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OFFICIAL CHILEAN STANDARD NCh2369.Of2003

INSTITUTO NACIONAL DE NORMALIZACION INN - CHILE

Earthquake-resistant design of industrial structures and facilities

CONTENTS Preface

7

1 Scope and field of application

9

2 References to standards

9

3 Terms, definitions and symbols

12

3.1 Terms and definitions

12

3.2 Symbols

14

4 Provisions of general application

17

4.1 Basic principles and hypotheses

17

4.2 Procedures for specifying the seismic action

19

4.3 Classification of structures and equipment according to their importance

20

4.4 Coordination with other standards

21

4.5 Loading combinations

21

4.6 Project and review of the seismic design

23

4.7 General provision on the application of this standard

23

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5 Seismic analysis

23

5.1 General provisions

24

5.2 Methods of analysis

25

5.3 Static elastic analysis

26

5.4 Dynamic elastic analysis

28

5.5 Vertical earthquake action

30

5.6 Robust and rigid equipment resting at ground level

30

5.7 Design by differential horizontal displacements

30

5.8 Special analyses

31

5.9 Structures with seismic isolation or energy dissipators

32

5.10 Other structures not specifically referred to in this standard.

34

6 Seismic deformations

47

6.1 Calculation of deformations

47

6.2 Separation between structures

48

6.3 Maximum seismic deformations

48

6.4 The P-Delta effect

49

7 Secondary elements and equipment mounted on structures

49

7.1 Scope

49

7.2 Forces for seismic design

49

7.3 Forces for anchoring design

52

7.4 Automatic shutoff systems

52

8 Special provisions for steel structures

52

8.1 Applicable standards

52

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8.2 Materials

53

8.3 Braced frames

54

8.4 Rigid frames

55

8.5 Connections

56

8.6 Anchorages

57

8.7 Horizontal bracing systems

58

9 Special provisions for concrete structures

63

9.1 Reinforced concrete structures

63

9.2 Precast concrete structures

64

9.3 Industrial bays composed of cantilever columns

67

10 Provisions for foundations

69

10.1 General design provisions

69

10.2 Shallow foundations

69

11 Specific structures

70

11.1 Industrial buildings

70

11.2 Light steel bays

70

11.3 Multi-story industrial buildings

73

11.4 Large suspended equipment

73

11.5 Piping and ducts

73

11.6 Large mobile equipment

73

11.7 Elevated tanks, process vessels and steel stacks

74

11.8 Ground supported vertical tanks

74

11.9 Rotary kilns and dryers

76

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11.10 Refractory brick structures

77

11.11 Electric equipment

77

11.12 Minor structures and equipment

77

11.13 Wood structures

77

Appendix A (normative) Typical details

79

Appendix B (normative) Design of beam to column connections in rigid steel frames

89

B.1 General considerations

89

B.2 Design of the panel zone of moment connections

89

B.3 Local bending of the column flange due to a tensile force perpendicular to it

93

B.4 Local web yielding due to compression forces perpendicular to the flange

94

B.5 Web crippling due to the compression force perpendicular to the flange

95

B.6 Compression buckling of web

96

B.7 Additional requirements for continuity stiffeners

97

B.8 Additional requirements for web reinforcing plates

98

Appendix C (informative) Commentaries

99

C.1 Scope

99

C.2 References

100

C.3 Terminology and symbols

100

C.4 Provisions for general application

100

C.5 Seismic analysis

103

C.6 Seismic deformations

112

C.7 Secondary elements and equipment mounted on structures

112

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C.8 Special provisions for steel structures

113

C.9 Special provisions for concrete structures

115

C.10 Foundations

117

C.11 Specific structures

117

C.B Design of beam-column connections in stiff steel frames

126

References

128

Figures Figure 5.1 a) Seismic zonification of Region I, II, and III

44

Figure 5.1 b) Seismic zonification of Regions IV, V, VI, VII, VIII, IX, X and Metropolitan Region

45

Figure 5.1 c) Seismic zonification of Regions XI and XII

46

Figure 5.2 ----

47

Figure 8.1 Examples of width to thickness ratios of table 8.1

62

Figure 8.2 -----

63

Figure A.1 Column base

79

Figure A.2 Roof bracing

79

Figure A.3 Detail of crane beam and columns

80

Figure A.4 External wall bracing

80

Figure A.5 Connection of column to masonry wall

81

Figure A.6 Rigid equipment inside of building

81

Figure A.7 Typical details of large suspended equipment, seismic connectors and anchor bolts

82

Figure A.8 Typical details of large mobile equipment

84

Figure A.9 Wheel rail system

84

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Figure A.10 Typical details of large tanks

85

Figure A.11 Typical rotary kiln and dryer details

86

Figure A.12 Typical details of industrial brickwork

87

Figure A.13 Typical details of minor structures and equipment

88

Figure B.1 Web reinforcing plates

91

Figure B.2 Panel zone forces

92

Figure B.3 .

95

Figure B.4 .

97

Figure C.1 Huachipato response spectra

108

Figure C.2 Huachipato Plant design spectra

110

Figures

118

Tables Table 5.1

Seismic zonification by municipalities of the Fourth to the Ninth Region

35

Table 5.2

Value of the maximum effective acceleration A0

39

Table 5.3

Definition of the types of foundation soil 39

Table 5.4

Value of type of soil dependent parameters 40

Table 5.5

Damping ratios

40

Table 5.6

Maximum values of the response modification factor 41

Table 5.7

Maximum values of the seismic coefficient 43

Table 7.1

Maximum values of the response modification factor of secondary elements and equipment

52

Table 8.1

Limits of the width to thickness ratio 60

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OFFICIAL CHILEAN STANDARD NCh2369.Of2003 Earthquake-resistant design of industrial structures and facilities Preface The Instituto Nacional de Normalizacin (INN) is the Chilean standards organization in charge of studying and preparing national technical standards. The INN is a member of the International Standards Organization (ISO) and the Pan American Technical Standards Commission (CO-PANT), and represents Chile in both organizations. The standard NCh2369 was prepared by the INN Standards Division. The following organiza-tions and persons took part in its study: Arze, Recin y Asociados Elas Arze L.

Ivn Darrigrande E. Asociacin de Industriales Metalrgicos ASIMET Rodrigo Concha P. Barrios y Montecinos Ingenieros Consultores Ramn Montecinos C. Bascun y Maccioni Ingenieros Civiles y Asociados Alberto Maccioni Q. CADE - IDEPE Alejandro Verdugo P. Consultores Particulares David Campuzano B.

Miguel Sandor E. IEC Ingeniera Jorge Lindenberg B. Instituto Nacional de Normalizacin - INN Pedro Hidalgo O. Instituto Chileno del Cemento y del Hormign Augusto Holmberg F. Marcial Baeza S. Y Asociados Marcial Baeza S. PREANSA S.A. Magno Mery G. RCP Ingeniera Ltda.. Rodrigo Concha P. SALFA I.C.S.A. Vladimir Urza M. S y S Ingenieros Consultores Ltda. Rodolfo Saragoni H. Universidad de Chile Maximiliano Astroza I.

Mara Ofelia Moroni Y. Rodolfo Saragoni H.

Universidad Tcnica Federico Santa Mara Patricio Bonelli C. Given the inexistence of international standards on this matter, this standard represents the state-of-the-art of Chilean seismic design, which is consistent with the practice of the countrys leading engineering enterprises. The efficiency and economy of this practice has been substantiated by the seismic behavior of locally designed structures, particularly regarding such past events as those of 1960 and 1985.

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Appendixes A and B are part of this standard. Appendix C is not part of this standard, but is issued as informative supplement. The meeting of the Board of the National Standards Institute on 29 May 2003 approved this Standard. This standard has been declared Official Standard of the Republic of Chile by Decree N 178, of the Ministry of Housing and Urbanism, dated 1 September 2003, and then was published in the Official Gazette of Chile on 30 September 2003.

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OFFICIAL CHILEAN STANDARD NCh2369.Of2003 Earthquake-resistant design of industrial structures and facilities 1. Scope and field of application 1.1. This standard establishes the requirements for the earthquake-resistant design of heavy

and light industrial structures and facilities. It shall be applicable to structures and to duct and pipe systems, mechanical and electrical process, equipment and their respective anchorages. The standard also shall be applied to industrial warehouse structures and to buildings structured with cantilever columns.

1.2. This standard is not applicable to such other structures as nuclear stations, electric power

generation plants and transmission lines, dams, tailings dams, bridges, tunnels, gravita-tional piers, retaining walls, underground ducts, etc.

1.3. Office buildings, cafeterias or buildings similar to those destined to dwellings can be

designed compliant to NCh433.Of96. 1.4. This standard is supplemented by Nch433.Of96 Seismic Design of Buildings. All provi-

sions of this latter standard are applicable provided they have not been specifically modi-fied.

