| Prestressed high strength concrete (PHC) piles have the advantages of highbearing capacity reliable quality, low cost and convenience in construction, whichhave been widely used in engineering. The range of application is restricted becausethe relatively poor behavior of PHC pile in earthquake. Therefore, it is important tostudy the seismic performance of PHC piles for expanding the application. In thispaper, seismic performance of PHC pile and PHC pile-to-pile cap connections undercyclic loading are analyzed in detail by means of tests and finite element analysis. Theresearch results could provide scientific basises for their applications in seismicregions.PHC piles are tested under low-cycle loading and monotonic loading. It isindicated from the results that the failure mode is bending damage. PHC piles failsuddenly and violently with loss of most of the bearing capacity. PHC piles have aminimal energy-absorbing hysteretic behavior. The ductility and seismic performanceof the type AB pile are better than the type Apile.The results from the non-linear finite analysis for PHC pile illustrate that thebearing capacity of PHC piles increase with the increasing of effective prestress, andthe stirrup ratio has small influence on the bearing capacity.The results of finite element analysis under cyclic loading indicate that maxcurvature of PHC piles should be controlled below0.01/m used in engineering for amagnitude7earthquake, and the axial compression ratio should be within0.35.PHC pile-to-pile cap connections are tested under low cyclic loading. The testresults show that flexural bending failure occurred in all connections. There are twomain failure modes. One is tensile rupturing of prestressed bars that causes the end ofpile to be damaged seriously, and the failure mode is brittle. The other type is due tothe yielding of anchor bar, and plastic hinge appears in connection that causes the endof pile and cap to be damaged seriously, the failure mode is ductility.The nonlinear finite element models are established to analyze the effects ofvarious parameters on the behavior of normal and cut-off connections. It is observedthat axial load influences significantly on bearing capacity and ductility of the twokinds of connections. The bearing capacity and ductility of normal connection is not significantly influenced by diameter of anchor bar, number of anchored bar andembedded depth of pile, while cut-off connection is significantly influenced.The improved pile-to-pile cap connections are tested and simulated under cyclicloading. It is shown that the cap of specimens appears to be squeezing spalling. Theanchor bars lose constraint, and formed a hinge that resulted in the connection rotatingunrestricted. Therefore, the connections should be designed with enough rotatingcapacity, and make sure the cap will not be damaged by squeezing or prying due tothe rotating of pile end. |
