Seismosoft | Earthquake Engineering Solutions

Dear Support Team,

I am looking to model the degradation of reinforcing steel material properties to account for the effects of corrosion.

For the designated corrosion levels, I have obtained degraded values for the following steel properties:

Yield strength
Ultimate tensile strength
Ultimate strain

However, in the material properties dialogue box, I can identify a direct input only for the yield strength. I would therefore appreciate clarification on the following:

How can the reduction in ultimate tensile strength due to corrosion be incorporated into the material model?
Is the fracture strain specified in the material properties equivalent to the ultimate strain of the reinforcing steel, or do these represent different quantities in the constitutive model?
From the stress–strain graph displayed alongside the material properties, there does not appear to be a separate ultimate stress value. The maximum stress shown in the graph also appears to be only slightly higher than the yield strength. Could you please clarify how the ultimate strength and post-yield behaviour are defined in this material model?

I am particularly interested in understanding how the material parameters should be modified when both the ultimate strength and ultimate strain are reduced due to corrosion, rather than modifying the yield strength alone.

I look forward to your clarification.

Graph shown in Seismostruct https://drive.google.com/file/d/1xMT7sE ... PIBa8/view

In general, corrosion is modelled in steel stress-strain curves by reducing key mechanical properties (yield strength, ultimate strength, and ductility) and/or scaling the rebar area as a function of mass loss. A good reference that describes the change of these parameters is:
https://www.ascjournal.com/down/vol18no3/Vol18no3_8.pdf
All these parameters can be adapted accordingly in all SeismoStruct steel models.
A simpler approach would be to assumes a uniform loss in the rebar area.
Seismosoft Support

seismosoft wrote: 19 Aug 2026, 12:54 In general, corrosion is modelled in steel stress-strain curves by reducing key mechanical properties (yield strength, ultimate strength, and ductility) and/or scaling the rebar area as a function of mass loss. A good reference that describes the change of these parameters is:
https://www.ascjournal.com/down/vol18no3/Vol18no3_8.pdf
All these parameters can be adapted accordingly in all SeismoStruct steel models.
A simpler approach would be to assumes a uniform loss in the rebar area.
Seismosoft Support

Thank you for your prompt response. I am aware of the various models in the literature for modelling the effects of corrosion deterioration. My specific query is concerning their implementation in SeismoStruct in relation to stl_mp material model. As I have observed, the input parameters explicitly include Yield Strength, I am confused about how the degradation in ultimate strength and ultimate strain can be incorporated. From my understanding, the ultimate strength is to be incorporated by modifying the strain hardening parameter, and the ultimate strain to be incorporated by modifying the fracture strain. Is this the right way to go about it? or is there another way to do the same in SeismoStruct?

There is no ultimate strain and ultimate stress parameter in the definition of the stl_mp model.
For all the material models, you can easily check easily their behavior either on the Materials module of the pre-processor, by adapting the strain values on the corresponding table. Note that with the pop-up menu of the table, you can easily input strain time-histories from Excel.
Alternatively, you can use the Stress points facility (Output module).
Seismosoft Support