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GB/T 50761-2018**GB/T 50761-2018: PDF in English (GBT 50761-2018) **

GB/T 50761-2018

GB

NATIONAL STANDARD OF THE

PEOPLE’S REPUBLIC OF CHINA

UDC

P GB/T 50761-2018

Standard for seismic design of

petrochemical steel equipment

ISSUED ON. JANUARY 16, 2018

IMPLEMENTED ON. SEPTEMBER 01, 2018

Issued by. Ministry of Housing and Urban-Rural Development of PRC;

General Administration of Quality Supervision, Inspection and

Quarantine of PRC.

Table of Contents

Foreword ... 6

1 General provisions ... 8

2 Terms and symbols ... 9

2.1 Terms ... 9

2.2 Symbols ... 10

3 Basic requirements ... 13

3.1 Classification of importance factors ... 13

3.2 Seismic influences ... 13

3.3 Equipment system design ... 14

4 Seismic action and seismic checking ... 16

4.1 General requirements ... 16

4.2 Seismic design response spectral of above-ground equipment ... 17

4.3 Horizontal seismic action of above-ground equipment ... 19

4.4 Horizontal seismic action of on-framework equipment ... 22

4.5 Vertical seismic action ... 23

4.6 Combination of loads ... 24

4.7 Seismic checking ... 25

5 Horizontal vessels ... 29

5.1 General requirements ... 29

5.2 Seismic action and seismic checking ... 29

5.3 Details of seismic design ... 30

6 Vertical vessels supported by legs ... 31

6.1 General requirements ... 31

6.2 Natural vibration period ... 31

6.3 Seismic action and seismic checking ... 33

6.4 Details of seismic design ... 33

7 Vertical vessels supported by lugs ... 34

7.1 General requirements ... 34

7.2 Natural vibration period ... 34

7.3 Seismic action and seismic checking ... 35

7.4 Details of seismic design ... 35

8 Vertical vessels supported by skirt ... 36

8.1 General requirements ... 36

8.2 Natural vibration period ... 36

8.3 Seismic action and seismic checking ... 38

8.4 Details of seismic design ... 39

9 Spherical tanks supported by legs ... 41

9.1 General requirements ... 41

9.2 Natural vibration period ... 41

9.3 Seismic action and seismic checking ... 44

9.4 Details of seismic design ... 45

10 Vertical cylindrical storage tanks ... 46

10.1 General requirements ... 46

10.2 Natural vibration period ... 46

10.3 Horizontal seismic action and seismic effect ... 47

10.4 Allowable compression longitudinal stresses of tank shell ... 49

10.5 Seismic checking of tank shell ... 49

10.6 Liquid sloshing height ... 52

10.7 Details of seismic design ... 53

11 Tubular heater ... 54

11.1 General requirements ... 54

11.2 Natural vibration period ... 54

11.3 Seismic action and seismic checking ... 60

11.4 Details of seismic design ... 62

Appendix A Horizontal seismic action of on-framework equipment ... 66

Appendix B Seismic checking of vertical vessels supported by legs ... 69

Appendix C Seismic checking of vertical vessels supported by lugs ... 75

Appendix D Calculation of flexible matrix element ... 79

Explanation of wording in this standard ... 83

List of quoted standards ... 84

Standard for seismic design of petrochemical steel

equipment

1 General provisions

1.0.1 In order to implement the national laws and regulations on earthquake

prevention and disaster reduction, implement a prevention-oriented policy,

mitigate the seismic damage by seismic-fortifying the petrochemical equipment,

reduce economic loss, this standard is hereby formulated.

1.0.2 This standard is applicable to the seismic design of the petrochemical

horizontal vessel, vertical vessels supported by legs, vertical vessels supported

by lugs, vertical vessels supported by skirt, spherical tanks supported by legs,

vertical cylindrical storage tanks, tubular heater, other steel equipment which

are used in the area where the basic seismic acceleration not exceeding 0.40

g or seismic fortification intensity of 9 degrees or less.

1.0.3 For the petrochemical equipment which is subjected to the seismic design

according to this standard, when it is impacted by the fortification earthquakes

equivalent to the seismic fortification intensity of the area, the body, bracing

member, anchoring structure shall not be damaged.

