Eurocode vs SNIP_rev00

SUBJECT: SNIP vs. Eurocode EXPLANATION: Comparison of EN1991 and EN1993 against SNIP 2.01.07-85 and SNIP II-23-81

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COMPARISON OF

SNIP vs. EUROCODE

SNIP 2.01.07-85 vs. EN 1990 and EN 1991 SNIP II-23-81 vs. EN 1993


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TABLE OF CONTENTS

1 GENERAL ............................................................................................................... 3 1.1 Scope ............................................................................................................... 3 1.2 Brief .................................................................................................................. 3

2 SNIP 2.01.07-75 LOADS AND EFFECTS ......................................................... 5 2.1 Classification of Loads according to SNIP................................................. 5 2.2 SNIP Load Combinations ............................................................................. 6 2.3 Reliability Coefficients for Load Cases ....................................................... 6

3 EN 1990 AND EN1991 ACTIONS ON STRUCTURES ................................... 7 3.1 Classification of Actions according to EN 1991 ........................................ 7 3.2 Principles of Limit State Design according to EN 1990 ........................... 8 3.3 Design Values of Actions.............................................................................. 8 3.4 Design Values of Material............................................................................. 8

4 SNIP II-23-81 STEEL STRUCTURES.............................................................. 12 4.1 Design Characteristics of Material ............................................................ 12 4.2 Centric Tension and Compression Components .................................... 12 4.3 Bending in SNIP........................................................................................... 13

5 EN 1993 DESIGN OF STEEL STRUCTURES ............................................... 14 5.1 Partial Factors for Material ......................................................................... 16 5.2 Tension in EN 1993 ..................................................................................... 16 5.3 Compression in EN 1993............................................................................ 17 5.4 Bending in EN 1993..................................................................................... 17 5.5 Compression Buckling in EN 1993 ........................................................... 18 5.6 Flexural Buckling in EN 1993..................................................................... 21

6 DISCUSSIONS AND CONCLUSIONS............................................................. 23


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1 GENERAL

1.1 Scope This report has been prepared for a general comparison of SNIP codes and Eurocodes

given below.

SNIP 2.01.07-85 vs. EN 1990 and EN 1991

SNIP II-23-81 vs. EN 1993

1.2 Brief PROBE engineers have been asked to prepare a report which will present a concise

comparison of SNIP codes and European codes used in the design of structural steel

buildings.

In general, the two design codes which are used by engineers in structural steel

building design are the codes SNIP 2.01.07-85 Loads and Effects and SNIP II-23-81

Structures that are design codes employed for loadings and design of structural steel

systems respectively.

Corresponding European codes for the above mentioned Russian design codes are

EN 1990 Basis of Design, EN 1991 Actions on Structures and EN 1993 Design of

Steel Structures. EN 1991 and EN 1993 are also recognised as Eurocode 1 and

Eurocode 3 respectively. The whole list of European standards is presented below for a

better understanding of the European norms.

EN 1990 Eurocode: Basis of Structural Design EN 1991 Eurocode 1: Actions on structures EN 1992 Eurocode 2: Design of concrete structures EN 1993 Eurocode 3: Design of steel structures EN 1994 Eurocode 4: Design of composite steel and concrete structures EN 1995 Eurocode 5: Design of timber structures EN 1996 Eurocode 6: Design of masonry structures EN 1997 Eurocode 7: Geotechnical design EN 1998 Eurocode 8: Design of structures for earthquake resistance EN 1999 Eurocode 9: Design of aluminium structures


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In the generation of the above European codes, general texts of each individual codes

and their parts are published by CEN and it is acknowledged that these codes may be

followed by National Annex documents of the countries who decide to implement these

European norms.

Therefore, it has to be noted by the designers that, in case a structural design is

conducted for a country using these norms, the National Annex documents of the

country of design also have to be followed in order to adopt the design correctly in

accordance with the local requirements, parameters and limitations of that country.

The details of the comparison of the codes mentioned will be presented in the following

sections of the report. The comparison is conducted in order to present the differences

of the two different approaches of the two types of codes to the structural steel design

of buildings. The statements below are general comments obtained after the review of

the two corresponding design codes. In order to have a more detailed comparison, it is

recommended that some case studies are to be carried out.


