proposed appendix e re-write 04-2004 - my committees materials... · draft ----for committee use...

DRAFT ----FOR COMMITTEE USE ONLY! Proposed Appendix E April 2004 Printed 4/2/2004 11:52 AM

1 2 3 4 5 6 7 8 9 10 11 12 13

Proposed Revision 14 APPENDIX E - SEISMIC DESIGN OF STORAGE TANKS 15

16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Prepared by 41 42

Stephen W. Meier, PE SE 43 Tank Industry Consultants 44


PART I - PROVISIONS..............................................................................................................................................4 1

E.1 SCOPE ..................................................................................................................................................................4 2

E.2 – DEFINITIONS AND NOTATIONS.................................................................................................................5 3

E.2.1 DEFINITIONS .....................................................................................................................................................5 4 E.2.2 NOTATIONS .......................................................................................................................................................5 5

E.3 PERFORMANCE BASIS.....................................................................................................................................9 6

E.3.1 SEISMIC USE GROUP .........................................................................................................................................9 7 E.3.1.1 Seismic Use Group III ...............................................................................................................................9 8 E.3.1.2 Seismic Use Group II ................................................................................................................................9 9 E.3.1.3 Seismic Use Group I..................................................................................................................................9 10 E.3.1.4 Multiple use ...............................................................................................................................................9 11

E.4 SITE GROUND MOTION.................................................................................................................................9 12

E.4.1 MAPPED ASCE 7 METHOD ...............................................................................................................................9 13 E.4.2 SITE-SPECIFIC SPECTRAL RESPONSE ACCELERATIONS ....................................................................................10 14

E.4.2.1 Site-Specific Study ...................................................................................................................................10 15 E.4.2.2 Probabilistic Site-specific MCE Ground Motion ....................................................................................10 16 E.4.2.3 Deterministic Site-specific MCE Ground Motion...................................................................................11 17 E.4.2.4 Site-specific MCE Ground Motions.........................................................................................................11 18

E.4.3 SITES NOT DEFINED BY ASCE 7 METHODS ....................................................................................................11 19 E.4.4 MODIFICATIONS FOR SITE SOIL CONDITIONS ..................................................................................................11 20 E.4.5 STRUCTURAL PERIOD OF VIBRATION ..............................................................................................................15 21

E.4.5.1 Impulsive Natural Period ........................................................................................................................15 22 E.4.5.2 Convective (Sloshing) Period..................................................................................................................16 23

E.4.6 DESIGN SPECTRAL RESPONSE ACCELERATIONS..............................................................................................17 24 E.4.6.1 – Spectral Acceleration Coefficients. ......................................................................................................17 25

E.5 SEISMIC DESIGN FACTORS .........................................................................................................................19 26

E.5.1 – DESIGN FORCES............................................................................................................................................19 27 E.5.1.1 Response Modification Factor ................................................................................................................19 28 E.5.1.2 Importance Factor...................................................................................................................................19 29

E.6 DESIGN ...............................................................................................................................................................20 30

E.6.1 DESIGN LOADS................................................................................................................................................20 31 E.6.1.1 Effective Weight of Product.....................................................................................................................21 32 E.6.1.2 Center of Action for Effective Lateral Forces .........................................................................................21 33 E.6.1.3 Vertical Seismic Effects ...........................................................................................................................23 34 E.6.1.4 Dynamic Liquid Hoop Forces .................................................................................................................23 35 E.6.1.5 Overturning Moment ...............................................................................................................................25 36 E.6.1.6 Soil-Structure Interaction........................................................................................................................26 37

E.6.2 RESISTANCE TO DESIGN LOADS ......................................................................................................................26 38 E.6.2.1 Anchorage ...............................................................................................................................................26 39 E.6.2.2 Maximum Longitudinal Shell Membrane Compression Stress................................................................29 40 E.6.2.3 Foundation ..............................................................................................................................................31 41 E.6.2.4 Hoop Stresses ..........................................................................................................................................32 42

E.7 DETAILING REQUIREMENTS......................................................................................................................32 43

E.7.1 ANCHORAGE ...................................................................................................................................................32 44 E.7.1.1 Self-anchored ..........................................................................................................................................32 45 E.7.1.2 Mechanically-anchored...........................................................................................................................32 46


E.7.2 FREEBOARD ....................................................................................................................................................33 1 E.7.3 PIPING FLEXIBILITY.........................................................................................................................................34 2

E.7.3.1 – Method for Estimating Tank Uplift.......................................................................................................35 3 E.7.4 CONNECTIONS.................................................................................................................................................35 4 E.7.5 INTERNAL COMPONENTS.................................................................................................................................36 5 E.7.6 SLIDING RESISTANCE ......................................................................................................................................36 6 E.7.7 LOCAL SHEAR TRANSFER.................................................................................................................................37 7 E.7.8 CONNECTIONS WITH ADJACENT STRUCTURES ................................................................................................37 8 E.7.9 SHELL SUPPORT ..............................................................................................................................................37 9 E.7.10 REPAIR, MODIFICATION OR RECONSTRUCTION .............................................................................................37 10


Proposed Revision 1 APPENDIX E - SEISMIC DESIGN OF STORAGE TANKS 2

3 4

Part I - Provisions 5

E.1 SCOPE 6

This appendix provides minimum requirements for the design of welded steel storage tanks that 7 may be subject to seismic ground motion. These requirements represent accepted practice for 8 application to welded steel flat-bottom tanks supported at grade. 9

The fundamental performance goal for seismic design in this Appendix is the protection of life 10 and prevention of catastrophic collapse of the tank. Application of this standard does not imply 11 that damage to the tank and related components will not occur during seismic events. 12

This Appendix is based on the allowable stress design (ASD) methods with the specific load 13 combinations given herein. Application of load combinations from other design documents or 14 codes is not recommended, and may require the design methods in this Appendix be modified to 15 produce practical, realistic solutions. The methods use an equivalent lateral force analysis that 16 applies equivalent static lateral forces to a linear mathematical model of the tank based on a rigid 17 wall, fixed based model. 18

The ground motion requirements in this Appendix are derived from ASCE 7 which is based on a 19 maximum considered earthquake ground motion defined as the motion due to an event with a 2% 20 probability of exceedance within a 50 year period (a recurrence interval of approximately 2500 21 years). Application of these provisions as written is deemed to meet the intent and requirements 22 of ASCE 7. Accepted techniques for applying these provisions in regions or jurisdictions where 23 the regulatory requirements differ from ASCE 7 are also included. 24

The pseudo-dynamic design procedures contained in this Appendix are based on response 25 spectra analysis methods and consider two response modes of the tank and its contents- 26 impulsive and convective. Dynamic analysis is not required nor included within the scope of this 27 Appendix. The equivalent lateral seismic force and overturning moment applied to the shell as a 28 result of the response of the masses to lateral ground motion are determined. Provisions are 29 included to assure stability of the tank shell with respect to overturning and to resist buckling of 30 the tank shell as a result of longitudinal compression. 31

The design procedures contained in this appendix are based on a 5% damped response spectra 32 for the impulsive mode and 0.5% damped spectra for the convective mode supported at grade 33 with adjustments for site specific soil characteristics. Application to tanks supported on a 34 framework elevated above grade is beyond the scope of this Appendix. Seismic design of 35 floating roofs is beyond the scope of this Appendix. 36

Optional design procedures are included for the consideration of the increased damping and 37 increase in natural period of vibration due to soil-structure interaction for mechanically anchored 38 tanks. 39


Tanks located in regions where S1 is less than or equal to 0.04 and SS less than or equal to 0.15, 1 or the peak ground acceleration for the ground motion defined by the regulatory requirements is 2 less than or equal to 0.05g, need not be designed for seismic forces; however, in these regions, 3 tanks in SUG III shall comply with the freeboard requirements of this Appendix. 4 “Dynamic analysis methods incorporating fluid-structure and soil-structure interaction are 5 permitted to be used in lieu of the procedures contained in this Appendix with Purchaser 6 approval and provided the design and construction details are as safe as otherwise provided in 7 this Appendix . 8 9

E.2 – DEFINITIONS and NOTATIONS 10

E.2.1 Definitions 11

ACTIVE FAULT: A fault for which there is an average historic slip rate of 1 mm per year or more and 12 geologic evidence of seismic activity within Holocene times (past 11,000 years). 13

