International Concrete Abstracts Portal

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.

In the aftermath of the 1995 Hyogo-Ken Nanbu Earthquake in which many severe failures of bridge piers occurred, numerous studies have been conducted on ways to retrofit existing RC columns and piers. As a result of this research, it has been found that continuous fiber sheet offers a feasible means of retrofitting. Consequently, several design guidelines on the use of FRP sheets for retrofitting highway, railway and subway structures have been proposed in recent years. The JSCE (Japan Society for Civil Engineers) Concrete Committee on FRP Sheet, which was setup in 1998, has been commissioned to establish a new design method for seismic retrofit of bridge columns and piers. It seeks to unify all the existing guidelines on a performance-based design concept. This paper describes mainly the new design method of shear strength and ductility of retrofitted RC structures using FRP sheet. Design equations for shear strength and ductility are also presented.

Prevalently compressed concrete columns can be transversely confined in order to obtain increase in strength and ductility. Generally, two principal methodologies of advanced confinement are used: the “Wrapping” technique which consists of wrapped concrete columns using thin carbon or glass flexible straps epoxy-bonded concrete surface; and concrete filled FRP tubes (CFFT) in which the tube is the pour form, protective jacket, confining mechanism, and shear and flexural reinforcement. The purpose of this paper is to theoretically model the stress-strain behavior of concrete confined by FRP straps or tubes, evidencing the straight dependence of s - e curve on the hoop mechanical properties of the transverse composite reinforcement. The proposed model consists of a generalization of the theory of elasticity, i.e. a step by step application of Navier classical relations which define the stress-strain laws in states of triaxial stress. The theoretical results are compared with experimental compression tests carried out on ten cylindrical concrete specimens confined with two different typologies of fiber composite tubes.