Direct design is a limit states design method. The design requirements are outlined in the following standards:
- CAN/CSA-S6-06 (Canadian Highway Bridge Design Code)
- American Society of Civil Engineers (ASCE), 15-98 - The standard practice for direct design of buried precast concrete pipe using standard installations (SIDD)
In the 1970s, software was developed to analyze soil pipe interaction (SPIDA - Soil Pipe Interaction Design and Analysis). The software was used by Dr. Frank J. Heger to generate a pressure distribution model which is now referred to as the Heger Pressure Distribution.
The design standards reference the Heger Pressure Distribution data to determine moments, thrusts, and shears in the pipe wall. The combination of the factored pressure distribution and the factored loads is used to determine the reinforcement areas required to handle the pipe wall stresses. Direct design takes into account flexure, concrete compression, crack control, diagonal tension, and radial tension as failure modes.
For assistance with this design process please contact the Engineering Department at Inland Pipe.