Diagonal Reinforcement Research Articles

Reinforcing of discontinuity regions in concrete deep beams with GFRP composite bars

The behavior of concrete deep beams internally-reinforced with glass fiber-reinforced polymer (GFRP) bars around regions of discontinuity is investigated. Twelve deep beam specimens were tested. One specimen was solid whereas the remaining eleven specimens included an opening in the shear span. Test variables included the opening height, concrete grade, and GFRP reinforcing configuration around the discontinuity regions. Three different GFRP reinforcing schemes around the discontinuity regions were employed. The scheme with diagonal GFRP reinforcement crossing the bottom chord was more effective in improving the shear resistance than that having diagonal GFRP reinforcement crossing the top chord. The strength gain caused by the GFRP reinforcement was more significant for the deep beams with the greater opening height. In contrast, increasing the opening height reduced the strength enhancement caused by increasing the concrete grade. Test results were compared to the strut-and-tie modeling (STM) predictions. The STM tended to provide reasonable predictions for the nominal shear strength of the beams reinforced with GFRP bars around the discontinuity regions. Provisions of the Canadian Standards Association provided more conservative predictions for the nominal strength compared with those provided by provisions of the American Concrete Institute.

Experimental Investigation on Cyclic Behavior of Reinforced Concrete Coupling Beams Under Quasi-static Loading

The current status of the reinforcement layouts stated in the codes and frequently used in new construction areas needs to be evaluated and determining its effects on the behavior of structural elements may provide essential contributions to the field. For this purpose, conventionally reinforced, diagonally reinforced (confinement of individual diagonals),and diagonally reinforced with full confined section concrete coupling beam specimens were designed according to ACI 318-14 and Turkish Earthquake Code 2018 in this study. ½-scale test specimens with aspect ratio two were tested under quasi-static cyclic loading using a new complex experimental setup. According to the results obtained, while for conventionally reinforced coupling beams ductile hysteretic behavior remained at 2.0% drift, for diagonal reinforced coupling beams it sustained up to 4.0% drift. Although the diagonal reinforcement enhanced ductility capacity of coupling beams compared to conventionally reinforced coupling beams having a comparably low post-elastic behavior, high ductility demands in the code requirements did not meet. For the same reinforcement ratio and layout, individual confinement around diagonal bars retarded bar buckling and ultimate strength and ductility capacity increased slightly compared to diagonally reinforced coupling beam with full confined section. After all, bar buckling that occurred after the life safety performance level given in the codes was seen at 3.5–4.0% drift. Diagonal reinforcing bars ensured life safety performance level up to 4.0% drift, but it remained at 3.0% drift for conventional reinforcement.

Mechanically robust lattices inspired by deep-sea glass sponges.

The predominantly deep-sea hexactinellid sponges are known for their ability to construct remarkably complex skeletons from amorphous hydrated silica. The skeletal system of one such species of sponge, Euplectella aspergillum, consists of a square-grid-like architecture overlaid with a double set of diagonal bracings, creating a chequerboard-like pattern of open and closed cells. Here, using a combination of finite element simulations and mechanical tests on 3D-printed specimens of different lattice geometries, we show that the sponge's diagonal reinforcement strategy achieves the highest buckling resistance for a given amount of material. Furthermore, using an evolutionary optimization algorithm, we show that our sponge-inspired lattice geometry approaches the optimum material distribution for the design space considered. Our results demonstrate that lessons learned from the study of sponge skeletal systems can be exploited for the realization of square lattice geometries that are geometrically optimized to avoid global structural buckling, with implications for improved material use in modern infrastructural applications.

Prediction of failure load of RC and R-ECC dapped-end beams

The dapped-end reinforcements of a control beam have been designed conforming to requirement of the PCI code. The dapped-end reinforcements of other beams were derived from the control beam that involve the scheme variation of the hanger or diagonal reinforcements. Some selected beams utilize the engineered cementitious composites (ECC) in the dapped-end region. Twenty-seven large-scaled beams with dapped-end have been prepared, cast and tested. All beams were tested under the three-point loading up to failure. To localize effect of the shear failure, the shear span-depth ratio (av/d) of 1.43 has been carried out. Dapped-end beam (DEB) specified in PCI code has nominal shear span-depth ratio (an/d) less than 1, but in this study, several beams use an/d larger than 1. For analytical purpose, the design equations specified in PCI code have been used for the analysis requirement. By comparing against the test results, the analysis results that using the design equations of PCI code provide a significant difference, in which the mean value of analysis-test results ratio is 0.71. The design equations specified in PCI code were reliable to design the dapped-end reinforcements, but these equations have not yet able to accommodate adequately, in analyzing and predicting the failure load of DEBs that have the dapped-end reinforcements scheme varied.