CHARACTERISTIC EARTHQUAKE: An earthquake assessed for an active fault having a magnitude 14 equal to the best-estimate of the maximum magnitude capable of occurring on the fault, but not less than 15 the largest magnitude that has occurred historically on the fault. 16

MAXIMUM CONSIDERED EARTHQUAKE (MCE): The most severe earthquake ground motion 17 considered in this Appendix 18

MECHANICALLY-ANCHORED TANK: Tanks that have anchor bolts, straps or other mechanical 19 devices to anchor the tank to the foundation. 20

SELF-ANCHORED TANK: Tanks that use the inherent stability of the self-weight of the tank and the 21 stored product to resist overturning forces. 22

SITE CLASS: A classification assigned to a site based on the types of soils present and their 23 engineering properties as defined in this Appendix. 24

E.2.2 Notations 25

Ai Impulsive design response spectrum acceleration coefficient, %g 26

Ac Convective design response spectrum acceleration coefficient, %g 27

Av Vertical earthquake acceleration coefficient, % g 28

Ci Coefficient for determining impulsive period of tank system 29

dc Total thickness (100 - ds) of cohesive soil layers in the top 30 m (100 ft). 30

di Thickness of any soil layer i (between 0 and30 m [100 ft]). 31

ds Total thickness of cohesionless soil layers in the top 30 m (100 ft) 32

D Nominal tank diameter, m ( ft) 33

E Elastic Modulus of tank material, MPa (psi) 34

Fa Acceleration-based site coefficient (at 0.2 sec period). 35

Fc Allowable longitudinal shell membrane compression stress, MPa (psi) 36


Fv Velocity-based site coefficient (at 1.0 sec period). 1

Fy Minimum specified yield strength of bottom annulus, MPa,(psi) 2

g Acceleration due to gravity in consistent units. m/sec2 (ft/sec2) 3

G Specific gravity 4

Ge effective specific gravity including vertical seismic effects = G(1-0.4Av) 5

H Maximum design product level, m (ft) 6

HS Thickness of soil, m (ft). 7

J Anchorage ratio 8

K Coefficient to adjust the spectral acceleration from 5% to 0.5% damping = 1.5 unless otherwise 9 specified. 10

L Required minimum width of the bottom annulus measured from the inside of the shell m (ft) 11

nA Number of equally spaced anchors around the tank circumference. 12

N Standard penetration resistance, ASTM D1536-84. 13

N Average field standard penetration test for the top 30m (100 ft)). 14

Nch Average standard penetration of cohesionless soil layers for the top 30m (100 ft) 15

Ni Impulsive hoop membrane force in tank wall, N/mm (lbf/in) 16

Nc Convective hoop membrane force in tank wall, N/mm (lbf/in) 17

Nh Product hydrostatic membrane force, N/mm ( lbf/in) 18

PI Plasticity index, ASTM D4318-93. 19

PAB Anchor design load, N (lbf) 20

PA’ Anchorage attachment design load, N (lbf) 21

Q Scaling factor from the MCE to the design level spectral accelerations; equals 2/3 for ASCE 7 22

R Force reduction coefficient for strength level design methods 23

Rwi Force reduction factor for the impulsive mode using allowable stress design methods 24

Rwc Force reduction coefficient for the convective mode using allowable stress design methods 25

S0 Mapped, maximum considered earthquake, 5-percent-damped, spectral response acceleration 26 parameter at a period of zero seconds (peak ground acceleration for a rigid structure), %g 27

S1 Mapped, maximum considered earthquake, 5-percent-damped, spectral response acceleration 28 parameter at a period of one second, %g. 29

Sa The 5-percent-damped, design spectral response acceleration parameter at any period based on 30 mapped, probabilistic procedures, %g. 31

Sa* The 5-percent-damped, design spectral response acceleration parameter at any period based on 32

site-specific procedures, %g. 33

Sa0* The 5-percent-damped, design spectral response acceleration parameter at zero period based on 34

site-specific procedures, %g 35


SDS The design, 5-percent-damped, spectral response acceleration parameter at short periods (T =0.2 1 seconds) based on ASCE 7 methods, %g. 2

SD1 The design, 5-percent-damped, spectral response acceleration parameter at one second based on 3 the ASCE 7 methods, %g. 4

SP Design level peak ground acceleration parameter for sites not addressed by ASCE methods. 5

SS Mapped, maximum considered earthquake, 5-percent-damped, spectral response acceleration 6 parameter at short periods (0.2 sec), %g. 7

su Undrained shear strength, ASTM D2166 or ASTM D2850. 8

s̄u Average undrained shear strength in top 30m (100 ft). 9

t Thickness of the shell ring under consideration, mm (in) 10

ta Thickness of the bottom plate under the shell extending at least the distance ,L, from the inside of 11 the shell, less corrosion allowance, mm (in) 12

tb Thickness of tank bottom less corrosion allowance, mm (in) 13

ts Thickness of bottom shell course less corrosion allowance, mm (in) 14

tu Equivalent uniform thickness of tank shell, mm (in) 15

T Natural period of vibration of the tank and contents, seconds 16

Ti Natural period of vibration for impulsive mode of behavior, seconds. 17

TC Natural period of the convective (sloshing) mode of behavior of the liquid, seconds 18

TL Regional-dependent transition period for longer period ground motion, seconds. 19

T0 0.2 FvS1 / FaSS 20

TS FvS1 / FaSS. 21

vs Average shear wave velocity at large strain levels for the soils beneath the foundation, m/s (ft/s). 22

sv Average shear wave velocity in top one 30m (100 ft), m/s (ft/s) 23

Vi Design base shear due to impulsive component from effective weight of tank and contents, N 24 (lbf) 25

Vc Design base shear due to the convective component of the effective sloshing weight, N ( lbf). 26

V Total design base shear, N (lbf) 27

w Moisture content (in percent), ASTM D2216-92. 28

wAB Calculated design uplift load on anchors per unit circumferential length, N (lbf) 29

wint Calculated design uplift due to product pressure per unit circumferential length, N/m (lbf/ft) 30

wL Resisting force of tank contents per foot of shell circumference that may be used to resist the shell 31 overturning moment, N/m (lbf/ft) 32

wrs Roof load acting on the shell, including specified snow load N/m (lbf/ft) 33

wt Tank and roof weight acting at base of shell, N/m ( lbf/ft) 34

Wc Effective convective (sloshing) portion of the liquid weight, N (lbf) 35


Weff Effective weight contributing to seismic response 1

Wf Weight of the tank floor, N (lbf) 2

Wfd Total weight of tank foundation, N (lbf) 3

Wg Weight of soil directly over tank foundation footing, N (lbf) 4

Wi Effective impulsive weight of the liquid, N (lbf) 5

Wp Total weight of the tank contents based on the design specific gravity of the product, N 6 (lbf) 7

Wr Total weight of fixed tank roof including framing, knuckles, any permanent attachments and 8 participating snow weight, if specified, N (lbf) 9

Wrs Total roof load acting on the tank shell including the specified snow loads, N (lbf) 10

Ws Total weight of tank shell and appurtenances, N (lbf) 11

T Total weight of tank shell, roof, framing, knuckles, product, bottom, attachments, appurtenances, 12 participating snow load, if specified, and appurtenances, N (lbf) 13

Xc Height from the bottom of the tank shell to the center of action of lateral seismic force 14 related to the convective liquid force for ringwall moment, m (ft) 15

Xi Height from the bottom of the tank shell to the center of action of the lateral seismic force related 16 to the impulsive liquid force for ringwall moment, m (ft) 17

Xr Height from the tank of the tank shell to the roof and roof appurtenances center of gravity, m (ft) 18

Xs Height from the bottom of the tank shell to the shell’s center of gravity, m (ft) 19

Xis Height from the bottom of the tank shell to the center of action of the lateral seismic 20 force related to the impulsive liquid force for the slab moment, m (ft) 21

Xcs Height from the bottom of the tank shell to the center of action of lateral seismic force 22 related to the convective liquid force for the slab moment, m (ft) 23

Y Distance from liquid surface to analysis point, (positive down), m (ft) 24

yu Estimated uplift for self-anchored tank, mm (in) 25

σc Maximum longitudinal shell compression stress, MPa (psi) 26

σs Hoop stress in the shell due to impulsive and convective forces of the stored liquid, MPa (psi) 27

