Splay rod install on pre-eng building 1

[strengineer17]

I have a pre-engineered steel building 100'x50' and i have done a fast foundation design for it. However i'm not sure if the building requires splay rods or not. I have design the columns to sit on concrete piers and the piers are tied into the surrounding foundation wall. Does anybody know where to get info on the design of splay rods?

 

[msquared48]

I am not familiar with the term "splay rods".

Are you talking about embedded hairpins in the slab to take the lateral kick of the mainframes?

Mike McCann
McCann Engineering

 

[JLNJ]

The hardest part of a pre-engineered building is handling the thrust loads to the foundations. Do you have the loads from the PEB manufacturer?

 

[cldea8]

If you are talking about thrust and hairpins, we have done some research on the matter. We try to use hairpins where we can to carry the thrust into the SOG. Our biggest question became when to use cross-ties from column to column. It seems there is a point (at some thrust magnitudes) where your force resisting elements become riddled with assumptions concerning friction, transfer across construction joints...etc. I would say that if you are in doubt and it is a rush job, do a thickened slab from column to column and embed cross ties.

During our search we learned about a book that Butler Manufacturing published in the mid 80s. It was a design guide on pre-engineered building foundations. It contained some test data and good 'rules of thumb'...so I am told. It is out of print for liability reasons.

If you find it let me know where to get it!

I would say that if you are in doubt and it is a rush job, do a thickened slab from column to column and embed cross ties. Then there is no question.

cldea8

 

[msquared48]

If you have to do cross ties, I do not do a thickened slab, but a separate grade beam under the slab so there is no worry of construction joints and expansion/contraction. It is a separate pour, and there is some eccentricity, but this can be easily controlled. Generally, with normal wind loads and reasonable eave heights, for mainframes 50' or less, single or double hairpins will work. More load and larger spans- go to tension ties in a grade beam. Whatever works.

Still do not know what he meant by "splay rods" though.

Mike McCann
McCann Engineering

 

[strengineer17]

Thankyou for your help, Splay rods is apparently just another name for hairpins.

 

[fasboater]

cldea8

I have a copy of the Butler Manufacturing Foundation Design and Construction Manual, although I have no idea how to get it out there for you. Any ideas?

 

[cldea8]

Really? I am sure it is something you have had for quite a while and you wouldn't know where to purchase it? Does it contain the 'rules of thumb' I read about online?

It is good to know it does exist anyway...

 

[fasboater]

It has a lot of good examples with design capacities. It is 176 pages long not including the appendix. Although I think most of the information you could get out of a good foundation design text with the exception of section that deals with foundations to resist horizontal forces. There is a lot of information in that section that I have not found elsewhere. I have the second edition, I don’t know if there are any editions released after.

 

[zaes73]

I have been designing pre-engineered buildings for a long time, and initialy found it very hard to find text related to the design of foundations of such buildings, because in all the concrete design books not much reference was available for foundations with high slip, and uplifting overturning moment.

Hair pin rebars uses the principle as tie rods, and in this system hairpin relies on the floor slab to function as the tie. Concrete itself cannot take much tension but the steel reinforcement within slab would. By lap splicing the horizontal loads are transfered to the floor slab.

to design a hairpin, divide the horizontal column reaction by an allowable tensile stress of the reinforcement (24 for Grade 60 steel, ) and you will get the area of steel to be used. The length of bar depends on the slab area to be engaged, it should be long enough for the assumed failure plane to intersect the desired number of slab rebar and to allow for their proper development.

Do keep in mind that for these hairpins your flooring should be reinforced. and not PCC. it would be a Slab on grade.

hope this helps