2. References to standards The following standards contain provisions, which referenced to in the text of this standard, con-stitute requirements of this standard. At the time of the issuance of this standard, the listed edition was in force. All standards are subject to revision. It is advisable that all parties that enter agreements based on this standard research the latest editions of the following standards: NOTE: The National Standardization Institute keeps a record of all national and international standards

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NCh203 Steel for structural applications Requirements NCh433 Seismic design of buildings. NCh1159 High strength low alloy structural steel for construction NCh1537 Structural design of buildings permanent loads and service live

loads NCh2745 Analysis and design of buildings with seismic isolation ACI 318 Building Code Requirements for Structural Concrete, 1999 ACI 350.3 Practice for the Seismic Design of Liquid Containing Structures. AISC 1989 Specifications for Structural Steel Buildings, Allowable Stress De-

sign. AISC 1999 Seismic Provision for Structural Steel Buildings Part 1: Structural

Steel Buildings. AISC 1999 Load and Resistance Factor Design Specifications for Structural

Steel Buildings. AISI 1996 Specification for the Design of Cold Formed Steel Structural Mem-

bers. API 620 Design and Construction of Large, Welded, Low-Pressure Storage

Tanks. API 650 Welded Steel Tanks for Oil Storage AWWA-D 100 Standard for Welded Steel Tanks for Water Storage. AWWA-D 110 Wire and Strand Wound Circular, Prestressed Concrete Water Tanks.AWWA-D 115 Circular Prestressed Concrete Water Tanks With Circumferential

Tendons. UBC 97 Uniform Building Code 1997

Seismic Design of Storage Tanks, Recommendations of a Study Group of the New Zealand National Society for Earthquake Engi-neering, 1996.

NZS 4203 General Structural Design and Design Loadings for Buildings, 1992. ASTM A6/6M-98 Specification for General Requirements for Rolled Structural Steel

Bars, Plates, Shapes, and Sheet Piling. ASTM A36/A36M-97a Specification for Carbon Structural Steel. ASTM A 242/A242M-97 Specification for High Strength Low-Alloy Structural Steel. ASTM A325-97 Specification for High-Strength Bolts for Structural Steel Joints. ASTM A490-97 Specification for Heat-Treated Steel Structural Bolts, 150 ksi Mini-

mum Tensile Strength. ASTM A500-98 Specification for Cold-Formed Welded and Seamless Carbon Steel

Structural Tubing in Rounds and Shapes. ASTM A501-98 Specification for Hot-Formed Welded and Seamless Carbon Steel

Structural Tubing. ASTM A502-93 Specification for Steel Structures Rivets. ASTM A572/A572M-97c Specification for High Strength Low Alloy Columbium-Vanadium

Structural Steel. ASTM A588/A588M-97a Specification for High Strength Low-Alloy Structural Steel with 50

ksi/345 MPa/Minimum Yield Point to 4 in. (100 mm) Thick. ASTM A 913/913M-97 Specification for High Strength Low-Alloy Steel Shapes of Structural

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Quality, Produced by Quenching and Self Tempering Process (QST). ASTM A992/A992M-96 Specification for Steel for Structural Shapes for Use in Building

Framing. ANSI/AWS A5.1-91 Specification for Carbon Steel Covered Arc Welding Electrodes. ANSI/AWS A5.5-96 Specification for Low Alloy Steel Electrodes for Shielded Metal Arc

Welding. ANSI/AWS A5.17-89 Specification for Carbon Steel Electrodes and Fluxes for Submerged-

Arc Welding. ANSI/AWS A5.18-93 Carbon Steel Electrodes and Rods for Gas Shielded Arc Welding. ANSI/AWS A5.20-95 Specification for Carbon Steel Electrodes for Flux-Cored Arc Weld-

ing. ANSI/AWS A5.23-90 Specification for Low-Alloy Steel Electrodes and Fluxes for Sub-

merged Arc Welding. ANSI/AWS A5.29-80 Specification for Low-Alloy Steel Electrodes for Flux-Cored Arc

Welding. NOTE. Those foreign standards which are deemed required may be quoted.

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3. Terms, definitions and symbols 3.1 Terms and definitions The following terms and definitions apply to this standard. They supplement the terminology of NCh433.Of1996: 3.1.1 Permanent load (CP): Action whose variation in the course of time can be ignored in

relation to its mean value or one for which the variation tends to a limit. The following actions are included under this definition: - Self-weight of structural elements and finishing. - Self-weight of stationary equipment and facilities. - Normal content of vessels, hoppers, belts, and equipment. - Weight of ducts without their accumulations or incrustations. Insulation. - Permanent pushing pressure. 3.1.2 Connection: region at which several precasted elements or one precasted element and

cast-in-place element are connected. 3.1.3 Strong connection: connection that remains elastic while the pre-determined plastic

hinge zone develops an inelastic response under severe seismic conditions. 3.1.4 Wet connection: any connection compliant to ACI 318-99 sections 21.2.6, 21.2.7 and

21.3.2.3 for joining precasted elements using cast-in-place concrete or mortar filler to fill the joint space.

3.1.5 Dry connection: connection between precasted elements that does not qualify as wet

connection. 3.1.6 Process engineer: engineer in charge of the production processes, general arrangement of

equipment and structures as well as of the industrial operating processes. 3.1.7 Braced frame: structural system with diagonal elements; its elements beams, columns

and braces mainly act under axial forces. 3.1.8 Ductile frames with non connected non-structural elements: the non-structural ele-

ments are separated from the frame columns by a space that is larger than or equal to the value dmax defined in section 6.3.

3.1.9 Ductile frames with connected non-structural elements: These are frames in which the

non-structural elements are separated from the frame columns by a space that is smaller than the value dmax defined in section 6.3. In this case, the non-structural elements shall be

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incorporated into the structural model preventing the shear failure at the beam-column joints.

3.1.10 Rigid frame: Structural system in which the beam-column joints are capable of transmit-

ting bending moment. Its lateral stability on its plane depends on the flexural stiffness of its components.

3.1.11 Fundamental vibration period: Natural period with greater equivalent translational

mass in the direction of analysis. 3.1.12 Professional specialist: Professional of renowned structural engineering expertise legally

authorized to work in Chile and with a record of at least 5-year proven experience in earthquake-resistant design.

3.1.13 Seismic hazard: Likelihood of a certain seismic event of occurring within a determined

zone and a predetermined time interval. 3.1.14 Service Live loads (SC): Static actions, variable in time, which are determined by the

function and the use of the building and the facilities it contains. They present frequent or continuous non-ignorable variations of their mean value.

According to this definition, the following items must be included under this concept:

- Uniform loads that correspond to the use of floors and platforms considering the

normal transit of persons, vehicles, minor movable equipment and the pileup of ma-terials.

- Dust incrustation and accumulation in ducts, equipment and structures. - Crane hoist loads - Non-permanent water or earth pressures - Inner pressure of containers. - Belt loads and similar.

3.1.15 Special operating live loads (SO): Dynamic actions that arise from the normal use of

facilities. According to the foregoing definition, the loads to be included are:

- Impact and dynamic loads in general, even when they are modeled as equivalent static actions.

- Braking. - Actions that arise from moving liquids or gases, as for instance: the water hammer.

3.1.16 Accidental operating loads (SA): Actions due to operational phenomena, which only

occur occasionally in the course of the normal use of the facilities.

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According to the foregoing definition, to be included are:

- Extreme impacts and explosions - Short-circuit loads - Loads due to the overfilling of tanks and hoppers

3.2 Symbols The symbols used in this standard have the following meaning:

A0 = effective maximum ground acceleration;

Ak = weighting factor for the level k associated weight;

C = seismic coefficient for horizontal seismic action;

Cij = coupling coefficient among modes i and j;

Cmax = maximum value of the seismic coefficient;

CV = seismic coefficient for the vertical earthquake action;

CP = permanent loads;

D = Outside diameter of circular section; diameter of process tank or vessel;

E = modulus of elasticity;

Fa = allowable compression stress;

Fk = horizontal force applied at level k;

Fp = horizontal seismic force for the design of a secondary element or equipment;

Fv = Vertical seismic force; Fy = Yield stress;

Fyf = Specified yield stress of the flange of the metal shape;

H = Highest level height over the base level; total height of the

building above the base level; height of the supports of a bridge or walkway;

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I = Coefficient relative to the importance, use and failure risk of a

structure or equipment;

K = Coefficient of buckling length

Kp = Dynamic amplification factor for the design of a secondary ele-ment or equipment

L = Length of an element, span of bridge or walkway

P = Total weight of building or structure over the base level

Pk = Seismic weight associated to level k;

Pp = Weight of a secondary element or equipment;

Qo = Base shear of the building or structure;

Qp = Base shear of secondary element or equipment;

Qmin = Minimum value of the base shear;

R = modification factor of the structural response;

R1 = modification factor of the structural response as defined under 6.1;

Rp = modification factor of the structural response of a secondary ele-ment or equipment;

S = Value resulting from spectral modal superposition; minimal sup-port length; separation between structures;

Sa = Spectral design acceleration for horizontal seismic action;

Sa,v = Spectral design acceleration for vertical earthquake action;

Se = Bending moment, shear or axial force in the connection associ-ated to the development of probable strength (Spr) at the prede-termined critical sections of the structure, based on the inelastic-ity controlling mechanism;