Seismic performance and shear strength of coupling beams using engineered cementitious composites with different reinforcement layouts

The coupling beam is the key component in high-rise coupled-wall and core-tube structures. To further improve the seismic performance and damage tolerance of traditional reinforced concrete coupling beams, engineered cementitious composites (ECC) becomes a prospective choice, due to the superior characteristics including tension strain-hardening and multi-cracking properties. However, there have been only limited researches on ECC coupling beams, causing the lack of comprehensive understanding of the seismic behaviour and practical design formula. In this study, eight large-scale ECC coupling beam specimens with different aspect ratios, transverse and diagonal reinforcement ratios are fabricated and cyclically tested. The seismic performance of coupling beams is thoroughly investigated in terms of the damage and failure modes, energy dissipation, stiffness deterioration, strength degradation and shear distortion. The contribution of ECC, transverse and diagonal reinforcement to the shear strength is evaluated and compared. Besides, the whole-process hysteretic curves of the axial force are reported for the first time. Finally, a shear strength equation is proposed based on the analysis of nineteen specimens collected from the literature and this study. The test results demonstrate that ECC coupling beams with a hybrid reinforcement layout exhibit superior seismic performance, which is a reasonable choice to balance both the seismic and construction performance. It is strongly recommended that axial force should be considered in the strength prediction of coupling beams, with a 10% axial force ratio suggested for design. The proposed method is verified and can give precise prediction for the bearing capacity of ECC coupling beams.

Effect of deviation angle between principal stress and diagonal reinforcement direction on seismic performance of RC coupling beams

In a coupled shear wall system, the reinforced concrete (RC) coupling beams are allowed to form plastic deformations in order to dissipate seismic energy while maintaining the stability of overall structural system. However, the coupling beams are generally shear-dominated members because of their short shear span-depth ratio, which is usually less than 2. Therefore, under high seismic shear demand, the energy dissipation capacity and ductility of these members are sharply reduced compared to RC beams with larger shear span-depth ratio due to severe pinching effect. In order to avoid any undesirable structural behavior, the current standards stipulate the use of diagonal reinforcing bars in RC coupling beams with short span-depth ratio. Previous studies show that the diagonal reinforcement arrangements improve the structural performance of coupling beams, but the behavior of such members under cyclic bending and shear may significantly vary depending on the orientation of diagonal reinforcement. In this study, the effects of deviation angle between principal stress and diagonal reinforcement direction in the failure region, were experimentally investigated considering the potential failure modes of the coupling beams. Six RC coupling beams were tested under reversed cyclic bending and shear during this research. Experimental results show that the ductility ratio and the energy dissipation capacity of RC coupling beams vary, depending on the orientation of the diagonal reinforcement even when the same amount of diagonal reinforcement is provided. The structural performance of RC coupling beams improves as the deviation angle between direction of principal stress and the diagonal reinforcement becomes smaller. Finally, a finite element method (FEM) analysis was carried out for the test specimens. The FEM analysis results closely agreed with experimental observations that both the ductility ratio and energy dissipation capacity were larger for members with lowest deviation angle.

Failure mode of truss system concrete beams strengthened with tensile reinforcement

Cracks usually precede beams failures. Cracks occurred due to the applied load exceeds the capacity of the cross-section in carrying the load. The use of a diagonal reinforcement or truss system can increase the flexural capacity of the beams. The previous research of using truss system reinforcement in the beam without concrete in the tension zone causes a decrease in flexural capacity due to the cracks in the area near the support. Therefore, it is necessary to add tensile reinforcement in the zone. This study uses a truss reinforced concrete beam specimen with dimensions of 15 cm x 20 m x 330 cm. There are four variations of the specimens, namely Normal Beams (BN) as control beam, BTRP 40D, BTRP 60D, and BTRP 80D. The flexural test is carried out by monotonic static loading. The results showed that the flexural capacity of BTRP 40D, BTRP 60D, and BTRP 80D increased due to the addition of tensile reinforcement in the support zone. Moreover, the failure mode of BTRP 60D and BTRP 80D are under reinforced and cracking does not occur in the support zone. Meanwhile, the BTRP 40D beam shows wide cracks in the support zone.

