Load-Induced Fatigue Category of Hand Holes and Manholes

Current steel bridge design and evaluation practices assume that large inspection access holes, such as manholes and hand holes, are presently classified as category D details. While category D is adequate for the fatigue evaluation of small open holes, such as an empty bolt holes, this has been shown to be overly conservative when the dimensions of the hole are larger. Specifically, the stress concentration of a hole decreases as the size of the hole relative to the size of the plate increases. In order to verify whether the reduction in stress concentration is significant enough to grant an improvement in the fatigue category, a parametric study using finite element analysis was conducted. The results of the parametric study revealed that larger holes may be reclassified as category C fatigue-prone details when certain geometrical features are met. To assist the implementation of the research findings, the current report also includes recommended modifications to the AASHTO LRFD Bridge Design Specification

Member-Level Redundancy of Built-Up Steel Girders Subjected to Flexure

The purpose of this research was to describe the behavior of mechanically fastened built-up girders in a partially failed condition. This was achieved by testing large-scale riveted and high-strength bolted built-up specimens to determine their fracture resilience at low temperatures and their fatigue capacity after a single component was failed. Additionally, a finite element parametric study was performed to understand the behavior of built-up girders and to better describe the load distribution that occurs locally in the region adjacent to a failed component

Experimental and Analytical Evaluation of the Strength of Selected Truss Members from the Approach Spans of the Winona Bridge

The following report details a research project comprised of two phases. Phase I included the full-scale experimental testing of two built-up truss chord members removed from service. The members were installed into a reaction frame and loaded to failure to determine remaining capacity in the presence of pack rust, as well as after-failure load redistribution behavior mimicking the member in a state following complete fracture of half the cross section. Phase I also included a finite element–based parametric study calibrated by the experimental work. The study was focused on two-channel axially loaded members for the purpose of developing closed-form solutions intended for evaluation of internal member redundancy. During Phase II of the project, a small round-robin-style inspection and load rating study was performed with certified bridge inspectors and practicing load rating engineers. The purpose was to investigate the variability in the inspection and evaluation of severely corroded steel tension members. This process evaluated two separate, but related, sources of variability within the inspection and load rating process. The variability in each task was controlled such that variability in the load ratings was not compounded by variability in the inspection findings

Member-Level Redundancy of Built-Up Steel Axially Loaded Members

Full-scale fracture tests were completed determining that mechanically-fastened steel built-up axially-loaded tension members are resistant to running fracture when a single component suddenly fractures. This characteristic of built-up member is referred to as Cross-Boundary Fracture Resistance (CBFR). A comprehensive finite element model-based parametric study was also performed investigating the post-fracture load redistribution behavior of multi-component built-up members. Simplified closed-form solutions were developed for engineering analysis of built-up members to evaluate for internal member redundancy and estimate safe inspection intervals that are based on the fatigue life of the member in the assumed faulted condition

A Simplified Approach for Designing SRMs in Composite Continuous Twin-Tub Girder Bridges

High torsional rigidity and attractive aesthetics in construction of twin-tub girder bridges make them preferable for the design of curved bridges. However, according to the concepts associated with the term “Fracture Critical (FC)” that are in place today, all two-girder bridges are classified as having FC members (FCMs) due to their perceived lack of load path redundancy. For a steel bridge with FCMs, the fracture of any of the FCMs is assumed to result in complete catastrophic failure or significant loss of serviceability; hence, every two years twin-tub girder bridges undergo very expensive hands-on field inspections. This report presents a simplified approach to ensure newly designed twin-tub girder bridges will meet all the requirements defined in the 2018 AASHTO Guide Specifications without performing in-depth FEA. AASHTO-ready proposed specifications are included in Appendix A. It is anticipated that these provisions could be incorporated into the AASHTO LRFD BDS as a new article 6.6.3 Special Provisions for Twin Tub Girder Bridges