Civil Engineering

 

Date of this Version

Spring 5-4-2012

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Civil Engineering, Under the Supervision of Professors Maher Tadros and George Morcous. Lincoln, Nebraska: May, 2012

Copyright (c) 20012 Ibrahim Lotfy

Abstract

Wind energy is one of the most commercially developed and quickly evolving renewable energy technologies worldwide. Wind turbines are commonly supported on tubular steel towers. As the turbines are growing and the towers are elevating, an increase in structural strength and stiffness is required to withstand the applied forces. Recent studies established concrete as a more economic and durable alternative to steel especially when the tower height exceed 240ft. Presently, concrete towers are not common due to their perceived heavy weight and assembly complexity. One of the systems that have been mentioned in the literature consists of precast rings that are post-tensioned together and assembled at the turbines site. While the tubular shape is compatible with wind variation and behavior, its construction process can be burdensome, demanding and expensive. In this thesis, an effort to reduce the construction cost is proposed by developing a precast prestressed concrete system that consists of vertical columns and horizontal panels. Composed of simple precast elements, this system is easy to transport, assemble and erect, plus it will reduce the post-tensioning costs. The proposed system has a triangular shaped cross-section that consists of three columns at each corner of the triangle connected together with commonly used precast concrete wall panels. The tower has a tapered profile to reduce the area subjected to wind thus lower the total weight and applied moment. It will also enhance the dynamic response of the tower and improve its overall stability. This thesis presents analysis and design of 240ft and 320ft high supporting systems under dead, wind and seismic loading. A comparison between the proposed system and current concrete and steel systems is also presented in terms of behavior, ease of construction and cost.

Advisors: Maher Tadros and George Morcous.

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