Practice Periodical on Structural Design and Construction

Most utility engineers in the United States use the National Electrical Safety Code (NESC) to determine minimum structural loading requirements for the design of transmission and distribution pole structures. The NESC specifies two weather loadings—combined ice and wind loading (rule 250B) and extreme wind loading (rule 250C). However, the current NESC excludes poles with heights above ground of 60 ft or less from the extreme wind loading (rule 250C) design requirement. ASCE 7-98 prescribes extreme wind load requirements for the design of buildings and other structures and contains no extreme wind load exclusion provision for short structures. This paper reviews the adequacy of the current NESC 60 ft exclusion provision for the design of poles located in the 90–140 mph 3 s gust wind speed based on ASCE 7-98.

Most utility engineers in the United States use the American National Standard for Wood Poles, American National Standards Institute (ANSI) 05.1, to determine the dimensional properties of different species of wood poles. ANSI 05.1 defines a groundline distance from the butt for each pole height for use when a definition of groundline is necessary in order to apply requirements relating to scars, straightness, and likewise. In addition, the groundline distance is used to determine the horizontal load capacity of each class of pole. This paper reviews the adequacy/fixity for different pole heights and species with setting depths based on the ANSI 05.1 groundline location in soils with different properties. The effects on the pole setting depths of backfill diameter and strength as well as groundline forces are also discussed.

Three bridges in Boone County, Missouri—Brown School Road, Coats Lane, and Creasy Springs Bridges—were selected for strengthening with carbon-fiber-reinforced polymer laminates in both shear and flexure. The objective of the rehabilitation program was to remove the 15-ton load posting that had been imposed on each of the bridges. To verify the results of the upgrade, load tests were performed before and after strengthening on two of the bridges—Brown School Road and Coats Lane Bridges. This paper presents the procedures followed in the design, installation, and load testing of the bridges. A recommendation regarding the removal of the load posting is made.

Sanitary and storm sewer collection systems are aging, and the reactive approach traditionally used for repair and rehabilitation is no longer appropriate. A comprehensive program including assessment of the existing infrastructure, adequate management, and clear understanding of the causes of deterioration in the sewer systems is imperative. Several rehabilitation alternatives are already in use, but on a restricted basis. This paper will discuss rehabilitation techniques used for concrete and brick sewers. The techniques considered include trenchless technologies such as slip liners, cured-in-place liners, and formed-in-place pipe liners. Also included are chemical grouts, coatings, and robotic rehabilitation. A comparison matrix and a case study of the Central Outfall Sewer in the city of Los Angeles are presented to compare different rehabilitation alternatives for underground infrastructure.

A multitude of recent studies has demonstrated that the construction of energy-efficient homes can result in major benefits to the homebuilder, homeowner, and the nation. Federal and state government agencies are spending significant efforts to demonstrate the benefits of energy-efficient homes. In spite of these major efforts, adoption of energy-efficiency technologies in new home construction has been slow. This paper presents a research project aimed at developing cost-effective energy-efficiency strategies for construction of Five Star Plus homes. Various combinations of energy-efficiency measures along with energy savings and cost premiums are developed in this research. Issues that relate to the adoption of these energy-efficiency strategies are identified and discussed in the paper.