Seismosoft | Earthquake Engineering Solutions

Hi everybody
why is difference between seismo_period and SAP_perid?
I have 4bay and 1 story frame that I defined w-section in infrmFBPH, and mass but SAP_perid=0.46 and Seismo_period=0.401, why?
thanks a lot

There could be any number of reasons for the difference, afakhimi.

Do both models use the same material densities for members? Does the SAP model mass source coincide with what is used by SeismoStruct? Are rigid end offsets used in SAP? Are total masses identical for the two models? Is E exactly the same for both models? Do database properties exactly match for the two models? etc . . . . .

I'm sure you'll find a reason for the difference if you go through the two models with a fine enough inspection.

HOw can i find natural period of vibration for a column in Seismostrcut ??? what analysis type to be used and any other particular point to remember while doing this Free vibration simulation ???
The column is fix at base , free at top with a Gravity mass of 19.24 ton.


Thanks

Regards
Zain Saeed

A simple model using elastic elements and an eigenvalue analysis will suit your needs.

when i started the eigen value analysis and want to inout lumped concentrated mass ..i am not getting the dilogue box that what are the terms Mx My and Mz and how to calulate them ,,,In my simulation i was having a column with 19.24 ton load on top ( in the form of concrete slabs) as shown in figure. Now i have to convert this load to the values of Mx My and Mz ..how ??

Also i saw in manual that they some time they apply like a
lumped mass at joint with value of 1 kip-­#8208;sec2/in in the Z direction only. What does this mean ???

I think you would be well served in consulting an introductory text on structural dynamics zsaeed. You will need to convert weights to masses by dividing by the appropriate value of g for your specified units. The issue of Mx, My, and Mz depends on your modeling strategy. Are you interested only in periods in a single horizontal direction? The set the lumped mass for that direction equal to W/g and the others zero.

Thanks for the prompt reply Sir ...In practical Or Experimental work of this research we had measured the time period for motion in North-South and East-West Direction which means that i have to enter value of Mx and My only..The dialogue box appeared in lumped mass asks for Mx or My in units of tonne ..should i provide the actual 19.24 Mton 0r Tonne value here or still multiply with a factor ??

Thanks alot

I am simulating a bridge pier (Reinforced Circular Column) as shown below

https://drive.google.com/file/d/0B7rekW ... sp=sharing

I am interested to compare the natural periods obtained through experimental work with seismostruct model for which i simulated Eigenvalue Analysis. The dialogue box apperad requiring values of Mx and My ...The load on column (in the form of slabs) was 19.24 Mton...Can someone please tell me that did i calculated the right values of these factors (Dialogue box shown below)

https://drive.google.com/file/d/0B7rekW ... sp=sharing

I used the Formulae I = (1/12) *(M)*(a2 + b2)

Thanks
Zain Saeed

Dear Zain Saeed,

My response in http://www.seismosoft.com/forum/topic.asp?TOPIC_ID=799 obviously applies here as well (since your query is the same).

In short, and for the sake of reiteration; background reading, hand-calculations, and numerical experimentation (i.e. "playing" with models and learning from the results), will go a long way in providing you with the answers that you are seeking.

Rui Pinho