Seismic Design of a Out-of-code High-rise Library

In order to meet the requirements of architectural design form, a high-rise library project appeared many structural seismic designs, such as plane thin waist concave, large area floor missing, tower offset and torsion irregularity. In accordance with the principle of economy, safety and reliability, many calculation measures are adopted in the structural design, such as the comparative analysis of software SATWE and ETABS, the special calculation of floor stress level, the combining floor analysis of missing floors and the strengthening performance analysis under medium and large earthquake. At the same time, according to the structural transfinite items, the structural strengthening measures are taken, such as optimizing the structural layout, reducing the eccentricity, increasing the thickness of the floor at the weak position, and adding diagonal reinforcement in the stress concentration area. Using the above treatment, the structure can meet the fortification target under three levels.

NUMERICAL STUDY OF STRENGTHENED SLENDER I‐GIRDERS WITH FIBER REINFORCED POLYMERS

AbstractThis study demonstrates the feasibility of applying diagonal reinforcements composed by fiber reinforced polymers (FRP) on the web surface of slender steel I‐girders. The use of such reinforcements contributes to a higher shear buckling strength capacity of the beam panels. This strengthening technique was evaluated by means of numerical analysis using the finite element software Abaqus®. In the analyzed models the connection between the reinforcement of composite material and the beam was made by structural adhesives. Additionally, beams with traditional diagonal reinforcements made of welded steel plate were simulated for comparison purposes, as well as another model without any diagonal reinforcement.

Effectiveness of diagonal shear reinforcement on reinforced concrete short beams

In the study, an experimental and numerical study is performed to investigate the efficiency of diagonal shear reinforcement (DSR) on reinforced concrete (RC) short beams. For this purpose, 7 RC short beam specimens were tested under a 4-point loading, and a numerical study is conducted by using finite element method. Additionally, the efficiency of addition of DSR to specimens is observed in the experimental study together with the increase in stirrup spacing. Analysis results are compared in terms of load-displacement behavior and failure modes. As a result of the study, a significant improvement both in shear and displacement capacities of the RC short beams are achieved along with addition of DSR in short beams. Moreover, it is deduced from the numerical results that increasing both the diameter and yield strength of DSR makes a significant contribution to the shear capacity and ductility of shear critical RC members.

Structural Performance of RC and R-ECC Dapped-End Beams Based on the Role of Hanger or Diagonal Reinforcements Combined by ECC

Twenty-seven large-scale beams with dapped-end have been prepared, cast and tested to failure in the three points loading arrangement. One control beam has been designed in accordance with requirement of standard code while the dapped-end reinforcement scheme of other beams has been derived from the control beam. In selected beams, engineered cementitious composites (ECC) has been utilized in the dapped-end region. The test results exhibited that DR is more appropriate and higher capacity than HR in resisting the shear force. In addition, the reinforced engineered cementitious composites dapped-end beams (R-ECC-DEB) showed higher structural performance compared to the normal reinforced concrete dapped-end beams (RC-DEBs). The strength of ECC also has direct effect on the failure capacity of the R-ECC-DEB, in which higher strength of ECC leads to higher failure capacity of R-ECC-DEB.

Anti-seismic behavior of composite precast utility tunnels based on pseudo-static tests

In this work, we have studied the effects of different soil thicknesses, haunch heights, reinforcement forms and construction technologies on the seismic performance of a composite precast fabricated utility tunnel by pseudo-static tests. Five concrete specimens were designed and fabricated for low-cycle reciprocating load tests. The hysteretic behavior of composite precast fabricated utility tunnel under simulated seismic waves and the strain law of steel bars were analyzed. Test results showed that composite precast fabricated utility tunnel met the requirements of current codes and had good anti-seismic performance. The use of a closed integral arrangement of steel bars inside utility tunnel structure as well as diagonal reinforcement bars at its haunches improved the integrity of the whole structure and increased the bearing capacity of the structure by about 1.5%. Increasing the thickness of covering soil within a certain range was beneficial to the earthquake resistance of the structure, and the energy consumption was increased by 10%. Increasing haunch height within a certain range increased the bearing capacity of the structure by up to about 19% and energy consumption by up to 30%. The specimen with the lowest haunch height showed strong structural deformation with ductility coefficient of 4.93. It was found that the interfaces of haunches, post-casting self-compacting concrete, and prefabricated parts were the weak points of utility tunnel structures. Combining the failure phenomena of test structures with their related codes, we proposed improvement measures for construction technology, which could provide a reference for the construction and design of practical projects.

