Return to index: [Subject] [Thread] [Date] [Author]

Loose Bolts with DTI Washers

[Subject Prev][Subject Next][Thread Prev][Thread Next]

Take some samples for either chemical analysis or mechanical testing.  I suspect
that the bolts are not high-strength bolts, but are comment or mild-steel.  High
strength bolts should not creep or elongate as you are suggesting.  A number of
years ago there was a problem with counterfit bolts that came in from outside
the US, that were marked just like A-325 bolts but were made of junk steel.

If so, you someone may have a whole lot of fun replacing them.


\From: "Michael D. Gregory" <tetoneng(--nospam--at)>
To: seaint(--nospam--at)
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