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2 SNIP 2.01.07-75 LOADS AND EFFECTS

The characteristic values of the loads to be taken into design of structures are specified

in this code. These specified values are considered as full and reduced. Reduced

values are to be considered when the duration of loading is taken into account.

A design value of a load is determined by the product of its specified value in the code

and a reliability coefficient f. These factors are given in various parts of the codes.

For instance, in Table 1 of the code and the reliability coefficients to be used for

structural components and soil are presented and the values change from 1.05 to 1.3

in accordance with the type of the structural components and soil.

These reliability coefficients may change from loading to loading. Therefore, the

designer may have to use different factors for different type of loads when determining

the design value of a load. It may also be noted that these factors are similar to the

load factors used in load combinations of EN.

2.1 Classification of Loads according to SNIP In the code, loads are divided into groups of dead and live. In addition to this, live

loads are also divided into the groups of sustained, instantaneous and special

loads.

Dead loads include the self weights of the building parts and weight - pressure of soils.

Sustained loads are given in section 1.7 of the code. Temperature effects, loads on

floors, snow loads with reduced specified values, climatic temperature effects are some

of the included ones in sustained loads list. Instantaneous loads are summarized in

section 1.8 as weight of people, bridge and suspended cranes, snow loads with full

specified values, climatic temperature effects with full specified values, wind loads and

sleet (frozen rain or hail) loads.

Seismic and explosion stresses are considered as special load case as given in section

1.9 of the code.


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2.2 SNIP Load Combinations Load combinations of loads consisting of dead, sustained and instantaneous live loads

are considered as main combinations. Loads consisting of dead, sustained,

instantaneous and one of special loads are considered under special combinations.

The design values of live loads are allowed to be reduced when taking into account not

less than two live loads by multiplying the design values by coefficients

In main combinations for sustained loads 1 = 0.95, for instantaneous ones 2 = 0.9

In special combinations for sustained loads 1 = 0.95, for instantaneous ones 2 = 0.9

Above coefficients are not used when considering one live load together with dead

loads in main load combinations.

2.3 Reliability Coefficients for Load Cases For clarity, reliability coefficients f are obtained from the code for a typical structural

steel design and presented below for possible loadings.

Weight of structural components f Steel 1.05

Concrete 1.10

Masonry 1.10

Wood 1.10

Live loads for slabs

< 200kPa 1.30

200kPa 1.20

Snow load 1.40

Wind load 1.40


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3 EN 1990 AND EN1991 ACTIONS ON STRUCTURES

As presented in the scope of EN 1990, EN 1990 establishes Principles and

requirements for the safety, serviceability and durability of structures, describes the

basis for their design and verification and gives guidelines for related aspects of

structural reliability.

EN 1991 forms guidance for the actions to be taken into account in the design of

structures. The following sections of the code may be required to be considered in

general during design of a typical structure.

EN 1991-1-1 Eurocode 1: Actions on structures: Part 1-1: General Actions Densities,

self weight, imposed loads for buildings

EN 1991-1-3 Eurocode 1: Actions on structures: Part 1-3: Snow loads

EN 1991-1-4 Eurocode 1: Actions on structures: Part 1-4: Wind actions

EN 1991-1-6 Eurocode 1: Actions on structures: Part 1-6: Actions during execution

As summary to the above discussion, EN 1990 is a generated for design of structures

where the designer can find the load combinations corresponding load factors to use in

the calculations, whereas in order to specify the characteristic values of the actual

loadings, such as wind load or snow load acting on the structure under consideration,

one has to refer to the corresponding parts of EN 1991.

3.1 Classification of Actions according to EN 1991 The loads are considered as permanent and imposed loads in EN 1991. Self weights of

structural and non structural members are considered as permanent load. Wind, snow,

crane actions and etc. are considered as imposed load.

Values of imposed loads are given in Table 6.2 in EN 1991-1-1 in accordance with

categories of the loaded areas defined in Table 6.1 based on the type of usage of the

structure under consideration. Imposed loads of roofs are presented in Cl. 6.3.4 of the

code.


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3.2 Principles of Limit State Design according to EN 1990 The design situations are classified as persistent, transient, accidental and seismic in

accordance with Section 3.2 of the code.