σh Product hydrostatic hoop stress in the shell, Mpa (psi) 28

σT Total combined hoop stress in the shell, MPa (psi) 29

µ Friction coefficient for tank sliding 30

ρ Mass density of fluid, kg/m3 (lbm/in3) 31

E.3 PERFORMANCE BASIS 32

E.3.1 Seismic Use Group 33

The Seismic Use Group (SUG) for the tank shall be specified by the purchaser. If it is not 34 specified, the Seismic Use Group shall be assigned to be SUG I. 35


E.3.1.1 Seismic Use Group III 1

Seismic Use Group III tanks are those providing necessary service to facilities that are essential 2 for post-earthquake recovery and essential to the life and health of the public; or, tanks 3 containing substantial quantities of hazardous substances that do not have adequate control to 4 prevent public exposure. 5

E.3.1.2 Seismic Use Group II 6

Seismic Use Group II tanks are those storing material that may pose a substantial public hazard 7 and lack secondary controls to prevent public exposure, or those tanks providing direct service to 8 major facilities. 9

E.3.1.3 Seismic Use Group I 10

Seismic Use Group I tanks are those not assigned to Seismic Use Groups III or II. 11

E.3.1.4 Multiple use 12

Tanks serving multiple use facilities shall be assigned the classification of the use having the 13 highest Seismic Use Group. 14

E.4 SITE GROUND MOTION 15

Spectral lateral accelerations to be used for design may be based on either “mapped” seismic 16 parameters (zones or contours), “site-specific” procedures, or probabilistic methods as defined 17 by the design response spectra method contained in this Appendix. A method for regions outside 18 the USA where ASCE 7 methods for defining the ground motion may not be applicable is also 19 included. 20 21 A methodology for defining the design spectrum is given in the following sections. 22

E.4.1 Mapped ASCE 7 Method 23

For sites located in the USA, or where the ASCE 7 method is the regulatory requirement, the 24 maximum considered earthquake ground motion shall be defined as the motion due to an event 25 with a 2% probability of exceedence within a 50 year period. The following definitions apply: 26

• SS is the mapped, maximum considered earthquake, 5-percent-damped, spectral response 27 acceleration parameter at short periods (0.2 seconds). 28

• S1 is the mapped, maximum considered earthquake, 5-percent-damped, spectral response 29 acceleration parameter at a period of 1 second. 30

• S0 is the mapped, maximum considered earthquake, 5-percent-damped, spectral response 31 acceleration parameter at zero seconds (usually referred to as the peak ground 32 acceleration). Unless otherwise specified or determined, S0 shall be defined as 0.4SS 33 when using the mapped methods. 34

35


E.4.2 Site-specific Spectral Response Accelerations 1

The design method for a site-specific spectral response is based on the provisions of ASCE 7. 2 Design using site-specific ground motions should be considered where any of the following 3 apply: 4

• The tank is located within 10 km of a known active fault. 5 • The structure is designed using base isolation or energy dissipation systems, which is 6

beyond the scope of this Appendix. 7 • The performance requirements desired by the owner or regulatory body exceed the goal 8

of this Appendix. 9

Site-specific determination of the ground motion is required when the tank is located on Site 10 Class F type soils. 11

If design for an MCE site-specific ground motion is desired, or required, the site–specific study 12 and response spectrum shall be provided by the Purchaser as defined this Section. 13

However, in no case shall the ordinates of the site-specific MCE response spectrum defined be 14 less than 80% of the ordinates of the mapped MCE response spectra defined in this Appendix. 15

E.4.2.1 Site-Specific Study 16

A site-specific study shall account for the regional tectonic setting, geology, and seismicity. This 17 includes the expected recurrence rates and maximum magnitudes of earthquakes on known faults 18 and source zones, the characteristics of ground motion attenuation, near source effects, if any, on 19 ground motions, and the effects of subsurface site conditions on ground motions. The study shall 20 incorporate current scientific interpretations, including uncertainties, for models and parameter 21 values for seismic sources and ground motions. 22

If there are known active faults identified, the maximum considered seismic spectral response 23 acceleration at any period, Sa

*, shall be determined using both probabilistic and deterministic 24 methods. 25

E.4.2.2 Probabilistic Site-specific MCE Ground Motion 26

The probabilistic site-specific MCE ground motion shall be taken as that motion represented by a 27 5-percent-damped acceleration response spectrum having a 2 percent probability of exceedence 28 in a 50 year period. 29

E.4.2.3 Deterministic Site-specific MCE Ground Motion 30

The deterministic site-specific MCE spectral response acceleration at each period shall be taken 31 as 150 percent of the largest median 5-percent-damped spectral response acceleration computed 32 at that period for characteristic earthquakes individually acting on all known active faults within 33 the region. 34

However, the ordinates of the deterministic site-specific MCE ground motion response spectrum 35 shall not be taken lower than the corresponding ordinates of the response spectrum where the 36 value of SS is equal to 1.5Fa and the value of S1 is equal to 0.6Fv. 37


E.4.2.4 Site-specific MCE Ground Motions 1

The 5% damped site-specific MCE spectral response acceleration at any period, Sa*, shall be 2

defined as the lesser of the probabilistic MCE ground motion spectral response accelerations 3 determined in Section E.4.2.2 and the deterministic MCE ground motion spectral response 4 accelerations defined in Section E.4.2.3. 5

The response spectrum values for 0.5% damping for the convective behavior shall be 1.5 times 6 the 5% spectral values unless otherwise specified by the Purchaser. 7

The values for sites classified as F may not be less than 80% of the values for a site class E site. 8

E.4.3 Sites Not Defined by ASCE 7 Methods 9

In regions outside the USA, where the regulatory requirements for determining design ground 10 motion differ from the ASCE 7 methods prescribed in this Appendix, the following methods may 11 be utilized: 12

1. A response spectrum complying with the regulatory requirements may be used providing 13 it is based on, or adjusted to, a basis of 5% and 0.5% damping as required in this 14 Appendix. The values of the design spectral acceleration coefficients, Ai and Ac, which 15 include the effects of site amplification, importance factor and response modification may 16 be determined directly. Ai shall be based on the calculated impulsive period of the tank 17 (see Section 4.6.1) using the 5% damped spectra, or the period may be assumed to be 0.2 18 seconds. Ac shall be based on the calculated convective period (see Section E.4.6.1) 19 using the 0.5% spectra. 20

2. If no response spectra shape is prescribed and only the peak ground acceleration, SP, is 21 defined, then the following substitutions shall apply: 22

PS SS 5.2= Eqn (1) 23

PSS 25.11 = Eqn (2) 24

E.4.4 Modifications for Site Soil Conditions 25

The maximum considered earthquake spectral response accelerations for peak ground 26 acceleration, shall be modified by the appropriate site coefficients, Fa and Fv from Tables E.4-A 27 and E.4-B. 28

Where the soil properties are not known in sufficient detail to determine the site class, Site Class 29 D shall be assumed unless the authority having jurisdiction determines that Site Class E or F 30 could apply at the site or in the event that Site Class E or F is established by geotechnical data. 31

Table E.4-A – Value of Fa as a Function of Site Class 32

Mapped Maximum Considered Earthquake Spectral Response Accelerations at Short Periods

Site Class Ss < 0.25 Ss =0.50 Ss = 0.75 Ss=1.0 Ss>1.25 A 0.8 0.8 0.8 0.8 0.8 B 1.0 1.0 1.0 1.0 1.0 C 1.2 1.2 1.1 1.0 1.0


D 1.6 1.4 1.2 1.1 1.0 E 2.5 1.7 1.2 0.9 0.9 F * * * * *

* Site Specific geotechnical investigation and dynamic site response analysis is required. 1

2

Table E.4-B - Value of Fv as a function of Site Class 3

Mapped Maximum Considered Earthquake Spectral Response Accelerations at 1 Sec Periods

Site Class S1 < 0.1 S1 = 0.2 S1 = 0.3 S1= 0.4 S1 > 0.5 A 0.8 0.8 0.8 0.8 0.8 B 1.0 1.0 1.0 1.0 1.0 C 1.7 1.6 1.5 1.4 1.3 D 2.4 2.0 1.8 1.6 1.5 E 3.5 3.2 2.8 2.4 2.4 F * * * * *

4

SITE CLASS DEFINTIONS The Site Classes are defined as follows:

A Hard rock with measured shear wave velocity, v̄s > 5,000 ft/sec (1500 m/s)

B Rock with 2,500 ft/sec < v̄s ≤ 5,000 ft/sec (760 m/s < v̄s ≤ 1500 m/s)

C Very dense soil and soft rock with 1,200 ft/sec < v̄s ≤ 2,500 ft/sec (360 m/s < v̄s ≤ 760 m/s) or with either N > 50 or s̄u > 2,000 psf (100 kPa)

D Stiff soil with 600 ft/sec ≤ v̄s ≤ 1,200 ft/sec (180 m/s ≤ v̄s ≤ 360 m/s) or with either 15 ≤ N ≤ 50 or 1,000 psf ≤ s̄u ≤ 2,000 psf (50 kPa ≤ s̄u ≤ 100 kPa)

E A soil profile with v̄s < 600 ft/sec (180 m/s) or with either

N < 15, s̄u < 1,000 psf, or any profile with more than 10 ft (3 m) of soft clay defined as soil with PI > 20, w ≥ 40 percent, and su < 500 psf (25 kPa)

F Soils requiring site-specific evaluations:

1. Soils vulnerable to potential failure or collapse under seismic loading such as liquefiable soils, quick and highly sensitive clays, collapsible weakly cemented soils. However, since tanks typically have an impulsive period of 0.5 secs or less, site-specific evaluations are not required but recommended to determine spectral accelerations for liquefiable soils. The Site Class may be determined in accordance with Sec. E.4.7.2.2, assuming liquefaction does not occur, and the corresponding values of Fa and Fv determined from Tables E.4-3 and E.4-4.

