Research On Fatigue Strength Of The Cast-in-Place Piles Foundation At River Wharf

In the river port project field, cast-in-place pile is the main bearing member oftruss-frame wharf. Fatigue is known as a main failure mode of the member material, andits research is of great significance. But the reinforced concrete is the composite bearingmember of steel and concrete, so that the bearing condition of the reinforced concrete ismore complex than that of single material. Therefore, the research on fatigue life of themember is not yet mature.Ship impact load, the main cyclic load of the wharf, is an important factor on thefatigue failure of the wharf structure material. Moreover, ship type, impact times, andimpact position change caused by water level fluctuation also have a direct influence onthe fatigue property of the material.Based on large quantities of research results, we analyzed fatigue life of thecast-in-place pile, and further derived the calculation formula of fatigue life, which issuitable for circular cross-section of the cast-in-place pile.This paper is divided into twoparts:(1) On the basis of a large number of references, we analyzed compression fatigueof the concrete and tensile fatigue of the steel in accordance with the principle of fatiguefailure; we summed up lots of test results of the plain round bars and deformed bars, andfurther selected the formula of the fatigue life suitable for our research; we studiedMiner linear fatigue cumulative failure theory and calculated load spectrum via rainflowcounting which was realized with programming, to data compression, and convert theamplitude of variation load convert to constant amplitude,it would greatly reduce thecomputational load of work,and accelerate the rate of fatigue life estimation.(2) Aimed at the Chongqing Bajiaojiao wharf project case, we analyzed forcecondition of pile with circular cross section under bending stress based on planecross-section assumption, furthermore, established the calculation formula for circularcross section of steel stress and fatigue life of cast-in-place pile. The calculation resultsof fatigue life were compared with the results of calculating by the Empirical formula inDesign and Construction Technical Standard for Cast in-Situ Pile of Harbour Engineering,andthe results of. the standard results were slightly dangerous.