• State Suggested Answer
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 112 subscribers
  • Views 824 views
  • Users 0 members are here

Model with Modal Response & Time History Analysis - Analysis Syntax

Chris Philpy
Offline

Staad.Pro Connect Edition - software version 22.04.00.40

I'm working on a structure in Japan where my goal is to perform both a modal response analysis and time history analysis, then complete design checks following the built-in AIJ 2005 code. I have watched a couple of guided video tutorials online regarding how to set up both static and dynamic seismic load cases for each analysis so hopefully my analysis command syntax isn't too bad (but any recommendations are welcomed!!).

Here's a link to the Youtube video tutorials I'm referencing: https://www.youtube.com/watch?v=3GOHhDuI-Qo&list=PL--XUorG-TOLtS9Zl3uy2gQwXWYK2I5HM&index=28 (Lessons 501 thru 507)

QUESTIONS:

  1. The default scale factor for my dynamic seismic loads (LC2001 thru 2004) is 1.0, but it's my understanding that this value needs to be adjusted per the ratio of the design base shear and modal base shear found in the postprocessing results. I am able to locate the SRSS base shears for each of the dynamic load cases but I can't find the static design base shear in the analysis output. Does the AIJ analysis results not provide this (see attached screen capture):

     

    Am I missing something here? 

  2. Within my seismic definition, I'm trying to capture the dead load masses of the floor deck and supported mechanical equipment at each level as a floor weight, is this appropriate? Is the magnitude an absolute value (so my -5 kN/m2 should really be 5 kN/m2). I have a Reference Load Case (R1: Dynamic Mass) that more accurately depicts the more heavily loaded areas that I would rather use in my seismic mass calculations. Could I replace the floor weight with Reference Load 1 in my seismic definition to achieve more accurate results?  

  3. Reviewing my steel design results, I'm concerned that my seismic loads are not applied correctly to my model. For example, I would expect my roof beam (a 600mm deep wide flange section) to be sufficient for a 7.1m clear span when the top flange is continuously braced and the web is braced at roughly 2m. Are my forces being amplified? Is the seismic load being applied appropriately to my roof members?

  4. How do I get STAAD to print the analysis results of my time history analysis?

Thanks in advance!

Bentley Support Model.STD

Parents
  • 0 Offline

    1. Yes it does seem like the base shear is not printed for the AIJ. What you can do is, sum up the total forces that are reported at each story level and that should be the static base shear. The output is available for the load 1001 in your model.

    2. Yes you can use FLOOR WEIGHT for defining the seismic weight for the equivalent static case but the value should be a positive number ( 5KN/m2). You can absolutely use R1 instead. In fact one of the reasons for defining a mass type reference load is that it may be used to generate seismic weight/mass for both static as well as dynamic seismic load generations.

    3. You can use the same R1 load for the Response Spectrum cases as well. In addition, I see that you have applied a direction factor of 1 for the response spectrum cases. The ASCE 7 allows scaling of the response spectrum by dividing the spectral data by R/I. You may want to check if you can use that for the AIJ as well because that can bring down the forces quite a bit.

    4. There are lot of ways in which you can access the results for the time history analysis. Maximum Time History Base Shear is printed in the analysis output file ( look at the section just before the design commands). The post processing tables would give you the maximum response for each node/beam for the time history load case. In addition you can get plot of time histories for displacement/velocities/accelerations, at any node, by choosing the options marked below

    You may right click on any of the graphs and choose Save data in a text file to get the data saved in a text file. This file will be saved within the model folder. Also I see that you have used the SAVE option as part of the time history definition which would create two files with extensions .frc and .tim. These files would contain the member forces/support reactions data and nodal displacement data at every time step for the time history load. Please be aware though that these files are going to be very large files as these would contain lot of data. So do not use the Save option unless you have to.



Reply
  • 0 Offline

    1. Yes it does seem like the base shear is not printed for the AIJ. What you can do is, sum up the total forces that are reported at each story level and that should be the static base shear. The output is available for the load 1001 in your model.

    2. Yes you can use FLOOR WEIGHT for defining the seismic weight for the equivalent static case but the value should be a positive number ( 5KN/m2). You can absolutely use R1 instead. In fact one of the reasons for defining a mass type reference load is that it may be used to generate seismic weight/mass for both static as well as dynamic seismic load generations.

    3. You can use the same R1 load for the Response Spectrum cases as well. In addition, I see that you have applied a direction factor of 1 for the response spectrum cases. The ASCE 7 allows scaling of the response spectrum by dividing the spectral data by R/I. You may want to check if you can use that for the AIJ as well because that can bring down the forces quite a bit.

    4. There are lot of ways in which you can access the results for the time history analysis. Maximum Time History Base Shear is printed in the analysis output file ( look at the section just before the design commands). The post processing tables would give you the maximum response for each node/beam for the time history load case. In addition you can get plot of time histories for displacement/velocities/accelerations, at any node, by choosing the options marked below

    You may right click on any of the graphs and choose Save data in a text file to get the data saved in a text file. This file will be saved within the model folder. Also I see that you have used the SAVE option as part of the time history definition which would create two files with extensions .frc and .tim. These files would contain the member forces/support reactions data and nodal displacement data at every time step for the time history load. Please be aware though that these files are going to be very large files as these would contain lot of data. So do not use the Save option unless you have to.



Children
No Data
Communities
Support and Services
Training and Learning
Social Media