Etabs 2013 - Story Shear, Deflections And Time Period

[batoul]

hello,

I am modeling an RC building using etabs 2013, I need help in several thing:

1- The story shear along X and Y are not equal

2- The deflection in z direction is so large

3- The period of the first 3 mode is very high

any help?

Thank u

[UmarMakhzumi]

Batoul,

 

1) What is your structural framing- I assume your building is somewhat rectangular and length is significant compared to other direction. Base shears can be different in both direction if your fundamental period is different and so will be the distribution. 

2) What is the deflection. The model may have an input error etc.

3) Period depends upon framing and "high" is a relative word. Please state how much?

 

Thanks.

[batoul]

Umar,

1- i am modeling a 31 floors building ( 136 m heigh) and the period in both direction is the same

2- deflection iz direction is about 15 cm 

3- period of first mode = 5.59 sec

Thanks.

[WR1]

hello,

I am modeling an RC building using etabs 2013, I need help in several thing:

1- The story shear along X and Y are not  equal

2- The deflection in z direction is so large

3- The period of the first 3 mode is very high

any help?

Thank u  

 

story shear along x and y direction might be different if you are performing dynamic analysis and the building has different  stiffness in different directions. are you performing static or dynamic analysis?

 

deflection in z is so large? how much large? is it like 50km? or just more than L/480? if its in km then support your nodes and check the model again. if its the second case, then stiffen the plates, beams, reduce loads etc.

 

period of mode is very high. again how much? if its like 20 seconds then support the nodes. one way to check is check deformed shape. if building is not deforming at all it means they are some nodes not properly modeled or connected. if T is more than 1s then the building is very flexible. what is the total height of building? stiffen the building by adding shear walls etc

[batoul]

hello rana,

Can i attach my model here ?

thank u

[batoul]

How can i know that the weight and stiffness are different in different direction

[EngrUzair]

batoul,

 

Yes. You may attach your model here, if you want to.

 

You will need to use 'More Reply Options' button, given below the 'Reply this topic' window, to view the option for attaching your file.

 

 

Regards.

 

 

[batoul]

this is my model if someone can take a look on my problems

model.EDB

[UmarMakhzumi]

How can i know that the weight and stiffness are different in different direction

Weight should stay the same for most cases. Stiffness can be different if structural framing is different. In other words your time period would be different in both directions if structural framing or lateral force resisting system is different in each direction.

Thanks.

[batoul]

thhe period is the same but my problem is only with the story shear

[WR1]

I dont have etabs 2013 so cannot open your model. how you are checking the story shear? by tables?

 

upload a screenshot of seismic load cases data in both x and y directions here

[batoul]

there are the values of story shear

Thank u

eqx.xlsx

eqy.xlsx

[WR1]

they are almost same. i will check it tomorrow in etabs 2013

[batoul]

this is a screen shot for the story stiffness

and this is the model that mustbe checked

thank u in advance

model.EDB

[WR1]

If you see tables of seismic calculations, you will notice period is 1s in each direction. Also story shear is same in x and y direction. Find the attached image of table.

 

base shear in EQ1x and EQ1y is same.

 

also base in x and y directions of EQ2 is same.

 

but EQ1 and EQ2 are different from each other because of difference in story range. You can check this in tables of your model.

[WR1]

this was the table i was talking about i forgot to attach.

[batoul]

thank u very much but i was comparing the values given the story response plot ( story shear).

They should not be the same?

[batoul]

and when i said tha the period is very high i meant the period of the first mode ( dynamic analysis)

[WR1]

period and base shear should be same in any way you view them in any software. where is the plot of story shear? did u attach it here?

[batoul]

there is the plot of story shear there is difference about 500 kn between eqx and eqy

eqx1.docx

eqy1.docx

[WR1]

I dont know if you are producing results from a different model than what you have posted here. I am getting the same results again and again in both directions.

 

for example see the attached image.

 

there is now live or sdl load applied in the model although included in mass source. also there are some warning while running the analysis.

 

you dont need to make separate load cases for different directions in etabs. you can do all in just one load case.

[batoul]

I DON'T UNDERSTAND ABOUT THE LOADS AND THE MASS SOURCE.

Can u explain plz?

[batoul]

what do you mean you don't need to separate load cases for different direction in etabs.?

[WR1]

why make your lift difficult like used to be in etabs 9 to define load cases different for each direction. in etabs 2013 you can just define one load case for E and one W and include all directions x y plus minus in just one case. just tick all 6 check boxes.

 

in mass source you will include 100% dead load plus 100% mech load in this building if any. 

[batoul]

according to ubc 97 mass source = 100% dead load + 0.25 live load

i meant by sdl the super imposed dead load wich included with the dead load 

this is my model 

model.EDB