Rehabilitation Of Concrete Structures Research Articles

Flexural Strengthening of Prestressed Bridge Slabs with FRP Systems

Fiber reinforced polymer (FRP) materials offer great potential for cost effective retrofitting of concrete structures. In response for the growing need for strengthening and rehabilitation of concrete structures and bridges, an experimental program was conducted to investigate the feasibility of using different strengthening techniques as well as different types of FRP for strengthening prestressed concrete members. Half scale models of a prestressed concrete bridge were constructed and tested to failure. The test specimens consisted of one simple span and two overhanging cantilevers. Each specimen was tested three times using a different load location in each case. The applicability of a nonlinear finite element analysis of post-tensioned bridge slabs strengthened with near surface mounted FRP reinforcement is enumerated.

Materials Considerations in FRP Rehabilitation of Concrete Structures

The use of fiber reinforced polymer (FRP) composites for the seismic retrofit of columns and piers, flexural strengthening of beams and girders, and strengthening of slabs has been fairly well established on a structural basis. However, aspects related to materials selection and use, design detailing, fracture and failure mechanisms, and durability are still not well understood. The functional efficiency of the rehabilitated structure is largely dependent on materials-related issues, which are highlighted in this paper, emphasizing effects pertaining to constituent materials, interfaces, and overall systems response. Major implications of processing and fabrication schemes are highlighted focusing on materials use efficiency, potential of defect formation, and effects on durability. Examples of the importance of detailing are shown, and design guidelines pertaining to materials are discussed.

Evaluation of the tensile strength of cement-based advanced composite wrapped specimens

The use of fiber-reinforced polymer (FRP) composite wrap is increasingly being used for repair and rehabilitation of concrete structures. In recent years, most of the mechanical properties of these materials have been studied; however, data on their tensile characteristics is still lacking. This paper presents tensile strength data for: (1) cement-based composites wrapped with FRP sheets, (2) FRP sheets without resin matrix, and (3) FRP sheets embedded in epoxy resin matrix. The tensile strength values were evaluated by using a simple hydraulic tensile technique that produces a uniform stress distribution throughout the specimen, thus, minimizing eccentricity and gripping effects. The tensile strength is derived from the hydraulic pressure and sample geometry. Three types of fiber-composite sheets, including two carbon and one glass, were applied with a two-part epoxy resin system. The tensile strength of the carbon-fiber-wrapped cement composites were in the range of 78 to 132 MPa. The glass-fiber composites were in the range of 40 to 55 MPa, while the unwrapped cement specimens were under 7 MPa. The results show a significant difference in tensile strength properties with the application of an epoxy–resin system. The tensile strength values are presented by using Weibull statistics. A rule-of-mixtures model is used to predict the tensile strength of the FRP composites. Fractography is used to locate the failure initiating defects and to identify the failure modes associated with the different composite wrap systems.

Strengthening of Reinforced Concrete Beams with Externally Bonded Composite Laminates

A particularly challenging problem confronting engineers in the revival of U.S. infrastructure is the rehabilitation of concrete structures. This paper summarizes the results of experimental and analytical studies concerning the flexural strengthening of reinforced concrete beams by the external bonding of high-strength, lightweight fiber reinforced plastic (FRP) plates to the tension face of the beam. Twenty-four large-scale beams were tested experimentally to evaluate the strength enhancement provided by the FRP plates. An inelastic section analysis procedure was developed that accurately predicts the load displacement response of the retrofitted beams. A nonlinear finite element method analysis was also conducted that corroborates the results from the experimental study and inelastic section analysis.

An experimental study of the anchorage length of carbon fibre composite plates used to strengthen reinforced concrete beams

Concrete structures deteriorate for various reasons and upgrading has been achieved for over 20 years by bonding steel plates using epoxy resins. Disadvantages of this method include transporting, handling and installing heavy plates and corrosion of the plates. The use of composite materials overcomes these problems and provides equally satisfactory solutions. The rehabilitation of concrete structures represents a large demand for efficient strengthening methods and composite materials are well suited to this application. It is now necessary to understand more about the factors that are important in the design of composite plate bonding, such as the influence of the plate anchorage length and additional plate end anchorage. Four point bending and cantilever loading are used to show that the ultimate capacities and failure modes of reinforced concrete beams, externally strengthened with bonded composite plates, are dependent on the shear span/depth ratio. Strengthened members are found to fail by separation of the concrete cover from the internal rebars throughout the whole of one shear span under low shear span/depth ratios, while a thinner concrete layer is separated at higher ratios. Peeling of the plate end is thought to occur under low shear span/depth ratios. The end of the bonded plate in the failed shear span experiences strain increases relatively soon after yield of the internal steel when the shear span/depth ratio is low, but the plate ends are less sensitive to yield under higher ratios, indicating the lower shear transferred into the concrete via the adhesive at the plate ends. Ultimate bending moments are found to reach an upper limit with increasing shear span/depth ratio in the range of ratios studied. Adhesive shear stresses are of greatest magnitude at the ends of the plate under low shear span/depth ratios.

An experimental study of the failure modes of reinforced concrete beams strengthened with prestressed carbon composite plates

Concrete structures deteriorate for various reasons and upgrading has been achieved for over 20 years by bonding steel plates using epoxy resins. Disadvantages of this method include transporting, handling and installing heavy plates and corrosion of the plates. The use of composite materials overcomes these problems and provides equally satisfactory solutions. The rehabilitation of concrete structures represents a large demand for efficient strengthening methods and composite materials are well suited to this application. Further advantages are gained by prestressing the plate before bonding to the concrete. The benefits of external prestressing using polymeric composite materials have been investigated only relatively recently and further work in this field is needed in order to understand the behaviour of members prestressed with composite materials, thereby allowing full advantage to be gained from the ease with which composites can be handled and applied, and from their excellent duarability. This artcile is concerned specifically with the failure modes of reinforced concrete beams prestressed in this way. Reinforced concrete beams of 1.0 and 4.5 m lengths were tested in four point bending after strengthening them with externally bonded carbon fibre reinforced polymer plates. The plates were bonded without prestress and with prestress levels ranging from 25% to 50% of the plate strength. The non-prestressed beams failed by separation of the plate from the beam, associated with concrete fracture in the cover to the internal rebars, while most of the prestressed beams failed by plate fracture. The plate prestress prevented cracking of the adhesive layer, a phenomenon associated with shear cracking in the concrete. The bonded plates failed progressively by longitudinal splitting and interlaminar fracture, rather than suddenly without warning. Under a shear span-beam depth ratio of 3.40, plate separation was initiated by a shear displacement in the concrete: a high prestress was required to enable the ultimate plate strain to be reached before the shear displacement reached its critical value.

Rehabilitation of concrete structures

Report of an International Conference held by RILEM and organized by the CSIRO Division of Building. Construction and Engineering, Melbourne, and the Australian Concrete Repairs Association, Melbourne, in cooperation with RILEM Technical Committee TC 124 ‘Repair Strategies for Concrete Structures Damaged by Steel Corrosion’.

International conference on rehabilitation of concrete structures: Melbourne, Australia, August 31 – September 2, 1992

International conference on rehabilitation of concrete structures: Melbourne, Australia, August 31 – September 2, 1992