Editor’s Note

The journal Publications Committee is pleased to present this special topic issue on mitigating the potential for progressive disproportionate structural collapse. This project is an outgrowth of a professional leave granted to me by my employer, Washington State University, to review the state-of-practice regarding the subject of progressive collapse and the design implications of emerging codes and standards. I spent spring semester and the summer of 2005 traveling throughout the United States, contacting leading design practitioners and researchers identified with developments in this field. I also traveled to England and Scotland to visit with practitioners and government officials regarding the evolution of related UK standards since the Ronan Point residential tower collapse of 1968.

Engineering News-Record (April 3, 2006, and April 10, 2006) identified proposed standards for progressive collapse mitigation as the most controversial among recommendations emerging from the National Institute of Standards and Technology (NIST) report on the performance of the World Trade Center towers on September 11, 2001. My studies confirmed the controversial nature of this subject, including such basic controversies as simple terminology. The term progressive collapse is rejected by a number of experts, since nearly all structural failures involve a certain degree of progression. These experts favor the term disproportionate collapse, whereas still others reject this terminology until disproportionate can be defined specifically in a way that rationally relates the scale of the triggering event to the scale of the resulting collapse. Furthermore, major controversies revolve around questions about which buildings the new guidelines should apply to and whether the guidelines should be mandatory. Finally, the appropriate degree of sophistication of analytical techniques is still open to question because a true representation of the complex nonlinear, dynamic character of progressive structural collapse incidents presents an enormous challenge to many engineering practitioners.

While undertaking my studies, it became clear to me that the most useful contribution that I could make to this effort is this coordinated collection of papers. I have been working with each of the authors for a year, and I believe that these papers accurately represent the current state of practice and research on the subject. A careful reading of these papers uncovers the controversies and the difficulties that the future generation of practitioners will face in confronting emerging challenges. You will find conflicting opinions here, as well as a number of contradictions. This result is to be expected while new standards are developed. I hope that this issue will serve as a useful contribution to that process. I also hope that readers will further the effort by contributing related papers or discussions.

Disproportionate collapse occurs frequently during construction, where a small event can result in substantial damage to the incomplete structure, particularly when temporary bracing is inadequate. Completed structures, even nonengineered structures, are less susceptible to progressive collapse because they almost always exhibit some inherent redundancies. Still, given the current state of affairs, it has become necessary for design professionals to consider the risks associated with low-probability, high-consequence events. It is therefore necessary to incorporate rational procedures for doing so, including procedures for mitigating the potential for disproportionate collapse.

I am grateful to Robert Smilowitz for his guest editorial that introduces the papers. His concise thoughtful statement identifies the challenge:

The ASCE Technical Council on Forensic Engineering (TCFE) has selected the Outstanding Paper published in this journal in 2005. The Outstanding Paper Award certificate and wall plaque will be given to David M. Bailey (Fig. 1) and Dane Bradford (Fig. 2) for their paper, “Membrane and Flashing Defects in Low-Slope Roofing: Causes and Effects on Performance,” which appeared in the August 2005 issue (Vol. 19, No. 3, pp. 234–243). The paper notes that “good roof performance requires proper design and specification, quality materials, professional workmanship, and proactive maintenance.” Research undertaken by the authors concludes that quality-assurance processes during installation are critical to optimal roof performance. The paper is very well written and includes substantial data resulting from an extensive study of a large inventory of United States Army low-slope membrane roofs.

David Bailey is a research engineer in the Facilities Division at the U.S. Army Engineer Research and Development Center (ERDC) Construction Engineering Research Laboratory. ERDC is the premier research and development center of the U.S. Army Corps of Engineers. Bailey’s research at the laboratory during the past 22 years has included investigations into roofing system performance and materials degradation. He is also the principal developer of the ROOFER Sustainment Management System, a practical decision-making tool used by facilities managers to help identify cost-effective strategies for repair and replacement of low-slope membrane and asphalt shingle roofs. He has a bachelor of science degree in civil engineering and a master’s degree in materials science and engineering from the University of Illinois Urbana-Champaign.

Dane Bradford is president of Bradford Roof Management, Inc., a 64-year-old commercial and industrial roof contracting and roof consulting firm based in Billings, Montana. He received a business management degree from Montana State University in 1981. Bradford is a past president of the National Roofing Contractors Association (NRCA). He served on the NRCA Manual Update Committee from 1993 to 1996, during the writing of the fourth edition of the NRCA Roofing and Waterproofing Manual. In addition to assignments on numerous NRCA committees, Bradford has served two terms as the chairman of the Technical Operations Committee and chaired the North American Conference on Roofing Technology in 1999 and the 12th International Roofing and Waterproofing Conference in 2002. He led in the development of a proprietary roof asset management software program that is used to analyze roof conditions and provide proactive maintenance budgeting and planning. He has also been a consultant in the continuing development of the ROOFER program. Bradford Roof Management, Inc., provides roofing contracting services on a regional basis in several Rocky Mountain and Plains states. Roof consulting services include comprehensive roof asset management services throughout the United States. Services provided include building-envelope forensics, expert witness services, roof surveys, planning and reroof design services and quality control/quality assurance expertise during roofing and waterproofing construction.

Other nominees for the Outstanding Paper Award were as follows:

Congratulations are extended to each of these authors. Nominations submitted by journal readers were appreciated.

The time has come to select the winner of our Outstanding Paper Award for 2006. The Publications Committee is studying the papers published in our four 2006 issues and will soon make a recommendation to the TCFE Awards Committee. Readers are invited to submit nominations. If you wish to nominate a paper that you found especially useful or informative, please write to me, indicating your reasons for the nomination. I can be contacted by mail: Kenneth L. Carper, School of Architecture & Construction Management, College of Engineering & Architecture, P.O. Box 642220, Washington State University, Pullman, Wash. 99164-2220; by phone at (509) 335-1229; by fax at (509) 335-6132; or by e-mail at [email protected].

This issue marks the end of the 20th year of publication of the Journal of Performance of Constructed Facilities. The Journal owes much of its success to the many manuscript reviewers who have donated their time to provide constructive comments to authors. Indeed, the reviewers play an equivalent role with the authors in maintaining the quality of this publication. Our reviewers serve without compensation. They are, without exception, highly respected individuals who are very busy in practice and/or academia. Yet, they find the time to contribute altruistically to the dissemination of useful information in this Journal.

At the end of each year’s final issue, we list those who have provided reviews during the year. I want to extend my personal appreciation for their efforts. If you recognize one of your colleagues in the list, please express your appreciation.