International Concrete Abstracts Portal

Upgrading often becomes a necessity due to changes in usage of buildings due to factors such as deterioration and aging, change in occupancy, or the need for installation of facilities such as air-conditioning, heating, escalators, elevators, additional skylights, or new façade structures. In a number of cases upgrading is related to changes which affect the load bearing components of the structure. Fiber reinforced polymer matrix composites provide an efficient means of both strengthening slabs for enhanced load carrying capacity and for strengthening slabs after installation of cut-outs. This paper reports on a series of tests conducted to assess the comparative efficiencies of a commercially available strip form and a fabric form of material vis-à-vis strengthening ability and ductility. It is shown that material tailoring can result in significant changes in efficiencies. The extension of this to the rehabilitation of cut-outs is also detailed and aspects of an on-going full-scale test program in that area are elucidated.

Current design methods for predicting deflections and crack widths at service load in concrete structures reinforced with steel bars may not be necessarily applicable in those reinforced with fiber reinforced polymer (FRP) bars. In this paper, methods for predicting deflections and crack widths and spacing of glass fiber reinforced polymer (GFRP) reinforced concrete beams were proposed. In order to use the effective moment of inertia for concrete beams reinforced with FRP bars, the effect of reinforcement ratios and elastic modulus of the FRP reinforcement were incorporated in Branson’s equation. This paper also presents a new equation to predict crack width. Six concrete beams reinforced with different GFRP reinforcement ratios were tested. Deflections and crack widths were measured and compared with those obtained by the proposed models. The comparison between the experimental results and those predicted was in good agreement.

This paper summarizes research findings on the use of carbon fibre reinforced polymer (CFRP) sheets for shear strengthening of pretensioned AASHTO bridge girders. The research includes an experimental program conducted at the University of Manitoba using scale models of pretensioned concrete girders in composite action with the deck slab. Seven ten meter long beams were strengthened with three different types of CFRP sheets using ten different configurations and were tested to failure at each end. The paper describes the experimental program, test results, failure mechanisms and the effectiveness of each configuration of CFRP sheets. A rational model is introduced to define the contribution of the CFRP sheets to the shear resistance in addition to the contributions provided by the stirrups and the concrete for I-shaped pretensioned concrete members. Test results are used to verify the proposed model.

FRP composite materials have mechanical properties which are beneficial and advantageous for design of bridges. The application of these FRP composite materials are currently being used for demonstration projects for repair/retrofit/ rehabilitation of existing bridges and a few for new installations. The future applications of these materials will depend upon the development of the appropriate material/product standards and performance criteria for special proprietary products. The need for coordinated research projects is outlined for the development of the necessary standards and design requirements. Only with proper documentation will the FRP composites become another material available to the construction marketplace for bridges. An outline for the required research projects is presented for the FRP composites for bridge construction.

Twenty cantilever type specimens and four beam specimens were tested to evaluate the bond behavior in reinforced concrete members confined with carbon or aramid FRP sheets. The main test variables were the vertical cover depth, the diameter and the number of longitudinal bars, and the type and the amount of FRP sheets. The test results showed that the confined specimens had higher bond strength, larger peak load slip displacement and lesser bond degradation after the peak than their unconfined prototype counterparts. Based on the test results, an equation was developed to predict the increase in bond strength due to the FRP sheet confinement. That increase was expressed similarly to that due to transverse steel reinforcement except that the elastic modulus of the FRP sheet was important but the number of longitudinal bars was not. The proposed equation was validated using results of column specimens tested in other research institutes and by cantilever and beam specimens tested by authors. It was proved that as long as the bond strength of an unconfined prototype specimen is evaluated properly, the total bond strength of confined specimens can be predicted accurately using the proposed equation although the limitations of the proposed equation still need to be clarified.