Editor’s Note

The May 2008 issue of the Practice Periodical on Structural Design and Construction contains eight papers and a Structural Forum. The forum and papers cover a variety of topics that are of importance to practicing engineers. Of special interest in this issue is a group of four papers on the subject of “below-the-hook” lifting devices. These papers provide a unique collection of discussions of design issues related to lifting devices—issues that have rarely been addressed in other structural engineering-related journals. The forum is another interesting and unique addition to this issue. It focuses on the subject of homeland security and what design engineers should know about this timely subject.

The first four papers in the May 2008 issue deal with the subject of lifting devices in general and below-the-hook lifting devices in particular. For those readers who are not familiar with such devices, the Editor would like to clarify that ASTM B30.20 defines four groups of such devices. Group I consists of structural and mechanical devices, Group II consists of vacuum lifting devices, and groups III and IV deal with magnet lifting devices.

David Duerr of 2DM Associates, Inc. is the author of the four papers on this subject in this issue. The first paper discusses the selection procedure for a service class and design category for lifting devices and indicates the importance of proper design standards to engineers, manufacturers, and purchasers of lifting devices. The paper provides a detailed discussion of the design category and service class definition of lifting devices as a means to guide the purchasers and users of below-the-hook lifting devices in specifying the correct design category and service class for these structures.

The second paper in this group discusses the publication of a new standard for the design of below-the-hook lifting devices by ASME. According to this paper, the ASTM standard defines design requirements for lifting devices used in conjunction with cranes, derricks, and other types of hoisting equipment. The paper provides an introduction to the new ASME standard along with an extended discussion of the methods for finding how the variations expected in the strength and applied loads are related to determining reliability and design factors.

Duerr’s third paper further discusses the ASME standard by focusing on provisions that are geared for pinned connections. The structural design requirements for lifting devices, as embodied in the ASME standard, are explained, and the paper mentions that the design provisions intended for pinned connections are significantly different from the more common specification requirements. The paper further indicates that the provisions for the design of pin-connected plates provide a level of reliability that is equal to or higher than that upon which the design factors in the standard are based.

The fourth paper on the lifting devices focuses on design of stiffened plate-lifting beams. Again, the ASME standard is discussed, but the paper specifically addresses stiffened plate-lifting beams that are more common in the construction industry. Design issues that are applicable to this type of lifting beams are reported to be lateral-torsional buckling, a combined tensile and shear stress state in the regions around pin-loaded holes, connections among the built-up elements of the beam, and the strength of the lower pin holes. A method for the design of stiffened plate-lifting beams is derived that is compatible with the ASME requirements and standards.

The May 2008 issue’s other four papers include one by Colin Gurley of the Sidney Institute of Technology in Australia on the subject of structural design for fire in tall buildings. Structural design for fire has become a popular topic in the Practice Periodical on Structural Design and Construction. This paper adds another informative source on fire loads and design considerations in buildings to the collection of papers previously published in this journal. The paper examines the implications of the final report on the collapse of the World Trade Center towers published by the National Institute of Standards and Technology (NIST) in 2005. Among other important subjects mentioned in the paper are (1) the significance of the new role of a new group of engineers (fire engineers) as members of design teams in buildings and (2) the significance of the wider role the structural engineer has to play in the overall building design when fire load effects are of concern.

Neil Woodroffe of Stantec Consulting, Inc. in Phoenix and Samuel Ariaratnam of Arizona State University are the authors of the sixth paper in this issue. They discuss the cost and risk evaluation for horizontal directional drilling versus that of the open-cut method in an urban environment. This paper is especially important in light of the challenges faced by the public sector in developing the most effective methods for installing new buried infrastructure systems while considering cost reduction. The risk involved in an underground system installation project and construction cost are two important factors in the selection of an appropriate method for implementing such a project. Accordingly, these two factors have been used in comparing two different methods for installation of underground systems: the horizontal directional drilling method as opposed to the traditional open-cut method. It is indicated that the horizontal directional drilling method can minimize the risk as well as reduce the construction cost of working in an urban environment.

The seventh paper in this issue, by David Jauregui from the New Mexico State University and his coworkers, is a study of the structural evaluation of a riveted steel arch bridge built in the early 1950s across the Los Alamos Canyon. The bridge underwent rehabilitation work in the early 1990s, and the paper discusses how the load rating of the bridge was affected and improved by the work. Specific attention is given to the floor system components such as stringers and floor beams and to their ratings. The paper is an excellent example of how the AASHTO-recommended rating method can be used to conduct an evaluation of a structural system whose members have been upgraded for enhanced performance and load-bearing capacity.

The eighth paper is written by Tarun Naik of University of Wisconsin. The subject of this paper is the sustainability of concrete structures. This paper is timely and touches upon an important issue in the building industry. The paper discusses the environmental hazards arising from the production of concrete, and outlines procedures and methods that can be employed in the manufacture of concrete for a more environmentally friendly product. This paper is of special interest to designers who have the “green” concept in mind.

The Structural Forum in this issue is devoted to the relationship of homeland security topics to structural design. Anatol Longinow of the Illinois Institute of Technology (IIT) and Nestor Iwankiw of Hughes and Associates in Chicago are the coauthors of the forum, which outlines the importance of design issues in enhancing security and is intended as general information for structural engineers and designers regarding the type of issues that will need to be integrated with a traditional design practice.

The eight papers published in the May 2008 issue and the forum all present important design and construction subjects that can be of interest to the readers. The forum is especially intended to open the door for further discussions on how homeland security issues affect structural design. Readers are invited and encouraged to discuss and comment upon the topics included in the Forum and in the collection of seven papers in this issue of the journal.