Page 558 - Forensic Structural Engineering Handbook

15.10 MATERIAL-SPECIFIC FORENSIC ANALYSES

procedures, 2) further the body of engineering knowledge to avoid similar failures in the
future, and 3) establish a factual basis for the failure in order to assign responsibility for any
economic loss. While the purpose of the investigation can be similar for many types of
building system failures, the scope and extent of the investigation depends on the nature,
severity, and consequences of the failure. Depending on the extent and nature of the failure,
the investigation process may require one investigator or a large team, and may require only
a few hours or up to several years to complete. Most facade failure investigations require a
level of effort somewhere between these extremes. The typical forensic investigation
involves a systematic, logical approach; it cannot be simplified to a prescriptive series of
steps that must be followed without variation. Free thought, imagination, and flexibility are
essential to the collection and synthesis of data fundamental to a successful investigation.
The failure investigation typically involves the following fundamental steps: 1) acqui-
sition of data, 2) analysis of data, 3) development and evaluation of hypotheses, and 4)
formulation and communication of opinions.

Initial Investigation. The goal of the initial site visit varies depending on the nature of
the failure being investigated. A wall or facade collapse with associated rescue and cleanup
effort requires prompt systematic collection of as much reliable information on the exist-
ing conditions as possible before the conditions and evidence are disturbed. A digital cam-
era and sometimes a video camera can capture the position of remaining facade or collapse
debris during or prior to cleanup operations. Unstable walls or facades in a state of incipi-
ent collapse require prompt assessment and implementation of emergency stabilization
measures after immediate notification of the responsible authorities. Investigations requir-
ing less urgent responses may also require careful coordination, as further discussed below.
A visual condition survey serves as a first step to document existing conditions. This
process usually involves annotating observations onto building elevation drawings and tak-
ing high-resolution photographs. The objectives of the condition survey are to accurately
identify the location and nature of deterioration and damage, to identify patterns of distress,
to establish potential scope and distress locations for repair work, and to produce a baseline
of information for subsequent detailed inspections. Binoculars and telephoto equipment are
often used to facilitate observation. Survey drawings prepared during the visual condition
assessment offer a valuable means of visualizing facade distress patterns, which provide
clues to the underlying causes. Conditions identified during the survey will usually help to
determine the nature of additional studies and testing required. Typical conditions identi-
fied during a masonry facade condition survey (depending on the materials present) include
cracks, spalls, displacements, corrosion, delamination, efflorescence, honeycombs, scaling,
and staining.
Documents that provide information relevant to the failure may be acquired from numer-
ous sources, and may include original structural and architectural drawings, specifications,
shop drawings, prior maintenance or repair records, interviews with persons involved with
construction and prior repairs, and field observations. In the case of collapses or other criti-
cal failures, news media coverage may also provide useful information. As the investigation
progresses, information from research, condition surveys, and laboratory and field tests,
adds to the investigator’s overall understanding of the conditions leading to failure.

Detailed Investigation. Close-up visual examination of distressed and undistressed areas
of the facade is necessary, often supplemented by inspection openings (probes) to gain
knowledge of as-built conditions and concealed construction elements such as anchorages.
Safe access for close-up examination may be from roofs, setbacks, balconies, or special
means of access (e.g., suspended scaffolding, pipe scaffolding, or personnel lifts).
Contractor assistance is usually required for close-up access and for making and repairing
probe openings. During detailed inspections various measurements can be taken, such as