×
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

Rebar slices where tension is changing rapidly

Rebar slices where tension is changing rapidly

Rebar slices where tension is changing rapidly

(OP)
The aashto and aci codes allow adjustment of the required reinforcement bar splice length based on the ratio of steel area provided to area required.

I am looking at some structures which include marginally spliced bars in cantilevered concrete bending members.  Accordingly, the tension requirements in the member drop rapidly and are significantly lower at the end of the splice than at the beginning.

Has anyone seen a treatment of the performance of splices where the tension requirement across the splice is not constant?

Curvbridger

RE: Rebar slices where tension is changing rapidly

For any loaded beam, the moment (or "tension requirement") will vary along the length of the splice(except for beams with equal and opposite moments applied at the ends).

For analyzing a tension lap splice, I would use the highest moment (Mu-max) along the splice length (usually at one end of the splice or the other) to determine As(req'd) and then divide by As(provided) (if you are splicing one #5 bar, then As(provided) = 0.31sq.in.)

Design of a tension lap splice requires some judgement and might require one or two iterations when calculating a "minimum code compliant" lap splice length.  My advice would be to be choose a location for the beginning of the splice and then analyze it to see if the calculated splice length is adequate.

I hope this helps.

RE: Rebar slices where tension is changing rapidly

(OP)
rowe,

Thanks for your response.  The method you describe is conservative, and is appropriate for design.

My problem is that the splices are part of a bridge we are rehabilitating and are in place.  My task is to analyze their adequacy.  I don't have the luxury of assuming a constant moment.

Maybe I am wrong, and the state of stress through the length of splice is insignificant in terms of the performance of the splice?  It seems intuitively, though, that it does matter.  Isn't that why splice length and development length are different (that is, required development length assumes no tension in the concrete along the developing bar)?

Thanks again for the interest.

Curvbridger

RE: Rebar slices where tension is changing rapidly

It seems to me that the development length of rebar is primarily based upon performance through use of the factors (AASHTO 8.25.2-3)  Likewise, splice length is also based upon performance (8.32).

For one bar, an ideal splice is assumed to exhibit the same effective As along the entire splice (along the splice length, the effective As of one bar goes from 100% to 0% linearly and the eff.As of the other bar goes from 0% to 100%)  Therefore, As-prov. is constant.  Since the As-prov. is constant, the As-req'd used in the ratio factor should be the highest As-req'd within the splice length.

For many cantilevered members, designers decrease the number of rebar as As-req'd dimenishes.  This situation is slightly different than analyzing a "splice".  If this is the case, you must satisfy AASHTO 8.24.1.2.1 as well as the development length.  I believe 8.24.1.2.1 is to ensure that rebar is sufficient if the moment diagram shifts laterally due to changes in the beam properties (cracking, construction tolerances, etc.).  When analyzing bar cutoffs, it can help a great deal to sketch the moment diagram and the capacity of the rebar.

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