Question: I noticed that with the updates of codes it seems that with the passage of time the seismic parameters (response spectral accelerations) are increasing. For example if we compare earlier versions of AASHTO (if we talk about bridges) and the 2013 version, the earthquake changed from 475 years to 1000 years return period earthquake, while the R factor and load factor for earthquake remained same. Wasn't this change in early 2000's a drastic? The earlier structures (bridges for Aashto) required retrofit? Should have been a huge retrofitting activity!For Pakistan we have only PGAs for 475 years in PBC. Practicing [...]

Question: Why in different building codes (UBC 97 or ASCE 7) the results of Response Spectrum Analysis (RSA) should be scaled such that the design base shear should match with the (e.g. 80%, 90% or 100% of the) design base shear obtained from the Equivalent Static Analysis? Answer: The requirement of a base shear scaling for the Response Spectrum Analysis (RSA) procedure is included in the building codes as a means to ensure that the minimum strength of a structure designed using the RSA procedure is similar to the strength that would be required if the structure was designed using [...]

Question: I am currently working in a Consultancy firm in Islamabad and have few queries regarding torsional Irregularity explained as follows: 1) As per UBC torsional irregularity exists if "Maximum story drift, computed including accidental torsion, at one end of the structure transverse to an axis is more than 1.2 times the average of the story drifts of the two ends of the structure". In our general practice, we compare the ratio of maximum displacement to average displacement with 1.2 to confirm if the torsional irregularity exists or not. But as per the above stated UBC Statement, we should [...]