Page 278 - Forensic Structural Engineering Handbook

8.18 CAUSES OF FAILURES

CAUSES OF CONSTRUCTION DEFECTS
IN DIFFERENT STRUCTURAL SYSTEMS

Each structural construction material has its unique set of detailing and construction intricacies
and associated challenges in uncovering any deficiency that may have originated during the
design or construction phases. Regional variations in design and construction practices make
the process of discovering design- and construction-related deficiencies as much an art as a sci-
ence. Commonly reported complaints such as cracking of finishes, lack of plumbness or
levelness, and damage caused by water penetration are the most frequent triggers for design-
and construction-defect-related claims. Deficiencies resulting in a structure’s or component’s
failure to perform its intended function are more straightforward to ascertain. However, latent
defects lurking behind a finished surface with no apparent manifestation of damage may lie
dormant for years until the requisite failure load level has been reached. Lack of any symptoms
of damage makes it challenging to determine the cause of construction- or design-related
defects since loads on the structure may not have achieved their ultimate or even service lev-
els. Discovery of latent defects thus requires a keen investigative sense to accurately isolate and
demonstrate these defects. Since demonstration of construction-related defects inevitably
requires invasive testing, a significant challenge is posed to the forensic engineer to precisely
locate the defects without unduly damaging the structure during the investigative process while
developing statistically meaningful sample sizes. Consequently, nondestructive testing tech-
niques in conjunction with limited verification by destructive means offer access to a larger
sample size at greater speed with substantially less intrusive testing.
An exhaustive and clear documentation of field conditions depicting design or con-
struction defects is an essential part of developing any professional opinion regarding the
matter. Extensive sets of tools and equipment are available to carry out field investigation
but by no means are all of them required to determine the cause of a design or construction
defect. Multiple tools may serve the same function, and each forensic engineer has a pref-
erence for a set of tools that he or she finds useful in completing the investigation.
Typical design and construction deficiencies that are prevalent in the four major structural
systems—wood, concrete, masonry, and steel—are discussed next.

Wood Structures
The flexibility offered by wood construction and the ability to easily make field changes
often makes this type of construction more susceptible to defects. Wood framing members
have anisotropic strength characteristics rendering them sensitive to the orientation of their
placement and method of attachment to the balance of the structure. Some of the parame-
ters that need to be verified during the course of identifying deficiencies in wood frame
construction are listed below:
• Change of members and type from those specified in contract documents, as-built drawings
or construction phase documentation, e.g., plywood panels substituted with oriented strand
board (OSB). A working knowledge of the various symbols and markings frequently pre-
sent on wood construction components is required for a meaningful investigative effort.
• Verification of proper fastener size and type used to secure sheathing members to wood
framing. Depth of fastener penetration into base material has to be considered as well
ascertaining the effectiveness of the sheathing panels. Extraction of several fasteners is
required to verify their size and type and the results need to be properly documented. The
use of a fastener verification gauge is recommended (see Fig. 8.12).
• A wood framed structure’s ability to properly transmit load is intricately linked to the
size, location, pattern, and embedment of fasteners into framing members. Verification