BE4E PLPAK Towards more realistic structural modeling

Transcription

1 BE4E PLPAK Towards more realistic structural modeling Eng: Mahmoud El Galad BE4E Lecture 05 EHSPAK Page 01

2 Table of content for lecture 5 Elastic Half Space Package (EHSPAK) - Soil modeling introduction. - Single layer models. - Two parameter models. - Elastic Half Space models. - Multi-layer analysis using Elastic Half Space. - How can the user make a model using EHSPAK? - What are the differences between Winkler & EHS models? - Practical example. Lecture 05 EHSPAK Page 02

3 Soil Modeling introduction Soil Models Multi-layer model Single layer model Solving as elastic model As Elastic Half Space. Single Parameter model As Winkler models Two Parameters model As Pasternak & Hetenyi models Elastic model As Elastic Half Space. Lecture 05 EHSPAK Page 03

4 Single layer model The most common soil model is Winkler model. The Winkler model is very suitable to be coupled with finite element models, as it is based on converting the soil media into discrete springs that can be added directly at the finite element nodes. There are two disadvantages for the Winkler models: - The Winkler model assumes that displacement occurs only at loaded springs and that the load has no effect on distant spring. - The other disadvantage is that Winkler model accuracy is greatly dependant on the value of the spring constant utilized and this value is normally retrieved from empirical data that has very wide ranges. Lecture 05 EHSPAK Page 04

5 Two Parameter models To improve the disadvantages of one parameter models, the two parameter models are created to model the soil support. The two parameter models include the shear modulus effect of the soil (Pasternak) or membrane effect (Hetenyi). The two parameter models have two problems: - The mathematical complexity. - The spring constants calculated are dependant on foundation shapes and applied loads. To improve this methodology the ACI recommend to use the Elastic Half Space method. This method models considered the soil as three-dimensional elastic medium. To achieve the elastic properties of the soil there are three assumption should be taken into consideration: - Soil has linear properties. - Soil has elastic properties. - No pore water present. Lecture 05 EHSPAK Page 05

6 Elastic Half Space models In the elastic half space there are three different elasticity solutions: Boussinesq, Mendlin, Steinbrenner. EHS model schematic Displacement calculated at different depths Infinite soil layer/ support on layer Load Boussinesq Infinite soil layer No Infinite soil layer Load Mindlin Infinite soil layer Depth Z Yes Infinite soil layer Load Steinbrenner Depth Z Yes Support on rigid base Rigid layer Lecture 05 EHSPAK Page 06

7 Multi layer analysis using Elastic Half Space In practical applications, it is very rare to find soil medium with a layer thick enough to consider it as alone as the supporting element. There are three different methodologies for calculating the stiffness of multi layer soil: 1- Staviridis method: Soil layer 1 E=E 1 V=V 1 Soil layer 2 E=E 2 V=V 2 = - + Soil layer 1 E=E 1 V=V 1 Soil layer 1 E=E 1 V=V 1 Soil layer 2 E=E 1 V=V 1 This method adopts a superposition scheme to calculate the equivalent soil stiffness Lecture 05 EHSPAK Page 07

8 Multi layer analysis using Elastic Half Space 2- Bowles method: Soil layer 1 E=E 1 Depth h 1 V=V 1 Soil layer 2 E=E 2 Depth h 2 = = Stiffness = K 2 Stiffness = K 1 V=V 2 Stiffness = K This method calculate the equivalent soil stiffness using the weighted average method. Lecture 05 EHSPAK Page 08

9 Multi layer analysis using Elastic Half Space 3- Equivalent spring method: Soil layer 1 E=E 1 V=V 1 Soil layer 2 E=E 2 V=V 2 Depth h 1 Depth h 2 = = Stiffness = K 2 Stiffness = K 1 Stiffness = K This method is simply calculate the equivalent soil spring by modeling the layers as springs connected in series. Lecture 05 EHSPAK Page 09

10 How can the user make a model in EHSPAK? The same steps of Winkler model until the user draw the soil support. Define model information, Define slab and load elements. Check the boundary element model in PLView. Draw rectangular soil support From point A B C D D C A B Lecture 05 EHSPAK Page 10

11 How can the user make a model in EHSPAK? Change the soil stiffness to any ve value, this value should be greater than 5 times slab thickness. Check soil division before going to core manager (PLCoreMan). Lecture 05 EHSPAK Page 11

12 How can the user make a model in EHSPAK? Open the PLCoreMan by pressing on run tab. OR From the PLCoreMan, open the EHSPAK from run menu. Lecture 05 EHSPAK Page 12

13 How can the user make a model in EHSPAK? The user should insert the dimension of the rectangular raft and insert the number of division in both X & Y-directions. There is an important note: the value of K3 should as same as the value defined in the PLGen. The user should insert the soil properties in EHSPAK Choose the type of solution mode theory and layers. Lecture 05 EHSPAK Page 13

14 How can the user make a model in EHSPAK? Save the soil file then compute soil stiffness. After running EHSPAK, open the PLCoreMan then run the model. Lecture 05 EHSPAK Page 14

15 How can the user make a model in EHSPAK? Open the PLPost to view the results. Show the soil reaction. Moment in X-direction Moment in Y-direction Lecture 05 EHSPAK Page 15

16 How can the user make a model in EHSPAK? Strip analysis. Rectangular contour. Lecture 05 EHSPAK Page 16

17 What are the differences between Winkler & EHS models? EHS model (moment in X- direction) Winkler model (moment in X-direction). Lecture 05 EHSPAK Page 17

18 What are the differences between Winkler & EHS models? EHS model (soil support reactions) Winkler model (soil support reactions). Lecture 05 EHSPAK Page 18

19 Practical Example In this practical example we are going to learn how can we use elastic half space model in non-rectangular raft. Lecture 05 Practical Example Page 19

20 Practical Example Slab Borders in AutoCAD and 4 points to draw the soil support. Columns & shear walls. Lecture 05 Practical Example Page 20

21 Practical Example Saving file as (.Dxf) then import file form PLGen. Adjusting Material properties, Load cases & Model information. Lecture 05 Practical Example Page 21

22 Practical Example Define the slab, then Define the column and shear wall loads. Define Slab Properties Define Column loads Define Wall loads Lecture 05 Practical Example Page 22

23 Practical Example D C Soil support properties A B Draw Soil support from point A B C D Lecture 05 Practical Example Page 23

24 Practical Example Check boundary element model from PLView. Lecture 05 Practical Example Page 24

25 Practical Example Form run tab open the PLCoreMan, then from run menu open EHSPAK. Lecture 05 Practical Example Page 25

26 Open the PLPost to show the straining actions. Practical Example Soil support reactions. Moment in X-direction Lecture 05 Practical Example Page 26

27 Practical Example Moment in Y-direction Straining action on strip. Lecture 05 Practical Example Page 27