Experimental Seismic Performance Evaluation of Coupling Beams: Comparison of Old with Modern Codes

ABSTRACT This study presents the results of an experimental investigation on the seismic performance of two reinforced concrete coupling beams (CBs) for coupled shear walls, one with a conventional reinforcement layout designed according to the old National Building Code of Canada (NBCC) 1941 and the other one with a diagonal reinforcement configuration designed according to modern NBCC 2015 and Canadian Standard Association (CSA) A23.3 2014 requirements. Experimental tests were conducted to investigate the behavior of specimens under reversed cyclic loading. The experimental results reveal that the diagonal reinforcement configuration could increase the load-resisting capacity and energy dissipation capacity by 4.4 and 10.2 times, respectively. Moreover, the maximum rate of stiffness degradation decreased from 96% in conventionally reinforced CB to 57% in diagonally reinforced CBs. Furthermore, diagonal reinforcement layout led to more stable hysteretic behavior without considerable pinching. In contrast and as expected, the conventionally reinforced CB did not comply with the requirements of the new design code. Therefore, such CBs should be retrofitted to upgrade their seismic performance in conformity with updated standards requirements.

Experimental investigation of the performance of diagonal reinforcement and CFRP strengthened RC short columns

In this study, quasi-static seismic performances of CFRP wrapped and diagonal reinforcement reinforced concrete (RC) short columns are presented. RC short columns have been tested experimentally under constant axial load and cyclic lateral load. In the scope of this study, the performance of eighteen RC short columns, which consist of six CFRP wrapped, six diagonal reinforcement and six reference (Ref) columns, have been examined. Ref columns are the perfect columns produced in accordance with the regulation requirements. Therefore, it is aimed to examine the proposed diagonal rebar and CFRP applications as an alternative to the design in the earthquake regulations. The use of Ø10 and Ø12 reinforcements as a shear reinforcement for Ref columns and columns with diagonal reinforcement has also been examined for the contribution of the diameter of shear reinforcement to performance. Besides the difference in the diameters of the shear reinforcement and the applied methods, the aspect ratio (αs) is another parameter. Eighteen test columns were divided into three series and tested with αs = 2, 1.5 and 1 aspect ratio in order to examine the effectiveness of the applied methods by increasing the effect of shear dominant behaviour. The experimental results showed that columns with diagonal reinforcement and CFRP wrapped columns succeeded in exceeding the performances of perfect Ref columns and could be an alternative to the existing design.

IMPROVEMENT OF REINFORCEMENT METHOD OF R/C CYLINDRICAL SHELL WITH OPENING

Reinforced concrete (R/C) chimney with a hole is prone to decrease the strength. Therefore, the particular reinforcements have been placed around the hole. Both meridional and hoop reinforcements have been placed additionally equivalent to the loss amount of reinforcements at the hole and the diagonal reinforcements have been placed to prevent the corner failures as well. Diagonal reinforcements in the shell were curved shape. It is the laborious work to place them. In this analysis, the improved reinforcement method was proposed instead of placing the conventional diagonal reinforcements. In the proposed methods, only the hoop and the meridional reinforcements were arranged around the corners instead of diagonal reinforcements. FEM analyses were done to evaluate the proposed reinforcing method. Numerical model was the cylindrical panel with a rectangular opening. From the numerical analyses, it was concluded that the R/C panel with proposed reinforcement method showed the same behavior as that with conventional reinforcement method.

Energy Absorption Capacity Of Layered Lightweight Reinforced Concrete Beams With Openings In Web

