ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/306198
A typical example of the county's newer construction is this four-span, precast, prestressed concrete I-beam structure— the T.C Jester Road Bridge over Harris County Flood Control Ditch. ASPIRE , Winter 2010 | 51 C O U N T Y H arris County, Tex., which includes Houston, is the third most populous county in the United States with an estimated 4.1 million residents in June 2009. The county's population has increased 19% since 2000. The unincorporated population of Harris County is approximately 1.4 million. The county would become the sixth largest city in the nation if it were a single incorporated city. The county's land area, 1778 square miles, is larger than Rhode Island and Connecticut combined. Harris County's road network consists of approximately 5900 miles of roads and 696 bridges (44 additional bridges are coming into service pending scheduled inspections). Appr oximately 60% of the r oad network is residential, with the remaining 40% either collector roads or thoroughfares. Sixty percent of the road network is reinforced concrete pavement, HARRIS COUNTY, TEXAS EXPERIENCE WITH CONCRETE BRIDGES by Jackie Freeman and Willard Puffer, Harris County, Texas EDITOR'S NOTE If your county has a high percentage of concrete bridges or some interesting and innovative concrete bridges and would like to be featured in ASPIRE™, please let us know at firstname.lastname@example.org. Number Main Span 6 Timber 10 Steel/Plate Girders 67 Concrete Slab/Box 52 PS Concrete Multiple Girders 28 Other PS Concrete 445 PS Concrete Box Girders 88 Culverts 696 Total 2009 Active Structures Table 1 Numbers of Bridges by Material Type Age (yrs) Number 70 2 60-69 6 50-59 14 40-49 41 30-39 134 20-29 276 10-19 154 0-9 69 TOTAL 696 Table 2 Age Distribution with asphalt and other materials comprising the remaining pavement types. The material of the county's bridges is almost exclusively concrete. The breakdown by materials of the main span is shown in Table 1. Seventy-seven percent of the inventory is precast, prestressed concrete multiple box girders (64%) and concrete culverts (13%). Ninety percent of the county's bridge inventory crosses water. Twenty-two bridges are at least 50 years old. In 2007, only eight bridges had a sufficiency rating less than 50. Of those eight bridges, four are timber and four are concrete bridges. Sufficiency rating is a numeric value which is indicative of bridge sufficiency to remain in service as defined by the state and FHWA Bridge Inspection Safety Assurance Program. The four concrete bridges with a 2007 sufficiency rating less than 50 have provided collectively nearly 200 years of safe service to the county. One of the four has been replaced, one repaired, and two are due to be replaced. Harris County is v er y pleased with the exceptional service life provided by its concrete bridges. The county has less than 1% of its concrete bridges with a sufficiency rating less than 50. The cost of service often goes unreported. Harris County has seen growth that frequently requires changes in road alignment resulting in early bridge replacement. However, in many situations, existing bridges have been widened by extending the substructure, installing additional precast, prestressed concrete box girders, and installing a new deck wearing surface allowing the existing structure to continue to provide many years of additional service. Concrete bridges continue to meet the Harris County's long-term needs and affordable life- cycle goals. ___________________ Jackie Freeman is deputy executive director of the Harris County Public Infrastructure Department and Willard Puffer is director of the Harris County Asset Management System, Houston, Tex. ASPIRE_Winter10.indb 51 12/18/09 2:31:01 PM