Joshua B. Kardon + Company Structural Engineers firstname.lastname@example.org University of California at Berkeley Department of Civil and Environmental Engineering email@example.com
About the Author
The author is a practicing structural engineer with 26 years of experience, the last 21 years as principal of his own firm, Joshua B. Kardon + Company Structural Engineers, Berkeley, California. He is also currently a PhD candidate in Civil and Environmental Engineering at the University of California, Berkeley, where his dissertation topic is the standard of care of structural engineers. The author has been a guest lecturer in undergraduate and graduate courses at UC Berkeley (Professors William Ibbs and Laura Demsetz), and at Stanford University (Professor Richard Meehan), on the topic of engineering failures, professional negligence, engineering judgment, and the standard of care. Some of the material in this paper is drawn from the manuscript of a chapter written by the author for a book on forensic structural engineering to be published soon by McGraw-Hill.
Well publicized instances of engineering failures are often cited in engineering education as archetypes of engineers' negligence. The notorious failures, however, may not be as salient to students as the more mundane calamities which befall the typical engineer. This paper briefly describes a few engineering failures with which the author has become familiar in his practice as a consultant and expert in construction defects lawsuits, and other engineering failures in the published record, in order to expose students to the concept of the engineer's standard of care.
The concept of the standard of care is described as the line between negligent and non-negligent error. Professional negligence is defined by reference to an approved jury instruction. Failure and liability case studies are then presented, starting with four from the author's own practice, followed by a discussion of five from the published record, including two well known incidents, the Hyatt Regency Kansas City walkway and the Tacoma Narrows Bridge. Each case study concludes with an comment regarding the standard of care of the engineer involved, and a statement of lessons which can be learned from the incident.
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Engineers have a duty to provide their services in a manner consistent with the "standard of care" of their professions. A good working definition of the standard of care of a professional is: that level or quality of service ordinarily provided by other normally competent practitioners of good standing in that field, contemporaneously providing similar services in the same locality and under the same circumstances (Paxton v. County of Alameda (1953) 119 C. A. 2d 393, 398, 259 P. 2d 934). An engineer's service need not be perfect. Since the engineer, when providing professional services, is using judgment gained from experience and learning, and is usually providing those services in situations where a certain amount of unknown or uncontrollable factors are common, some level of error in those services is allowed (City of Mounds View v. Walijarvi 263 N. W. 2d 420, 424 (Minn. 1978)). When you hire an engineer you "purchase service, not insurance," so you are not justified in expecting perfection or infallibility, only "reasonable care and competence" (Gagne v. Bertran 1934 43 C. 2d 481, 275 P. 2d 15).
The fact that an engineer makes a mistake that causes injury or damage, is not sufficient to lead to professional liability on the part of the engineer. In order for there to be professional liability, it must be proven the services were professionally negligent, that is, they fell beneath the standard of care of the profession. When one hires an engineer, one accepts the risk, and the liability, of that professional making a mistake similar to mistakes other normally competent engineers make, using reasonable diligence and their best judgment.
The standard of care is not what an engineer should have done in a particular instance, it is not what others say an engineer would do, or what others say they themselves would have done, it is just what competent engineers actually did in similar circumstances.
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Error is fact of life: "To err is human." Some error comes from variability and uncertainty in what the engineer is dealing with: real materials, natural and man-made loads, and humans and their organizations. Error can lead to failure, which can cause injury, and result in damages. An engineer is not liable, or responsible, for damages from every error. Society has decided, through case law, that when you hire an engineer, you buy the engineer's normal errors. However, if the error is shown to have been worse than a certain level of error, the engineer is liable. That level, the line between non-negligent and negligent error, is the "standard of care."
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Standard of care
A trier of fact, a judge or jury, has to determine what the standard of care is and whether an engineer has failed to achieve that level of performance. They do so by hearing expert testimony. People who are qualified as experts express opinions as to the standard of care and as to the defendant engineer's performance relative to that standard. The trier of fact weighs the testimony from all sides and decides in each case what the standard of care was and whether the defendant met it.
