## 5 Discussions and Suggestion  
Through the investigation in this research, the exact cause of abnormal deformation of the beam-arch combination bridge was found to be the temperature effect of the typhoon. The arrival of the typhoon led the temperature of the entire top and bottom to drop to a very low temperature field in a short time, which aggravated the inconsistency of the temperature field between the top and bottom plates. The inconsistency of the temperature field changed the internal force and deformation of the steel box girder, led to the failure of some of the top pipes of the frame scaffolding by shear, and the frame scaffolding damage exacerbated the abnormal deformation. The internal force induced by the temperature action of the bridge gradually acted on the frame scaffolding, and changes in the bridge geometry gradually appeared because of the constraints between internal components of bridge structures. Changes in the bridge geometry appeared after several days, once the typhoon had passed. After the later removal of the frame scaffolding, once the low temperature weather appeared, the twisting deformation at the end of the box girder above the abutment inevitably reappeared. Therefore, the possibility of wind load or the settlement of the foundation of the frame scaffolding can be excluded as the exact cause. Furthermore, if the abnormal deformation is due to the wind load or the settlement of the foundation, the twisting deformation could be recovered in the subsequent construction stages, and would not reappear at certain times such as at nighttime and daytime with low temperatures.  
Figure 36: Elevation of the box girder after demolition of rehabilitation measures.  
Figure 37: Measured force value of the main arch hanging rods.  
Hence, when the steel box girder of the beam-arch combination bridge is assembled in open air, the temperature inevitably increases in the daytime along the cross-section of the girder segment; therefore, it is necessary to propose control measures to ensure the uniform distribution of the temperature field inside and outside the steel girder during the construction period. Otherwise, similarly to the background bridge in this article, unrecoverable abnormal deformation under extreme temperature fields is likely to occur, which brings great harm in the construction of similar bridges. Moreover, due to the temperature difference of the box girder segments before and after girth-welding in the open air, some residual thermal deflections will appear on the box girder segments because of the change of the boundary conditions of the structure by the girth-welding [22].  
Combined with the temperature control measures taken in the construction of the steel box girder of other bridges that have already been built [30; 31], the following suggestions are proposed to avoid abnormal deformation occurring: (1) to ensure the uniform distribution of the temperature field inside and outside the steel box girder, it is necessary to establish a construction shed with a constant temperature during assembling and welding in the daytime. (2) Girth-welding of the divided parts of the box girder segment should be performed during a period when the vertical temperature difference of the girder is within 1 \({}^{\circ}\)C, such as after 22:00.