Ideal Secondary Beam Directions in ETABS 1

[SteelStructureDesign]

Hello,

I think, secondary beam (composite beam) and steel deck directions in the attached picture are basically wrong and it will be better if I change the directions.

What is your opinions? I will be glad if you look at it share your experiences and help me.

Thank you already now.
Latif

 

[slickdeals]

No, the directions are correct. The deck always spans perpendicular to the beams.

It looks like your bays are almost square or have a ratio of 1:1.2 or something like that. In that case you are better off spanning the girders in the short direction.

So from the looks of it, it seems like what you have is correct.

 

[SteelStructureDesign]

Your answer is very useful for me.

Yes I know that deck must be perpendicular to the secondary beams. I wanted to understand the second detail that you mentioned also.

Thank you very much!
Latif

 

[SteelStructureDesign]

After reading your message again I think I misunderstood what you mean. I thought that the directions wrong because of the out to out distance of the building. And this raito is aprox 1:2

I thought that if I change the direction of the secondary beams it may help defence for lateral loads (earthquake).

I did not mean the raito of X and Y spans. Yes you are also right about it but that was not the point I wanted to understand clearly.

So let us make the subject clear now.

a) I think correctly or because beams help for lateral resistance also.
b) It does not matter at all. When we make a composite system the directions are not important for lateral loads at all.

What is your answer? a or b?

Best Regards..
Latif

 

[slickdeals]

Secondary beams do not contribute to lateral resistance because they are typically pin-ended and in theory do not offer any rotational restraint. Moment connections are made along column lines only. Internal secondary beams have no effect on stiffness.

You have shearwalls in the building that can resist lateral loads. I don't think you will need any additional moment frames, but I may be mistaken.

Looking at your building, you will need to take care of restraint cracking of concrete. I don't know how long this building is, but the concrete shrinkage is being restrained by the shear walls at all corners. The building will try to shrink towards the center and the walls will prevent shrinkage causing cracking. You will need to account for this.

 

[Skicat]

I agree with slickdeals. The shearwall locations are not optimal for the geometry of your building.

 

[SteelStructureDesign]

Thank you very much.

So you suggest that I have to design using completely steel without any concrete wall for upper part of the building?

It is 40 mt. The problem is even I use concrete walls till end of the building, some of the program gives me very big columns for two points.

From bottom to top like this : 2HEM900-2HEM800-2HEB700-2HEA400-...

But two other symmetrical point to above criticla points are like this: 2HEA450-2HEA400-...

Although the building is completely symmetrical the final column sections are different for these 4 symmetrical points. I dont understand at all why. I tried to define lateral earthquake loads for both directions (+X-X+Y-Y) also.