Si = Maximum value of the i-mode contribution with its sign;

SA = Accidental operating live load;

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SC = Service live load;

SO = Special operating live load;

Ti = Vibration period of the i-mode;

T = Soil type dependent parameter;

T* = Fundamental vibration period in the direction of the seismic analysis;

Zk = Level k height above the base level;

a = Live load reduction factor;

ap = Acceleration at the support level of an element or equipmen;

ak = Acceleration at level k of a structure;

b = Live load amplification or magnification factor; half of the flange width in rolled or welded T, double T or TL shapes; nominal flange width of rolled channel and angle shapes; distance from the free flange edge to the bend initiation of cold formed sections; distance between the interior flange bends of bended Z, CA and shapes; distance from the free edge to the first connector line or weld, or width between plate connector lines or welds;

bf = Flange width

d = Horizontal seismic deformation; total height of rolled and welded T shapes;

dd = Horizontal seismic deformation, calculated considering reduced earthquake loads by factor R;

maxdd = Maximum allowable value of dd;

di = Maximum horizontal seismic displacement of structure i;

do = Deformation due to non-earthquake service loads;

e = Flange thickness of a metal section; thickness of tank shell, stack or process vessel;

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g = Gravity acceleration;

h = Free distance between the flanges of welded shapes; free distance between flanges minus filet dimension of rolled sections; dis-tance between the nearest connectors in bolted shapes; distance in web between the initial points of the fold curves in cold formed sections; structure height at a certain level above the base level; height between two points of a structure located on the same ver-tical;

k = Factor that affects the limitation of the width to thickness ratio of double T, T and channel shapes;

n = Parameter determined by the type of soil; number of levels; r = Radius of gyration; ratio between the periods associated to two

vibration modes;

t = Flange thickness of a metal shape;

tw = Web thickness of a metal shape;

= Damping ratio;

b = Coefficient of strength reduction as defined in AISC LRFD;

r = Limit of the width to thickness ratio to prevent local buckling;

p = Limit of the width to thickness ratio to enable complete plastifi-cation of the section.

4. Provisions of general application 4.1. Basic principles and hypotheses 4.1.1. The design provisions of this standard to be applied jointly with those of each material-

specific provisions are set forth for meeting the following objectives: a Protection of life in industry

a.1 To prevent the collapse of structures in the event of severe over-design earth-quakes.

a.2 To prevent fire, explosions or emission of toxic gases and liquids.

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a.3 For environmental protection.

a.4 To assure the operability of seismic emergency exits during the seismic emer-gency.

b Continuity of operation in industry

b.1 Non-interruption of essential processes and services.

b.2 To prevent or minimize the standstill of operations.

b.3 To enable the inspection and repair of damaged elements.

4.1.2. In general terms, it is accepted that seismic analyses are based on the utilization of linear models of the structures; however, the design of resistant elements shall comply with the corresponding material-specific method, which may be by allowable stresses or ultimate loads.

4.1.3. For fulfilling the objectives of 4.1.1, a.1) the structures shall have an ample reserve of

strength and/or be capable of absorbing large quantities of energy, beyond the elastic range, prior to failure. To this end, the global structural system shall meet the following requirements:

a) To ensure the ductile behavior of the resistant elements and their connections in or-der to prevent instability or fragile failure or else to ensure their elastic behavior.

b) Provide more than one earthquake-resistant line for the earthquake actions. Earth-

quake-resistant systems shall be redundant and hyperstatic. The only exception to this provision is the explicit approval of the professional specialist defined under 3.1.12.

c) Use simple and clearly identifiable systems for the transmission of the earthquake

forces to the foundations, avoiding structures of high asymmetry and complexity.

To fulfill the objectives regarding the continuity of industrial operations and those of foregoing paragraphs a.2) and a.3), all structures, equipment, and their anchorage sys-tems shall be designed so that during severe over design earthquakes, they meet the fol-lowing requirements in addition to those set forth under a), b) and c): d) To limit the non-linear incursions, if they imply jeopardizing operational continuance

or rescue operations.

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e) Damages must occur at visible and accessible sites.

f) All emergency and control equipment, whose operation shall be guaranteed during emergencies, shall be duly certified in conformance with international standards and the approval of the process engineers and professional specialist.

4.1.4. The achievement of ductility during the cyclic behavior of the earthquake-resistant struc-

ture in accordance with 4.1.3.a.) requires the meeting of the provisions set forth under clauses 8, 9 and those in Appendix B.

4.1.5. The professional specialists and process engineers as defined in 3.1.12 and 3.1.6 shall

determine in each project the seismic design conditions of every structure, equipment and their anchorages, so as to meet the objectives set forth under 4.1.1. In particular, for each structure and equipment its seismic classification, methods of analysis, criteria, relevant parameters and illustrative drawings shall be displayed. This data shall be set on record in the project specifications. The seismic design of equipment may be made by the equip-ment manufacturers engineers, however the approval shall be done by the professional specialist defined under 4.6.2.

4.1.6. Location

The location of an industry shall be determined considering the hazards of earthquake-related phenomena, such as topographic amplifications, tsunamis, displacements gener-ated by soil faults and soil sliding, liquefaction and densification. To this end, in addition to complying with the provisions 4.2 of the Chilean standard NCh433.Of96, it is impera-tive that specialists undertake the corresponding geological, topographic, tsunami, and geotechnical studies.

4.2. Procedures for specifying the seismic action

The seismic actions can be specified according to one the following procedures:

a) by way of horizontal and vertical earthquake coefficients applied to the weight of the various components in which the system has been divided for analysis purpose, according to provisions 5.3, 5.5 and 5.6.

b) by way of response spectra of single-degree-of-freedom linear systems for the hori-

zontal and vertical motion of the foundation soil, according to 5.4 and 5.5.

c) by assigning descriptive values to ground movements, such as horizontal or vertical peak acceleration, velocity and displacement of the soil, in horizontal and vertical direction, or similar ones, according to 5.8.1.

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d) by real or synthetic accelerograms, duly formulated for the horizontal and vertical movements of the foundation soil, as defined in 5.8.2.

The application of the alternatives a) and b) requires the meeting of the provisions on seismic zonification of the national territory (Figure 5.1 and Table 5.1), stipulated under 4.1 of the Chilean standard NCh433.Of96 and under 4.2 of this latter standard on the ef-fects of the foundation soil (Table 5.3) and the topography on the characteristics of the seismic motion. The utilization of alternatives c) and d) shall be consistent with the results of the studies on seismic hazard, which consider the regional and local seismicity, geological, geotech-nical and topographic conditions, as well as the direct and indirect consequences of struc-ture and equipment failures. In any case, the provisions under 5.8.1 and 5.8.2 are manda-tory. Suspected near-field effects require a special analysis that takes them into account.

4.3. Classification of structures and equipment according to their importance 4.3.1. Classification

For appropriate application of this standard, structures and equipment are classified ac-cording to their importance as follows: - Category C1. Critical structures and equipment based on any one of the following

reasons:

a) Vital, must be kept in operation so to control fire, explosion and ecological damage, render health and first help services.

b) Dangerous, if their failure implies hazard of fire, explosion or air and water poisoning.

c) Essential, if their failure generates protracted standstills and serious production losses.

- Category C2. Normal structures and equipment, which may be affected by normal easily repairable failures, which do not cause protracted standstills or important production losses or hazard to other category C1 structures.

- Category C3. Minor or provisional structures and equipment, whose seismic failure

does not cause protracted standstills nor exposes to hazard other category C1 and C2 structures.

4.3.2. Importance coefficient

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The importance coefficient I for each category has the following values:

C1I = 1.20 C2I = 1.00 C3I = 0.80

4.4. Coordination with other standards 4.4.1. Chilean standards

The provisions of this standard shall be applied jointly with other material-specific load or design standards as defined in 5.3 of NCh433.Of96.

4.4.2. Foreign standards

In case of loads or materials not included under 5.2 and 5.3 of standard NCh433.Of96, in-ternationally accepted standards or criteria shall be used provided they are accepted by the professional specialist who approves the project (see 4.6.2).

In any event, these standards and criteria shall meet the principles and basic hypotheses set forth under 4.1 of this standard.

4.5. Loading combinations

The combination of earthquake loads with permanent loads and the various types of live loads shall be done by using the following rules of superposition:

a) When the allowable stress method is used in design , then

i) CP + aSC + SO*) + SA*) Horizontal Earthquake + Vertical Earthquake**)

*) Loads SO and SA are combined with seism only in case of the verification of one of the two following conditions for them:

i) Action SA is derived from the seismic occurrence. In this case it shall be considered with its sign.

ii) It is normally expected that the load is acting when a seism starts and goes on without in-terruption, or does not stop during the seism due to its action

If the seism generates such an effect that necessarily interrupts the actions SO or SA at the beginning of the basal accelerations, this action shall not be considered.

**) The vertical earthquake only is considered in the cases detailed under 5.1.1; its magnitude shall be determined according to 5.5.

