International Concrete Abstracts Portal

Four 6.5 m long two span continuous beams were tested to investigate the feasibility of using FRP grids as shear reinforcement. The beams were longitudinally reinforced with equal amounts of CFRP reinforcement while transversely two beams were reinforced with steel stirrups and two with CFRP grids. The two spans of each beam had identical amount and disposition of reinforcement, and were symmetrically loaded with a point load at the center of each span. For the beams with steel stirrups, the so-called Av/s = 2.0 mm while for the ones with CFRP grids the equivalent quantity was 1.75 mm. The elastic modulus of the grid was half the elastic modulus of the steel. The beams were monotonically loaded to destruction and they all failed in flexure. Despite their lower shear reinforcement ratio, the beams with the CFRP grid performed as well as those with the steel stirrups. They actually failed at 10% higher load than the beams with steel stirrups. Strain values of up to 0.4% were measured in the grids. Recognizing the practical convenience of grid shear reinforcement over custom manufacturing of stirrups, and considering their satisfactory performance, as observed in the present testing program, the use of FRP grids as shear reinforcement is indeed feasible.

A closed-form high-order analytical approach for the analysis of concrete beams strengthened with externally bonded fiber-reinforced polymer (FRP) stripes, on the tensile faces of the RC beam in positive and negative bending moment regions, is presented. The model is based on equilibrium and compatibility requirements in and between all constituents of the strengthened beam, i.e. the concrete beam, the FRP stripe, the adhesive layers and at the interfaces between the various parts. The governing equations of the mathematical model of the strengthened beam are derived and an analytically closed-form solution is determined. A numerical example of a typical continuous reinforced concrete beam strengthened with externally bonded FRP stripes is discussed with emphasis on the shear and transverse normal (peeling) stress concentrations at the adhesive-concrete and adhesive-FRP interfaces at the edges of the FRP stripes. Results concerning the edge stresses at three characteristic locations that have been determined using the closed-form high-order model are discussed. In the sequel a summary, conclusions, and recommendations for the design of the strengthened beam are presented.

The objective of this paper is to develop the effective retrofitting method applicable to reinforced concrete columns connected with monolithically cast wing walls by CFRP (Carbon Fiber Reinforced Plastics) sheet jacketing. To clarify the improving mechanism of deformation capacity under earthquake loading by applying CFRP sheet jacketing, eight column specimens with or without wing walls were tested under reversals of horizontal load mainly in the large deformation zone. Test results show that CFRP sheet jacketing methods proposed in this paper are useful for retrofitting works of existing apartment buildings designed in accordance with the old building code. Based on the test evidence, a proposal for estimating the ultimate strength and the deformation capacity of columns with wing walls strengthened by CFRP sheet jacketing are presented.

In seismic retrofit of existing buildings, there is a great demand that retrofitting work can be done while continuing operations in the building. In order not to disrupt the normal operations in the building, strict limitations on the amount of noise, vibration, dust, and on the use of fire need to be adopted. Since some evaluation methods of retrofitting effects for wrapped RC independent columns with continuous fiber sheets which has an advantage in construction work were proposed, application of this method are dramatically increasing in Japan. However, these evaluation methods can not be applied to the columns with side walls and columns with finishing mortar. When this retrofitting method are applied to these types of columns, finishing is removed and side wall concrete at the boundary portion to the columns is also removed to treat the column with side walls as an independent rectangular column. Then development of the newly effective retrofitting method is necessary to meet the above-mentioned strong demand. This paper reports the test results on the retrofitting effect of RC columns with finishing mortar without removal of finishing and RC columns with side walls without removal of the side wall concrete at the boundary portion. Test results indicates the feasibility of the seismic retrofit of RC columns by fiber sheet wrapping without removal of finishing and side wall concrete.

Wrapping of columns by means of FRP (fiber reinforced polymer) reinforcement enhances the structural behaviour of concrete columns considerably. At the Magnel Laboratory for Concrete Research a test programme is set-up to evaluate some specific problems in the modelling of FRP confined concrete, i.e. effective circumferential FRP failure strain and effect of increasing confining action. Parameters studied are FRP type, bonded or unbonded wrapping application, column shape and strengthening lay-out. Both wrapped cylinders and wrapped columns are investigated. An analytical verification of the test results is performed according to different models. From the test results obtained so far, the efficiency of this strengthening technique has been demonstrated, both in terms of structural performance and ease-of-application. Quality of the application (voids, protrusions, etc.) and the wrapping concept (bonded or unbonded, partial wrapping, etc.) influence the strengthening effect.