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Loose Bolts with DTI Washers

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Michael,

Charlie gave a pretty thorough reply but I would add one more item.  About
15 years ago we were supplied counterfeit DTIs to a project in Southern
California.  A company in Texas was punching the dimples on plain hardened
washers.  We also had some DTIs that the material certs said were
manufactured in London, England.  Luckily we are a big firm and we had
someone from our British office go to the printed address only to find an
unrelated warehouse.

You might want to send a few of the DTIs to a testing laboratory.

Thomas Hunt, S.E.
Duke/Fluor Daniel

----- Forwarded by Tom Hunt/DFD on 02/04/01 01:47 PM -----
                                                                                                                   
                    "Michael D.                                                                                    
                    Gregory"             To:     seaint(--nospam--at)seaint.org                                                 
                    <tetoneng@srv        cc:                                                                       
                    .net>                Subject:     Loose Bolts with DTI Washers                                 
                                                                                                                   
                    02/02/01                                                                                       
                    04:19 PM                                                                                       
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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
tetoneng(--nospam--at)srv.net
208-357-2420