base shear

[yasir1989]

Hi every one
In a response spectrum analysis, the base shear does not match the summation of shears I get at the base of the columns. Which one should I use as base shear ? how to solve this problem?

 

[ayelamayem77]

this link will show mr/yasier1989 problem

http://www.mediafire.com/download/6u48pysmbbl79g5/3d-new-modified.rar

summation of section cut forces for all frames as shown on the model under response spectrum analysis doesn't equal to total base shear given by etabs..
i tried hard to find a solution but i failed !!!!
so please help.

 

[inggelu]

Hello ayelamayem77
First at all on your model one mistake (and from my point of view is a big one) when you define the Mass sources you double them.

Because you Check the Element self mass and after that you add the DEAD Load with 1 multiplier as Specified Load Patterns.

This alter the fundamental period of building with this, is 1.57 in place of 1.91.

So be careful in the future with this. If you check the self mass of element don;t add as Specified Load Patterns DEAD load or if you add put the multiply 0 (Zero).


How you calculate the horizontal forces? Did you check on manual calculation?
Can you give me the pages of your design codes where is note how to estimate the base shear for a building also how is distribute on the story level? It should be manual calculated not with the computer.
Also to be clear cause we are talking about the same think we refer at method equivalent static lateral forces for this you check the base shear?

My suggestion is to use not so complicated model to estimate the shear base and to see what is happens. It can be use an ease 3-4 story building with one direction frame X or Y not 3d one.

Keep in touch and good luck.

 

[ayelamayem77]

dear inggelu,

please note the followings:

if you go to define > static load case > dead load self multiplier = 0 (in this case the mass that was calculated based on (from self and specified mass and loads) will not be doubled at all as you assumed,it will be doubled if the previous multiplier was set to 1 in static load case menu.

 

[ayelamayem77]

also the answer to yasir1989 about how the program calculate base shear case of response spectrum analysis can be found in this link:

http://www.mediafire.com/download/iokmw53hajal7ba/answer.rar