[Eurocode] Fatigue Analysis for Composite Girder Bridge – MIDAS Support

Intro

This plugin performs fatigue analysis for composite bridges based on the Eurocode, and it also supports the Italian National Annex, NTC 2018. It integrates seamlessly with MIDAS Civil NX and enables fatigue evaluation for concrete, reinforcing steel, and steel girders. Users can configure fatigue parameters, import structural data, and efficiently generate fatigue safety check results.

Developed with

MIDAS CIVIL NX 2025(v2.x)

Applicable Standards

EN 1991-2;2003 — Eurocode 1: Actions on structures – Part 2: Traffic loads on bridges
EN 1992-1-1;2004 — Eurocode 2: Design of concrete structures – Part 1-1: General rules and rules for buildings
EN 1992-2;2005 — Eurocode 2: Design of concrete structures – Part 2: Concrete bridges
EN 1993-1-1;2005 — Eurocode 3: Design of steel structures – Part 1-1: General rules and rules for buildings
EN 1993-1-9;2005 — Eurocode 3: Design of steel structures – Part 1-9: Fatigue
EN 1993-2;2006 — Eurocode 3: Design of steel structures – Part 2: Steel bridges
NTC 2018 (Italy) — Norme Tecniche per le Costruzioni (Italian National provisions / National Annex)

Benefits of this plugin

Complies fully with Eurocode fatigue design provisions and the Italian National Annex (NTC 2018).
Supports multiple fatigue checks: Concrete, Reinforcing Steel, Steel Girder
Provides visual outputs such as safety factor charts, stress range diagrams, and correction factor summaries.
Allows smart data import from MIDAS Civil via API
Manages fatigue cases with add / edit / copy / delete
Enables result export for engineering documentation

Supported Fatigue Case Types

This plugin supports the following fatigue evaluation types:

🔗 Common (Railway & Road)

Concrete Shear (Not Require Reinforcement)
Concrete Shear (Require Reinforcement)
Steel Girder (Direct Stress)
Steel Girder (Shear Stress)

🚆 Railway Only

Concrete Compression (Damage Equivalent Stress Method)
Reinforcing Steel (Damage Equivalent Stress Method – Railway)

🚗 Road Only

Concrete Compression (Simplified Method)
Reinforcing Steel (Damage Equivalent Stress Method – Road)

Supported Section

COMPOSITE-I
COMPOSITE-T
STEEL-I (Type-1)
Steel Box Type1
Steel I Type1
Steel Tub Type1
Steel Box Type2
Steel I Type2
Steel Tub Type2

How to use this plugin?

This documentation demonstrates the workflow using Reinforcing Steel as an example.

① Launch the Plugin** – Open the application to access the dashboard for fatigue checks and MIDAS API linking. At launch, select the bridge type (Railway or Road) for the fatigue analysis.

② Connect to MIDAS Civil API – Connect to an open MIDAS Civil NX model to automatically retrieve structural data for fatigue analysis.

③ Set Global Parameters – Define the partial safety factor (γ) and project life (number of years or cycles).

④ Select Fatigue Type – Choose a fatigue check method

⑤ Manage Fatigue Cases – View a list of created fatigue cases. Use edit, copy, or delete to manage multiple scenarios.

⑥ Import MIDAS Civil NX Results – Click the button to fetch stress or force results from MIDAS Civil (load cases, stages).

⑦ Import from Midas Civil NX – Import element IDs selected in MIDAS Civil.

⑧ Load Data – Confirm the elements to be analyzed and load values based on their assigned fatigue conditions.

⑨ [Optional] Enter fatigue-specific parameters if required. This tab is available only for certain fatigue methods.

⑩ [Optional] Calculate Correction Factors –Compute λ (lambda) values according to NTC:2018.

⑪ Run Fatigue Analysis – The plugin calculates equivalent stress, damage index, and fatigue safety.

⑫ View Fatigue Results – Results may include stress range comparisons, correction factors, or fatigue safety factors depending on the selected fatigue case.

⑬ Save Fatigue Results – Save the current analysis result and export it for reporting or further review.

Detail Input Guide for "Concrete Compression (Simplified Method)"

Page 1: Fatigue Settings

Case name
Name of the fatigue case (auto-generated: case_001, case_002 …)
fck (MPa)
Characteristic compressive strength of concrete
σc,max (MPa)
Maximum compressive stress in concrete
σc,min (MPa)
Minimum compressive stress in concrete

^{※ Note: Both σc,max and σc,min must represent compressive stresses only. If either value is ≤ 0 (tensile stress or zero), the case is excluded from evaluation.}

Detail Input Guide for "Concrete Shear (Not Require Reinforcement)"

Page 1: Shear Force Settings

Case name
Name of the shear force case (auto-generated: case_001, case_002 …)
Vsd,max (kN)
Maximum shear force in the girder (imported from MIDAS Civil load combinations containing CB)
Vsd,min (kN)
Minimum shear force in the girder (imported from MIDAS Civil load combinations containing CB)