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ii) CP + SA*) Horizontal Earthquake Vertical Earthquake**) The allowable stresses in these combinations can be increased by 33.3%.

b) When the ultimate load design method is applied, then

i) 1.2 CP + aSC + SO*) + SA*) b Horizontal Earthquake b Vertical Earthquake**)

ii) 0.9 CP + SA*) b Horizontal Earthquake 0.3 Vertical Earthquake**)

Where

a = Factor that affects live load SC determined without considering any type of re-duction. It should be equal to 1.0, except in case the process engineer author-izes a reduction of the previous value. Such reduction shall take into account the probability of simultaneous occurrence of live load with the level of the earthquake action determined by this standard. In any case, the value of a will at least be equal to:

TYPE OF AREA OR ELEMENT

a

Warehouses and main storage areas with low turnover

0.50

Areas of normal use, operating platforms

0.25

Diagonals supporting vertical loads

1.00

Maintenance walkways and roofs 0

b = Amplification factor of the earthquake loads as determined according to the methods of material-specific analyses in current use. It adopts the following values:

Steel structures or equipment b = 1.1

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Concrete structures or equipment b = 1.4

In the combinations i) detailed under a) and b) above, the + or signs of the vertical earthquake shall be applied so that to obtain an effect that results in its addition to that of the loads CP and SC. In the combinations ii) shown under a) and b), the signs + or of the vertical earthquake shall be applied so that to obtain the inverse effect, namely, the re-duction of the effect of the loads CP and SC.

The earthquake action is an eventual load that shall not be combined with other eventual loads. Special locations in mountainous and high zones, where normally wind and snow may occur in great magnitudes and duration, require special studies for determining the values of these likely coincident loads with the design earthquake.

If deemed that several content levels of vessels, pipes or tanks ought to be considered, the number of these combinations grows for covering the different situations.

4.6. Project and review of the seismic design 4.6.1. The original seismic design shall be carried out by professional specialists (see 3.1.12).

The only exception to this rule is equipment designed by foreign manufacturers. 4.6.2. The seismic design of all structures, equipment and anchorage, whichever their origin,

shall be approved by professional specialists different from their designers. 4.6.3. Drawings and calculation records shall at least contain the data set forth under 5.11 of

NCh433.Of96. The drawings and calculation records shall be signed by the original de-sign engineer referred in 4.6.1 and the professional specialist referred in 4.6.2.

The only exception are structures and equipment of category C3, which only require the presentation of the drawings signed by the original design engineer, including dimensions and materials of the resistant elements, their weight, center of gravity and anchorage de-tails.

4.6.4. The review and approval of the seismic design does not release original design engineers

from their total responsibility of fulfillment with the standards and specifications. 4.7. General provision on the application of this standard

If the type of structure is expressly stated in this standard, all corresponding design provi-sions must be used. In case the structure may be associated with various classifications that imply different design provisions, the strictest one shall be used.

5. Seismic analysis

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24

5.1. General Provisions 5.1.1. Direction of earthquake action

Structures shall be analyzed considering the earthquake loads at least in two horizontal, approximately perpendicular directions.

The effect of vertical earthquake accelerations shall be considered in the following cases:

a) hanging bars of suspended equipment and their supporting elements and beams of

rolled, welded or bent plate steel, with or without concrete slab as composite beam, located within the seismic zone 3, where permanent loads represent over 75% of the total load.

b) Structures and elements of prestressed concrete (pretension and post tension cable). c) Foundations and elements for anchorage and support of structures and equipment. d) Any other structure or element in which the variation of the vertical earthquake action

significantly affects its detailing, as for instance, cantilever structures and elements. e) Structures with seismic isolation sensitive to the vertical effects.

5.1.2. Combination of the effects of the horizontal components of the earthquake action.

In general the design of earthquake-resistant elements does not require that the effects of both horizontal seismic components be combined. It will be assumed that said effects are not concurrent and in consequence, the elements may be designed considering that the seism acts along each direction of analysis considered separately.

The exceptions to this simplifying rule are structures which present notorious torsional ir-regularities or have rigid frames in both directions with common columns on two inter-secting resistant lines. In these cases, the elements shall be designed based on the stresses that result from considering 100% of the earthquake acting in one direction plus the stresses which result from considering 30% of the earthquake that act in orthogonal direc-tion with respect to the previous one, and vice-versa. The largest stresses resulting from the aforementioned combinations shall be considered.

5.1.3. Seismic mass for the structural model

When calculating the horizontal inertial forces induced by an earthquake, the operating live loads may be reduced in accordance with the likelihood of its simultaneous occur-rence with the design earthquake.

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25

Irrespective of the previous provision, service live loads may be reduced by multiplying them by the following coefficients:

- Roofs, platforms, walkways for operation as well as for maintenance purposes

: 0

- Storage warehouses, file rooms and similar. : 0.5

The determination of the effects of vertical earthquake components in the cases detailed under 5.1.1 shall not consider any reduction of the vertical loads, except those detailed in NCh1537 for live loads.

5.2. Methods of analysis 5.2.1. General

Normally the seismic analyses shall be carried out using linear methods, for seismic ac-tions as defined under 4.2.a) or 4.2.b) or 4.2.c). In special cases, the analysis may be based on a non-linear response to a seismic action, as defined in 4.2.d).

5.2.2. Linear methods

Three procedures may be used:

a) Static analyses or analysis of equivalent static forces, which can only be applied to structures of up to 20 m height, provided their seismic response might be assimilated to a single-degree-of-freedom system.

b) Modal spectral analysis, which is applicable to any type of structure.

c) Special methods for structures featuring elastic behavior, as detailed under 5.8.

5.2.3. Non-linear methods

Non-linear methods of analysis correspond to the special methods of analysis detailed un-der 5.8, which meet the conditions of the time-history analysis as defined in 5.8.2. In conformance with the provisions 4.1 of this standard, non-linear incursion shall be moderate so to guarantee the continuity of industrial operations. The non-linear model must appropriately model the resistant capacity and the behavior of the structural elements, backed up by specific laboratory test carried out with this purpose or by normally accepted experimental studies.

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The ductility demand shall not exceed the established limit in accordance with the allow-able damage. In no element section shall surpass 2/3 of the available local ductility. The calculated maximum non-linear displacements shall not be reduced and shall conform to the limits established under 6.3. The non-linear model may incorporate the dynamic soil-structure interaction, however its influence shall be limited up to 75% of the results obtained from the same non-linear model but with rigid base.

5.3. Static elastic analysis 5.3.1. Mathematical model of the structure 5.3.1.1. The mathematical model of the structure shall be capable of appropriately represent the

load transmission from the points of application toward the supports. To that end, at least to be included are all elements of the earthquake-resistant system, the stiffness and strength of all elements that are relevant in the distribution of forces, and the correct spatial placement of masses.

5.3.1.2. In general, a three-dimensional model shall be used, excepting cases in which the be-

havior can be forecasted with two-dimensional models. 5.3.1.3. In structures without rigid horizontal diaphragms a sufficient number of nodal degrees

of freedom associated to translational masses shall be defined. If necessary, the rota-tional masses shall also be considered.

5.3.1.4. In structures with rigid horizontal diaphragms a model with three degrees of freedom

per story may be used. 5.3.1.5. In structures that support equipment, which influences the response, the mathematical

model shall consider the equipment/structure system. 5.3.1.6. In case of large suspended equipment, the mathematical model must include the suspen-

sion and interconnection devices between the equipment and the supporting structure. 5.3.1.7. If the soil characteristics or type of foundation require that the effect of soil-structure

interaction be considered, decoupled springs may be used for translational and rotational movement.

5.3.1.8. The effects of natural torsion and of accidental torsion can only be considered at levels

with rigid diaphragms. The effect of accidental torsion can be included by considering the possible variations of the distribution of self-weights and live loads. In case that no previous information is available to carry out the aforementioned, the requirement set forth under 6.2.8 in NCh433.Of96 shall be used.

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5.3.2. Horizontal base shear

The horizontal base shear shall be calculated according to the following expression: Qo = CIP

(5-1)

where Qo = base shear;

C = Seismic coefficient as defined in 5.3.3;

I = Coefficient of importance as defined in 4.3.2;

P = Total weight of the building above the base level, calculated as required under 5.1.3. To this aim, base level is the plane that separates the foundation from the structure, except indication in contrary of the professional specialist.

5.3.3. The seismic coefficient is determined from: 4.0

*

'0 05,075.2

=

n

TT

gRAC

(5-2)

where

Ao = Maximum effective acceleration as defined in Table 5.2 according to the seismic zonification of Figure 5.1 and Table 5.1;

T, n = Parameters relative to the foundation soil, to be de-termined according to Tables 5.3 and 5.4;

T* = Fundamental period of vibration in the direction of the analysis;

R = Response modification factor as defined in Table 5.6;

= Damping ratio as established on Table 5.5. 5.3.3.1. C need not be higher than the value specified in Table 5.7.

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5.3.3.2. C in no case shall be lower than 0.25 Ao/g. 5.3.4. Fundamental vibration period

The fundamental vibration period T* shall be calculated by a well-founded theoretic or empiric procedure.

