Spandrel Beams Research Articles

Seismic collapse performance assessment of high‐strength steel framed‐tube structures with shear links fabricated using low‐yield‐point steel

SummaryA high‐strength steel framed‐tube structure with shear links fabricated using low‐yield‐point steel (HSSFTS‐LYPSL) was developed in this study to improve the seismic performance and resilience of the conventional steel framed‐tube structure. When this HSSFTS‐LYPSL is subjected to strong earthquake excitation, its shear links undergo significant plastic deformation to dissipate seismic energy while critical components such as the spandrel beams and columns maintain their elasticity. Furthermore, the replacement of damaged links was facilitated by the use of bolted end‐plate connections. This study designed three typical HSSFTS‐LYPSL examples with 20, 30, and 40 stories to investigate the seismic collapse performances of HSSFTS‐LYPSLs at different seismic intensity levels. Three‐dimensional nonlinear finite element analysis models of these example structures were developed using the OpenSEES software, and the accuracy and effectiveness of the modeling approach was validated by comparing its results with those of quasi‐static tests on sub‐structure assemblies. Next, 40 records each of far‐field and pulse‐type near‐field ground motions were selected and applied with an incremental dynamic analysis (IDA) to obtain response curves for the example structures and calculate their collapse fragility curves and collapse margin ratios (CMRs) utilizing a modified collapse fragility model. Finally, based on the collapse fragility and seismic hazard curves, the seismic collapse risk probability curves of the HSSFTS‐LYPSLs were obtained under far‐ and near‐field earthquakes, revealing that at the maximum considered earthquake level, the CMR values ranged from 5.74 to 7.25 and from 4.85 to 6.67, respectively; at the very rare earthquake (VRE) level, the CMR values ranged from 3.83 to 4.85 and from 3.24 to 4.46, respectively. These results demonstrate that HSSFTS‐LYPSLs exhibit sufficient potential for seismic collapse resistance. As pulse‐type near‐field earthquakes had more significant and adverse impacts on the seismic collapse performances of the HSSFTS‐LYPSLs than far‐field earthquakes, the seismic collapse design of an HSSFTS‐LYPSL should particularly consider the influence of near‐field effects. In addition, the seismic hazard function had a greater effect on the structural seismic collapse risk curves than the collapse fragility function, suggesting that seismic collapse risk curves could provide a comprehensive assessment of HSSFTS‐LYPSL seismic collapse performance. Under far‐ and near‐field earthquakes, the annual collapse risk probabilities of the HSSFTS‐LYPSL examples at the VRE level were within 1.18 × 10−5–4.53 × 10−5, which is below the seismic collapse risk threshold recommended by others, indicating that HSSFTS‐LYPSLs can meet the fourth‐level performance objective of “no collapse failure at the VRE level.” However, this study only conducted seismic collapse and risk assessments using example HSSFTS‐LYPSLs; future research will focus on determining the seismic recovery capacities of and developing post‐earthquake repairability methodologies for HSSFTS‐LYPSLs.

The analysis of variants of the main frame of the two-nave steel hall for sports purposes

The objective of the analysis was the choice of the cross sections of the Steel hall’s main frame. The minimisation of weight of the construction elements was assumed as a criterion of optimisation. Initially, the forces which load the main frame, caused by constant interactions, snów interactions and wind interactions, were calculated. In the first phase of the analysis, the choice of cross sections for the elements of the lattice girder was madę. Ninę variants of the lattice girder were considered and the lightest truss was chosen. In the second phase, the analysis of the cross sections of the spandrel beam and the columns was performed. Four variants of these elements were considered. Similarly to the first phase, the variant considered best in terms of weight of the elements was chosen. The results of the calculations from both phases were shown in the bar graphs

Floor slab composite action effects on hysteresis behaviors of steel-framed-tube structures with shear links