2. Peats and/or highly organic clays (HS > 10 ft [3 m] of peat and/or highly organic clay, where H = thickness of soil)

3. Very high plasticity clays (HS> 25 ft [8 m] with PI > 75)

4. Very thick, soft/medium stiff clays (HS > 120 ft [36 m])

The parameters used to define the Site Class are based on the upper 100 ft (30 m) of the site profile. Profiles containing distinctly different soil layers shall be subdivided into those layers designated by a number that ranges from 1 to n at the bottom where there are a total of n distinct layers in the upper 100 ft (30 m). The symbol i then refers to any one of the layers between 1 and n.

where:


vsi = the shear wave velocity in ft/sec (m/s).

di = the thickness of any layer (between 0 and 100 ft [30 m]).

1

1

n

ii

s ni

i si

dv

dv

=

=

=∑

∑ (3.5-1)

where 1

n

ii

d=∑ is equal to 100 ft (30 m).

Ni = the Standard Penetration Resistance determined in accordance with ASTM D 1586, as directly measured in the field without corrections, and shall not be taken greater than 100 blows/ft.

1

1

n

iin

i

i i

dN

dN

=

=

=∑

∑ (3.5-2)

1

sch m

i

i i

dNdN=

=

∑ (3.5-3)

where 1

m

i si

d d=

=∑ .

Use only di and Ni for cohesionless soils.

ds = the total thickness of cohesionless soil layers in the top 100 ft (30 m).

sui = the undrained shear strength in psf (kPa), determined in accordance with ASTM D 2166 or D 2850, and shall not be taken greater than 5,000 psf (240 kPa).

1

cu k

i

i ui

dsds=

=

∑ (3.5-4)

where 1

k

i ci

d d=

=∑ .

dc = the total thickness (100 - ds) of cohesive soil layers in the top 100 ft (30 m).

PI = the plasticity index, determined in accordance with ASTM D 4318.

w = the moisture content in percent, determined in accordance with ASTM D 2216.


STEPS FOR CLASSIFYING A SITE: Step 1: Check for the four categories of Site Class F requiring site-specific evaluation. If the site corresponds to

any of these categories, classify the site as Site Class F and conduct a site-specific evaluation.

Step 2: Check for the existence of a total thickness of soft clay > 10 ft (3 m) where a soft clay layer is defined by: su < 500 psf (25 kPa), w ≥ 40 percent, and PI > 20. If these criteria are satisfied, classify the site as Site Class E.

Step 3: Categorize the site using one of the following three methods with v̄s, N and s̄u computed in all cases see Table E.4-C:

a) v̄s for the top 100 ft (30 m) (v̄s method)

b) N for the top 100 ft (30 m) ( N method)

c) N for cohesionless soil layers (PI < 20) in the top 100 ft (30 m) and average s̄u for cohesive soil layers (PI > 20) in the top 100 ft (30 m) (s̄u method)

1 2

Table E.4-C Site Classification

Site Class

v̄s

N or chN

s̄ua

E

< 600 fps

( < 180 m/s)

< 15

< 1,000 psf ( < 50 kPa)

D

600 to 1,200 fps (180 to 360 m/s)

15 to 50

1,000 to 2,000 psf

(50 to 100 kPa)

C

1,200 to 2,500 fps (360 to 760 m/s)

> 50

> 2,000

( > 100 kPa)

B 2,500 to 5,000 fps (760 m/s to 1500 m/s)

A > 5,000 fps (1500 m/s)

Note: a If the s̄u method is used and the chN and s̄u criteria differ, select the category with the softer soils (for example, use Site Class E instead of D).

3

Assignment of Site Class B shall be based on the shear wave velocity for rock. For competent 4 rock with moderate fracturing and weathering, estimation of this shear wave velocity shall be 5 permitted. For more highly fractured and weathered rock, the shear wave velocity shall be 6 directly measured or the site shall be assigned to Site Class C. 7


Assignment of Site Class A shall be supported by either shear wave velocity measurements on 1 site or shear wave velocity measurements on profiles of the same rock type in the same 2 formation with an equal or greater degree of weathering and fracturing. Where hard rock 3 conditions are known to be continuous to a depth of 100 ft (30 m), surficial shear wave velocity 4 measurements may be extrapolated to assess v̄s. 5

Site Classes A and B shall not be used where there is more than 10 ft (3 m) of soil between the 6 rock surface and the bottom of the tank foundation. 7

E.4.5 Structural Period of Vibration 8

The pseudo-dynamic modal analysis method utilized in this Appendix is based on the natural 9 period of the structure and contents as defined in this section. 10

E.4.5.1 Impulsive Natural Period 11

The design methods in this Appendix are independent of impulsive period of the tank. However, 12 the impulsive period of the tank system may be estimated by Eqn (3) 13 14

=

EDtHCT

u

ii

ρ2

Eqn (3) 15

16 17

FIgure E.4-1 Coefficient Ci

6

6.5

7

7.5

8

8.5

9

9.5

0 0.5 1 1.5

H/D

Ci

18 19 20 21 22


1

E.4.5.2 Convective (Sloshing) Period 2

The first mode sloshing wave period, in seconds, shall be calculated by Equation (4) where Ks is 3 the sloshing period coefficient defined in Eqn (4c): 4 5 6 7 In SI units: 8

9

DK = T sc 8.1 Eqn (4a) 10

11 12

or, in customary US units; 13 14

DK = T sc Eqn (4b) 15

16

=

DH

Ks68.3tanh

578.0 Eqn (4c) 17

E.4.6 Design Spectral Response Accelerations 18

The design response spectrum for ground supported, flat bottom tanks is defined by the 19 following parameters: 20

E.4.6.1 – Spectral Acceleration Coefficients. 21

When probabilistic or mapped design methods are utilized, the spectral acceleration parameters 22 for the design response spectrum are given in the following equations. Unless otherwise 23 specified by the Purchaser, TL shall be taken as the mapped value found in ASCE 7. For tanks 24 falling in SUG I or SUG II, the mapped value of TL shall be used to determine convective forces 25 except that a value of TL equal to 4 seconds shall be permitted to be used to determine the 26 sloshing wave height. For tanks falling in SUG III, the mapped value of TL shall be used to 27 determine both convective forces and sloshing wave height except that the importance factor, I, 28 shall be set equal to 1.0 in the determination of sloshing wave height. In regions outside the 29 USA, where the regulatory requirements for determining design ground motion differ from the 30 ASCE 7 methods prescribed in this Appendix, TL shall be taken as 4 seconds. 31 32

For sites where only the peak ground acceleration is defined, substitute SP for S0 in Eqns (5) thru 33 (9). The scaling factor, Q, is defined as 2/3 for the ASCE 7 methods. Q may be taken equal to 34 1.0 unless otherwise defined in the regulatory requirements where ASCE 7 does not apply. Soil 35 amplification coefficients, Fa and Fv; the value of the importance factor, I; and the ASD response 36 modification factors, Rwi and Rwc, shall be as defined by the local regulatory requirements. If 37 these values are not defined by the regulations, the values in this Appendix shall be used. 38


