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ACI Fall 2008 Convention
The Design of Outer Concrete Containments of LNG-Tanks for Operation and Hazard Scenarios
Josef Roetzer & Hamish DouglasDywidag International, Munich, Germany
November 2- 6, St. Louis, MO
Practical Use of Finite Element Analysis in the Design of Concrete Structures
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
Contents
1. Function and Layout of LNG-Tanks ........... 3 - 52. Normal and Emergency Load Cases . 6 - 93. Superposition of Single Load Cases .. 104. Modeling and Mesh Generation . 11 - 145. Linear Elastic and Non-linear Calculation .. 15 - 166. Typical Results ... 17 - 227. Checking and Verification of Numerical Results... 23 - 248. Summary . 25 279. References & Codes . 28 - 30
2
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
1. Function and Layout of LNG-Tanks 3
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
1. Function and Layout of LNG-Tanks
Trinidad Export Terminal
4
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
The concrete tank consists of a bottom slab, a prestressed wall shell and a reinforced concrete roof.
1. Function and Layout of LNG-TanksA Full Containment Tank consists of a concrete outer tank and a steel inner tank.
The liquid gas is stored in the steel inner tank made of cryogenic resistant 9%-nickel steel.
Between concrete outer and steel inner tank an insulation layer of approximately one meter thickness is placed.The concrete outer tank protects the steel inner tank against external hazards, such as fire, impact, blast wave and earthquake and the environment from possible internal impacts such as liquid spill.
5
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
2. Normal and Emergency Load Cases
Operation and Test Load Cases:
Dead load Product filling Prestressing including creep and shrinkage Internal pressure Ambient temperature Live load Wind Hydrotest and pneumatic test Operating Basis Earthquake OBE
6
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
2. Normal and Emergency Load Cases
Emergency Load Cases:
Liquid spill inner tank
Blast wave
Adjacent tank fire
Safe Shutdown Earthquake SSE
Pressure relieve valve fire
Impact
7
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
2. Normal and Emergency Load CasesExamples:
Define only maximum allowable radiation at concrete surface
Determination of material strength reduction
Mechanical requirementsLayout of pressure relief valves
Calculation of isotherms in the concrete roof section
Civil & structural requirements
Determination of temperature gradient and temperature difference
Valve Fire:Codes:
8
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
2. Normal and Emergency Load Cases
Hydrostatic pressure and temperature acting on outer tank concrete wall
Calculation of isothermal curves in discontinuity zones
Liquid Spill failure of the inner tank:
Determination of temperature gradient and temperature difference
Temperature gradient T causes strains greatly in excess of concrete tensile strength
9
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
3. Superposition of Single Load Cases
PL = permanent load, EL = emergency load, LL = live load
10
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
4. Modelling and Mesh Generation
Micro: Using separate elements for concrete, reinforcement and bondMesa: Using separate elements for concrete and reinforcement, simplified bond modelsMacro: Using combined elements for reinforced concrete
11
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
4. Modelling and Mesh Generation
real structure mechanical model numerical model FEMconcrete outer tanksteel inner tankroof steel platform
12
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
4. Modelling and Mesh Generation
The modeling of the spherical structure of the concrete outer tank is done with layered shell elements. The structure is idealized only by its centre line.
The so-called 2-D model uses layered elements. A linear stress distribution is assumed in each layer. The sum of the several layers represents the thickness of the element.
Based on the Bernoulli-hypothesis of a linear strain distribution in the cross section, this approach allows the use of non-linear constitutive equations for calculation of stresses in each layer.
Internal forces are obtained by stress integration over the cross section.
13
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
4. Modelling and Mesh Generation 14
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
5. Linear Elastic and Non-linear Calculation 15
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
5. Linear Elastic and Non-linear Calculation 16
In a first step a linear elastic calculation is generated. It is obviously that the tensile stress exceed the concrete tensile strength.
Nonlinear calculations investigate a superposition load case.
Thereby the stiffness is reduced and the sectional forces are redistributed.
The Eurocode allows for ULS the utilization of a concrete tensile strength. Thereby a concrete wedge in the interior element is generated.
In the nonlinear calculation the concrete layers crack.
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
6. Typical Results dead load
M 1 : 953XY
Z
2558
1575
-769
694
-417
-231
-61
48
-44
-42
-26
-10
7
3
2
-1 -1
Sector of system Group 0...2 4...14 20...24Bending moment m-nn in Nodes, Loadcase 10 total dead load, 1cm 3D = 8663. kNm/m (Min=-768.8) (Max=2558.)
-60000. -40000. -20000. -0. 20000. mm
0
.
