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/532296
PERSPECTIVE Overview of the 2012 ASBI Durability Survey by Brett H. Pielstick, Eisman & Russo Inc. In the fourth edition of the American Segmental Bridge Institute’s (ASBI’s) Durability Survey of Segmental Bridges,1 released in 2012, the performance of 363 segmental bridges is compared to that of 373,670 bridges built within the same period. The results were favorable, as discussed in this summary. The study began by pulling the National Bridge Inventory (NBI) data from 2011, which included 604,426 bridge condition ratings throughout the United States. Since durability is a time-dependent function and segmental bridges first debuted in the early 1970s, the 2011 NBI data set was filtered to eliminate all bridges built prior to 1970. The new data set contained 373,670 bridges. To increase the accuracy of the segmental bridge data, the NBI data set was supplemented by inspection data received directly from participating states. Thus, condition ratings were provided for segmental more bridges up to 2 years beyond that reported within the filtered NBI data set. The modified NBI data set was then broken down into two bridge types as defined in the Federal Highways Administration’s publication Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation’s Bridges.2 Based on this breakdown, steel bridges built since 1970 were about 26% of all bridge types. Concrete bridge types make up 71% of the bridges built since 1970, with all other types making up the remaining 3%. Segmental bridges were then identified, separated from the data set for comparison, and supplemented and corrected with data from the ASBI master inventory list. The master list identified over 450 segmental bridges, of which 363 had condition ratings available within the 2011 NBI data set—which represents 0.11% of bridges in the data set (Fig. 1). With the 2011 NBI data set broken down, an analysis was run on the filtered 2011 data set to identify structurally deficient and functionally obsolete bridges across all bridge types. This revealed that 24% of all bridges in the set were classified as structurally deficient or functionally obsolete, with 11% of bridges in the data set classified as structurally deficient and 13% classified as functionally obsolete. The next task was to identify the percentage of each bridge type represented in the overall 11% structurally deficient number. Steel bridges accounted for 43% of the structurally deficient bridges while, within this same data set, concrete structures (71% of the total bridges built) accounted for only 39% of the deficient bridges (Fig. 2). Timber bridges, while representing only 2.8% of the total bridges built, represent 17.5% of the structurally deficient bridges.