1 2 Impulsive spectral acceleration parameter, Ai: 3

=

=

wia

wiDSi R

ISQFRISA 05.2 Eqn (5) 4

However, 007.0≥iA Eqn (6)and, 5

for seismic design categories E and F only, 6 7

=

≥

wiP

wii R

ISRISA 875.05.0 1 Eqn (7) 8

9 Convective spectral acceleration parameter, Ac: 10 11

When, TC < TL iwcC

Sv

wcCDc A

RI

TT

SKQFRI

TKSA ≤

=

= 01 5.21 Eqn (8) 12

When, TC > TL , iwcC

LSv

wcC

LDc A

RI

TTTSKQF

RI

TTKSA ≤

=

= 2021 5.2 Eqn (9) 13

E.4.6.2.1 Site Specific Response Spectra 14

When site-specific design methods are specified, the seismic parameters shall be defined by Eqns 15 (10) through (12). 16 17 Impulsive spectral acceleration parameter: 18 19

*05.2 a

wii S

RIQA

= Eqn (10) 20

21 Alternatively, Ai, may be determined using either (1) the impulsive period of the tank system, or 22 (2) assuming the impulsive period = 0.2 sec; 23 24

*a

wii S

RIQA

= Eqn (11) 25

where, Sa* is the ordinate of the 5% damped, site-specific MCE response spectra at the 26

calculated impulsive period including site soil effects. See Section E.4.4.1. 27 28 Exception: 29 Unless otherwise specified by the Purchaser, the value of the impulsive spectral acceleration, 30 Sa*, for flat bottom tanks with H/D < 0.8 need not exceed 150%g when the tanks are: 31

• self anchored, or 32


• mechanically anchored tanks that are equipped with traditional anchor bolt and chairs at 1 least 18 inches high and are not otherwise prevented from sliding laterally at least 1 inch. 2

3 Convective spectral acceleration: 4 5

*a

wcc S

RIQKA

= Eqn (12) 6

where, Sa* is the ordinate of the 5% damped, site-specific MCE response spectra at the calculated 7

convective period including site soil effects. See Section E.4.4.2. 8 9 Alternatively, the ordinate of a site-specific spectrum based on the procedures of E.4.2 for 0.5% 10 damping may be used to determine the value Sa

* with K set equal to 1.0. 11

E.5 SEISMIC DESIGN FACTORS 12

E.5.1 – Design Forces 13

The equivalent lateral seismic design force shall be determined by the general relationship 14

effAWF = Eqn (13) 15

where, 16 A = lateral acceleration coefficient, %g 17 Weff = Effective weight 18

E.5.1.1 Response Modification Factor 19

The response modification factor for ground supported, liquid storage tanks designed and 20 detailed to these provisions shall be less than or equal to the values shown in Table E.5-A. 21 22

23 Table E.5-A, Response Modification Factors for ASD Methods 24

25

E.5.1.2 Importance Factor 26

The importance factor (I) is defined by the Seismic Use Group and shall be specified by the 27 purchaser. See Section E.3 and Table E.5-B. 28 29

Anchorage system Rwi, (impulsive), Rwc, (convective) Self – anchored 3.5 2 Mechanically-anchored 4 2


Table E.5-B - Importance Factor (I) and Seismic Use Group Classification 1 2

Seismic Use Group

I

I

1.0

II

1.25

III

1.5

E.6 DESIGN 3

E.6.1 Design Loads 4

Ground-supported, flat bottom tanks, storing liquids shall be designed to resist the seismic forces 5 calculated by considering the effective mass and dynamic liquid pressures in determining the 6 equivalent lateral forces and lateral force distribution. This is the default method for this 7 Appendix. The equivalent lateral force base shear shall be determined as defined in the following 8 sections. 9 10 The seismic base shear shall be defined as the square root of the sum of the squares (SRSS) 11 combination of the impulsive and convective components unless the applicable regulations 12 require direct sum. For the purposes of this Appendix, an alternate method using the direct sum 13 of the effects in one direction combined with 40% of the effect in the orthogonal direction is 14 deemed to be equivalent to the the SRSS summation. 15 16

22ci VVV += Eqn (14) 17

Where, )( ifrsii WWWWAV +++= Eqn (15) 18

ccc WAV = Eqn (16) 19

E.6.1.1 Effective Weight of Product 20

The effective weights Wi and Wc shall be determined by multiplying the total product weight, 21 Wp, by the ratios Wi/Wp and Wc/Wp, respectively, Equations (17) through (19). 22

When D/H is greater than or equal to 1.333, the effective impulsive weight is defined in Equation 23 (17), 24 25

pi W

HD

HD

W866.0

866.0tanh

= Eqn (17) 26

When D/H is less than 1.333, the effective impulsive weight is defined in Equation (18), 27 28


pi WHDW

−= 218.00.1 Eqn (18) 1

2 The effective convective weight is defined in Equation (19), 3

4

=

DH

HDWc

67.3tanh230.0 Eqn (19) 5

6

E.6.1.2 Center of Action for Effective Lateral Forces 7

The moment arm from the base of the tank to the center of action for the equivalent lateral forces 8 from the liquid is defined by Equations (20) through (27). 9 10 The center of action for the impulsive lateral forces for the tank shell, roof and appurtenances is 11 assumed to act through the center of gravity of the component. 12

E.6.1.2.1 Center of Action for Ringwall Overturning Moment 13

The ringwall moment, Mrw, is the portion of the total overturning moment that acts at the base of 14 the tank shell perimeter. This moment is used to determine loads on a ringwall foundation, the 15 tank anchorage forces, and to check the longitudinal shell compression. 16 17 The heights from the bottom of the tank shell to the center of action of the lateral seismic forces 18 applied to Wi and Wc, Xi and Xc, may be determined by multiplying H by the ratios Xi /H and Xc 19 /H, respectively, obtained for the ratio D/H by using Equations (20) through (). 20 21 When D/H is greater than or equal to 1.3333, the height Xi is determined by Equation (20), 22 23 24 HX i 375.0= Eqn (20) 25

26 When D/H is less than 1.3333, the height Xi is determined by Equation (21), 27 28

HHDX i

−= 094.05.0 Eqn (21) 29

30 The height Xc is determined by Equation (22), 31 32 33

H

DH

DH

DH

X c

−

−=67.3sinh67.3

167.3cosh0.1 Eqn (22) 34


1

E.6.1.2.2 Center of Action for Slab Overturning Moment 2

The “slab” moment, Ms, is the total overturning moment acting across the entire tank base cross 3 section. This overturning moment is used to design slab and pile cap foundations. 4

When D/H is greater than or equal to 1.3333, the height Xis is determined by Equation (23), 5 6

H

HD

HD

X is

−

+= 0.1866.0tanh

866.0333.10.1375.0 Eqn (23) 7

8 When D/H is less than 1.3333, the height Xis is determined by Equation (24), 9 10

HHDX is

+= 060.0500.0 Eqn (24) 11

12 The height, Xcs, is determined by Eqn (25): 13 14

H

DH

DH

DH

X cs

−

−=67.3sinh67.3

937.167.3cosh0.1 Eqn (25) 15

16

E.6.1.3 Vertical Seismic Effects 17

When specified, vertical acceleration effects shall be considered as acting in both upward and 18 downward directions and combined with lateral acceleration effects by the SRSS method unless 19 a direct sum combination is required by the applicable regulations. Vertical acceleration effects 20 for hydrodynamic hoop stresses shall be combined as shown in Section E.6.1.3.1. Vertical 21 acceleration effects need not be combined concurrently for determining loads, forces and 22 resistance to overturning in the tank shell. 23

The maximum vertical seismic acceleration parameter shall be taken as 0.14SDS or greater for the 24 ASCE 7 method unless otherwise specified by the Purchaser. Alternatively, the Purchaser may 25 specify the ertical ground motion acceleration parameter, Av. The total vertical seismic force 26 shall be: 27

effvv WAF ±= Eqn (26) 28

Vertical seismic effects shall be considered in the following when specified: 29 • Shell hoop tensile stresses (see Section E.6.1.4) 30


• Shell membrane compression (see Section E.6.2.2) 1 • Anchorage design (see Section E.6.2.1) 2 • Fixed roof components 3 • Sliding 4 • Foundation design (see Section E.6.2.3) 5 6

In regions outside the USA where the regulatory requirements differ from the methods 7 prescribed in this Appendix, the vertical acceleration parameter and combination with lateral 8 effects may be applied as defined by the governing regulatory requirements. 9

