Strip Footings for 3-sided Culverts

Owned by Becca Alford (Unlicensed)
Jun 22, 2020
3 min read

Supported Specifications

The strip footing module comes with support for AASHTO LRFD 6th edition with 2013 Interims. The strip footing module will only be available if Eriksson Culvert has this specification selected.

 

Loads

 

Vertical Loads

The Dead Load consist of the soil weight plus the weight of the concrete slab (slab and pedestal). The program is capable of accepting any number of additional loads which act at the center of the keyway. The depth of the keyway is assumed to be zero for the analysis.

 

Applied Loads

The applied loads are automatically acquired from the reactions of the three-sided culvert (from Eriksson Culvert). The strip footing module stores a loading condition for each truck / fill depth combination and will design the strip footing to satisfy all of the loading conditions. The user also has the ability to modify / add / delete any of these loads if they desire.

 

Bearing Pressure

A trapezoidal distributed load is applied to the bottom of the strip footing. This load is picked in order to enforce equilibrium on the system and thus varies depending on the load combination we are checking.

 

Load Combinations

The strip footing module checks all possible load combinations from the loads on the system. For each load combination the analysis is performed and the controlling cases are reported.

 

Flexural Strength

The flexure strength is calculated assuming singly reinforced member with a uniform concrete stress block. Thus, the following equation is used,

When selecting reinforcement the bar size / spacing pairs is iterated through until the pair with the lowest area of steel (which exceeds demand) is found.

 

Shear Strength

 

One Way Shear

The one way shear capacity is found using the general procedure defined in LRFD Appendix B5. The strip footing module checks two critical sections’ one way shear capacities. Those being at the left and right hand side of the pedestal / keyway (if no pedestal) extended by the shear depth, . The controlling load combination and their shear capacities and shear demands are reported.

 

Two Way Shear

The strip footing module also checks to make sure the wall loading will not cause a two-way shear failure of the slab. For this check the critical section is on each side of the pedestal / keyway (if no pedestal) extend by half of the shear depth, . This module assumes the strip foot ends at the end face of the wall. Thus, , the shear perimeter, is . The shear capacity is then found using LRFD Equation 5.13.3.6.3-1.

 

Shrinkage and Temperature Reinforcement

The strip footing module automatically chooses shrinkage and temperature reinforcement for the user. This reinforcement is designed in order to meet the requirements set by LRFD section 5.10.8. The selected reinforcement is reported in the text report.