In the state of Illinois on April 15, 2016 Circular Letter 2016-10 was sent to all agencies concerning Load Ratings for bridges. New truck configurations are being allowed, causing there to be more load per axle. This letter stated that new load ratings are to be assigned for ALL bridges. Engineering judgement is no long an acceptable form of bridge rating, and new ratings are to be assigned based on actual calculations.
To help identify the structures that need in-depth analysis, a checklist has been established for all structures. In response to changes in the AASHTO Manual for Bridge Evaluation (MBE), a September 29, 2011 FHWA memo allowed assigned load ratings so long as the following conditions are met. The checklist is due for all identified structures by December 31, 2016. IDOT has set up an Inspection Date Notification System in which the following checklist may be answered.
1. The bridge was designed and checked using either the AASHTO Load and Resistance Factor Design (LRFD) or Load Factor Design (LFD) methods to at least HL-93 or HS-20 live loads, respectively; and
2. The bridge was built in accordance with the design plans; and
3. No changes to the loading conditions or the structure condition have occurred that could reduce the inventory rating below the design load level; and
4. An evaluation has been completed and documented, determining that the force effects from State legal loads or permit loads do not exceed those from the design load; and
5. The checked design calculations, and relevant computer input and output information, must be accessible and referenced or included in the individual bridge records.
Question Number 4 was done by IDOT and results complete on October 5, 2016. Our county alone has almost 200 structures that need the checklist submitted. If all 5 conditions cannot be met, bridge plans MUST be electronically submitted to IDOT. Item 5 is very difficult for our agency in general to locate because most of our bridges were built using IDOT’s standard bridge plans which have since been retired, or by using consultants. Access to calculations which may be 40-50 years old in some cases just isn’t feasible. That leaves the only option of submitting bridge plans. The main issue will be FINDING the existing bridge plans. This could potentially be a logistical nightmare. Some of the older plans were large-format (24″x36″), and access to a copier/scanner that large may not be an option for some agencies. And some agencies plain and simple may not have bridge plans for older structures. There will be THOUSANDS of sets of bridge plans that will be submitted. I cannot imagine who will be responsible for sifting through all of these, not to mention the space it will take to electronically store them.
There are approximately 26,000 bridges in Illinois. Lets guess that half of them have the information available. That leaves 13,000 bridges that must have plans submitted. The bulk of that will be up to local agencies that may not have the personnel or equipment to make copies of everything. My point of view is this: Isn’t every set of bridge plans submitted to IDOT? Why don’t they already have copies?
I have sent a couple of e-mails to the IDOT Bureau of Bridges and Structures with questions about this last item. So far no one has returned my message, but when I find something out for certain, I will update this post.
The IDOT Bureau of Bridges and Structures has responded to my email. They say if plans identify the loads as HS-20 or HL-93 and have the stamp of a Licensed Structural Engineer (Licensed Professional Engineer before 1989), then conditions One and Five are met. If Standard Plans were used, they are considered signed by a Structural Engineer.