Keywords: wall bracing, skyscrapers, circular, numerical model, wind, seismic.

Still higher skyscrapers are natural architectural dominants in many world and European towns [1]. New findings for the constructional systems and materials are very important to reach the maximal heights because of the extreme conditions that are applied to high buildings. The main constructions are of steel and high-strength steel was also considered.

The research project described in this paper concentrates on the verification of a new bracing system for skyscrapers. The new bracing system is designed to reach the maximal height and minimal weight of the skyscraper; all important specifications (mainly maximal deflection, allowed oscillation, etc.) should be satisfied at the same time.

The requirements for the bracing system increase with height. The bracing system should not only transfer all horizontal loads to the ground but it also should eliminate horizontal deflections and the dynamic response of the structure due to wind [2,3] and seismic loads [4]. The goal of the proposed bracing system is to use the circular straining beam construction system which is loaded by mostly axial compressive forces. This type of bracing system also carries part of the vertical loads. The stiffness and the complex stability of the circular straining beam uses pre-stressed string bars (similar to the bicycle wheel).

Pilot numerical models use a height-width ratio of 7:1. It is difficult to make a model of the skyscraper directly so a smaller model has been selected with an equilateral triangle basement with an edge length equal to 10m. The height of 70m is divided to 14 floors; each floor is supported at the corners of the triangle by the continuous columns which ale compressed mainly.

To find the optimal solution for the stiffened circular bracing beam several two-dimensional models have been tested. Five of them are present and compared in the paper. The parametric study shows that the most effectual ratio between the number and weight of the spring bars and the circular straining beam cross-section can be found. The most effective model has been found to be a three-dimensional model of the tower building. The best three-dimensional numerical models are presented and compared.

After some research, the new bracing system can possibly find its place for industrial use. The models presented do not satisfy the serviceability criteria and more research is required to satisfy these.

1

A. Terranova, "Skyscrapers", White Star, Vercelly, 2003.

2

European standard EN 1993-3-1, Eurocode 3, "Design of steel structures - Part 3-1: Towers, masts and chimneys - Towers and masts", Brussels, 2006.

3

European standard EN 1991-1-4, Eurocode 1, "Actions on structures - Part 1-4: General actions - Wind loads", Brussels, 2005.

4

European standard EN 1998-1, Eurocode 8, "Design of structures for earthquake resistance - Part 1: General rules, seismic actions and rules for buildings", Brussels, 2004.

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