CVEEN Table of Contents

Transcription

1 CVEEN 7330 Table of Contents Table of Contents... 1 Objectives:... 2 FLAC Input:... 3 Model Inputs... 3 Create Grid and Assign Properties... 4 Create Foundation... 4 Create Forcing Function... 4 Create Dynamic Boundary Conditions and Assign Damping... 4 Apply Forcing Function... 4 Create Histories of Output... 5 Solve and Save Output... 5 Required Outputs from FLAC:... 6 Required Calculations and Discussion:... 6

2 Objectives: This model uses FLAC to calculate pressure and displacement time histories for a machine foundation undergoing sinusoidal loading.

3 FLAC Input: Figure 1. Boundary conditions for model. Model Inputs This subroutine called setup establishes the inputs for the model. These variables are later assigned in other parts of the FLAC code to execute the model. config dynamic set dynamic on def setup; defines constants stress_amp = 0.1e6 ; Stress amplutde (0.1 Mpa = 1 tsf) frq_cent = 10 ; Forcing frequency in hz per = 1.0 / frq_cent ; Period omega = 2.0 * pi * frq_cent ; circular frequency ftglength = 10 ; out-of-plane length of ftg. soil_den = 2000 ; soil density vs_soil = 150 ; shear wave velocity sh_mod = soil_den*vs_soil*vs_soil ; shear modulus

4 po_rat = 0.4 ; Poisson's ratio bu_mod = sh_mod*(2.0*(1.0+po_rat))/(3.0*( *po_rat)); Bulk modulus end setup Create Grid and Assign Properties g ; creates 20 x 10 grid gen 0,-20 0,0 40,0 40,-20 ; maps grid to 20 x 40 x-y space m e ; declares grid as elastic ; prop den=soil_den shear=sh_mod bulk=bu_mod ; assigns soil properties Create Foundation struct prop=1 e=1 i=1 a=1 den=1e-3 ; declares structural properties struct beam beg grid end grid ; creates beam struct beam beg grid end grid ; creates bean struct node 2 slave y 1 ; collapse beam to 1DOF in y-direction struct node 3 slave y 2 Create Forcing Function def s_wave s_wave = sin(omega * dytime) end Create Dynamic Boundary Conditions and Assign Damping app xquiet yquiet i=1 app xquiet yquiet i=21 app xquiet yquiet j=1 apply ff i 21 ; set dy_damp rayl 0.05 frq_cent ; 5 percent Rayleigh damping for material damping ; 3D radiation damping set 3d_damp ff=2 set 3d_damp on set 3d_damp width=ftglenfth Apply Forcing Function

5 app syy=stress_amp hist=s_wave i=11,12 j=11 Create Histories of Output hist dytime hist syy i 11 j 10 ; pressure history top soil under ftg. hist syy i 11 j 5 ; pressure history middle soil under ftg. hist syy i 11 j 1 ; pressure at base of soil under ftg. hist syy i 5 j 10 ; pressure at 5 m from ftg top of soil hist syy i 5 j 5 ; pressure at 5 m from ftg middle. of soil hist syy i 5 j 1 ; pressure at 5 m from ftg. bottom of soil. hist ydis i 11 j 11 ; y disp of ftg. hist ydis i 5 j 11 ; y displace 5 m from ftg Solve and Save Output solve dytime 2 save model5.sav 'last project state'

6 Required Outputs from FLAC: These plots should be prepared for a 5 tsf oscillating vertical load at 8 Hz on a 4-m wide strip footing. Assume that the shear wave velocity of the soil is 150 m/s, Poisson s ratio is 0.4 and the mass density of the soil is 2000 kg/m 3. In this solution, you must incorporate the dynamic effects on the soil stiffness by adjusting the shear modulus. 1. Plot of model with boundary conditions and applied load 2. Pressure vs. time plot at top of soil for center of footing. 3. Pressure vs. time plot at middle of soil profile for center of footing. 4. Pressure vs. time plot at bottom of soil profile for center of footing. 5. Pressure vs. time plot at top of soil for horizontal distance 10 m from edge of footing 6. Pressure vs. time plot at middle of soil profile for horizontal distance 10 m from edge of footing. 7. Pressure vs. time plot at bottom of soil profile for horizontal distance 10 m from edge of footing. 8. Displacement vs. time plot at top of soil for center of footing. 9. Displacement vs. time plot at surface for a horizontal distance of 10 m from edge of footing. 10. FLAC Code Required Calculations and Discussion: 1. Calculate the fundamental period of the soil model (assuming it is 1D). 2. Repeat plots 8 and 9 above by changing the frequency of vibration from 8 to 16 and 32 Hz. Discuss how the change in frequency of vibration has affected the displacements. 3. Repeat plots 8 and 9 by changing the length of the footing to 5 m and 2 m and the keeping the frequency of vibration at 8 Hz. Discuss how the change in the finite footing has affected the displacements at 10 m from the footing compared to the infinite case. (Note that these footing sizes can no longer be modeled using a plane-strain 2D model such as FLAC2D without adjustments. See Ch. 15 of Foundations Engineering by Gazeta to determine the correct shear modulus to input into the model.)