splice length

[Lutfi]

In reviewing some recent plans I noticed that the splice of the bars is tabulated in terms of bar diameter. I thought ACI has several factors in determining splice length other than X*bar diameters.

Any comments?


Regards,
Lutfi

 

[haynewp]

There are a lot of add'l factors that go into splice development, but it all depends on what the engineer is assuming for the placement of the bars. If all the bars are going into the same strength and weight concrete, with the required cover, clear spacing etc., you could develop a simple table giving the appearance that it is based only on the bar diameter, which I see quite often. Or he could be using an envelope of the most strict splicing requirements on the project and putting it in a simple "X*dia" form to avoid confusion.

 

[WillisV]

As haynewp said we put a table based on X*dia format which has three categories generated considering the different cover requirements etc. based on all the ACI provisions. This is done quite often.

 

[SlideRuleEra]

Lutfi - Using bar diameters is how the masonry industry historically addressed the need to define splice length. It was originally empirical and came into use more or less in parallel with more scientific methods used by ACI and CRSI.

I know that there has been a lot of "cross-over" in it's use with reinforced concrete - in the 1970s, bridge construction superintendents that I worked with would fall back on bar diameter rules-of-thumb if the lap length was not clearly defined.

http://www.SlideRuleEra.net

 

[Lutfi]

SlideRule, I agree with you and I used to practice the same for CMU and concrete. However, I have changed on concrete a while ago and recently changed the practice for CMU. Florida Building Code differs or has slight variation in the lap splice length that the ACI 530-99 code! Those of you who design in Florida need to take a note of this. See FBC 2004, section 2107.3!!! The new splice requirement is similar to the one in ACI-530-05. It is more involved and has several variables. The equations is as follows:

Ld = (0.16*db^2*fy*gamma)/(k(f’m)^0.5)

The lap of 48*bar diameter may not be accurate as you start using larger bar sizes.

On my plans i have a table with various concrete strength and depth of rebar (over or under 12 inches of cover) and I am very explicit with the exact lap length for each bar.

I am always concerned with leaving it up to the contractor to perform calculations. That is my point of raising this question.

I want to thank all for their input.


Regards,
Lutfi