The utilization of spandrel beams with a low span-to-depth ratio in a Steel-Framed Tube (SFT) structure can potentially diminish its ductility and energy dissipation characteristics. Conversely, integrating an SFT with end-plate-connected, replaceable low-yield-point steel shear links (SFT-RLYPSL) may significantly enhance its seismic response. This study introduces a prototype SFT-RLYPSL configuration designed to mitigate the premature separation of a reinforced concrete (RC) slab from the spandrel beams, a phenomenon observed in prior research. A series of finite element (FE) models were established, utilizing the prototype structure as a basis, to systematically investigate the impact of various parameters, including the presence and thickness of the RC slab, concrete strength, shear link length, and initial spandrel beam stiffness, on the cyclic behavior of an SFT-RLYPSL substructure module. Additionally, the failure mechanisms of the substructure module were assessed. The findings of this study reveal that the utilization of T-shaped connectors can effectively delay the pull-out of studs from the RC slab, especially under substantial vertical displacement of the spandrel beam. The initial elastic stiffness and load-carrying capacity of the substructure module can be significantly enhanced through the promotion of RC slab composite action. An optimal shear link length ratio falls within the range of 0.95 to 1.25, and given the assumption of LYP225 steel shear links with length ratios of 0.95 to 1.25 in the SFT-RLYPSL, the recommended minimum thickness and concrete grade for the RC slab, based on numerical simulation results, are 120 mm and C30, respectively. It is further recommended to employ C30 concrete for an RC slab with a thickness of 120 mm. Finally, a restoring force model is proposed, accurately reflecting the observed mechanical behaviors of the SFT-RLYPSL substructure module.

Hysteretic behaviors of steel framed-tube structures with end-plate-connected shear links using finite element modeling

Shear links are increasingly used as replaceable energy dissipating elements to achieve resilient structural systems. In this study, the seismic performances of steel framed-tube structures with end-plate-connected low-yield-point steel shear links (SFTS-EPC-LYPSLs) were investigated using finite element analysis (FEA) models informed by cyclic loading tests of LYP225 steel coupons and validated against previously obtained experimental data. Furthermore, a comprehensive design methodology for the bolted end-plate connection between the deep spandrel beam and link was proposed. Finally, an FEA-based parametric analysis conducted in ABAQUS quantified the influences of key design variables on the hysteretic behaviors of the SFTS-EPC-LYPSLs. The results demonstrate that: when the connection configuration satisfied the limit calculated by the proposed design methodology, the SFTS-EPC-LYPSLs exhibited desirable inelastic behaviors and energy-dissipation capacities, with the plastic shear deformation and deformation proportion reaching 0.18 rad and 91%, respectively; the end plates of the spandrel beam and link remained elastic under severe cyclic loading; the design equivalent stiffness ratio of a spandrel beam with a midspan shear link should be greater than 0.7; shear link length ratios of 0.75–1.69 provided overstrength factors of 1.61–2.05, exceeding the 1.5 value stipulated by the design standards; the link length ratio should be 0.75–1.31 to reach a plastic rotation capacity exceeding 0.12 rad; finally, the link web stiffener spacing should satisfy the specification limits to prevent severe web shear and lateral–torsional buckling. The results of this study inform a consistent design methodology to foster the engineering application of SFTS-EPC-LYPSLs.

Experimental study and numerical simulation on the transverse force transmission mechanism of discretely connected precast RC floor

An innovative discretely connected precast RC floor (DCPCF) is presented, in which precast flat slabs (solid slab, sandwich slab or hollow slab) and spandrel beams (walls) are the basic components that connected by distributed mechanical connectors. The experimental program consisting six full-scaled DCPCF specimens and two cast-in-situ slab (CIS) specimens were conducted to evaluate the influence of slab joint structure on force transmission mechanism of DCPCF in orthogonal slab laying direction (OSLD), which in terms of the failure mode, deflection, strain development, etc. The results revealed that the slab joint connectors of DCPCF had good force transmission performance in OSLD, which can effectively transmit the flexural moment and connect the adjacent precast slab. Compared with CIS specimens, DCPCF specimens had no obvious plastic stage and entered elastoplastic stage earlier. The deflection of DCPCF in OSLD was mainly caused by the opening deformation of the slab joint and the rotational deformation of the precast slabs. For DCPCF specimens, the more connectors in each slab joints or the fewer slab joints, the greater the flexure stiffness in OSLD. Based on the test results, finite element models (FEMs) were developed to simulate force transmission mechanism of DCPCF in OSLD, and the accuracy was confirmed by the test results. Finally, it was verified that increasing the number of anchor bars and increasing the diameter of diagonal anchor bars can effectively enhance the anchoring measures of slab joint connectors to achieve replaceability of perforated steel plates.