E.6.1.4 Dynamic Liquid Hoop Forces 10

Dynamic hoop tensile stresses due to the seismic motion of the liquid shall be determined by the 11 following formulas: 12 13 For D/H ≥ 1.333: 14 15 In SI units: 16

17

−=

HD

HY

HYGDHAN ii 866.0tanh5.04.21

2

Eqn (27a) 18

19 or, in customary US units; 20

−=

HD

HY

HYGDHAN ii 866.0tanh5.018

2

Eqn (27b) 21

22 For D/H < 1.33 and Y < 0.75D: 23 In SI units: 24

25

−=

22

75.05.0

75.016.13

DY

DYGDAN ii Eqn (28a) 26


−=

22

75.05.0

75.011

DY

DYGDAN ii Eqn (28b) 29

30 For D/H < 1.333 and Y ≥ 0.75D: 31 32 33 34 In SI units: 35

36


26.6 GDAN ii = Eqn (29a) 1


254.5 GDAN ii = Eqn (29b) 4

5 For all proportions of D/H: 6

7 In SI units: 8

9 ( )

−

=

DH

DYHSGDCA

Ncc

c 68.3cosh

68.3cosh1.33 2

Eqn (30a) 10

11 12

( )

−

=

DH

DYHSGDCA

Ncc

c 68.3cosh

68.3cosh9.3 2

Eqn (30b) 13

14 1. When the Purchaser specifies that vertical acceleration need not be considered (i.e; 15

Av=0), the combined hoop stress shall be defined by Eqn 31. The dynamic hoop tensile 16 stress shall be directly combined with the product hydrostatic design stress in determining 17 the total stress. 18

19

tNNN cih

shT

22 +±=±= σσσ Eqn (31) 20

21 2. When vertical acceleration is specified. 22 23

( )t

NANNN hvcih

shT

++±

=±=

222

σσσ Eqn (32) 24

25 26

E.6.1.5 Overturning Moment 27

The seismic overturning moment at the base of the tank shell shall be the SRSS summation of 28 the impulsive and convective components multiplied by the respective moment arms to the 29 center of action of the forces unless otherwise specified. 30 31 Ringwall Moment, Mrw: 32


1

[ ] [ ]22 )()( cccrrssiiirw XWAXWXWXWAM +++= Eqn (33) 2

3 Slab Moment, Ms: 4 5

[ ] [ ]22 )()( csccrrssisiis XWAXWXWXWAM +++= Eqn (34) 6

7 Unless a more rigorous determination is used, the overturning moment at the bottom of each 8 shell ring shall be defined by linear approximation using the following: 9

1. If the tank is equipped with a fixed roof, the impulsive shear and overturning moment is 10 applied at top of shell 11

2. The impulsive shear and overturning moment for each shell course is included based on 12 the weight and centroid of each course. 13

3. The overturning moment due to the liquid is approximated by a linear variation that is 14 equal to the ringwall moment, Mrw at the base of the shell to zero at the maximum liquid 15 level. 16

17

E.6.1.6 Soil-Structure Interaction 18

If specified by the Purchaser, the effects of soil-structure interaction on the effective damping 19 and period of vibration may be considered for tanks in accordance with ASCE 7 with the 20 following limitations: 21

• Tanks shall be equipped with a reinforced concrete ringwall, mat or similar type 22 foundation supported on grade. Soil structure interaction effects for tanks supported on 23 granular berm, or pile type foundation are outside the scope of this Appendix. 24

• The tanks shall be mechanically anchored to the foundation. 25 • The value of the base shear and overturning moments for the impulsive mode including 26

the effects of soil-structure interaction shall not be less than 80% of the values 27 determined without consideration of soil-structure interaction. 28

• The effective damping factor for the structure-foundation system shall not exceed 20%. 29

E.6.2 Resistance to Design Loads 30

The allowable stress design (ASD) method is utilized in this Appendix. Allowable stresses in 31 structural elements applicable to normal operating conditions may be increased by 33% when the 32 effects of the design earthquake are included unless otherwise specified in this Appendix. 33

E.6.2.1 Anchorage 34

Resistance to the design overturning (ringwall) moment at the base of the shell may be provided 35 by: 36

• the weight of the tank shell, weight of roof reaction on shell Wrs, and by the weight of 37 a portion of the tank contents adjacent to the shell for unanchored tanks 38

• mechanical anchorage devices. 39


E.6.2.1.1 Self-anchored 1

For self-anchored tanks, a portion of the contents may be used to resist overturning. The 2 anchorage provided is dependent on the assumed width of a bottom annulus uplifted by the 3 overturning moment. The resisting annulus may be a portion of the tank bottom (i.e. ta = tb) or a 4 separate butt-welded annular ring (i.e. ta > tb). The resisting force of the annulus that lifts off the 5 foundation shall be determined by Eqn (35) 6 7 In SI units: 8

9

eyaa HGFtw 99= ≤ 196 HDGe Eqn (35a) 10

11 In customary US units 12

eyaa HGFtw 9.7= ≤ 1.28 HDGe Eqn (35b) 13

14 15 16 Equation (35) for wa applies whether or not a thickened bottom annulus is used. 17 18 The tank is self-anchored providing the following conditions are met: 19

1. The resisting force is adequate for tank stability (i.e. the anchorage ratio, J < 1.54). 20 2. The maximum width of annulus for determining the resisting force is 3.5% of the 21

tank diameter. 22 3. The shell compression satisfies section E.6.2.2. 23 4. The required annular plate thickness does not exceed the thickness of the bottom shell 24

course. 25 5. Piping flexibility requirements are satisfied. 26

E.6.2.1.1.1 Anchorage Ratio, J 27 28

( )( )avt

rw

wAwDMJ

+−=

4.012 Eqn (36) 29

Where: 30

+= rs

st w

DWwπ

Eqn (37) 31

32 33 34

35 36 37 38

Table E.6-A - Anchorage Ratio Criteria 39 J Criteria


anchorage ratio J < 0.785 No calculated uplift under the design seismic overturning moment.

The tank is self anchored. 0.785 < J <1.54 Tank is uplifting, but the tank is stable for the design load providing the

shell compression requirements are satisfied. Tank is self-anchored. J > 1.54 Tank is not stable and cannot be self-anchored for the design load.

Modify the annular plate if L < 0.035D is not controlling or add mechanical anchorage.

1

E.6.2.1.1.2 Annular Plate Requirements 2

The thickness of the tank floor plate provided under the shell may be greater than or equal to the 3 thickness of the general tank floor plate (i.e. ta > tb) with the following restrictions. (Note- In 4 thickening the bottom annulus, the intent is not to force a thickening of the lowest shell course, 5 thereby inducing an abrupt thickness change in the shell, but rather to impose a limit on the 6 bottom annulus thickness based on the shell design). 7

1. The thickness, ta, used to calculate wa in Equation (35) the first shell course thickness, ts, 8 less the shell corrosion allowance, 9

2. Nor shall the thickness, ta, used in Equation (35) exceed the actual thickness of the plate 10 under the shell less the corrosion allowance for tank bottom. 11

3. When the bottom plate under the shell is thicker than the remainder of the tank bottom 12 (i.e. ta> tb) the minimum projection of the supplied thicker annular plate inside the tank 13 wall, Ls, shall be equal to or greater than L: 14

15 In SI units: 16 17

DHGFtL eya 035.001723.0 ≤= Eqn (38a) 18

19 In customary US units 20 21

eya HGFtL 216.0= , ≤ 0.035D (ft) Eqn (38b) 22

23 24

E.6.2.1.2 Mechanically-anchored 25

If the tank configuration is such that the self-anchored requirements can not be met, the tank 26 must be anchored with mechanical devices such as anchor bolts or straps. 27 When tanks are anchored, the resisting weight of the product shall not be used to reduce the 28 calculated uplift load on the anchors. The anchors shall be sized to provide for at least the 29 following minimum anchorage resistance, : 30 31 32


( )

−−= vt

rwAB Aw

DMw 4.01273.12 Eqn (39) 1

2 Plus 0.4 times the uplift, in N/m (lbf/ft2) of shell circumference, due to design internal pressure. 3 See API 650 Section 3.12 for load combinations. If the ratio of operating pressure to design 4 pressure exceeds 0.4, the purchaser should consider specifying a higher factor on design. Wind 5 loading need not be considered in combination with seismic loading. 6 7 The anchor seismic design load, PAB, is defined in Eqn (40) 8 9

=

AABAB n

DwP π Eqn (40) 10

where, nA is the number of equally spaced anchors around the tank circumference. PAB shall be 11 increased to account for unequal spacing. 12

