From: "Sprague, Harold O." <SpragueHO(--nospam--at)bv.com>
Date: Mon, 5 Feb 2001 12:07:42 -0600
1) Other than improper installation/tightening of the bolts, are
any other reasons or explanations as to why the nuts would be loose
Since the bolts are initially tensioned beyond the service loads,
improper initial tensioning is the most likely cause.
2) What is the history of DTI washers? How reliable are they? What
the likelihood that the washers are defective? What tests or
are employed to determine if a washer is defective? What are the
pitfalls of using these washers?
DTI washers were invented in the early 1960's and have been commonly
used for at least 20 years in one form or another. The tests are made with
a Skidmore with bolts. Check out Turner's web site at
http://www.jmtdti.com/. The pitfalls are proper special inspection. Most
inspectors don't know they are still supposed to verify tension with a
3) Is it possible that the bolts can be fully tensioned and yet the
bumps on the DTI washers not be flattened as specified?
It is not very likely, but anything is possible.
4) On connections that are tight, but the DTI washer is not
compressed, are there tests that can be performed to determine if
bolt is adequately tensioned, after ten years?
You could use a Biach or other hydraulic tensioner, and jack until
the tension is off the washer. It would not be totally accurate, but it
would give you an idea. Talk to the people at Turner, they are much more
knowledgeable than me.
5) What tests or methods can be employed to determine if the loose
were ever tensioned?
The hydraulic tensioner is about all that I know of.
6) Any thoughts on re-tightening the loose bolts.
Tighten them with new DTI's, and provide verification with special
inspection and a Skidmore. You can also use a hydraulic tensioner to verify
the tension, but for special inspection, the Skidmore is the accepted
methodology. Re-tensioning bolts is the engineers call. If you were using
turn-of-the-nut, I would advise using all new bolts, but re-tensioning of
existing bolts should be no problem for DTI's. The problem is with
inelastic thread deformation for A325 bolts that have been tensioned.
Harold O. Sprague
> \From: "Michael D. Gregory" <tetoneng(--nospam--at)srv.net>
> To: seaint(--nospam--at)seaint.org
> Subject: Loose Bolts with DTI Washers
> Content-Type: text/plain; charset=us-ascii
> Content-Transfer-Encoding: 7bit
> I have been asked to investigate a very large, 10-year old steel
> structure with bolted connections (there are approximately 11,000 bolts
> in the building). The problem is that some of the bolts are falling
> out. The owner hired an engineer who inspected 20% (2236) of the bolts
> and found that 36% (798) were either loose, missing or not tightened
> properly. Direct Tension Indicator (DTI) washers were used and were
> installed properly, but not necessarily tensioned properly. All of the
> bolts are 3/4 inch or 1 inch diamter A325 bolts. It is believed that
> the DTI washers were installed on the bolt side of the connection, since
> the engineer references using a 0.015 feeler gage. The drawings and
> specifications call for DTI washers to be installed on all high-strength
> bolts, regardless of connection type. The building supports overhead
> cranes and is also subjected to other dynamic loads (buffeting winds).
> Here are the questions:
> 1) Other than improper installation/tightening of the bolts, are there
> any other reasons or explanations as to why the nuts would be loose ten
> years later?
> 2) What is the history of DTI washers? How reliable are they? What is
> the likelihood that the washers are defective? What tests or methods
> are employed to determine if a washer is defective? What are the
> pitfalls of using these washers?
> 3) Is it possible that the bolts can be fully tensioned and yet the
> bumps on the DTI washers not be flattened as specified?
> 4) On connections that are tight, but the DTI washer is not properly
> compressed, are there tests that can be performed to determine if the
> bolt is adequately tensioned, after ten years?
> 5) What tests or methods can be employed to determine if the loose bolts
> were ever tensioned?
> 6) Any thoughts on re-tightening the loose bolts.
> I have studied both the Manual of Steel Construction - ASD (8th Edition)
> and LRFD (2nd Edition) and am familiar with their requirements. I am
> seeking information outside the scope of these references. Thanks!
> Michael D. Gregory
> Teton Structural Engineers
> Idaho Falls ID