tension only material

[soo]

Hi everyone
I’m trying to assign a tension only material to truss element for simulation of steel plate shear wall. First I used Here is the two material that I used uniaxialMaterial ElasticPPGap with zero value for $gap and then I tried uniaxialMaterial Hysteretic with negligible values in compression.

uniaxialMaterial ElasticPPGap 300 $E $Fyw 0.0 0.02
uniaxialMaterial Hysteretic 500 $Fyw [expr $Fyw/$E] [expr $Fyw+$E*0.02*10*($Fyw/$E)] [expr ($Fyw/$E)*11] -1.e-2 -1.e-2 -1.e-2 [expr -($Fyw/$E)*11] 1. 1. 0.0 0.0

But during unloading path these two material acted differently, the uniaxialMaterial Hysteretic did not went back to zero.
Could anyone help me how to solve the issue?

[mhscott]

These materials have very different unloading behaviors.

[soo]

These materials have very different unloading behaviors.

Thank you for your answer.
The web plate of self-center steel plate shear wall simulated as two set of parallel uniformly spaced truss element which inclined in direction of α and – α. The unloading paths of two material are the same, but as they approach to origin, the truss elements in – α direction assign with hysteretic material which supposed to be in compression (have no force), gradually start to get tension force and prevent the frame to go back to origin. The behavior is so weird whereas the truss elements assigned with uniaxialMaterial ElasticPPGap act as expected.