1.0.4 The design parameters of ground motion or the seismic fortification

intensity shall be determined in accordance with the relevant provisions of the

current national standard “Seismic ground motion parameter zonation map of

China” GB 18306. For the construction site where the seismic safety evaluation

is completed, it shall carry out the seismic fortification according to the approved

design parameters of ground motion or the seismic fortification intensity.

1.0.5 The seismic design of petrochemical steel equipment shall, in addition to

complying with this standard, also comply with the relevant current national

standards.

2 Terms and symbols

2.1 Terms

2.1.1 Seismic design

A specialized design for equipment that requires seismic fortification, including

seismic calculations and seismic measures.

2.1.2 Seismic fortification intensity

The seismic intensity which is approved according to the authority as specified

by the state as a basis for seismic fortification of a region.

2.1.3 Seismic action

The dynamic effects of equipment caused by ground motion, including

horizontal seismic action and vertical seismic action.

2.1.4 Seismic effect

Internal forces or deformations generated by the equipment under seismic

action.

2.1.5 Design parameters of ground motion

The time-history curve of acceleration of ground motion, the response spectrum

of acceleration, the peak acceleration which are used for seismic design.

2.1.6 Design basic acceleration of ground motion

The design value of the acceleration of ground motion which exceeds the

probability of 10% in the 50-year design base period.

2.1.7 Characteristic period of ground motion

In the seismic influence factor curve for seismic design, the period value

corresponding to the starting point of the falling segment which reflects the

factors such as seismic magnitude, epicentral distance, site category, and other

factors.

2.1.8 Seismic influence factor

The statistical mean of the ratio of the maximum acceleration response to the

gravitational acceleration of a single-mass point elastic system under seismic

action.

meq - The equivalent total mass of equipment;

mi, mj - Respectively, the masses concentrated on the particles i, j;

meqv - The vertical equivalent mass of equipment;

mi - The mass concentrated at the particle i;

mj - The mass concentrated at the particle j;

Sj - The effect produced by the horizontal seismic action of the vibration-

mode j;

Sh - Horizontal seismic effect;

Xji - The horizontal relative displacement of the particle i of the jth vibration-

mode.

2.2.2 Performance and resistance of materials.

Et - The modulus of elasticity of the material at the design temperature;

Rel - The yield strength of material;

σ - The stress value under the action of load combination;

[σ] - The allowable seismic stress of the material;

[σ]t - The allowable stress of the material at the design temperature;

[σ]b - The allowable seismic tensile stress of the material;

[σ]bc - The allowable seismic compressive stress of the material;

τ - The value of the shear stress under the action of load combination;

[τ] - The allowable seismic shear stress of the material;

[τ]b - The allowable seismic shear stress of the material.

2.2.3 Calculation coefficient.

α1 - The horizontal seismic action factor corresponding to the basic natural

vibration period of the equipment or structure;

αj - The horizontal seismic action factor corresponding to the natural vibration

period of the jth vibration-mode of the equipment;

αmax - The maximum value of the horizontal seismic action factor;

4 Seismic action and seismic checking

4.1 General requirements

4.1.1 The seismic action and seismic checking of the equipment shall comply

with the following provisions.

1. It shall calculate the seismic action in the horizontal direction and make

seismic checking;

2. When the design basic acceleration of ground motion is 0.20 g ~ 0.40 g,

or seismic fortification intensity is 8 degrees or 9 degrees, for the

horizontal vessel which has a diameter of more than 4 m and the spacing

between two seats of more than 20 m, as well as the vertical vessels and

the floor chimney of the tubular heater which have a height of more than

20 m, it shall calculate the vertical seismic action and make seismic

checking;

3. For the on-framework equipment, it shall take into account the seismic

amplification of the structure in which the equipment is located.

4.1.2 When the design basic acceleration of ground motion is equal to 0.05 g

or the seismic fortification intensity is 6 degrees, the category-1 and category-

2 equipment may not be subjected to the calculation of seismic action, but it

shall meet the requirements for seismic measures.

4.1.3 For the seismic calculation of equipment, it should use the following

methods.

1. The following equipment may use the bottom shear method.

1) The vertical vessel which has a height less than or equal to 10 m;

2) The vertical vessel which has an aspect ratio of less than 5 and a

relatively uniform distribution of mass and stiffness along the height

direction;

3) Equipment that can be simplified to a single-particle system.

