Retrofit of reinforced concrete members using advanced composite materials (2000)

Practical applications for the use of composite materials for retrofitting of reinforced concrete structural members of buildings and bridges were investigated in this research project. Carbon and glass advanced composite materials (CACM and GACM) saturated in an epoxy resin matrix were used to enhance their structural performance. The following experimental work, supported by analytical work, was carried out in the investigation: 1. Use of Advanced Composite Materials (ACM) in bridge girders to increase the service load capacity. Eleven T-shape simply supported beams, representing half scale bridge girders, were tested under repeated cyclic and monotonic load conditions. CACM laminates bonded to the soffit of the beams were used to increase the service live load carrying capacity. In some test units the laminates were cut-off whereas in others the laminates were bonded to the whole span of the beam, except at the supports. Additional GACM U-strips were applied to the sides of some beams to improve the bond performance of the longitudinal laminate and to provide additional shear stiffness and strength. The side U-strips were anchored to the beam with glass fibre filaments. One beam was subjected to one million cycles in the service load range to study the fatigue behaviour of the retrofit scheme. The fatigue test showed the excellent behaviour that can be expected from well-detailed retrofit schemes incorporating carbon and glass fibre laminates. Design recommendations are proposed based on the results obtained from the tests and from analytical work. 2. Experimental work was conducted to investigate the seismic response of ACM-strengthened/retrofitted beams that present shear and bar curtailment deficiencies. Two full-scale T-section cantilever beams were built and tested under reversed cyclic loading. One unit was tested in its "as-built" condition until a flexure-shear failure developed at the curtailment point of the negative longitudinal reinforcement. The test unit was then repaired by applying GACM laminates across the top of the-slab and to the sides of the beam in the damage region. It was again re-tested under reversed cyclic loading. The other unit was retrofitted before testing in the same manner as the previous damaged unit and then subjected to reverse cyclic loading. A seismic assessment on the prototype unit was proposed to provide a simple evaluation on the beam with deficiencies in flexural design of T-beam, shear, and longitudinal bar curtailment. The tests show that the presence of a GACM laminate can successfully correct the deficiency by relocating the negative plastic hinges to occur in the beam at the column face. To ensure the adequate seismic performance of the retrofit scheme, shear deformations in the beams must be kept to a minimum to reduce the kinking effect and potential de bonding of the ACM laminate. 3. The analytical and experimental study proposed a method for evaluating the short-term axial load strength of rectangular and square reinforced compression members confined with an ACM jacket and steel hoops. The results of this study can also be applied to the use of ACMs for column seismic retrofitting. Three 300 mm square and three 300 mm by 450 mm short reinforced columns were concentrically loaded first in tension, then in compression to failure. Either two or six layers of GACM jackets were applied to four of these columns. Two control units were tested in order to evaluate the enhancement of the axial load carrying capacity and to observe whether the ACM jackets were able to preclude premature buckling of the longitudinal reinforcement in the wrapped columns. The results clearly showed the efficiency of the jackets in enhancing the ultimate strain and strength of the columns. The jackets were also very effective in preventing longitudinal bar buckling from occurring. Designed equations in closed form were derived based on the calibration of the analytical model to provide a design of ACM-wrapped reinforced concrete column subjected to the concentric axial load.