BBCGEN,<panel>,<ShearModel>,[fc],[fy],[Pn],[Nu],[bre],[bys],[CrackForceLevel]

Auto-generate a backbone curve for a panel using the Ultimate Shear value for the panel generated by the SHEAR. This command will always generate a 22 point BBC the first point cracking point of the curve. The next 20 points will equidistant spaced along the strain percentage axis until the yield point is reached. The final point all BBCs will be at (2%,1.02*Ultimate Shear). All of the Shear model variables specified by the user are optional. If the user leaves a shear model argument blank the command will use 0 for that variable. This command assumes the panel references a non-empty group with a uniform material across all elements.

• panel - panel number. If panel = 0 BBCs will be generated for all panels defined by the user.
• ShearModel - Numeric code for which shear model will be used to generate ultimate shear of the backbone curve. The shear model equations can be found in the description of the SHEAR command. The upper or lower bound will be used for the BBC if the calculated shear for ACI 318-08 or Wood 1990 fall outside the bounds specified in the model equations.
  • 1 - ACI 318-08
  • 2 - Wood 1990
  • 3 - Barda 1977
  • 4 - UB Empirical
• fc - compressive strength (ksi or kN/m²)
• fy - reinforcement yield strength (ksi or kN/m²)
• Pn - web reinforcement ratio
• Nu - axial force (kips or kN)
• bre - boundary element reinforcement area (ft² or m²)
• bys - boundary element reinforcement yield strength (ksi or kN/m²)
• CrackForceLevel - floating point scalar used to determine the cracking point of the backbone curve. Any scale that falls outside of the range and isn't 0 will cause an error that will be reported to the Command History screen.
  • 0 - Use the equation [3.5*sqrt(fc)*cross-sectional area] (ASCE 4-17 standard recommendation in Section C.3.3.2) as the cracking shear.(default)
  • [0.1-0.5] - Use [CrackForceLevel* utimate shear] as the cracking shear.