STRUCTURAL ENGINEERING FORUM OF INDIA [SEFI]

vipul939 · SEFI Regulars Joined: 28 Mar 2011 Posts: 23

Dear Sefians,

Wishing very happy new year to all,

I am using Staad and Etabs both for analysis as well design of structures.......

The thing that I want to know is that, In model we are making column member with line and shear wall with shell element. The software will analyse the model as per given information. The question arise in my mind is that if required column size in approx 12"x60" and I model it in software with either line element or shell element. The analysis results will definitely difference. But how the structure would perform practically, as per line or shell element.

Should we model column with line member or with shell element. Please clarify......

我的问题可能很傻embers, I want to know what actual happens because both will give different solutions and may structure behave differently.

Or the reinforcement given in such size (12"x60") columns will be OK to analyse with line member or we are making blunder with model. Please try to reply as earliest.......

Thanks in advance .........

Vipul Mehta

manjutl · Posted: Mon Nov 10, 2014 5:13 amPost subject:

Dear Er. Vipul Mehta

Yes definitely both the results should give a difference. As we classify the Column as if D/b <4> 4 the same concept shall be applied to model the elements thereof. The line element will receive the moments from both horizontal orthogonal directions, whereas the shell element is only take in its major axis. The Engineer has to make the decision for using the elements.

When the col. sizes are small the length of the beams doesn't affect much, when there are huge length of columns/shear walls the length of the beams decrease and intern the flexibility. So affecting the overall behavior of the structure in the direction of placement.

Thanks,
Manjunatha T L
Consulting Structural Engineer

vipul939 · SEFI Regulars Joined: 28 Mar 2011 Posts: 23

亲爱的Manunatha T L,

Still question arise in my mind is that the structure behaves on stiffness of member/element. I think that both member/element (i.e. for size having 12"x60") stiffness will defined by I= b*d^3/12, which will gave same value of stiffness for column. Then why the structure modeled with line member and with element member (shear wall) give different stiffness and different modes. Base on those analysis/design will be different, So which will be the correct one.

In general as far as I know, structure with shear wall model will have greater stiffness than the model with line member. Correct me if I am wrong........

Please clarify......

Thanks in Advance.....

Vipul Mehta

manjutl · Posted: Mon Nov 10, 2014 10:12 amPost subject:

Definately Yes, "
structure with shear wall model will have greater stiffness than the model with line member".

Because, the length of the members connecting walls (beams) reduces and therefore the decreasing the flexibility( increasing the stiffness in other words). When we check the behavior of both the systems, structure with walls (Columns modeled as) feels to be more rigid and stiff than the other.
We have been observed this in behavior of high rise buildings ranging from 17 to 35 stories over a period. So, we follow a simple method to ease of the analysis based on our previous experiences as explained below.

Columns/walls D/b <4> 4 - modeled as Shell elements with proper manual meshing with aspect ratio between 0.8 - 1.0

Thanks,
Manjunatha T L
Consulting Structural Engineer