-
2
0
0
0
0
.
M 1 : 940XY
Z
2.41
2.08
-1.29
-0.
45
0.39-0.23
0.16
0 .00
Sector of systemNodal displacement in global X in Nodes , Loadcase 10 totaldead load, 1 cm 3D = 3.61 mm (Min=-1.29) (Max=2.41)
0. 20000. 40000. 60000 . mm
-
2
0
0
0
0
.
-
4
0
0
0
0
.
M 1 : 913XY
Z
-1205
-5 42
-46 6
-4 65
-4 61
-451-271
-270
-269
-267
-267
-23
6
12
Sector of system Group 0...2 4...14 20...24Normal forces n-nn in Nodes, Loadcase 10 total dead load, 1 cm3D = 1804. kN/m (Min=-1205.) (Max=11.8)
-60000. -40000. -20000. -0. 20000 . mm
0
.
-
2
0
0
0
0
.
M 1 : 773XY
Z
Sector of systemDeformed Structure from LC 10 total dead load Enlarged by 100.0
-10000. 0. 10000. 20000. 30000. 40000. 50000 . mm
0
.
-
1
0
0
0
0
.
-
2
0
0
0
0
.
-
3
0
0
0
0
.
17
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
6. Typical Results horizontal prestressing
M 1 : 988XY
Z
676
592
512
-441
-240
-125
73
68
-65
-53
12
6- 4
-4
3
0
0
0
Sector of system Group 0...2 4...14 20...24Bending moment m-nn in Nodes, Loadcase 61 prestressing, t=0, 1cm 3D = 1303. kNm/m (Min=-441.2) (Max=675.7)
-60000. -40000. -20000 . -0. 20000. mm
0
.
-
2
0
0
0
0
.
M 1 : 917XY
Z
-14.10
-4.46
-0.59
-0.57
-0.01
-0.
00
Sector of systemNodal displacement in global X in Nodes , Loadcase 61prestressing, t=0, 1 cm 3D = 12.8 mm (Min=-14.1)
-20000 . 0. 20000. 40000. 60000 . mm
-
2
0
0
0
0
.
-
4
0
0
0
0
.
M 1 : 1086XY
Z
-660
-656
-651
-649
-227
66
-
41
27
4
-3
- 3
1
0
Sector of system Group 0...2 4...14 20...24Normal forces n-nn in Nodes, Loadcase 61 prestressing, t=0, 1cm 3D = 832.1 kN/m (Min=-659.9) (Max=65.6)
-60000. -40000. -20000 . -0. 20000 . mm
0
.
-
2
0
0
0
0
.
M 1 : 812XY
Z
Sector of systemDeformed Structure from LC 61 prestressing, t=0 Enlarged by100.0
-10000. 0. 10000. 20000. 30000. 40000. 50000. 60000 . mm
-
1
0
0
0
0
.
-
2
0
0
0
0
.
-
3
0
0
0
0
.
-
4
0
0
0
0
.
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ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
6. Typical Results LNG filling
M 1 : 918XY
Z
-2261
982
398
361
72
59
-28
-3
0
0
0 0
0
0
0
Sector of system Group 0...2 4...14 20...24Bending moment m-nn in Nodes, Loadcase 7 LNG-filling, 1 cm 3D= 6542. kNm/m (Min=-2261.) (Max=982.4)
-60000. -40000. -20000. -0. 20000 . mm
0
.
-
2
0
0
0
0
.
-
4
0
0
0
0
.
M 1 : 893XY
Z
-2.64
-0.47 0.38
0.15
-0.01
0.00
0.000 .
00
0.00
Sector of systemNodal displacement in global X in Nodes , Loadcase 7LNG-filling, 1 cm 3D = 12.8 mm (Min=-2.64) (Max=0.381)
-20000. 0. 20000. 40000. 60000. mm
0
.
-
2
0
0
0
0
.
M 1 : 898XY
Z
441
439
437
435
434
-19
0
0
0 0
0 0
0
0
Sector of system Group 0...2 4...14 20...24Normal forces n-nn in Nodes, Loadcase 7 LNG-filling, 1 cm 3D =832.1 kN/m (Min=-19.3) (Max=440.7)
-60000. -40000. -20000 . -0. 20000. mm
0
.
-
2
0
0
0
0
.
-
4
0
0
0
0
.
M 1 : 872XY
Z
Sector of systemDeformed Structure from LC 7 LNG-filling Enlarged by 100.0
-20000. 0 . 20000. 40000. 60000. mm
0
.
-
2
0
0
0
0
.
