Experimental study of hybrid composite cylinders

In this study, a new type of hybrid confining device, a tubular steel lattice that is externally protected by a thin fiber reinforced polymer (FRP) skin is proposed and experimentally investigated. Two types of grid configurations were investigated. One was an axial grid and the other was a helical grid. For comparison purposes, conventional solid steel tubes, which were also protected by a FRP skin, and conventional FRP tubes were also used. Seven cylinders were prepared out of each type of confining tubes. A total of 28 cylinders were prepared, which had an inner diameter of 101.6 mm and a height of 304.8 mm. The 28 cylinders were divided into two groups. Sixteen tubes, with four tubes from each type, were directly filled with fresh concrete, creating a conventional bonded interfacial condition; the remaining twelve tubes, with three tubes from each type, were modified with a plastic liner before casting concrete, creating an “abnormal” debonded interfacial condition. Two types of experiments were conducted. One was an axial compression test and the other was a push-out test. Strain gages were used to monitor the local stress–strain distributions. Flat FRP coupon tests were conducted to determine the mechanical properties of the FRP jacket and the FRP tube. The structural performance of the hybrid composite cylinders was evaluated based on the test results.