5.3.5. Distribution along height

Seismic forces shall be distributed along height according to the following expression:

Fk = ojj

nkk QPA

PA

1

(5-3)

Ak = HZ1

HZ1 k1k (5-4)

where

Fk = Horizontal seismic force at level k ;

Pk, Pj = Seismic weight at levels k and j ;

Ak = Parameter at level k (k = 1 is the lower level);

n = Number of levels;

Qo = Base shear;

Zk, Zk-1 = Height above the base of k and k1 levels;

H = Highest height levels above the base level; 5.4. Dynamic elastic analysis 5.4.1. Mathematical model of the structure

Provisions 5.3.1.1 to 5.3.1.7 of the static elastic analysis shall be used. 5.4.2. Design spectrum

The modal spectral analysis shall conform to the following design spectrum:

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29

Sa = 4.0

05,0'75.2

no

TT

RIA (5-5)

where

T = Vibration period of the considered mode.

However, the value of Sa shall not be higher than ICmax g, where Cmax shall be deter-mined according to Table 5.7.

5.4.3. Number of modes

The analysis shall include a sufficient number of vibration modes for the sum of equiva-lent masses in each analysis direction is equal to or higher than 90% of the total mass.

5.4.4. Mode superposition

Earthquake loads and deformations shall be calculated by superposing the maximum mo-dal values by means of the Complete Quadratic Superposition method according to the following formulas:

jiijji SSCS = (5-6)

Cij = )r1(r4)r1)(r1(

r822

5.12

+++

r = jT

Ti

(5-7)

where

S = Modal combination;

Si , Sj = Maximum values of mode contributions i and j ;

= Damping ratio as defined in Table 5.5;

Ti , Tj = Period of modes i and j. 5.4.5. Minimum base shear

If the base shear Qmin is lower than the following value:

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30

Qmin = 0.25 I gAo P

(5-8)

for design purposes all deformations and internal forces shall be multiplied by the quo-tient Qmin/ Qo.

5.4.6. Accidental torsion

The effect of accidental torsion shall be considered only in levels with rigid diaphragm. In such cases, this effect can be included considering the possible variations of self-weight and live load distribution. In absence of background data for doing so, the provi-sion 6.3.4 of the Chilean standard NCh433.Of96 shall be used.

5.5. Vertical earthquake action 5.5.1. The vertical earthquake action may be considered as static in the following way:

a) In the cases detailed under 5.1.1. a) and 5.1.1. b) an even vertical earthquake coeffi-cient equal to Ao/g shall be applied on all elements. Therefore the vertical earthquake force must be Fv = (Ao/g) IP, where P is the sum of permanent loads and live loads.

b) For the cases considered under 5.1.1. c) and 5.1.1. d) the seismic coefficient shall be

2/3Aog.

c) For the cases considered under 5.1.1.e) the procedure detailed under 5.9 shall be ap-plied.

5.5.2. Alternatively a vertical dynamic analysis may be carried out with the acceleration spec-

trum of expression (5-5) for R = 3 and = 0.03. In this case, the spectral ordinate does not require to be higher than IAo. Any damping ratio in excess of 0.03 shall be specifically justified.

5.6. Robust and rigid equipment resting at ground level

This provision refers to equipment whose self fundamental period is smaller or equal to 0.06 s, including the effect of its connecting system to the foundation. These equipments can be designed by static analysis with a horizontal seismic coefficient of 0.7 Ao/g and a vertical earthquake coefficient of 0.5 Ao/g.

5.7. Design by differential horizontal displacements

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For bridges or walkways that connect buildings, towers or other equipments, horizontal supports shall be provided that enable the actual seismic displacement between structures or equipment indicated in 6.2. In no case the support length shall be smaller than S, where:

S [cm] = 20 + 0.2 L + 0.5 H; L 60 m (5-9)

where

S = Minimum length of the support (see Figure 5.2)

L = Bridge or walkway span in meters between supports;

H = Height in meters of bridge or walkway supports over the foundation seal of the highest structure or equipment.

5.8. Special analyses 5.8.1. Spectral analyses 5.8.1.1. Special spectra may be developed for a specific project, such that they consider the

characteristics and importance of the structures to be built, the geotechnical conditions of the site, the distance from seismogenic sources, their characteristics, as well as the local amplification or reduction factors of the ground movement intensity in terms of site topography, the eventual effects of the wave directionality or subsoil configuration and type.

Toward this aim, a series of parameters can be determined, such as the maximum values of acceleration, velocity and displacement of the soil, and with these to configure spe-cial spectra for the viscous damping levels of Table 5.5 or for determining others, which enable similar formulations to that presented in NCh433.Of96.

5.8.1.2. For design purposes, the determination of the maximum acceleration, velocity and dis-

placements values shall take into account historical or deterministic data, which can be applied or related to the site under study. These can be supplemented with the probabil-istic values obtained from seismic risk analyses, which consider a 100-year return pe-riod. The attenuation formulas used in risk analyses shall correspond to the anticipated acceleration, velocity and displacement values, belonging to the characteristics of the seismogenic sources considered in the study.

5.8.1.3. The base shear obtained from the spectrum defined by means of this special analysis,

shall not be smaller than 75%; nor require to be larger than 125% of those resulting from the methods described under 5.4.

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32

5.8.2. Time-history analysis 5.8.2.1. For the time-history analyses at least three actual records shall be used, which must be

representative of the considered seismogenic zones. This data must be escalated so that the resulting spectrum from combining the spectra of each record by means of the square root of the average of the squares of the escalated individual values, is not lower than the design spectrum (5.8.1) at any point of the frequency range of interest.

5.8.2.2. Alternatively, a synthetic record may be used, whose spectrum yields larger values than

the one defined under 5.8.1, for the whole frequency range of interest. 5.8.2.3. When three different records are used, the design shall adopt the maximum values of the

parameter of interest, obtained from applying each one of them. Under this definition the meaning of parameter of interest is the action, axial force, shear, bending moment or the deformation obtained for each single element or for the global structure.

5.8.2.4. In linear time-history analyses, the resulting forces on the elements can be divided by

the R factors detailed in Table 5.6, provided the calculated displacements are compati-ble with the limits imposed in 6.3.

5.8.2.5. Time-history analyses shall consider at each time the movements in only one of the

main directions of the structure, simultaneously acting with the vertical excitation. 5.8.2.6. In time-history analyses, the damping shall be taken from Table 5.5 and the duration of

the record must be equal to or higher than 120 s, unless a seismic risk study justifies the use of a different duration.

5.8.3. Minimum base shear

If the base shear defined according to 5.8.1 or 5.8.2 is lower than

Qmin = 0.25I PgAo (5-10)

All deformations and stresses shall be multiplied by the quotient Qmin/ Q0, except when a non-linear time-history analysis has been made.

5.9. Structures with seismic isolation or energy dissipators 5.9.1. General considerations 5.9.1.1. Seismic isolation or energy dissipation systems consist of any device that has been in-

corporated into the resistance system of a structure with the purpose of modifying its dynamic properties, be it by modifying its fundamental vibration period or by increasing

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33

its energy dissipation capacity or by modifying the distribution of forces with the pur-pose of enhancing its seismic response.

5.9.1.2. The structures lateral force resisting system and the isolation and/or energy dissipation

system shall be designed so to withstand the demand of deformation and strength pro-duced by the seismic movement, as required under 5.9, 5.8.1 and 5.8.2 of this standard.

5.9.1.3. The mathematical model of the physical structure must represent the distribution of

masses and stiffness of the structure at a suitable level for calculating the significant characteristics of the dynamic response. A three-dimensional model of the superstruc-ture that considers the vertical displacements in the isolators shall be used. The cases mentioned under 5.1.1.e) require a model that includes vertical degrees of freedom in the dynamic analysis. The damping ratios to be used shall be those corresponding to the isolation or energy dissipation systems.

5.9.1.4. The analysis and verification of the isolation and energy dissipation systems shall be

made by modal spectral analysis or time-history response or frequency response analy-sis. The modal spectral analysis can only be applied if the device or isolator is suscepti-ble of being modeled as an equivalent validated linear system.

5.9.1.5. Spectral analyses (see 5.4 and 5.8.1) or time-history response analysis (see 5.8.2) shall

consider one by one the horizontal components acting in plant in the most unfavorable direction, simultaneously with the vertical component if necessary according to 5.1.1 e).

5.9.1.6. The constitutive force-deformation relationships considered in the analysis for the se-

lected devices shall be duly founded and be backed by laboratory test. 5.9.1.7. The base shear limitations defined under 5.3.3.2 and 5.4.5 are not applicable in struc-

tures outfitted with isolation and/or energy dissipation systems. Likewise, in structures with isolators, the maximum deformation restriction defined under 6.3 is applicable only to the superstructure but not to the isolation interface.

5.9.2. Structures with seismic isolators

Seismic isolation systems shall be analyzed and designed in accordance with the provi-sions of NCh2745.

5.9.3. Structures with energy dissipators 5.9.3.1. Every structure with energy dissipation systems shall be designed using the spectra de-

scribed under 5.4 or 5.8 and subsequently be verified by three records compatible with the implicit demand level of the design spectrum, according to the methodology defined under 5.8.2.

