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Anchorages Effects on CFRP-to-concrete Bond Strength:

In this study, the effect of the number of applied anchorages, arrangement, and types of anchorage on stress distribution between the CFRP strip and the concrete surface were studied. Two different anchoraging arrangements with two types of anchorage and three different numbers of anchorages are tested on 12 test specimens by keeping the concrete compressive strength and the CFRP strip bond length constant. In addition, two test specimens without any anchorages, totalling 14 specimens, were tested. It is observed that the anchorages had an impact on the stress distribution of the CFRP strips and increased the strength and the stiffness of the specimens. The specimens did not fail by peeling of the CFRP strips, instead they were ruptured at the point where the anchorages were situated.

Improving Shear Capacity and Ductility of Shear-deficient RC Beams Using CFRP Strips

The results of an experimental investigation are presented in this article for improving the shear capacity and ductility of reinforced concrete beams by using CFRP strips. The purpose of this study is to obtain ductile flexural behavior for shear-deficient reinforced concrete beams. The experimental program consisted of 10 T cross-sectioned half scale simply supported beam specimens, seven of which were constructed with deficient shear reinforcement and the remaining three without any shear reinforcement. One beam was used as a reference and nine beams were strengthened using U-shaped CFRP strips with or without fan type anchorage. Three different CFRP strip spacing such as sf = 125 mm, 150 mm, and 200 mm were used. The effect of anchorages that were used at the ends of the strips on shear strength and behavior of the strengthened specimens was investigated. CFRP strips without anchorages improved the shear strength, but no flexural behavior was observed. specimens failed with brittle shear failure due to peeling of CFRP strip from RC beam surfaces. specimens with deficient shear reinforcement that were strengthened with anchored CFRP strips showed improved shear strength and ductile flexural behavior was observed. Similar behaviors were observed for specimens even without any shear reinforcement. When the CFRP strip strains of the specimens with anchorages and without anchorages were compared, maximum strains at anchored strips were approximately 56% larger than that of without anchorages.

Response of reinforced concrete beams with clamps applied externally: an experimental study

In recent years, there has been an increased interest in strengthening and repairing existing concrete structures, and this process requires a vast monetary investment. Therefore, today there is a need to find an appropriate and economical method to strengthen and to repair existing concrete structures. The purpose of this study is to perform experiments to understand the behavior of beams under flexure by attaching external clamps, which will behave like stirrups to improve their shear strength. This current paper reports on the study of 13 beams with differing levels of shear reinforcement deficiency. These beams were strengthened by external clamps and then experiments were performed on two groups in which the ratio of the shear span to the effective height of the beam is equal to 4.5 and 3.3 (M/Vd=a/d). Experimental results showed that this strengthening method is effective and the specimens’ strength, rigidity and ductility were improved. Clamps controlled any shear cracks and they also helped to improve ductile flexural behavior of the members.

Effect of Corrosion on Shear Behavior of Reinforced Engineered Cementitious Composite Beams

The objective of this study was to evaluate the effect of corrosion level on shear behavior of engineered cementitious composite (ECC) beams. Reinforced normal concrete (R-NC) specimens with compressive strength equal to the ECC specimens were also used for control purposes. Ten reinforced concrete beams (five ECC and five NC) with dimensions of 150 x 220 x 1400 mm (5.91 x 8.66 x 55.12 in.) were manufactured for the study. Using accelerated corrosion through the application of a constant current of 1 ampere, four levels of corrosion were established at 5%, 10%, 15%, and 20% of mass loss of the reinforcing bars. To ensure the highest probability of shear failure mode, all beams were tested under a four-point loading system with a shear span-effective depth ratio of 2.5. General structural behavior, strength, stiffness, failure mode, and energy absorption capacities of ECC and R-NC beams subjected to different corrosion levels were evaluated and compared. Experimental results showed a high correlation between calculated mass loss and measured mass loss in reinforcing bars due to accelerated corrosion. Compared to NC, ECC beams exhibited significantly higher strength, stiffness, and energy absorption capacity, along with superior performance in terms of the restriction of damage caused due to corrosion. The increase in corrosion level negatively influenced the structural behavior of the ECC beams tested.

Tests of high-performance fiber-reinforced concrete beams with different shear span-to-depth ratios and main longitudinal reinforcement

Test results of 12 reinforced concrete (RC) beams having three shear span to effective depth ratios and two main longitudinal reinforcement amounts are reported. Six of the test specimens were produced with engineered cementitious composites (ECCs) and another corresponding six with ultra high-strength fiber-reinforced cementitious composite (RMC). The shear span to effective depth ratios of test specimens were selected low to investigate the shear performance of ECCs and RMC characterized by ultra high ductility-moderate strength and ultra high strength-moderate ductility, respectively. Shear-carrying capacity and ductility ratios of large-scale reinforced ECC and RMC beams were compared and interpreted for different shear spans, energy absorption capacities, and stiffnesses. The experimental results showed that for the three different shear spans, the RMC beams had higher shear capacity results than the ECC beams. Using both concrete types markedly restricted shear cracking and led to flexural failure. Overall findings suggest that RMC beams have higher shear capacity and yield stiffness than ECC beams, while ECC beams have a higher deflection ductility ratio and energy absorption capacity.

