calculate the uniform load(in addition to beam weight) that will cause the section in figure 1 to begin to crack if the are used for 28ft simple span.
fc’=4000psi, fr=7.5√fc’ and reinforced concrete weight =150 lb/ft3.
for the above example, we need to calculate the value of the cracking moment. using cracking moment we can calculate the required load. I=(bh^3)/12=(14*(24^3))/12=16,128in4 y is the distance from the neutral axis to extreme fiber in the tension zone. neutral axis will be located at the center of the beam due to symmetry. therefore, y=12 in Mcr=(474.34*16,128)/12=637,512.96Ib.in the maximum moment for simply beam =(w.l^2)/8 uniform load=542.10-beam weight =542.10-150*(24/12)*(14/12)=192.1Ib/ft construction management: concrete construction
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