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/297024
6 | ASPIRE , Spring 2012 R E A D E R R E S P O N S E Editor, I ' m a re g u l a r re a d e r o f ASPIRE ™ magazine and the AASHTO LRFD feature. I'm fascinated by Dr. Me rtz' thorough knowledge and explanations of subjects pertaining to the code. I would like to ask a question in regard to applicability of creep and shrinkage forces to be used in the design of integral columns in multi-span, continuous concrete bridge structures. What is the best methodology to calculate the effects of cree p and shrinkage for substructure design? The AASHTO LRFD Bridge Design Specifications includes CR and SH as part of all service and strength limit states (Table 3.4.1-1), but no guideline is provided on how to quantify these forces for design of columns and other substructure elements. The concrete columns that are integrally connected to the superstructure will deform due to the cree p and shrinkage of the superstructure. The LRFD Specifications does not address how to determine the column moments and shears resulting from creep and shrinkage. Can you please answe r this question in your AASHTO LRFD page? Please feel free to email me if you have any questions. Name and company withheld San Francisco, Calif. [Editor's Note] We completely agree that Dr. Mer tz' knowledge of and ability to explain provisions of the LRFD Specifications is invigorating. We continue to receive similar compliments about his articles and we appreciate his time and skills in contributing to ASPIRE. He carefully considered this reader's question and has responded in his column on page 56. Editor, Love the magazine! One suggestion: In some of the articles (e.g., "Texas' Longest Beams," page 29, Winter 2012), it's not clear exactly where the project is located because no mention is made of nearby cities. How about a small map for such articles? Kathleen Bergeron Federal Highway Administration Washington, D.C. [Editor's Note] We like this suggestion and apologize to readers who may have been left wondering about the location of this or other such projects. In the future, we will more carefully describe locations or provide a locator map! Editor, Our company was the general contractor for the Mayor Mike Peters Bridge featured in your Winter 2012 issue (pages 18-20). Would it be possible to have some additional copies of the magazine sent to us? We'd like a few copies for us and will send some to a few of our subcontractors. Brendan Parker Loureiro Contractors Inc. Plainville, Conn. [Editor's Note] Happy to send them, Brendan. Nice project in a tough location. The results speak for themselves. Editor, On behalf of myself and my co-authors, we would like to thank you and the dedicated team at ASPIRE for your very nice job with the Presidio Viaduct article (pages 30-33). The article really looks good with the combination of photos, rendering, and diagrams. Great job. Ahmed M. M. Ibrahim California Department of Transportation Sacramento, Calif. Editor, I m u s t c o m p l i m e n t y o u o n y o u r productions. I read almost every article and find them to be well written and informative. I am happy that you were able to put together this very useful magazine for the industry. A. Joseph Siccardi FIGG Bridge Engineers Denver, Colo. Editor, I am a long time reader of the ASPIRE magazine and find it contains a lot of interesting and practical information. Hong Guan CH2M HILL Bellevue, Wash. Editor, I receive and enjoy ASPIRE. It is the highlight of my "work" magazines. Andrew Howe OBEC Consulting Engineers Salem, Ore. Editor, ASPIRE is a high quality publication… Kent Barnes Montana Department of Transportation Helena, Mont. Editor, I read with interest the ASPIRE article on the Route 22 Bridge over the Kentucky River near Gratz, Kentucky (Winter 2011 issue, pages 24-27). The measures taken to design and build the structure were interesting. I was e ven more intrigued when I was asked about the design and construction requirements for a precast, spliced post- tensioned girder for a 500 ft. span. I returned to the article on the Route 22 Bridge and read it again considering the possibilities. I was hoping that you may have provided some of the design parameters or dimensions of the girder. I looked at your website to see if other girder dimensions or description of construction equipment might be contained the re some whe re, but found no furthe r information. While I am skeptical, I will at least look into the Route 22 Bridge and consider if the 500 ft. span is possible or if it is simply impractical. If you have any of that information or can point me in the right direction I would be grateful. That was a very interesting article. Keep up the good work! Bruce Kates Jacobs Engineering Group Inc. St. Louis, Mo. [Editor's Note] We t r y t o i n c l u d e a s m u c h t e c h n i c a l information in the articles as we can while staying within the space available and telling the story about the bridge. You may be able to obtain more information about the Route 22 Bridge by contacting the author. NCHRP Report 517— Extending Span Ranges of Precast Prestressed Concrete Girders is available to download at www.trb.org/NCHRP/NCHRP.aspx and click on Project Reports under PUBLICATIONS on the left side. Book_Spr12.indb 6 4/3/12 9:17 AM