Experimental analysis of shear deficient reinforced concrete beams strengthened by glass fiber strip composites and mechanical stitches

Ceyhun Aksoylu 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.40 No.2

This study was conducted to present a new technique to increase the capacity of reinforced concrete beams with insufficient shear reinforcement. Four beam specimens at ½ scale were produced. One of these beams was used for reference, while the other three were strengthened using different methods. The strengthening methods were performed using Mechanical stitches (MS), Glass fiber reinforced polymer (GFRP), and a hybrid of the two (GFRP and MS). In the experiments, the reference beam (E0), the MS-strengthened beam (E1), the GFRP-strengthened beam (E2), and the GFRP+MS-strengthened (E3) beam were tested under vertical load. Following the experiment, vertical load-bearing capacity, ductility value, initial stiffness value, and energy dissipation capacity were calculated for each beam. Afterward, extensive micro and macro damage analyses were performed. In the experiment, the E0 specimen resulted in a failure mode with direct shear damage. The strengthened E1 and E2 beams showed a typical bending behavior. The vertical load-bearing capacity of the E1 and E2 beams increased by 16.8% and 18.1%, respectively, compared to E0. The load-bearing capacity of the newly proposed technique, the hybrid E3 beam, was increased by 19.2%, although it failed with shear damage. Thus, this study has clearly demonstrated that beams with insufficient shear reinforcement can be strengthened using single-layer GFRP (E2). Considering its cost-efficiency compared to other composite materials, it has been suggested that GFRP should be used more widely in the market. In addition, it is reccommended that future studies can use the proposed E1 strengthening for beams weak against shear. The experiments revealed the most appropriate strengthening method for shear beams to be E1>E2>E3 in terms of performance/cost. Finally, the results suggest that the proposed hybrid strengthening (E3) can be turned to a ductile behavior through further experiments with different configurations.

Shear strengthening of reinforced concrete beams with minimum CFRP and GFRP strips using different wrapping technics without anchoring application

Ceyhun Aksoylu 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.44 No.6

In this study, the performance of shear deficient reinforced concrete (RC) beams with rectangular cross-sections, which were externally bonded reinforced (EBR) with high strength CFRP and GFRP strips composite along shear spans, has been experimentally and analytically investigated under vertical load. In the study, the minimum CFRP and GFRP strips width over spacing were considered. The shear beam with turned end to a bending beam was investigated by applying different composite strips. Therefore various arising in each of strength, ductility, rigidity, and energy dissipation capacity were obtained. A total of 12 small-scaled experimental programs have been performed. Beam dimensions have been taken as 100x150x1000 mm. Four beams have been tested as unstrengthened samples. This paper focuses on the effect of minimum CFRP and GFRP strip width on behaviours of RC beams shear-strengthened with full-wrapping, U-wrapping, and U-wrapping+longitudinal bonding strips. Strengthened beams showed significant increments for flexural ductility, energy dissipation, and inelastic performance. The full wrapping strips applied against shear failure have increased the load-carrying capacity of samples 53%- 63% interval rate. Although full wrapping is the best strengthening choice, the U-wrapping and U-wrapping+longitudinal strips of both CFRP and GFRP bonding increased the shear capacity by 53%~75% compared to the S2 sample. In terms of ductility, the best result has been obtained by the type of strengthening where the S5 beam was completely GFRP wrapped. The experimental results were also compared with the analytically given by ACI440.2R-17, TBEC-2019 and FIB-2001. Especially in U-wrapped beams, the estimation of FIB was determined to be 81%. The estimates of the other codes are far from meeting the experimental results; therefore, essential improvements should be applied to the codes, especially regarding CFRP and GFRP deformation and approaches for longitudinal strip connections. According to the test results, it is suggested that GFRP, which is at least as effective but cheaper than CFRP, may be preferred for strengthening applications.

Numerical and analytical investigation of parameters influencing the behavior of shear beams strengthened by CFRP wrapping

Ceyhun Aksoylu,Yasin Onuralp Özkılıç,Şakir Yazman,Mohammed Alsdudi,Lokman Gemi,Musa Hakan Arslan 국제구조공학회 2023 Steel and Composite Structures, An International J Vol.47 No.2

