×
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

Retrofitting Basement Retaining Wall for large 1st floor slab opening

Retrofitting Basement Retaining Wall for large 1st floor slab opening

Retrofitting Basement Retaining Wall for large 1st floor slab opening

(OP)
I am working on a project where the architect wants to put in a fairly large slap opening parallel to an existing concrete basement retaining wall (approximately 18').

The basement wall is a daylighting condition (1 story one side, 2 stories on the other side). The opening would be on the retaining side. The building consists of concrete exterior walls, one-way concrete elevated 1st floor slab, and wood framed hipped roof. The structure was built ~1910. I will be reinforcing the 1st floor slab as part of the project, but my main concern is with the concrete wall. We are in a high seismic area, relatively low wind area. It is likely that the basement wall was originally designed as pin-pin between the basement level and the elevated first floor slab.

One option I have been kicking around is the use of FRP. I was envisioning putting in horizontal strips of FRP on the inside of the concrete basement wall and designing the basement wall at the penetration as pin-pin spanning horizontally across the opening. I was then thinking of putting in vertical strips either side of the opening to reinforce the wall to transfer a higher load back to the slab. I would need to check the slab connection and extend the horizontal strips far enough as necessary to engage a large enough section of vertical wall area that is in contact with the slab. As an alternate, a similar approach could be done utilizing steel channels or tubes.

Above grade, I have not completely thought out my approach. It may be similar but it is a higher value area so eliminating the FRP would be ideal. Possibly, I could use the horizontal strips just near the first floor intersection to form a beam to span the opening. Still thinking about the approach.

Just wanted to get some opinions on this approach, and if you all have used another solution for similar penetrations in floor slabs supporting concrete walls.

RE: Retrofitting Basement Retaining Wall for large 1st floor slab opening

What is the proposed length of the slab opening at the wall and how much earth is the wall retaining?

Mike McCann, PE, SE (WA)


RE: Retrofitting Basement Retaining Wall for large 1st floor slab opening

how about some helical tie-backs?

RE: Retrofitting Basement Retaining Wall for large 1st floor slab opening

(OP)
I don't have the drawings in front of me but the proposed length of the slab cut is approximately 15'-18' and the wall is retaining ~9'.

RE: Retrofitting Basement Retaining Wall for large 1st floor slab opening

In a similar situation, I installed an exterior side horuzontal concrete beam (girt) dowelled into the existing wall a few feet below grade.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Retrofitting Basement Retaining Wall for large 1st floor slab opening

(OP)
Thanks Koot. This could be an excellent solution. There is some sitework outside of the building, so that may be a deal breaker, but I will explore a bit.

RE: Retrofitting Basement Retaining Wall for large 1st floor slab opening

Glad to hear it jdengineer. I live in a wintery wasteland. When I've used this detail, I've put frost cushion under the girt and or beveled the exterior face of it to mitigate frost heave issues. I'm not sure how necessary that is but it's something to consider.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Retrofitting Basement Retaining Wall for large 1st floor slab opening

You could also look onto leaving an interior strip of slab that could serve as a beam if an adequate tension element was either present or added. Frp on the underside could take the shear.

Mike McCann, PE, SE (WA)


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