Editor’s Note

The August 2010 issue of the Practice Periodical includes two companion papers dealing with suspended scaffold structural support elements. The first paper focuses on design of such elements; the second on their certification. Standards related to the design and certification of such elements are maintained by the federal Occupational Safety and Health Administration (OSHA). These standards include structural requirements for elements that support suspended scaffolds and fall-arrest lanyards. Ensuring that applicable requirements are met is the responsibility of a qualified person—typically a professional engineer. However, navigating through and applying the OSHA structural provisions can be difficult, primarily because relevant requirements are not contained in a single document, structural requirements vary for different uses, and these requirements are not always written in a manner consistent with typical structural engineering practice.

The first of the two papers provides information that will promote rational application of key OSHA structural provisions for the design of suspended scaffold support elements and lifeline anchorages. This paper also provides the foundation for the companion paper, whose objective is to promote rational application of sound engineering principles when certifying the adequacy of existing elements and their compliance with OSHA standards. The authors state not only that certain trends and recent developments in the facade access equipment industry have made proper certification of support elements more difficult than it needs to be, but that irrational approaches and conclusions are, at times, actually encouraged by industry groups.

The third paper in this issue is titled “Integral Abutment Bridges: The European Way.” In integral abutment bridges (IAB) the superstructure and substructure move together to accommodate the required translation and rotation. There are no bridge expansion joints and, in the fully integral abutment bridges, no bearings. Such bridges have proved themselves to be less expensive to construct, easier to maintain, and thus more economical to own over their life span than bridges with superstructures and substructures that are not integral.

Integral abutment bridges are becoming more popular in Europe; however, design and construction traditions differ from country to country. This has led each country to different technical solutions for the same problem. A survey was conducted in 2007 to identify and compare criteria used by the various European countries in the design of such bridges. The results of the survey were compared to some recently conducted surveys of state agencies in the United States. Similarities and differences are presented and discussed by the authors.

The next two papers deal with historic wooden bridges in the United States. The first paper describes the Old Camelback Bridge designed and built by Theodore Burr across the Susquehanna River at Harrisburg, Pennsylvania, in the early nineteenth century. This bridge was built in two sections with an island in between. Each of the two sections had five spans with an average span length of about 235 ft. The total length was 3,631 ft. The road over the island connecting the two bridges was 771 ft long.

The second paper describes the bridge built over the Schuylkill River near the city of Philadelphia in 1811–1812. The bridge is commonly known as The Colossus and was built by Lewis Wernwag. It was the longest single-span (340 ft 3 in.) wooden bridge in the United States for many years. It was burned by an arsonist in 1838 and replaced by Charles Ellet’s Fairmont Suspension Bridge in 1842. Both of these papers are well written and well illustrated. They were prepared by Francis E. Griggs Jr., who is well known for his numerous articles on historic bridges.

The next paper in this issue deals with design and costs for simple-made-continuous rolled steel girder bridges. The method presented appears to enable significant cost savings. Specifically, it allows the designer to avoid steel bridge girder splices and to design the steel sections for the self-weight and weight of the slab as simply supported and then the addition of live load and remaining dead load as continuous. This balances the moments between the positive and negative regions allowing for a prismatic section and even adds speed of construction since the field splices are not needed. This paper is a literature survey on this topic.

The final paper in this issue analyzes stability of columns composed of deformable bars, with the particular goal of studying the influence of bracings. The bars are assumed to be deformable by bending, axial forces, shearing forces, and torsion. A computer program was developed to determine the critical loading of the structure by taking into account geometric nonlinearity. The stiffness method is used to describe the structural response in three dimensions. Global instability is considered to have been achieved when a given loading introduces singularities in the global stiffness matrix. When the critical loading has been determined, it is possible to determine global instability parameters such as effective buckling coefficients. An example problem is presented and results are compared to ANSYS results to demonstrate the potential of the process.

The Construction Forum in this issue is “Construction Engineering and Security.” The author discusses potential terrorist threats at construction sites and provides suggestions as to how such threats may be mitigated.