19
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
6. Typical Results internal pressure
M 1 : 914XY
Z
-476
-280
149
54 53
28
20
13
8
6
2
-1
-1
00
Sector of system Group 0...2 4...14 20...24Bending moment m-nn in Nodes, Loadcase 91 max. operatingpressure, 1 cm 3D = 1303. kNm/m (Min=-476.0) (Max=149.4)
-60000. -40000. -20000. -0. 20000. mm
0
.
-
2
0
0
0
0
.
-
4
0
0
0
0
.
M 1 : 1073XY
Z
-0.95
0.61
0.58
0.35
-0.20
-0.13
0.07
0.03
-0.
0 0
Sector of systemNodal displacement in global X in Nodes , Loadcase 91 max.operating pressure, 1 cm 3D = 1.74 mm (Min=-0.953)
-20000. 0. 20000. 40000 . 60000. mm
0
.
-
2
0
0
0
0
.
-
4
0
0
0
0
.
M 1 : 994XY
Z
313
309
308
306
3 06
194
156
151
151
78 78 78 77 77
Sector of system Group 0...2 4...14 20...24Normal forces n-nn in Nodes, Loadcase 91 max. operatingpressure, 1 cm 3D = 832.1 kN/m (Min=-3.42) (Max=313.1)
-60000. -40000. -20000. -0. 20000. mm
-
2
0
0
0
0
.
-
4
0
0
0
0
.
M 1 : 844XY
Z
Sector of systemDeformed Structure from LC 91 max. operating pressure Enlargedby 300.0
0. 20000. 40000 . 60000. mm
-
2
0
0
0
0
.
-
4
0
0
0
0
.
20
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
6. Typical Results operation temperature
M 1 : 880XY
Z
-1401
-1130
-884770
162
117
115
111
-55
-41
-32
-12
- 9
-8
Sector of system Group 0...2 4...14 20...24Bending moment m-nn in Nodes, Loadcase 202 temperature summer,1 cm 3D = 1303. kNm/m (Min=-1401.) (Max=770.1)
-60000. -40000 . -20000. -0. 20000. mm
0
.
-
2
0
0
0
0
.
M 1 : 784XY
Z
10.20
9.49
9.32
9.26
-8.90
-8.71
3.97
-0.00
Sector of systemNodal displacement in global X in Nodes , Loadcase 202temperature summer, 1 cm 3D = 22.5 mm (Min=-8.90)
-10000 . 0. 10000. 20000 . 30000. 40000. 50000. 60000. mm
-
1
0
0
0
0
.
-
2
0
0
0
0
.
-
3
0
0
0
0
.
-
4
0
0
0
0
.
M 1 : 799XY
Z
1393
13891385
1384
13121298
1173267
-6
-5
- 4
-1
0 0
0 0
Sector of system Group 0...2 4...14 20...24Normal forces n-nn in Nodes, Loadcase 202 temperature summer,1 cm 3D = 832.1 kN/m (Min=-13.6) (Max=1393.)
-50000. -40000. -30000 . -20000. -10000. -0. 10000. 20000. mm
-
1
0
0
0
0
.
-
2
0
0
0
0
.
-
3
0
0
0
0
.
-
4
0
0
0
0
.
M 1 : 812XY
Z
Sector of systemDeformed Structure from LC 202 temperature summer Enlarged by100.0
-10000. 0. 10000. 20000. 30000. 40000. 50000 . 60000. mm
-
1
0
0
0
0
.
-
2
0
0
0
0
.
-
3
0
0
0
0
.
-
4
0
0
0
0
.
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ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
6. Typical Results superposition nonlinear
M 1 : 928XY
Z
3537
2349
-640
621
-525
507
-308
-108
-91
-43
-21
-8-8
-2
Sector of system Group 0...2 4...14 20...24Bending moment m-nn in Nodes, Loadcase 4100 linear combinationmax M-nn, 1 cm 3D = 15000. kNm/m (Min=-640.2) (Max=3537.)
-60000. -40000. -20000. -0. 20000. mm
0
.
-
2
0
0
0
0
.
M 1 : 1048XY
Z
-2339
-1581
-752
653
-
397
346
-319
-273
-242
- 140
-124
117
- 97
-83
-5 4
-21
Sector of system Group 0...2 4...14 20...24Bending moment m-nn in Nodes, Loadcase 4200 linearcombination min M-nn, 1 cm 3D = 15000. kNm/m (Min=-2339.)
-60000. -40000. -20000. -0. 20000. mm
0
.
-
2
0
0
0
0
.
-
4
0
0
0
0
.
