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Abstract：In this paper，the stress states of the two orthotropic bridge decks at different stress conditions and control points at different cross-sections are compared，and the difference of mechanical properties between the two bridge decks is analyzed. The results show that the maximum stress at the top and center of the polyurethane core layer of the orthotropic bridge deck with polyurethane-steel sandwich structure occurs at the fulcrum section.
Keywords：Mechanical analysis;Cross-sea steel frame bridge;Quality monitoring
General technical ideas：
The stress-strain response of bridge deck to vehicle load is very local，and the stress-strain peaks in the width range of two stiffeners near the load，and then decays rapidly around. Usually，the inner sides of abutments at both ends，the tops of piers，the midpoints of bridge spans，the tops of towers and the roots of towers are all places where deformation observation points should be set [1].
Generally，the durability degradation of steel frame bridges can be divided into two stages（Figure 1），namely，steel bar passivation stage（）and steel bar corrosion stage（）. The corrosion stage can be divided into two periods with the expansion and crack point of concrete cover as the boundary. From an economic point of view，if it is worthwhile to carry out the repair work in stage（），and the repair design and construction in stage（）are often costly，the most economical and effective way is to take durability redesign measures（pre-plan）before the steel bar is blunted [2].
Figure 1 Relationship between reinforcement corrosion and service time of structure
Calculation results and analysis：
For the orthotropic bridge deck with polyurethane-steel sandwich structure，if the longitudinal stiffening ribs are completely eliminated，the transverse width of the bridge deck is 7.5m，and the absolute maximum normal stress and maximum deflection of each point in the midspan and fulcrum section are as follows：
Table1 Maximum stress value and deflection value of each point in midspan and fulcrum section without longitudinal stiffener
Conclusions：
In case of emergency braking，the transverse shear stress of pavement bonding layer is close to the longitudinal shear stress，so the influence of transverse shear stress and longitudinal shear stress of pavement should be considered comprehensively when analyzing the shear failure of bonding layer. The numerical simulation in this paper is only a theoretical model. In practical engineering，due to the stress concentration phenomenon at the action point of the force，it is usually supported or rounded at the interface between the web and the flange to prevent the stress concentration phenomenon.
References：
[1]Chen dong，yuan zhi-yang，Chu hai-feng. mechanical performance analysis of a new type of steel truss overhaul vehicle. journal of Chongqing university of science and technology（natural science edition）
[2]Shang Wennian，Wu Qiongyao，Liu Xiaoyun，et al. Study on mechanical properties of beam-column joints of steel structure in distribution equipment building of steel structure substation. Industrial Architecture
（作者單位：Dalian University of Technology）
Keywords：Mechanical analysis;Cross-sea steel frame bridge;Quality monitoring
General technical ideas：
The stress-strain response of bridge deck to vehicle load is very local，and the stress-strain peaks in the width range of two stiffeners near the load，and then decays rapidly around. Usually，the inner sides of abutments at both ends，the tops of piers，the midpoints of bridge spans，the tops of towers and the roots of towers are all places where deformation observation points should be set [1].
Generally，the durability degradation of steel frame bridges can be divided into two stages（Figure 1），namely，steel bar passivation stage（）and steel bar corrosion stage（）. The corrosion stage can be divided into two periods with the expansion and crack point of concrete cover as the boundary. From an economic point of view，if it is worthwhile to carry out the repair work in stage（），and the repair design and construction in stage（）are often costly，the most economical and effective way is to take durability redesign measures（pre-plan）before the steel bar is blunted [2].
Figure 1 Relationship between reinforcement corrosion and service time of structure
Calculation results and analysis：
For the orthotropic bridge deck with polyurethane-steel sandwich structure，if the longitudinal stiffening ribs are completely eliminated，the transverse width of the bridge deck is 7.5m，and the absolute maximum normal stress and maximum deflection of each point in the midspan and fulcrum section are as follows：
Table1 Maximum stress value and deflection value of each point in midspan and fulcrum section without longitudinal stiffener
Conclusions：
In case of emergency braking，the transverse shear stress of pavement bonding layer is close to the longitudinal shear stress，so the influence of transverse shear stress and longitudinal shear stress of pavement should be considered comprehensively when analyzing the shear failure of bonding layer. The numerical simulation in this paper is only a theoretical model. In practical engineering，due to the stress concentration phenomenon at the action point of the force，it is usually supported or rounded at the interface between the web and the flange to prevent the stress concentration phenomenon.
References：
[1]Chen dong，yuan zhi-yang，Chu hai-feng. mechanical performance analysis of a new type of steel truss overhaul vehicle. journal of Chongqing university of science and technology（natural science edition）
[2]Shang Wennian，Wu Qiongyao，Liu Xiaoyun，et al. Study on mechanical properties of beam-column joints of steel structure in distribution equipment building of steel structure substation. Industrial Architecture
（作者單位：Dalian University of Technology）