Thrust Block Bearing Area at a Pipe Bend (AWWA M41)
The thrust a pipe bend throws, and the bearing area a block needs to take it.
Example
You enter
- Internal pressure (psi, test/surge) 100
- Pipe outside diameter (in) 8.625
- Bend angle (deg) 90
- Allowable soil bearing (psf) 2000
You get
- Resultant thrust 8263
- Required bearing area 6.20 ft^2
Checked against published worked examples from: IAPMO UPC Appendix I (Hawaii Plumbing Code 2021, via UpCodes).
Details, formula, and sources
ScopeResultant thrust at a bend T = 2 P A sin(theta/2) and the bearing face Ab = Sf x T / (allowable soil bearing) with a ~1.5 safety factor (AWWA M41 / DIPRA). An 8 in main (OD 8.625), 100 psi, 90-degree bend, 2000 psf soil -> T 8,263 lb, Ab 6.20 ft^2; a 45-degree bend halves the thrust (the sin(theta/2) term). Use the test/surge pressure. A design aid; the engineer of record governs.
Formula or tableA = (pi/4) OD^2; T = 2 P A sin(theta/2); Ab = Sf x T / (allowable soil bearing), Sf ~1.5.
Source and editionThe AWWA M41 thrust-block resultant-thrust and bearing-area method for a pipe bend, by name.
Free accessThe resultant-thrust T = 2 P A sin(theta/2) and the bearing-area check are the standard published AWWA thrust-restraint relations.
What governsEstimate. AHJ and licensed professional govern.
API field namespressure_psi, od_in, bend_deg, soil_bearing_psf, thrust_lb, bearing_area_ft2
- Resultant thrust T = 2 P A sin(theta/2), A = (pi/4) OD^2AWWA M41
- Bearing area Ab = Sf x T / (allowable soil bearing), Sf ~1.5 (input)AWWA M41 / DIPRA; EBAA Connections PD-1
- Design pressure use the test/surge pressure and a geotechnical soil valuescope of this tile