Abstract

The paper presents the Mixed-Integer Non-linear Programming (MINLP) approach to the synthesis of trusses. The solution of continuous/discrete non-convex and non-linear optimization problems is discussed with respect to the simultaneous topology, shape and discrete sizing optimization of trusses. A truss MINLP superstructure of different topology and design alternatives has been generated, and a special MINLP model formulation for trusses has been developed. In the optimization model, a mass objective function of the structure has been defined and subjected to design, load and dimensioning constraints. The MINLP problems are solved using the Modified Outer-Approximation/Equality-Relaxation (OA/ER) algorithm. Multi-level MINLP strategies are introduced to accelerate the convergence of the algorithm. The Modified Two-Phase and the Sequential Two-Phase MINLP strategies are proposed in order to solve highly combinatorial topology, shape and discrete sizing optimization problems. The importance of local buckling constraints on topology optimization is also discussed. Some simple numerical examples are shown at the end of the paper to demonstrate the suitability and efficiency of the proposed method.

Highlights

  • Optimization of different processes and systems has become an important factor in every aspect of human life, especially in the fields of science, industry and business.Numerous attempts have been made in the past in order to improve the efficiency and economic viability of structures in structural engineering

  • The present paper introduces the structural synthesis of trusses performed by the Mixed-Integer Non-linear Programming (MINLP) optimization approach

  • The Proposed MINLP Strategies for Truss Synthesis. Both the TP and Linked Two-Phase (LTP) multi-level MINLP strategies were applied to truss synthesis problems

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Summary

Introduction

Optimization of different processes and systems has become an important factor in every aspect of human life, especially in the fields of science, industry and business. At the end of the previous millennium, many efficient optimization techniques were developed for solving the discrete/continuous topology, shape and discrete dimension optimization. These techniques were developed for the solution of real engineering structures with discrete/standard dimensions. The present paper discusses the simultaneous topology, shape and discrete/standard dimension optimization of trusses using the Mixed-Integer Non-linear Programming (MINLP) approach. The general MINLP model formulation for truss structures is presented. This discrete/continuous non-convex and non-linear optimization problem is proposed to be solved by the Modified Outer-Approximation/Equality-Relaxation (OA/ER) algorithm by Kravanja and Grossmann [4]. The suitability and efficiency of the proposed method are shown through some numerical examples

Optimization of Trusses
Topology Optimization
Discrete Sizing Optimization
Simultaneous Topology and Discrete Dimension Optimization
MINLP Approach to Truss Synthesis
Development of the MINLP Model Formulation for Truss Superstructures
The General MINLP Problem Formulation
The MINLP Model Formulation for Truss Superstructures
Definition of Structural Elements
Variables
Objective Function
Structural Analysis Constraints
Logical Constraints
Solution of the MINLP Truss Synthesis Problem
Multi-Level MINLP Strategies
The Proposed MINLP Strategies for Truss Synthesis
Numerical Example
Input Data
The Superstructure and Topological Alternatives
The MINLP Syntheses
Discussion of Results
Conclusions
Methods
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