Page 550 - Forensic Structural Engineering Handbook

15.2 MATERIAL-SPECIFIC FORENSIC ANALYSES

Window and Curtain Wall Investigation Methodology 15.26
Document Review 15.26
Visual Condition Survey 15.26
Close-up Examination 15.26
Field Testing 15.28
Structural Testing 15.28
Water Penetration and Air Infiltration Testing 15.29
Materials Testing 15.32
Repairs 15.32
ACKNOWLEDGMENT 15.32
REFERENCES 15.33

INTRODUCTION

The building structure usually functions satisfactorily for the economic life of the building
with little attention. In comparison, the building envelope (exterior walls, windows, and
roof) requires relatively frequent maintenance. Facade materials are subject to deterioration
from exposure to wind, rain, ultraviolet radiation, and other environmental conditions,
while the building structure is generally protected from these effects (with the exception of
earthquakes and wind pressures).
Prior to the late nineteenth century, building walls served not only to protect the building
interior from weather but also as load-bearing components to support the building’s floors and
roofs. Contemporary buildings have become taller and exterior walls have become lighter and
thinner, as in the case of curtain wall construction. While these thinner exterior walls still
serve to keep the weather out, in most cases they no longer support the structure.
Building facades constructed with lighter and thinner systems are more susceptible to the
effects of weather exposure than load-bearing masonry walls. Thinner walls are also less for-
giving than traditional load-bearing masonry construction, making them more vulnerable to
the problems associated with deficiencies in detailing and execution. Facade failures are not
limited only to collapse, cracks, or excessive water or air infiltration. Considering that mod-
ern building envelope systems often contain complicated and interdependent components,
understanding why they fail to perform as expected can be a challenging task. Failures can
originate from a wide variety of factors, such as unaccommodated movement of the cladding
system, inadequate or defective water management system, or material incompatibility.
Special diagnostic techniques and a clear understanding of the behavior of cladding systems
are needed to identify and remediate facade failures in contemporary buildings.
Once building facades fail, repairs can be very costly. Some failures may affect safety
of the building occupants and the public, and the cost of facade repair or replacement can
exceed the original cost of the entire building. Proper evaluation of building facade com-
ponents is needed to fully understand deficiencies and develop appropriate repair or
replacement recommendations.

CODES AND STANDARDS

Building codes and standards usually provide the minimum requirements for the design and
construction of building elements. In addition to widely used building codes such as the
International Building Code (IBC), a municipality may employ its own building code. Codes
pertaining to the building envelope generally emphasize safety, fire protection, structural
capacity, and durability, and also may address specific serviceability issues such as air infil-
tration and water leakage. Building envelope performance issues are also governed by certain