In this study, a parametric study was performed considering material properties of concrete, material properties of steel, the number of longitudinal reinforcement (reinforcement ratio), CFRP ply orientations, a number of layers as variables by using ABAQUS. Firstly, the parameters used in the Hashin failure criteria were verified using four coupon tests of CFRP. Secondly, the numerical models of the beams strengthened by CFRP were verified using five experimental data. Finally, eighty numerical models and eighty analytic calculations were developed to investigate the effects of the aforementioned variables. The results revealed that in the case of using fibrous polymer to prevent shear failure, the variables related to reinforced concrete significantly affected the behavior of specimens, whereas the variables related to CFRP composite have a slight effect on the behavior of the specimens. As a result of numerical analysis, while the increase in the longitudinal tensile and compression reinforcement, load bearing capacity increases between 23.6%-70.7% and 5.6%-12.2%, respectively. Increase in compressive strength (29 MPa to 35 MPa) leads to a slight increase in the load-carrying capacity of the specimens between 4.6% and 7.2%. However, the decrease in the compressive strength (29 MPa to 20 MPa) significantly affected (between 6.4% and 8.1% decrease observed) the behavior of the specimens. As the yield strength increases or decreases, the capacity of specimens increase approximately 27.1% or decrease 12.1%. The effects of CFRP ply orientation results have been obtained as a negligible well approximately 3.7% difference. An increasing number of CFRP layers leads to almost no effect (approximately 2.8%) on the behavior of the specimen. Finally, according to the numerical analysis, the ductility values obtained between 4.0 and 6.9 indicate that the beams have sufficient ductility capacity.

Investigation of Precast New Diagonal Concrete Panels in Strengthened the Infilled Reinforced Concrete Frames

Ceyhun Aksoylu,Rifat Sezer 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.1

Major part of the structural stock in Turkey doesn’t have sufficient endurance, rigidity and ductility against possible large earthquakes. Strengthening of structures against earthquakes always appears on the agenda and structures are being strengthened by using different techniques. In this context, cast in place reinforced concrete shear walls is a highly effective and reliable method for improving the system behavior. However, construction work takes long time in this method, so the structure is required to be emptied before the practice. For this reason, it is required to develop the strengthening methods which facilitates lives of people and which is economic and effective in terms of structure. The principle of the technique recommended in this study is to convert plastered hollow brick walls of the structure to shear walls equivalent to reinforced concretes (RC) by strengthening them with high-strength precast new diagonal concrete panels. For this purpose, a reinforced concrete frame, which is 1/3 scaled, low-strengthened against earthquake, has two-story and single span unreinforced brick infilling wall, has been produced with failures frequently seen especially in concrete buildings of our country as reference sample. Moreover, strengthening three reinforced concrete infilled frame wall having same features with reference sample by new diagonal concrete panels which are precast, high strengths in different shapes used for the first time in the literature, their behaviors under reversible-repeatable horizontal loading simulating earthquake effect have been tested. Results of the experiment have been compared with the analytic study and it has been observed that applied technique has increased the energy dissipation capacity of test elements and improved the earthquake behaviors.

Optimum amount of CFRP for strengthening shear deficient reinforced concrete beams

Lokman Gemi,Mohammed Alsdudi,Ceyhun Aksoylu,Şakir Yazman,Yasin Onuralp Özkılıç,Musa Hakan Arslan 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.43 No.6

The behavior of shear deficient under-balanced reinforced concrete beams with rectangular cross-sections, which were externally strengthened with CFRP composite along shear spans, was experimentally investigated under vertical load. One of the specimens represents a reference beam without CFRP strengthening and the other specimens have different width/strip spacing ratios (wf/sf). The optimum strip in terms of wf/sf, which will bring the beam behavior to the ideal level in terms of strength and ductility, was determined according to the regulations. When the wf/sf ratio exceeds 0.55, the behavior of the beam shifted from shear failure to bending failure. However, it has been observed that the wf/sf ratio should be increased up to 0.82 in order for the beam to reach sufficient shear reserve value according to the codes. It is also observed that the direction and weight of the CFRP composite are one of the most critical factors and 240 gr/m2 CFRP strips experienced sudden ruptures in the shear span after the cracking of the concrete. It is considered as a deficiency that the empirical shear capacity formulas given for the beams reinforced with CFRP in the regulations do not take into account both direction and weight of CFRP composites.

Numerical evaluation of effects of shear span, stirrup spacing and angle of stirrup on reinforced concrete beam behaviour

Yasin Onuralp Özkılıç,Ceyhun Aksoylu,Musa Hakan Arslan 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.79 No.3

Shear and bending strength of reinforced concrete beams depend on many parameters. It is extremely important to take the necessary precautions in terms of shear in order for the beams to reach their bending capacity. For this reason, it is necessary to determine the effective parameters especially on shear capacity in beams. However, the actual capacity calculation is quite difficult according to regulations that are very conservative in terms of design. Therefore, many experimental studies have been conducted on the shear capacity of the beams. However, this situation is not meaningful in terms of both time and cost, since many experiments will be required to interpret the beam shear behavior, which depends on many parameters. For this reason, the use of advanced software whose verification is performed according to experimental data has become widespread. In this study, a numerical study was carried out on 36 different beam models using the ABAQUS finite element program to examine the effect of the shear span/effective depth (av/d) ratio, stirrup spacing (sw) and the angle of stirrup (α). The results showed that as the av/d increase, the behavior of a shear deficient beam tends to typical bending behavior. Although the effect of stirrup angle on shear capacity is quite high, stirrup angles of 30° and 60° give very similar results. The effect of stirrup spacing is quite limited at relatively high av/d. Stirrups with 90° do not contribute to ductility in beams with high av/d.