Effectiveness of embedded through-section technique in strengthening reinforced concrete spandrel beams

Spandrel beams are typically subjected to a series of vertical eccentric loadings when used in parking structures or the abutments of bridges. The embedded Through-Section (ETS) technique is a recently developed technique to increase the shear capacity of reinforced concrete members using steel reinforcing bars. This study presents an experimental program conducted on spandrel beams to get a deeper understanding considering different parameters including the aspect ratio of the section (i.e., height/thickness) and the strengthening system (i.e., the implementation of the ETS technique). This study focuses on the test results including the ultimate shear-torsion capacity, cracking load, load-twisting, and load-deflection responses. The outcomes had shown the superior performance of the ETS technique, where the increase in torsion capacity attained 45% compared to the control spandrel beams. Also, the embedded steel bars restricted the progress of the deflection and rotation of spandrel beams due to the improvement of the spandrel's stiffness. The rotation improvement for the strengthened spandrel beams attained 50% compared to the control spandrel beams. The skewed failure plane for the strengthened spandrel beams attained the web's top surface which is attributed to the positive influence provided by embedded steel bars. The results obtained for spandrel beam strength were found to be in good agreement with the predicted by the PCA notes on the ACI code outcomes.

Efficiency of CFRP torsional strengthening technique for L-shaped spandrel reinforced concrete beams

Abstract The present study aims to get experimentally a deeper understanding of the efficiency of carbon fiber-reinforced polymer (CFRP) sheets applied to improve the torsional behavior of L-shaped reinforced concrete spandrel beams in which their ledges were loaded in two stages under monotonic loading. An experimental program was conducted on spandrel beams considering different key parameters including the cross-sectional aspect ratio (i.e., web height/web thickness), and the availability of the CFRP strengthening system. The ledge of the spandrel beams was exposed during testing to a very high eccentric load, which was transferred to the web of the spandrel beam causing high shear, torsion, and bending moments. Consequently, the applied load resulted in in-plane and out-of-plane deformations of the web accompanied by flexural and shear cracks. This article demonstrates the advantage of using CFRP sheets to strengthen the mentioned members. The applied CFRP sheets increased the failure torsional load by about 37% compared to the identical L-spandrels without strengthening. The outcomes indicate that using CFRP sheets show improvement in restricting the deflections and rotation of L-spandrels due to increasing spandrel stiffness. The reduction in the degree of rotation attained more than 33% in comparison to the spandrel beams without strengthening. The experimental program confirmed the applicability of the proposed strengthening technique for compacted and slender L-shaped spandrel-reinforced concrete beams.

Experimental investigation of full-scale reinforced concrete beams under reversed-cyclic pure torsion

Many sub-assemblies of Civil Engineering structures such as columns and primary (spandrel) beams are subjected to torsion. This study aims to evaluate the torsional behavior of reinforced concrete (RC) members under reversed-cyclic pure torsional loading. An experimental program was conducted on nine full-scale specimens including the parameters such as concrete compressive strength, and transverse and longitudinal reinforcement ratios. During the tests, a new test setup was designed to allow the specimens to elongate at one end and to apply the moments at the other end along the specimen’s rotational axis. Ultimate, peak and yield torques, torsional stiffness, energy dissipation capacity, and torsional bearing capacity of specimens were evaluated. In some specimens, longitudinal elongation was measured. Out of all test parameters, it has been concluded that the most important parameter on the torsional capacity of the members was the transverse reinforcement ratio. The concrete strength became a more effective factor in determining the fracture mode. Thus, the amount of longitudinal reinforcement was observed to be the parameter that mostly affected the flexibility of the elements.

