# Retrofit Fatigue Cracked Diaphrag Cutouts Using Improved Geometry in Orthotropic Steel Decks
## 5 Results and Discussion  
### Stress Distribution Along the Edge of Diaphragm Cutouts  
The test results of two typical longitudinal loading cases, at locations L3 and L10 in Figure 14b, are presented and analyzed to verify the effects of geometry optimization of cutouts and summarize the stress distributions along the edges of diaphragm cutouts. In the load case L3, the central axis and the rear axis were located on either side of the test diaphragm at equal spacing (0.75 m). The out-of-plane moment of the diaphragm is equal to zero, and the in-plane forces within the diaphragm are transmitted mainly from the U-ribs as shear forces. The maximum stress was recorded in zone A around the diaphragm cutout for this load case, and its stress distribution is shown in Figure 16. In the load case L10, the center of the rear axle is 1.5 m away from the diaphragm and is located midway between the two diaphragm plates. From the test and FEA results, it can be found that:  
Figure 15: Strain gauges arranged at the section of cutout (**a**) before rehabilitation; (**b**) after rehabilitation. Strain gauges arranged at the side of the diaphragm (**c**) before rehabilitation; (**d**) after rehabilitation. On-site strain gauge arrangement (**e**) before rehabilitation; (**f**) after rehabilitation.  
(1) The experimental data is in good agreement with the FEA results, in terms of the stress distributions. The experimental data from several stress gauges, such as those at locations 5 and 6, are less than the corresponding maximum stress in FEA, because the stress values obtained by strain gauges is the mean value over a strain gauge's length of 2 mm. The comparison indicates that large stress concentrations occur under vehicular loads leading to fatigue cracks around diaphragm cutouts.  
(2) The maximum principal stress measured in zone A, which is at cutouts C1 and C2, is -146.8 MPa for the load case L3, before the diaphragm cutout was retrofitted. The tested stress after retrofitting is -58.5 MPa, and the stress range is reduced by 59.9%. For the load case L10, the stress range decreases by 55.5%, as shown in Figure 16b, which indicates that the optimization of diaphragm cutouts can effectively reduce the stress range in zone A and hence improve fatigue life.  
(3) The maximum tensile stress measured in zone B at cutouts C1 and C2 is 96.2 MPa before the retrofitting of the diaphragm cutout for the load case L3. The tested stress after retrofitting is minus 42.7 MPa, and the stress range is reduced by 55.6%. For the load case L10, the stress amplitude decreases by 47.4%, indicating that the optimization of diaphragm cutouts can also effectively reduce the stress range in zone B and improve fatigue life.  
(4) The stress around cutout C3, which is 600 mm from cutout C1, is much smaller, because the influence of the wheel load in the transverse region is limited around the location of a U-rib. It is also observed that the stress reduction of zone A and zone B in cutout C3 is minus 35.2 MPa after retrofitting, which is about half the stress before retrofitting.  
(5) Except for the gauges located in zone A and zone B, the gauges at other locations along the edge of diaphragm cutouts were less affected by cutout retrofitting; since the vehicular load induced stress is small at these locations the potential fatigue damage may not take place.