings of these experimental investigations. [ABSTRACT FROM AUTHOR]

Present work contains a 3-D finite element (FE) model created in Abaqus to examine bond behavior in controlled/non-corroded reinforced concrete beams. Study evaluated the compatibility between corrosion levels and beam deflections. Cohesive surface-based interaction method is applied to the Data obtained from recent studies in which corrosion was induced by accelerated corrosion technique. The cohesive surface-based interaction approach has been found to be suitable for simulating the interfacial binding between reinforcement bars and the concrete. Analysis of Control and corroded beams along with mesh sensitivity were used for the validation of the work. It is found that maintaining uniform mesh size for steel and concrete is necessary as varying mesh size influences the load - deflection relation. The developed FE model of RC beam under corrosion could be adopted to obtain the load at failure with considerable accuracy. Hence, the model can be adopted to numerically simulate the influence of various parameters on response of corroded RC beams. This would avoid the expensive laboratorial tests. Study demonstrated that experimental and analytical research are in good agreement with considered level of corrosion and corresponding deflections. Rebar yield capacity of corroded RC beam in tension zone declined, resulting in a decrease in load-carrying capability. The modelling outcomes can be used to validate the bond behaviour of Reinforced concrete cantilever beams without considering the influence of stirrups. [ABSTRACT FROM AUTHOR]

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Steel rebars require significant energy to produce and are prone to corrosion when exposed to ambient air. Therefore, Iraqi bamboo replaces steel stirrups and steel rebars in this research. Five reinforced concrete beams are tested using four-point load testing. The first beam was cast without stirrups to achieve shear failure and is labeled a control specimen. Three other beams had Iraqi bamboo instead of steel at the critical sections. The last beam had steel stirrups spaced at a distance half of the effective depth of the beam. It is found that the Iraqi bamboo can increase the load-carrying capacity of the beam by up to 15% if compared with the beam with no stirrups. Also, the ductility of the beam has increased by 17%. However, the maximum load-carrying capacity of the steel stirrup beam was larger than that of the bamboo stirrups by at least 21%. The main reason is the spacing of the stirrups, which is the main factor influencing the beams' behavior prone to shear failure.

Push-off samples are simulated using nonlinear finite element analysis (NLFEA) to evaluate the effects of increased temperatures on the interface shear strength. Firstly, a control shear-key model is created, calibrated, and confirmed against independently published experimental data. Twenty-four NLFEA models are then created with different variables, including temperature (23°C (Room Temperature), 250°C (Raised temperature), 500°C, and 750°C and the number of steel stirrups (none, 1, 2, 3, 4, and 5). The NLFEA results demonstrate that the decreased fracture opening and slide in the damaged shear keys compared to the intact control sample represent the amazing effect of the number of steel stirrups. In addition, it has been revealed that the longitudinal shear force and slide, mode of failure, rigidity, and toughness are all significantly impacted by the degree of heat damage. In particular, a simplified approach is proposed for calculating the shear strength of push-off samples subjected to higher temperatures.

This study re-examines the origins of stirrups and related issues by reassessing two prevailing theories: the "leather toe loop theory" and the "toe stirrup theory." Through analysis of original archaeological material from the Scythian, Indian, and the Yunnan Dian cultures, along with new insights from fieldwork and examination of a variety of horse tack, this study points out that both outdated theories misinterpret the original material and present unreliable arguments. Consequently, it is unconvincing to claim that stirrups originated from either leather toe loops or toe stirrups. The improvement of saddle structure should not be ignored in an exploration of the origin of stirrups. The solid-tread saddle, which first appeared during the Wei and Jin periods, not only stimulated the invention of the stirrup but also provided necessary structural support for its use. [ABSTRACT FROM AUTHOR]