^{※ Note: Both Vsd,max and Vsd,min must represent valid shear force values from concrete design load combinations (CB). If no such combinations exist or values are invalid, the case will be excluded from evaluation.}

Page 2: Section Properties

d (mm)
Effective depth of section
bw (mm)
Web thickness of girder
Qn (mm³)
First moment of area
J (mm⁴)
Moment of inertia
Vrd,c (kN)
Shear resistance of section

^{※ Note: Section properties are auto-loaded from the selected girder element only if the section includes a concrete tension part. If the section type does not satisfy this condition, users must enter the values manually. For convenience, the}^{Section Property Calculator}^{can be used to obtain the required values. and calculate shear}^{resistance manually}

Detail Input Guide for "Concrete Shear (Require Reinforcement)"

Page 1: Fatigue Settings

Case name
Name of the fatigue case
Span length, L (m)
Effective span length
Effective height, d (mm)
Effective depth of the section.
Shear load, Vsd (kN)
Shear load imported from MIDAS NX

Page 2: Fatigue Parameters

Shear reinforcement type
Stirrup or Others.
Mandrel diameter(mm)
Mandrel diameter for shear reinforcement.
Number of arms
Number of legs of shear reinforcement.
Shear reinforcement diameter (mm)
Diameter of shear reinforcement bar.
Shear reinforcement pitch (mm)
Spacing of shear reinforcement bars.

Traffic condition (Road bridges only)

Number of tracks, Nc
Traffic type: Long distance, Medium distance, Local traffic
Pavement roughness: Good / Medium
Support type: Continuous Beam, Single Span Beam, Carriageway Slab
Traffic category: Category 1~4 (auto-sets Nobs/year)

Traffic condition (Railway bridges only)

Number of tracks, Nc
Traffic type: Standard traffic, Heavy traffic
Tons of trains per year per track, Vol
Support type: Simply supported, Continuous beams (mid span / end span / intermediate support)

Page 3: Correction Factors

λc0 ~ λc4
Correction factors
Road: λs = φfat · λs1 · λs2 · λs3 · λs4
Railway: λs = λs1 · λs2 · λs3 · λs4
φfat
Fatigue factor linked to pavement roughness (Road only).

Detail Input Guide for "Steel Girder (Direct Stress)"

Page 1: Fatigue Settings

Case name
Name of the fatigue case
Span length, L (m)
Effective span length
Detail category
Select from standard categories (e.g., 160, 140, 125, …). Determines nominal fatigue stress range Δσ_amm.
Nominal fatigue stress range, Δσ_amm (MPa)
Automatically set based on the detail category.
Direct Stress Input
Import from MIDAS Civil NX or enter manually.
Railway bridges: Requires both Δσ₁ and Δσ₁₊₂.
Road bridges: Requires Δσ₁ only.

Page 2: Correction Factor

Railway bridges / Road bridges

λc0 ~ λc4
Correction factors
λs (Total correction factor)
Calculated as λ₁·λ₂·λ₃·λ₄, but limited by λmax.

^{※ Note: λs is auto-calculated. If λs > λmax, the value is capped at λmax.}

Detail Input Guide for "Steel Girder (Shear Stress)"

Page 1: Fatigue Settings

Case name
Name of the fatigue case
Span length, L (m)
Effective span length
Detail Category (Shear)
Detail category for shear detail (default: 100 or 80).
Nominal fatigue stress range, Δτ_amm (MPa)
Assigned automatically from the selected detail category.
Shear Stress Load, Δτ₁ (MPa)
Imported from MIDAS Civil (static load case) or manually input.

^{※ Note: Only static load cases can be imported. Moving loads must be converted to static loads before use. MIDAS NX option “Analysis / Main Control Data / Calculate Equivalent Beam Stresses” must be enabled.}

Detail Input Guide for "Concrete Compression (Damage Equivalent Stress Method)" (Railway Only)

Page 1: Fatigue Settings

Case name
Name of the fatigue case
fck (MPa)
Characteristic compressive strength of concrete
Span length, L (m)
Effective span length
σc,max,71 (MPa)
Maximum compressive stress in concrete (imported from MIDAS Civil results)
σc,perm (MPa)
Permanent compressive stress in concrete (imported from MIDAS Civil results)

^{※ Note: Both σc,max,71 and σc,perm must be greater than 0. If either value is ≤ 0, the case will be excluded from evaluation.}

Page 2: Fatigue Parameters

Vol
Tons of weight trains passing per year per track
Nc
Number of trains considered for fatigue analysis
Traffic Type
Selection of traffic category (Standard traffic, Heavy traffic)
Support Type
Structural support condition (Simply Supported, Continuous mid span, End span, Intermediate support area)
Analysis Zone
Stress evaluation zone (Compression zone, Precompressed tensile zone)

Page 3: Correction Factor

Δσ₁ (MPa)
Stress range due to Load Model 71 on a single track
Δσ₁₊₂ (MPa)
Stress range due to Load Model 71 on two tracks
λc0 ~ λc4
Correction factors
λc
Overall correction factor (product of λc0 ~ λc4)

Detail Input Guide for "Reinforcing Steel (Damage Equivalent Stress Method – Railway)"

