دانلود رایگان مقاله انگلیسی ظرفیت باربری گروه های شمعی تحت بار خارج از مرکز عمودی - اشپرینگر 2018

Abstract

The paper deals with the problem of the bearing capacity of pile groups under vertical eccentric load. Widespread practice is to consider the achievement of the axial capacity on the outermost pile as the ultimate limit state of the pile group. However, this approach neglects the ductility of the foundation system and may be thereby overconservative. With the aim of proposing an alternative and more rational approach, a novel formulation for interaction diagrams based on theorems of limit analysis is presented and discussed. The methodology is applicable to the general case of groups of unevenly distributed, dissimilar piles. Piles’ connections to the pile cap are modeled as either hinges or rigid-plastic internal fixities. An application example to a slender structure is also provided, showing that the proposed approach can lead to significant advantages over the traditional design.

6 Conclusions

The common approach employed to assess the bearing capacity of pile groups under vertical eccentric loads assumes as ultimate strength that corresponding to the achievement of the axial capacity on the outermost pile. Such an approach is unduly conservative, since it does not exploit the ductility of the system, and may lead to oversize significantly the pile foundation.

This work suggests an alternative, more rational approach for ultimate moment-axial force interaction diagrams. The problem under examination consists of a rigid cap, clear from the ground, surmounting a group of unevenly distributed, dissimilar piles, each of them having specified values of ultimate load in compression and uplift. The piles’ connections to the cap are modeled as either hinges or rigid-plastic fixities. Under the assumption of hinged heads, closed form, exact solutions are provided for the most general case, giving rise to an interaction diagram which is always a convex domain consisting of straight lines and characterized by a point of polar symmetry. For rigid-plastic fixities, a closed-form, lower bound to the collapse load, almost coincident with the exact solution, is provided. Usually, the effect of yielding moment is negligible for slender piles, while it may be important for large diameter, squatty piles.