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34

5.9.3.2. The seismic analysis of structures with energy dissipation systems shall be carried out by using dynamic analysis procedures that appropriately consider the constitutive force-deformation relation of the devices included in the structure.

5.9.3.3. The dissipation systems to be used in a structure shall have previously been subjected to

experimental studies, which prove a stable cyclic behavior for the device as well as pos-sible variations of its properties with temperature.

5.10. Other structures not specifically referred to in this standard.

If the base shear Q0 determined for these structures is lower than

Qmin = 0.50 I PgAo

(5-11)

All deformations and internal forces must be multiplied by the quotient Qmin/ Q0 for the purpose of the design. This provision shall not be applied to the structures, which are explicitly quoted in Table 5.6.

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35

Table 5.1 Seismic zonification by municipalities of the Fourth to the Ninth Region

Region Zone 3 Zone 2 Zone 1

Andacollo Combarbal Coquimbo Illapel La Higuera La Serena

4th Region Los Vilos Mincha

Monte Patria Ovalle Paiguano Punitaqui Ro Hurtado Salamanca Vicua

Algarrobo Calle LargaCabildo Los AndesCalera San EstebanCartagenaCasablancaCatemuConcnEl QuiscoEl TaboHijuelasLa CruzLa Ligua

5th Region LimacheLlayllayNogalesOlmuPanquehuePapudoPetorcaPuchuncavPutaendoQuillotaQuilpuQuinteroRinconadaSan AntonioSan FelipeSanta MaraSanto DomingoValparasoVilla AlemanaVia del MarZapallar

(continues)

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Alhu BuinCuracav Calera de TangoEl Monte CerrillosLampa Cerro NaviaMara Pinto ColinaMelipilla ConchalSan Pedro El BosqueTiltil Estacin Central

HuechurabaIndependenciaIsla de Maipo

Metropolitan La CisternaRegion La Florida

La GranjaLa PintanaLa ReinaLas CondesLo BarnecheaLo EspejoLo PradoMaculMaipuoaPainePedro Aguirre CerdaPeaflorPealolnPirqueProvidenciaPudahuelPuente AltoQuilicuraQuinta NormalRecoletaRencaSan BernardoSan JoaqunSan Jos de MaipoSan MiguelSan RamnSantiagoTalaganteVitacura

(continues)

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37

La Estrella Chpica

Las Cabras Chimbarongo Litueche Codegua Lolol Coinco

6th Region Marchigue Coltauco Navidad Doihue

Palmilla Graneros Peralillo Machal Paredones Malloa Peumo Mostazal Pichidegua Nancagua Pichilemu Olivar Pumanque Placilla Santa Cruz Quinta de Tilcoco Rancagua Rengo Requnoa San Fernando San Vicente de Tagua Tagua

Cauquenes Colbn Chanco Curic Constitucin Linares Curepto Longav Empedrado Molina

7th Region Huala Parral Licantn Pelarco

Maule Rauco Pelluhue Retiro Pencahue Ro Claro San Javier Romeral Talca Sagrada Familia Vichuqun San Clemente Teno Villa Alegre Yerbas Buenas

(continues)

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Arauco Antuco Bulnes Coihueco Cabrero El Carmen Caete Los Angeles Chilln Mulchn Cobquecura iqun Coelemu Pemuco Concepcin Pinto Contulmo Quilaco Coronel Quilleco Curanilahue San Fabin Florida San Ignacio Hualqui Santa Brbara Laja Tucapel Lebu Yungay

8th Region Los Alamos Lota Nacimiento Negrete Ninhue Penco Portezuelo Quilln Quirihue Ranquil San Carlos San Nicols San Rosendo Santa Juana Talcahuano Tira Tom Treguaco Yumbel

Angol Collipulli Curarrehue Carahue Cunco Lonquimay Galvarino Curacautn Melipeuco Los Sauces Ercilla Pucn Lumaco Freire Nueva Imperial Gorbea Purn Lautaro

9th Region Renaico Loncoche Saavedra Perquenco Teodoro Schmidt Pitrufqun Toltn Temuco Traigun Victoria Vilcn Villarrica

(continues)

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39

Table 5.2 Value of the maximum effective acceleration A0

Seismic Zone A0 1 0.20 g

2 0.30 g

3 0.40 g

Table 5.3 Definition of the types of foundation soil. (Only to be used with Table 5.4)

Type of

soil Description

I

Rock: Natural material, with in-situ shear wave propagation speed Vs equal or higher than 900 m/s, or else with uniaxial compression strength of intact samples (without fissures) that is equal to or higher than 10Mpa and RQD equal to or higher than 50%.

II

a) Soil that features Vs equal or higher than 400 m/s in the upper 10 m, increasing with depth; or else

b) Dense gravel, with dry unit weight d equal to or higher than 20 kN/m3, or density index ID(RD) (relative density) equal to or higher than 75%, or compacting index over 95% of the modified Proctor value, or else:

c) Dense sand of ID(RD) over 75%, or standard penetration index N over 40 (nor-malized for an effective overburden pressure of 0.10 Mpa), or compacting index over 95% of the Modified Proctor value, or else,

d) Hard cohesive soil, with undrained shear strength Su equal to or greater than 0.10 Pa (simple compression force qu equal to or greater than 0.20 Mpa) in samples without fissures.

These conditions must be met in every case, without regard to the position of the phreatic level and the minimum stratum thickness shall be 20 m. In case the thickness over the rock is under 20m, the soil shall be classified as type I.

III

a) Permanently non-saturated sand of ID(DR) between 55 and 75%, or N over 20 (with-out normalizing at 010 Mpa effective overburden pressure); or else,

b) Non-saturated gravel or sand of compacting index below 95% of the Modified Proctor Value; or else,

c) Cohesive soil with Su between 0.025 and 0.10 Mpa (qu between 0.05 and 0.20 Mpa) without regard to the phreatic level; or else,

d) Saturated sand with N between 20 and 40 (normalized at 0.10 Mpa of effective over-burden pressure).

Minimum stratum thickness: 10m. In case the stratum thickness over the rock or over type II soil is under 10m, the soil shall be classified as type II.

IV

Saturated cohesive soil with Su equal to or under 0.025 Mpa (qu equal or under 0.050 Mpa). Minimum stratum thickness: 10m. In case the stratum thickness over any of the soil types I, II or III is lower than 10m, the soil shall be classified as type III.

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Table 5.4 Value of type of soil dependent parameters

Type of soil T (s) n

I 0.20 1.00

II 0.35 1.33

III 0.62 1.80

IV 1.35 1.80

Table 5.5 Damping ratios

Resistant system

Welded steel shell; stacks; silos; hoppers; pressure vessels; process towers; piping, etc. 0.02

Bolted or riveted steel shell; 0.03

Welded steel frames with or without bracings 0.02

Steel frames with field bolted connections, with or without bracings 0.03

Reinforced concrete and masonry structures 0.05

Precast reinforced concrete, purely gravitational structures 0.05

Precast reinforced concrete structures with wet connections, connected to the non-structural elements and incorporated into the structural model

0.05

Precast reinforced concrete structures with wet connections, non-connected to the non-structural elements

0.03

Precast reinforced concrete structures with dry connections, non-connected and connected: With bolted connections and connections by means of bars embedded in filling mortar With welded connections

0.03

0.02

Other structures not included in above list or assimilable to the foregoing ones.

0.02

NOTES

1) When using an analysis that considers soil-structure interaction in which the values of the first damping mode ratio are higher than those of this table, the increase of this ratio shall not be 50% higher than the foregoing values. Values for all other modes shall be those listed in this table.

2) In case of uncertainty regarding the classification of a resistant system, apply provision 4.7.

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Table 5.6 Maximum values of the response modification factor

Resistant system

R

1. Structures designed for remain elastic 1

2. Other structures not included nor similar to those in this list1) 2 3. Steel structures 3.1 Buildings and structures of ductile steel frames with non-connected non-

structural elements 5

3.2 Buildings and structures of ductile steel frames with connected non-structural elements that are incorporated into the structural model

3

3.3 Buildings and structures of braced frames with ductile anchorages 5 3.4 One-story industrial buildings with or without overhead traveling crane

and continuous roof bracing 5

3.5 One-story industrial buildings without overhead traveling crane, without continuous roof bracing, which are compliant to 11.1.2

3

3.6 Light steel bays that are compliant to the conditions of 11.2.1 4 3.7 Inverted pendulum structures2) 3 3.8 Earthquake-resistant isostatic structures 3 3.9 Steel plate or steel shell structures whose seismic behavior is controlled

by local buckling 3

4. Reinforced concrete structures 4.1 Building and structures of reinforced concrete ductile frames with non-

connected non-structural elements 5

4.2 Buildings and structures of reinforced concrete ductile frames with con-nected non-structural elements that are incorporated into the structural model

3

4.3 Reinforced concrete buildings and structures with shear walls 5 4.4 One-story industrial buildings with or without overhead traveling crane

and with continuous roof bracing 5

4.5 One-story industrial buildings without overhead traveling crane, without continuous roof bracing that are compliant to 11.1.2

