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RE: What Is The Material Spec For "Lag Screw"?

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The Simpson SDS screws your refer to have been around for some time.  They are, as you noted, specified for connection of the Simplified Structural System - Hardy Frame and Panels to the double plates above for drag, I believe for use with the Simpson Strong Wall and also for the PHD line of Pre-deflected holddowns.
For those who were not aware, Simpson has also had a line of 8d, 10d and 16d (If I recall correctly) x 3" long common nails - the N series - for many years. Unlike conventional common nails, the Simpson nails were manufactured with consideration to the depth of the wood members being connected (i.e., (2) 1-1/2" member requiring only 3" penetration.
 
I do agree that connectors have been a neglected issue, however, I don't believe the problem is industry standard so much as an assumption that the capacities given for metal connectors by Simpson and others, unlike bolted connectors which rely on the capacity of the wood and require the engineer to calculate, are pre-determined based on the weakest member capacity, the rated capacity of the common nail in shear or the empirically tested and reduced to working stress capacity of the proprietary connector. In other words, the value of the connection was predicated upon proper installation of the connector in accordance with the manufacturers requirements.
 
It seems redundant to me to specify the number of nails and size to be used in a Simpson HPAD strap, for example, when the manufacturer states it in the product literature and the framer is required to abide by the manufactures instructions. Furthermore, one the engineer specifies the size and number of connectors, should the contractor substitute another manufacturers product, there is no quarantine that the capacity is equivalent. Therefore, it is easier to specify that manufacturers proprietary connector and to specify "or equal" to allow the framer to make the substitution and to verify the equivalency.
 
While others may not agree, if it is considered that virtually every connector has multiple alternative sources the time required of the EOR to evaluate substitutions is an unreasonable request. Most manufactures like USP have equivalency charts and supporting ICBO's to justify their products. There is no reason in my opinion for the EOR to be involved in most substitutions. If, however, the EOR is adamant on the choice of connector - he (or she) can specifically state "no substitutions" on the plans.
 
I didn't mean this to be as defensive as it sounds. I just thought it important to make a few issues clear that I thought might have either been implied in Bill's message or relevant to the subject of proprietary connections that most designers should know or be aware of. There I go - ending a sentence with a proposition!>)
 
Dennis S. Wish, PE 
 
 -----Original Message-----
From: Williston L. Warren, IV - S.E. [mailto:Bill_Warren(--nospam--at)sesol.com]
Sent: Sunday, June 03, 2001 11:59 AM
To: ListServer SEAint
Subject: What Is The Material Spec For "Lag Screw"?

Simpson Strong-Tie is now producing and supplying 1/4" dia x (1.5" to 3.5") wood screws, the screws have ICBO ES reports on the capacities.  Fasteners are one area where the industry has failed. 
 
I have a client who supplies pre-fabricated building components and uses fasteners to attach them, well they are putting these components on California schools which means a DSA (Division of the State Architect) review and the question arises, what are the fastener capacities.
 
Will I found the IFI references which allowed for capacity determination, then DSA want to know how to check the fasteners to determine that the contractor is supplying the correct items. 
 
I remember a 60 minutes report about the black market in bolts, in the aircraft industry specific bolts need periodic replacement (like the ones that hold the engines on) and they are very special and very expensive bolts, they found that people had been counterfeiting them and selling them for half price, something like 120ksi bolts to be used and the counterfeit are 36ksi.
 
So go figure
 

Williston "Bill" L. Warren, IV - S.E.
Structural Engineering SOLutions
Newport Beach, California
 
 
 
 
From: "Nels Roselund, SE" <njineer(--nospam--at)att.net>
To: <seaint(--nospam--at)seaint.org>
Subject: Re: What Is The Material Spec For "Lag Screw"?

Bruce,

I hope you are on the trail of suppliers and specifications for lag screws.
I have not been able to find a way of being sure that the lag screws on a
project conform with my specifications nor to tell a contractor where to
purchase the screws I have specified.  I generally specify the yield
strengths in the footnotes of NDS Table 9.3A, but have never been able to
find out what was delivered to the job.

Nels Roselund
Structural Engineer
South San Gabriel, CA
njineer(--nospam--at)att.net