Comparative Study of LRFR and LFR Methods of Rating for Missouri Steel Bridges
Metadata[+] Show full item record
Bridge load rating is a method used to check on the ability of bridges to carry a given live load. Bridge rating is important to ensuring public safety in that it helps the concerned agencies to enforce weight restriction on heavy vehicles to safeguard the structures from failure. Before the bridge is rated, the current condition of the bridge needs to be known and this is done through routine inspections specified by the concerned agencies depending on the type of inspection required. The knowledge of the current conditions of the bridge ensures that rating is done accurately and reflects the current structural ability and performance of the bridge, and this guides the public on the weight restrictions, which can be done by erecting signages visible to the road users. Since the inception of the idea of bridge rating, several methodologies have been employed and these methods have changed as the knowledge base and technologies have advanced along with the new software developed and new research done to improve the rating methods and procedures. The research herein explores the two methodologies of bridge ratings that exist and are in use today by all the Departments of Transportation (DOT) in the United States of America, namely the Load Factor Rating (LFR) and The Load and Resistance Factor Rating (LRFR). LRFR methodology is based on LRFD bridge design specifications (AASHTO, 2017) while LFR rating is based on the LFD specifications (American Association of State Highway and Transportation Officials, 2002). Some DOTs require that new bridges be rated for these two methods while others will only require one method. Another methodology used is the Allowable Stress Rating (ASR) which is primarily used for timber-based bridges. Missouri Department of Transportation (MoDOT) has been using LFR methodology of rating to determine the load posting of bridges. Procedures and policies for this process are specified in MoDOT’s Bridge Inspection Rating Manual (MoDOT, 2022). The primary goal of this research project is to help in establishing new LRFR posting methodology which should have a similarity with the current LFR methodology used in Missouri. The findings of this study established that for the new methodology of LRFR, there was an increase in the number of bridges to be posted by 22% for H20L,14.3% for CZSU, 30.5% for MO 3S2 and 23.8% for CZRT, furthermore a minimum posting factor of 0.91 and enveloping posting values for H20L, MO 3S2, CZRT and CZSU were established for the current vehicle models being used in the State of Missouri.
Table of Contents
Introduction -- Background -- Results for steel bridges -- Conclusions and recommendations
M.S. (Master of Science)