The
design made by some FEM softwares for reinforced concrete members, sometimes
result in less area of reinforcement. This does not mean that the design is not
valid! You may need to check if the concrete tensile strength is counted in the
design stage by the program. fctm is the tensile strength of concrete which
equals 0.70 ? fc as per the ACI and we normally ignore this small value when the
steel reinforcement is involved as it has no significant involvement in strength
compared to that provided by steel bars.Concrete tensile strength is one of the
magic functions in concrete. Sometimes especially for pipes encasement and
manholes up to certain depths, concrete might work without the need of
reinforcement because of concrete tensile strength is quite enough to resist the
forces induced by earth pressure, live loads, etc.

This may lead us to avoid adding the waterproofing membrane which will have no
function without reinforcement and save time and money!