The Hoan Bridge Failure

In The Hoan Bridge Failure, you'll learn ...

• Information about the Hoan Bridge’s construction history and failure
• Details about the design of the tied-arch span and approach spans
• Specifics on the joint connecting the lower lateral bracing to the web plate of the girder
• Overview of material failure criteria including von Mises, Tresca, and maximum normal stress

Overview

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Credit: 3 PDH

Length: 44 pages

On the very cold, early morning of December 13, 2000, a section of a northbound approach span of the Hoan Bridge began to buckle and crack as motorists were driving over the structure. One of those motorists called 9-1-1 to report the problem to the Milwaukee County Sheriff’s Office. A sheriff’s deputy was dispatched to the scene and confirmed that the deck was sagging approximately three to five feet. The Hoan Bridge was immediately closed in both directions after 26 years of service. The County Sherriff’s Office contacted a bridge inspector. He responded immediately and verified that two of the three girders in the failed span had full depth fractures, leaving the span near collapse. The entire Bridge was inspected for similar problems.

The failed northbound span was removed on December 28, 2000, by demolition to prevent potential damage to the remainder of the Bridge and buildings below. The southbound span was found capable of handling traffic with a short-term retrofit. The southbound span was reopened to traffic on February 17, 2001 to traffic in both directions but with weight and speed restrictions. On the other hand, a failure investigation was initiated for the northbound span to determine the cause of failure and develop a permanent retrofit solution for the Bridge. Ultimately, the demolished northbound approach span was replaced, a retrofit design was implemented for the joint, and the Bridge reopened on November 1, 2001.

This course begins with an overview of the unique construction history of the Daniel Webster Hoan Memorial Bridge. We then discuss the Hoan Bridge’s tied-arch span design and approach span design. We include the joint design that connected the lower lateral bracing to the web plates of the girders in this discussion. Subsequently, we discuss events surrounding the failure of the Bridge.

Next, we discuss in detail the failure investigation. In this section, we first provide an overview of the prior inspections that focused on fatigue cracks in some girders. Then we consider the specifics of the material property testing, fractographic examination, global structural finite-element models, and load analyses. We examine potential problems for the joint design that was identified as the primary cause of failure due to constrained triaxial stresses. Finally, we discuss the actions taken to retrofit the Hoan Bridge and long-term implications of the Bridge’s failure on other bridges with similar joints and on code changes.

Specific Knowledge or Skill Obtained

This course teaches the following specific knowledge and skills:

• Standards requirements for the A-36 and A-588 steels
• Specific about the failure investigation including material property testing, fractographic examination, loads analysis, and finite-element models of the global structure and joint
• Effect of cold temperature and loading rate on impact toughness and brittle fracture propagation
• Differences between bridge loading rates and dynamic loading rates
• Details about the Hoan Bridge’s retrofit design
• Information about the influence of the Hoan Bridge’s failure on other bridges with similar joints and on code changes for bridges with similar joints

Certificate of Completion

You will be able to immediately print a certificate of completion after passing a multiple-choice quiz consisting of 15 questions. PDH credits are not awarded until the course is completed and quiz is passed.