Page 157 - Forensic Structural Engineering Handbook

4.6 DESIGN AND CONSTRUCTION PRACTICES

assist in designing efficient and effective repairs for failed or defective construction. The
forensic structural engineer is also asked to express opinions concerning the performance
of a structural engineer.
To offer an opinion as to whether a structural engineer met the standard of care, the
forensic expert must first determine what level of skill, judgment, and diligence was pos-
sessed by normally competent structural engineers practicing in similar circumstances.
Society has determined that “normal competence” of a structural engineer includes a cer-
tain amount of error. This is because the competent structural engineer applies judgment
gained from variable training and experience, while dealing with materials, forces, and pro-
cedures which are fraught with uncertainty.
When forensic structural engineers testify in deposition or at trial, they are asked for
their expert opinion to assist the trier of fact in their decision. The trier of fact (a judge or a
jury) determines whether a particular defendant engineer has or has not met the standard of
care of that engineer’s particular practice discipline. In determining that fact, the opinions
of expert witnesses qualified in that discipline may be considered. Expert opinions can be
taken by the jury as facts to be considered in their deliberations.
The admissibility of expert opinion as fact, rather than its rejection as hearsay, origi-
21
nated in English common law in 1782, in the case of Folkes, Bart v. Chadd, et al. Folkes
owned a dike protecting low-lying pastures near the harbor at Wells, a town on the east
coast of England. Chadd, et al. were trustees of the harbor who had obtained an injunction
against Folkes, requiring him to remove the dike because it was causing silting in the har-
bor. Folkes sued Chadd to have the injunction set aside, and during the trial, Folkes put on
the stand John Smeaton, an engineer knowledgeable in the fields of dikes and harbor silt-
ing. Smeaton testified his opinion was that the dike had nothing to do with the silting.
Chadd’s attorney objected on the grounds of hearsay, but the court ruled that, “Of this [mat-
ter], such men as Mr. Smeaton alone can judge. Therefore we are of the opinion that his
judgment, formed on facts, was very proper evidence.”

STANDARD OF CARE

Uncertainty
One reason structural engineers’ services contain errors is that the services are provided in
circumstances of uncertainty or variability. There is uncertainty in the natural world of
loads, materials, and the environment, and there is uncertainty in the man-made world. The
structural engineer practicing under these uncertain conditions has as a goal a finished
structure that satisfies all its intended purposes over its intended service life. To accomplish
this goal, the structural engineer anticipates the levels of uncertainty and builds into the
structure appropriate strength, stiffness, stability, redundancy, and robustness. Building
codes and standards are drawn up with an appreciation of the variability and uncertainty in
loads and materials; prescribed live loads and load combinations; allowable stresses and
deflections, safety factors, load and resistance factors, and other limits on materials, ele-
ments, and assemblies less than their theoretical maxima attest to this appreciation.
Building codes, however, cannot stand in for the structural engineer’s professional judg-
ment regarding the variability in the loads, materials, and human factors which will act
upon the structure over its expected life. Lev Zetlin has said, 22 “Engineers should be
slightly paranoiac during the design stage. They should consider and imagine that the
impossible could happen. They should not be complacent and secure in the mere realiza-
tion that if all the requirements of the design handbooks and manuals have been satisfied,
the structure will be safe and sound.”