Civil Engineering Reference
In-Depth Information
Arrows indicate
iterations
Stress
∆s
3
Stress—strain curve
∆
s
2
∆
s
1
Strain
∆
e
1
∆
e
2
∆
e
3
Figure 6.1
Constant stiffness method
Stress
Arrows indicate
iterations
∆σ
3
Stress strain curve
∆σ
2
∆σ
1
Strain
∆ε
1
∆ε
2
∆ε
3
Figure 6.2
Variable (tangent) stiffness method
failure is approached, because the elastic (constant) global stiffness matrix starts to seriously
overestimate the actual material stiffness.
Less iterations per load step are required if the second approach, the “variable” or
“tangent” stiffness method is adopted. This method, shown in Figure 6.2, takes account
of the reduction in stiffness of the material as failure is approached. If small enough load
