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The Experimental Study on Steel Fiber Reinforced Concrete Thick Cap with Two and Five Piles

Author: SunChengFang
Tutor: PengShaoMin；LiJiXiang
School: Wuhan University of Technology
Course: Structural Engineering
Keywords: Steel Fiber Concrete Pile Thick Cap Failure Model Braced Arch Model
CLC: TU473.1
Type: Master's thesis
Year: 2002
Downloads: 73
Quote: 19
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Abstract

Nowadays, with the construction of large quantities of high-rise buildings, pile foundations have been more and more widely used due to their great advantages such as high bearing capacity, and being able to reduce the uneven settlement of groundsill. As an important part of pile foundations, piles cap is a connecting link between the preceding and the following and should be taken into account in designing. Therefore, making a thorough research on the mechanic performance of piles cap possesses important theoretic and engineering value.An experimental research on two-pile caps and five-pile caps is presented in this paper on the basis of experimental researches on three-pile caps and four-pile caps in Wuhan University of Technology. These experimental researches are embellished subjects for Specification for Design and Construction of Steel Fiber Reinforced Concrete Structures (CECS38: 92), and in order to provide some background information for Technical Specification of Fiber Reinforced Concrete as well.The calculating methods on piles cap are summarized in this paper. Steel fiber concrete, as a new kind of composite material, is applied in reinforced concrete pile caps in the research. 42 piles cap specimens in 1/5 ratio, in which 30 specimens are two-pile caps and 12 are five-pile caps, are tested in the experiments.The experimental results show that The effects of many factors such as volumetric ratio of steel fiber, concrete strength, slenderness ratio of steel fiber, ratio of distance and thickness, effective thickness of piles caps, reinforcement ratio and form of piles cap on bearing capacity of steel fiber concrete piles cap are analyzed.According to the crack configuration, it is showed that the first crack happens to thick piles cap when cracking load is reached, and the crack goes on extending with load increased. The crack extends slowly and some slanting cracks appear and extend to the center of column when 70% of ultimate load is reached. With being about failure, slanting cracks develop rapidly and the crack width increases until the specimen is damaged. Hence the failure of thick piles cap doesn’t have the characteristics of bending failure.According to the correlative curve of load and concrete strain of piles cap, a higher tension region (accounting for about 80% of total height) is formed on the bottom of piles cap after exceeding elastic stage, and there is smaller compressive region on the top of piles cap while compressive stain of concrete is far from ultimate compressive strain of concrete. Though the section behavior of piles cap can’t be explained by the mid-span behavior of flank of piles cap, it is valid to a certain extend that the even section assumption of average strain, which is one of important assumption for design of bending structure, can’t be applied in analysis of thick piles cap.According to the correlative curve of load and reinforcement’s stress of piles cap, there is less difference in reinforcement’s stress in the mid point of reinforcement that is along the same direction within the pile diameter, which shows these reinforcement has a uniform working stress. To the same reinforcement bar, its stress at the mid point and at the side of piles is almost the same, especially before being about failure; it is more the same, which show that the stress of reinforcement has little change along the length of reinforcement bar. Thus it can been seen that the reinforcement bars within the piles diameter can be considered to workas tension member, by which a reliable experimental basis is provided for braced arch model that is developed in the paper.By means of the description of experimental course and phenomena and analysis on the experimental result, some problems were studied in this paper hereinafter:1. Failure configuration with ratio of distance and thickness w/ho decreasing is researched in the experiment. When w/h0 is larger, ultimate bearing capacity of files cap is determined by splitting tensile failure happened to steel fiber concrete wi

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