ACI 318-05 Class B Tension Lap Splices

[pcronin]

In Section 12.15.1 in the notes under the splice requirements of 1.3(ld) for Class B splices it states, "where ld is calculated in accordance with 12.2 to develop fy without the modification factor of 12.2.5". The modification factor in 12.2.5 is the As provided/ As req'd reduction. Linear reduction in the capacity based on the reduced development length. The commentary under 12.15.1 states "The development length ld used to obtain lap length should be based on fy because the splice classifications already reflect any excess reinforcement at the splice location; therefore the factor from 12.2.5 for excess As should not be used".

I am reviewing a project for a client of ours (we didn't do the design for this project) and the dowels for the pier reinforcement only have a splice of around 16". The pier experiences minor uplift and the reinforcement specified is complete overkill(designed by others). (4)#7 bars = 4*.6*60*.9 = 129.6 kips (ultimate tensile load)

I checked the strength using the reduced capacity of section 12.2.5 and it works, but is this allowed at a splice location? Are the requirements of 12.2.5 just for straight development length? I have always allowed for reduced capacity of bars at lap splices, but this project might go to the courts. I want to have all my ducks in a row.

 

[DaveAtkins]

I think your approach is correct. What the Commentary is saying is you cannot assume you have twice the area of steel AT a splice just because there are two bars at the splice (well, duh, that is what a splice is...). But if you have more steel than you need ADJACENT to the splice, I think you can use the As req'd/As prov'd reduction.

DaveAtkins

 

[JAE]

I think the code explicitly says you cannot use the As(req'd)/As(prov) factor here. If you look at the Commentary Table R12.15.2, it shows that in some cases you can use a reduced splice length (i.e. a Class A splice) when you have lower stress conditions, but if all of the bars are spliced you must use a Class B splice and cannot use 12.2.5.

 

[pcronin]

I think the wording of the code is flawed. I am looking at the capacity of the (4) vertical bars, not the (8) total bars at the splice.

So based on the way the code is written, any length less than the full lap splice means the splice has zero capacity? My uplift load is minor and less than 10% of the full capacity of the bars. Even with a 16" lap, I have a safety factor of 2.3 (in addition to the LRFD factors)

Attorney speak, I may have to agree with JAE. Good engineering judgement and I am with Dave.

 

[JAE]

"Attorney speak, I may have to agree with JAE. Good engineering judgement and I am with Dave. "

I'd agree with that.

 

[civilperson]

Top layer reinforcement for Crack control if surface is visible.

 

[haynewp]

pcronin

Section 12.2.5 pertains to "flexural" members anyway and it sounds like you have a direct tension member.

 

[pcronin]

haynewp - didn't even see the "flexural" reference. learn something new everyday. don't really understand the difference, since in a flexural member the reinf is in pure tension anyhow.

i guess the code gods must know somthing we don't know. most code revision serve a purpose of overcomplicating our profession while our fees need to remain the same. some code revisions are valid though. but that is another topic for another day.

thanks for the imput. I am going with sound engineering judgement on this one.

 

[haynewp]

ACI becomes a little more strict with splicing in tension only members depending on the amount of force. Your case may or may NOT qualify under section 12.15.5, but this is usually how I design tension members like tie beams for metal buildings. They don't allow lap splicing of reinforcing if the tension member meets 12.15.5.

 

[kslee1000]

If I remember correctly, Type B Splice is to be specified for splices without offset/staggering. The 1.3 factor is more of a practical concern over poor construction practice that resulting in the manner - uniform weakness accorss a common plane within calculated Ld. It has little to do with area of reinforcing (As). Thus As (prov)/As (req'd) is not completely justified.

 

[smokiibear]

Fellows, what is a type B and type a splice? or better yet, where do I look to get that information? At rough glance, I don't see them in the ACI 318.

Thanks.

 

[OldPaperMaker]

Smokiibear,
In ACI 3180-08 Section 12.15.1 & 12.15.2 talks about the Class A or B tension splices.