2. Except for the equipment in item 1 of this clause, it should use the mode

decomposition response spectrum method.

3. When the design basic acceleration of ground motion is more than or

equal to 0.30 g, the vertical vessel which has an aspect ratio of more than

120 m and the vertical cylindrical storage tanks which are more than 15 x

104 m3 should be supplemented by time-history analysis.

Fhji - The design value of the horizontal seismic action at the particle i of the

jth vibration-mode (N);

αj - The horizontal seismic influence factor corresponding to the natural

vibration period of the jth vibration-mode of the equipment, which is

determined according to the provisions of clause 4.2 of this standard;

γj - The participation factor of the jth vibration-mode;

Xji - The horizontal relative displacement at the particle i of the jth vibration-

mode.

2. The horizontal seismic effect shall be determined as follows.

Where.

Sh - The horizontal seismic effect;

Sj - The effect produced by the horizontal seismic action of the jth vibration-

mode, taking the first 2nd ~ 3rd vibration-mode. When the basic natural

vibration period is greater than 1.5 s, the number of vibration-modes is not

less than 3.

4.4 Horizontal seismic action of on-framework equipment

4.4.1 When the mass ratio of the framework to the equipment is more than or

equal to 2, the horizontal seismic action of the equipment should be calculated

in accordance with the provisions of this clause.

4.4.2 The design value of the horizontal seismic action of on-framework

equipment may be calculated as follows.

Where.

Fhk - The design value of horizontal seismic action of on-framework

equipment (N);

Km - The amplification factor of seismic action of on-framework equipment,

which is selected according to Table 4.4.2.

5. Design value of horizontal and vertical seismic action;

6. Snow load, considering the combination factor of 0.5, which takes 0 for

high-temperature parts and for the small load-bearing surface of

equipment;

7. Other loads, including the reaction force of the seat, the base ring, the lugs

and other types of supports, the force of the connecting pipeline and other

components, the force caused by the difference in temperature gradient

or thermal expansion, etc.;

8. Live loads, including major moving loads such as people, tools, repairs,

shocks, vibrations, etc.

4.7 Seismic checking

4.7.1 When using the limit state design, it shall carry out seismic checking

according to the relevant provisions of the current national standard “Code for

seismic design of buildings” GB 50011.

4.7.2 When using the allowable stress design, it shall carry out seismic checking

according to the following provisions.

1. When the equipment is subjected to seismic checking, the stress value of

the checked part under the action of load combination shall meet the

requirements of the following formula.

Where.

σ - The stress value under the combination of loads (MPa);

Φ - Welded joint factor, which takes 1.0 when compressed;

[σ] - Seismic allowable stress of the material (MPa);

τ - Shear stress value under combination of loads (MPa);

[τ] - Seismic allowable shear stress of the material (MPa).

2. The allowable stress for seismic checking of equipment shall be

determined in accordance with the following provisions.

1) The body and bearing member may be calculated as follows.

5 Horizontal vessels

5.1 General requirements

5.1.1 The seismic design of horizontal vessel shall comply with the provisions

of this clause.

5.1.2 The basic natural vibration period of horizontal vessel may be taken as

0.10 s; when multiple vessels overlap, the basic natural vibration period may

be 0.15 s.

5.2 Seismic action and seismic checking

5.2.1 For the calculation of horizontal seismic action of horizontal vessel, the

seismic influence factor may be taken as the maximum value according to the

provisions of clause 4.2.1 of this standard.

5.2.2 For the horizontal vessels installed above-ground, it shall follow the

requirements of clause 4.3 of this standard to respectively calculate its axial

and lateral seismic actions. For the on-framework horizontal vessels, it may

follow the requirements of clause 4.4 of this standard to respectively calculate

its axial and lateral seismic action.

5.2.3 The damping ratio of horizontal vessel may be 0.05.

5.2.4 For overlapping horizontal vessels, both axial and lateral directions can

be regarded as a multi-degree-of-freedom system (Figure 5.2.4). The seismic

action of overlapping horizontal vessels installed above-ground may be

calculated according to the clause 4.3 of this standard. The seismic influence

factor may be taken as the maximum value of the horizontal seismic influence

factor; the total seismic action of the overlapping on-framework horizontal

vessels and the horizontal seismic action of each particle may be calculated

according to clause 4.4 of this standard.

h - The height from the foundation’s top surface to the centroid of the

equipment (mm).

