[146] in APO Printshop
Re: Fwd: W20 roof leak
daemon@ATHENA.MIT.EDU (Charley Hamilton)
Wed Jun 22 19:37:08 2005
Date: Wed, 22 Jun 2005 16:33:16 -0700
From: Charley Hamilton <chamilto@uci.edu>
To: Mitchell E Berger <mitchb@MIT.EDU>
CC: apo-exec@MIT.EDU, apo-printshop@MIT.EDU
In-Reply-To: <200506222101.j5ML1bpD006527@zamboni.csail.mit.edu>
Greetz, Mitch.
I figured I'd weight-in, being nominally a structural engineer
and all. You get some cracks in concrete because it usually dries
(evaporative process) as it cures (chemical process). You will
also get cracks under load, as concrete isn't worth more than a few
hundered psi in tension. (Stop laughing. Civil engineers in the US
still use US customary units. It's not my fault.) That's why there's
reinforcing steel in it. The 'bumps' on the steel rebar enhance
interlock with the concrete and allow the steel to carry tension
across the cracks in the concrete. Properly detailed concrete should
only show sub-visible to barely visible (< 0.5mm) cracks. Anything
bigger could be a problem. Sorry, I slipped into lecturer mode. ;-)
Water infiltration into the interior structure can be a bad thing
where concrete is concerned, and you might want to see if you can
get a look at the plans to see what structural elements the potential
leak path intersects on its way the the APOffice. The exterior clear
cover from air to first rebar is typically spec'd at 1.5-2 inches. The
interior cover is often as low as 1. Thinner cover can create easier
paths for water infiltration into the structural members.
Also, I don't recall whether or not W20 is all concrete construction.
It will be worse if W20 has structural steel components proximal to
the leak path. I haven't seen plans for W20 in a long time. It's probably
best for all concerned that you don't ask how I saw plans in the first
place. ;-) See if you can talk CAC/Phys Plant and an upper-divison
(junior/senior) Course 1 into looking over them with you. Better yet,
if we have a graduated Course 1 brother in the area, snag them. All of
us that I remember are OOBA (out of Boston area), and too far to drop by
for the plans. I could look at electronic drawings in PDF, DXF, or Autocad
format, although I doubt that Phys Plant will have them that way.
As far as freeze-thaw action, you should be able to see those effects.
Cracks that are relatively large and spalled chunks of concrete are a
few of the signs. Also, if you see rust stains on the concrete or
sections of debonded concrete cover (sounds hollow when tapped with a ball
peen hammer), these can be indicative of corrosion in the rebar. The forces
developed by formation of corrosion products can be huge, so they will often
pop off a section of the cover concrete. As a result, spalls may be
indicative of corrosion as well.
Most often, roof leaks are the result of failures in roofing membranes
or in sealing compounds. As long as this leads to water dripping *past*
interior structural members, it's just a mold and water intrusion problem.
If the water flows over or through the members, you may see degradation.
Wish I could be more help, but I'm in SoCal. Distance makes the site inspection
go slower. ;-)
YiLFS,
Charley
AXcoAPO F'93
Course 1C S'97
--
Charles Hamilton, PhD EIT PGR and Lecturer
Department of Civil and Phone: 949.824.3752
Environmental Engineering FAX: 949.824.2117
University of California, Irvine Email: chamilto@uci.edu
