Optimization of outrigger locations in tall buildings subjected to wind loads

© 2010 Yau Ken ChungThe study of the response of tall buildings to wind has become more critical with the increase of super tall buildings in major cities around the world. Outrigger-braced tall building is considered as one of the most popular and efficient tall building design because they are easier to build, save on costs and provide massive lateral stiffness. Most importantly, outrigger-braced structures can strengthen a building without disturbing its aesthetic appearance and this is a significant advantage over other lateral load resisting systems. Therefore this thesis focuses on the optimum design of multi-outriggers in tall buildings, based on the standards set out in the Australian wind code AS/NZS 1170.2. As taller buildings are built, more outriggers are required. Most of the research to date has included a limited number of outriggers in a building. Some tall buildings require more outriggers especially for those more than 500m building height. Therefore there is a need to develop a design that includes many outriggers (e.g. more than 5). In addition, wind-induced acceleration is not covered in most of the research on outrigger-braced buildings. The adoption of outrigger-braced systems in tall buildings is very common and therefore a discussion of wind-induced acceleration will be included in this thesis. Most of the current standards allow for the adoption of a triangular load distribution in estimating the wind response of a structure. However, there are only few publications on the utilization of a triangular load distribution to determine the optimum location of a limited number of outriggers. This issue will be addressed in this thesis and will be compared with a uniformly distributed wind load. Further to this, an investigation will be carried out on the factors affecting the efficiency of an outrigger-braced system in terms of the core base bending moment and the total drift reduction. This thesis principally provides a preliminary guide to assess the performance of outrigger-braced system by estimating the restraining moments at the outrigger locations, core base bending moment, the total building deflection, along-wind and crosswind acceleration of a tall building. While many computer programs can provide accurate results for the above, they are time-consuming to run. For designers working on the preliminary design in the conceptual phase, a quick estimation drawn from a simpler analysis is preferable. Therefore, as an alternative to computer-generated estimations, a methodology for an approximate hand calculation of the wind-induced acceleration in an outrigger-braced structure will be developed