Ultimate torsional resistance and failure modes of FRP-strengthened reinforced concrete members: A nonlinear design model

Reinforced concrete (RC) structural members, especially flanged and spandrel beams, bridge girders, curved beams, and eccentrically loaded beams may be subjected to significant torsional loading. Despite extensive research on the strengthening of RC members, far too little attention has been paid to the torsional behavior of RC members strengthened with fiber-reinforced polymer (FRP) sheets. Therefore, a limited number of guidelines specified the design of externally bonded FRP systems in torsion. This study provides an important opportunity to advance the understanding of the torsional behavior of FRP-strengthened members by developing a nonlinear design model predicting the failure mode and ultimate torsional resistance of FRP-strengthened RC members subjected to torsion. Serious discussions and analyses of desired failure modes emerge by defining two balanced conditions between the components, and eight failure regions. The first balanced condition defined between FRP and concrete specifies the failure mode of the member, and the second balanced condition defined between steel and concrete is used for the analysis of steel reinforcement stresses. A clear design approach is proposed in this study to access the desired percentage of the externally applied FRP sheets based on the required torsional strength. Moreover, the ultimate stresses and strains of concrete struts, steel reinforcements, and FRP sheets are derived by incorporating the nonlinear behavior of concrete. To evaluate the validity of the design method, 70 FRP-strengthened specimens are collected from 11 previous studies; then, a comparative analysis is conducted among the experimental results, the estimations of the presented model, and the predictions of the commonly available guidelines for torsional strengthening. The excellent agreement between the test results and the presented model estimations confirms the validity and accuracy of the presented model.

Evolution of the L-shaped spandrel beam

Evolution of the L-shaped spandrel beam

Beam torsion effect of monolithic precast concrete beam-column substructures during progressive collapse

To investigate the effect of spandrel beam torsion on the progressive collapse resistance of the monolithic precast concrete (PC) spatial frames, three PC substructures (a cantilever beam substructure PC-c, a double-span planar substructure PC-p and a spatial substructure PC-s) were designed. They were tested under a middle column removal scenario, to simulate the progressive collapse of the PC frame structures. The test results indicated that the torque developed in spandrel beams of the spatial substructure PC-s leaded to more severe concrete cracking and crushing at its beam ends. The existence of torque in the PC spatial substructure weakened the mobilization of compressive arch action (CAA) and catenary action (CA). The CA capacity of the spatial PC substructure was reduced by 27.23% compared with the planar substructure PC-p, and the CA action was ended in advance. Additionally, a three-dimensional joint model considering the torsion effect was proposed herein, which accurately captured the progressive collapse behavior of spatial substructures. Based on the verified numerical model, the difference between the combined torsion–bending interaction in the spandrel beam of planar and spatial substructures was analyzed. The effects of reinforcement configuration and span-depth ratio of spandrel beams on the collapse resistance were studied. Finally, a conservative calculation method of the increased gravity loads GN was given when the torsion effect needs to be considered.

Parametric study of hysteretic performance of high-strength steel framed-tube structures with web-bolted connected shear links

High-strength steel framed tube structures with web-bolted connected shear links (HSSFTS-WCSLs) combine the advantages of replaceable shear link and high-strength steel (HSS) and can effectively improve the seismic performance and recoverability of traditional steel framed-tube structures. This parametric study investigates the effects of design parameters on the hysteretic behaviors of HSSFTS-WCSL using finite element analysis. The parameters include the length ratio of the shear link, span-to-depth ratio of the spandrel beam, intermediate link web stiffener space, and design details of the web-bolted connections. According to the numerical simulation results, the recommended length ratios of the web-bolted connected shear link are between 0.84 and 1.40. The span-to-depth ratios of the spandrel beams significantly influence the strength of the structures. The web-bolted connected shear links should be placed at the middle of the spandrel beams with span-to-depth ratios lower than 4.6. The link web stiffener spaces barely influence the seismic performance of HSS-FTS-RSLs. The allowable link web stiffener spaces given in the design codes can provide reliable capacities of the structures. The details of the web-bolted connections determine the energy dissipation performance of the structure, and this effect can be optimized by effectively increasing the diameter of the bolt and thickness of the reinforcement plate. The bolts should have sufficient shear strength to avoid shear failure. Increasing the thickness of the reinforcement plates of the connections can significantly enhance the energy dissipation capacities of HSS-FTS-RSLs. The overstrength factors of the web-bolted links with length ratios between 0.84 and 1.60 range from 1.42 to 1.79.

