Practice Periodical on Structural Design and Construction

The Federal Occupational Safety and Health Administration (OSHA) maintains standards related to the design of suspended scaffolds and fall protection systems. 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 and applying the OSHA structural provisions can be difficult, primarily because relevant requirements are not located in a single document, structural requirements vary for different uses, and structural requirements are not always written in a manner consistent with typical structural engineering practice. This paper 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, “Certifying That Existing Suspended Scaffold Structural Support Elements and Lifeline Anchorages Comply with Federal OSHA Requirements,” which is included in this publication.

The Federal Occupational Safety and Health Administration (OSHA) maintains standards (Standards) that define structural requirements for elements that support suspended scaffolds and fall arrest lanyards when this equipment is used to access facades and other elevated portions of buildings. The Standards are available online at www.osha.gov. Ensuring that applicable requirements are met is the responsibility of a qualified person—typically a professional engineer. However, navigating and applying the OSHA structural provisions can be difficult primarily because relevant requirements are not located in a single document, structural requirements vary for different uses, and structural requirements are not always written in a manner consistent with typical structural engineering practice. The rational application of key OSHA structural provisions when designing suspended scaffold support elements and lifeline anchorages is the subject of a companion paper, “Designing Suspended Scaffold Structural Support Elements and Lifeline Anchorages in Conformance with Federal OSHA Requirements,” which is included in this publication. The objective of this paper is to promote the rational application of sound engineering principles when certifying the adequacy of existing elements and their compliance with OSHA Standards. Unfortunately, certain trends and recent developments in the facade access equipment industry have made proper certification more difficult than it needs to be; irrational approaches and conclusions are, at times, actually encouraged by industry groups.

Integral abutment bridges are becoming more popular in Europe, but the traditions differ from country to country. This leads to different technical solutions for the same problem in each country. A European survey was conducted in early 2007 to illustrate the design criteria used by each different country for integral abutment bridges. The survey requested information useful to a designer comparing the design requirements and restrictions of various European countries. As an added measure of comparison, these results were compared to some recently conducted surveys of state agencies within the United States. When looking at the results of the European survey responses and past surveys of U.S. transportation agencies, it is clear that there are many similarities in design assumptions and construction practices. Yet, there are also significant differences.

Theodore Burr built many wooden bridges in the early 19th century, but his most well known was the one he built across the Susquehanna River at Harrisburg, Pa. The current bridge is called the Market Street Bridge, but Burr’s bridge on the same site that survived from 1816 to 1902 was called the Old Camelback Bridge. It was built in two sections with an island in between. The span lengths for the eastern section (Harrisburg side) were $225^{\prime }$ , $248^{\prime }$ , $250^{\prime }$ , $240^{\prime }$ , and $202^{\prime }$ . The road over the island was $771^{\prime }$ long and the western or Camelback section had span lengths of $212^{\prime }$ , $245^{\prime }$ , $258^{\prime }$ , $247^{\prime }$ , and $222^{\prime }$ for a total length of $3,631^{\prime }$ .

Lewis Wernwag was one of the leading long span wooden bridge builders in the early 1800s. While he built many major bridges, his most well known one was a bridge he built across the Schuylkill River in 1811–1812, commonly known as The Colossus. It was the longest single span (340 ft and 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 Fairmount Suspension Bridge in 1842.

The method of simple-made-continuous for steel bridges is becoming more popular throughout the United States because it enables significant cost savings. Specifically, the method allows one to avoid steel bridge girder splices and design the steel sections for the self weight and the weight of the slab as simply supported and then the addition of live load and remaining dead loads 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. In 2006, the Colorado DOT sponsored a study to (1) review current approaches to simple-made-continuous using standard rolled sections and (2) develop design charts for rapid sizing of steel bridge beams and cost estimation for simple-made-continuous. This paper presents a state-of-the-art review up until 2007 for this type of construction and focuses on several of the most recent and successful transportation department projects.

This article analyzes the 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 has been developed to determine the critical loading of the structure by taking into account geometric nonlinearity. The stiffness matrix technique 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 is presented and compared to ANSYS results to demonstrate the potential of the process.