When mechanical anchorage is required, the anchor embedment or attachment to the foundation, 13 the anchor attachment assembly and the attachment to the shell shall be designed for PA, the 14 anchor attachment design load, PA, shall be the lesser of the load equal to the minimum specified 15 yield strength multiplied by the as-built cross-sectional area of the anchor or three times PAB. 16

The maximum allowable stress for the anchorage parts shall not exceed the following values for 17 anchors designed for the seismic loading alone or in combination with other load cases: 18 19

• An allowable tensile stress for anchor bolts and straps equal to 80% of the published 20 minimum yield stress. 21

• For other parts, 133% of the allowable stress in accordance with Section 3.10.3. 22 • The maximum allowable design stress in the shell at the anchor attachment shall be 23

limited to 170 MPa (25,000 psi) with no increase for seismic loading. These stresses can 24 be used in conjunction with other loads for seismic loading when the combined loading 25 governs. 26

27

E.6.2.2 Maximum Longitudinal Shell Membrane Compression Stress 28

E.6.2.2.1 Shell Compression in Self-anchored Tanks 29

The maximum longitudinal shell compression stress at the bottom of the shell when there is no 30 calculated uplift, J < 0.785, shall be determined by the formula 31 32 In SI units: 33

34

( )s

rwvtc tD

MAw1000

1273.14.01 2

++=σ Eqn(41a) 35

or, in customary US units; 36 37


( )s

rwvtc tD

MAw12

1273.14.01 2

++=σ Eqn (41b) 1

2 3

The maximum longitudinal shell compression stress at the bottom of the shell when there is 4 calculated uplift, J > 0.785, shall be determined by the formula 5 6 In SI units: 7 8

( )[ ] s

aavt

c tw

JwAw

10001

18667.0607.0)4.01

3.2

−

−++

=σ Eqn (42a) 9


( )[ ] s

aavt

c tw

JwAw

121

18667.0607.04.01

3.2

−

−++

=σ Eqn (42b) 12

13 14 E.6.2.2.2 Shell Compression in Mechanically-anchored Tanks 15 The maximum longitudinal shell compression stress at the bottom of the shell for mechanically-16 anchored tanks shall be determined by the formula 17 18 In SI units: 19

20

( )s

rwvtc tD

MAw1000

1273.14.01 2

++=σ Eqn (43a) 21


( )s

rwvtc tD

MAw12

1273.14.01 2

++=σ Eqn (43b) 24

25 E.6.2.2.3 Allowable Longitudinal Membrane Compression Stress in Tank Shell 26 The maximum longitudinal shell compression stress σc must be less than the seismic allowable 27 stress FC, which is determined by the following formulas and includes the 33% increase for 28 ASD. These formulas for FC, consider the effect of internal pressure due to the liquid contents. 29 30 When GHD2/ t2 is greater than or equal to 44 (SI units) [106 U.S. Customary Units], 31 32 In SI units: 33

FC = 83 ts / D Eqn (44a) 34 35

Or, in US Customary units: 36 37 FC = 106 ts / D Eqn (44b) 38

39


1 In SI units: 2 When GHD2/ t2 is less than 44, 3 4

FC = 83 ts / (2.5D) + 7.5 √( GH) <0.5Fty Eqn (45a) 5 6 Or, in customary US units; 7 When GHD2It2 is less than 106, 8 9

FC = 106 ts/ (2.5 D) + 600√( GH) < O.5 Fty Eqn (45b) 10 11 12 If the thickness of the bottom shell course calculated to resist the seismic overturning moment is 13 greater than the thickness required for hydrostatic pressure, both excluding any corrosion 14 allowance, then the calculated thickness of each upper shell course for hydrostatic pressure shall 15 be increased in the same proportion, unless a special analysis is made to determine the seismic 16 overturning moment and corresponding stresses at the bottom of each upper shell course (See 17 Section E.6.1.5). 18

E.6.2.3 Foundation 19

Foundations and footings for mechanically-anchored flat-bottom tanks shall be proportioned to 20 resist peak anchor uplift and overturning bearing pressure. Product and soil load directly over the 21 ringwall and footing may be used to resist the maximum anchor uplift on the foundation, 22 provided the ringwall and footing are designed to carry this eccentric loading. 23

Product load shall not be used to reduce the anchor load. 24

When vertical seismic accelerations are applicable, the product load directly over the ringwall 25 and footing 26

1. When used to resist the maximum anchor uplift on the foundation, the product pressure 27 shall be multiplied by a factor of (1-0.4Av) and the foundation ringwall and footing shall 28 be designed to resist the eccentric loads with or without the vertical seismic accelerations. 29

2. When used to evaluate the bearing (downward) load, the product pressure over the 30 ringwall shall be multiplied by a factor of (1+0.4Av) and the foundation ringwall and 31 footing shall be designed to resist the eccentric loads with or without the vertical seismic 32 accelerations. 33

34 The overturning stability ratio for mechanically-anchored tank system excluding vertical seismic 35 effects shall be 2.0 or greater as defined in Eqn (46). 36 37

[ ]0.2

5.0≥

++++

s

gfdTfp

MWWWWWD

Eqn (46) 38

39 Ringwalls for self-anchored flat-bottom tanks shall be proportioned to resist overturning bearing 40 pressure based on the maximum longitudinal shell compression force at the base of the shell in 41


Eqn (47). Slabs and pile caps for self-anchored tanks shall be designed for the peak loads 1 determined in Section E.6.2.2.1. 2 3 4

( )

++= 2

273.14.01D

MAwP rwvtf Eqn (47) 5

6

E.6.2.4 Hoop Stresses 7

The maximum allowable hoop tension membrane stress for the combination of hydrostatic 8 product and dynamic membrane hoop effects shall be the lesser of: 9

• The basic allowable membrane in this standard for the shell plate materialincreased by 10 33%; or, 11

• 0.9Fy times the joint efficiency where Fy is the lesser of the published minimum yield 12 strength of the shell material or weld material. 13

14

E.7 DETAILING REQUIREMENTS 15

E.7.1 Anchorage 16

Tanks at grade are permitted to be designed without anchorage when they meet the requirements 17 for self-anchored tanks in this appendix. 18

The following special detailing requirements shall apply to steel tank mechanical anchors in 19 seismic regions where SDS > 0.05g. 20

E.7.1.1 Self-anchored 21

For tanks in SUG 3 and located where SDS = 0.5g or greater, butt welded annular plates shall be 22 required. Annular plates exceeding 3/8 inch thickness shall be butt-welded. The corner weld of 23 the tank shell to bottom annular plate shall be checked for the design uplift load. 24

E.7.1.2 Mechanically-anchored 25

When mechanical-anchorage is required, at least six anchors shall be provided. The spacing 26 between anchors shall not exceed 3 m (10 ft). 27

28 When anchor bolts are used, they shall have a minimum diameter of 25 mm (1 in.), excluding 29 any corrosion allowance. Carbon steel anchor straps shall be ¼ inch minimum thickness and 30 have a minimum corrosion allowance of 1/16 inch on each surface for a distance at least 75 mm 31 (3 inches) but not more than 300 mm (12 inches) above the surface of the concrete. 32

Hooked anchor bolts (L or J shaped embedded bolts) or other anchorage systems based solely on 33 bond or mechanical friction shall not be used when seismic design is required by this Appendix. 34 Post-installed anchors may be used provided that testing validates their ability to develop yield 35 load in the anchor under cyclic loads in cracked concrete and meet the requirements of ACI 355. 36


E.7.2 Freeboard 1

Sloshing of the liquid within the tank or vessel shall be considered in determining the freeboard 2 required above the top capacity liquid level. A minimum freeboard shall be provided per Table 3 E.7-A. See Section E.4.6.1. Purchaser shall specify whether freeboard is desired for SUG I 4 tanks. Freeboard isrequired for SUG II and SUG III tanks. The height of the sloshing wave 5 above the product design height can be estimated by: 6

fs Da5.0=δ Eqn (48) 7

8

For SUG I and II, 9

When, TC < 4

=

=

C

Sv

CDf T

TISKQF

TIKSa 01 5.21

Eqn (49) 10

When, TC > 4 ,

=

= 2021

45.24

C

Sv

CDf T

TISKQFT

IKSa Eqn (50) 11

12

For SUG III, 13

14

When, TC < TL

=

=

C

Sv

CDf T

TSKQF

TKSa 01 5.21 Eqn (51) 15

When, TC > TL,

=

= 2021 5.2

C

LSv

C

LDf T

TTSKQFTTKSa Eqn (52) 16

17

18 TABLE E.7-A Minimum Required Freeboard 19

Value of SDS

I

II

III SDS<0.33g

0.7δs (a)

0.7δs (a)

δs (c) SDS < 0.50g

0.7δs (a)

0.7δs (b)

δs (c) 20

a A freeboard of 0.7δs is recommended for economic considerations but not required. b A freeboard equal to 0.7δs is required unless one of the following alternatives are provided:

1. Secondary containment is provided to control the product spill. 2. The roof and tank shell are designed to contain the sloshing liquid.

c Freeboard equal to the calculated wave height, δs, is required unless one of the following alternatives are provided:

1. Secondary containment is provided to control the product spill. 2. The roof and tank shell are designed to contain the sloshing liquid.

