Fatigue Categorization of Obliquely Oriented Welded Attachments

In current bridge design specifications and evaluation manuals from the American Association of State Highway and Transportation Officials (AASHTO LRFD) (AASHTO, 2018), the detail category for base metal at the toe of transverse stiffener-to-flange fillet welds and transverse stiffener-to-web fillet welds to the direction of the web and hence, the primary stress) is Category C′. In skewed bridges or various other applications, there is sometimes a need to place the stiffener or a connection plate at an angle that is not at 90 degrees to the web. As the plate is rotated away from being 90 degrees to the web, the effective “length” of the stiffener in the longitudinal direction increases. However, AASHTO is currently silent on how to address the possible effects on fatigue performance for other angles in between these two extremes. This report summarizes an FEA study that was conducted in order to investigate and determine the fatigue category for welded attachments that are placed at angles other than 0 or 90 degrees for various stiffener geometries and thicknesses. Recommendations on how to incorporate the results into the AASHTO LRFD Bridge Design Specifications are included in this report

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

Maintenance Actions to Address Fatigue Cracking in Steel Bridge Structures: Proposed Guidelines and Commentary

This document provides guidelines for the maintenance actions to address fatigue cracking and details at risk of constraint-induced fracture (CIF) in steel bridges. It is a synthesis of best practices from published literature, project reports, past and ongoing research projects, as well as input from industry professionals gathered through a web-based survey. Intended to be a very practical reference text, it is written with everyone in mind from a maintenance contractor to an asset manager and design engineer, providing detailed descriptions of the driving causes of fatigue cracking and CIF in steel bridges and accepted methods for repair or retrofit. A number of case studies are discussed giving context for the different detail susceptibilities and utilizing a mixture of real-world and rendered images to illustrate the problems and solutions. For each case, a suggested sequence of steps is also provided as a ‘‘how-to.’