Ant system based structural design of a roof in ultra-high performance concrete

Abstract

Objective The recently developed material ultra-high performance concrete (UHPC) has compressive strengths of over 150 MPa and a ductile behaviour. It has a higher stiffness and superior durability characteristics in comparison with ordinary concrete. The opportunity emerges to find new optimal structural topologies for this material. The ant system is the first of a family of algorithms that are nowadays all referred to with the term ant colony optimisation (ACO). It is a computational algorithm that is able to solve combinatorial optimisation problems. Its optimisation process is based on the foraging behaviour of ants. ACO is not widely explored for structural design cases. In the city of Apeldoorn a new sports centre called Omnisport is under construction. The centre consists of several halls, one of them containing a cycling and athletics track. The roof of this hall spans an elliptic area of about 120 by 100 metres. This thesis focuses on the creation and evaluation of a structural topology design algorithm, based on the concept of the ant system, for ultra-high performance concrete structures. The algorithm is applied to the design case of the Omnisport sports hall roof. Algorithm A new application for ant colony optimisation is developed in this thesis. Structures are mapped to a binary search space, which forms the link between the structure, ant colony optimisation and the finite element package DIANA. Structures are generated randomly in the first iteration of the routine by assigning material to some elements in a meshed space and leaving others empty. Elements that together form a well-performing structure are more likely to be chosen again in a next iteration. The process is based on a performance that can be any function, and is not necessarily limited to structural information only. In the case considered in the thesis, the UHPC structure is optimised towards a combination of minimum volume, mould surface, pre-stress and the availability of holes for ducts and walking bridges. The algorithm’s multi-objective optimisation process results in a structural topology. Design The algorithm has been applied to the case of the Omnisport hall roof. Based on the results, a preliminary design for the load-bearing structure of the roof in UHPC has been made. A load-bearing structure in this material is found to be possible. The proposed design consists of truss-like supporting elements for the roof. A connection strategy is proposed, member sizes and necessary pre-stress are indicatively determined. Rough cost estimates show that the design is not necessarily more expensive than the current design in steel.