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Re: Formation of plastic hinges

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Will plastic hinges form in prestressed/post-tensioned concrete?  I've done some
inspection on these types of structures and have noted spalled concrete with
exposed strands/tendons.  I'm under the impression that any corrossion in the
wires will lead to breaks in the wires (which I have also noted in several
structures) since they are under extremely high tension.  With very little
residual strength remaining in the strands/tendons you can lose many wires and
subsequently the entire structure.  Although, I did go to a seminar on
non-destructrive testing and they pointed out several structures with broken
wires which are still performing as designed.

What is the extent of corrosion?  Spalled concrete ?  Pitting on the wires?
Corrosion of mild reinforcement?  If only the wires are damaged/broken you can
try adding external post-tensioning.  If the concrete is in poor condition,
there are many ways for rehabilitating it from patching to chloride ion
extraction.

Why don't you contact PCI (Precast/Prestressed Concrete Institute) directly to
find out if they know any references  (312) 786-0300.

Hector

P.S.  If you feel the structure is about to collapse, I hope you have
constructed some temporary shoring (use strongbacks if shoring can't be placed
underneath) and have posted the structure for reduced live loading.







"AGHBAL YOUNESSE" <aghbal(--nospam--at)hotmail.com> on 09/28/99 03:57:43 PM

Please respond to seaint(--nospam--at)seaint.org

To:   seaint(--nospam--at)seaint.org
cc:    (bcc: Hector Morera/NYC/AmmannWhitney)
Fax to:
Subject:  Formation of plastic hinges





Hi everyone,

I'm looking for some good websites or programs which explain the formation
of plastic hinges leading to failure mechanism. I'mworking now on a project
of rehabilitation of prestressed (post tensioned) concrete bridge with
single beams that are extremely damaged because of the extreme corrosion. So
the probability of a collapse is 85%. The question is : HOW THE COLLAPSE
wiLL HAPPEN ?

THANKS IN ADVANCE.
------------------------------------------------------

M.AGHBAL KAMAL
Structural engineer,
OCP firm,
MOROCCO.
E-mail : aghbal(--nospam--at)hotmail.com
------------------------------------------------------