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/768999
AASHTO LRFD The AASHTO LRFD Bridge Design Specifications: Section 5 Reorganization by R. Kent Montgomery, FIGG, Dr. Shri Bhide, Bentley Systems Inc., and Gregg Freeby, Texas Department of Transportation The first edition of the American Association of State Highway and Transportation Officials’ AASHTO LRFD Bridge Design Specifications was published in 1994. Since that time, the AASHTO LRFD specifications have been continuously updated with interim revisions. After nearly 25 years some users were expressing some frustrations about the concrete design section of the specifications, Section 5. Many engineers felt the organization of the section had become confusing and that there were inconsistencies among articles. Therefore, there was a need to reorganize Section 5 of the AASHTO LRFD specifications to provide better organization, clarity, and consistency among articles. Reorganization Process A pooled fund project to reorganize Section 5 was initiated by the AASHTO T-10, Concrete Design Technical Committee of the Subcommittee on Bridges and Structures (SCOBS). Oversight throughout the project was provided by the AASHTO T-10 committee and the Federal Highway Administration (FHWA). To obtain a broader perspective, the AASHTO T-10 committee invited industry liaisons, including the Precast/Prestressed Concrete Institute (PCI) and the American Segmental Bridge Institute (ASBI), to participate in the reorganization. Modjeski and Masters, along with Dr. Dennis Mertz, was selected as the contractor for the reorganization process, with Dr. John Kulicki and Dr. Dennis Mertz taking the lead roles in editing and tracking changes. The project began with a survey of stakeholders early in 2013. The results of this survey were remarkably consistent as to what improvements to Section 5 were needed and provided clear direction to the augmented reorganization committee. Past interim revisions were critically reviewed for accuracy, as well as to make sure no inconsistencies with other articles had been introduced into Section 5. At this point a revised table of contents (TOC) was developed by the reorganization committee. This TOC set the major reorganization of the section. A working draft of the reorganized articles was then developed as the starting point for determining what further changes, clarifications, and updates were needed. It was determined that the reorganization should be an evolution of Section 5 to make it easier to understand and utilize. It was not to be a revolution of new concepts and procedures, unless especially needed. Major decisions included: • Keeping the units of kips and inches • Advancing the concept of beam and disturbed design regions (B-Regions and D-Regions) and promoting the use of the strut-and-tie model (STM) for the analysis of disturbed regions • Keeping the current bending and axial design articles for B-Regions • Reducing the number of shear design procedures • Consolidating prestressed reinforcement details, non-prestressed reinforcement details, and seismic details into three separate articles • Having topics and procedures appear only once in the section • Organizing Section 5 such that more common design provisions appear before more unique design provisions During the project, the reorganization committee determined that two major changes were especially needed. These changes were a significant reformulation of the STM provisions and the addition of an article on anchors. The reformulation of the STM provisions was deemed of such importance that the changes were developed ahead of the reorganization and were included in the 2016 Interim Revisions. During the course of the reorganization, there were five working meetings of the reorganization committee and seven draft documents. Over 1000 comments on the drafts were addressed and incorporated. In late 2015, the reorganization committee had a completed draft that satisfied the original goals. This draft was made available to AASHTO members for review and comment through the typical SCOBS process. Additionally, a webinar was held to help inform the AASHTO members about the reorganized Section 5. The webinar was taped and is available for those interested in viewing this resource. A final version of Section 5 was balloted at the 2016 annual SCOBS meeting and unanimously passed. The reorganized Section 5 will be included in the Eighth Edition of the AASHTO LRFD Bridge Design Specifications available in 2017. Reorganized Section 5 — The Big Picture Articles 5.1 through 5.5 are largely unchanged except for the introduction of B-Regions and D-Regions in Article 5.1 and articles defining these regions in Article 5.5. Old Article 5.6 received a lot of comments from the survey and contained somewhat miscellaneous information, including provisions for imposed deformations and the STM method. These provisions have been moved to more appropriate articles in Section 5. Articles 5.6 and 5.7 now cover the sectional (B-Region) design provisions for flexure and axial loads, and shear and torsion, respectively. The shear design section has been condensed. This article now covers general shear and torsion requirements, such as minimum reinforcement and bar spacing, one shear design procedure (modified compression field theory [MCFT]), and shear friction provisions. The outdated prestressed concrete beam shear design