• Structural Engineering and Mechanics
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• v.56 no.6
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• pp.899-916
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• 2015

Upgrading or strengthening of existing reinforced concrete (RC) infrastructure is an emerging demand nowadays. Near Surface Mounted (NSM) technique is very promising approach for flexural strengthening of RC members. However, premature failure such as concrete cover separation failure have been a main concern in utilizing this technique. In this study, U-wrap end anchorage with carbon fiber reinforced polymer (CFRP) fabrics is proposed to eliminate the concrete cover separation failure. Experimental programs were conducted to the consequence of U-wrap end anchorage on the flexurally strengthened RC beams with NSM-steel. A total of eight RC rectangular beam specimens were tested. One specimen was kept unstrengthened as a reference; three specimens were strengthened with NSM-steel bars and the remaining four specimens were strengthened with NSM-steel bars and U-wrap end anchorage using CFRP fabrics. A 3D non-linear finite element model (FEM) was developed to simulate the flexural response of the tested specimens. It is revealed that NSM-steel (with and without end-anchors) significantly improved the flexural strength; moreover decreased deflection and strains compared with reference specimen. Furthermore, NSM-steel with end anchorage strengthened specimens revealed the greater flexural strength and improve failure modes (premature to flexure) compared with the NSM-steel without end anchorage specimens. The results also ensured that the U-wrap end anchorage completely eliminate the concrete cover separation failure.

• Journal of the Korea Concrete Institute
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• v.12 no.5
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• pp.35-46
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• 2000

In this paper, an analytical model is proposed to predict the shear strenth of RC beams strengthened by FRP. This predictional model is composed of two basic models-the upper bound theorem for shear failure (shear tension or shear compression criteria) and a truss model based on the lower bound theorem for diagonal tension creteria. Also, a simple flexural theory based on USD is used to explain flexural failure. The major cause of destruction of RC beams shear strengthened by FRP does not lie in FRP fracture but in the loss of load capacity incurred by rip-off failure of shear strengthening material. Since interfacial shear stree between base concrete and the FRP is a major variable in rip-off failure mode, it is carefully analyzed to derive the shear strengthening effect of FRP. The ultimate shear strength and failure mode of RC beams, using different strengthening methods, estimated in this predictional model is then compared with the result derived from destruction experiment of RC beams shear strengthened using FRP. To verify the accuracy and consistency of the analysis, the estimated results using the predictional model are compared with various other experimental results and data from previous publications. The result of this comparative analysis showed that the estimates from the predictional model are in consistency with the experimental results. Therefore, the proposed shear strength predictional model is found to predict with relative accuracy the shear strength and failure mode of RC beams shear strengthened by FRP regardless of strengthening method variable.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.463-468
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• 2002

For the Externally bonded FRP systems, flexural design method is studied focusing on the reinforcement layer of the carbon fiber sheets. As the FRP layer is added, strengthening rate increases, but not proportionally as the FRP layer increases. This is reflected in the design formula appropriately by the bond cofficients from the added layers. As the number of FRP layer increases, the stress reinforcement and FRP sheet decreases, and it generally corresponds to the decrease rate of member flexural strength. This phenomenon is appearing indentically in a design formula and experimental result. The rate of $M_{test}$ and $M_n$ is 1.19 and it is estimated as safety factor which is the reduction factor, ${\psi}_f = 0.85$.

• Journal of the Korean Ceramic Society
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• v.23 no.6
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• pp.59-65
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• 1986

Flexural strength fracture toughness and strengthening mechanisms of cordierite ceramics reinforced by SiC whiskers up to 40vol% were investigated. The specimens were hot pressed at Ar atmosphere. The porosity increased with the SiC whisker content. Flexural strength and single edge notch beam fracture toughness were measured up to 1,000$^{\circ}C$. Extrapolating to zero porosity the reinforced composites exhibited in-creasings in flexural strength and fracture toughness with the SiC whisker content. The composites were strengthened mainly by load transfer crack impediment and partially by crack deflection mechanisms. Impurities played an important role in determining the mechanical properties of the composites.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.469-474
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• 2002

Recently fiber sheets are used for strengthening the damaged concrete structures due to its many advantages such as its durability, non-corrosive nature, low weight, ease of application, cost saving, control of crack propagation, strength to thickness ratio, high tensile strength, serviceability and aesthetic. However, the lack of analytical procedures for predicting the nominal moment capacity by the fiber sheet reinforcement leads to difficulties in the effective process of decisions of the factors in the strengthening procedure. In this work, flexural strengthening effects by fiber sheets bonded on soffit and web of the member are theoretically studied for the reinforced concrete T beam. The analytical solutions are compared with experimental results of several references to verify the proposed approach.