21


E.7.3 Piping Flexibility 1

Piping systems connected to tanks shall consider the potential movement of the connection 2 points during earthquakes and provide sufficient flexibility to avoid release of the product by 3 failure of the piping system. The piping system and supports shall be designed so as to not 4 impart significant mechanical loading on the attachment to the tank shell. Local loads at piping 5 connections shall be considered in the design of the tank shell. Mechanical devices which add 6 flexibility such as bellows, expansion joints, and other flexible apparatus may be used when they 7 are designed for seismic loads and displacements. 8

Unless otherwise calculated, piping systems shall provide for the minimum displacements in 9 Table E.7-B at working stress levels (with the 33% increase for seismic loads) in the piping, 10 supports and tank connection. The piping system and tank connection shall also be designed to 11 tolerate 1.4Cd times the working stress displacements given in table E.7.B without rupture, 12 although permanent deformations and inelastic behavior in the piping supports and tank shell is 13 permitted. For attachment points located above the support or foundation elevation, the 14 displacements in Table E.7-B shall be increased to account for drift of the tank or vessel. 15

Table E.7-B Design Displacements for Piping Attachments

Condition

ASD Design

Displacement (in.)

Mechanically-anchored tanks

Upward vertical displacement relative to support or foundation:

Downward vertical displacement relative to support or foundation:

Range of horizontal displacement (radial and tangential) relative to support or foundation :

1

0.5

0.5 Self-anchored tanks

Upward vertical displacement relative to support or foundation:

Anchorage ratio less than or equal to 0.785: Anchorage ratio greater than 0.785:

Downward vertical displacement relative to support or foundation:

For tanks with a ringwall/mat foundation: For tanks with a berm foundation: Range of horizontal displacement (radial and tangential) relative to support or foundation

1 4

0.5 1

2

16 The values given in Table E.7-B do not include the influence of relative movements of the 17 foundation and piping anchorage points due to foundation movements (such as settlement or 18 seismic displacements). The effects of foundation movements shall be included in the design of 19 the piping system design, including the determination of the mechanical loading on the tank or 20 vessel consideration of the total displacement capacity of the mechanical devices intended to add 21 flexibility. 22

When SDS < 0.1, the values in Table E.7-1 may be reduced to 70% of the values shown. 23


E.7.3.1 – Method for Estimating Tank Uplift 1

The maximum uplift at the base of the tank shell for a self anchored tank constructed to the 2 criteria for annular plates (see Section E.6.2.1) may be approximated by Eqn (53): 3 4

5 6

In SI units: 7 8 9

“later” Eqn(53a) 10 11

Or, in customary US units; 12 13

b

yu t

LFy

83300

2

= Eqn (53b) 14

E.7.4 Connections 15

Connections and attachments for anchorage and other lateral force resisting components shall be 16 designed to develop the strength of the anchor (e.g., minimum published yield strength, Fy in 17 direct tension, plastic bending moment), or 4 times the calculated element design load. 18

Penetrations, manholes, and openings in shell components shall be designed to maintain the 19 strength and stability of the shell to carry tensile and compressive membrane shell forces. 20

The bottom connection on an unanchored flat-bottom tank shall be located inside the shell a 21 sufficient distance to minimize damage by uplift. As a minimum, the distance measured to the 22 edge of the connection reinforcement shall be the width of the calculated unanchored bottom 23 hold-down plus 12 in. 24

E.7.5 Internal Components 25

The attachments of internal equipment and accessories which are attached to the primary liquid 26 or pressure retaining shell or bottom, or provide structural support for major components shall be 27 designed for the lateral loads due to the sloshing liquid in addition to the inertial forces. 28

Seismic design of roof framing and columns shall be made if specified by the purchaser. The 29 purchaser shall specify live loads and amount of vertical acceleration to be used in seismic 30 design of the roof members. Columns shall be designed for lateral liquid inertia loads and 31 acceleration as specified by the purchaser. Seismic beam-column design shall be based upon the 32 primary member allowable stresses set forth in AISC (ASD), increased by one-third for seismic 33 loading. 34

Internal columns shall be guided or supported to resist lateral loads (remain stable) even if the 35 roof components are not specified to be designed for the seismic loads, including tanks that need 36 not be designed for seismic ground motion in this Appendix (see Section E.1) 37


E.7.6 Sliding Resistance 1

The transfer of the total lateral shear force between the tank and the subgrade shall be 2 considered: 3

For self-anchored flat bottom steel tanks, the overall horizontal seismic shear force shall be 4 resisted by friction between the tank bottom and the foundation or subgrade. Self-anchored 5 storage tanks shall be proportioned such that the calculated seismic base shear, V, does not 6 exceed Vs: 7

The friction coefficient, µ, shall not exceed 0.4. Lower values of the friction coefficient should 8 be used if the interface of the bottom to supporting foundation does not justify the friction value 9 above (e.g., leak detection membrane beneath the bottom with a lower friction factor, smooth 10 bottoms, etc). 11

12 ( )( )vpfrss AWWWWV 4.00.1 −+++= µ Eqn (54) 13

14 No additional lateral anchorage is required for mechanically-anchored steel tanks designed in 15 accordance with this Appendix even though small movements of approximately 1 inch are 16 possible. 17

The lateral shear transfer behavior for special tank configurations (e.g., shovel bottoms, highly 18 crowned tank bottoms, tanks on grillage) can be unique and are beyond the scope of this 19 Appendix. 20

E.7.7 Local shear transfer 21

Local transfer of the shear from the roof to the shell and the shell of the tank into the base shall 22 be considered. For cylindrical tanks, the peak local tangential shear per unit length shall be 23 calculated by: 24

D2V=Vπmax Eqn (55) 25

Tangential shear in flat bottom steel tanks shall be transferred through the welded connection to 26 the steel bottom. The shear stress in the weld shall not exceed 80% of the weld or base metal 27 yield stress. This transfer mechanism is deemed acceptable for steel tanks designed in accor-28 dance with the provisions and SDS < 1.0g. 29

E.7.8 Connections with Adjacent Structures 30

Equipment, piping, and walkways or other appurtenances attached to the tank or adjacent 31 structures shall be designed to accommodate the elastic displacements of the tank imposed by 32 design seismic forces amplified by a factor of 3.0 plus the amplified displacement of the other 33 structure. 34

E.7.9 Shell Support 35

Self-anchored tanks resting on concrete ringwalls or slabs shall have a uniformly supported 36 annulus under the shell. The foundation must be supplied to the tolerances required in Sec 5.5.5 37


in to provide the required uniform support for items b, c, and d below. Uniform support shall be 1 provided by one of the following methods: 2 a. Shimming and grouting the annulus, 3 b. Using fiberboard or other suitable padding 4 c. Using double butt-welded bottom or annular plates resting directly on the foundation, 5

Annular plates or bottom plates under the shell may utilize back-up bars welds if the 6 foundation is notched to prevent the back-up bar from bearing on the foundation. 7

d. Using closely spaced shims (without structural grout) provided that the localized bearing 8 loads are considered in the tank wall and foundation to prevent local crippling and spalling. 9

10 Mechanically-anchored tanks shall be shimmed and grouted. 11

E.7.10 Repair, Modification or Reconstruction 12

Repairs, modifications or reconstruction (i.e. cut down and re-erect) of a tank shall conform to 13 industry standard practice, API653 and this Appendix. Tanks that are relocated shall be re-14 evaluated for the seismic loads for the new site and the requirements of new construction. 15

-end- 16

proposed appendix e re-write 04-2004 - my committees materials... · draft ----for committee use...

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