Need of expansion joints

[Struengin]

Hello

I have a question about the need of expansion joints in concrete structures. I'm involved in designing prototypes and would like to know if you guys have came across any guideline for calculating the maximum length allowed without expansion joints and/or if it possible to a way to overcome thermal loads with maybe adding extra thermal reinforcements?

I've come across the ACI 224.3R-95 document, it includes graphs based from an empirical method showing maximum lengths depending on local temperature difference, but I think this is conservative, and I'm sure there are recent more accurate guidelines.

I have analysed the structures on Etabs by adding the temperature loads, but would like to know how to verify if the current design is safe and serviceable.

I would appreciate if you can throw me a recent guideline/method/source relative to the subject.

Thanks.

 

[Struengin]

Anyone?

 

[rowingengineer]

I think that probably what you will find is that empirical options are based on experience and may or may not be conservative, but are a source for judgement and previous experience.

While FEA would be able to provide some stress forces concentrations which should help with overall engineering judgement decisions it will not provide complete calculation.

Problems with finding an exact solution will be because of the amount of inputs required.

some items hat would need to be accounted for if you wanted an exact solution.
1. moisture content of concrete at casting
2. temp state at casting.
3. Exposure to thermal sources and temp change speed
4. likely micro-cracking and stress change from concrete to steel during the strength gain process.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[hokie66]

There is no definitive answer to this question. As RE pointed out, it depends on a lot of things. The most important thing is irregularity in the floor plan.

My target limit for movement joints (I resist calling them expansion joints) is 40 to 50 metres between joints, and double column joints are preferred. Halving joints require a lot of attention to detail.

 

[Hokie93]

Following are a few references in my library that may be of interest.

1.) "Expansion Joints in Buildings", Technical Report No. 65, Federal Construction Council - National Research Council, 1974.
2.) "Expansion Joinsts: Where, When, and How" by James M. Fisher, Modern Steel Construction, April 2005. Available at

http://www.modernsteel.com.

3.) "Building Movements and Joints", Portland Cement Association, 1982.
4.) Handbook of Concrete Engineering by Mark Fintel, second edition, Chapter 4.

As Hokie66 indicated, the shape of the floor plan is a significant factor.

 

[Struengin]

Thanks for the help guys!

The reason for asking this is I've heard of buildings reach around 120m in length with no expansion joint, and have no problems. So the 50-60m limit could be a conservative one.

As for the irregularity of the floor plan, what is the relationship? Regular is better? Any design tips here?

Thanks

 

[hokie66]

The way I look at it, more than 50 m without movement joints is unconservative. Yes, regular is better. That is not only a principle for normal shrinkage and thermal movement, but for lateral loading as well.

 

[KootK]

I've known people to build long buildings with temporary expansion joints that get locked up once the structure is enclosed and tempered. If you live in a region where mean day/night temperature fluctuations are significant, those temperature swings can wreak havoc on your structure while it's under construction.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[bellowsmfg]

You may want to reference EJMA Handbook. I believe it deals with this to some degree.

Bellows Manufacturing and Research, Inc.

https://bellowsmfg.com

 

[jimstructures]

What does EJMA stand for??? I can think of many meanings, but I have not a clue what you are referring to.

Jim

 

[iv63]

Just google it

 

[zaes1980]

When Required ?
its a matter of experience and the engineer's choice. most of the engineers would do it to make the building regular from irregular, and when i say irregular i am referring the Definition of Irregular building defined in UBC or IBC ( i think there is a table for irregularities in UBC97). For example the irregular floor would be the one with its center of rigidity outside 5% of the center of mass. this creates floor torsion, so as a good structural practice a construction joint is placed at a location which would remove this irregularity from the building.
Where you should place it ?
check your floor irregularity, ETABS is capable of telling you this. so first of all remove this irregularity, Secondly the irregularity of length should be removed this depends on the proportion there is clear guidance in UBC about this as well. For example you don't want a building of 10m x 200m. if the building plan is 10m x 200m i would do 10m x 40m (x 5 buildings) with found construction joints. So it all depends on you.

Share the plan so i can suggest what i think you should do !