Modelling Philosophy Series of instructions cook-book (training - - PDF document

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Modelling Philosophy Series of instructions cook-book (training - - PDF document

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4/06/2020 ENGINEERING IN THE PUB 2020 Finit Finite Elem Element Analy Analysis sis Softw Software Emil Jankulovski Director, Inducta 1 Modelling Philosophy Series of instructions cook-book (training > skills)

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4/06/2020 1 ENGINEERING IN THE PUB 2020

Finit Finite Elem Element Analy Analysis sis Softw Software

Emil Jankulovski – Director, Inducta

Modelling Philosophy

 Series of instructions “cook-book”

(training > skills)  Understanding of the principles and underlying theory and awareness of the issues. (education > knowledge)

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Computer Modelling Modelling: Definition

  • Devise a representation, by an appropriate simplification of reality, of a

phenomenon or system.

  • Engineering Modelling – 2 Parts

1) Physical / Empirical Modelling:

  • used to develop equations to describe the physical reality
  • e.g. laboratory tests, scale wind tunnel tests

2) Theoretical Modelling:

  • using a mathematical model of the phenomenon or system based on relevant underlying

assumptions to predict its behaviour before it occurs.

  • e.g. theory of elasticity, finite element computer analysis.

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Modelling: Definition

  • Mathematical Model: description of a physical event using mathematical

concepts by identifying the parameters that influence the physical reality and constructing relationships between these parameters.

  • Analytical Model / Solution: mathematical models that have a closed form solution (can

be expressed as a mathematical analytical function).

  • Numerical Model / Solution: mathematical models that use numerical stepping procedure

to obtain the phenomenon or system’s behaviour at a point in space and time.

  • Computer Modelling: simply modelling with the assistance of computer.

Modelling Procedure

Physical Event: An occurrence in nature Theoretical Model 2) Mathematical Problem: Given a case, find the results of interest within the mathematical model. e.g. numerical solution (finite element) or, an approximation 3) Implementation of Numerical Solution: Numerical solution of the mathematical problem e.g. making the model in the software and analysing Analytical Solution E.g. Frame model approximation

(loss of information, accuracy)

Physical Model 1) Mathematical Model: Description of physical event e.g. theory of elasticity 4) Interpretation

  • f Results

(loss of information, accuracy)

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Structural Modelling: The Challenge

  • Predict structural response of a non‐existent structure.
  • Response: behaviour under different loading conditions.
  • Main Concerns:
  • Accuracy
  • Efficiency
  • Computer model only as accurate as the mathematical model.

Wall stresses

Mathematical Problem

Building’s Response Under Earthquake Loading

Δ M S Numerical Solution: 3D Dynamic Spectral Analysis Analytical Solution: Stick 2D cantilever Multiple mode shapes Spectral curve Equivalent Static EQ Load …or

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Structural Modelling Using Software

“Black Box” Computer Software

  • FEA Theory
  • Engineering Theory

?? Input ?? ?? Output ?? ?

Why FEA Software is considered to be a “Black Box”

  • FE Theory is complicated.
  • Numerical solution of higher order partial differential equations.
  • Results of complex structural systems can be difficult to rationalise.
  • Implementation is complicated.
  • Must use computer programs.
  • Technology is still inaccessible to / avoided by some.
  • Insufficient education.
  • Lack of knowledge of more complex engineering principles.
  • Plate Theory
  • Dynamic Analysis
  • Hesitation to use / trust FEA.

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Design Codes – making things more confusing

  • Insufficient and confusing instructions for some cases.
  • Prone to interpretation.
  • Too complicated.
  • Incomplete
  • Many gaps
  • Too old
  • Does not reflect current design practice and state of the art of science
  • Not sufficient for buildings.

Modelling Process – How it is commonly perceived

Computer Software Results

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Modelling Process – Reality

Computer Software

Results knowledge experience Imaginary structure Structural system Review Software features

Two Major Aspects in Modelling

  • Overall Philosophy / General Approach e.g.
  • stick model (1D) or 2D or 3D model
  • linear vs non‐liner analysis
  • Details e.g.:
  • column ends rigid link
  • how to model the header beam
  • how to model the soil
  • stiffness of elements
  • other items covered in “Modelling Specific” Section

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Finite Element Analysis Overview

Basic Basic Concep Concept ‐ Stif Stiffn fness ess

𝐿 · 𝑣 𝑄 𝐿 𝐵 ∗ 𝐹 Solve for u (unknown) 𝑣 𝑄 𝐿 Once u is known, calculate internal stresses: ε 𝑣 𝑀 𝜏 𝐹ε P u L A,E

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Degr Degrees ees of

  • f Fr

Freedom eedom Fr Fram ame Elem Element (B (Beam and and Colum Column)

2D 3D 12 12 2 4 6 2

2D 2D Str Stress ss Pr Problems ms

In‐plane stresses

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Pla Plate Bending Bending Com Combina natio tion Mo Model del

2D stress Truss Frame Plate

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FE FE Pr Procedure ure – S – Structure D. D.O.F.

