Dissertation

Design optimization of reinforced concrete building frameworks

Moharrami, Hamid

1993

Overview

The design of reinforced concrete frameworks is a complex task. To produce an economic design of a reinforced concrete structure in traditional design practise requires the services of a competent structural engineer with years of experience in the field. With the current progress in computer technology, the development of computer-based design tools to aid the task of engineers is now possible and, indeed, needed in this era of strict time deadlines. This study addresses the problem of design of reinforced concrete building frameworks. The design problem is formulated in a relatively detailed manner with the width, depth and longitudinal reinforcement of members taken as the design variables, consideration of architectural and construction requirements, and account for the performance conditions imposed by the ACI 318-89 code of practice for reinforced concrete structures. The design is cast as an optimization problem involving the minimization of the overall cost of two-dimensional planar frameworks while satisfying all performance constraints concerning member strength, beam deflection and structure side-sway. The cost of the framework is considered to be the summed cost of concrete, reinforcement and formwork. Various load conditions at the service load level are considered for the beam deflection and structure-sway constraints, and several other load conditions at the ultimate load level are considered for the member strength constraints. Size limits are imposed on the dimensions of beams and columns to reflect architectural and construction requirements. As well, limitations are placed on the amount of reinforcement in accordance with the ACI 318-89 design code. To account for the slenderness effects of columns, both P- $\\Delta$analysis and an approximate 'moment magnification factor' method are separately considered. The design problem is formulated as a standard optimization problem by using first-order Taylor series expansions to express the performance constraints as explicit functions of the design variables. Sensitivities (derivatives) of the constraints with respect to the design variables are derived for all performance constraints, for both member responses and member capacities. Then, an efficient optimality criteria resizing technique based on the Kuhn-Tucker optimality conditions at the optimum point is formulated and implemented in an iterative design procedure. Several design examples, including a 23-story 4-bay frame under multiple load conditions, are solved and the features and capabilities of the design procedure are discussed. Overall, the design output meets the requirements of the ACI 318-89 design code and complies with the principles of good design practice.

• Publisher: ProQuest Dissertations & Theses
• Subject: Civil engineering
• ISBN: 9780315845848, 0315845848