In this study, the clinical application and efficacy of three different methods for placing and repositioning patients in the lithotomy position over the bed using stirrups were evaluated.Methods: A total of 240 surgical patients who underwent surgery in Chongqing Traditional Chinese Medicine Hospital between July and November 2022 were selected as study participants. Using envelopes, they were randomly divided into three groups of 80 cases each using a randomization method. The groups included the traditional over-bed method, the postural trolley-assisted over-bed method, and the direct over-bed method. Using the Kruskal–Wallis rank-sum test, analysis of variance, and multiple linear regression equations, the placement time, over-bed repositioning time, and total time of the three methods for placing and repositioning in the lithotomy position supported by stirrups were analyzed statistically. In addition, we investigated and examined the satisfaction of nurses and doctors with the aforementioned techniques.Results: The placement time, repositioning time, and total time were significantly higher for the traditional over-bed method than for the postural trolley-assisted over-bed method and the direct over-bed method (both P < 0.01). However, there was no statistically significant difference between the postural trolley-assisted over-bed method and the direct over-bed method (P > 0.05). Nurses and doctors reported significantly higher satisfaction with the postural trolley-assisted over-bed method and the direct over-bed method compared to the traditional over-bed method (both P < 0.01). In addition, nurses were more satisfied with the direct over-bed method than the postural trolley-assisted over-bed method (P < 0.05).Conclusion: The results of this study demonstrate that the direct over-bed method is preferred for positioning and repositioning patients in the lithotomy position with the support of stirrups. [ABSTRACT FROM AUTHOR]

In this paper, a model to predict the residual shear capacity of RAC beams with corroded stirrups was established, and the simulation analysis was conducted on recycled concrete beams with different corrosion level using ANSYS. The reliability of the finite element analysis model was verified by comparing the finite element results with experimental results. [ABSTRACT FROM AUTHOR]

Based on the experimental results, this paper investigates the shear mechanism of reinforced concrete deep beams without stirrups. By analyzing the kinematics of the critical shear crack, it can be found that the compression of concrete above the critical shear crack causes the crack sliding and that the combined action of the elongation of longitudinal reinforcement and the compression of concrete above the critical shear crack causes the crack opening. Based on the new-found crack kinematics and test data, the aggregate interlock force is calculated by two methods. The dowel action is also calculated. The results reveal that the shear forces transmitted by the aggregate interlock and the dowel action are relatively small, ranging from 0.5% to 9.2%. The uncracked concrete in the compression zone provides the primary resistance. Both the aggregate interlock and the uncracked concrete in the compression zone can cause a size effect. But because of the small proportion of the aggregate interlock, the size effect of shear strength is mainly caused by the size effect of uncracked concrete in the compression zone. A modified strut-and-tie model (STM) is established based on the shear mechanism found in the test. It considers the size effect using the modified size effect law. The modified STM is evaluated by comparing the calculation results with the experimental results of 194 beams. It is shown that the prediction of the modified STM is more accurate than those of the other five models, with a mean value of Vu/Vu,cal of 1.01 and a coefficient of variation value of 0.22. The proposed model well captures the effect of the shear span-to-effective depth ratio and the size effect on the shear strength. The modified STM reflects the actual shear transfer mechanism of deep beams without stirrups and has the advantages of simple calculation and accurate prediction. [ABSTRACT FROM AUTHOR]

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The shear performance of recycled aggregates beams reinforced with basalt fiber-reinforced polymer (BFRP) bars is evaluated and compared with that of similar beams made with natural aggregates (NA). Six beams with a shear span-to-effective depth ratio (a/d) of 3.0 were tested to failure. Test variables consisted of the recycled concrete aggregate (RCA) replacement percentage (60 and 100%) and the presence of BFRP stirrups in the shear span. Experimental results showed that a RCA replacement of 60% marginally reduced (5%) the shear capacity. However, the reduction in the shear capacity was more pronounced (17%) for the specimen made with 100% RCA. The contribution of BFRP stirrups to the shear capacity decreased with an increase in the RCA replacement percentage. The width of the major shear crack at a given value of load was higher for the beams with RCA. The deflection values at the ultimate load were greater for beams made with RCA. A codified analytical approach as well as a model published in the literature were employed to predict the shear capacity of the tested beams. Predictions of the codified analytical approach were very conservative. The analytical model published in the literature provided a more reasonable prediction for the shear capacity of the tested beams than that of the codified analytical approach. [ABSTRACT FROM AUTHOR]