6.3 Seismic action and seismic checking

6.3.1 For the calculation of horizontal seismic action of vertical vessels

supported by legs, the seismic influence factor shall comply with the provisions

of clause 4.2 of this standard for the fortified earthquakes.

6.3.2 The seismic action of the vertical vessels supported by legs installed

above-ground shall be calculated in accordance with clause 4.3.1 of this

standard; the seismic action of the vertical vessels supported by legs installed

on-framework shall be calculated in accordance with clause 4.4 of this standard.

6.3.3 The damping ratio of the vertical vessels supported by legs may be 0.05.

6.3.4 The seismic checking of the casings, legs, connecting weld between legs

and cylinder, anchor bolts, etc. of vertical vessels supported by legs shall

comply with the provisions of clause 4.7 of this standard.

6.3.5 The seismic checking method for vertical vessels supported by legs can

be carried out in accordance with the provisions of Appendix B of this standard.

6.4 Details of seismic design

6.4.1 The number of legs shall not be less than 3, the fortification intensity shall

be 8 degrees or 9 degrees. When the diameter of the equipment is more than

800 mm, the number of legs should not be less than 4.

6.4.2 Each leg shall be provided with anchor bolts. The diameter of the bolts

should not be less than M16. The nuts shall be provided with anti-loose

measures.

8 Vertical vessels supported by skirt

8.1 General requirements

8.1.1 The seismic design of the vertical vessels supported by skirt shall comply

with the provisions of this clause.

8.1.2 When the height is greater than 20 m and the design basic acceleration

of ground motion is greater than or equal to 0.20 g or the seismic fortification

intensity is 8 degrees and 9 degrees, it shall take into account of the influence

of the vertical seismic action.

8.2 Natural vibration period

8.2.1 The vertical vessels supported by skirt can be simplified to a multi-particle

system to calculate the natural vibration period.

8.2.2 For the equal-diameter & equal-thickness vertical vessels supported by

skirt installed on the ground foundation, the basic natural vibration period may

be calculated as follows.

Where.

T1 - The basic natural vibration period of the equipment (s);

H - The height from the foundation’s top surface to the equipment’s top (mm);

m0 - The total mass of the equipment (kg);

Et - The modulus of elasticity of the material (MPa);

Di - The inner diameter of the cylinder of the equipment (mm);

δe - The effective thickness of the cylinder of the equipment (mm).

8.2.3 For the unequal-diameter or unequal-thickness floor-standing vertical

vessel, it may consider the equipment whose diameter, thickness, material

changes along height into a multi-particle system (Figure 8.2.3). The basic

natural vibration period may be calculated according to the following formula.

influence factor may take the maximum value of the horizontal seismic influence

factor of the fortified earthquake.

8.3.4 For the vertical vessel supported by skirt which has a height of more than

10 m and an aspect ratio of more than 5, it may use the vibration-mode

decomposition method for calculation.

8.3.5 The damping ratio of the vertical vessel supported by skirt may be

determined as follows.

1. When the basic natural vibration period of the equipment is less than or

equal to 1.5 s, it may take 0.035.

2. When the basic natural vibration period of the equipment is more than 1.5

s and less than or equal to 2.0 s, it may be calculated as follows.

3. When the basic natural vibration period of the equipment is more than 2.0

s, it may take 0.01.

8.3.6 The vertical seismic action of the vertical vessel supported by skirt shall

be calculated in accordance with the provisions of clause 4.5 of this standard.

8.3.7 The casing, the skirt cylinder, the foundation ring, the anchor bolt seat,

the connecting weld of skirt and casing, the connecting weld of bolt seat and

skirt cylinder, the anchor bolts of the vertical vessel supported by skirt shall be

subjected to seismic checking, meanwhile it shall comply with the provisions of

clause 4.7 of this standard.

8.4 Details of seismic design

8.4.1 The platform of the equipment should not be directly connected to other

equipment or structures.

8.4.2 The heavier auxiliary equipment outside the equipment should be

provided with a separate bracing structure, which should not be directly braced

by the equipment.

