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.

The U.S. Army Construction Engineering Research Laboratory, in partnership with the Composites Institute of the Society of Plastics Industry, Inc. and in support of the Army’s facility seismic rehabilitation efforts, is investigating the applicability of fiber reinforced polymer (FRP) composite materials systems to strengthen unreinforced masonry (URM) walls. The end product of the research will be the design guidance and construction specifications necessary for the Army to use these materials systems. Much of the Army’s inventory of facilities is constructed of masonry bearing walls. The masonry walls of these facilities are usually either lightly reinforced or unreinforced. This structural system has been shown to perform poorly in past earthquakes and requires upgrading to ensure safety and mission operation during and after an earthquake. This research will develop procedures for the rehabilitation and/or upgrade of masonry walls using typical advanced composite materials systems. New 4-ft by 4-ft double wythe brick wall panels with FRP composite reinforcing applied to one face were constructed and will be tested. The shear performance of different widths and thicknesses of FRP composite applied across brick mortar joints of brick triplets, three brick high prisms with the center brick offset by half an inch, was also tested. Using FRP composites for seismic rehabilitation of URM walls show great potential. Triplet tests showed consistent strengthening of the mortar joints as a function of the width of the FRP composite overlay. With multiple layers of FRP applied, the shear strength of the mortar joints increased sufficiently to cause failure to occur via brick compression failures instead of via shear failure at the mortar joints.

This paper suggests an approach to the design of glass fiber reinforced polymer dowels (GFRP) for transverse joints of highway pavement slabs. It also discusses some of the research being conducted at Iowa State University to confirm this procedure. Preliminary results from this research indicate that the GFRP dowel bars appear to be a feasible solution to the deterioration of the transverse joints of highway pavement slabs as long as the diameter of the dowel is increased, spacing decreased, or a combination of both. This adjustment is necessary in order to keep the deflection of the joint and thus the flexural stresses in the concrete equivalent to those experienced by their steel counterparts.

CFRP reinforcement sheets are proposed as reinforcement for unreinforced brick masonry subjected to out of plane loads. The investigation consisted of testing unidirectional sheet bonded carbon fiber as a reinforcing material for brick masonry prisms. Two types of brick and FRP materials were utilized in these experiments. The masonry materials exhibited high and low porosity, indicated by initial rate of absorption tests, while high and low modulus FRP materials were used. Strain gauge and full field photoelastic strain analysis was conducted to obtain a record of the strain transfer from the FRP to the masonry. From this analysis, a finite element model was then constructed to predict the mode and magnitude of failure. Results indicate that shear failure of the brick or debonding of the FRP were the general failure modes of the composite specimens tested. When comparing the results of different brick types, it is seen that, in the molded brick, the failure mode was shear failure of the brick at the end of the FRP reinforcement. In these specimens, it is clearly seen in the photoelastic strain results that strain transfer into the brick occurred in an area adjacent to the FRP. Failure in the extruded brick specimens was governed by the debonding of the FRP at the interface with the prism. It is conjectured that the viscosity of the epoxy and the porosity of the brick, characterized by initial rate of absorption tests, directly affect the bond of the composite structure and, therefore, the failure mode. Photoelastic results reveal that strain transfer does occur at high loads when the FRP remains bonded to the masonry. A linearly elastic finite element model was generated to match the experimental results and predict the failure mode for future design purposes. This model can be used for various configurations of FRP in the future.

The linear characteristics of fiber reinforced polymers (FRP) up to failure and their relatively low elastic modulus and strain at ultimate has raised concerns with structural engineers regarding their use as reinforcement for flexural members. Based on a nonlinear finite element analysis and testing of a full-scale model at the University of Manitoba, Canada, design guidelines on the use of glass and carbon fiber reinforced polymers (GFRP and CFRP) as reinforcement for bridge deck slabs are proposed. The accuracy of the nonlinear finite element model is demonstrated by comparing the predicted behavior to test results of two models. The influence of the degree of edge restraint, percentage of reinforcement of CFRP and GFRP, type of reinforcement and presence of top reinforcement on the structural behavior and mode of failure of continuous concrete bridge decks is discussed. Based on serviceability and ultimate capacity requirements, reinforcement ratios of CFRP and GFRP for typical bridge deck slabs are recommended.