Ensuring the safety and stability of buildings during earthquakes is of utmost importance. This can be achieved by assessing the seismic performance of reinforced concrete structures with consideration of design details. This study focused on the seismic behavior of reinforced concrete buildings by comparing the effects of two different types of stirrups, namely those with a 135° angled end-hook shape and straight hooks, with variation of concrete strength. Pushover analysis of a sample building was performed to determine the effect of hook shape on stirrup reinforcement with a constant volumetric ratio for various concrete strength classes. The results of the analysis indicated significant differences in concrete strength and seismic behavior between the two stirrup configurations. The hooked stirrups demonstrated superior energy dissipation capability and ductility, which led to better seismic performance compared to unhooked stirrups across varying levels of concrete strength. To extend the investigation, the study compared the Mander et al., Kent–Scott–Park, and Kappos–Konstantinidis concrete models with different concrete classes (C50-C25-C20-C16-C10). The findings emphasized the importance of stirrup configuration in the design of earthquake-resistant structures. The study concluded that RC structural performance with the 135-degree hooked concrete members exhibited much better behavior of the 90-degree members for the various concrete strength. In this way, it has been revealed the arrangement and detailing of reinforcement in the construction beams and columns improves the governing effect on seismic structural performance. [ABSTRACT FROM AUTHOR]

The lateral confinement of stirrups can improve the load‐bearing capacity and ductility of reactive powder concrete (RPC) columns. To explore the compression behavior of RPC confined with high‐strength stirrups, 45 specimens were prepared and tested under axial compression. The concrete strength was in the range of 99.86–138.24 MPa, the tensile strength of stirrups was Grade 800, Grade 970, and Grade 1270, and the volumetric ratios of stirrups were in the range of 0.9%–2.0%. The results showed that the failure modes of RPC confined with stirrups were shear expansion failure. The compressive strength and ductility of confined RPC were improved with the increase of stirrups volumetric ratios, while stirrups strength slightly affected the compressive strength and ductility. In addition, the peak stress, peak strain, and residual stress prediction models were proposed. Furthermore, the ductility index prediction models were proposed, which can be applied to determine the volumetric ratio of stirrups in stirrups confined concrete columns. [ABSTRACT FROM AUTHOR]

The present paper proposes a mechanical model for the prediction of the response of slender reinforced concrete beams with corroded transverse and longitudinal reinforcements. The proposed model is based on the Modified Compression Field Theory and is able to predict the load–displacement curve of members subjected to monotonic displacement‐controlled tests up to their peak load. The corrosion‐damage effects are considered by means of an effective width of the beam and by means of reduced values of both cross‐sectional area and strain capacity of steel bars. The accuracy of the model is evaluated by comparison with results of tests reported in the literature. Moreover, a simple relation is suggested for the estimate of the shear strength of reinforced concrete beams with low values of the effective geometric percentage of (corroded) stirrups. [ABSTRACT FROM AUTHOR]

In this paper, four full-scale concrete columns with high-strength spiral stirrups (HSSS) are constructed and tested under low-cycle repeated loading. The specimens consisted of two castin-place columns and two precast concrete columns encased by a partly square steel pipe and bolt bars. The structural analysis of the HSSS columns of precast concrete conducted here is novel, and past experimental data for this are not available. To assess the seismic behavior and failure mechanisms of the new connections, quasi-static tests were carried out on columns prefabricated with them and cast-in-place specimens. The responses of all columns were compared, and the results showed that the failure modes of all columns are the large eccentric damage, and the destruction of all specimens occur at the column foot. The anti-seismic property of the precast HSSS concrete columns was comparable to that of the HSSS cast-in-place columns. A comparison of such performance parameters as energy dissipation and coefficient of ductility revealed that the precast HSSS concrete columns are suitable for use in earthquake zones. [ABSTRACT FROM AUTHOR]

