Presented by Tom C. Xia, DCI Engineers
Performance based design (PBD) for tall building is becoming quite popular in recent years. Concrete core wall is one of the most used lateral force resisting systems because it is well suited for vertical transportation as well as providing strength and stiffness for a tall building. The common effect observed in tall buildings is the increase in shear force as compared to the code level design. The range of this increased demand varies between 2 to 4 times the code level design. One of the reason behind the increase is the higher mode effects of the structure which is more significant for a tall building. However, almost all performance based design in US is done for buildings much taller than 240’. There is very little study done for buildings shorter than 240’. It is unclear if and how the higher mode effect changes with buildings heights. The intent of this paper is to compare the PBD results with code level design for buildings with different height (5, 10, 15, 20, 25, 30 and 40 stories) and to study its influence on shear demand increase. Part of the reason for this study is that the City of Seattle will require higher shear force for a core wall building taller than 160’. There are also discussions among some of the engineers and researchers to change the national code (NEHRP and ASCE 7) to require higher shear demand for buildings taller than 160. This paper will be served as an initial study and hopefully to shed the light on this important topic.
