20/05/2008 LimitState:GEO launch & technology briefing - ICE London 04/06/2014geo1.0 LimitState:GEO...

20/05/2008 LimitState:GEO launch & technology briefing - ICE London 10/04/23 geo1.0

LimitState:GEOLimitState:GEOLaunch event & technology Launch event & technology

briefingbriefing20 May 2008 - ICE London20 May 2008 - ICE London

Matthew Gilbert BEng PhD CEng MICE

Managing Director, LimitState Ltd

Colin Smith MA(Cantab) PhD

Director & LimitState:GEO Product Manager, LimitState Ltd

20/05/2008 LimitState:GEO launch & technology briefing - ICE London

Programme

1. Introduction to LimitState2. LimitState:GEO & how it works3. Verification------------------------------------------ Coffee break------------------------------------------4. Practical Case Study5. Design to Eurocode 76. Closing remarks


Introduction to LimitState


About LimitState

• Striving to:– Provide engineers with an unrivalled suite of fully

supported software for ultimate limit state analysis & design

– Take full advantage of state-of-the-art algorithms & optimization technology

– Ensure applications have industry leading levels of ease of use

– Strong emphasis on robustness and extensive validation


Current Product - LimitState:RING

• Rapid analysis software for masonry arch bridges

• Launched May 2007• Builds on research

software already used in >40 countries

• Clients include:


Current Product - LimitState:RING

• For more details visit:

www.masonryarch.com

• Or attend a LimitState:RING seminar:– May 21st London (IStructE)– June 4th Glasgow– June 25th Dublin

(see website for details)


LimitState:GEO


Context

• Traditional stability analysis techniques are not serving geotechnical engineers well enough!– Single application programs

• E.g. for slope stability; retaining walls etc• Often not very easy to use; engineers need to learn how to

use several programs; each has very narrow applicability

– Complex numerical analysis programs• E.g. based on non-linear finite element• Powerful and flexible but numerous input parameters; careful

tuning needed to avoid numerical stability problems; arguably too cumbersome for routine use


Where does LimitState:GEO fit in?

Hand calculations / simple programs

Limit Equilibrium

Geotechnical Category 2

Numerical limit analysis

Geotechnical Category 2+

Non-linear finite elements

Complex material models

Geotechnical Category 3

• more complex

• more input parameters

• more expertise required

• [potentially] more accurate

LimitState:GEO


Example application: slope stability

• Traditional methods still dominate: – over 40 commercial slope

stability programs listed at www.ggsd.com


• Typical LimitState:GEO solution:

• i.e. more complex failure mechanisms may be critical!

Example application: slope stability

20/05/2008 LimitState:GEO launch & technology briefing - ICE London geo1.0

Example applications: footings & tunnels


Example applications: combined problems

Combination problem with weak underlying layer

Combination slope stability / gravity wall / footing


Any other geometry…

LimitState:GEO can model any geometry and any set of boundary conditions. The above example shows a solution available in the literature compared with the solution derived using LimitState:GEO.

LimitState:GEO solutionGunn’s (1980) 3-variable block mechanismAnchor in cohesive soil


LimitState:GEO: how it works…


How does it work?• At collapse a soil mass will break up into a series of

individual blocks of soil• LimitState:GEO uses novel numerical limit analysis

technique Discontinuity Layout Optimization (DLO) to find the optimal arrangement of sliding blocks

• Outcome of University of Sheffield / EPSRC funded research:– Layout optimization research since 2000– Discontinuity layout optimization research since 2005– DLO paper published Proc. Royal Society A in 2007


How does it actually work?• The problem is initially formulated

not in terms of soil blocks (or ‘elements’) but in terms of the lines of discontinuity between them

• The critical layout of these lines is determined using rigorous optimization techniques

discontinuity layout optimization

• The steps in the process will now be outlined


Step 1: discretize using nodes


Step 2: connect nodes to form a set of potential discontinuities


Step 3: setup optimization problem

• Upper bound (‘mechanism’) formulation:– Find minimum multiplier on specified loads (margin of

safety, or ‘adequacy factor’) • Subject to nodal compatibility constraints:


Step 4: solve & display!

• Problem is a simple linear optimization problem (easy to solve)

• After solving can identify and then deform solid blocks to help interpretation:


Key points:

1.Central to DLO method is that discontinuities can crossover• Therefore get many

more elements for our money

2.More nodes gives more accurate solution

3.Frictional materials & self weight present no special difficulties


More advanced usage

• Can also treat many other types of problem, e.g containing:– Rotational failure mechanisms– Pre-existing slips– Structural elements– Etc etc.


Questions?

20/05/2008 LimitState:GEO launch & technology briefing - ICE London 04/06/2014geo1.0 LimitState:GEO...

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