Fatigue reistant foundation system

Abstract

A fatigue resistant gravity based spread footing under heavy multi-axial cyclical loading of a wind tower having a central vertical pedestal, a substantially horizontal continuous bottom support slab with a stiffened perimeter, a plurality of radial reinforcing ribs extending radially outwardly from the pedestal and a three-dimensional network 500 of post-tensioning elements that keep the structural elements under heavy multi-axial post compression with a specific eccentricity that is intended to reduces stress amplitudes and deflections and allows the foundation to have a desirable combination of high stiffness and superior fatigue resistance. The foundation design reduces the weight and volume of materials used, reduces cost, and improves heat dissipation conditions during construction by having a small ratio of concrete mass to surface area thus eliminating the risk of thermal cracking due to heat of hydration.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]This invention relates to a method for building fatigue resistant foundations for supporting columns, towers and structures under heavy cyclical loads such as wind turbines towers for onshore and offshore installations.[0003]The proposed foundation system will be used specifically for the Multi-Megawatt class wind turbines. Several wind turbine manufacturers have successfully developed large wind turbines with rated power ranging from 1.5 to 10 MW. Several wind turbine manufacturers are planning mass production of large multi Megawatt turbines for onshore and offshore installations. The installation of the E-126 model turbine by Enercon with a 7 MW rated power required a xx meter diameter circular foundation with 1,400 cubic meters of concrete and xx tons of rebar. The installation of the 5M turbine by RePower with a 5 MW rated power required a 23 meter diameter circular foundation with 1,300 cubic meters of concrete an...

AI Technical Summary

Benefits of technology

[0014]It is desired to have cost-effective foundation system that can reduce construction materials and labor for large wind turbines. The wind turbine foundations can then be built to the standards of the Fatigue Resistant Foundation System which uses concrete rib stiffeners, with a cast in place slab on grade element and a central pedestal to build an integral foundation that will behave structurally as a monolithic foundation structure. Other concrete components can be included such as secondary and perimeter beams, diaphragms, or intermediate stiffeners and rib stiffened or flat slab sections. The foundation system relies on the use of many prefabricated components including rebar meshes and cages, pedestal cage assembly, pre cut post-tensioning strands, preassembled strand bundles, pre-cut post-tensioning duct sections and prefabricated concrete forms.

[0015]The present invention pertains to a fatigue resistant foundation for wind towers which comprises a plurality of components, namely a central vertical pedestal, a substantially horizontal continuous bottom support slab with stiffened perimeter, a plurality of radial reinforcing ribs extending radially outwardly from the pedestal and a three-dimensional network of vertical, horizontal, diagonal, radial and circumferential post-tensioning elements embedded in the footing that keeps all the structural elements under heavy multi-axial post compression, reduces stress amplitudes and deflections and allows the foundation to have a desirable combination of high stiffness and superior fatigue resistant while improving heat dissipation conditions during construction by having a small ratio of concrete mass to surface area thus eliminating the risk of thermal cracking due to heat of hydration.

Problems solved by technology

When concrete is cast in massive sections for wind tower foundations, temperature can reach high levels and the risk of thermal cracking becomes very high unless cooling techniques or special admixtures are applied.

Thermal cracking often compromises the structural integrity of the foundations.

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