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One thing that I learned while dealing with above mentioned building is that area of the floor has significant effect on structural system to resist seismic loads. The building, under discussion, has an area of about 45000 sqft/floor. The building is 4 stories, the bay length is 26ft, the column size is 30 inches, and beams are 15x30 inches. Even then, one requires shear walls of about 130 ft length in both direction to satisfy strength and serviceability requirement of code. The shear in one wall exceeds the maximum limit set by the code if one uses lesser shear walls. The problem is base story shear, which is about 5000 kipps at second level.

I dont have any exp in PBD but here are my 2 cents. Please correct me if wrong. Performance based design is a nonlinear dynamic problem. By this we try to model post-yield ductility and energy dissipation for example under an earthquake. Ductility is very important in seismic design and ductility is actually a ratio of Nonlinear response / linear response This is handled by R factors in code. Again R factors are for all the modes of vibrations. Which in reality is not true. In linear elastic analysis we design structures for earthquakes for very small forces and actual EQ forces are quite large. But still structures desgined like this have performed well because the structure show a ductile behaviour which is very difficult to model from code based approach. So we assume the remaining portion of forces are handled by ductility. This ductility is handled by proper reinforcement detailing of members and joints. Where as in PBD as the name suggests we design based on performance of a structure. We try to model energy dissipation of structures. For example kinetic energy is applied to structure in an earthquake this is converted to elastic strain energy. Think of this as a car moving (it has kinetic energy) and then it hits a spring fixed on wall...This kinetic energy will be transferred to this spring and the spring will compress and it has now elastic strain energy. Now this SE must be dissipated from the spring otherwise it can react back to car and can throw its passengers outside. This energy dissipation in buildings is handled by damping (really difficult to predict) In buildings damping consists of 1. any external equipment like tuned dampers (liquid dampers, mass tuned dampers, braces etc) 2. Material inbuilt properties 3. Joints (e.g. beam column joints) We assume all above 3 to give around 1-5% of Critical damping. Critical damping is the damping where a structure vibrates and never crosses its mean position. Think of it as container filled with liquid and a spoon is immersed in it. Now the spoon will vibrate if external force is applied. Now increase the viscosity of the liquid in container and keep increasing to the point where the spoon vibrates from its mean position to left and comes back to its mean position and stops there (does not go to right). This viscosity of the liquid has critical damping Cc.(that's why we call it viscous damping/dampers). In buildings the damping is 1-5% of this Cc. In PBD we try to model these dampers.

This can only be answered if someone is involved in performance based design, which a lot of people are not. To address your questions, I think both approaches are beneficial where needed. You don't want to design a single story house based on performance based design or a cantilever garage porch. But you may want to consider performance based design for a tall high rise building or structure where you would like to limit the extent of structural damage when subjected to an environmental event because of your Client needs. Also, performance based design is a great topic for undergrad final year students. My friend actually got employed in a firm because he did his undergrad project on performance based design, although he remembered nothing. Thanks.