Evaluating the role of cross-frames in stress distribution of steel I-girder bridges by "holistic" assessment of finite element analysis data
Date
2017
Authors
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Publisher
University of Delaware
Abstract
Cross-frames are bridge structural members that provide lateral-load resistance and stability during construction, reduce buckling length of the compression flanges of steel girders, and to contribute to distribution of traffic loads among girders at in-service bridges. It is hypothesized that cross-frames, play positive role in load distribution among the girders, and by extension contribute in increasing bridge system capacity. Furthermore, understanding the mechanisms behind the load sharing among bridge components at design and inelastic load levels could help with better understanding system-level behavior of bridges, In the light of the nationwide high inventory of structurally deficient bridges, the application of system-level analysis would allow for better identification and prioritization of the most critical structures and allow for a more efficient use of the limited financial resources available for infrastructure investments. Therefore, to goal of this study was to investigate the role that cross-frame play in bridge stress distribution at in-service bridge. Prior research showed that for highway steel I-girder bridges, bridge skew, cross-frame type, and cross-frame placement can significantly affect bridge response in terms of stress distribution. Cross-fame designs (K-frame vs. X-frame), cross-frame layouts (inline vs. staggered) and bridge five skews (0°, 25°, 46°, 55° and 63°) were selected as parameters of interest. Additionally, FE models without the cross-frames (No-frame models) were added to each bridge skew. Combining all parameters of interest total of 25 bridge FE modes were built and analyzed. ☐ Stress distributions of main bridge components (girders, deck and cross-frames were extracted) from the models and evaluated using “holistic” level approach. The “holistic” level approach refers to comprehensive assessment of all FEA stress distribution data, not only peak values. The results showed that by using “holistic” evaluation of stress distribution data, we were able to identify and quantify best performing cross-frame configuration. However, results also indicate that removing cross-frames from bridges did not substantially affected stress distributions throughout the bridge. This finding was further strengthen by Tensor decomposition analysis of stress distribution data. This method found that removing cross-frames from the bridge models did not affect substantially stress distributions at design load levels. Although, removing cross-frames from the bridge models did affect stress distribution at first yield and system yield load level, it did not affect overall system capacity of the bridge.