## 2 Finite Element Modeling and Verification
### Verification of Finite Element Models  
#### 2.2.1 Laboratory Tests at the Turner-Fairbank Highway Research Center  
Phase one of the full-scale laboratory test was performed at the Turner-Fairbank Highway Research Center in McLean, Virginia (CSBRP project) [30]. This involved testing a horizontally curved composite slab-on-girder bridge subjected to construction and vehicle loads in order to verify the FE modeling. The bridge erected for this investigation was a 27.5 m simple-supported bridge with three steel concentric girders (G1, G2 and G3) spaced at intervals of 2.7 m. The ratio of curvature (k) to G2 was 0.45. A plan view and cross section of this bridge is shown in Figure 3. Tubular K-type cross frames with a diameter of 12.70 cm and a thickness of 0.635 cm were installed at different locations between the girders, as shown in Figure 1a. Full depth bearings were installed at multiple locations along the girders; the boundary conditions for the spherical bearings at the abutments are also shown in Figure 1. Load was applied to approximately the third point of each girder for the bending component test and this placed the load on G3 outside of the splices shown in Figure 3. Load application was accomplished by jacking the girders away from a series of loading frames that were tied with DYWIDAG bars to the laboratory strong floor. The frames consisted of channel pairs placed back-to-back and connected orthogonally to one another so that they formed the boxes shown in Figure 3d. Another back-to-back channel pair bisected each box and was used as a spreader beam to apply the loads. DYWIDAG bars, which were attached to the ends of the spreader beams, were selected because they provide high tensile strengths with minimal flexural stiffness. The mid-span girder deflections, rotations and strain distribution across the flanges and through the webs were recorded using potentiometers and tilt meters.  
The entire bridge was modeled using CSIbridge software according to the previously described simulation technique in order to comprehensively verify the results of the FE modeling. Table 1 compares the girder vertical deflections and web rotations at the mid-span of the bridge obtained from the simulation and test when the bridge deforms elastically subject to its self-weight. The maximum discrepancy between the data recorded experimentally and the FE results is 8% for the vertical deflections at the mid-span and about 6% for the rotation of the girders.  
In order to evaluate the capacity of the FE modeling to predict girder responses, Figures 4 and 5 show the normal strain values at the flanges and web of girder G3 recorded during the laboratory tests and those obtained from the FE analysis. A maximum discrepancy of 6% was observed for both the web and flanges, confirming that the FE modeling technique can be used to analyze composite slab-on-girder bridges with adequate accuracy.  
Figure 2: Typical finite element (FE) model of a skewed composite I-girder bridge.  
Figure 4: Strain at flanges and web of G3 from Test and FE analyses: (**a**) flange width; (**b**) web height.  
Figure 3: Scaled bridge constructed for the laboratory tests at Turner–Fairbank Highway Research Center: (**a**) plan view; (**b**) cross-section; (**c**) location of instruments; (**d**) loading conditions.