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[Vijayanarayanan]

Dear Sefians,

I guess there exists a wide spread consensus that flat slab in the high seismic region are designed to resist the gravity load along with the lateral drift induced unbalanced moment only. The entire lateral load is designed to be resisted by the lateral resisting system in place.

Now, assuming the flat slab structure is in the low seismic zone, say in zone 2, the following question arise,

1)should we differentiate the design philosophies in the low and high seismic zones??


2)should we design the flat slab for gravity load and the unbalanced moment only?

3) should we consider the contribution of the slab and column in the flat slab towards the lateral resistance?

4) how do we decide whether the region is supposed to be low seismic or high seismic?

5) how good is our seismic zoning, for us to rely on it?

Now that we have a very good understanding about the design philosophies in the high seismic region we have to proceed to discussion on low seismic region

Vijaya narayanan
MTech student
IIT Kanpur

[jiwajidesai]

Dear Mr Narayanan
As I understand it a slab, whether a beam and slab system or a flat plate, is a diaphragm which is the source of lateral forces on the vertical lateral resistant systems like the shear walls. To this model, no slab system can be strictly a part of lateral resistance – it gives rise to-and may distribute depending on its relative stiffness characteristics-forces to be transferred to the foundations by vertical resisting elements.
A beam and slab system is more efficient and much less severe in structural terms, than a flat plate, in transferring lateral forces on to columns and walls as the beams form a rigid grid , which is laterally much stiffer, between the slab diaphragm and the vertical elements. This tends to inherently take care of punching due to unbalance moments, drift-effects in a lateral load situation.

I would say, yes, design flat slabs only for gravity loads, make it as stiff as permitted, and design the shear walls and columns as per Codal provisions for lateral loads arising out of the lataeral movements of the flat slabs diaphragms.

Seismic zoning is as good, or as bad, as the political rather than the geographical divisions in today’s world.

Regards

Jiwaji Desai


From:vijaya narayanan [mailto:forum@www.buonovino.com]
Sent:Tuesday, December 30, 2008 3:45 PM
To:econf@www.buonovino.com
Subject:[ECONF] Design of flat slab structure in low seismic region


Dear Sefians,

I guess there exists a wide spread consensus that flat slab in the high seismic region are designed to resist the gravity load along with the lateral drift induced unbalanced moment only. The entire lateral load is designed to be resisted by the lateral resisting system in place.

Now, assuming the flat slab structure is in the low seismic zone, say in zone 2, the following question arise,

1)should we differentiate the design philosophies in the low and high seismic zones??


2)should we design the flat slab for gravity load and the unbalanced moment only?

3) should we consider the contribution of the slab and column in the flat slab towards the lateral resistance?

4) how do we decide whether the region is supposed to be low seismic or high seismic?

5) how good is our seismic zoning, for us to rely on it?

Now that we have a very good understanding about the design philosophies in the high seismic region we have to proceed to discussion on low seismic region

Vijaya narayanan
MTech student
IIT Kanpur

Posted via Email

[Vijayanarayanan]

Respected Sir,

I understand form your post, you suggest no matte which earthquake region we are in, we could design the flat slab system to resist the gravity load and lateral drift only.It is very clear that the flat slab, as such, cannot be designed to resist lateral load. But in this above case,one need to note that we don't consider the lateral force that could be resisted by the columns in place too.

Now, considering the region to low seismic, can we account for the lateral resistance that is offered by the column in to consideration, when we design the lateral resisting system??

Don't you think developing a lateral resiting system without considering the effect of resistance offered by the columns,in low seismic regions, in place could prove to be uneconomical??

Vijaya narayanan
MTech student
IIT Kanpur


[quote="jiwajidesai"]Dear Mr Narayanan
As I understand it a slab, whether a beam and slab system or a flat plate, is a diaphragm which is the source of lateral forces on the vertical lateral resistant systems like the shear walls. To this model, no slab system can be strictly a part of lateral resistance � it gives rise to-and may distribute depending on its relative stiffness characteristics-forces to be transferred to the foundations by vertical resisting elements.
A beam and slab system is more efficient and much less severe in structural terms, than a flat plate, in transferring lateral forces on to columns and walls as the beams form a rigid grid , which is laterally much stiffer, between the slab diaphragm and the vertical elements. This tends to inherently take care of punching due to unbalance moments, drift-effects in a lateral load situation.

I would say, yes, design flat slabs only for gravity loads, make it as stiff as permitted, and design the shear walls and columns as per Codal provisions for lateral loads arising out of the lataeral movements of the flat slabs diaphragms.

Seismic zoning is as good, or as bad, as the political rather than the geographical divisions in today�s world.

Regards

Jiwaji Desai

[arunkashikar]

To add to the question raised below – what is low seismic zone – can we consider columns to be part of lateral load resisting system up to zone III or Zone II?

Regards,
Arun Kashikar

Board line: +91 22 2571 9000 | Direct: +91 22 2571 9058 | Cell: 9819055576
Fax: +91 22 2571 9300 | Email:akashikar@hirco.com(akashikar@hirco.com) | Website:www.hirco.com


From:vijaya narayanan [mailto:forum@www.buonovino.com]
Sent:Wednesday, December 31, 2008 12:55 PM
To:econf@www.buonovino.com
Subject:[ECONF] Re: Design of flat slab structure in low seismic region



Respected Sir,

I understand form your post, you suggest no matte which earthquake region we are in, we could design the flat slab system to resist the gravity load and lateral drift only.It is very clear that the flat slab, as such, cannot be designed to resist lateral load. But in this above case,one need to note that we don't consider the lateral force that could be resisted by the columns in place too.

Now, considering the region to low seismic, can we account for the lateral resistance that is offered by the column in to consideration, when we design the lateral resisting system??

Don't you think developing a lateral resiting system without considering the effect of resistance offered by the columns,in low seismic regions, in place could prove to be uneconomical??

Vijaya narayanan
MTech student
IIT Kanpur


[quote="jiwajidesai"]Dear Mr Narayanan
As I understand it a slab, whether a beam and slab system or a flat plate, is a diaphragm which is the source of lateral forces on the vertical lateral resistant systems like the shear walls. To this model, no slab system can be strictly a part of lateral resistance – it gives rise to-and may distribute depending on its relative stiffness characteristics-forces to be transferred to the foundations by vertical resisting elements.
A beam and slab system is more efficient and much less severe in structural terms, than a flat plate, in transferring lateral forces on to columns and walls as the beams form a rigid grid , which is laterally much stiffer, between the slab diaphragm and the vertical elements. This tends to inherently take care of punching due to unbalance moments, drift-effects in a lateral load situation.

I would say, yes, design flat slabs only for gravity loads, make it as stiff as permitted, and design the shear walls and columns as per Codal provisions for lateral loads arising out of the lataeral movements of the flat slabs diaphragms.

Seismic zoning is as good, or as bad, as the political rather than the geographical divisions in today’s world.

Regards

Jiwaji Desai

Posted via Email