Page 373 - Forensic Structural Engineering Handbook

11.4 MATERIAL-SPECIFIC FORENSIC ANALYSES

INTRODUCTION

Forensic investigation of structural failures is essential to both the integrity of existing struc-
tures and the design of new ones. Without learning from the mistakes and errors associated
with failures, we jeopardize public safety without understanding why a structure failed. Steel,
in particular, because of its extensive use in a wide variety of structures (e.g., bridges, build-
ings, power plants, vehicles, etc.) and its relatively easy fabrication by welding, has become
the most widely evaluated material with respect to failures. The use of welding has, in fact,
been a major contributor to the failure of steel structures. Welded joints inherently contain
flaws or discontinuities such as cracks, incomplete penetration, slag and/or porosity. Further,
welds often exhibit residual stresses that are near the yield stress levels, and can adversely
affect mechanical and metallurgical properties of the base metal. In fact, the number of steel
structural failures increased dramatically beginning around World War II when welding
began to be used more widely in the fabrication of steel structures. Only after advances in steel
manufacturing, in fracture mechanics and fatigue analyses, and in the development of a
greater understanding of the detrimental presence of flaws did the number of steel structural
failures decrease.
In steel structures, another term for failure analysis or forensic engineering is root
cause analysis. The root cause(s) of a structural steel failure is the identifiable fundamen-
tal reason the structure failed, the reoccurrence of which can, in most cases, be prevented
with reasonable and effective corrective actions. In this regard, root cause analysis is a
comprehensive methodology that provides engineers with the ability to determine (1)
what happened, (2) how it happened and, most importantly, (3) why it happened.
Unfortunately, because of the litigious environment we work in today, most forensic
analyses are conducted to assign blame to a specific party. However, the most important
goal of any forensic or root cause assessment should be establishing the underlying cause
of a failure so that it can be prevented from re-occurring. Clearly, determining “why” a
failure occurred is the means engineers have to develop reliable corrective actions plans
and/or improve new designs. A competent root cause analysis relies on factual informa-
tion, verifiable analyses and conclusions, and implementable corrective actions. Thus, at
a minimum, a competent root cause or forensic engineering analysis will consist of the fol-
lowing activities and considerations:

• Document the failure event
• Establish what happened
• What structure, component, or equipment was involved
• When did it happen (short or long term)
• Where did it happen
• Are there unforeseen consequences
• Investigation team
• Is an emergency response required
• Root cause investigation personnel
• Multidisciplinary approach (structural, materials, hydraulics, etc.)
• Identify team leader
• Site response and who has jurisdiction control
• Collection of evidence
• Identify key components/members
• Identify sections to be removed
• Collect and preserve evidence