Page 1: Fatigue Settings

Case name
Name of the fatigue case
Span length, L (m)
Effective span length
Concrete compressive strength, fck (MPa)
Characteristic compressive strength of concrete.
Steel modulus, Es (MPa)
Elastic modulus of reinforcing steel.
Concrete modulus, Ec (MPa)
Elastic modulus of concrete.
Effective depth, d (mm)
Effective depth of the section.
Crack state detection
Option to determine whether the section is cracked or non-cracked.
Manual: User directly selects “Non-cracked section” or “Cracked section”.
Auto: System calculates fb from construction stage stress data and compares with fctd.
If fb > fctd → Section is treated as Cracked.
If fb ≤ fctd → Section is treated as Non-cracked.
Fatigue load import
Non-cracked section: Requires tensile stress values (Δσ₁, Δσ₁₂).
Cracked section: Requires bending moment Msd (kN·m).

Page 2: Steel & Traffic Conditions

Steel type
Selection of reinforcing or prestressing steel type (e.g., straight bars, welded bars, tendons).
ΔσRsk (MPa)
Characteristic resisting stress range of steel. Auto-calculated based on steel type.
A (mm²)
Steel area (for cracked section input).
n
Number of steel elements (for cracked section input).
Nc
Number of tracks considered in the fatigue analysis.
Vol
Tons of weight trains passing per year per track.
Traffic type
Traffic category (Standard traffic or Heavy traffic).
Support type
Structural support condition (Simply supported, Continuous beams – mid span, end span, or intermediate support).

Page 3: Correction Factor

λs1 – λs4
Individual correction factors calculated
λs
Total correction factor, product of λs1 – λs4.

^{※ Note: Correction factors are auto-calculated, but can be manually overridden if auto-calculation is disabled.}

Detail Input Guide for "Reinforcing Steel (Damage Equivalent Stress Method – Road)"

Page 1: Fatigue Settings

Case name
Name of the fatigue case.
The system automatically generates a unique ID when a new case is created.
If the user edits an existing case, the current ID is reused.
Span length, L (m)
Effective span length of the girder.
Input is required to determine λs1 (correction factor depending on span and support type).
Effective depth, d (mm)
Effective depth of the section.
Used in stress range calculation (especially for cracked sections where bending moment is imported).
Concrete compressive strength, fck (MPa)
Characteristic compressive strength of concrete.
Used to calculate tensile strength fctd for crack state detection.
Steel modulus, Es (MPa)
Elastic modulus of reinforcing steel.
Used together with σc,traz and Ec to evaluate equivalent stress in non-cracked sections.
Concrete modulus, Ec (MPa)
Elastic modulus of concrete.
Used in the same way as Es for stress transfer between concrete and steel.
Crack state detection
Auto/Manual toggle.
Auto: Crack state is determined by comparing the combined stress fb (from MIDAS load import + tensile stress) against the tensile resistance fctd.
If fb > fctd → section is marked as Cracked.
If fb ≤ fctd → section is marked as Non-cracked.
Manual: User directly selects Non-cracked section or Cracked section without automatic evaluation.
Fatigue load import
For Non-cracked: Tensile stress σc,traz [MPa] must be provided. Can be imported automatically from MIDAS or entered manually if import is disabled. This value is multiplied by Es/Ec and λs to calculate equivalent stress.
For Cracked: Bending moment Msd [kN·m] must be provided. Can be imported automatically from MIDAS or entered manually. This value is used along with d, Asteel, and nsteel to compute stress in reinforcing steel.

^{※ Note: Section type (cracked vs non-cracked) must be determined before proceeding, since it changes the fatigue load input type and calculation formula.}

Page 2: Steel & Traffic Conditions

Steel type
Select reinforcing steel or tendon type (e.g., straight/bent bars, welded bars, splicing devices, pre/post-tensioning options).
Steel area, A (mm²)
Cross-sectional area of reinforcing steel (required for cracked sections).
Number of steel elements, n
Total number of reinforcing bars or tendons (required for cracked sections).
Characteristic resisting stress range, ΔσRsk (MPa)
Auto-calculated based on selected steel type (read-only).
Number of tracks, Nc
Total number of traffic lanes considered.
Number of loaded tracks, Nt
Number of simultaneously loaded lanes.
Traffic type
Select traffic category (Long distance, Medium distance, Local traffic).
Road traffic category
Defines the annual heavy vehicle flow category.
Heavy vehicles per year, Nobs
Annual number of heavy vehicles. Auto-calculated if volume auto option is enabled; otherwise input manually.
Pavement roughness
Quality of pavement surface (Good or Medium). Used to determine roughness factor φfat.

Page 3: Correction Factors

λs1 – λs4
Individual correction factors calculated
φfat

Note

Requires MIDAS Civil NX 2025(v2.x)

Conclusion

With this plugin, engineers can conduct fatigue checks for composite bridges quickly and reliably based on Eurocode and NTC:2018. From importing data to generating correction factors and calculating safety ratios, the tool simplifies fatigue design and enhances confidence in engineering decisions.