raft and soil-structure interaction pdisp and gsa raft

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Raft and Soil-Structure InteractionPdisp and GSA Raft


Peter Debney

Senior Consultant

Today’s Team


1. Viewer Window 2. Control Panel

Raft and Soil-Structure Interaction

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Agenda

• Product demonstration• Pdisp• GSA Raft

• Questions and Answers

NB: this webinar is designed as an introduction to Pdisp and GSA Raft and to provide an overview of functionality. If more is required then it can be done at a later date on an individual basis.


Who is Oasys?

• Wholly owned by Arup

• Formed in 1976 to develop software for in-house and external use

• Most developers are engineers who have moved to programming

• In recent years have added marketing and sales staff

• Since 2003 have expanded the development team worldwide


Oasys Customers


Structural

Geotechnical

CAD

Document Management

Sustainability

Crowd simulation


Soil Settlement and Soil-Structure Interaction Pdisp & GSA Raft


Soil settlement and Soil-Structure interaction – is it a problem?


What structures are affected?

Ground stiffer than structure – No



Structure stiffer than ground – No



Ground & structure similar stiffness– Yes

Structure sensitive to movement– Yes


How does Pdisp and GSA Raft work?


What is Pdisp?

• Calculates soil displacements under load

• Uses• Boussinesq (gives

stresses and displacements in soil)

• Mindlin (gives displacements only)


What is GSA?

• Structural finite element analysis

• Linear and non-linear static

• Vibration• Buckling• Bridge loading• Form finding• Element design• Soil-structure interaction


What is GSA Raft?

• Combination of GSA and Pdisp

• Soil-structure interaction:• Vertical for rafts• Vertical & Horizontal for piles

• Choice of methods• Boussinesq (rafts)• Mindlin (rafts and piles)

• Iterative process


GSA – Pdisp Iteration Solution

1. GSA assumes a spring stiffness

2. GSA analyses to get soil pressures & displacements

Soil pressure: p = f / AIf p < pmin then p = pmin

If p > pmax then p = pmax

3. Pdisp analyses spring forces to get soil settlements

4. GSA calculates new spring stiffnesses from forces & settlements

5. Repeat from 2 until GSA and Pdisp movements converged


Soil Data

• Define soil properties in the vertical direction

Top levelEtop mEbot

rigid level – deformation below is ignored

Etop

mTop level

Ebot

Etop

m

Top level

Ebot

Layer 1

Layer 2

Layer 3


Soil Data

• Define Soil Zones in plan

Zone 1 (profile i)

Zone 2 (profile j)

Zone 3 (profile k)


Schematic view of piled-raft model

raft

piles

Non

-line

ar S

prin

gs

Soil

Soil

See next slide


sy.b

Bx

By

Hsx

sy

tz

tz

sy.t

A pile section:represented by a single node on pile


Non-linear soil springs

• Every nodes on the piles are connected by 3 non-linear springs to represent the soil non-linear behaviour immediately around the piles in x, y & z directions. The non-linear springs are then attached to the ground (soil). The soil is still considered as elastic media that the settlements are calculated using Mindlin method

A node on pile

Representing soil: they all coincide with the node on pile

Non-linear springs with interaction

forces Fx, Fy & Fz


Interaction Forces

• The interaction forces in the non-linear springs will be the interaction forces between pile and soil

• The interaction forces equal the pile-soil contact stress times the interaction area, i.e.

zzz

yyy

xxx

AF

AF

AF


Pile-Soil Contact Stresses

• The pile-soil contact stresses equal pile-soil

interaction coefficient C times the soil strength, i.e.

zzz

yyy

xxx

fc

fc

fc


Pile-Soil Interaction Coefficient

• The pile-soil interaction coefficient C shown below, is a function of:1. The relative displacements between piles and soil at

the relevant pile point2. The dimensions of the piles

1.0

-1.0

dx/By etc

c


Pdisp and GSA Raft in action


GSA Raft Case study


Aspire Tower, Doha, Qatar

http://www.oasys-software.com/casestudies?id=14/


Any Questions?


Contact us: [email protected]

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raft and soil-structure interaction pdisp and gsa raft

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