Numerical Investigation of the Flexure Behavior of Reinforced Concrete Spandrel Beams with Distributed Tension Reinforcement

When the flange of a reinforced concrete spandrel beam is in tension, current design codes and specifications enable a portion of the bonded flexure tension reinforcement to be distributed over an effective flange width. The flexural behavior of the RC L-shaped spandrel beam when reinforcement is laterally displaced in the tension flange is investigated experimentally and numerically in this work. Numerical analysis utilizing the finite element method is performed on discretized flanged beam models validated using experimentally verified L-shaped beam specimens to achieve study objectives. A parametric study was carried out to evaluate the influence of various factors on the beam’s flexure behavior. Results showed that as the percentage of the reinforcement distributed has increased over a greater width of the flange, a considerable drop in beam flexure strength was observed with excessive deflection. According to the study, not more than 33% of the web tension reinforcement might be distributed over an effective flange width less than ln/10, including the web region, as recommended by the ACI318-14.

Seismic performance of high‐strength steel framed‐tube structures with web‐bolted double‐channel shear links

SummaryAn innovative high‐strength steel framed‐tube structure system with web‐bolted double‐channel shear links (SFTS‐WSL) is introduced herein as an alternative solution to strengthening the seismic performance and earthquake resilience of structures while maintaining the recognized advantages of conventional steel framed‐tube structures (SFTS). In the SFTS‐WSL, the shear links consist of a double‐channel section connected to the ends of spandrel beams via web‐bolted connections. A 2/3‐scale subassembly was tested under cyclic loading to investigate the seismic behavior and replaceability of the links. The results indicate that the expected ductile failure mode is characterized by the web fracture of the links. To readily replace the links, the allowable residual story drift ratio should be 0.31%. Thereafter, a simplified numerical model was developed using OpenSees, which provides accurate predictions for the hysteretic response of the SFTS‐WSL. Additionally, the superior performance of the SFTS‐WSL was benchmarked against that of the SFTS. Under the maximum considered earthquake conditions, the average base shear and inter‐story drift ratio (IDR) of the SFTS‐WSL were 18.33% and 15.13% lower than those of the SFTS, respectively. Meanwhile, a small residual IDR of well below 0.31% enabled replacement of the damaged links to achieve post‐earthquake repair.

Collapse testing of steel-concrete composite floor systems under an exterior-column-removal scenario

To evaluate the influence of openings in floor slabs on the collapse performance of steel-concrete composite floor (SCCF) systems, 2 one-third scale 1 × 2 bay SCCF substructures were fabricated and tested under static load up to final collapse in an exterior-column-removal scenario. The experimental results indicated that arch-shaped and radial cracks emerged on the top and bottom surfaces of the floor slab, respectively, for the SCCF substructure without openings in the floor slabs. Meanwhile, local buckling of the steel girders at the beam ends successively occurred during the loading procedure. As for the SCCF system with openings in the floor slabs, the crack distribution appeared more irregular, and torsion of the spandrel beam became prominent because of the discontinuity of the floor slab. The ultimate collapse resistance and the corresponding displacement of the failed column for the substructure with openings in the floor slabs were about 0.85 and 0.55 times as large as those of the substructure without openings. Owing to the existence of the openings, the tensile membrane action in the floor slab was weakened prominently, which further decreased the collapse resistance capacity of the SCCF system. After the removal of the exterior column, load was redistributed among the columns around the failed column and much more load was assigned to the adjacent exterior column. The flexural action and catenary action of the composite beams, as well as the tensile membrane action of the floor slabs worked together to resist collapse load at the large deformation stage.