Jury instructions have been standardized. A Bench Approved Jury Instruction (BAJI, 1986) reads:
"In performing professional services for a client, a (structural engineer) has the duty to have that degree of learning and skill ordinarily possessed by reputable (structural engineers), practicing in the same or similar locality and under similar circumstances. It is (the structural engineer's) further duty to use the care and skill ordinarily used in like cases by reputable members of the (structural engineering) profession practicing in the same or similar locality under similar circumstances, and to use reasonable diligence and (the structural engineer's) best judgment in the exercise of professional skill and in the application of learning, in an effort to accomplish the purpose for which (the structural engineer) was employed. A failure to fulfill any such duty is negligence"
Four key items in this instruction bear repeating:
- ...have learning and skill ordinarily possessed by reputable engineers practicing in the same or similar locality and under similar circumstances.
- ...use care and skill ordinarily possessed by reputable engineers practicing in the same or similar locality and under similar circumstances.
- ...use reasonable diligence and best judgment.
- ...to accomplish the purpose for which the engineer was employed.
If any one of these conditions is not met, the engineer has failed to meet the standard of care, and is professionally negligent.
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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 standards for sampling and testing concrete. 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 question. Some of these examples are from the published record and some are from the author's experience.
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Steel frame design
A two-story, mixed-use, wood-framed building on a corner lot incorporated two full-height moment frames, one on each of two adjacent sides facing the streets, in order to accommodate 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. A thorough and detailed computer-aided analysis performed during an investigation of the building showed that the frame as originally designed was 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 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 deflections 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; they substantiate the judgment the engineer used in arriving at the engineering solution. The engineering effort is in knowing what to calculate, and how to model the real world, so that the solution, the real structure, actually performs the way the engineer wants it to. The quality of the calculations, their clarity, thoroughness and accuracy, 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 substitute for, the judgment of the structural engineer. The structural engineer of this example designed his steel frames without exhaustive calculations, but as a detailed analysis indicated, 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 complete 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.
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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 reinforced earth type retaining structure. The structural engineer had never designed such a wall before. The retaining wall system vendor provided sample calculations to the structural engineer as an example of how to design the wall, but the method included errors. The structural engineer used the calculation method provided. After the wall was completed, during heavy rains, a portion of the wall failed.
During the meetings and depositions that ensued, an experienced expert forensic engineer who had designed and analyzed "thousands of these walls," and who had developed his own calculation method, described the structural engineer as negligent.
The use of "canned" calculations and design approaches without understanding their application and limitations can be beneath the standard of care and can be an instance of professional negligence. However, the practice of the experienced expert, far exceeding that of a normally competent engineer, is not the standard of care. The question was not, "How did the defendant engineer's performance compare with the expert's?" It was more appropriately, "Did the defendant engineer utilize his best diligence and reasonable care given the fact that he hadn't designed such a retaining wall before?"
The answer to that second question, in this author's opinion, was ,"No." Best diligence would have resulted in the error in the "canned" calculations becoming apparent to the structural engineer. Reasonable care would have resulted in the structural engineer reverting to first principles, as described in readily accessible soils engineering texts on retaining wall design. The failure may or may not have happened anyway, given the intensity and duration of the rain, but the actions of the design engineer would have been defensible under a standard of care defense.
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A large condominium project was built in six phases, spread out over several years. For Phases I through III the soils engineer recommended the foundation be a drilled pier type, and that the piers be 4 feet deep. When construction of Phase IV started, he recommended 6 feet deep piers. Later, during construction of Phases V and VI, the structural engineer went back to 4 feet piers. All the buildings in all six phases were of the same design, based on the same soils report. The soils were similar in all Phases. Was the structural engineer negligent in not carrying forward the soils engineer's Phase IV recommendations?
Management and control of information is part of diligent engineering practice. It was argued that the structural engineer's failure to carry forward the revised soils engineering parameters represented an error inconsistent with the standard of care.
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Unreinforced masonry wall collapse
Engineering design drawings and specifications for the seismic strengthening of a circa 1888 unreinforced brick masonry building included the requirement for the general contractor to produce shoring and bracing plans and submit them to the structural engineer of record (SER) for review. Construction started without the knowledge of the SER, and work took place without those plans. The SER was excluded from the construction process, including the review of shoring and bracing plans, by the owner and the contractor. Due to the absence of shoring and bracing, a brick wall collapsed during construction, killing the contractor's foreman. The SER was sued for professional negligence and wrongful death. Two years after the "accident", and after a 6-week trial, the jury found the SER not negligent and not liable. The jury found against the owner and, through an indemnity clause in the construction contract, the contractor, and awarded the foreman's widow and step-daughters over $1 million in damages.