This research presents the flexural behavior on reinforced concrete beam with transverse web opening constructed from layered concrete. The layered concrete combining normal concrete and lightweight aggregate concrete (LWC) are depended in present study. In the experimental program, 13 models of normal and layered reinforced concrete beams are tested under the effect of four-point loads. All beams had the same overall geometrical dimensions and main longitudinal top and bottom with internal diagonal reinforcement provided around the openings. One of the beam specimen is tested as control beam and the other specimens are divided into three groups [G1, G2, and G3] to study the effects of the following variables: effect of presence of web openings, layered system, lightweight aggregate (partially volumetric replacement of normal aggregate by thermostone) on the ultimate load, cracking load, cracking pattern and energy absorption capacity. The existing of an opening in beam specimens reduced the flexural capacity of beams with a percentage depending on the size of opening and opening number. The test data obtained from the adopted layered technique of (NEW) and (LWC) have shown that for beams constructed from two layered concrete (LWC with thermostone in the web and bottom flange of I-beam section) ultimate load is decreased about (9.3%-48.8%). It has also, the beams constructed from three-layered of concrete (LWC with thermostone in the web of I-beam section), their ultimate load is decreased about (25.6%-58.1%). On the other hand, magnitude increased of energy absorption capacity are achieved by the decreased opening size, introducing the full size opening of dimension (100×1000) mm reduces the energy absorption capacity of the RC I-section beams at least 80% compared to solid beam while the beam with opening size (100×100) mm decrease up to 16%. In the case of the layered concrete beams specimen, the real influence of lightweight concrete (LWC) type in the layered reinforced concrete is observed significantly after increasing the length of opening more than 100 mm.

A kinematics-based approach for the shear strength of short fibre-reinforced concrete coupling beams

Short coupling beams are susceptible to brittle shear failures that are typically suppressed with dense transverse and/or diagonal reinforcement. To reduce the amount of shear reinforcement and improve the service behavior of the beam, researchers have proposed a solution with steel fiber-reinforced concrete (FRC). However, while this solution is promising, there are no sufficiently simple mechanical models capable of capturing the shear strength and displacement capacity of short FRC coupling beams without diagonal reinforcement. This paper proposes such a model based on first principles: kinematics, equilibrium, and constitutive relationships for the mechanisms of shear resistance. The model accounts in an explicit manner for five shear mechanisms across the critical shear cracks: diagonal compression in the critical loading zones, aggregate interlock, tension in the stirrups and in the steel fibres, and dowel action of the longitudinal reinforcement. These mechanisms are predicted and the results are compared to 20 tests from the literature as well as to FEM predictions. It is shown that the proposed approach models well the effect of beam aspect ratio, concrete strength, stirrup ratio, and amount of steel fibres. Furthermore, the model is used to develop relationships outlining the effectiveness of steel fibres to reduce conventional stirrup reinforcement in coupling beams with various properties.

Diagonal Reinforcement as Strengthening to Increase the Stiffness and Strength of Concrete Frame

Diagonal Reinforcement as Strengthening to Increase the Stiffness and Strength of Concrete Frame

Shear behavior of slender geometry RC coupling beams in seismic response

Coupling beams have geometric sizes with special heights known as deep beams, and the design usually takes up more space. Focus of this research is to analyze slender coupling beams with a diagonal reinforcement angle design of less than 20 degrees to the longitudinal reinforcement. New alternative design for slender coupling beams was experimentally investigated where the parameter was the span-to-depth ratios (2.75; 3.0; 3.25). Coupling beams should not be considered as load receiver, but instead as connector between the couple shear walls for working together. The result of the test indicated that coupling beams with a slenderness ratio of 3.25 has capacity to behave as coupling beams which function is to distribute the energy.

Cyclic behavior of diagonally reinforced slender HPFRCC coupling beams with reduced diagonal and transverse reinforcement

Slender diagonally reinforced coupling beams (DRCBs) have been increasingly used for coupled shear wall systems in high-rise buildings, which can reduce the height of buildings and associated construction costs. However, in practice, it is difficult to make slender DRCBs according to current design provisions due to heavy reinforcement congestion. To alleviate the reinforcement congestion problem and improve the cyclic behavior of the coupling beams, High Performance Fiber-Reinforced Cementitious Composite (HPFRCC) DRCBs with new reinforcement arrangements or a reduced amount of reinforcement have been developed. The objective of this study is to explore the cyclic behavior of slender DRCBs made of HPFRCC with polyvinyl alcohol (PVA) fibers. Experimental tests were conducted with six DRCB specimens with a length-to-height (ln/h) of 3.5 to investigate the effect of the HPFRCC and the amount of diagonal and transverse reinforcement on the cyclic behavior of slender DRCBs. In this study, an empirical equation for predicting the shear strength of slender HPFRCC DRCBs was also proposed, considering the contributions of the HPFRCC and the amounts of diagonal and transverse reinforcements. The proposed equation was verified by using HPFRCC DRCB specimens with ln/h ranging from 2.0 to 3.5.