1 2

u

3 4 7 8 5 6

FE FE Solution Solution – S – Stiffness Assem Assemble le

𝐿

i

7

1 2 3 4 𝐿 1 2 … 7 … u 1 2 … 7 … u 1 2 3 4 1 2 3 4

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FE FE Solution Solution ‐ ... ... Unkno Unknowns ns

𝐿 𝑣 𝑄 𝑣 𝑣 𝑣 ⋮ 𝑣 … … … … … … ε 𝑔 𝑣 𝜏 𝑔ε, 𝑣 Use σ for strength design

Solve: Deformations Derive: Internal Forces Known: Structure (stiffness) Loading

Reference Books

Finite Element – Fundamental Theory and Numerical Solutions

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Reference Books

Theory of Elasticity and Plates and Simple Stress Analysis

Reference Books

Practical guidelines for finite element modelling

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FEA Software

Software for Structural Analysis and Design

  • Which software is better:
  • Which software is more accurate:
  • Which software is easy to use:
  • Modelling speed:
  • Complexity:
  • Familiarity:
  • Widely accepted:
  • Integrated design:
  • Do the design features reflect local practice:

         General purpose or problem specific?

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Software Types

Analysis Integrated Design Manual Design General Purpose FEA

  

Problem Specific (Buildings)

     

The Ideal Approach to Structural Modelling

Two models Two different software Two different engineers …Compare results

  • Expensive
  • Time consuming
  • Too hard to match
  • Difference in underlying assumptions:
  • Modelling assumptions of the engineer
  • Varying built‐in settings of different software.
  • Conflicts: which set of results to use/trust?

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Modelling Review/Check

Model 1 Model 2

2 Models / Different software:

Discussion

3 People:

Modeller 1

(Junior)

Modeller 2

(Senior)

Supervisor

Consensus

Structural Modelling: Approach

  • Several Models of increasing complexity
  • Start with simple models (prelim design)
  • Quickly understand the general behaviour of the structure.
  • Hard to rationalise the results of complex models.
  • Seemingly simple structures can have complex load paths for example.
  • Several iterations of the structural model as the design

progresses.

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How to check the results?

  • Understand structural response (behaviour)
  • Sensitivity analysis
  • Vary input parameter to determine overall effect on final results
  • Simple hand calculation
  • Does not always match complex model (FEA vs stick cantilever)
  • Start with simple, increase complexity
  • Some results cannot be checked

The model has to be as simple as possible, but sufficient to capture the behaviour used in design.

Modelling Specific Details

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Modelling Specifics

  • Structural system
  • Elements
  • Connections
  • Supports
  • Stiffness

Stiffness Manipulation

Pin‐pin column Slab 10% of Igross Walls work hard

?

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Stiffness manipulation can “hide” problems

  • The model does not represent the structure
  • Walls are over‐designed
  • Columns are under‐designed:
  • No M in columns
  • Increased N due to overturning
  • No clear understanding of the structural response

Suggested Modelling Approach

  • No stiffness manipulation
  • Model to capture the structural response as closely as

possible.

  • Apply safety (conservatism) at the very end on the final

results.

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Final Remarks on Structural Modelling

  • Minimum complexity to capture structural response
  • Do not “skew” the model (no stiffness manipulation)
  • Understand structural response
  • Apply conservatism at the end of modelling to the entire

structure.

Version 2.0: Coming July / August 2020

  • New Graphics Engine:
  • Improved CAD & Bitmap importing.
  • Displaying results, mesh and colouring is

faster.

  • Editing features are faster and more

intuitive to use.

  • Cleaner model can be created faster than

ever before!

  • Available for RCB, SLB and PTD.
  • Version 2.0 update is free for all users

with an active license.

  • Contact info@inducta.com.au for a

free trial.

Column Scheduling in RCB

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