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RE: distortion from heating

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I agree with Harold;  it's an art.  I also had the opportunity to observe a
bridge girder straightened in place.  It was supported by a crane (this was
during construction) during the process and jacks were used to facilitate
the straightening.  V-heating was done at several locations along the bottom
flange with a rosebud. We had the good fortune of having the person who
wrote the book (literally) on heat curving supervise the work.  The book is
"Criteria for Heat Curving Steel Beams and Girders" by R. L. Brockenbrough,
Journal of the Structural Division, Proceedings ASCE, 96, No. ST10, October,
1970.  I believe this was also published separately as a design guide by US
Steel.

As for your 3/8" plate, I'd guess that, as Harold alluded, the heat input
from welding would not be enough to affect the rigidity, but if a more
widely distributed heat were applied, I'd expect gravity to win.

Tony Powers

> -----Original Message-----
> From:	Harold Sprague [SMTP:harold.sprague(--nospam--at)neenan.com]
> Sent:	Tuesday, January 05, 1999 5:08 PM
> To:	'seaint(--nospam--at)seaint.org'
> Subject:	RE: disortion from heating
> 
> Roy,
> 
> Residual compressive stresses are trapped in steel as it is rolled.  If
> the
> heat is applied uniformly across an entire surface, the residual
> compressive
> stresses are relieved and the heated section contracts.  That is why heat
> cambering uses large heated wedges which will contract and camber the
> beam.
> 
> If heat is applied locally, the heat will cause the local area to expand.
> Heat straightening is an art.  It is another of the arts that I can't do,
> but I can appreciate.
> 
> Welding heat is highly localized.  The only thing I can say about your
> example is that the plate will distort.
> 
> Regards,
> Harold Sprague
> The Neenan Company
> harold.sprague(--nospam--at)neenan.com
> 
> 
> -----Original Message-----
> From: RoyLevy(--nospam--at)aol.com [mailto:RoyLevy(--nospam--at)aol.com]
> Sent: Tuesday, January 05, 1999 5:37 PM
> To: seaint(--nospam--at)seaint.org
> Subject: disortion from heating
> 
> 
> Many years ago I heard of a team of technicians who had developed a
> technique
> to straighten deformed steel bridge structures  in place by flame-
> straightening.
>  
> To help me understand the principles, this is my question:
> 
> Assume a steel plate say 3/8" thick by 4" wide and 3 ft long, simply
> supported
> at the ends, say resting on a pair of saw horses.   Heat is applied across
> the
> top at the center, for example by welding a 1/4 x 4 " wide gusset plate at
> the
> center, across  and perpendicular  to the plate ( 2  3/16"  f illet welds,
> 4
> '' long , for example)  .
> 
> Will the center of the plate rise or will it sag ?  In another form, the
> question is which will prevail -  The loss of rigidity while the top is
> molten
> or the contraction effect upon cooling?
> 
> 
> 
>