Low bidders and "Can-Do" kinds of guys kill people. Construction is a dangerous pastime, and builders sometimes take undue risks in order to save time or money. The engineer may be forced to accept the consequences that risk under the worst circumstances. In this case, the jury decided that the general contractor and the owner actively prevented the SER from fulfilling his obligation to exercise care and diligence. The Jury found the actions of the SER were not beneath the standard of care, and they placed responsibility where it belonged.
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Tacoma Narrows Bridge collapse
In 1940, wind-induced oscillations destroyed the brand new Tacoma Narrows suspension bridge. One hundred years earlier, the dangerous dynamic effects of the wind were known, and suspension bridge design of that era included measures to counter those effects. The engineer for the Tacoma Narrows Bridge superstructure, described as "among the highest authorities in suspension bridge design" (Condron, 1938), was not thought by many at the time to be negligent. This was in spite of the fact that normal competence of suspension bridge designers of almost a century earlier included avoidance of this kind of failure.
Diane Vaughan (1996) wrote about the Challenger explosion. She describes the actions of the engineers and managers of the Space Shuttle program as succumbing to the "normalization of deviance," the gradual acceptance of sequential minor errors and failures, accumulating and culminating in a major catastrophe. The Tacoma Narrows failure may have been an example of this phenomenon. Suspension bridges were being designed and built with ever longer and more slender spans. Construction workers, and the operators and users of the bridges, noticed the tendency of the new bridges to oscillate in the wind. To some extent, the bridge designers accepted that response as reasonable and acceptable performance in light of the tradeoff for lightness, economy and aesthetics. The Tacoma Narrows Bridge was the most slender suspension bridge built up to that time, and its oscillations, so pronounced that the bridge was nicknamed "Galloping Gertie,"ultimately caused its collapse.
The advancement of the state of the art is not always forward. The designer of the Tacoma Narrows Bridge was not considered negligent in his failure to accommodate dynamic wind effects, despite almost a century of bridge design experience pointing to that as a critical design condition. Suspension bridge design and analysis methods, the materials used in bridge construction, and the longer and more slender profiles of the modern bridges, were thought to be sufficiently different from those of the 19th century, that the designer of the Tacoma Narrows Bridge was not held to the standard of care of the earlier era.
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Hyatt Regency Kansas City walkway collapse
A minor, "non-structural", feature of a hotel, a walkway suspended from the roof and spanning a central atrium, collapsed suddenly, killing and injuring a great number of people. The detail of the connection of the walkway beam to the suspender was not carried out as drawn, but was changed by the contractor for constructibility reasons.
The structural engineer, who reviewed and approved the change, was found to be negligent. Several important lessons can be learned from this tragedy. Among them are: 1) Attention to the constructibility of a detail is essential to good design; 2) Communication of field changes to the designer is essential; 3) Shop drawing and change order review is important, and shouldn't be performed without the participation of an experienced practitioner; 4) The smallest detail can cause a major problem, and 5) In practice, the consequences of an error can have a bearing on the evaluation of negligence.
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CitiCorp Building, New York
To accommodate a smaller building on the site, the high-rise CitiCorp tower was designed and constructed with its main columns at the middle of each side, rather than at the corners. The New York City Code, and high-rise structural engineering practices, required the building frame to be analyzed and designed to resist winds acting perpendicular to each face. Well after the building was completed and occupied, the design engineer reviewed the frame for adequacy against "cross-corner" winds. He found that based on that loading assumption, the building had a small but unacceptable probability of collapse. Work to strengthen the building was carried out. It was widely agreed that the structural engineer's performance was not beneath the standard of care. That is, the structural engineer exercised an acceptable degree of care and diligence, and therefore, the error was not professional negligence.
This situation illustrates the importance of a rapid response to the discovery of error, and the fact that even non-negligent errors can be dangerous and very expensive.
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Lighting tower collapse
Competent engineering practice includes timely communication of information. A recent tragic construction failure resulted in significant liability on the part of an engineer ("Suspended...", 1996). The SER for the Olympic Stadium in Atlanta, Georgia, discovered an error in his design of a portion of a steel light tower to be built as part of the stadium. He notified his client, the architect for the stadium, and designed a repair for the error. The SER was not aware of the progress of construction, and did not consider the error and the repair an emergency. Unbeknownst to the SER, construction had indeed progressed to the point that the light tower was being erected ten days after the SER informed the architect of the error and the need for repair. The repairs had not been carried out by that time. During erection, the light tower collapsed as a result of the design error, killing one iron worker and injuring another.