8.4.3 The internal load-bearing members of the equipment shall be securely

connected to the casing.

8.4.4 When the aspect ratio of the equipment is more than 5 and the seismic

fortification intensity is greater than 7 degrees, the equipment’s cylinder should

not be overlapped with the skirt seat.

9 Spherical tanks supported by legs

9.1 General requirements

9.1.1 The seismic design of spherical tanks supported by legs of the adjustable

and fixed tie-bar structure (hereinafter referred to as spherical tanks) which are

braced by tangential or inter-cross column around equator shall comply with the

provisions of this clause.

9.1.2 The seismic action of the spherical tanks supported by legs shall be

calculated taking into account of the impact of the stored liquid.

9.2 Natural vibration period

9.2.1 The equivalent mass of the spherical tank supported by legs under

operating conditions shall be calculated according to the following formula.

Where.

meq - The equivalent mass of the spherical tank under operating conditions

(kg);

m1 - The mass of spherical shell (kg);

m2 - The effective mass of the stored solution (kg);

m5 - The mass of the spherical tank’s thermal-insulation layer (kg);

m6 - The mass of the brace and tie-bar (kg);

m7 - The mass of accessories (kg), including manholes, adaptors, level

gauges, internal components, sprinklers, safety valves, ladder platforms,

etc.;

mL - The mass of the stored solution in spherical tank supported by legs (kg);

φ - The effective mass factor of the stored solution, which is selected based

on the fullness of the solution in spherical tank according to Figure 9.2.1.

9.3.2 The horizontal seismic action of spherical tanks supported by legs may

be calculated in accordance with clause 4.3.1 of this standard.

9.3.3 The damping ratio of the spherical tank supported by legs may be 0.035.

9.3.4 The total bending moment generated by the horizontal seismic action on

the upper segment of bracing shall be calculated as follows.

Where.

M - The total bending moment produced by the horizontal seismic action on

the upper segment of bracing (N • mm);

FEK - The design value of the horizontal seismic action on the spherical tank

supported by legs (N);

L - The distance from the equatorial plane of the spherical shell to the center

of the upper lug pin (mm).

9.3.5 The seismic verification of the braces, the connecting welds between

bracing and spherical shell, the tie-bar, the accessories of tie-bar, the baseplate

of brace, the anchor bolts, etc. shall comply with the requirements of clause 4.7

of this standard.

9.4 Details of seismic design

9.4.1 The diameter of the anchor bolt of the spherical tank’s braces shall not be

less than M24, the nut shall be provided with anti-loose measures.

9.4.2 The connecting welds between the spherical tank’s shell and the braces,

the braces and the lug plates, the tie-bar and the wing plates, the braces and

baseplates shall be the equal-strength welds of the thinner parts. The weld shall

be full and free from surface defects.

9.4.3 The tension of the tie-bar be moderate, the tension of each tie-bar shall

be substantially the same, the intersection of the tie-bars shall not be welded.

10 Vertical cylindrical storage tanks

10.1 General requirements

10.1.1 The seismic design of vertical cylindrical steel-welded flat-bottom

storage tanks (hereinafter referred to as storage tanks) which has an aspect

ratio of tank wall of not more than 1.6 and a nominal volume of more than or

equal to 100 m3 shall comply with the provisions of this clause.

10.1.2 The space between the upper surface of the stored solution of the fixed-

top storage tank and the top cover shall be less than 4% of the nominal volume

of the storage tank.

10.1.3 The calculation of the seismic action of the storage tank shall take into

account of the impact of the stored solution.

10.2 Natural vibration period

10.2.1 The basic natural vibration period of the couple vibration of the stored

solution of the storage tank may be calculated as follows.

Where.

T1 - The basic natural vibration period of the couple vibration of the stored

solution of the storage tank (s);

Kc - The factor of couple vibration period of the stored solution, which can be

found from Table 10.2.1, where the intermediate value may be calculated by

the interpolation method;

Hw - The designed maximum liquid level of the storage tank (mm);

R - The inner radius of the storage tank (mm);

δ1/3 - The nominal thickness of the tank wall at a position of 1/3 height to the

baseplate, after deducted by the negative deviation of the thickness of the

steel plate or the actual thickness (mm).

Where.

