Slab-shear wall behaviour seismically

[mhdhamood]

Dears

in flat slab-wall systems how the slab at junction with shear wall behave seismically?!

i mean if the connection is hinged there then can it transmit seismic?

 

[WR1]

Some background can be found in chapter 3 "lateral load resisting systems" in the book "reinforced concrete design of tall buildings" by Tranath.

[UmarMakhzumi]

On 2017-01-13 at 5:47 AM, mhdhamood said:

Dears

in flat slab-wall systems how the slab at junction with shear wall behave seismically?!

i mean if the connection is hinged there then can it transmit seismic?

 

Slab in such a case would be monolithically casted with shear walls. Even if your connection arrangement allows rotation at the shear wall face, it would still be able to transfer the lateral load. It is just that your lateral load system is a simple shear wall system. Whereas, for a building where we have, say a concrete frame, and the connection b/w column and beam allows rotation, that system would fail under seismic as your lateral resistance for a moment frame comes from frame action of beam and column assembly. No frame action, no lateral resistance.

Thanks.

[mhdhamood]

thanks guys so much 

 

On 1/14/2017 at 8:31 PM, UmarMakhzumi said:

Slab in such a case would be monolithically casted with shear walls. Even if your connection arrangement allows rotation at the shear wall face, it would still be able to transfer the lateral load. It is just that your lateral load system is a simple shear wall system. Whereas, for a building where we have, say a concrete frame, and the connection b/w column and beam allows rotation, that system would fail under seismic as your lateral resistance for a moment frame comes from frame action of beam and column assembly. No frame action, no lateral resistance.

Thanks.

Mr.UmarMakhzumi;

I understand the beam column connection it shall be not allowed to rotate but for shear wall -flat slab connection joint why it can be rotated how the seismic will be resisted?

thanks in advance.

[UmarMakhzumi]

10 hours ago, mhdhamood said:

I understand the beam column connection it shall be not allowed to rotate but for shear wall -flat slab connection joint why it can be rotated how the seismic will be resisted?

The situation what I can think of where a slab panel allows rotation at end, is where you have got a precast slab panels bolted to the face of a shear wall. Such a connection shall allow moment to be released and shear and axial to be transferred. Now, seismic force shall be transferred from slabs to walls as an axial force of slab and a lateral force to shear wall through the shear connection. Please see attached sketch.

Thanks.

 

Shear wall and slab pin connection.pdf

[mhdhamood]

I have to points:
1. That means in shear wall -flat slab system case we dont need to design the flat slab for seismic effect.

I mean its enough to design the slab for dead and live loads.

2. how we call vertical element a column or a wall ?  

[WR1]

On 1/15/2017 at 7:31 AM, UmarMakhzumi said:

for a building where we have, say a concrete frame, and the connection b/w column and beam allows rotation, that system would fail under seismic as your lateral resistance for a moment frame comes from frame action of beam and column assembly. No frame action, no lateral resistance.

Thanks.

What about if columns at base are fixed and lateral resisting system becomes a cantilever column system?

 

On 1/13/2017 at 4:47 PM, mhdhamood said:

Dears

in flat slab-wall systems how the slab at junction with shear wall behave seismically?!

i mean if the connection is hinged there then can it transmit seismic?

 

First of all in flat slab system, connection is not hinged with shear walls or columns. Else it becomes a cantilever system for lateral loads.

 

7 hours ago, mhdhamood said:

I have to points:
1. That means in shear wall -flat slab system case we dont need to design the flat slab for seismic effect.

I mean its enough to design the slab for dead and live loads.

See above comments. Yes but would you design the system as cantilever columns? and make sure base is always fixed? Consider flat slab as wide shallow beam spanning between columns. Lateral load is resisted by axial and bending stiffness of beams and columns. Beams and columns will bend in double curvature developing the frame action. However in case of cantilever system (beams pinned), there will be no shear force and hence no moment in beams only the axial force and hence axial deformations. In columns there will be only bending deformations not axial.

Just now, mhdhamood said:

I have to points:

2. how we call vertical element a column or a wall ?  

Several definitions;

Aspect ratios

Walls resist in-plane bending and shear, columns usually resist biaxial moments

Rigid body rotation at base in case of walls

poisson effects in shell elements as far modelling and fea is concerned

Columns are usually compression elements, walls develop tension compression over large area.

 

[UmarMakhzumi]

20 hours ago, mhdhamood said:

I have to points:
1. That means in shear wall -flat slab system case we dont need to design the flat slab for seismic effect.

I mean its enough to design the slab for dead and live loads.

2. how we call vertical element a column or a wall ?  

For 1, the discussion is only for cases where the connection allows moment release like explained above. You can't use it for all configurations.

Coming to your question, if your connection is pinned, that means you don't have any moment, but your slab is still part of the lateral/ seismic load path and you need to design  for the forces it is transferring to the wall. Check cord, collector and whatever is applicable.

2. You can detail it based on wall or column's contribution to total shear being resisted. Walls are detailed for ductility as they attract lion's share of floor shear . Columns aren't detailed to the same level (it is not a very good comparison aals both items behave differently and parallels can't be drawn) because see previous sentence. Use judgement.

Thanks.

 

[UmarMakhzumi]

6 hours ago, Rana said:

What about if columns at base are fixed and lateral resisting system becomes a cantilever column system?

They have to be fixed or else your framing would be unstable. You can call it a cantilever wall system.

On a general note, I would advise to have braced bays in such a case(where slabs are pinned connected) in addition to walls.

Thanks.