With increasing the use of ultra-high performance fiber reinforced concrete (UHPFRC) in recent years, torsional design of UHPFRC beams has become of great importance. This paper presents an experimental and numerical study to investigate the torsional behavior of UHPFRC shallow and deep beams with fcu equal to 190.2 MPa. Ten UHPFRC beams with steel fibers volume fraction of 1.5% subjected to pure torsion were investigated. The provided torsional web reinforcement ratio, the area of longitudinal bars and the tested span to total height ratio (L/h = 6.0, 4.0, 2.0 and 1.0) were the studied parameters. A numerical model has been proposed to predict the torsional response of tested beams. Experimental results showed that increasing stirrups' spacing for the beams of the same L/h ratio (to be 235% of the maximum given by ACI 318-2019 code), reduced the experimental ultimate torsional strength by only 6.7%. The torsional web reinforcement ratio of UHPFRC shallow and deep beams can be safely taken to be 40% of the minimum required by ACI 318-2019. The maximum stirrups spacing can be safely taken the lesser of twice the beam width or 300 mm. The equation used by ACI 318-2019 and ECP-203-2020 for calculating the cracking strength in torsion has been modified to be suitable for UHPFRC beams by taking into consideration the L/h ratio and steel fibers percent. The proposed 3-D numerical model showed good predictions for the torsional strength of tested UHPFRC shallow and deep beams. [ABSTRACT FROM AUTHOR]

Push-off samples are simulated using nonlinear finite element analysis (NLFEA) to evaluate the effects of increased temperatures on the interface shear strength. Firstly, a control shear-key model is created, calibrated, and confirmed against independently published experimental data. Twenty-four NLFEA models are then created with different variables, including temperature (23°C (Room Temperature), 250°C (Raised temperature), 500°C, and 750°C and the number of steel stirrups (none, 1, 2, 3, 4, and 5). The NLFEA results demonstrate that the decreased fracture opening and slide in the damaged shear keys compared to the intact control sample represent the amazing effect of the number of steel stirrups. In addition, it has been revealed that the longitudinal shear force and slide, mode of failure, rigidity, and toughness are all significantly impacted by the degree of heat damage. In particular, a simplified approach is proposed for calculating the shear strength of push-off samples subjected to higher temperatures. [ABSTRACT FROM AUTHOR]

Presence of Late Nomads in the territory of the right bank of the Lower Danube is attested by both written and archaeological sources. The following article presents six graves with equestrian attributes from the 11th to 13th c. These graves either hold items of a rider’s equipment alone or these items in combination with horse remains. Based on analysis of artifacts found in the graves and of specific details of the funeral ritual (as they are compared with analogies from the wider region of the Eurasian Steppe and its surrounding areas), the graves were dated according to standard chronological periods. A whole horse was allegedly buried with a man in the grave from Veliki Preslav, but unfortunately there is no detailed information about this grave’s inventory or find circumstances. Based on the funeral rite presented by the grave and sherds of clay cauldrons alleged to have been found in it, it can be dated to the period of the Cuman domination of the Pontic Steppe. Three graves contain only partial remains of a horse; when this occurs, usually the skull and ends of limbs are present. A skull and a whole set of four limbs were found in a mound by the village Bozhurets. Even with many analogies from regions beyond the Danube, this grave can only be widely dated to the 11th – 13th c. Graves found near Pliska in Mound No. XXV and at Histria can be dated with greater confidence to the second half of the 11th into the 13th c. Datable elements in the mound near Pliska are a coffin made from a hollowed-out tree trunk and the remains of a saber. The same dating of the grave at Histria is made possible by the eastern orientation of the deceased woman it holds. The first type of equestrian grave characterized by the presence of riding equipment without horse remains is attested at two complexes in the research area. The first, the burial in Baba Cave in Dobrudzha, is very unusual for the area, and its inventory is unfortunately very badly preserved. Nevertheless, some aspects of the saber blade and perhaps the shape of the stirrup found here points to a date in the 12th or 13th c. The final equestrian grave analyzed here was unearthed by Pliska’s southern wall in Grave No. 20 and contained a full set of riding equipment that can with high certainty (based on numerous analogies to artifacts in the Cuman milieu) be dated to the second half of the 11th c. at the earliest but most likely to the following 12th or 13th c. The eastern orientation of the body in this grave suggests this dating as well.