Basement Wall Design

[mhdhamood]

Dear all;
May you please provide me with a guidlines to design basement walls.and a solved example.
Regards
 

[mhdhamood]

I mean . Do I have to design the basement wall as column or as beam

[Waqas Haider]

The reinforcement in basement wall is similar to reinforcement in slabs. So design basement wall as a slab. Model an area element resembling your basement wall with suitable edge conditions... apply back fill load and gravity UDL loads. Mess/Divide the wall. Run the model and read moment at critical locations. and Provide reinforcement for these moments. You can also read shear force. Check thickness of wall against this shear force.

 

But if your wall is very long and acts as one way cantilever slab, then you can design it as beam or slab. Basement walls are basically designed as three edge supported slabs. 

 

But in high seismic regions, i think your walls will also behave as shear walls so proper consideration should be given to seismic induced forces. 

[UmarMakhzumi]

You can design it as propped cantilever. The presence of top floor and foundation would enforce one way bending (Case of a square panel with two sides having stiff supports)

For areas where you don't have a top floor, you can use the information provided in the link below to design your wall as 2 way slab panel.

 

http://www.sepakistan.com/topic/16-rectangular-concrete-tanks/

 

Thanks.

[Waqas Haider]

Umar bhai,

Can i design retaining wall as shear wall? because this concrete retaining wall is also going to resist in plane forces along with out of plane forces? In ETABS ho to cater it?

[UmarMakhzumi]

Since the length of basement wall would likely to be much longer when compared to a conventional shear wall, lateral shear resisted / unit foot of basement wall would not be significant. Critical case for basement wall (generally speaking) should be lateral load due to earth + any increase in that lateral load due to earthquake. This load would be perpendicular to wall.

 

Also, have a look at the following topic (there are 5 threads) as you may find them interesting:

 

http://www.sepakistan.com/tags/forums/Highrise%2Bwith%2Bbasements/

 

Thanks.

[Muneeb Badar]

Dear Shaker,

 

The better way is to model this retaining wall as vertical beam element for 1 meter width. Apply the appropriate boundary conditions such as fix at bottom and free or pin at top. Apply the soil pressure laterally and then simply take moments and shear. Shear force will be used to decide the thickness. So just use the general shear formula which we normally use for one way shear and decide the thickness.  For flexure use beam flexure formula to calculate reinforcement.

 

Dear Waqas,

 

you are right. Actually in basements the seismic shear/forces are transferred fro retaining wall to shear walls. So there will be inplane forces in the retaining wall. For flexural reinforcement you can use earth pressure but as you know there is a distribution reinforcement in the retaining wall as well. This reinforcement  will be designed for inplane forces. 

This is very simple to calculate. Assign the one side of retaining wall as one pier. Extract V2 force and the use the length of retaining wall as depth  and use one way shear formula and calculate reinforcement as in case of shear wall.

 

Thanks

 

Muneeb

[mhdhamood]

thanks so much guys..... This is the best forum 

[mhdhamood]

But let me add one more thing ; we shall add the axial load and moment carried by the basement wall from the slab.
Am I right ?? or we can neglect the axial load and just taking the moment due to fixity consideration

[WR1]

You have to take all the forces for design of walls, axial, shear, lateral earth/water pressure. But usually walls are quite strong in compression and you can assume pinned connection of basement wall with floor. That way you design only for lateral earth/water pressure with propped-cantilever condition (fixed at base, pinned at top).

 

Model a line element in a structural software and check the moments.

 

a. For a triangular load (earth pressure) maximum moment at base will be -2WL/15 and positive moment somewhere above base will be 0.0596WL with 1/4th reaction on pinned support.

where W is the total load in KN.

 

b. For a uniform load (surcharge) max mom at base is WL²/8 and max positive moment is 9/128 WL² with 3/8th reaction going to pinned base.

where W is the load per m in Kn/m.

 

 

Then just add a and b together (superposition for linear analysis).

[mhdhamood]

Great brothers his is the greatest forum 

[Waqas Haider]

dear shaker,

in case you are having just concrete wall as basement and no columns in wall and the length of wall is long then your wall will bend as one way slab. in such case i prefer to model as line element of unit width. But still you need to provide proper consideration to the corner of the wall where this one way action will be restrained. 

 

But in case we are having columns with in the wall then our slab will be showing a dishing effect which depends on the stiffness of wall and columns. in this case i prefer to model the real model consisting of columns and wall so that i may see actual deformation and i will read forces from this model. because at interface of column and wall behavior will be changed than mid span.

 

I need opinion of seniors over this. Thanks. 

[Ayesha]

Here is a solved example as well.

Buried Concrete Basement Wall Design.pdf

Edited May 24, 2017 by Ayesha