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Join Date: Oct 2010
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Lapping of Steel in Tie Beam Foundations

10/22/2010 10:50 AM

how is lapping done in tie beam in isolated footings.is anchoring of beam necessary at ends of beam

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Guru

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#1

Re: Lapping of Steel in Tie Beam Foundations

10/22/2010 12:29 PM

Yes. You need a mentor or a good book to tell you how. Sorry, I can't help with the book, I haven't bought a book in many years, I don't know what is available there days.

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#2

Re: Lapping of Steel in Tie Beam Foundations

10/23/2010 8:50 AM

I am suggesting that you obtain a copy of the following concrete engineering text book:

"Reinforced Concrete Design, 4th Edition", Leonard Spiegel, PE/PH.D & George F. Limbrunner, PE, Prentiss-Hall, Inc., 1998.

Both authors were Civil Engineering Professors at Hudson Valley Community College located in Troy, NY. The textbook will show you how to calculate rebar lap lengths, depict rebar placement, and how to physically attach rebar together. Additionally, the textbook will show you how to anchor rebar.

I'm assuming that your "tie beam" is a concrete "grade beam" tying two or more isolated (spread) column footings together due to structural considerations? If yes, you MUST anchor the rebar into the concrete footings and the column piers in a concise and proper manner. The textbook covers this requirement as well.

You can purchase a new or used copy of the text in Ebay or Amazon.com for a relatively painless price.

I highly recommend the aforementioned textbook. I had both authors for teachers when I attended HVCC many moons ago and can attest to their solid engineering approach to reinforced concrete design.

You may also want to obtain a copy of the following textbooks:

"Reinforced Concrete Design", Wang & Solomon.

"Foundation Design & Analysis", Joesph E. Bowles.

I hope that information helps you. Any further questions just ask away!

===CaptMoosie, PE/PH.D

Civil, Structural & Environmental Engineer

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#3

Re: Lapping of Steel in Tie Beam Foundations

10/23/2010 4:22 PM

20 bar diameters is standard specification. Take the strap footing bars through the column footing and bend an L that you tie to the perpendicular bars, do the same with the perimeter footings. If there is any concern about soil bearing value, stratified clays like marine or any highly plastic material stop what you are doing and get a qualified structural/geotechincal engineers you provide a real solution.

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#4
In reply to #3

Re: Lapping of Steel in Tie Beam Foundations

10/23/2010 11:45 PM

20 bar diameters would be the development length for 3/4" diameter and smaller bars with a yield strength of 40 ksi.

Reinforcing bars are at least 60 ksi these days. Therefore the development length would be about 30 bar diameters and the lap length about 40 bar diameters.

These numbers would be higher for bars larger than 3/4" diameter and also if the bars were top bars with more than 12" of concrete below them.

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#5
In reply to #4

Re: Lapping of Steel in Tie Beam Foundations

10/24/2010 9:11 AM

I made the assumption that this was a very small project since there is no engineer involved which leads me to the logical assumption that #6 would be largest rebar involved. Anything larger would come from a fabricator based on details in a set of engineered drawings. I walked away from construction 22 years ago but never had a structural failure.

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#6
In reply to #4

Re: Lapping of Steel in Tie Beam Foundations

10/24/2010 9:48 AM

they a hv given a detailed drawing but lap in continous beam was not clearly shown.in roof beams they hv shown at mid span in top bars and for bottom rods over columns.they hv given lap length as 50 times bar dia.so it is it right to take the lap at mid span and over column supports as shown in roof beams continous ? 20mm dia bar used

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#7
In reply to #6

Re: Lapping of Steel in Tie Beam Foundations

10/24/2010 11:17 AM

Hello Adityaarun,

Exactly who is "they"? The Engineer who designed the structure and prepared the construction plans? A non-licensed or a licensed Structural Engineer? EXACTLY WHERE ARE YOU LOCATED & WHAT ARE THE GOVERNING STRUCTURAL CODES? ARE THE ENGINEERS USING ACI-318 OR ANOTHER CONCRETE CODE??????

What necessarily works in a reinforced concrete roof or floor beam will not necessarily work in a grade beam tying column footings together. There are a host of different factors involved in the PROPER design of the latter, not limited to just differences in magnitude of design Bending Moments (Mu) and Shears (Vu). Also, depending on the location of the reinforcement, lap lengths and minimum embedment lengths can vary and there is a whole host of variable "conditions" to satisfy, including multiplying factors x the BDL. You just cannot use 20 db, 30 db, 40 db etc for lap splices throughout (as suggested by others herein) because some multipliers can (and usually do) come into play in determining minimum lap splice lengths. And don't forget about proper termination locations of the lapped rebar.

Due to your statements that the plans (ie "hv shown") my suggestion for you is ask the designer for clarifications via a RFI regarding lap splices, rebar termination points, and embedment requirements throughout (especially at the column pier and footings) within the tie-in grade beam. Also I noticed that you made no mention of installation of stirrups along the grade beam to control the propagation of shear cracking. I'd have that in the RFI as well!

Good luck and we await your further postings containing clarifications and answers to questions.

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#11
In reply to #7

Re: Lapping of Steel in Tie Beam Foundations

10/26/2010 1:33 PM

they means the consultant structural engineers. .reg stirupps they hv given midspan ie span/3- 5/m and at both ends 7/m.reg codes i will chek with them?...THIS IS PLAIN TIED LAPPING .NO WELDING /MECHANICAL ONE.

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#9
In reply to #6

Re: Lapping of Steel in Tie Beam Foundations

10/26/2010 8:09 AM

Are "THEY" the "DESIGNERS".

What is the length of the tie beam?

In case the supports / columns are more than 10 meters seperated, you should get designer approval for location of lapping.

Otherwise provide 50xdia as lap length as thumb rule and read my earlier post for location of lap.

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#10
In reply to #9

Re: Lapping of Steel in Tie Beam Foundations

10/26/2010 9:03 AM

The OP has never said where they're from and where this project is.

If in the USA, then the ACI Code 318 must be utilized. Lap Splices are covered in Chapter 12 (in the '95 edition....sorry I don't have the latest revision on hand here at home).......Tension lap splices and compression lap splices are treated quite differently, and hence using a general rule of thumb is a very dangerous way to design a RC member, as consideration of cut-off points, etc., must be taken into account plus development length requirements beyond the theoretical cut-off locations. Also, it depends on whether the rebar is in the top or bottom of the beam....plus there are several types of splice classes to take into consideration. Welded and mechanically lapped splices are treated totally differently that p;ain tied lap splice are staggerring of the lap splices are required a given distance. depending on the type of splice and bar diameter.

Sorry, you just cannot apply a multiplier to the bar diameter and pray that it'll work later throughout the design lifetime of the structure. It's a little more complicated than that.......IMO a bad suggestion and over simplication that may result in non-conformance to the ACI Code in some instances.

As I stated before it is the responsibility of the OP to issue a "RFI" to the "Engineer of Record" to clarify outstanding structural issues found on the Construction Drawings, and since we are not a party to those details it is not wise for any of us to provide "simplified" answers to a cloudy questions with too many unknowns.

---Signed,

CaptMoosie, PE / PH.D

Licensed NYS Civil & Structural Engineer

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#8

Re: Lapping of Steel in Tie Beam Foundations

10/26/2010 7:57 AM

Be more specific about lapping of bars in tie beams. Normally in all beams, provide lapping to bars in compression area.

Yes, anchoring is necessary. Otherwise if you want to remove anchoring, get designer approval.

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