Experimental and numerical study of seismic performance of high-strength steel fabricated framed-tube structures with replaceable shear links

Steel moment-resisting frames (MRFs) dissipate earthquake energy via the deformation of plastic hinges at beam-ends. To ensure that such plastic hinges are long enough to serve their purpose, their designs are based on a minimum span–depth ratio of beams as per seismic design codes. However, in steel framed-tube structures (SFTSs), deep spandrel beams having large cross-sections with flexural plastic hinges at beam-ends cannot be adequately developed, which is the reason behind SFTSs presenting lower ductility and energy dissipation capacities. To address this issue, high-strength steel (HS)-fabricated SFTSs with bolted web-connected replaceable shear links (HS-FTS-RSLs) have been proposed. In HS-FTS-RSLs, shear links are fabricated from conventional steel and placed in the middle of the deep spandrel beams to behave as ductile fuses that dissipate seismic energy, and the spandrel beams and columns use HS. In this study, a 2/3-scaled HS-FTS-RSL specimen with a very short shear link was fabricated, and cyclic loading tests were performed to investigate the hysteretic behavior of the specimen. The finite-element models (FEMs) of four full-scale sub-structures of HS-FTS-RSLs were established. Subsequently, the effects of the length of the very short bolted web-connected shear links on the cyclic performance of the HS-FTS-RSLs were investigated via nonlinear numerical analyses. The test results showed that the specimen developed the expected failure modes and showed good ductility and energy dissipation capacities. The shear link entered the plastic stage to dissipate energy, while spandrel beams and columns remained in the elastic stage under the cyclic loads. Moreover, the use of a shorter shear link was shown to yield a higher load-carrying capacity and initial elastic lateral stiffness; however, a lower ductility and energy dissipation capacity for HS-FTS-RSLs were induced. The performance of the specimen was comparable to that of the original sub-structure specimen after replacement of the shear link. The expected post-earthquake recoverability and resilience of the structure could be achieved via replacement of the shear link. The acceptable residual interstory drift, which simplifies the replacement of the bolted web-connected shear link, was 0.23%. The length ratios e/(Mp/Vp) of very short bolted web-connected shear links should not be lower than 0.53 in HS-FTS-RSLs, as per the numerical analysis results. The overstrength factor of the very short bolted web-connected shear link could reach 1.9, which is much higher than the proposed value of 1.5 for the shear link in the eccentrically braced frame in AISC 341–16.

Analysis of slab action on the seismic behavior of external RC beam-column joints

The correct evaluation of beam flexure capacity is of paramount importance in the capacity design process of reinforced concrete (RC) frame structures. Even though few experimental studies on beam-column joints have considered the presence of slab, its action as a tension flange in modifying beam-column strength hierarchy has been clearly found. This is mainly due to the increased hogging moment capacity of beams. Nevertheless, European and Italian seismic codes do not explicitly consider slab action as tension flange nor indicate proper values for effective slab width.To better understand this action, an accurate 3D finite element model has been calibrated based on the results of past experimental tests carried out on a full-scale beam-column joint. Afterwards, the calibrated model has been equipped with a portion of the adjacent spandrel beam and slab in order to evaluate their effect on the beam-column connection's behavior through numerical analyses. Alike previous studies, numerical results show that the tension flange effect of slab can significantly increase hogging (negative) moment in beams framing into beam-column joints. Additionally, it has been found that this effect is a function of slab steel amount, also highlighting the role of slab reinforcement orthogonal to the beam. Based on the above, practical indications have been provided for the evaluation of hogging moment in beams specifically concerning effective slab width to be considered in resisting moment calculations as a function of slab steel amount.

