Page 556 - Forensic Structural Engineering Handbook

15.8 MATERIAL-SPECIFIC FORENSIC ANALYSES

FIGURE 15.3 Example of severe bowing of thin marble panels caused
by hysteresis. (Courtesy of Wiss, Janney, Elstner Associates, Inc.)
An understanding of the mechanism of potential water entry points and migration paths
within the wall is needed to address water-related failures. Water that penetrates the
exposed facade surface or water vapor that condenses within the wall must be collected and
diverted out of the wall by an internal wall drainage system. Internal wall cavities serve to
convey water to through-wall flashings that are watertight, continuous, and properly
enveloped. Weep holes must be configured to effectively drain water that collects on the
flashing. Blocked or bridged wall cavities, breached flashings, and blocked or poorly posi-
tioned weep holes may each result in water leakage to the interior. Exterior walls built
directly above interior spaces are especially problematic in terms of water leakage because
failure of the wall drainage system results in direct water entry to the interior.
Another factor contributing to deterioration of facade materials in service is differential
thermal- and moisture-related expansion. For example, composite cladding panels com-
prised of materials having different thermal and/or moisture expansion characteristics may
deform and debond as these materials move differentially in service (Fig. 15.5).

Failure Investigation Methodology
Building facades can fail in a variety of ways and from numerous causes. Investigation of
the cause of the failure is required in order to 1) assess and develop appropriate repair