Accessing Stress Range or Fatigue values in Grasshopper

[langleyrex68-dot]

I am trying to get fatigue values for welds in grasshopper. I seem to be only able to get weld stress utilization from running the analysis. Is there any way to get values of the weld stress that i could use to estimate fatigue or even better fatigue values themselves.

Any help on this is much appreciated.

@DavidSapakIdeaStatica
@PetrHanakIDEA
@nathanlukeIDEA
@Idonotuse
@TomKohoutek

[twgarmzoscar-glitch]

please answer this!! I am struggling with the same issue at the moment

[sam-pollard]

Me too! Struggling big time trying to get some research done

[OndraZitko]

Hi @langleyrex68-dot @sam-pollard @twgarmzoscar-glitch , thanks for raising this — great question.

We investigated the API and the Grasshopper plugin and here is the full picture.

Where the values are

Both tables you see in IDEA StatiCa Connection desktop app — Welds and Weld sections (fatigue) — are available through the API, but only via the raw results endpoint on the Calculation Controller:

POST /projects/{projectId}/connections/rawresults-text

The values map as follows:

Welds table (Check of welds for extreme load effect) → fatigueWelds dictionary in the JSON response:

App column	JSON field	Unit
σ_wf,max	sigmawf	Pa
τ_wf	tauxwf	Pa
τ_wf,max	tauxwf (opposite side entry)	Pa
σ_wf	sigmawf (opposite side entry)	Pa

Weld sections table (Nominal stresses in weld sections) → fatigueChecks dictionary:

App column	JSON field	Unit
σ_max	normalStress	Pa
τ	shearStress	Pa
τ_max	shearStress2	Pa
σ	normalStress2	Pa

The stress diagrams (Normal stress / Shear stress charts in the app) are in fatigueChecks[key].stressDiagram and fatigueChecks[key].stressDiagramTau — arrays of [position, stress] pairs.

Current Grasshopper support

We are sorry, but we do not currently have a dedicated Grasshopper component that wraps this endpoint. The existing GetResults component only returns simplified unity check values — no stress
breakdown, no fatigue stresses.

Workaround — Python Script component in Grasshopper

As a workaround you can use the GHPython Script component directly in Grasshopper. Here is a ready-to-use script:

Inputs on the Python component:

Name	Type	Example
base_url	str	"http://localhost:5000"
project_path	str	"C:/path/to/your.ideaCon"
connection_id	int	1

import sys
import os
import json

if not project_path:
  print("Please connect a project_path input")
else:
  project_path = project_path.strip()
  base_url = base_url.strip()

  import ideastatica_connection_api
  import ideastatica_connection_api.connection_api_service_attacher as attacher

  with attacher.ConnectionApiServiceAttacher(base_url).create_api_client() as api_client:

      # 1. Open project
      api_client.project.open_project_from_filepath(project_path)
      project_id = api_client.project.active_project_id

      # 2. Switch connection to fatigue analysis type
      connection = api_client.connection.get_connection(project_id, int(connection_id))
      connection.analysis_type = "fatigues"
      api_client.connection.update_connection(project_id, connection_id, connection)

      # 3. Calculate
      api_client.calculation.calculate(project_id, [int(connection_id)])

      # 4. Get raw results
      raw = api_client.calculation.get_raw_json_results(project_id, [int(connection_id)])
      result = json.loads(raw[0])

      # ── WELDS TABLE (fatigueWelds) ─────────────────────────────────────
      welds_out = []
      for key, w in result.get("fatigueWelds", {}).items():
          welds_out.append({
              "name":        w.get("name"),
              "joinedItem":  w.get("joinedItemName"),
              "length_mm":   round(w.get("length", 0) * 1000, 1),
              "sigmawf_MPa": round(w.get("sigmawf", 0) / 1e6, 1),
              "tauxwf_MPa":  round(w.get("tauxwf",  0) / 1e6, 1),
          })

      # ── WELD SECTIONS TABLE (fatigueChecks) ───────────────────────────
      sections_out = []
      for key, fc in result.get("fatigueChecks", {}).items():
          sections_out.append({
              "joinedItem":      fc.get("joinedItemName"),
              "length_mm":       round(fc.get("length",        0) * 1000, 1),
              "sigmaNormal_MPa": round(fc.get("normalStress",  0) / 1e6,  1),
              "tau_MPa":         round(fc.get("shearStress",   0) / 1e6,  1),
              "tauMax_MPa":      round(fc.get("shearStress2",  0) / 1e6,  1),
              "sigma_MPa":       round(fc.get("normalStress2", 0) / 1e6,  1),
          })

      # ── Outputs ────────────────────────────────────────────────────────
      welds_table    = json.dumps(welds_out,    indent=2)
      sections_table = json.dumps(sections_out, indent=2)


[Panel: base_url]      ──┐
[Panel: project_path]  ──┤→ [Python Script] → [Panel: welds_table]
[Panel: connection_id] ──┘                  → [Panel: sections_table]

No other components needed — the script handles opening the project, updating the analysis type, calculating, and parsing the results in one step.

---

Could you confirm a few things so we can better support your use case:

1. Are the Welds table values (σ_wf,max, τ_wf, etc.) sufficient, or do you also need the Weld sections stress diagrams?

3. Are you using Grasshopper specifically, or would a pure Python script also work for your workflow?
4. Which design code are you working with (EN, AISC, other)? Some field names differ between codes.

