The approach for retrofitting projects of the standards changed from "resistance" to "capacity". In classical approach, the external loads are calculated and the building is designed so that it can resist the external loads. Also the building needs to satisfy some additional conditions. While we are investigating an existing building, the capacity concept is used. Again the external loads calculated, but this time some disqualifications are allowed in the structure because the loads that can't be carried by damaged members will be distributed to other members. This is the basic idea of material non-linearity. In this help file, Sta4CAD' s retrofitting functions and menus will be described. The target of the retrofitting is usually fulfill seismic needs.

Firstly, the building must be defined in order to find its capacity. Defining existing building has two topics:

1. Defining geometry and material
2. Defining bars used in the building

Generally defining geometry of the building is not complicated. If the project of the building does not exist, it can be measured. But it is very difficult to determine existing bars. Sta4CAD offers two methods to define existing bars. The project exists so the bars can be directly entered from relevant bar menu. The project does not exist, but the bars can be predicted. We know that the building stands on its self loads, so we can run a dead load analysis and we may predict the minimum reinforcement in the members. After the building is defined, the capacity of the building must be find out. The damages in the members will be calculated to determine the capacity.