Abstract
This project presents the analysis results from the parametric study done by Caltrans in 2014 in which Caltrans studied the difference between the results that come from 2D (Spine) model versus the 3D (shell) model for a single span box girder bridge. Caltrans is currently using the 2D (spine) model for design purposes. However; it is not cleared if spine model fully captures all responses or not and when it is necessary to perform 3D (Shell) model analysis. The case study done in 2014 was limited to few scenarios and because of that, there was no conclusion drawn and the topic was pending. In this project, cases are expanded and 180 cases of 2D and 180 cases of 3D were analyzed in order to make a sound conclusion. This report will present several configurations of box girder bridges using 3D and 2D models and each configuration will have different curvatures (L/R=0, 0.2, 04, 0.6, 0.8). L/R=0 is straight, 0.2 corresponds to central angle of 12° (limit of straight model used for curved), 0.6 corresponds to central angle of 34° (limit of spine model being used). ‘L’ is the length of span and ‘R’ is the curve radius. In the current code, it is been briefly mentioned that for L/R=0.6 or greater, spine model analysis is insufficient and this claimer is being studied more in details in the scope of this report. Furthermore since there was no evidence in the code of how to analyze the L/R=0.8 and to find out whether the 2D model is sufficient enough or not, this case is also being considered. The case studies are as follow: Simple-spans of 100’ and 140’ span lengths and 2 cell and 4 cell cross sections and each section use different girder spacing of 6’, 8’ and 11’ with various L/R (0, 0.2, 0.4, 0.6, and 0.8). Two-span bridge of 100’ and 100’ span lengths with similar cross section as the simple span are analyzed. 2-cell cross sections have a single column with 4’ diameter and 4-cell cross sections have two columns and each configuration has different column heights of 25’ and 50’ and L/R (0, 0.2, 0.4, 0.6, and 0.8). There-span bridge of 100’, 125’, 100’ span lengths with similar cross sections as the simple-span will be analyzed. 2-cell cross sections have a single column with 4.5’ diameter and 4-cell cross sections will have two columns and each configuration will have different column heights of 25’ and 50’ with various L/R (0, 0.2, 0.4, 0.6, and 0.8). Load cases include dead load (self-weight) of the structure, pre-stress (post-tension), design live load (HL-93) and permit live load (CA-P15). Response values are gathered at 10th point of spans and these include section moment, girder shear and girder normal stresses. The 2D (spine) and 3D (shell) models will be compared as well as the effect of curvature on the 3D results that come directly from plate and shell models (CSI-Bridge).