3

Continued

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42

4.6 Inverted pendulum structures2) 3 4.7 Isostatic seismic structures 3 5. Precast reinforced concrete structures 5.1 Purely gravitational precast structures 5 5.2 Precast structures with wet connections, connected to the non-structural

elements and incorporated into the structural model 3

5.3 Precasted structures with wet connections, non-connected to the non-structural elements

5

5.4 Precast structures with dry connections, non-connected and connected to the non-structural elements with: Bolted connections and connections by means of bars embedded in mor-tar3)

Welded connections3)

4

4

5.5 Precast inverted pendulum structures2) or with cantilever pillars 3 5.6 Earthquake-resistant isostatic structures 3 6. Masonry structures and buildings 6.1 Reinforced block masonry with total filling of voids 4 6.2 Reinforced block masonry without total filling of voids and reinforced

block masonry with ceramic units of grid type. 3

6.3 Confined masonry 4 7. Tanks, vessels, stacks, silos and hoppers 7.1 Stacks, silos and hoppers with continuous down-to-floor shells 3 7.2 Silos, hoppers and tanks supported on columns, with or without bracing

between columns. 4

7.3 Vertical axis steel tanks with continuous down-to-floor shell 4 7.4 Vertical axis reinforced concrete tanks with continuous down-to-floor

shell 3

7.5 Tanks and conduits of composite synthetic material (FRP, GFRP, HDPE and similar materials)

3

7.6 Horizontal vessels supported on cradles with ductile anchorages 4 (continues)

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43

8. Towers, piping and equipment 8.1 Process towers 3 8.2 Cooling towers made of wood or plastic 4 8.3 Electric control cabinets resting on floor. 3 8.4 Steel piping except their connections 5 9. Storage racks 4 NOTES

1. Except that a study proves that an R value other than 2 can be used. Structures whose resistant system is explicitly included in this table are not assimilable to this classification.

2. Over 50% of the mass above the upper level. Only one resistant element. 3. The value R = 4 is an upper limit. If the R value is lower for the equivalent rein-

forced concrete structural system, said lower value shall be used. 4. In case of uncertainty regarding the classification of a resistant system, provision

4.7 shall be applied.

Table 5.7 Maximum values of the seismic coefficient

Cmx.

R = 0.02 = 0.03 = 0.05 1 0.79 0.68 0.55 2 0.60 0.49 0.42 3 0.40 0.34 0.28 4 0.32 0.27 0.22 5 0.26 0.23 0.18

NOTE These values are valid for seismic Zone 3. For application to zones 2 and 1, these values shall be multiplied by 0.75 and 0.50, respectively.

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Figure 5.1 a) Seismic zonification of Regions I, II and III

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Figure 5.1 b) Seismic zonification of Regions IV, V, VI, VII, VIII, IX, X and Metropolitan Region

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Figure 5.1 c) Seismic zonification of Regions XI and XII

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Figure 5.2

6. Seismic deformations 6.1 Calculation of deformations

When the analysis considers R-factor reduced earthquake loads, the deformations shall be determined as follows:

d = d0 + R1 dd (6-1)

where

d = Seismic deformation

d0 = Deformation due to non-seismic service loads

R1 = Factor resulting from multiplying the R factor derived from Table 5.6 by the quotient Q0/Qmin, provided that Q0/Qmin be lower or equal to 1.0. However, for the quotient Q0/Qmin a value under 0.5 shall not be used. If this quotient is higher than 1.0, R1 = R shall be used

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dd = Deformation calculated with R-factor reduced earth-quake loads.

If anelastic methods are used, deformation d shall be obtained directly from the analysis.

6.2 Separation between structures 6.2.1 With the purpose of preventing impacts between adjoining structures, their separation

shall be bigger than the highest of the following values:

j0i02

djj12

dii1 dd)dR()dR(S +++=

(6-2)

S = 0.002 (hi + hj)

S = 30 mm

(6-3)

where

ddi , ddj = Deformations of the structures i and j calculated as per 6.1;

R1i , R1j = response modification factors R1 used for the design of the structures i and j, and

hi , hj = height at the considered level of the structures i and j measured from their respective base levels.

6.2.2 The separation between the structure and rigid or fragile non-structural elements, whose

impact is required to be prevented, must be higher than the relative deformation between the levels where the element is located and calculated with the corresponding d values, but not less than 0.005 times of the element height.

6.3 Maximum seismic deformations

Seismic deformation must be restricted to values that do not damage piping, electric sys-tems or other elements, connected to the structure, which shall be protected. The deformations calculated by the expression (6-1) shall not exceed the following val-ues:

a) Precast concrete structures composed exclusively of an earthquake-resistant system

based on walls connected by dry connections.

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dmax = 0.002 h (6-4)

b) Structures of masonry walls with partitions that are rigidly fastened to the structure.

dmax = 0.003 h (6-5)

c) Unbraced frames with non-connected masonry fill.

dmax = 0.0075 h (6-6)

d) Other structures

dmax = 0.015 h (6-7)

where

h = height between floors or between two points located on the same vertical.

The foregoing restrictions may be obviated if it is proved that a bigger deformation can be tolerated by the structural and non-structural elements.

6.4 The P-Delta effect

The P-Delta effect shall be considered in case the seismic deformations exceed the fol-lowing value

d = 0.015 h (6-8) 7. Secondary elements and equipment mounted on structures 7.1. Scope

Secondary elements are interior partitions and other appendages attached to the resistant structure but that are not part of it. Equipment anchored on several levels of the structure shall conform to provision 11.3.2.

7.2. Forces for seismic design

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7.2.1. According to 5.3.1.5 , in case that the secondary element or equipment is included in the modeling of the supporting structure, they shall be designed with the following horizontal earthquake loads acting in any direction:

Fp = pp

1p PR

RQ2.1 < (7-1)

where

Qp = Shear load that appears at the base of the secondary element or equipment according to an analysis of the building with R-factor reduced seismic loads;

R1 = Factor defined in 6.1

Rp = Response modification factor of the secondary ele-ment or equipment according to Table 7.1;

Pp = Weight of the secondary element or equipment.

7.2.2. If it is not necessary that the equipment has to be included in the modeling of the struc-

ture, except for its mass, the design of the secondary elements and equipment may be car-ried out with the following seismic forces:

a) When the acceleration ap is known at the support level of the element or equipment as

derived from the dynamic modal analysis of the building with R-factor reduced earth-quake loads:

Fp = ppp

pp PPR

Ka0.3 < (7-2)

Where the coefficient Kp must be defined alternately by means of one of the two follow-ing procedures:

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i) Kp = 2.2 (7.3)

ii) Kp = 0.5 + 222 )3.0()1(

5.0 + (7.4)

where

= 1 for 0.8 T* *1.1 TTp

= 1.25 (Tp/ T*)

for Tp < 0.8 T*

= 0.91 (Tp/ T*)

for Tp > 1.1 T*

where

Tp = Natural period of the fundamental vibration mode of the secondary element including its anchorage system and T* is the period of the mode with the highest equivalent transla-tional mass of the structure in the direction in which the secondary element may enter in resonance. The determina-tion of requires that the value of T* be over 0.06 s.

b) When no modal dynamic analysis of the building has been carried out:

Fp = ppp

pk PPR

Ka

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7.2.5. The seismic design force determined as per 7.2.1 or 7.2.2 shall not be lower than

0.8A0Pp/g. 7.3. Forces for anchoring design 7.3.1. All secondary elements and equipment shall be duly anchored to the resistant structure by

means of bolts or other devices. The design shall be made with the forces established in 7.2 with the modifications detailed under 7.3.2 and 7.3.3.

7.3.2. When the anchorage to concrete elements includes anchor bolts on the surface (bolts with

a length-diameter ratio under 8), the seismic forces established under 7.2 shall be in-creased by 50%, or else, they shall be calculated with Rp = 1.5. The same provision shall be applied to anchor bolts designed without the exposed length specified under 8.6.2.

7.3.3. When the anchoring system is built with non ductile materials, the seismic forces of 7.2

must be amplified by 3, or else be calculated with Rp = 1.0. 7.4. Automatic shutoff systems

Ducts, vessels and equipment containing high temperature gases and liquids, explosives or toxic materials must be equipped with automatic shutoff systems which fulfill the pro-visions of 8.5.4 of NCh433.Of96.

Table 7.1 - Maximum values of the response modification factor of

secondary elements and equipment

Secondary elements or equipment

Rp

- Rigid or flexible equipments or elements with non-ductile materials or appendages

1.5

- Precast secondary elements. Elements in cantilever. Partitions.

