Hannah Breton

Date of Award

8-2013

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

William Davids

Second Committee Member

Roberto Lopez-Anido

Third Committee Member

Habib Dagher

Abstract

This study examines the design and testing of FRP composite strips designed for use as mechanically fastened flexural strengthening systems for flat-slab concrete bridges. The FRP composites consisted of woven glass- or carbon-fabric core laminate layers, oriented at ±45° or 0°/90°, sandwiched between uni-directional glass outer laminate layers. Composites were manufactured by a commercial, custom composites manufacturing company. Mechanical strengths of each system were determined according to ASTM D3039 specifications.

The composites were exposed to extreme environmental conditions of freeze - thaw cycles and saltwater submersion to evaluate the environmental durability of the composites for use in bridge applications. Strength retention through single-fastener bearing tests was used to evaluate the durability performance of each system. The carbon core systems outperformed the glass core systems and were further evaluated in flexural testing.

Using mechanical fasteners to transfer shear stresses from the concrete to the FRP, steel-reinforced concrete beams designed to mimic a flat-slab concrete bridge were strengthened with FRP and tested in four-point bending to failure. All beam specimens failed due to concrete crushing within the load span and exhibited yielded reinforcing- steel behavior and bearing failure at FRP-connection locations. Beams strengthened with the ±45° oriented carbon core system (GC45) saw an average increase in yield and ultimate capacities of 41% and 47%, respectively, and decreased the average displacement at failure by 31% compared to control specimens. Beams strengthened with the 0°/90° oriented carbon core system (GC90) saw an average increase in yield and ultimate capacities of 46% and 49%, respectively, and decreased the average displacement at failure by 36% compared to control specimens. At ultimate loads, 48% and 37% of the GC45 and GC90 ultimate tensile capacity was utilized.

Both GC45 and GC90 systems are capable of increasing the flexural capacity of steel-reinforced concrete beams while providing adequate deflection warning prior to failure. Based on the results reported in this study and the relative ease of manufacturing the GC90 system compared to the GC45 system, it is recommended that the GC90 be considered for field application pending the results of fatigue performance testing and flexural testing of FRP strengthening of steel-reinforced beams, constructed with Grade 40 bar.

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