Project 2a: Reliability-based Evaluation of Bridge Components for Consistent Safety Margins - MS&T

Status

Sequential Number

Identification Number

Matching Research Agency

Missouri Department of Transportation (MoDOT) and Missouri University of Science & Technology (Missouri S&T)

Principal Investigator

Student Involvement

Project Objective

The objective of this project is to calibrate load and resistance factors in LRFD to achieve a more uniform level of safety (reliability) in bridge design. The calibration of the load and resistance factors, specifically considering Missouri environment, will lead to a reduction in the up-front cost of bridges. Load factors will be calibrated to achieve two goals: 1) the bridge components should have consistent safety margin, and 2) the bridge components designed with LRFD should be compatible with components designed with LFD which have performed well for the past years.

Project Abstract

The objective of this project is to calibrate load and resistance factors in LRFD Design Guidelines, (LRFD hereafter) under Service Limit State. The project will be carried out with three main tasks. Task 1 of the project will include identification of service load in Missouri, identification of Service Limit State of existing bridges designed with Load Factor Design, (LFD hereafter), and associated cost to maintain the bridge performance. Extensive data for the past twenty to thirty years will be collected including daily traffic, bridge maintenance records, and relevant costs. The collected data will be organized in efficient and extensible database which can be used in Task 2 and 3 as well as for a future study. Service Limit State will be determined based on the performance of bridges in the past years. In the Task 2 of the project, reliability of bridge components designed with LRFD will be analytically evaluated. The focus of the reliability analysis will be on Service Limit State. Load models and Service Limit States from Task 1 will be used in reliability analysis. Load factors will be calibrated with two main objectives: 1) the bridge components should have consistent safety margin, and 2) the bridge components designed with LRFD should be compatible with components designed with LFD which have performed well for the past years. In the Task 3 of the project, based on the results from Task 2, revised load factors for LRFD Guidelines will be suggested. In addition, necessary changes in the current MoDOT Standard Plans for Highway Construction will be identified and made in consultation with MoDOT bridge engineers. The revised Standard Plans will guide private consultants and MoDOT engineers for new bridge designs that are consistent with the LRFD Bridge Design Manual. The calibrated load and resistance factors are expected to save overall cost in bridge construction and maintenance. The outcome of this project will provide sound background on load factors for Service Limit State, which has been determined primarily based on engineering judgment.

Task Description

N/A

Anticipated Benefits

The outcomes of this project are a reduction in the up-front cost of bridges and a sound rationale on load factors and resistance factors for service limit state, which has been determined primarily based on engineering judgment.

Milestones

Relationship to other Research/Projects

Structures faculty in University of Missouri System and MoDOT engineers identified research needs in two theme areas: Extending service life of MoDOT’s existing bridges and Optimizing MoDOT’s bridge design and construction for effective cost reduction. The proposed project is one of the four projects in the second theme area. The four projects collectively will contribute to optimize design of new bridges in Missouri.

Technology Transfer Activities

The outcome of the research will be published in journal papers and will be presented in annual TRB meetings.

Transportation Research Board Keywords

LRFD calibration, LRFD bridge design, service limit state, highway bridge