dear Mitesh Surana

thank you Mitesh Surana for your answer,

if i use 7 ground motion (in code say average from 7 GM,), how to perform the procedure?  whether I should averaging every period of 7 ground motion? or is there another way to combine(SRSS) ?

thank you

Dear Mitesh Surana,

thanks for your answer,, iam being do it.. 

You need to know the nature of your design, target spectrum. Most design spectra have historically been geometric mean of the two as-recorded horizontal components. AASHTO still uses geometric mean spectra, while ASCE/NEHRP have recently switched to maximum direction design spectra. The best source I have found for ground motion selection and modification is NIST GCR 11-917-15, Selecting and Scaling Earthquake Ground. Motions for Performing Response History Analysis, freely available (http://www.nehrp.gov/pdf/nistgcr11-917-15.pdf). Equations for calculating the required scale factor to minimize error over a range of periods may be found in the Technical Report for the PEER Ground motion database (http://ngawest2.berkeley.edu/Technical_Report.pdf). You will need to set up a free account to access the report.

 thankyou so much for answer,,,yes i used that,,

Yes, I also just found that the new ASCE-7-16 requires maximum-direction spectrum instead of SRSS of the two horizontal components for scaling to the target spectrum.

But if still adopt ASCE-7-10 or IBC-2016, then spectral match or amplitude scaling of SRSS of two horizontal component from selected (based on de-aggregation within the PSHA) original ground motions could be done. 7-pairs of ground motions are needed and average of SRSS of the pairs shall not fall below the target spectrum within the range of periods (0.2-1.5Ts).

By the way for complience to ASCE-7-16, we need to construct maximum-direction spectrum instead of the SRSS. Anyone know or suggest available software for this maximum-direction spectrum?

ASCE 7-16 develops maximum direction spectra by applying a factor of 1.1 to the geometric mean Ss and a factor of 1.3 to the geometric mean S1. See ASCE 7-16 for additional details. That is to generate the target. BiSpec by Earthquake Solutions will generate maximum direction spectra from the two horizontal records. TSPP is freely available at

daveboore.com

TSPP will also generate the maximum direction spectra from two components. BiSpec has a nice gui but is not free.

You can actually use either a geomean target or a maxdir target, as long as you know which one you are using. See, for details:

https://ascelibrary.org/doi/abs/10.1061/%28ASCE%29SC.1943-5576.0000461?af=R

Dear Boby,

Use performance based design approach followed by rules CHBDC S6-14(elastic dynamic analysis). Rayleigh damping (mass and stiffness proportional damping) and ground motion analysis, stressed load, geometric nonlinearity, load combination hysteresis type with proportion damping in the modes may be used. Total rotation vs ground motion record number with minimal damage can give idea about the time history.

Ashish