steel truss load assessment using fea to as 5100 plus

Steel Truss Load Assessment using FEA to

AS 5100

Plus (bonus) – Sensors and FLA

Steel Truss Load Assessment for Aging Bridges using FEA and AS5100:2017

The Want

The Method

Old style

AS 5100 2017

Validation

The Result

Limitations

2

Outline


QR operate/maintain a series of steel truss bridges over major

water crossings from Brisbane to Cairns – North Coast Line

(NCL)

The bridges vary in age, from circa 1880’s to 1960’s

Load rating and remnant life assessment required

Traditional methods too conservative or limited

As-is condition

3

The Want


Disclaimer – I was part of the project team, but I did not drive

ANSYS. If you have technical questions about the use of the

software, I will take that on notice and refer to my colleagues.

Example for 80 foot truss

Some may recognise the truss from David’s presentation – part

of a multi-faceted project (sub-structure, bearing replacement,

remediation etc).

4

The Want


The Want


Rockfield scope

Create full 3D solid models and FE models of 3 unique truss

spans

Analyse and load rate to AS5100.6

Allow for significant corrosion

Instrument with strain gauges and measure for a few months

Calculate remnant life

6

The Want


Beam element model

Solid model

Finite element model

Finite element analysis

Sensors

Fatigue and remnant life

7

The Method


Beam element model

Faster, moving load etc

Familiar

Sanity check

Lower bound capacity estimate

Limitations – joint stiffness, corrosion

Connection design

8

The Method


Solid model

Easier in 3D modelling package

9

The Method


Finite element model

ANSYS

Solid-Shell elements

Fully bonded

connections U.N.O

Beam elements for

simple members

10

The Method

Solid element Shell + beam element


Old style

Modify Young’s

Modulus

Compare beam

capacity FEA vs

hand calc

Adjust stress-strain

curve to suit

11

The Method

AS5100 vs ANSYS results

12

Old style

Capabilities and Project Examples

ANSYS non-linear

buckling analysis

AS5100

Compression test

(Max. compression

force)

738kN 739kN

Moment test (Max

load)

6.8 kN/m 6 kN/m

Force

310UB46, 4m , simply supported, solid element

310UB46, 8m, simply

supported, shell element

UDL

Last converged load=738kN

φNc=739kN (AS4100)


Analysis to AS 5100.6 2017

13

The Method


Modified Stress-strain curve

Soften E a little bit

Factored yield

14

The Method

207

184

225

0

50

100

150

200

250

0 0.001 0.002 0.003 0.004 0.005 0.006

Str

ess [M

Pa]

Strain [με]

Stress-Strain Curves for steel

Original Steel Rivet New Bracing System


Real beams = imperfections

Local = plate buckling e.g. Ms, Ns, V

Global = member buckling e.g. Mb, Nc

15

The Method


Local Imperfections

Linear eigenvalue buckling of critical load cases

Save the mode shape data

Scale the shapes to real displacements

Input to the model – move the nodes to match the scaled shape

Zero stress

16

The Method


Global Imperfection

Push member sideways with a unit UDL to yield lateral

displacement. Restrain all other members.

Scale the displacement

Input to the model – move the nodes to match the scaled

shape

Zero stress

17

The Method


The MethodVerticals Cross Girders Diagonals

Long Girders End Portal Top Chord

Girder

Bracing

Flexural and compression members only.

Tension not important


Non-linear

contacts at special

joints, particularly

out-of-plane

Fully bonded

would be too stiff

19

The Method

Rivets

LG

CG

CGLG

LG angle


Non-linear

contacts at special

joints, particularly

out-of-plane

20

The Method


Corrosion

Scan thickness

survey data and

decide what is

significant

Simplify thickness

loss for modelling

21

The Method


Analysis

Apply PE and wind first

Apply rail traffic in increments

Wheel positions targeting critical members determined from BEA.

Increase rail traffic until solution does not converge i.e. “failure”

22

The Method


Analysis - Identify failure modes

23

The Method


Analysis - Calculate capacity, allowing for DLA and LL factors

If X is positive (X>0), then (1+X)>1.0, and truss has sufficient capacity for 200A loading.

Similar, but not identical to, Load Rating Factor (RF), or Equivalent Ratio Traffic ERT

24

The Method

200𝐴(+) = 𝐺 +𝑊 + 𝑄200𝐴 1 + 𝑋

൯200𝐴(+) = 𝛾𝑔𝑆𝑊 + 𝛾𝑔𝑠𝑆𝐷𝐿 + 𝛾𝑔𝑏𝑇𝐿 +𝑊 + 𝛾𝑄 𝑎𝑥𝑙𝑒200𝐴 1 + 𝛼 + 𝐵𝐹 + 𝑁𝐹 (1 + 𝑋

𝑄 )200𝐴(+ = 𝑄200𝐴 1 + 𝑋


Validation

Strain gauges

Load test

Longer term for Fatigue Life

25

The Method


Compare

measurements

against model

26

The Method

Good shape correlation

FEA magnitudes a little

higher (conservative)


Fatigue/remnant life

Rainflow measured

data

FLA to BS 7608

Select joint classes

Scaling factors for

traffic history, N

27

The Method


Fatigue/remnant life

Model moving load

Critical location not the same as measurement location

Scaling factors for stress, s

Calculate fatigue damage fraction to date

Calculate remaining time to reach damage fraction = 1.0 i.e. remnant life

28

The Method


Improved capacity compared to traditional calculations

BEA – limiting capacity = 0.71 end cross girder (AS-NEW)

FEA – truss capacity = 0.77 (AS-IS)

Better modelling of corrosion affected areas

Good correlation with sensor data

Remnant life assessment based on real usage

29

The Result


In-plane shear connections – too much time and complexity, hand calcs good enough

Time

Modelling

Debugging

Solving

Select load cases

Whole truss rating, not per member

30

Limitations

Thank you.

steel truss load assessment using fea to as 5100 plus

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