Steel decking plastic nuetral axis

[shahrizan]

Dear all,

I have calculated the plastic neutral axis for steel and make a comparison with elastic neutral axis. However the plastic axis from bottom of decking is lower than elastic axis. That make me confuse a little bit because to calculate the plastic moment for partial interaction base on R.P Johnson book, the lever arm z is calculated using the equation :-

z= ht - 0.5hc-ep + (ep - e) Ncf/Npa

ht= overall slab thickness
hc= top of decking slab thickness
ep=plastic neutral axis from bottom of decking
e=elastic neutral axis from bottom of decking

From the equation, it shows that the plastic axis usually more than elastic axis. However, for me it depends on the steel decking section. How about your opinion ? Do any one know about this.


Best regards,

Shahrizan.