Why the Location of Center of Rigidity Changes for Each Story Even for Symmetric Structures?

By |2020-07-19T05:48:35+00:00July 18th, 2020|FAQs, Structural Engineering|

Question: Why the Location of Center of Rigidity Changes for Each Story Even for Symmetric Structures? Answer: The center of rigidity is the center of resistance of a floor or diaphragm against lateral forces. It is the stiffness centroid located within a floor-diaphragm plan. If the lateral forces are applied at this center, the floor diaphragm will experience only the translational displacement (i.e. no rotation). Other levels are free to translate and rotate since the actual behavior is coupled both in plan and along height. The location of center of rigidity is an inherent structural property and has nothing [...]

The Definition of Design Basis Earthquake Level and the Retrofit Need for Structures Designed for Older Codes

By |2020-06-21T05:56:03+00:00June 21st, 2020|FAQs|

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 [...]

Why building codes require a base shear scaling for the RSA procedure?

By |2020-05-13T18:34:40+00:00May 13th, 2020|FAQs|

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 [...]

Torsional Irregularity Check and Accidental Torsion

By |2020-03-12T07:23:09+00:00March 12th, 2020|FAQs|

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 [...]

Go to Top