Effect of the GFRP wrapping on the shear and bending Behavior of RC beams with GFRP encasement

Yasin Onuralp Özkılıç,Lokman Gemi,Emrah Madenci,Ceyhun Aksoylu,İlker Kalkan 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.45 No.2

The need for establishing the contribution of pultruded FRP encasements and additional FRP wraps around these encasements to the shear strength and load-deflection behavior of reinforced concrete beams is the main motivation of the present study. This paper primarily focuses on the effect of additional wrapping around the composite beam on the flexural and shear behavior of the pultruded GFRP (Glass Fiber Reinforced Polymer) beams infilled with reinforced concrete, taking into account different types of failure according to av/H ratio (arch action, shear-tension, shear-compression and pure bending). For this purpose, nine hybrid beams with variable shear span-to-depth ratio (av/H) were tested. Hybrid beams with 500 mm, 1000 mm, and 1500 mm lengths and cross-sections of 150x100 mm and 100x100 mm were tested under three-point and four-point loading. Based on the testing load-displacement relationship, ductility ratio, energy dissipation capacity of the beams were evaluated with comprehensive macro damage analysis on pultruded GFRP profile and GFRP wrapping. The GFRP wraps were established to have a major contribution to the composite beam ductility (90-125%) and strength (40-75%) in all ranges of beam behavior (shear-dominated or dominated by the coupling of shear and flexure). The composite beams with wraps were showns to reach ductilities and strength values of their counterparts with much greater beam depth.

Lateral torsional buckling of doubly-symmetric steel cellular I-Beams

Mehmet Fethi Ertenli,Erdal Erdal,Alper Buyukkaragoz,Ilker Kalkan,Ceyhun Aksoylu,Yasin Onuralp Özkılıç 국제구조공학회 2023 Steel and Composite Structures, An International J Vol.46 No.5

The absence of an important portion of the web plate in steel beams with multiple circular perforations, cellular beams, causes the web plate to undergo distortions prior to and during lateral torsional buckling (LTB). The conventional LTB equations in the codes and literature underestimate the buckling moments of cellular beams due to web distortions. The present study is an attempt to develop analytical methods for estimating the elastic buckling moments of cellular beams. The proposed methods rely on the reductions in the torsional and warping rigidities of the beams due to web distortions and the reductions in the weak-axis bending and torsional rigidities due to the presence of web openings. To test the accuracy of the analytical estimates from proposed solutions, a total of 114 finite element analyses were conducted for six different standard IPEO sections and varying unbraced lengths within the elastic limits. These analyses clearly indicated that the LTB solutions in the AISC 360- 16 and AS4100:2020 codes overestimate the buckling loads of cellular beams within elastic limits, particularly at shorter span lengths. The LDB solutions in the literature and the Eurocode 3 LTB solution, on the other hand, provided conservative buckling moment estimates along the entire range of elastic buckling.

Lignocellulosic Sugar Palm Fibre-Reinforced Thermoplastic Composites: Mechanical, Thermal and Dynamic Mechanical Properties

M. R. M. Asyraf,K. Z. Hazrati,Desmond Daniel Chin Vui Sheng,M. Rafdah,W. Ashraf,Emrah Madenci,Yasin Onuralp Özkılıç,Ceyhun Aksoylu,N. M. Nurazzi 한국섬유공학회 2023 Fibers and polymers Vol.24 No.8

Lignocellulosic fibre obtained from forest biomass has various advantages, especially in product development due to its abundance and ability in mechanical properties. Sugar palm fibre (SPF) has emerged as promising fibre reinforcement in composite industries to form high-strength and stiffness biocomposites. Due to environmental concerns such as air pollution and global warming, the global community has worked together to replace conventional plastic with biomass waste like SPF in various product types. Traditionally, sugar palm by-products are useful for various traditional uses such as traditional foods, gula kabung, and alcohol, while SPF is applied as rope, brooms and brushes. Numerous researchers have taken initiatives to implement SPF in the packaging sector and transport uses such as lifeguard boats. Some works have proved that SPF-reinforced polymer composites exhibit high mechanical strength and remarkable properties in thermal degradations. However, like other lignocellulosic fibres, the SPF exhibits high water absorption properties, which causes problems binding with thermoplastic matrix, reducing its performance. Based on the literature survey, no review has been carried out on discussing the mechanical and thermal behaviour of SPF-reinforced thermoplastic composites. Hence, the current review aims to establish concise and collective findings from previous works on SPF/thermoplastic composites to provide a good source of literature for further research on this topic.