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Seismic performance of pretensioned spun high strength concrete piles Taksinrote, Worapol

Abstract

Pretensioned spun high strength concrete piles manufactured by Industrials Concrete Products (ICP) Berhad, Malaysia were studied in this experimental program. The objective was to investigate the seismic performance of the piles under varying axial compression and lateral load reversals. Ten test specimens, ranging in length from 1 m to 4 m, were cut from 250 mm diameter piles. Rather than attempting to simulate the complex loading on a real pile, idealized boundary conditions were used in the test: one end was a fixed support, and the free end of the pile was subjected to a lateral load. Using instrumentation and electronic equipment, a wide variety of data was recorded during the test, and subsequently employed for analysis. Aspects of the test specimens that were investigated include loaddisplacement characteristics, failure mechanisms, crack patterns, crack widths, strain limits, and curvature capacities. While some diagonal cracking was observed in the very short specimens, the behavior of all specimens was dominated by flexure. The flexural failure mechanisms for the piles involved either concrete crushing in compression or fracture of the prestressing strands in tension. Both failure modes were very brittle. The experiments indicated that the observed compression strain limit is about 0.5 %, and the tension strain limit is between 1.5 % and 2.0 %. It is interesting to note that the tension strain limit determined from the current pile tests are considerably smaller than what was determined from bare bar tests of the prestressing strands. An analytical model called Response-2000 was used to predict the bending moment-curvature relationships and curvature capacities of the specimens. The model was also used to study the shear response of the specimens. The most important result from the current experimental study is the relationship between the curvature capacity of the piles and the applied axial compression. Predictions of the curvature capacity using Response-2000 and the measured strain limits were found to be in good agreement with the test observations. Thus Response-2000 and these strain limits can be used to predict the curvature capacity of other sizes of ICP pretensioned spun high strength concrete piles.

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