Steel not failing

[nsharmanishant]

Dear All,
I am trying to carry out monotonic pushover analysis on a rectangular reinforced concrete cantilever column (fixed at base) having dimension of 0.6m*0.75m with 32 19mm steel bars (with fy=420Mpa) distributed uniformly on all four sides and have used Fiber section (distributed plasticity). The length of the column is 3.25m and has been dicretized using 6 elements. The material model used for steel is Reinforcingsteel with $Esh=0.008*$Es and $esh=0.011 and $eult=0.145. Assigning these properties the stress-strain behaviour of steel in both compression and tension is being monitored.

It is observed that the at around the strain value of 0.12, there is a sudden drop in stress and also with increase in displacement the strain values reduce for a certain number of steps. With further progress in analysis, the stress increases with increasing strain even beyond 0.145 and only after a strain of about 0.18 the stress starts reducing but that too very gradually so much so that even after a strain value of 0.48 the stress reduces by only 3% of maximum stress. This is the behaviour of steel in compression. For the steel in tension the stress keeps on increasing and does not reduce at all and no failure of steel is encountered.

Initially the analysis used to stop just around the time when the core concrete failed, 40mm displacement (it showed convergence not achieved after the assigned number of iterations). However with the incorporation of the code, developed by Silvia to overcome convergence problem, the analysis is able to proceed to as much displacement as desired (even upto 1500mm -3000mm) without the steel failing.

My query is that is it possible for the steel to have such stress-strain behavior. Shouldn't the steel fail after 0.145 strain or at least the stress in steel drop down significantly after the strain value of 0.145 and show failure? It would be very helpful if some light is shed on this.

ThankYou
Nishant

[fmk]

everything is possible especially if you start playing with the optional extras .. as the interaction of the concrete and steel may be clouding the issue, i suggest creating a strain history and then putting a single steel material through that strain history to to see what the stresses are.

if that is satisfactory, then as i am not sure what script you are referring to (and i probably don't want to know!) but record the stress and the strain in the material to see what the actual strain history the material is undergoing in the actual model.