Page 161 - Forensic Structural Engineering Handbook

4.10 DESIGN AND CONSTRUCTION PRACTICES

CASE STUDIES

The question of a structural engineer’s performance relative to the standard of care arises
when errors occur, or when there is a failure of a constructed facility to achieve its intended
safety, durability, serviceability, or utility. The standard of care is not a fixed “standard” in
the way other standards are, such as the ACI standard method of taking concrete samples.
The standard of care of structural engineers varies with time, locale, and circumstances and
depends on the specific practice being examined. It is informative to review instances in the
past where a structural engineer’s performance relative to the standard of care was in ques-
tion. Some of these examples come from the published record, and others are from the
author’s experience.

Steel-Frame Design
A two-story, mixed-use, wood-frame building on a corner lot incorporated two full-height
moment frames, one on each of two adjacent sides facing the streets, in order to accom-
modate storefronts and office windows. The location was in seismic zone 4, close to a
known, active fault. The engineer of record produced a set of calculations for the frames.
One frame was designed based on five lines of calculations; the other frame was designed
based on one line of calculations, which read, “Similar.” The calculations did not include
any treatment of the vertical loads which the frame had to support, or any evaluation of
earthquake-induced drift. After construction was completed and the building was occupied
and in use, water leaks were observed at walls, doors, and windows. A law suit was filed
by the building owner. During preparation for the trial, a thorough and detailed computer-
aided analysis was performed which showed that the steel frames as originally designed
were adequate in terms of stiffness and strength for code-required loads. In fact, the analysis
showed the frames were a very efficient and economical design.
The original calculations were not adequate to describe the design intent of the structural
engineer. They did not include the evaluation of the performance of the frames under code-
required dead and live loads, or any required combinations of loads. The stresses and deflec-
tions induced by required or anticipated loads were not compared with allowable values.
Was the structural engineer negligent in his design of the steel frame? Calculations are
not in themselves engineering. However, they do convey the thought process and the design
intent of the engineer. The quality of the calculations, their clarity, thoroughness, and accu-
racy, can be considered an indication of the level of care and diligence exercised by the
structural engineer. However, even the best calculations only substantiate, but do not sub-
stitute for, the judgment of the structural engineer. The structural engineer of this example
designed the steel frames without exhaustive calculations, but as a detailed analysis indi-
cated, not without apparently a clear understanding of good structural engineering design.
The in-plane lateral load-resisting design of the steel frames of this example was not, in
this author’s opinion, beneath the standard of care. There certainly was an absence of com-
plete documentation substantiating the in-plane lateral design of the frame. However, the
frame design—the actual size, configuration, and details of the beams and columns—was
not in error. The engineer may have proportioned the frame members correctly by intuition,
but it was not an erroneous design.

Retaining Wall Design
A structural engineer provided design services to a subcontractor who was building a
retaining wall for a developer. The subcontractor had selected a proprietary retaining wall
system utilizing precast, prestressed concrete modules to be assembled into a crib wall and