Plain Concrete Manhole Cover 1

[john1525]

I need to determine the plain concrete strength of an existing 4" thick 24" diameter concrete tank cover in flexure due to a 500 lbs load at the center. Chapter 22 commentary (R22.2.2) indicates that plain concrete should be limited to members that are primarily in a state of compression. However, section 22.5 provides the nominal moment strength of plain concrete. Is it acceptable to use equation 22.5 to determine its strength?

Any suggestions will be appreciated

 

[cntw1953]

For a concentrate load on the center, wouldn't be shear more critical? Yes, you can use criteria developed for structural plain concrete, but remember to check both shear & flexural.

 

[JAE]

Section 22.2 limits you. You can't use plain concrete for a flexural member with air under it.

 

[cntw1953]

I have to admit my mistake. Thank JAE for pointing out.