Análise e dimensionamento de vigas de seção “L” de concreto pré-moldado utilizando o Método das Bielas

Dentre os elementos presentes nas estruturas de concreto pré-moldado estão as vigas de seção “L”, largamente utilizadas no perímetro (bordas e fachadas) das edificações. A geometria tridimensional e as cargas externas aplicadas excentricamente na aba lateral fazem com que este tipo de viga esteja submetido simultaneamente a tensões normais e tensões de cisalhamento, gerando assim um complexo estado tensional. O fato das ligações com os apoios também estarem submetidas a torção torna o projeto estrutural das vigas de seção “L” um dos mais complexos entre os elementos da indústria de concreto pré-moldado por particularidades que não ocorrem nos modelos de vigas convencionais. Nesse contexto, o presente artigo tem como objetivo apresentar a análise e dimensionamento de vigas de seção “L” utilizando o Método das Bielas. Para tanto, foi desenvolvido um estudo de caso com auxílio do software CAST contemplando todas as etapas de dimensionamento e respeitando os parâmetros recomendados pela ABNT NBR 6118:2014. Por fim a metodologia apresentada foi validada através de diferentes métodos analíticos alternativos presentes na literatura internacional, demonstrando que o Método das Bielas é uma ferramenta bastante atrativa para o dimensionamento de vigas de seção “L” de concreto pré-moldado.

Behavior of RC Beams with Large Openings Subjected to Pure Torsion and Retrofitted by Steel or CFRP Plates

Torsion considered with an increasingly great importance by structural engineers. Some of the typical cases are space frames, spandrel beams, beams supporting balconies, eccentrically loaded beams, spiral staircases, horizontally curved beams, skew bridges, etc. Transverse openings, in Reinforced Concrete (RC) beams may be essential required for accommodating utility services in a building structure. Provision of an opening through a beam, however, changes its simple mode of behavior to a more complex one. Therefore, the design of such beams needs special treatment. Strengthening or retrofitting of concrete structures to compensate the presence of transverse opening not only depends on the applied material but also depends on the used technique. Carbon Fiber Reinforced Polymers (CFRP) plates, provide a more technical alternative to the traditional methods of strengthening in many cases as it gives high strength, low weight, corrosion resistance, easy and quick installation and less changes in structural geometry. An experimental test program of twenty-one RC beams with central large openings subjected to pure torsion were strengthened by using additional layers of externally bonded steel or CFRP plates with different techniques. The behaviors of the tested specimens were investigated and compared to identify the effectiveness of each method and material of strengthening to increase the torsional strength of beam with different opening sizes. The main conclusions and recommendations drawn from the study were discussed and summarized. The research shows that the methods of strengthening by using externally bonded steel strips fixed by eboxy and steel dowels and CFRP plates gave best results.

Experimental cyclic behavior of code-conforming exterior wide beam-column connections

Reinforced concrete (RC) frames with wide beams are efficient systems for resisting against lateral and gravity loads. However, there are limited experimental studies on the performance of wide beams under cyclic lateral loading. This paper presents the results of an experimental investigation on seismic behavior of RC exterior wide beam-column connections. Four 3:5 scale wide beam-column connections were tested under combined constant axial and quasi-static cyclic lateral loads. Different spandrel beam types including conventional and wide beam and three column geometries (square, rectangular and circular) were used in the specimens. The specimens all were designed in accordance with ACI 318-14 and ACI 352R-02 provisions. Special attention was given to reinforcement detailing of wide beam and spandrel beam at the joint area. The test results showed that although all specimens were code conforming and similarly designed for interaction of bending, shear and torsion, more torsional cracks developed in the cases that transverse beam was wide. The performance of all the specimens was satisfactory in terms of strength, ductility and energy dissipation capacity. It was observed that the load transfer mechanism from wide spandrel beam to column is a combination of torsion and bending. In the specimen with circular column, higher displacement ductility and lower energy dissipation were observed compared with the similar specimen containing square column. Besides, the importance of fine reinforcement detailing for wide and spandrel beam at the joint zone was confirmed by the test results.