Expectations in Current Codes
The Uniform Building Code (UBC) follows a prescriptive, traditional approach, as was stated in the introductory section of notes. The performance goals, which are shown below, are traditional as expected.
The definitions of the frequency of an earthquake's occurence and the corresponding desired performance are vague and subjective. Terms such as "limited damage" and "one or more times" are good examples of this. Three levels of performance under different earthquakes are desired, but only one design earthquake is given - the major event. Since no design earthquakes are given for the minor and moderate events, an indirect approach is employed to attempt to achieve the desired performance. Various checks are employed, but no design checks are specifically tied to a limit state goal, such as the drift limit. The uncertainty as to which limit state a particular provision is targeting and the ambiguity of in the definitions discussed above lead to wide variations in interpretation of the code. Thus, the performance of structures designed according to the UBC can vary widely as well.
Other Current Codes
current codes also contain ambiguous performance goals and are plagued
by the same variability in interpretation and performance as the UBC.