What is an acceptable level of performance? In reference to the contributed article, "Licensed not to kill," by Gary Hart, Ph.D., C.E., in the September 2005 issue of Structural Engineer … in most cases, it is impractical to upgrade older steel [moment-resisting] frames to comply with FEMA 350, and the requirement to do so may result in buildings being demolished. This is because in many cases, frames cannot be made to fully satisfy FEMA 350 requirements, even if frame connections are modified for compliance. Omitted from this article is mention of other, perhaps more effective strengthening schemes such as adding shear walls, BRBFs, campers, and base isolators. These may be more feasible to install, more effective, and more economical.

Hart’s article gives the impression that FEMA 350 resolved all the issues.

Although we recognize that much good work was carried out in the SAC project, we are afraid that the lack of fully determining the causes of the failures may come back to haunt the engineering community.

The recommendation to fully upgrade older moment frames using FEMA 350 as a standard should not be made without acknowledging possible unintended and undesirable consequences.

Hart’s concern for structural engineers’ moral obligation to protect lives is correct. However, in our view, structural engineers are only perceived as successful if they achieve economy in design and not for implementing measures above minimum code requirement to benefit performance. Hopefully, Hart’s article will help tip the current trend toward the other direction.

Hart mentions determination of the calculated level of confidence, presumable using FEMA 351. Personally, we do not believe that this approach is a realistic way of assessing existing steel frame buildings, which have limited drift capacity.We feel that a deterministic approach should be established at least for collapse prevention, rather than the probabilistic approach given in FEMA 351.

To conclude, the above mentioned issues leave us in a dilemma with somewhat conflicting interests of life safety and economic considerations.

Nevertheless, we strongly recommend that the engineering community seek to debate these issues and related concerns.

The broader issue of acceptable level of structural performance is for society to debate and decide.We can only explain available options and consequences, continue to develop systems that are capable of better performance, and perhaps exert our influence in the decision making. Beyond a minimum level of life safety though, we cannot force society to accept what we deem right.

Robert T. Lyons, S.E., and Peter J. Maranian, S.E.
via e-mail