Page 306 - Forensic Structural Engineering Handbook

DEFECTS, DETERIORATION, AND DURABILITY 9.17

Human Perceptions of Durability
Another complication to predicting durability is that there is no industry consensus on what
constitutes the end of service, or failure point, for many construction products. For exam-
ple, some exterior seals begin degrading due to environmental exposure soon after they are
installed; even with proper design and installation, they degrade continuously until at some
arbitrary point it is determined that they must be replaced. Before replacement is imple-
mented, some owners will allow the seals to degrade further than other owners, perhaps
allowing water infiltration to become pervasive before replacing the seals. An owner’s def-
inition of the end of service life may depend on corporate policies, budgets, and tolerance
for deterioration.
Expectations for durability vary between communities, and certain prevailing weather
conditions affect durability as well. For example, solar radiation causes more rapid dete-
rioration of organic materials in the southern regions of the United States than in the
northern regions; therefore, faded paint may be more accepted in some southern com-
munities, while such deterioration may be dubbed a failure in the north. The quality of
“average” and “acceptable” workmanship and building condition varies between com-
munities as well.

MAINTENANCE

Even without the presence of design, fabrication, or construction defects, some components
will require maintenance to control natural deterioration. The term “maintenance” has been
used historically to describe vastly different procedures; for example, consider the differ-
ences between repairing concrete spalls on precast concrete cladding panels, replacing
sealant joints, and underpinning a foundation. Of these examples, only repairing concrete
spalls is the type of intervention that is envisioned when a component is termed “maintain-
able” in Table 9.2.
It is reasonable to expect that it will be necessary during the design life of precast con-
crete cladding panels to perform some condition-based maintenance like spall repairs.
Underpinning a foundation, however, is necessary only when the foundation (a “perma-
nent” component) suffers premature failure. Sealant joints are not maintainable compo-
nents, and instead are categorized as “replaceable” at the end of their service life. These
different operations imply different uses of the word “maintenance.” Therefore, it is useful
to define categories of reasonable maintenance types. BSI 19 defined three categories of
maintenance, as shown in Table 9.4.

TABLE 9.4 Maintenance Levels 18

Level description Scope Examples
1. Corrective maintenance Maintenance restricted to Reglazing broken windows;
restoring items to their original remedying sources of active leaks
function after a failure
2. Scheduled maintenance Maintenance at predetermined Repainting; sealant replacement;
time intervals; regular cycle recoating roof membrane with solar
reflective paint
3. Condition-based Maintenance as a result of Tuck-pointing masonry; replacing
maintenance distress roof membrane