Flexural Capacity of RC Beams with Opening Strengthened using CFRP Sheet

The use of Carbon Fibre Reinforced Polymer (CFRP) in strengthening has found to be an effective material which comprises of characteristic that comply to the requirement of structural component. CFRP was selected as strengthening material because of the capability to resist the corrosion and could regain the loss capacity due to presence of opening. The opening in structural member was essential in order to provide the route for the utility pipe, air conditioning, water supply and electrical conduit. However, the presence of opening has contributed to the reduction of stiffness, increase of deflection and extension of cracking of the beams. Therefore, this research was conducted to overcome the problem where the flexural capacity and the load deflection behavior of RC beam with opening strengthened by using CFRP sheet was analyzed. A total of five beam have been casted and tested. The specimens consist of beams with different type of opening which are rectangular and circular. The size of all specimen was 200 mm width, 250 mm height and 2000 mm for total length. The size of circular opening was 150 mm in diameter while rectangular opening was 150 x 200 mm. Bi-directional CFRP sheet were applied at the opening area as strengthening material and all beams were tested until failure. All of specimen were produced with the designed using 30 mm concrete cover, 6 mm link size and 10mm main bar size. The testing of specimens comprises of cube compressive test and four-point load for beam testing in order the determine the flexural strength of RC beam. The result from this research indicated that strengthened beam with circular opening which is SBOC-BI exhibit the highest ultimate load of 71.5 kN with flexural failure as the mode of failure.

Activated Ductile CFRP NSMR Strengthening

Significant strengthening of concrete structures can be obtained when using adhesively-bonded carbon fiber-reinforced polymer (CFRP) systems. Challenges related to such strengthening methods are; however, the brittle concrete delamination failure, reduced warning, and the consequent inefficient use of the CFRP. A novel ductile near-surface mounted reinforcement (NSMR) CFRP strengthening system with a high CFRP utilization is introduced in this paper. It is hypothesized that the tailored ductile enclosure wedge (EW) end anchors, in combination with low E-modulus and high elongation adhesive, can provide significant strengthening and ductility control. Five concrete T-beams were strengthened using the novel system with a CFRP rod activation stress of approximately 980 MPa. The beam responses were compared to identical epoxy-bonded NSMR strengthened and un-strengthened beams. The linear elastic response was identical to the epoxy-bonded NSMR strengthened beam. In addition, the average deflection and yielding regimes were improved by 220% and 300% (average values), respectively, with an ultimate capacity comparable to the epoxy-bonded NSMR strengthened beam. Reproducible and predictable strengthening effect seems obtainable, where a good correlation between the results and applied theory was reached. The brittle failure modes were prevented, where concrete compression failure and frontal overload anchor failure were experienced when failure was initiated.

Strengthening of shear deficient RC deep beams using GFRP sheets and mechanical anchors

This paper presents the test results of an experimental study on shear deficient reinforced concrete (RC) deep beams strengthened with externally bonded glass fibre reinforced polymer (GFRP) sheets and mechanical anchors. A total of nine deep beams are prepared. One beam is kept as un-strengthened. Four beams are strengthened using GFRP sheets only at shear spans by varying the number of layers. The remaining four beams are strengthened using both GFRP sheets and mechanical anchors at shear spans. The shear capacity, failure mode, and deflections are studied with respect to the different strengthening techniques. The optimum enhancement in shear capacity of these beams is observed as 25.64% and 55.5% for GFRP strengthened beams and GFRP strengthened anchored beams, respectively with respect to the un-strengthened beam. Moreover, the experimental results are also compared with the results predicted from the design guidelines and models available in the literature, which shows good agreement.

Test Study on Composite Strengthened Beam with CFRP Board, Angle Steel and External Prestressed Steel Strand

The composite strengthening beam combined with a variety of reinforcement technology, complementary advantages.In order to study the mechanical behavior of T-beam strengthened with CFRP board, external angle steel and external prestressed steel strand, six reinforced test beams were fabricated to compare and analyze the structural characteristics of bending stiffness, crack development and bearing capacity. The research shows that the beam strengthened by CFRP board, external angle steel and external prestressed steel strand has good working performance. The rebound force of the bending deformation of the external angle steel and the upward force of the external prestressed steel strand reliably anchor the carbon fiber board, avoiding the bond failure and slippage of the CFRP.The three kinds of reinforcing materials work together and complement each other, which can give full play to their respective strength. The composite strengthened beam with CFRP board, external angle steel and external prestressed steel strand can greatly improve the cracking load, structural stiffness and ultimate bearing capacity of the original beam, and the reinforcement effect is optima.

Toughness of Timber Beams Strengthened with Jute Fibers

This research involves investigating the toughness behavior of timber beams strengthened by jute fibers with various forms of strengthening. Ten timber specimens with dimensions (70×100×1000) mm are divided into four groups and loaded under a third point loading. The experimental program was carried out to investigate shear and flexural strengthening effects on toughness, toughness indices, ultimate loads, and the mid-span deflection of the tested beams. One beam as a control beam (un-strengthened beam), four specimens are wrapped in U technique in single and double layers along the whole length of the beam in full and strips wrapping technique, three specimens are wrapped in full technique along the whole length of the beam in full and strips wrapping technique, three timber specimens wrapped in flexural strengthening technique with two, four, and six layers of jute fibers. The results show that jute fibers strengthening increases the toughness ratios of timber beams by about (175%-320%), (190%-401%), and (106%-240%) for U, full, and flexural strengthening techniques, respectively, at the ultimate loads compared with the control beam. Furthermore, it is found that the highest toughness ratio is when the beam is wrapped in full strengthening technique.

