×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

GRADE BEAM DESIGN

GRADE BEAM DESIGN

GRADE BEAM DESIGN

(OP)
Our office has had much debate about this one.

The scenario is you have a grade beam spanning from drilled pier to drilled pier, supporting more rigid load bearing concrete walls (several levels) above. Do you design the grade beam taking into account the stiffer wall elements above will deflect less than the beam and try to transfer the loads directly to the piers? Or do you design the grade beam as it if is transfering the full load to the piers? The two approaches can yield significantly different grade beam design results, not to mention pier reactions.

Your thoughts & input are greatly appreciated.  

RE: GRADE BEAM DESIGN

We don't even design grade beams underneath the walls.

The walls are more than capable of spanning between piers.

RE: GRADE BEAM DESIGN

I would agree with frv. If anything they should be able to carry the weight of the concrete pour and formwork. Although the soil is most likely able to support that amount of weight.

RE: GRADE BEAM DESIGN

In general, agree with above two responses. But sometimes the grade beams need to be formed due to underlying services and utilities. The contractor typically strips the grade beam bottoms, adds re-shoring, forms the walls and the slabs, pour walls and slabs in one shot, strips slab after two days, reshores the slab..... a common scenario. Moreover, many times the contractors assigned for below grade, below cellar work, are different from the ones who take up superstructure work.    
It is difficult to predict field conditions and means and methods the sub-contractor may employ during construction. We always design grade beams to support load from at least one or two storys without counting on the underlying soil.   

RE: GRADE BEAM DESIGN

In my area, due to potential frost heave, grade beams are always underlain by a void form, usually four or six inches thick. The void form is capable of carrying the weight of the grade beam without too much settlement but not much more so the grade beam must able to carry the wet concrete above it.

If the first story wall is continuous, it may be relied upon to support the upper stories.  If there are door or window openings, engineering judgment is required as to what portion of load is carried by the grade beam.

BA

RE: GRADE BEAM DESIGN

One reason for the presence of the grade beam over a drilled pier, similar to a pile cap, is to allow for variance from the plan of the actual drilled pier location.  The grade beam is able to be placed over the pier, not necessarily centered over it, but directly under the wall, serving as a lateral location adjustment for the foundation system.  It also serves as an expanded area for the anchorage of the wall to the foundation system if needed.   

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
 

RE: GRADE BEAM DESIGN

I have used grade beams with void forms below (may not be your case) and I would design the beams to carry an amount of the wall weight as it is being poured (I would note this on the drawings), subsequent to the walls reaching some cured strength level they should be able to carry the additional walls poured above and the floor weights if the walls are detailed for continuity between piers.  

RE: GRADE BEAM DESIGN

I agree that the grade beam may not be needed and the wall should be able to span.

We once had a building plans reviewer, rightly so, do a strut-and-tie analysis for a planar shear wall that was supported by pile caps at each end. A finite element stress analysis indicated that this wall acted as a purely compression member until the first floor (about 10 feet) high and then as a deep beam, looking at the compression struts. The wall was 30 feet long. We ended up providing some hooked #8 bars at the base.

RE: GRADE BEAM DESIGN

(OP)
Thank you all for your comments. As always it's appreciated. Personally I think the design falls somewhere in between the two approaches. The grade beam will take some load, as much as its stiffness allows, and the stiffer walls will transfer more of the load to the piers. That is not to say that the walls above could not span between the piers without help from the grade beam.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources