Proceedings of the 25 th CANCAM London, Ontario, Canada, May 31 – June 4, 2014 VIBRATION CONTROL OF TALL BUILDINGS USING AERODYNAMIC OPTIMIZATION Ahmed Elshaer Civil and Environmental Department Western University London, Ontario, Canada aelshae@uwo.ca Girma Bitsuamlak Civil and Environmental Department Western University London, Ontario, Canada gbitsuam@uwo.ca Ashraf El-Damatty Civil and Environmental Department Western University London, Ontario, Canada damatty@uwo.ca ABSTRACT Traditionally the shape and orientation of tall buildings are driven by architectural considerations, functional requirements, and site limitations rather than aerodynamic considerations. As a result, they are bluff bodies characterized by high wind-structure interaction induced motion. Vibration control is becoming an important aspect of tall building design in order to keep the building’s motions within comfortable limits. In this study, an optimization procedure is presented for minimizing the wind-induced vibrations of tall buildings by aerodynamic mitigation of corners. Computational Fluid dynamics (CFD) models are used to simulate the aerodynamics of wind around a building. An optimization problem is presented to demonstrate the developed procedure. KEYWORDS: Tall Buildings, vibration, Optimization, CFD, Wind-induced responses INTRODUCTION Tall buildings attract people and businesses because of their elegant shape and being considered landmarks. However, this appeal could be affected due to vibrations resulting from lateral loads such as wind and earthquake. For super-tall buildings, wind-induced motion will be even more significant. This will be even more significant in the recent generation of tall buildings owing to being elaborate and slender. Tall buildings can be susceptible to excessive motion during wind events that can cause occupant discomfort and reduce the overall appeal of the structure [1]. Furthermore, keeping the motions of a tall building within comfortable limits could sometimes govern the design rather than the strength requirements. Improving the aerodynamics of a building through corner modification can result in a significant reduction in the lateral load and limit vibrations caused by the wind leading to a more economic and comfortable tall building. One of the most significant vibrations that buildings experience is the across-wind motion resulting from wind vortex shedding. Some cross-sections such as lens shape are more prone to across-wind buffeting because their streamlined shape causes them to act somewhat like a vertical airfoil. This results in generating high across-wind force variations for relatively small changes in wind angle of attack caused by turbulence. Shape changes that make them less like an airfoil can be effective in this situation [2]. LITERATURE REVIEW The aerodynamic performance improvement for tall buildings using shape modifications has prompted many scholars to study the relationship between the aerodynamic characteristics of a structure and the resulting wind–induced responses. These include Dagnew [3], Kawai [4], Irwin and Breukelman [5], Tamura and Miyagi [6], Bitsuamlak et al. [7], Elshaer et al. [8], and Kareem et al. [9]. Rather than the classical sharp edged corner of most buildings, building corners can be chamfered, rounded, recessioned, fined, or any other non-uniform shapes. Tse et al. [10] investigated the effect of chamfered and recessed corners on tall building responses. Kwok et al. [11][12] studied the effects of chamfered corners and slotted corners of prismatic tall buildings on the wind-induced responses. The latter reported that chamfering 10% of the building’s width may result in a 30% to 40% reduction in both alongwind and crosswind induced motions. Also, the corners on “Taipei 101” were stepped in order to reduce across-wind responses and drag, resulting in 25% reduction in base moment [2]. Most of these studies primarily discuss the advantage of group of modifications compared to others. However, they fall short in advising what type of mitigations provide a “near optimal” solution rather than an “ad-hoc” solution that may or may not be “optimal”. OPTIMIZATION PROCEDURE The Aerodynamic Shape Optimization (ASO) for tall buildings’ corners procedure starts by choosing the objective function and the design variables. The objective function is an aerodynamic characteristic that is intended to be minimized or maximized. The design variables are geometric parameters controlling the shape of the corner. Different combinations of design variables will form different candidates in the optimization problem. Those candidates were ranked according to their fitness (achieving of the objective function). Values of the objective function for different candidates