Headed deformed bar development length for highly loaded piles 1

[bumbler]

Our office is designing a deep foundation system for a large multi-family building. The deep foundation system consists of piles and grade beams due to a seismic design category of D and a site class of E. We have already been through permit and are now getting strong pushback from the contractor and rebar suppliers on our pile design for the construction set. We have three zones for the building that we worked out with geotech based on soil quality. Zone 1 and zone 2 have better soil and therefore we can use fewer vertical bars and can easily use headed deformed bars for development into the pile cap/grade beam. Zone 3 has terrible soil and our design uses (7) #10 for an 18" pile and (12) #10 for a 24" pile. Per ACI 318-14 section 25.4.4.1(g), clear spacing between bars must be at least 4db, which is about 5.1" for a #10 bar. Per our calculations we have 2.8" and 3.0" clear spacing for 24" and 18" piles, respectively. We have used hooked bars for embedment in Zone 3.

The contractor has pushed back hard on this, saying that they are going to use headed bars for all embedment despite what we say. They have sent older drawings that allow headed bars which appear to not be code compliant, and had a peer review conducted. The peer review cited R25.4.4.1 to justify ignoring 25.4.4.1(g), particularly the sentence "To avoid congestion, it may be desirable to stagger the heads." I don't understand what that has to do with the vertical clear spacing requirement, and it seems to me if there was any way around it then the code would explicitly say that. Does anybody have more experience with this problem or some advice? I've rarely used headed deformed bars and the contractor refuses to budge on this.

 

[BAretired]

Offhand, I would guess that a headed bar offers better anchorage than an 'L' shaped hook, but I have never used them. The contractor may have valid reasons for his position on this matter, but it seems to me that he cannot change your design without your approval, so you are going to have to come to a meeting of the minds if you are the EOR accepting responsibility for the structural design.

BA

 

[dik]

There's a lot of information out there, for anchor rods, anyway, where headed anchor rods are far better than 'J' or 'L' bars, but I've never used this for rebar. I've been using headed anchor rods for over 2 decades, and on my own projects they are the only things I use. I suspect the results for rebar should be similar. I don't know what the impact of the deformations would have on this. One of the reinforcing steel institutes should be able to provide guidance.

"HRC 555 headed reinforcing bar is a deformed or plain steel bar with a head attached to one or both ends. HRC 555 reduces anchorage length, congestion, and construction time while providing superior performance. A great alternative to standard hooks throughout your concrete structure, from pile anchorage to beam/column joints.

Research has shown headed lap splices are very effective for closure pours and according the Section 12.6 of ACI 318-08 the HRC 555 Series headed bars have the shortest required development length compared to standard hooks or straight bars. Great for closure pours and other locations not permitting the length of conventional lap splices. The use of Headed Reinforcement improves the form, fit and functional performance of reinforced concrete structures at a low cost. The concrete also benefits because adequate space for pouring and vibrating will give better concrete consolidation. Reduced congestion and the ease of placing Headed Reinforcement will improve constructability and speed up the project." There is even an ASTM Spec

https://www.document-center.com/standards/show/ASTM-A970

https://www.hrc-usa.com/hrc-555-headed-rebar/

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[cliff234]

We use headed deformed bars all the time. They greatly reduce congestion. Regarding the spacing of headed bars, ACI 318-19 now allows headed bars to be spaced as close as 3 x bar diameter (center to center). (3.81" spacing for #10 bars.) The penalty for using the closer spacing is that a greater development length is required.

 

[dik]

Thanks cliff... didn't know that. Name's cliff... drop over.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik