A307 vs A325 bolt 4

[upk]

About 3 years ago while casting the upper part of a building. I asked in this forum whether to use A307 or A325 bolt for future roofing addition. Someone recommended A307 over A325.. I couldn't find the thread pertaining to it and the exact reason but it's something along the line of the A325 being high strength and more brittle in connections.. so I used A307. But reviewing their strength now.. I seemed to regret choosing A307.

I'd like to know what application do you exactly use the A307 bolt over A325? Does the A325 require special torqueing in the nuts or longer embedment length.. is there special reason to use the A307?

 

[TehMightyEngineer]

I've never used A307 for anything requiring loads enough to actually go through and calculate it. The "brittleness" of A325 and A490 bolts is really a misnomer. A325 and A490 bolts can be bent into pretzels before they'll start to fracture.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[upk]

Are you saying the A307 is not usually used as anchor bolts (Edit: can't be used on anything with metal plates). then what is it usually used for? can't it be part of any bolts to support any roof?

 

[Jerehmy]

Wood uses A307 exclusively. I'll sometimes use it for little crap jobs like a new roof top unit needs a support frame. Loads are small.

 

[upk]

how weak is the A307 really.. what is its yield strength? I think it's close to Grade 40 rebars with yield strength of about 36 ksi (grade 40 rebars is 40 ksi).. so if the load can be taken by grade 40 rebars.. then the A307 may take the load too (4 ksi less)?

 

[XR250]

I use them on residential and light commercial.
Probably alot cheaper then A325

 

[upk]

XR.. you mean on wooden residential and light commercial? because it seems they only use it for wood.. has anyone actually use this on metal plates on concrete?

 

[Jerehmy]

they don't define its yield, just rupture.

quote from Salmon:
"Bolts of low-carbon steel designated ASTM A307 are the least expensive bolt. They may not, however, produce the least expensive connection since more are required for a particular connection. Their primary use is in light structures, secondary or bracing members, platforms, catwalks, purlins, girts, small trusses, and similar applications in which the loads are primarily small and static in nature. Such bolts are also used as temporary fitting-up fasteners in cases where high-strength bolts, rivets, or welding may be the permanent means of connection."

quote from Breyer:

".... Without a published value for yield strength, there is a conecptual problem in using the yield limit model with ASTM A307 bolts. As a practical matter, A307 bolts have performed satisfactorily in the past, and these fasteners must have a reasonable Fy. The tables in the NDS are based on F[sub]yb[/sub] = 45ksi, which is generally thought to be a conservative value of yield strength for A307 bolts."

 

[EngineeringEric]

I use it only on wood. It is my understanding it is a lot cheaper than A325, and come in longer lengths which would be required for wood. The wood bearing governs so often that the capacity of the steel connection is rarely seen, not always but in my experience with heavy timber and light framing the wood governs or i add bolts, never increase bolt strength like steel framing.

 

[upk]

Ok thanks guys. I'm now convinced the A307 is poor. There is still hope. I found out I can use post installed Hilti chemical bolts with tested 75.3 ksi. see:

https://www.us.hilti.com/anchor-rods

 

[wannabeSE]

I have never seen A307 or A325 bolts specified for concrete anchors. Older drawings often times specified A36. Today, F1554 is the recommended specification for anchor bolts. There are 3 grades of F1554: Gr. 36, Gr. 55, and Gr. 105. An A307 bolt has material strengths similar to F1554 Gr.36.

The A307 bolts may be OK. You need an engineer to verify the demand does not exceed the capacity.

 

[port125]

In our office we usually specify F1554 Gr 36 for our cast-in anchor rods. The reason for using the lower grade anchor Is that if the anchor is damaged or mis-located low it may be possible to weld an extension to the rod (Where using the higher yield Gr 55 and Gr 105 you would need to specify that the anchors are of a weldable alloy). this may have been why you used A307?I think you can weld to A307 because it is not heat treated. I don't believe you can weld to A325 without loosing the steels temper.

http://www.eng-tips.com/

 

[XR250]

So if A307 has a 36 ksi yield, what is the difference between it and F1554 Grade 36? Is it the consistency of the alloy or different manufacturing processes?

 

[JStephen]

In the A307 spec, there was a Grade C for anchor bolts made from A36 material, now replaced by the F1554 Gr. 36.

 

[XR250]

I don't see any difference in the mechanical properties of the two. What is wrong with using A307 if it meets the capacity requirements?

 

[SAIL3]

XR250..nothing that I am aware of.....

 

[wannabeSE]

Sail3 and XR250,
See

http://www.portlandbolt.com/technic...-a-hex-bolts-for-f1554-grade-36-anchor-bolts/

and

http://www.portlandbolt.com/technic...grade-36-be-replaced-with-astm-a307-grade-36/

 

[XR250]

So it's just a certification thing. Makes sense.

 

[upk]

So it's unanimous the A307 is unreliable? Also when one of you says A307 is used for light trusses, how light is light? The base plate it's connecting to just support 2 pcs of 18 foot rafters (size w8x21) coming from sides.. like this.

X--------W---------X

where the "-------" is the 18 foot w8x21 rafter, the base plates on the columns above (the W and X) with A307 bolts support the rafter.. is this loading low or big? The rafter just supports typical purlins and light roof material sheet.

This picture is the top of the column:

(or see

http://www.pbase.com/image/161555922

if no image shows up)

 

[Ron]

upk....how on earth did you get that A307 is unreliable from the comments above? Please read them again...that's not what they say or even imply!

A307 used in most building construction will have an ultimate strength of 60 ksi....as someone noted, 45ksi is a reasonable yield.

A307 is commonly used where high strength bolts (A325 and A490) are not necessary. There is nothing wrong with A307 bolts provided you have done an appropriate analysis of the loads and apply appropriately. That's no different than designing with any other bolt.