Slab parameters for Open Grid Steel Flooring in ETABs

[Osama Anwar]

Assalamu Alaikum Warahmatullahi Wabarakatuh

I'm designing a Industrial building made up of steel which has a open grid steel flooring in one of its floor. I need to know what material properties I need to use and what slab parameter I need to select to model the open grid steel flooring in Etabs. The following site gives an idea about detailing of open grid steel flooring.

Open Grid Steel Flooring – Structural Detailer

In material properties I have taken Modulus of Elasticity as 0.00001. Also Specific Weight Density as 0 because I am applying its self weight as shell loads.

And in Slab Property Data I have taken Modelling type as Shell-Thin and Type as Slab and Thickness 1".

Is it alright or I need to change something to better mimic the reality?

 

 

 

 

[Badar (BAZ)]

You seem to be approaching your modelling without clear and basic understanding of what constitutes as structural system in this kind of floor.

What I see, when I look at this picture is: a floor in which loads are carried directly by beams, which in turn transfer the forces to girders; beams are laterally braced by cross-members. So, you need to model your beams and girders with line elements.

And why would you take your modulus of elasticity as 0.00001? E is responsible for providing stiffness. If E is 0, it means do not have any structural member! I am sure that is not the case.

[UmarMakhzumi]

Wsalaam!

This is basically "Steel Grating" sitting on steel structure. I personally think its not appropriate to call it Open Grid Steel Framing System.

The standard industry practice is that we don't model the grating. You can consider the weight of grating based on manufacturer's catalogue (you can google if you don't have any, as this data is very common). Grating spans one-way and  you can calculate the load based on its span. Normally you will need to provide in-fill beams to meet span requirements against occupancy loads.

The steel that supports this grating will need horizontal (plan) and vertical bracing. Normally for steel, the beam to column connection in major axis is moment, and braced frames are used in minor axis. Very common.

Thanks.

 

[Osama Anwar]

8 hours ago, UmarMakhzumi said:

Wsalaam!

This is basically "Steel Grating" sitting on steel structure. I personally think its not appropriate to call it Open Grid Steel Framing System.

The standard industry practice is that we don't model the grating. You can consider the weight of grating based on manufacturer's catalogue (you can google if you don't have any, as this data is very common). Grating spans one-way and  you can calculate the load based on its span. Normally you will need to provide in-fill beams to meet span requirements against occupancy loads.

The steel that supports this grating will need horizontal (plan) and vertical bracing. Normally for steel, the beam to column connection in major axis is moment, and braced frames are used in minor axis. Very common.

Thanks.

 

Jazak Allah Umar bhai

I had already considered the weight and taken clear span (5' in my case) from the online sources. I had also provided secondary and tertiary beams for this purpose as my primary beams span are very large (32' in one direction and 70' in other direction). 

What I understand is that I do not need to consider slab for this case, I just have to take loads and directly transfer them to beams.

8 hours ago, Badar (BAZ) said:

You seem to be approaching your modelling without clear and basic understanding of what constitutes as structural system in this kind of floor.

Jazak Allah for the reply Badar bhai

It is class assignment. That's what assignment are for, to build basic understanding.

8 hours ago, Badar (BAZ) said:

And why would you take your modulus of elasticity as 0.00001? E is responsible for providing stiffness. If E is 0, it means do not have any structural member! I am sure that is not the case.

I did that as lecturer told me to do so, but he did not go into much detail that is why I am asking. I have selected suitable steel grating for clear span of 5' using online catalogues and also corresponding weights, deflections are already catered for. I needed to know that can I model it as a slab that would automatically transfer loads to beams? Because assigning loads to hundreds of beams is a hectic job. That is also the reason I took stiffness equal to 0 by taking E=0.

Should I model the slab or just transfer corresponding loads?

[Badar (BAZ)]

One do not start to develop basic understanding by working on a actual structure from the start. If you are at that stage, then you must have studied engineering mechanics, internal distribution of stresses in cross-sections for a particular external force, strength of materials, strength of cross-sections for a particular demand, and methods to estimate the distribution of forces in connected members meant for a structural behavior.

If you are not designing the open floor itself, and your intention is to investigate the girders and columns; and to do that, you want to use area elements so that you do not have to apply gravity loads manually, then you need to ask yourself:

• Is my floor one-way or two-way?
• Can my floor transfer moments to supporting members?
• Do I want to model the self weight of the open floor through the use of area elements?

For one way distribution, you could use deck slab or one way load distribution option. For two way action, add thin shell area elements.

Second point: You can do that by setting a very low value of E, as well as releasing the rotational restraints at the ends of  slab panel.

Third point: Select appropriate thickness for a particular unit weight.

 

 

[Osama Anwar]

21 hours ago, Badar (BAZ) said:

If you are not designing the open floor itself, and your intention is to investigate the girders and columns; and to do that, you want to use area elements so that you do not have to apply gravity loads manually

I only want to investigate loads on beams and columns.

Steel gratings panel are made up of bearing bars and intermediate bars. Bearing bar orientation is perpendicular to the span (c/c distance of adjacent beams) which varies from 2'-5' so I have to subdivide slab in such a way that beams are at 5' c/c in one direction. Length of grating may be equal to span or greater than span. I have not seen it, I know this from web surfing.

21 hours ago, Badar (BAZ) said:

• Is my floor one-way or two-way?
• Can my floor transfer moments to supporting members?
• Do I want to model the self weight of the open floor through the use of area elements?

I don't think it will be able to transfer moments. What do you think? I think it would act as one way. I wanted to model self weight through area element so I took mass of material as 0. 

21 hours ago, Badar (BAZ) said:

For one way distribution, you could use deck slab or one way load distribution option. For two way action, add thin shell area elements.

Second point: You can do that by setting a very low value of E, as well as releasing the rotational restraints at the ends of  slab panel.

Third point: Select appropriate thickness for a particular unit weight.

I am using membrane with E almost equal to zero WITHOUT one way option. Will it do? Isn't deck for composites?

If I am applying self loads through shell loads option i.e. unit weight equal to zero, setting the thickness won't matter. Right?

Thanks for the great explanation. Much appreciated. 

Btw is there a steel frame in your profile picture? I was wondering which steel section we use as bracing in Pakistan? Angle or circular HSS or other?

Edited June 20, 2021 by Osama Anwar