1. Two loading Conditions
Exam 2 – CE S.Ramesh
Two loading Conditions
full water head (hydrostatic pressure) no gravity.
full water head (hydrostatic pressure) with gravity.
f’c=3500psi

2. Finite Element Model (For both Load Cases):

3. Finite Element Mesh (For both Load Cases):

4. Explain your choice of finite element for performing the analysis
2D plane strain is assumed (Length of dam>>>width, height of dam). Loading Conditions are
taken to be constant along the length of the dam.
The varying hydrostatic pressure and only in one side of the dam produces non-uniform moment distribution
along the height of the dam.
Stress and as well as strain distribution is not uniform along the height of the dam.
Non-rectangular elements have to be selected if quadrilateral elements are to be selected because of
the geometry of the cross section of the dam.
Hence, Q8 Element (CPE8R)(which has quadratic strain variation within the element) is better than other
2D elements to represent this model. (Strain is constant within the element in CST, Strain is linear within the
element in LST, The linear variation of the strain does not change along the length of the element in Q4 and
Q6 elements).
Reduced integration is used to reduce the effects from the over stiffness.
Total Number of Elements : 1134
ABAQUS/CAE Version is used for FE analysis.

5. Load and Boundary Conditions (For Load case 1: Hydrostatic Pressure):

6. Load and Boundary Conditions (For Load case 2: Hydrostatic pressure with gravity):

7. Explain the boundary conditions used in the model.
Two loading Conditions
1) full water head (hydrostatic pressure) no gravity.
2) full water head (hydrostatic pressure) with gravity.
have been analyzed. The calculations of the forces are shown below.
Boundary Condition Selected:
Keys are generally constructed to prevent the movement (in 1- and 2-directions)and rotation (about 3-direction) of the dam mounted on soil profile. In this model also it is assumed to be the same and it is assumed that the keys are provided all along the base of the dam to enough depth to prevent movement and rotation of the dam. (However the actual situation is not generally like this). Fixed boundary condition is assumed all along the base of the dam.

8. Calculations associated with:
(a) defining the material properties, and (b) defining the loading conditions.
Homogeneous, isotropic, elastic behavior
of concrete is assumed.
All the units entered in the ABAQUS are in kips and inches
Hence, the results are in kips and inches.

10. 2) Present the results from the finite element analysis of each loading condition. For each analysis, present
the contour plots of all the normal, shear, and principal stresses. Indicate the maximum values (locations
and magnitudes) on the plots.
Load Case 1:
S11

11. S22
Load Case 1:

12. Load Case 1:
S33

13. S12
Load Case 1:

14. Maximum in-plane principal stresses
Load Case 1:

15. Minimum in-plane principal stresses
Load Case 1:

16. Out-of-plane principal stresses
Load Case 1:

17. Load Case 2:
S11

18. S22
Load Case 2:

19. S33
Load Case 2:

20. S12
Load Case 2:

21. Maximum in-plane principal stresses
Load Case 2:

22. Minimum in-plane principal stresses
Load Case 2:

23. Out-of-plane principal stresses
Load Case 2:

24. 3]. Calculation of Applied forces and Comparison with Reactions got from FEM AnalysisB C

25. Reactions are reported in the “Reaction” Files also.

26. RF1-Load case 1

27. RF 2-Load case 1

28. RF Magnitude-Load case 1

30. RF1-Load case 2

31. RF2-Load case 2

32. RF Magnitude-Load case 2

37. Are there any other simple calculations you can suggest or perform to check
the analysis results?
For a point in a horizontal section along the length of the dam (can be base of the dam), stress due to gravity
of the part above that section (P/A + Pey/I) and the stress due to moment coming from the hydrostatic
pressure (My/I) can be calculated and checked with S22 obtained from the FE Analysis.
One of the principal stresses would be zero at the free boundary.
One of the principal stresses would be equal to (-) Hydrostatic pressure at the boundary adjacent to the Water.
Hydrostatic pressure can be calculated along the face of the dam and checked with the principal stresses.
Can pick one element and check for equilibrium. This is normally approximately satisfied.
Displacements at fixed points are zero. For example at Node 1: U1= E-33 in, U2= E-30 in

