The Load and Resistance Factors window when using the LRFD specification:
The Load and Resistance Factors window when using the Standard or AREMA specifications:
The Load and resistance Factors window when using the CHDBC specification:
Locked/Unlocked
By default the form will be locked. Click this button to unlock the form to edit the values on the form.
Load Factors
For LRFD and CHBDC, input load factors for the various load cases. For STND and AREMA, input Gamma, Beta-D, and Beta-L values. Note that these live load factors will be used for flexure and shear calculations only. For ratings calculations, the program will use the live load factors assigned on the Moving Loads dialog box.
Resistance Factors
For LRFD, input values for Shear and Moment, along with the compression and tension values for the points on the internal P-M diagram. For STND and AREMA, input values for Shear and Moment as well as P-M Diagram values for Slabs, Exterior Wall, and Interior Wall. For CHBDC, the user can assign values to both the phi factor for concrete and the phi factor for steel.
The STND Specification strength reduction phi factors are listed as 0.90 for flexure, 0.85 for shear, 0.75 axial compression (spirals) and 0.70 axial compression (ties). These have been used as a basis when selecting the default values for the P-M diagram used internally by the program to calculate the flexural resistance of the various members of the culvert.
A phi factor of 0.85 is the default for slabs. For shorter spans in the range of 12 feet or less, shear will usually control the slab design so a value of 0.85 was selected. For longer spans where flexure controls, the user has the option of increasing the phi factor to 0.90 for a less conservative design.
A phi factor of 0.70 is the default for interior walls. Interior walls take the majority of the axial forces on multi-cell (multi-span) structures so a phi factor for axial compression was selected. It can be assumed horizontal wall reinforcement behaves more like “ties” than “spirals”, so the lower value phi factor of 0.70 is used.
A phi factor of 0.80 is the default for exterior walls. Exterior walls of culverts behave more like beam-columns than pure compression or pure flexural members. The default value of 0.80 is midway between a pure compression member (phi = 0.70) and a pure flexural member (phi = 0.90) for exterior walls.
For LRFD, the phi factor for moment is actually a variable number based on the location on the P-M curve. The value assigned here is used to in the preliminary estimate of the area of steel required in design mode, and to calculate the area of steel needed to satisfy minimum steel requirements (Mcr). This value is also used to calculate the flexural capacity when the user selects the analysis option ‘Ignore Axial Thrust’, and in this instance a variable phi is not calculated.
Load Modifiers
For LRFD only, input values for Ductility, Redundancy for Dead Load, Redundancy for Live Load, and Importance.
Capacity Modifiers
For LRFD only, input values for Condition and System modifiers.