Ft - The lifting force per unit length in the circumferential direction of the

bottom of the tank wall (N/mm).

10.5.2 The anti-lifting force per unit length in the circumferential direction of the

bottom of the tank wall shall be calculated according to the following formula.

Where.

FL - The anti-lifting force per unit length in the circumferential direction of the

bottom of the tank wall (N/mm);

FL0 - The maximum anti-lifting force of the stored solution and tank’s bottom

(N/mm), which takes 0.02 HwD1ρsg x 10-9 where it is more than 0.02 HwD1ρsg

x 10-9, meanwhile the width of the inner edge plate of the tank takes 0.035D;

N1 - The gravity as undertaken at the bottom of the first ring of tank wall (N);

δeb - The effective thickness of the bottom edge plate of the tank (mm);

ReL - The yield strength of the material of the bottom edge of the tank (MPa);

ρs - The density of the stored solution (kg/m3).

10.5.3 When the lifting force (Ft) per unit length in the circumferential direction

of the bottom of the tank wall is more than 2 times the anti-lifting force (2FL),

the storage tank shall be anchored to the foundation.

10.5.4 The anchorage of storage tanks shall comply with the following

requirements.

1. The vertical compressive stress at the bottom of the storage tank wall shall

be calculated according to the following formula.

bottom of the tank wall (Ft) is more than the anti-lifting force (FL) and less

than or equal to 2 times the anti-lifting force (2FL), it shall be calculated

according to the following formula.

Where.

CL - The bottom lifting influence factor.

3. The vertical compressive stress at the bottom of the tank wall shall meet

the requirements of the following formula.

4. When the vertical compressive stress (σc) at the bottom of the tank wall is

more than the allowable critical stress of stability ([σcr]), it may use one or

more of the following measures, meanwhile it shall repeat the calculations

of item 1 and item 2 of this clause, until it meets the requirements.

1) Reduce the aspect ratio of the storage tank;

2) Increase the thickness of the first ring of tank wall;

3) Increase the thickness of the bottom edge of the tank;

4) Anchor the storage tank to the foundation.

10.5.6 When the thickness of the first ring of tank wall as obtained by seismic

checking according to this clause is more than the thickness as calculated

based on the hydrostatic pressure (excluding the corrosion allowance), the

thickness of the other rings of tank wall shall also be calculated based on the

thickness as calculated according to the hydrostatic pressure, through seismic

checking ring by ring.

10.6 Liquid sloshing height

10.6.1 The liquid sloshing wave height of the liquid level in the storage tank

under horizontal seismic action shall be calculated according to the following

formula.

11 Tubular heater

11.1 General requirements

11.1.1 Except for the ethylene cracking furnace, the seismic design of the

collection flue duct and chimney of the tubular heater, the auxiliary combustion

chamber, the sulfur tubular heater, the waste heat recovery system shall comply

with the provisions of this clause.

11.1.2 The calculation of the seismic action of the tubular heater structure shall

comply with the following provisions.

1. For the frame structure of the box-type tubular heater and the cylindrical

furnace’s convection chamber, it shall calculate the horizontal seismic

action in the two main axial directions on the horizontal plane, respectively,

meanwhile perform the seismic checking. The horizontal seismic action in

each direction shall be undertaken by the lateral force-resisting member

in this direction;

2. For the horizontal tubular heater, it may only calculate the horizontal

seismic action of the body along lateral direction, and carry out seismic

checking;

3. For the floor-standing chimney, when the design basic acceleration of

ground motion is 0.20 g ~ 0.40 g or the seismic fortification intensity is 8

degrees and 9 degrees, it shall calculate the vertical seismic action and

follow the relevant provisions of the current national standard “Code for

seismic design of buildings” GB 50011 to combine with the horizontal

seismic action, and carry out seismic checking;

4. For the tubular heater which has a height of more than 30 m (including the

height of the heater-top-chimney, when the design basic acceleration of

ground motion is 0.4 g or the seismic fortification intensity is 9 degrees, it

shall calculate the vertical seismic action and follow the relevant

provisions of the current national standard “Code for seismic design of

buildings” GB 50011 to combine with the horizontal seismic action, and

carry out seismic checking;

11.2 Natural vibration period

11.2.1 The tubular heater may be simpli......

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