## 4 Calculation Results of the Phased Construction Process
### Analysis of the Bridge Completion Stage  
This stage is the bridge completion stage of the main beam and the secondary loads have been included. By analyzing the bending moment of the steel girder, it can be found that the negative bending moment of the steel girder in sections d4 and d5 has been significantly improved.  
Figure 9: CS2 bridge floor and V-shaped pier stress: (**a**) bridge floor stress; (**b**) stress on the upper flange of the V-leg; (**c**) lower flange stress of the leg. (Instructions: in the picture, e + 000 means 10,000, e + 001 means 10,001, and so on).  
The stress curve of the upper flange of the steel girder is no longer as continuous as that of CS1 and CS2 and a sudden increase in stress occurs in each negative bending moment section. The reason is that the construction of the negative moment section has been completed and the medium weight of the span has been unloaded. However, due to the restraint of the studs by concrete, the elastic deformation of the flange plate on the steel beam is difficult to recover and the tensile stress level in the steel beam is maintained to a certain extent. By analyzing the stress curve of the lower flange of the steel beam, it is found that the linear characteristics of the curves have not changed and there is no sudden change in the stress curves. This shows that the method of gravity has little effect on the stress characteristics of the lower flange of the main girder. At this time, the maximum tensile stress and compressive stress of steel girder under dead load are 110.0 MPa and 95.1 MPa, respectively. The stress of the steel girder during the completion stage is shown in Figure 10.  
When the bridge is completed, the upper edge of the concrete deck in the negative moment area of P1 and P2 piers' top is in the compression state, as shown in Figure 11. The upper edge of the concrete bridge deck in the negative bending moment area of the pier top of the P3 and P4 V-shaped pier has certain tensile stress, up to 0.52 MPa. The main girder span has little difference and, according to the construction plan, the weight of different spans has been adjusted accordingly. The pressure of the large span is slightly heavier than that of the small span. It can be seen by calculation that the pier crest of a vertical pier is obviously better than that of V-shaped piers by the weight method.  
The V-shaped pier control section is still close to the V-shaped pier bottom plate on the side span side and the maximum compressive stress at this stage is 46.5 MPa. At this time, the stress of the V-shaped pier continues to maintain obvious asymmetry. In the finished state, the stress level at the root of the V-shaped pier caused by the self-weight of the structure is not significant compared with the strength of the materials used.  
The FEM model can accurately simulate the process of phased construction of the bridge and the change in section stiffness during the construction. In the finished state, the bridge is always in the stage of elastic change and the concrete is only subjected to very small tensile stress at the top of the V-shaped pier. Because the influence of reinforcement in concrete on the stiffness of the concrete slab is not taken into account, the actual calculated tensile stress is still too large.  
Figure 10: Stresses of the steel main girder in the bridge completion stage (MPa).