- Electric and mechanical equipment in general. - Stacks, tanks, steel towers - Other non specified cases in this table

3

- Storage shelves - Secondary structures

4

8. Special provisions for steel structures 8.1. Applicable standards

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Until the issuance of the new edition of the Chilean Standard on detailing and construc-tion of steel structures, the provisions of this standard shall be used complemented with the following standards:

a) Load and Resistance Factor Design Specifications for Steel Buildings, 1999, Ameri-

can Institute of Steel Construction (AISC); or Specifications for Structural Steel Buildings, Allowable Stress Design; 1989, AISC.

b) Specifications for the Design of Cold Formed Steel Structural Members, 1996, Ameri-

can Iron and Steel Institute (AISI), covering the design of cold formed elements not included in the AISC standards

c) In matters of seismic design, the AISC standards shall be supplemented by the provi-

sions of Seismic Provisions for Structural Steel Buildings, Part 1: Structural Steel Buildings, 1999, AISC, or the provisions contained in clause 8 and Appendix B of this standard.

8.2. Materials 8.2.1. Structural steel shall fulfill the following provisions:

- Exhibe at tensile testing a pronounced natural ductility plateau with a yield point under 0.85 times of the ultimate strength and minimal fracture elongation of 20% in 50 mm test specimen.

- Guaranteed weldability in conformance with AWS standards.

- Minimum toughness of 27 at 21C measured with Charpy test compliant to ASTM 6.

- Yield point not over 450 Mpa.

8.2.2. In addition to the conditions specified under 8.2.1 , the materials shall fulfill one of the

following specifications:

- ASTM A36; A242; A572 Gr. 42 and Gr. 50; A588 Gr. 50; A913 and A982 for structural shapes; plate; bars; common bolts and anchor bolts).

- DIN 17 100, qualities St. 44.2; St. 44.3 and St. 52.3 for the same foregoing elements.

- NCh203 A 42-27ES; A 37-24ES; and NCh1159 A 52-34ES for the same foregoing ele-

ments.

- ASTM A500 Gr. B and C; A501 and A502 for structural tubes.

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- AWS 5 for welding.

Materials that meet other than the foregoing specifications may be used prior approval by the professional specialists of each project.

8.2.3. Earthquake-resistant groove welds shall be complete joint-penetration type with elec-

trodes of minimum toughness of 27 Joules at -29 C, measured with Charpy test according to ASTM A6.

8.3. Braced frames 8.3.1. Braced frame configurations with diagonal elements that only resist tension are not al-

lowed, except in case of light steel bays, which are governed by the provisions detailed under 11.2.

8.3.2. Every resistant line shall include braces to take tension and braces to resist compression.

As a minimum the strength provided by the diagonal resisting tension in each direction of the seismic action, shall be equivalent to 30% of the shear load of the resisting line at the corresponding level.

8.3.3. The elements of vertical earthquake-resistant systems under compression shall have

width to thickness ratios under r according to Table 8.1 (see Figure 8.1). The slender-ness ratio of the element shall be less than 1.5 yFE / .

8.3.4. The diagonal elements in an X brace shall be connected at the point of intersection. This

point can be considered fixed in perpendicular direction to the plane of the braces for de-termining the members buckling length when one of the diagonal elements is continuous.

8.3.5. In industrial buildings with V-bracing or inverted V-bracing bracing, beams shall be con-

tinuous over the intersection point with the diagonal elements and they shall be designed to resist the vertical loads assuming that they are not supported by the diagonal elements. In addition, the diagonal elements shall be capable of supporting the self-weight loads and the beam-induced live loads plus the seismic loads gotten from analysis, amplified by 1.5. The upper and lower beam flanges shall be designed to resist a transversal load located at the point of intersection with the diagonal elements, equal to 2% of the nominal strength of the flange, that is, Fy bf t ,

where

Fy = yield stress of the flange; bf = width of the flange t = Flange thickness

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8.3.6. The earthquake stress in the compressed diagonal elements shall be less or equal to 80% of the resistant capacity defined in the steel design specification.

8.3.7. Seismic K-braces in which the diagonal elements intersect in an intermediate column

point are not allowed, except that at that point exists a strut that is part of the bracing sys-tem.

8.3.8. Provisions 8.3.3, 8.3.5, and 8.3.6 shall not be applied to bracings whose majorated earth-

quake stresses are lower than one third of the stresses of the combination that controls the design.

8.4. Rigid frames 8.4.1. Moment connections of earthquake-resistant rigid frames shall be totally rigid (TR). Par-

tially rigid (PR) connections are not allowed. These connections shall be designed so that to enable the development of the plastic hinge in the beam at a reasonable distance from the column, which can be achieved by reinforcing the connection or weakening the beam at the desired position of the plastic hinge.

8.4.2. Abrupt changes of the beam flange width are not allowed at the potential plastic hinge

development areas or near them, unless when dealing with a reduced beam section appro-priately designed to induce the plastic hinge at that position.

8.4.3. The transversal sections of the columns and beam beams in rigid earthquake-resistant

frames shall qualify as compact, that is, their width to thickness ratios shall be under p of Table 8.1.

8.4.4. In multi-story structures in which the total earthquake-resistance depends from rigid

frames designed with R1 greater or equal to 3, the sum of the bending strength capacities of the columns that concur at a node shall be greater or equal to 1.2 times the sum of the bending strength capacities of the connected beams.

It is not necessary to fulfill this requirement in whichever of the following cases:

a) If the seismic shear load of every column for which the abovementioned requirement

is not met, is 25% lower than the seismic shear load of the corresponding story.

b) If the analysis and detailing of the structure is made by taking seismic forces equal to the double of the values established under clause 5 of this standard.

c) If a non-linear analysis (see 5.2.3) proves that the structure is stable in the face of the

deformation demands imposed by the earthquake. 8.4.5. The design of the beam-column panel zone of earthquake-resistant rigid frames shall be

compliant to Appendix B.

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8.4.6. The compression strength in columns with prevailing compression, disregarding the ef-

fect of the flexural moment, shall be greater than the axial loads obtained from the loading combinations of 4.5, in which the earthquake loading condition of these loading combina-tions has been amplified by 2. Prevailing compression is defined as the situation in which the axial stress obtained from the loading combinations of 4.5 is greater than 40% of the design compression strength of the column.

8.4.7. The provision of 8.4.3 is not applicable to rigid frame elements in which the stresses from

majorated seismic loads are lower than one third of the stresses of the load combination which controls the design.

8.5. Connections 8.5.1. Materials shall fulfill the following requirements:

- The bolts of earthquake-resistant connections shall be exclusively high strength mate-rial, quality ASTM A325 or ASTM A490, or equivalent.

- Arc welding electrodes and fluxes shall be compliant to AWS A 5.1, A 5.5, A 5.17, A

5.18, A 5.20, A 5.23, and A 5.29 or equivalent specifications.

- Electrodes shall feature a minimum Charpy toughness of 27 Joules at 29C according to ASTM A6.

8.5.2. The connections of seismic diagonal elements shall be designed to resist 100% of the ten-

sile capacity of their gross section. 8.5.3. The moment connection strength between beams and columns of rigid earthquake-

resistant frames shall be at least equal to the strength of the connected elements. 8.5.4. The upper and lower beam flanges in beam-column connections of rigid frames shall have

lateral supports designed for a force equal to tbF02.0 fy . 8.5.5. The groove welds of earthquake-resistant joints shall be of complete penetration type. 8.5.6. High-strength bolts shall be installed with the pretension specified for slip-critical connec-

tion (70% of tensile strength for A325 and A490 bolts). However, the design strength of bolted joints can be calculated as that corresponding to bearing stress connections. The contact surfaces shall be cleaned with mechanical roller, or by sand blasting or shot blast-ing; they shall not be painted but galvanizing is acceptable.

8.5.7. Not allowed are connections whose resistance depends on a combination of weldings with

high-strength bolts or rivets. Excepted are the modifications of existing riveted structures.

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8.5.8. Field joints shall fulfill the following requirements:

a) In connections made with high-strength bolts, methodologies of tightening and control that assure the pretension required under 8.5.6 shall be applied.

b) Welding is allowed only in plane position, vertical and horizontal, and with the welder

protected against wind and rain.

c) Welds shall be complete-penetration groove welds or filet-welds. Groove welds shall be controlled by means of ultrasonic or X-ray.

8.5.9. Column splices shall fulfill the following conditions:

a) In buildings the distance between the column splice and the upper beam flange shall be greater or equal than the lower value between 900 mm and half of the clear column height.

b) The splices shall be sized for the design forces obtained from the load combinations of

4.5, in which the seismic load condition has been amplified by 2. 8.6. Anchorages 8.6.1. The supports of structures and equipments, which transfer seismic loads to the founda-

tions or other concrete element, shall be anchored by means of anchor bolts, anchor plates, reinforcing bars or other appropriate means.

8.6.2. Anchor bolts subjected to tension according to the procedures of analysis detailed under

clauses 4, 5 and 7 shall have chair and the bolt shall be visible for allowing their inspec-tion and repair and the thread shall have the sufficient length to enable retightening of the nuts (see Appendix A, Figure A.1). The exposed length of the bolts shall not be less than 250 mm nor eight times their diameter, nor the thread length under the nut be less than 75 mm.

Exception is made to this requirement for anchor bolts with sufficient capacity to resist loading combinations, in which the seismic loads are amplified by 0.5 R times, but not less than 1.5 times, the value specified in clauses 5 and 7.

Important equipments, such as very high process vessels and in the structure of large sus-pended equipments, such as boilers and simil