We are tracking the missing dedicated Grasshopper component internally and your feedback helps us prioritize it.

I am attaching RasResponse.json example, gh script with python component and ideaCon that can be used
Examples.zip

[langleyrex68-dot]

@OndraZitko Thank you for your help so far, it’s been really useful. I am now able to see the values wanted.

However I’m currently a bit stuck with updating parameters. I’m able to change things like cross-sections using the built-in functions in IDEA StatiCa, but these changes don’t seem to affect the results when I run the GH Python script you provided.

Is there a way to reliably update parameters such as cross-sections and load cases through the API so that the results update correctly? I’ve been trying to get this working for a few hours now but haven’t had much luck.

Also, is it possible to trigger the weld sizing operation through the API?

To answer your questions, I am using Grasshopper as part of a parametric/optimisation workflow, and I believe the outputs extracted using your provided code (weld stresses, lengths, etc.) should be sufficient for my use case. I am working with the EN design code.

Thanks again for your support, any further help on these issues is much appreciated.

[OndraZitko]

Hi @langleyrex68-dot
Thanks for following up and sharing more details — really helps!

---

Why parameter and cross-section changes weren't affecting the results

We are not 100% sure what was causing this in your specific setup, but we think the most likely culprit is the way the built-in Grasshopper components and the Python Script connect to the REST API service.

The two talk to the API as separate clients and do not share the same in-memory project state. So when you update parameters or cross-sections through the built-in GH components, those changes live in memory under the GH client session. When the Python Script then opens the original .ideaCon file from disk, it gets a fresh copy — and all those changes are gone.

The fix is to add a Save Connection Project component (SP) at the end of your GH component chain, just before the Python Script. It downloads the current in-memory state — including all your parameter and cross-section updates — to a .ideaCon file on disk. The Python Script then opens that saved file and always sees the latest version.

---

Weld sizing

We don't have a dedicated Grasshopper component for weld sizing yet. The Weld sizing button from the desktop app (Design tab → CBFEM group) is available through the API though, and the Python Script below handles it automatically before running the fatigue calculation.

Available methods — pick the one that matches your preference:

Script value	UI label
"fullStrength"	To full strength
"minimumDuctility"	To minimum ductility (EN code only)
"overStrengthFactor"	To overstrength factor

---

Full Python 3 Script

Here is modified code for python script. You can also check attached gh script where you can find Python 3 Script component with this updated code.

import sys
import os
import json

if not project_path:
    print("Please connect a project_path input")
else:
    project_path = project_path.strip()
    base_url = base_url.strip()

    import ideastatica_connection_api
    import ideastatica_connection_api.connection_api_service_attacher as attacher

    with attacher.ConnectionApiServiceAttacher(base_url).create_api_client() as api_client:

        # 1. Open project
        api_client.project.open_project_from_filepath(project_path)
        project_id = api_client.project.active_project_id

        # 2. Switch connection to fatigue analysis type
        connection = api_client.connection.get_connection(project_id, int(connection_id))
        connection.analysis_type = "fatigues"
        api_client.connection.update_connection(project_id, connection_id, connection)

        # 3. Auto weld sizing — uncomment the design_type that matches your preference:
        #   "fullStrength"
        #   "minimumDuctility"
        #   "overStrengthFactor"
        api_client.operation.pre_design_welds(project_id, int(connection_id), design_type="fullStrength")

        # 4. Calculate
        api_client.calculation.calculate(project_id, [int(connection_id)])

        # 5. Get raw results
        raw = api_client.calculation.get_raw_json_results(project_id, [int(connection_id)])
        result = json.loads(raw[0])

        # ── WELDS TABLE (fatigueWelds) ─────────────────────────────────────
        welds_out = []
        for key, w in result.get("fatigueWelds", {}).items():
            welds_out.append({
                "name":        w.get("name"),
                "joinedItem":  w.get("joinedItemName"),
                "length_mm":   round(w.get("length", 0) * 1000, 1),
                "sigmawf_MPa": round(w.get("sigmawf", 0) / 1e6, 1),
                "tauxwf_MPa":  round(w.get("tauxwf",  0) / 1e6, 1),
            })

        # ── WELD SECTIONS TABLE (fatigueChecks) ───────────────────────────
        sections_out = []
        for key, fc in result.get("fatigueChecks", {}).items():
            sections_out.append({
                "joinedItem":      fc.get("joinedItemName"),
                "length_mm":       round(fc.get("length",        0) * 1000, 1),
                "sigmaNormal_MPa": round(fc.get("normalStress",  0) / 1e6,  1),
                "tau_MPa":         round(fc.get("shearStress",   0) / 1e6,  1),
                "tauMax_MPa":      round(fc.get("shearStress2",  0) / 1e6,  1),
                "sigma_MPa":       round(fc.get("normalStress2", 0) / 1e6,  1),
            })

        # ── Outputs ────────────────────────────────────────────────────────
        welds_table    = json.dumps(welds_out,    indent=2)
        sections_table = json.dumps(sections_out, indent=2)

Take a look on attached gh script please. ExampleWithParametersAndLoadEffectUpdate.zip

Hope this gets you unstuck — if anything still isn't working or something isn't clear, just drop a comment and we'll take another look!

[langleyrex68-dot]

Hi @OndraZitko
Thank you very much for the help on this. I have had to slightly pivot my research due to a tight time schedule. I do plan on implementing this as first planned down the line though. So thank you for all the help!