The SER's engineering registration was suspended for three years by the Georgia Board of Registration for Professional Engineers and Land Surveyors, and the SER has been sued for wrongful death. The professional negligence alleged by the plaintiffs was the SER's failure to "explicitly indicate to the project manager (the architect) that emergency action was required." The error in the design was not negligent, but the lack of urgency in the SER's response to uncovering the error was.
The lack of urgency only became significant because the SER was unaware of the progress of the construction. Coordination or communication which should have occurred in order for the SER to have been aware of the progress of construction was apparently absent. Despite the possibility the SER may have had nothing to do with this absence of coordination or communication, the SER was on the hook. In this case, the engineer's liability apparently existed at least partially because of the failure of others to keep him informed. This is an important lesson for practicing engineers. They should make sure that important information flows in a timely manner to all appropriate parties.
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Bridge collapse and the duty to warn
Another duty of an engineer is the duty to warn. California Attorney General's Opinion Number 85-208 (1985) (Acret, 1991), states that a registered engineer hired to investigate the integrity of a building has a duty to warn the building's occupants if the engineer determines they face an imminent risk of serious injury due to a hazard the engineer observes. The Opinion requires the engineer to warn the occupants even though the building owner client of the engineer requires confidentiality on the part of the engineer.
The extent to which the duty to warn extends varies with location and circumstance, and the standard of care in one locality may not be the standard of care in another. The following case study is an example of this fact.
A 77-year old county-owned suspension bridge for pedestrian traffic, nicknamed Swinging Bridge, collapsed into the Little Red River in Arkansas in 1989 ("Appeals ...", 1996). Forty people were on the bridge at the time, engaged in the apparently popular activity of forcing the bridge to swing from side to side. The bridge collapsed, five people were killed and dozens were injured.
In 1982, seven years prior to the collapse, an engineering study evaluated and analyzed the bridge, and came to the opinion that the bridge was sound, and that it could provide adequate service for as long as an additional century. The engineer recommended further study be carried out, and although the bridge cables were free of rust, he recommended a protective coating be applied. The County did not follow the engineer's recommendations.
The victims and their relatives sued the County, charging it with failure to warn of the hazard presented by the bridge. The court ruled against the plaintiffs, stating, "Mere knowledge of danger to the individual does not create an affirmative duty to protect." The pedestrians caused the collapse and the County had nothing to do with it. The court apparently decided the defendants did not have to warn anyone, and the plaintiffs had to bear the consequences of their actions themselves.
This finding may not have been the conclusion of a court in a different jurisdiction, one where juries are more sympathetic to plaintiffs. If it were known the bridge could be damaged by being forced to swing back and forth, or if that fact should have been known, and if it were known that pedestrians regularly engaged in such activity, a more sympathetic court may have found the engineer who evaluated Swinging Bridge negligent in his failure to warn of the dangers. This tragedy could certainly have been prevented.
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- Acret, James. Architects and Engineers, 2nd Edition, Shepard's/McGraw-Hill, Colorado Springs, 1991.
- "Appeals Panel Finds No Fault in Bridge Collapse." Civil Engineering News, page 15, November, 1996.
- BAJI (Bench Approved Jury Instruction) 6.37, "Duty of a Professional." California Jury Instructions, Civil. West Publishing Company, January, 1986.
- Condron, T. L., Supervisory Engineer, 1938. Appendix IV of Section B, "The Failure of the Tacoma Narrows Bridge: A Report to the Honorable John M. Carmody, Administrator, Federal Works Administration, Washington, D. C." by Othmar B. Ammann, Theodore von Karman, and Glen B. Woodruff, Pasadena, California, 1941. Reprinted in the Bulletin of the Agricultural and Mechanical College of Texas, Texas Engineering Experiment Station, College Station, Texas, 4th Series, Vol. 15, No. 1, January 1, 1944.
- "Suspended Engineer's Lesson: Never Wait Until It Is Too Late." Engineering News Record, page 12, June 24, 1996.
- Vaughan, Diane. The Challenger Launch Decision: Risky Technology, Culture, and Deviance at NASA. The University of Chicago Press, Chicago, 1996.