There are three methods for the design of concrete pipes for use in sewer sanitary. Direct design of method of concrete pipes, its applicability and criteria are discussed.
Generally, there are three major approaches including standard installation direct design, standard installation indirect design, and Marston-Spangler Theory of Loads and Supporting Strength that can be used for the structural design of rigid pipe sewer sanitary system.
Certain methods are only employed for specific pipe materials while other approaches could be used for almost all pipe materials.
In this article, direct design of sewer sanitary concrete pipe will be discussed briefly.
Fig.1: Reinforced Concrete Pipe
Fig.2: Reinforced Concrete Sewer Pipe
Requirements for Design of Concrete Pipes
There are several criteria that required to be determined so as to be able to design the concrete pipe.
For instance, the intension of the pipe utilization, inside diameter of the pipe, needed pipeline plan and profile drawings with placement cross sections, design the height of backfill material above the pipe, type of cement if it is different from pipe joint performance requirements, crack width control criteria, design live and surcharge loading if present, permissible standard installation type according to ASCE standard 15-38, soil data adequate to specify overfill weight per volume and in situ situations for permissible ASCE standard installation, and finally design internal hydrostatic pressure intermittently.
Direct Design of Sewer Sanitary Concrete Pipe
It is one of the techniques that can be utilized for the design of reinforced concrete sewer sanitary pipe only. Standard Practice for Direct Design of Buried Precast Concrete Pipe Using Standard Installations (15-98) provides necessary guidance on standard design installations of reinforced precast concrete pipe.
This method employs two standard installation namely one in trenches as shown in Figure-3 and one in embankments which can be seen in Figure-4, in addition to requirements of soil classification and compaction requirements for four soil types. All of these are dependent on the interaction between pipe and soil in combination with experience, procedure, equipment, and construction practice evaluation.
The design of reinforced concrete pipe for a specific standard installation type is dependent on the hypothesis that the specified design bedding and filling requirements is obtained during the installation construction.
Soil and compaction requirements for trench installation and embankments are provided in Table-1 and Table-2 respectively.
Table-1: Standard Trench Installation Soils and Minimum Compaction Requirements
Table-2: Standard Embankment Installation Soils And Minimum Compaction Requirements
Direct design of sewer sanitary sewer pipe approach takes the interaction between soil and the pipe into account while loads and earth pressure imposed on the pipe is computed.
Both loads and pressures will be employed to estimate not only moment and shear and thrust in the pipe walls but also reinforcement ratio for standard installation.
It should be said that, concrete pipe structural design is dependent on the limit state design procedure that takes both strength and serviceability criteria into consideration.
The design of sanitary sewer pipe using standard installation direct design can be carried out employing hand calculation, but the need to analyze several states make the application of computer program desirable.
PIPECAR is a program that employ standard installation direct design method to design concrete sewer sanitary pipe.
Fig.3: Standard Trench Installation of Concrete Pipe
Fig.4: Standard Embankment Installation of Concrete Pipe