M 1 : 917XY
Z
2596
1478
-855
586
-496
-323
-103
-72
-41
-15
-4 -43
Sector of system Group 0...2 4...14 20...24Bending moment m-nn in Nodes, nonlinear Loadcase 4101non-linear combination max M-nn, 1 cm 3D = 15000. kNm/m
-60000. -40000. -20000. -0. 20000. mm
0
.
-
2
0
0
0
0
.
M 1 : 998XY
Z
-1461
-644
-366
-34
9
-296
-286
-253
152
-1 24
-110
-94-93
-80
-64
62
-5 8
-23
Sector of system Group 0...2 4...14 20...24Bending moment m-nn in Nodes, nonlinear Loadcase 4201non-linear combination min M-nn, 1 cm 3D = 15000. kNm/m
-60000. -40000. -20000. -0. 20000. mm
0
.
-
2
0
0
0
0
.
-
4
0
0
0
0
.
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ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
7. Checking and Verification of ResultsThe FEM-calculations provide correct results for the uniform sections of roof, wall and bottom slab of the tank.However this is not appropriate for zones of discontinuity.In these discontinuity zones detailed investigations with the help of strut-and-tie models are required.
23
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
7. Checking and Verification of ResultsLiquid tightness of concrete sections liquid spill scenario:
The temperature gradient T generates a restraint strain.
Increasing reinforcement quantity does not influence the gradient of strain.
This is only achievable with a modification of the normal force.The effect of prestressing modification on the states of strain and crack generation can be demonstrated using the approach presented in Ref. [3] .
24
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
8. Summary FE Method
The highly developed simplification of the input data, the handling of the calculations, the representation of the results and the fact that the method allows evaluation of the areas and even location of the reinforcement makes the FEM a near perfect tool.
The implied accuracy of the results suggests to many users that this is an exact calculation method, but obscures the fact that expert knowledge and experience are required.
Controlling the idealization and results is an important element of the calculation.
The frequently used displacement elements do not fulfill the most important mechanical conditions, namely equilibrium, boundary and transition conditions.
25
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
8. Summary Tank DesignThe task of the civil engineer is not restricted to prepare a series of sophisticated FEM calculations, but includes also the dimensioning of the concrete tank.
The overall quality of the structure depends in our opinion - in addition to the correct interpretation of the results of the FEM-calculation also to great extent on the correct dimensioning of the concrete sections, the bottom slab dimension, the sizing and arrangement of post-tensioning and the arrangement and choice of diameters and layout of the reinforcement.
The large number of superpositioning possibilities requires the calculation of the single load cases as a first step. In a second step these single load cases are superimposed. For these elastic calculations the principle of superpositioning remains further valid.
One calculation is no calculation. This means that a series of calculations have to be performed because:
26
ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
8. Summary Tank DesignThe required reinforcement will be determined for the governing superpositioned sectional forces.The reinforcement has to be adjusted considering buildability and site requirements. Based on that reinforcement and the post-tensioning the emergency load cases are calculated as superposition load cases.In cross sections of the tank where the specified requirements (such as crack width, compressive zone, steel stress) are not fulfilled, reinforcement or concrete cross section or post-tensioning has to be modified.Only after a large number of calculations can the production of reinforcement drawings be started, as for the calculations the entire structural system has to be considered.Not yet discussed in these simplified explanations are the far more complex dynamic investigations of the combined outer and inner tank system and the roof platforms.
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ACI Fall 2008 Convention, St. Louis Practical Use of Finite Element Analysis in the Design of Concrete Structures
The Design of Outer Concrete Containments of LNG-Tanks
9. References
[1] Kemmler, R.; Ramm, E.: Modellierung mit der Methode der Finiten Elemente (Modeling with the Finite Element Method). Beton-Kalender 2001. Ernst & Sohn, Berlin. Page 143 208.
[2] Hofstetter, G.; Mang, H. A.: Computational Mechanics of Reinforced Concrete Structures. Vieweg, Braunschweig, 1995.
[3] Roetzer, J.; Baumann, Th.: Outer concrete containments of LNG-Tanks -Design against thermal shock. fib Symposium: Taylor Made Concrete Structures, Amsterdam, 2008. Page 877 882.
[4] Roetzer, J.; Salvatore, D.: The Effect of a Valve Fire to the Dome structure of a LNG-Tank. IABSE Symposium: Structures and Extreme Events, Lisbon, 2006. Page 877 882.
[5] Roetzer, J.; Douglas, H.; Maurer, H.: Hazard and Safety Investigations for LNG-Tanks. Part 1: Earthquake, Part 2: Blast Wave, Part 3: Liquid Spill. LNG-Journal 2005 & 2006.
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