# Shear Lag Effect of Ultra-Wide Box Girder under Influence of Shear Deformation
## 4 Experimental and Case Studies  
To validate the displacement function for the flexural strength of the box girders under the influence of the shear deformation in each plate, the results of the theoretical method used in this study were compared with finite-element calculations and experimental measurements for the physical model of an organic-glass, single-box, three-chamber, simply supported box girder [32].  
Figure 6 presents the structural dimensions, measurement-point arrangement, and loading effects of the aforementioned Plexiglas simply supported box girder test model [32]. The box girder test model had a span of \(L=1000\) mm. Its elastic modulus and Poisson's ratio, which were measured from a test stretch, were \(E=2600\) MPa and \(\
u=0.385\), respectively. The boundary condition was simulated by supporting steel columns of the same gauge underneath the bottom plates corresponding to all the web ends of the girder. Loads were applied on top of all the webs of the \(L/2\) span section of the single-box, three-compartment, simply supported box girder using a loading system. A computer-controlled voltage jack with a load value of \(P/4=0.4\) kN was used for the centralized force. Photographs of the loading system are shown in Figure 7.  
The MIDAS/FEA NX 2021 spatial finite-element software was used to build a solid simulation model of a single-box, three-chamber, simply supported box girder. The cross-section of the finite-element model was a single-box, three-chamber box section. The dimensions and arrangement of the measurement points are shown in Figure 8 and the space finite- element model are shown in Figure 9. Model tests used 120 resistance strain  
Figure 6: Schematic of the structural dimensions, measurement points, and loads of the model (unit. mm).  
gauges to measure the longitudinal strain of the box girder under load. A total of 24, 15, and 9 strain gauges were, respectively, arranged on the cross-section, top plate, and bottom plate, and they were affixed to the surface of the box girder using structural adhesive. The measurement points of the finite-element model and locations of the measurement points of the experimental model had a correspondence; the span of the model was \(L=30000\) mm, and the material was C30 concrete with a Young's modulus of \(E=3.0\times 10^{4}\) MPa and Poisson's ratio of \(\
u=0.2\). In the finite-element model of the three-chamber box girder, three  
the finite-element calculation results and the measured values of the model test reported in [32].  
As shown in Tables 1 and 2, the theoretically derived flexural displacement function of the thin-walled box girder subjected to bending under the influence of the shear deformation of each plate in this study agreed sufficiently with the measured values of the test and the finite-element numerical simulation values. Most key points of the shear lag coefficient had a relative error of \(<\)10.00%. There are several reasons for the occurrence of result discrepancies: firstly, differences in the material properties between the experimental model and the material used in the finite-element numerical simulation; secondly, inherent errors in the experimental setup; thirdly, differences in boundary constraints between the cantilevered plate and the top plate in the model.