UC Irvine

The thesis focuses on the experimental, analytical and finite element modeling results of structural evaluation of hybrid LDPE/FRP composite beams. Two composite reinforcement details were evaluated in this investigation. In addition, results of axial tensile and compression coupon tests to characterize the short-term mechanical properties of LDPE/FRP matrix are presented and discussed. Test results of two large-scale beam specimens subjected to quasi-static four-point loading are discussed. Results obtained from the experimental tests showed that due to the hybrid nature of the beam specimens and the viscoelastic/elastoplastic behavior of the LDPE matrix, flexural stiffness of the two beams were dependent on the stress level as well as on the loading rate as expected. The change in the stiffness can also be attributed to the initial cyclic loading that was performed up to 10 kips (44.5 kN) which typically will result in a slight permanent set similar to the typical behavior of other construction materials including similar reinforced concrete members. Due to the absence of ASTM and Caltrans procedures for experimentally calculating the flexural stiffness of these hybrid beams, the flexural stiffness was calculated at different loading level. The behavior of the specimen was linear up to about 80% of the ultimate load, after which the behavior became non-linear up to the ultimate load. In all tests, no failure or cracks were observed in the plastic matrix, and the governing mode of local damage could be observed in the form of relative slippage of the FRP rebars at the ends, especially the top compressive reinforcements that resulted in stiffness degradation. The maximum load for the tests was limited by the maximum actuator stroke. An analytical model developed by Mosallam (2005) is described and verified with the experimental results. In addition finite element models were developed for different beam geometry and results are discussed. Conclusions and recommendations for future research in this area are also presented.