• Structural Engineering and Mechanics
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• v.21 no.3
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• pp.333-350
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• 2005

This paper presents results of an experimental study to evaluate a new retrofit technique for strengthening shear deficient short concrete beams and columns. In this technique a mortar jacket reinforced with expanded steel meshes is used for retrofitting. Twelve short reinforced concrete specimens, including eight retrofitted ones, were tested. Six specimens were tested under a constant compressive axial force of 15% of column axial load capacity based on original concrete gross section, $A_g$, and the concrete compressive strength, ${f_c}^{\prime}$. Main variables were the spacing of ties in original specimens and the volume fraction of expanded metal in jackets. Original specimens failed before reaching their nominal calculated flexural strength, $M_n$, and had very poor ductility. Strengthened specimens reached their nominal flexural strength and had a ductility capacity factor of up to 8 for the beams and up to 5.5 for the columns. Based on the test results, it can be concluded that expanded steel meshes can be used effectively to strengthen shear deficient concrete members.

• Journal of the Korea institute for structural maintenance and inspection
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• v.5 no.1
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• pp.228-236
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• 2001

When RC beams are strengthened for flexure with steel plate, reinforced member has initial strain due to the dead load and is subject to partial damage. Strain of steel strengthening is zero at initial state. The effect of strengthening flexural member might be influenced by the quantity of initial strain. In this study, when He beams are strengthened for flexure with steel plate, its behavior is experimentally compared for the reinforcement efficiency of members due to the existence of different levels of initial strain. It is confirmed that reinforcement efficiency varies depending on the difference of initial strain.

• Structural Engineering and Mechanics
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• v.70 no.3
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• pp.303-310
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• 2019

Any revision of seismic codes usually demands a higher capacity from structural members, making existing structures unsafe particularly from strength considerations. Retrofitting of capacity deficient members is very suitable for tackling such situations. This paper presents an experimental study on different retrofitting measures adopted for strengthening a series of reinforced concrete (RC) beams. Four identical RC beam specimens were casted, out of which three specimens were strengthened by different schemes (viz., bolted hot rolled flat, bolted cold-formed steel channel, and carbon fibre reinforced polymer (CFRP) laminate, respectively) on their tension face and tested under four-point monotonic loading. This study focuses on the investigation of the flexural behaviour of these retrofitted beams, observed in terms of strength and stiffness. It was concluded that all retrofitting measures improved the structural performance of these beams. However, the cost involved with each strengthening mode was proportional to the improvement in the performance achieved.

• Structural Engineering and Mechanics
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• v.69 no.2
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• pp.163-175
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• 2019

Structural deterioration arises due to aging, environmental effects, deficiencies during design and construction phase, and overloading. Experimental and numerical investigations are carried out in this study to evaluate the performance of control and flexural deficient reinforced concrete (RC) beams under monotonic loading. Three levels of flexural deficiency are considered in this study. After confirming load carrying capacities of control and flexural deficient beams, the flexural deficient RC beams are strengthened with carbon fibre reinforced polymer (CFRP) fabric. CFRP strengthened RC beams are tested under monotonic loading and compared with the performance of control specimen. Further, non-linear finite element analyses are also carried out to evaluate the flexural performance of control, deficient and CFRP strengthened flexural deficient RC beams. There is good correlation between results of experimental and numerical investigations. Numerical approach presented in this study can be adopted for assessing the adequacy of CFRP retrofit measure.

• Structural Engineering and Mechanics
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• v.70 no.1
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• pp.67-80
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• 2019

Strengthening with near surface mounted carbon fibre reinforced polymers (NSM-CFRP) is a strengthening technique that have been used for several decades to increase the load carrying capacity of reinforced concrete members. In Iraq, many concrete buildings and bridges were subjected to a wide range of damage as a result of the last war and many other events. Accordingly, there is a progressive increase in the strengthening of concrete structures, bridges in particular, by using CFRP strengthening techniques. Near-surface mounted carbon fibre polymer has been recently proved as a powerful strengthening technique in which the CFRP strips are sufficiently protected against external environmental conditions especially the high-temperature rates in Iraq. However, this technique has not been examined yet under repeated loading conditions such as traffic loads on bridge girders. The main objective of this research was to investigate the effectiveness of NSM-CFRP strips in reinforced concrete beams under repeated loads. Different parameters such as the number of strips, groove size, and two types of bonding materials (epoxy resin and cement-based adhesive) were considered. Fifteen NSM-CFRP strengthened beams were tested under concentrated monotonic and repeated loadings. Three beams were non-strengthened as reference specimens while the remaining were strengthened with NSM-CFRP strips and divided into three groups. Each group comprises two beams tested under monotonic loads and used as control for those tested under repeated loads in the same group. The experimental results are discussed in terms of load-deflection behavior up to failure, ductility factor, cumulative energy absorption, number of cycles to failure, and the mode of failure. The test results proved that strengthening with NSM-CFRP strips increased both the flexural strength and stiffness of the tested beams. An increase in load carrying capacity was obtained in a range of (1.47 to 4.49) times that for the non-strengthened specimens. Also, the increase in total area of CFRPs showed a slight increase in flexural capacity of (1.02) times the value of the control strengthened one tested under repeated loading. Increasing the total area of CFRP strips resulted in a reduction in ductility factor reached to (0.71) while the cumulative energy absorption increased by (1.22) times the values of the strengthened reference specimens tested under repeated loading. Moreover, the replacement of epoxy resin with cement-based adhesive as a bonding material exhibited higher ductility than specimen with epoxy resin tested under monotonic and repeated loading.