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/306864
56 | ASPIRE , Summer 2010 A A S H T O L R F D Agenda Item 14 deals with crack-control reinforcement for the strut-and-tie model of Article 184.108.40.206. This reinforcement controls crack widths and ensures ductility so that the development of straight concrete struts is possible. While the ratio of reinforcement area to concrete area is still taken as not less than 0.003 in each direction, the first sub-item provides equations that clarify the zones over which the reinforcement is required. Many designers consider this amount of steel to be extreme. Recent research suggests that 0.003 is appropriate but this revision may reduce the required reinforcement through more precise specification of the application of the provisions. The second sub-item includes a modification to the commentary and adds a figure illustrating the distribution of crack-control reinforcement in a concrete strut. Agenda Item 15 modifies Article 220.127.116.11.2 and includes four sub-items. The first sub-item clarifies the definition of ε s in the notation for use in Article 18.104.22.168.2. Previously, the definition stated that the strain was in the nonprestressed tensile reinforcement when the strain should be a function of both the nonprestressed and the prestressed tensile reinforcement present in the section. The second sub-item clarifies this definition in the article itself. Previously, Article 22.214.171.124.2 required the designer to ignore nonprestressed reinforcement t e r m i n a t e d a t a d i s t a n c e l e s s t h a n t h e development length from the section under consideration, while elsewhere in the article the designer is allowed to logically use the nonprestressed reinforcement in proportion to its development. Sub-item 3 of Agenda Item 15 eliminated this contradiction. Finally, sub-item 3 and sub-item 4, added absolute-value signs to two comparisons of M u to (V u - V p )d v , so that the proper comparison is made. 2010 interim revisions related to Concrete structures Part 2 by Dr. Dennis R. Mertz, professor of civil engineering, University of Delaware t he 5th Edition of the AASHTO LrFD Bridge Design Specifications was published recently. This new edition includes five interim revisions related to concrete structures that the American Association of State Highway and Transportation Officials (AASHTO) Subcommittee on Bridges and Structures (SCOBS) considered and adopted at their annual meeting in New Orleans, La., in July of 2009. Technical Committee T-10, Concrete Design, developed Agenda Items 9, 10, 12, 14, and 15 over the past several years and moved them to the subcommittee ballot for consideration in New Orleans. Agenda Items 9, 10, and 12 were reviewed and discussed in the previous issue of ASPIrE™. The final two items are described in this article. ASP10-1625.indb 56 6/21/10 12:20 PM