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Re: Bridge collapse

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Given the fact that a 2.4 m girder spacing is pretty much average and a deck
slab can easily be designed to carry the wheel loads for that span length, I
believe that the transverse post-tensioning is soley to assist in transversely
distributing the wheel loads.  Usually for structures with precast concrete
I-girders, we place mild reinforcement continuously in the transverse direction
and cast in place the diaphragms.  For multiple longitudinal member structures,
I have only use post-tensioning for multiple-box structures (not spread box)
where it is difficult to cast-in-place a continuous transverse diaphragm.  Given
the fact that 45 m is a good size span for precast concrete girders (hence their
2.6 m depth), I believe the longitudinal post-tensioning is designed to carry
the live-loads (maybe also some superimposed dead loads).

Has there been a load-rating performed on the structure for the AS-INSPECTED
condition ?  Despite the losses (unless of course tensile cracks are evident at
midspan), there may be enough residual strength in the remaining tendons and
concrete to accommodate the imposed loads.  The biggest problem I have with load
rating these types of structures is determining the amount of prestressing
losses.  You might want to strain gauge the structure to determine how it is
responding to the imposed live loads.

Aghbal, I am sending to you privately a report in electronic format from NCHRP
on Durability of Post-Tensioning Segmental bridges.  It mainly covers segmental
bridges but some of the information may apply to your case.  It also has a
bibliography which references some books, at least one of which covers the
collapse of a post-tensioned segmental bridge.

Hector






"Greg Smith" <strusup(--nospam--at)gte.net> on 10/03/99 11:11:53 AM

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

To:   seaint(--nospam--at)seaint.org
cc:    (bcc: Hector Morera/NYC/AmmannWhitney)
Fax to:
Subject:  Re: Bridge collapse




If the longitudinal direction is the direction that a car goes on the bridge
and the transverse direction is 90 degrees to that horizontally,  how are
the beams connected longitudinally and transversly and at what spacing
longitudinally and transversely?

Greg
-----Original Message-----
From: AGHBAL YOUNESSE <aghbal(--nospam--at)hotmail.com>
To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
Date: Saturday, October 02, 1999 1:48 PM
Subject: Bridge collapse


>
>Hi everyone,
>
>
>I'm working on a project of rehabilitation of a post tensioned bridge,
which
>is very damaged (loss of prestressed tendons, spalling of concrete...)
>because of marine corrosion.
>
>Bridge features : (French units)
>
>* Bridge location : MOROCCO
>* Length : 3,616 km
>* Spans fixation : single spans
>* Beams bearing : Elastomeer baerings (EB)
>* Span length : 45 m
>* Prestressing mode : post tensioned beams and piers
>* Each span contains 3 beams connected each other by a prestressing effort
>in the horizontal sense, and by concrete connection (see the presentation
>below)
>
>* Height of a beam is 2,60 m
>* space between two beams in a span is : 2,40 m
>
>
>
>
>
>
>The question is : how it will collapse (the failure mechanism )???
>
>Is there anyone can I help me.
>
>Thanks in advance.
>---------------------------------------------------------------------
>M. Kamal AGHBAL
>Structural engineer,
>OCP firm,
>Laayoune,
>MOROCCO,
>E-mail : aghbal(--nospam--at)hotmail.com
>-------------------------------------------------------------------
>
>
>
>
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