38. Checking the Finite Element model for convergence
Load Case 1: Mesh is refined with 4752 Elements (almost 4 times)instead of 1134 elements
(which were earlier) and the displacements are compared.
Mesh with 1134 Elements Mesh with elements
Max U1= in Max U1= in

39. Max U2= in Max U2= in

40. Max U magnitude = 0.3662 in Max U magnitude = 0.3662 in

41. Load Case 2: Mesh is refined with 4752 Elements (almost 4 times)instead of 1134 elements
(which were earlier) and the displacements are compared.
Mesh with 1134 Elements Mesh with elements
Max U1= in Max U1= in

42. Max U2= in Max U2= in

43. Max U magnitude = 0.2301 in Max U magnitude = 0.2301 in
The displacement pattern and the values are seemed to be very similar. This implies the convergence of the model.
Stresses and reactions are calculated from the displacements by FEM. They are generally approximately similar.

44. 4) From your analysis results, identify the maximum compressive and tensile stresses
in the concrete dam. Determine whether the structure will crack (in tension) or crush
(in compression) under the given loading conditions?
Let us use Rankine Theory for concrete (Brittle Material).
Compressive strength of the concrete = 3.5 ksi
Modulus of Rupture of the concrete =7.5*(3500)^0.5*1/1000 ksi =0.44 ksi
For Load case 1:
From the FE Analysis the maximum maximum principal stress =0.713 ksi (Tension) >0.44 ksi cracking
(0.889 ksi (Tension) from refined mesh>0.44 ksi)
max. (in magnitute ) minimum principal stress = ksi (compression) <3.5 ksi No Crushing
( ksi (Com.) from refined mesh <3.5 ksi)
For Load case 2:
From the FE Analysis the maximum maximum principal stress = ksi (Tension) <0.44 ksi No cracking
( ksi (Tension) from refined mesh>0.44 ksi
cracking )
max. (in magnitute ) minimum principal stress = ksi (compression) <3.5 ksi No Crushing
( ksi (Com.) from refined mesh <3.5 ksi)
[Note: Tensile strength of the concrete = 6(f’c)^0.5. ACI suggest to consider the modulus of rupture to check for cracking.
US Army Corps of Engineers Manual also recommends to consider modulus of rupture for checking for cracking.]

45. (ii) dominates the problem. For mesh with 1134 elements (coarse mesh)
5) From the analysis results, discuss which of two loading conditions (i) or
(ii) dominates the problem.
For mesh with 1134 elements (coarse mesh)
Loading Condition
σp1 (max)
(ksi)
σp3
(max in mag.) (ksi) U1
(max)
(in) U2
U(mag) 1
0.713
0.1925
0.3579
0.3662 2
0.3457
0.2927
0.1984
0.231
The tensile stresses and deflections are higher for loading condition 1. Hence, we could say that the loading
condition 1 dominates the Problem.
Due to the gravity, compressive stress increases and tensile stress decreases. Concrete can take up to 3.5 ksi
of compressive stress (with out no load factors and reduction factors). Hence the loading case 2 is more safe than loading case 1.

46. 6) Identify some of the other loading conditions or design criteria that must be checked for the
concrete dam structure. Provide a reference (citation only) that you used to determine these.
Will the finite element model you developed be useful for these additional cases?
US Army Corps of Engineers Manual for gravity dam design list the following loading cases to be considered.
(1) Uplift.
(2) Forces due to temperature effects.
(3) Earth and silt pressures.
(4) Ice pressure.
(5) Earthquake forces.
(6) Wind pressure
(7) Wave pressure. (hydro dynamic forces).
(8) Reaction of foundation.
Citation: US Army Corps of Engineers Manual for gravity dam design (1995)
If there is life load during construction or after construction, vehicle loads if there
will be a road along the top of the dam they also should be considered.
The Finite element model developed here will be useful for these additional cases. Dynamic analysis For
earthquake and hydrodynamic forces, and thermal analysis for forces due to temperature effects should be done.