Development length 1

[precast78]

Lets say I have a rebar that I need to splice (transfer the tension force to another rebar), but the transverse distance (ACI 318 12.14.2.3) is too far apart. What are my options? Can I make the lap length longer?

 

[strucguy]

how far is too far?? If there is little gap between bars that are being lapped, that is actually good as it increases the exposed perimeter of the bars and helps in reducing lap length. But if they are too far apart, you have to look at other factors that may be at play.

 

[precast78]

struct guy... maybe about 3 to 8 inches. That is what I am trying to figure out strucguy. Basically this is a cast in anchor for a pole and it has too much tension for Appendix D. I need to transfer the tension to rebar in the concrete and the anchor may not be very close to the vertical steel in the foundation.

 

[dcarr82775]

If it is cast in, why not just provide bar in the bottom portion in the right place? Is the bottom bit already cast?

For what you describe I often change the steel in the bottom bit so that the appendix D breakout cannot happen. Then you don't have a lap splice.

 

[precast78]

dcarr, I am trying writing an excel spreadsheet that will cover more scenarios when the anchor bolts rely on the vertical steel in the foundation. Our vertical steel is usually standard (4-#5 vertical rebar in 24" diameter x 7'+ long foundation). We cast in the anchors per whatever the customer wants. If appendix D calc is too low, obviously we need to transfer the anchor tension to the vertical rebar. But these vertical rebars are always about 2" from the skin, where as the anchors are per whatever bolt circle needed for the lightpole. Unfortunately there is always a gap between the engineer, pole manufacturer, and foundation manufacturer(or cast in place). I believe a lot of light pole bases foundation built today do not have the pull out capacity. Most of the time the appendix D capacity is too low and it seems they just put the anchors where ever they want without thinking about how to transfer the load to the vertical rebars.

 

[ESse]

You need to be careful with this situation. The ACI provision allows for bars to offset transverse to the plane of a layer of bars, such as a wall or slab. In this situation described by the OP, the offset between anchors and foundation bars is not transverse, but out-of-plane. The out-of-plane offset creates a tendency for splitting due to the concrete between the offset acting like a diagonal strut. If there isn't adequate confinement steel, the concrete will split before the bars are developed.

I researched this offset for a retaining wall failure with out-of-plane offset lap splice. I posted information in this thread:

http://www.eng-tips.com/viewthread.cfm?qid=356939

. See the article from Washington State DOT on smaller diameter bridge pier connection to larger diameter caisson contained in the other thread for additional information.

 

[IDS]

I'd recommend everyone follow ESse's link, and download the attached paper. See short extract below:

Failure in the preliminary specimens occurred when the applied loads reached values of approximately 40-60% of the bar yielding force

Non-ductile failure at a load of 40% of what you thought it would be is not something to take lightly.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[Agent666]

In New Zealand, our code states that you use the development length plus 1.5 times the spacing between the bars in this situation.

I thought there was something similar in ACI 318 as our code is based on the ACI code?

 

[TLHS]

If you're outside the regular intention of the usual code provisions, then design the load transfer as strut and tie.