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Different excitation at supports

Different excitation at supports

Different excitation at supports

(OP)
I upload here 3 files from SAP2000 v15 for comment on my first ever different excitation at supports time history. Look first the AVI to get a general appraisal of the thing.

I have set a very lightly loaded portal frame with knee braces, solved it as planar problem, and followed in general (I think) what I understand are guidelines in CSI wiki. For one inexpert in this kind of models the results don't look to me bad.

Essentially, I have subjected each of the supports to horizontal movement of 3 cm amplitude, one following a sine function whilst at the same time the other follows the cosine function.

I have used m and kN to set the displacements and loads.

DEAD load case only has selfweight, and SDL loadcase has 2.5 kN/m on the sloped roof members.

When setting the mass source I have chosen from element masses and additional loads. Since the structural mass will be counted directly as mass, and I want to count as well the whole SDL as mass source, I have set it (just the SDL, but not the DEAD loadcase) with a multiplier of 1.

I used a minimum of 10 inner divisions per frame element.

I have set all to direct integration, and everyyhing -I think, have not thoroughly examined- stays elastic along the 100 steps to 5 seconds time history performed wholly at the service level.

1. I endear your comments looking for errors or convenient changes in the intent.

2. I am also interested in confirming that when we say something has 0.05% damping to SAP2000 we must enter 0.05, and when we want to say something has 5% damping, we must enter 5 in the input box.

3. Then, for the Time History Loadcases, I am interested in confirming that if we want it concomitant with some loading, we would create a Loadcase of the Time History type that has all what we think concomitant plus the TH case or cases, and so we'll become able to examine the stresses and everything along the steps with the concomitant loadings. This is what I have tried to make in the TH+DEADS time history loadcase applying to the pure TH case concomitant DEAD and SDL time history loads following a UNIFTH time history function to the 5 secs life of the analysis.

I continue exploring SAP2000 and studying these things; whatever related advice is welcome.

Thanks beforehand.

 

RE: Different excitation at supports

(OP)
Erratum: The horizontal displacement at the supports is set to vary between -3cm and 3cm according to sine and cosine laws. Hence the 3 cm was the HALF amplitude of the imposed displacements at supports.

RE: Different excitation at supports

(OP)
In partial answer to my own question,

I have found a CSI resource that (as I suspected) establishes that 5% damping must be entered as 0.05 in the input form.

http://sap2000.org/isap/Modal_Damping_Form.htm

"As an example, to apply 5% damping, enter 0.05 in this edit box"

This seems to be in contradiction with other threads in this forum.

See for example,

http://www.eng-tips.com/viewthread.cfm?qid=283097&page=3

In any case, previously to any practical use better check conformity with some well established answer by the input.

 

RE: Different excitation at supports

(OP)
Maybe is not a CSI resource, follow the link, anyway.

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