Live Load Analysis:
Automatically Set Traffic Direction to Account for Skew Effects
For LRFD and CHBDC, check this box to have the analysis automatically set the traffic direction perpendicular to the main reinforcement when the skew is greater than 15 degrees for all fill depths, regardless of the Lane Direction setting for the Vehicle Properties. The Lane Direction setting will be used otherwise. Uncheck this box to have the analysis use the Lane Direction setting for all skew angles. For STND, the program always adjusts the distribution width to account for skew effects when the fill depth is less than 2 feet, see the discussion in Engineering Theory.
Include Impact on Bottom Slab
Check to include impact on the bottom slab. This option was included to have the live load results more closely equal the previous PCANY Culvert program, which included impact on the bottom slab.
Limit Distribution Width to Culvert Length
Select the appropriate option to have the moving load calculations limit the live load distribution width to the culvert length for, no culverts regardless of fill depth, all culverts regardless of fill depth, or only if the fill is greater than 2 feet deep, or only if the fill is less than 2 feet deep.
Longitudinal and Transverse Axle Combination Methods
Select the desired axle combination method:
Do Not Combine
The axle loads will be applied to the top slab as is, and will be allowed to overlap where the axle spacing is less than the fill depth multiplied by the fill slope. Note that this option is no longer valid when using LRFD 2013 Interims and later.
Combine Maximum of 2 Overlapping Distributions
The moving load algorithm will combine overlapping axle distributions, but no more than two axles will combine.
Combine all Overlapping Distributions
The moving load algorithm will combine all overlapping axle distributions.
Distribute Wheel Load if Fills < 2 ft
Under LRFD, for fill depths less than 2 feet, wheel loads may be assumed to be directly on the top slab, or they may be distributed through the fill. Checking this option will distribute the load through the fill. If this option is not checked, then the program will place the wheel load directly on the top slab.
Note: if you are using the ASTM charts to select your steel, you will need to use this option to match the model used to create the charts.
Note: STND and CHBDC requires that the wheel load is always placed on the top slab for fill depths less than 2 feet.
Axle Increment for Analysis
Input the number of axle increments to be used in the moving load analysis. Assigning a high number will greatly slow down the moving load analysis. The minimum value allowed is 10, which places the axles at the tenth points on each cell. The default value is 20.
Reinforcement:
Individual Top and Bottom Slab Design
Check to perform individual top and bottom slab design. If not checked, the governing slab will be used to determine thickness and steel area.
Individual Interior and Exterior Wall Design
Check to perform individual interior and exterior wall design. If not checked, the governing wall will be used to determine thickness and steel area.
Distribution Slab Has Been Provided
If checked the program will assume that a separate distribution slab has been placed on top of the top slab, and therefore no distribution steel will be necessary in the box itself. This will only apply to designs will fill depths less than 2’.
Always Include Distribution Steel
If checked the program will always calculate and display distribution steel, even when the fill depth is greater than or equal to 2 feet. If unchecked, the program will only calculate distribution steel for fill depths less than 2 feet. Note that even if distribution steel is not calculated, some minimum reinforcement may be used.
Use M-dimension for bar length calculations
If checked, the program will use the calculated M-dimension for the horizontal length of the A1 and A2 bars.
Epoxy
Select which bars you would like epoxied, the options are ‘none’, ‘top steel if fill < 2ft’ and ‘all steel’. If ‘top steel if fill < 2ft’ is selected the program will always assume the top layer of steel in the top slab is epoxy coated for fill depths less than 2 feet. Otherwise, all steel in the culvert is assumed to be uncoated at all fill depths. If ‘all steel’ is selected, the program will assume all steel is epoxy coated at all fill depths.
Live Load Deflection Criteria
Select the live load deflection criteria. Live load deflections of single cell culverts are compared with the clear span divided by either 800 or 1000. The user can also define their own criteria by selecting ‘User Defined’.
Slenderness
Select Check Slenderness and input a K Factor to have the analysis perform a slenderness check.
Structural Analysis Modeling:
Model Haunches in the Slabs
If this option is selected then the stiffness of the haunches (if any) are incorporated into the structural model at the ends of the top and bottom slabs. This will cause a redistribution of the top and bottom slab moments from the center to the ends.
Note: if you are using the ASTM charts to select your steel, you will need to use this option to match the model used to create the charts.
Model Haunches in the Walls
If this option is selected then the stiffness of the haunches (if any) are incorporated into the structural model at the top and bottom of the exterior walls. This will cause a redistribution of the wall moments mid-height to the top and bottom of the walls.
Critical Sections:
Critical Section Locations
The following options for critical section locations are given:
Flexure Critical Section Locations
Face of support
1.5 * depth of slab (this is the location where the depth of the slab + haunch equals 1.5 * depth of slab)
End of haunch
Shear Critical Section Locations
Face of support
dv beyond support
End of haunch
dv beyond haunch
Include Haunch Depth
You have the option in include haunch depth for all critical sections, no critical sections, or only flexure/shear critical sections. This will add the depth of the haunch to ds and dv, which can also effect the shear critical section locations.
Use Max Moment with Max Shear
The shear analysis will either use the maximum moment or the corresponding moment. If checked, the maximum moment at the face of the wall will be used in the interaction between Vu and Mu to calculate the shear capacity of the member. If unchecked, the moment at the critical section for shear will be used instead.
Flexure:
Use Eq. 12.10.4.2.4a-1
If checked, the flexural moment capacity is calculated using LRFD Eq. 12.10.4.2.4a-1. The program applies a factor to the Nu term in the equation, thereby allowing the user to ignore the effects of axial thrust if desired. Note that this equation is modified in CHBDC. See the theory section for the revised equation.
Ignore Axial Thrust
If unchecked, the flexural moment capacity is taken from a location (based on the applied P) on a P-M diagram built internally by the analysis routine for AASHTO Codes. If checked, the flexural moment capacity is set to where the P-M diagram crosses the horizontal axis (P = 0), causing Ma (allowable) to be equal to Mu (pure flexure) in the printout. Also if checked, the variable phi will not be calculated under LRFD, and will be set to that which the user has input on the Load and Resistance Factors page.
Shear:
Always Check Iterative Beta
If checked, the program will calculate the shear capacity of the concrete using the iterative beta method in LRFD Appendix B5. This value is then compared to the shear capacity already calculated using the internal decision table (see Section 5.7) and the larger of the two values is used for the current member.
Use LRFD 5.14.5.3
If checked, the program will calculate the shear capacity of the top slab of a 3-sided culvert with more than 2 foot of fill using LRFD 5.14.5.3, which is usually only used in 4-sided culverts. However, some states allow this provision to be used for 3-sided culverts as well.
Maximum As used in Vc Calcs
In LRFD, when the shear capacity of the concrete is calculated using the iterative approach in Appendix B5, a preliminary estimate of the reinforcing steel is based on moment demand. Then the area of steel is used to calculate the shear capacity and checked against the shear demand. If the preliminary estimate of the area of reinforcing steel is unsatisfactory the program enters a loop inside the shear calculations to increase the area of steel until this requirement it met. This area of steel should be limited to around 2.0 in2/foot for practical purposes, and can be adjusted up or down here. If this limit of the reinforcing steel cannot be satisfied then the program increases the member thickness, recalculating the structural steel demand, and re-starts the shear demand loop.
Environmental:
Apply Environmental Durability Factors
If checked, the program will calculate the and apply the environmental durability factors (as defined in ACI-350) to the flexural demand.
Exposure
Select the appropriate exposure option for your design, the options are ‘normal’ and ‘severe’. This is used in computing the environmental durability factors, defined in ACI-350.