Pre-stressed Solid and Voided Concrete Slabs
In experimental studies on solid and voided slab bridge models, members were retrofitted
with carbon composite laminates. The tests demonstrated the feasibility of strengthening
structurally damaged concrete members with FRP laminates. The results were used
to evaluate the effectiveness of enhancing the strength and stiffness of solid and
voided slabs.
The effect of FRP laminates, bonded to the tension side of the slabs, was investigated
in terms of flexural strength, deflections, cracking behavior and failure modes.
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Underside View at Failure |
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Collapse at Ultimate Load |
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Voided Slab After Testing |
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The original designs of these slab bridge models were based on Prestressed Concrete
Institute (PCI) specifications. The slabs were loaded to their ultimate design capacity.
In many cases, the severity of the cracking and spalling of concrete required restoring
the slab section to the original shape using a standard concrete mix. The slabs
were then retrofitted with the MAS2000 Fiber Wrap System.
Preliminary analyses were made to determine the number of FRP laminates required
to ensure failure of the retrofitted slabs. Based on the analyses, the optimum number
of FRP laminates was bonded to the tensile face of each slab. After complete cure
of the adhesive, the slabs were tested again under four-point loading.
Strain gages were installed at several locations at the level of the prestressing
strands. Deflections at critical locations were measured using Linear Variable Displacement
Transducers (LVDT's).
The results of the investigation indicated that retrofitting severely damaged slabs
using FRP laminates significantly enhanced their flexural capacities. The ultimate
loads for the retrofitted solid and voided slabs were up to 178 % that of the pre-cracked
slabs. This noted the significant contribution of the FRP laminates to flexural
strength.
The retrofitted slabs exhibited larger deflection than the pre-cracked slabs at
both service and ultimate loads. However, the ultimate load of the retrofitted slabs
were equal to or greater than that of the pre-cracked slabs, indicating the significant
strengthening effect and retention of composite action by the FRP laminates.
Crack patterns for the retrofitted slabs were identical to those of the pre-cracked
slabs. Although the crack width increase was considerable, the restraining effect
of the FRP laminates allowed for a high stress transfer between the cracks, resulting
in enhanced Flexural capacity.
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