Numerical Investigation on Dynamic Response of RC T-Beams Strengthened with CFRP under Impact Loading

To precisely evaluate the retrofitting effectiveness of Carbon Fiber Reinforced Plastic (CFRP) sheets on the impact response of reinforced concrete (RC) T-beams, a non-linear finite element model was developed to simulate the structural response of T-beams with CFRP under impact loads. The numerical model was firstly verified by comparing the numerical simulation results with the experimental data, i.e., impact force, reaction force, and mid-span displacement. The strengthening effect of CFRP was analyzed from the section damage evaluation. Then the impact force, mid-span displacement, and failure mode of CFRP-strengthened RC T-beams were studied in comparison with those of un-strengthened T-beams. In addition, the influence of the impact resistance of T-beams strengthened with FRP was investigated in terms of CFRP strengthening mode, CFRP strengthening sizes, CFRP layers and FRP material types. The numerical simulation results indicate that the overall stiffness of the T-beams was improved significantly due to external CFRP strips. Compared with the un-strengthened beam, the maximum mid-span displacement of the CFRP-strengthened beam was reduced by 7.9%. Additionally, the sectional damage factors of the whole span of the CFRP-strengthened beam were reduced to less than 0.3, indicating that the impact resistance of the T-beams was effectively enhanced.

Experimental study on shear behavior of hollow slab beam strengthened with pasting steel plates

PurposeConsidering the “size effect” and the properties degradation of building materials on the strengthened engineering, in this paper, the technology of pasting steel plate was adopted to shear strengthen a 16 m prestressed concrete hollow slab, which had serviced 20 years in cold regions. The shear properties of shear strengthen beams are analyzed.Design/methodology/approachShear loading test of the shear strengthened beam and the contrast beam was conducted. Then the mechanical characteristics, failure mechanism, the mechanical response and shear capacity of shear strengthened beam and contrast beam had been discussed.FindingsThe failure mode of shear strengthened beam and contrast beam was shear compression failure, and the bond failure between concrete and prestressed reinforcement happened in both of test beams. The shear strengthening method of pasting steel plate can effectively improve the mechanical response for the shear strengthened beam. Compared with the contrast beam, the cracking load and failure shear capacity for the shear strengthened beam can be effectively increased by 12.2 and 27.6%, respectively.Originality/valueThe research results can be a reference for the detection and evaluation of shear strengthened bridges, which are strengthened by pasting steel plate. Engineers can refer to the shear strengthening method in this paper to strengthen the existing bridge, which can guarantee the safety of shear strengthened bridges.

Flexural Response of R.C. Tee Beams Strengthened with Ferrocement

Ferrocement is the composite of Ferro (Iron) and cement (cement mortar). Ferrocement can be considered as a type of thin-walled reinforced concrete construction in which small-diameter wire meshes are used uniformly throughout the cross-section instead of discretely placed reinforcing bars and in which Portland cement mortar is used instead of concrete. In this investigation, 23 reinforced concrete Tee beams were tested for their flexural strength. Three sets of Tee beams were predamaged up to 60, 70, and 80 percent of the ultimate load level of control beams respectively. Beams pre-damaged up to 60% are designated as W1 and F1. Similarly 70% as W2 and F2 and 80% as W3 and F3. Two beams are undamaged, but they are strengthened are designated UW and UF. UW, W1, W2 and W3 set (3 beams in each set) of beams were strengthened with three faces of the web using ferrocement. UF, F1, F2 and F3 set (3 beams in each set) of beams were strengthened with three side faces of the web + bottom of the flange using ferrocement. After proper curing, all the strengthened beam specimens were tested for their flexural strength. The results were compared with corresponding control beams and presented. From the experimental investigation, it is seen that the ultimate Flexural strength capacity of Reinforced concrete Tee beams strengthened with ferrocement is significantly increased.

Shear Behavior of RC Deep Beam Strengthened by V-Shaped External Rods

This research investigated the shear strengthening technique of Reinforced Concrete (RC) deep beams using a V-shaped external rod system. Shear behavior, the stress in an external rod, and the shear capacity at the diagonal shear failure of a strengthened beam were focused mainly. Experimental tests of control and two strengthened beams were carried out to observe the effect of the external rod on shear behavior of RC deep beam. A theoretical approach to compute the stress in the external rod and the nominal strength of the strengthened beam in the diagonal shear failure were examined based on the experimental test results and verified using Finite Element Method (FEM) in ABAQUS. The computed nominal shear strength of the strengthened beam was 10% higher than the experimental test. The strengthening technique shifted the brittle shear failure to ductile shear failure and improved the performance of RC deep beam.