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Soil settlement and structure interaction with Pdisp and GSA Raft

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Presentation on theme: "Soil settlement and structure interaction with Pdisp and GSA Raft"— Presentation transcript:

1 Soil settlement and structure interaction with Pdisp and GSA Raft
Oasys

2 Today’s Team Nigel Rees Peter Debney Senior Consultant
Business Development Manager Peter Debney Senior Consultant

3 GoToWebinar Attendee Interface
1. Viewer Window 2. Control Panel Oasys Software : Concrete Design

4 Agenda Product demonstration Questions and Answers
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.

5 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

6 Oasys Customers

7 Geotechnical software
GSA basic concepts Structural software Geotechnical software Document Management software 5 structural 13 geotechnical 2 document management 2 CAD 2 sustainability Other programs produced for internal use CAD software Sustainability software

8 Soil Settlement and Structure Interaction with Pdisp and GSA Raft
GSA basic concepts Soil Settlement and Structure Interaction with Pdisp and GSA Raft

9 Soil settlement and Soil-Structure interaction – is it a problem?
GSA basic concepts Soil settlement and Soil-Structure interaction – is it a problem?

10 What structures are affected?
GSA basic concepts What structures are affected? Ground stiffer than structure – No

11 What structures are affected?
GSA basic concepts What structures are affected? Structure stiffer than ground – No

12 What structures are affected?
GSA basic concepts What structures are affected? Ground & structure similar stiffness – Yes Structure sensitive to movement – Yes

13 How does Pdisp and GSA Raft work?

14 Calculates soil displacements under load
What is Pdisp? Calculates soil displacements under load Uses Boussinesq (gives stresses and displacements in soil) Mindlin (gives displacements only)

15 Structural finite element analysis
What is GSA? Structural finite element analysis Linear and non-linear static Vibration Buckling Bridge loading Form finding Element design Soil-structure interaction

16 What is GSA Raft? Combination of GSA and Pdisp
GSA basic concepts 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 includes the Pdisp engine, so that the analysis can use both engines. You do not need Pdisp but of you do then you gain additional options for GSA 8.3 can analyse rafts GSA 8.4 can now analyse the shear stresses necessary for piled analysis Both methods calculate soil settlements under loads Mindlin, Boussinesq: Boussinesq provides the stress distribution but is in other respects inferior to Mindlin. Boussinesq is sensitive to the user defined number of intermediate calculation layers; this can lead to significant errors, especially for concentrated localised loads. Mindlin is not sensitive to this. Boussinesq relies on the user specifying a global PR which is not less than the local values. Mindlin has a better approximation for this (which probably could also be used in the formulation of Boussinesq). Raft and Piled-Raft analysis are iterative processes linking GSA’s linear static solver for the structure with Pdisp’s non-linear solver for soil settlement

17 GSA – Pdisp Iteration Solution
GSA basic concepts GSA – Pdisp Iteration Solution GSA assumes a spring stiffness GSA analyses to get soil pressures & displacements Soil pressure: p = f / A If p < pmin then p = pmin If p > pmax then p = pmax Pdisp analyses spring forces to get soil settlements GSA calculates new spring stiffnesses from forces & settlements Repeat from 2 until GSA and Pdisp movements converged Add vertical support springs to the nodes on raft that interact with soil (default stiffness Ko = 1.0e7kN/m) Do static analysis of the raft model only to obtain forces Fi & displacements draft at the interaction nodes Calculate the pressure Pi for each of the interaction areas and apply them to soil Pi = Fi/Ai if Pi < Pmin, let Pi = 0 if Pi > Pmax, let Pi = Pmax Do Pdisp (soil settlement) analysis only to obtain soil settlements dsoil at the interaction points Compare dsoil & draft, If the differences between them are smaller than the preset tolerance for all the interaction nodes, STOP, otherwise go to step 6 Update support spring stiffness according to the spring forces and the soil settlements Ki+1 = Fi/ draft Go to step 2

18 Soil Data Define soil properties in the vertical direction m Etop
Top level Etop m Ebot rigid level – deformation below is ignored Layer 1 Layer 2 Layer 3

19 Soil Data Define Soil Zones in plan Zone 2 (profile j)
Zone 1 (profile i) Zone 2 (profile j) Zone 3 (profile k)

20 Schematic view of piled-raft model
GSA basic concepts Schematic view of piled-raft model raft piles Non-linear Springs Soil See next slide

21 A pile section: represented by a single node on pile
GSA basic concepts A pile section: represented by a single node on pile sy.b Bx By H sx sy tz sy.t

22 Non-linear soil springs
GSA basic concepts 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 Non-linear springs with interaction forces Fx, Fy & Fz Representing soil: they all coincide with the node on pile A node on pile

23 GSA basic concepts 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.

24 Pile-Soil Contact Stresses
GSA basic concepts Pile-Soil Contact Stresses The pile-soil contact stresses equal pile-soil interaction coefficient C times the soil strength, i.e.

25 Pile-Soil Interaction Coefficient
GSA basic concepts Pile-Soil Interaction Coefficient The pile-soil interaction coefficient C shown below, is a function of: The relative displacements between piles and soil at the relevant pile point The dimensions of the piles c 1.0 dx/By etc The pile-soil interaction coefficient C needs to be defined by the users at this version of GSA Can be got from American Petroleum Institue RP2A -1.0

26 Pdisp and GSA Raft in action
GSA basic concepts Pdisp and GSA Raft in action

27 GSA basic concepts

28 Any Questions? GSA basic concepts
Now does anyone have any questions? Just write them in the question box in your right hand toolbar. Let me know if there’s some part of the software that you’d like me to go over. Ok well lets see what questions we have. Sorry we don’t have time to answer all your questions right now but we will be answer all your questions by very soon. And if you didn’t get a chance to put your questions in I’ll send out a survey which you can put any additional questions in.

29 Masterclass on Analysis Stages in GSA June 30
GSA basic concepts Next Webinars Masterclass on Analysis Stages in GSA June 30

30 Contact us: oasys@arup.com
GSA basic concepts Contact us:


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