Institute for Transportation

The National Bridge Inspection Standards requires
bridges be inspected biannually and when conditions
warrant that a load rating must be conducted. There are
more than 575 thousand bridges in existence today. As
these structures age, load rating should be conducted
when a significant change in condition occurs. Load
ratings are time consuming and costly. With ever
decreasing maintenance budgets, an economical and
versatile load rating worksheet or a computer program
would be of benefit to many local, state and federal
agencies. With the broad availability of computers, this
process can be accomplished quickly and accurately with
computer spreadsheets or programs. This paper will
discuss two different computer programs developed to
load a rate single span, one lane, glulam beam bridges for
a standard AASHTO HS20 vehicle.
The two methods developed, used a Mathcadå¨ 6+
worksheet and a QuickBASIC program to calculate load
ratings for a Glulam Beam bridge. Mathcadå¨ 6+ is a
powerful mathematical tool that allows equations to be
written in both real math notation and in a worksheet.
Two additional functions were developed for calculating
moments and shears using a Dynamic Linked Library
(DLL) in Mathcadå¨ 6+. QuickBASIC is a computer
language that is widely used and is easy to learn.
The single span, one lane bridge type was used because
it is standard type structures for the U.S.D.A. Forest
Service and many local municipalities. Alterations may
be made with ease for load rating other bridge types and
multiple lane structures. Load rating bridges using a
Mathcadå¨ 6+ worksheet and a QuickBASIC program
turned out to be a very economical and viable solution
for this bridge type.