Horizontal ties at Change in retaining wall thickness
Horizontal ties at Change in retaining wall thickness
(OP)
http://ladbs.org/LADBSWeb/LADBS_Forms/PlanCheck/PC...
The link above is to Los Angeles City's standard grading plan check list.
Item G. 2 (on page 5 of 6) states "Provide retaining wall details on plans, show: surface drains, subsurface drains, slope of backfill, tie at change in wall thickness and reinforcement."
What is meant by "tie at change in wall thickness and reinforcement"?
Please see attached sketch. The ties drawn in that are what the plan checker is requesting - I have never seen these and do not know what purpose they could serve. Anyone have any idea?
The link above is to Los Angeles City's standard grading plan check list.
Item G. 2 (on page 5 of 6) states "Provide retaining wall details on plans, show: surface drains, subsurface drains, slope of backfill, tie at change in wall thickness and reinforcement."
What is meant by "tie at change in wall thickness and reinforcement"?
Please see attached sketch. The ties drawn in that are what the plan checker is requesting - I have never seen these and do not know what purpose they could serve. Anyone have any idea?






RE: Horizontal ties at Change in retaining wall thickness
RE: Horizontal ties at Change in retaining wall thickness
RE: Horizontal ties at Change in retaining wall thickness
I didn't know any of my details got to California!
Mike McCann
MMC Engineering
RE: Horizontal ties at Change in retaining wall thickness
My initial thought was the plan check list is poorly worded and these ties are not the intent, as so far no one can provide a code reference.
The item starts out very general. "Provide retaining wall details on plans," then mentions a few key things these details should show. I think the "tie" part is a really bad way to say "show the required embeds/laps where wall thickness changes."
The plan checker says it's in the UBC masonry code, but they have an example worked out with 12" o/ 8" block with no mention of these ties (though that example may only use a single layer of reinforcement in the 12" stem).
My only contact with the plan checker is through a third party, as he won't respond to my phone calls or emails directly.
RE: Horizontal ties at Change in retaining wall thickness
RE: Horizontal ties at Change in retaining wall thickness
RE: Horizontal ties at Change in retaining wall thickness
Therefore in a sense, you get more shear capacity, although it is impossible to calculate the actual shear capacity in the case you don't have those ties.
Likewise, it is impossible as far as I know to calculate the contribution of the ties. All I know is those ties should prevent the 8" CMU from shearing off the 12" CMU - something I never worried about here in AZ, but probably an issue there in CA.
RE: Horizontal ties at Change in retaining wall thickness
RE: Horizontal ties at Change in retaining wall thickness
Just got off the phone with the plan checker. The ties aren't in any code because he's simply referring to tying the vertical bars in place.
RE: Horizontal ties at Change in retaining wall thickness
Mike McCann
MMC Engineering
RE: Horizontal ties at Change in retaining wall thickness
RE: Horizontal ties at Change in retaining wall thickness
RE: Horizontal ties at Change in retaining wall thickness
RE: Horizontal ties at Change in retaining wall thickness
RE: Horizontal ties at Change in retaining wall thickness
Our note specifies top and bottom of wall and at 8' on center.
RE: Horizontal ties at Change in retaining wall thickness
This retaining wall detail with an "offset splice" between the flexural reinforcing bars is problematic. My company has had a bad experience (partial collapse) in a very similar situation with a cast-in-place concrete retaining wall with stepped changes in thickness on the non-exposed face (the flexural tension face of the wall). If this wall were concrete, ACI 318 requires that non-contact lap splices be not spaced transversely farther apart that the smaller of one-fifth the required lap splice length and 6 inches. The offset is permitted to be transverse only (i.e. in the plane of the wall) since splitting will be resisted by the plane of the wall itself. Offset splices in the "out-of-plane" direction are not specifically addressed by the code. In this detail, there is a compression strut that develops between the bars, unfortunately, there is no "tie" to complete a strut-and-tie system and thus the detail is prone to splitting failure before the bars can be developed. Draw a free-body diagram with the flexural tension on each of the bars and you can see that the eccentricity between the flexural tension bars is unresolved unless confining ties are present.
See the attached article on tests that were performed by the Washington State DOT on offset splices at bridge column shaft to caisson interfaces. Their conclusion is that splitting occurs prior to yielding of the bars unless the splice is confined with ties.
As it is uncommon to have confinement ties in wall construction and I believe that this detail should be avoided.
RE: Horizontal ties at Change in retaining wall thickness
RE: Horizontal ties at Change in retaining wall thickness
RE: Horizontal ties at Change in retaining wall thickness
Anyway, the update is that the plan checker was apparently not asking for vertical bar ties. Instead, he wants the top horizontal bars (wherever we use two layers of reinforcement) tied together with seismic hooks each side.
RE: Horizontal ties at Change in retaining wall thickness
Mike McCann
MMC Engineering
RE: Horizontal ties at Change in retaining wall thickness
RE: Horizontal ties at Change in retaining wall thickness
I don't have the code in front of me, but I think using the longitudinal bars for confinement can cut your splice/embedment length by up to half. It also changes the nature of the failure, making it less sudden and brittle. All music to the code official's ears.
Is the upper bar offset on purpose or does it just look that way in the sketch? If it's too close to the face shell you might not be able to develop the bar properly. Maybe the bar's location and propensity to be misaligned in the field is a concern to the plan reviewer.
RE: Horizontal ties at Change in retaining wall thickness