Index: /issm/trunk-jpl/src/c/classes/Elements/Penta.cpp
===================================================================
--- /issm/trunk-jpl/src/c/classes/Elements/Penta.cpp	(revision 20655)
+++ /issm/trunk-jpl/src/c/classes/Elements/Penta.cpp	(revision 20656)
@@ -329,4 +329,5 @@
 	IssmDouble	tau_xz[NUMVERTICES];
 	IssmDouble	tau_yz[NUMVERTICES];
+	IssmDouble	tau_eff[NUMVERTICES];
 	GaussPenta* gauss=NULL;
 
@@ -355,4 +356,9 @@
 		tau_xz[iv]=2*viscosity*epsilon[4];
 		tau_yz[iv]=2*viscosity*epsilon[5];
+
+		tau_eff[iv] = tau_xx[iv]*tau_xx[iv] + tau_yy[iv]*tau_yy[iv] + tau_zz[iv]*tau_zz[iv] +
+		  2*tau_xy[iv]*tau_xy[iv] + 2*tau_xz[iv]*tau_xz[iv] + 2*tau_yz[iv]*tau_yz[iv];
+
+		tau_eff[iv] = sqrt(tau_eff[iv]/2.);
 	}
 
@@ -364,4 +370,5 @@
 	this->inputs->AddInput(new PentaInput(DeviatoricStressyzEnum,&tau_yz[0],P1Enum));
 	this->inputs->AddInput(new PentaInput(DeviatoricStresszzEnum,&tau_zz[0],P1Enum));
+	this->inputs->AddInput(new PentaInput(DeviatoricStresseffectiveEnum,&tau_eff[0],P1Enum));
 
 	/*Clean up and return*/