Composite bridges with continuous steel girders and concrete reinforced slabs are commonly designed. Because there is a massive difference in the material's stress capacity in tension, considering tensile zones in the reinforced concrete components is essential. RM Bridge, inside OpenBridge Designer, has a solution for designing with cracked concrete in the tensile zone in composite structures. One of the three described and discussed methods below can be used:

• Linear elastic redistribution: Action ReloadSup, uses the complete composite system and it's based on a linear-elastic analysis, but with no change occurs in stiffness, only at the results, as  shown below; 

   

communities.bentley.com/.../reload-superposition-or-loading-case-no-tension-elements

• Ignoring concrete elements: full composite cross-section is considered only in areas where the concrete is predominantly in compression, the reinforcement can still be considered; 

   

• Nonlinear material: generally used only for specific loadings due to computational costs and the impossibility to combine superposition results. 

Each method has its advantages and limitations and careful selection should be done for each case. More information can be found in the document and by running the example files:

• rm9-elastic.tcl
• rm9-2CS.tcl
• rm9-non_linear.tcl