Comparison of Seismic Performance of RC Frames Strengthened with Four Different Techniques

The purpose of this experimental study is to compare the strengthening techniques that are applied to non ductile low rise RC frames under seismic loads. In this study, 1/3 scale, one-bay, one-storey, nonductile RC frames with masonry infill walls were strengthened using four different techniques and are tested experimentally under reversed cyclic lateral loading. The four frames were constructed with masonry infill walls and three were strengthened with a mesh reinforced mortar layer, CFRP and steel strips wrapping, respectively. The remaining one without any extra strengthening was tested as a reference. A final specimen of the experimental program was strengthened with RC infill instead of masonry infill. Strength, stiffness, storey drift, ductility and failure modes of the specimens were evaluated and compared experimentally. Each strengthening technique proved to have different types of effectiveness on the lateral strength and stiffness of non ductile RC frames. Different strengthening techniques changed the ultimate lateral strengths and stiffnesses within the ranges of 53% to 381% and 82% to 601%, respectively.

Retrofitting of shear damaged RC beams using diagonal CFRP strips

The results of an experimental investigation for the retrofitting of shear-damaged RC beams using diagonal CFRP strips are presented in this article. The experimental study consisted of seven shear-deficient, T-cross-sectioned, ½-scale, simply supported beam specimens. One beam is used as the reference specimen. The remaining six specimens are tested in two stages. At the first stage, specimens are shear damaged severely and the shear-damaged RC beams are retrofitted using diagonal CFRP strips by wrapping them around the beam in the shape of a ‘U’. Then, retrofitted beams are tested to failure. In this study, 50 mm wide CFRP strips are used with three different spacings such as sf = 125, 150, and 200 mm. One of the two specimens with the same spacing is tested with anchorages at the ends of the CFRP strips. Although the strips without anchorages improved the shear strength of the shear-damaged beam, they could not prevent the shear failure. Shear-damaged specimens that are retrofitted with anchoraged CFRP strips showed to improve the shear strength, and ductile flexural behavior was observed in them. When the CFRP strains of the strips with and without anchorages are compared, maximum strains at anchoraged strips are approximately 1.55 times larger than those without anchorages. Calculated shear load carrying capacity of the specimens, according to ACI 440 and FIB regulations, are approximately 2% larger than the experimental one.

Nonlinear three-dimensional FE analyses of RC beams retrofitted using externally bonded CFRP sheets with or without anchorages

Abstract In this study, behavior of reinforced concrete (RC) beams retrofitted using carbon fiber-reinforced polymer (CFRP) strips and anchorages is investigated by performing nonlinear finite-element (FE) analyses. The main aim of the study is testing the applicability of current FE techniques in the field of CFRP-retrofitted concrete elements. In the study, effect of CFRP strip width, presence of fan-type anchorages and CFRP patches were considered as main variables. In the study, eight RC beams with varying cross sectional properties along beam length are simulated. The simulated beams were tested in a former experimental study. The nonlinear FE analyses are conducted using the ANSYS FE software. The results obtained from the former experimental study are compared with the FE analyses results. From the results, it is observed that when properly modeled, FE simulations are efficient tools to estimate the nonlinear behavior of CFRP-retrofitted RC beams and similar structural elements.

Nonlinear finite element analysis of masonry wall strengthened with CFRP strips

In many experimental studies, it has been proved that unreinforced masonry (URM) brick walls have high strength against lateral forces acting in plane. However, out-of-plane strength of URM brick walls against lateral forces has found to be quite low. According to the experiences that were obtained from the major earthquakes, the low out-of-plane performance of URM brick walls resulted in excessive loss of human lives during an earthquake, hence the strengthening of URM brick walls with CFRP strips has been appeared to be a very important subject. However, very limited literature has been found. Especially, the data obtained from experimental studies must be increased for the true understanding of the behavior of strengthened brick walls under out-of-plane lateral forces. However, in most cases, this procedure required large number of expensive experiments. At this stage, numerical analysis can be an appropriate choice, thus in this paper a finite element model is presented for modeling URM brick walls that are strengthened with CFRP strips. The numerical results are compared with the experimental ones and consistent results are obtained from the finite element model. General purpose finite element analysis software ANSYS is used throughout this study. Contact elements are used along the masonry wall–CFRP strip interfaces for the investigation of the stress distribution and load – strain behavior.

Behavior of RC Square Column Strengthening with CFRP Strips Subjected to Low Velocity Lateral Impact Loading

Reinforced concrete (RC) square columns are vulnerable to sudden dynamic impact loadings such as vehicle impact to bridge column or air blast shock due to blast effects. In this experimental study, RC square columns strengthened with CFRP strip subjected to sudden low-velocity lateral impact loading were investigated. A free falling weight test setup was used to apply the impact loading to RC square columns. The test specimens were manufactured with square cross sections with one-third geometric scale. In scope of the study, four test specimens were manufactured and tested. The main variables considered in the study were the application point of impact loading and CFRP strip spacing. A 9.0 kg mass was allowed to free fall from a height of 1.0 m to apply the impact loading on the columns. During the impact tests, acceleration, impact force, column midpoint displacement, and CFRP strip strains measurements were taken. The general behavior of test specimens, collapse mechanisms, acceleration, displacement, impact load, and strain–time relationships were interpreted and the load–displacement relationships were obtained. The data from the experimental study was used to investigate the effect of variables on the impact performances of RC columns.