Persistent design situation refers to the normal use conditions, whereas transient refer

to temporary conditions such as construction stages or maintenance. Accidental

situation refers to explosions, impacts and etc.

Therefore, a building is mostly designed according to persistent and seismic design

situations using EN 1990 unless transient or accidental cases are not within the scope

of the design.

3.3 Design Values of Actions The design values of actions Fd is multiplication of Frep and a partial load factor f,

where Frep can be found by multiplying the characteristic value of the action Fk with a

coefficient , where the coefficient is either 1.00, 0, 1 or 2.

3.4 Design Values of Material The design value Xd of a material is

Xd = Xk / m

where m is the partial factor for the material and Xk is characteristic value of the

material. For mean value of conversion factor , please refer to Cl. 6.3.3. of the code

EN 1990. Alternatively, the design resistance may be simplified to

Rd = Rk / m

The following ultimate limit states shall be verified as relevant :

a) EQU : Loss of static equilibrium of the structure or any part of it considered as a

rigid body, where :

minor variations in the value or the spatial distribution of actions from a single

source are significant, and

the strengths of construction materials or ground are generally not governing ;

b) STR : Internal failure or excessive deformation of the structure or structural

members,


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including footings, piles, basement walls, etc., where the strength of construction

materials of the structure governs ;

c) GEO : Failure or excessive deformation of the ground where the strengths of soil or

rock are significant in providing resistance ;

d) FAT : Fatigue failure of the structure or structural members.

In Annex A1 of EN 1990, the application of partial load factors to the buildings is

presented in detail.

Recommended values of factors for buildings are presented in Table A1.1 of the

code and also presented below.

Table 1: Recommended values of factors for buildings


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Design values of actions for EQU and Seismic cases are presented in the tables below.

For the other cases such as STR or GEO, please refer to the Annex A1 of EN 1990.

Table 2: Design values of actions (EQU) (Set A)


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Table 3: Design values of actions for use in accidental and seismic combinations of actions


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4 SNIP II-23-81 STEEL STRUCTURES

The design of steel structural systems of buildings is governed by this code SNIP II-23-

81. The code is not applicable to design of bridges, transportation tunnels and culverts

under embankments.

4.1 Design Characteristics of Material The SNIP code approach to the design resistance of a design material is simply to

adjust the characteristic rated resistance Rn of the material by a reliability material

factor m.

R = Rn / m

In Table 1 of the code, the design resistance formulae are presented. In order to obtain

the design resistance to tension, compression and bending of the sheet rolled steels

Table 51 of the code is to be examined. In accordance with Table 2 and Table 51of the

code, it is noted that for a normal structural steel with yield strength of 235MPa, the

corresponding design resistance is to be taken as 230MPa using a material reliability

factor m of 1.025 for a member wall thickness less than 20mm.

It has to be acknowledged that for different parts of the structure, different reliability

material factors are to be utilized. Therefore, for a better understanding of the details of

the method, the code shall be reviewed by the designer appropriately.

4.2 Centric Tension and Compression Components The strength of components subject to tension or compression by force N shall be

conducted by the formula

N / An Ry / c

where c is the working condition factor to be taken from Table 6 of the code and the

value varies between 0.80 to 1.15 in accordance with the type of the structural

component.


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Stability analysis of the solid-wall components subject to central compression by force

N shall be conducted by the following formula.

N / ( A) Ry / c

Numerical values of are given in Table 72 of the code.

Therefore, it can be said that in SNIP code the stability analysis (buckling) of a

compression strut is carried out simply by reducing the tensile capacity of the profile by

employing the coefficient .

4.3 Bending in SNIP The strength analysis of components subject to bending shall be conducted by the

formula

M / Wn,min Ry / c

The stability analysis of a component under bending is conducted by the formula

below.

M / (b Wc) Ry / c

where Wc is determined using the compression chord and b is a factor determined in

accordance with Appendix 7 of the code. The calculation of b in Appendix 7 is

presented as below for a double-T section (I section).

1 = (Jy / Jx) (h / lef)2 (E / Ry)

where values are to be adopted from Tables 77 and 78 of the code. For rolled

double-T sections

=1.54 (Jt / Jy) (lef / h)2

where lef is the design length of beam in accordance with Section 5.15 of the code.

Then, b = 1 at 1 0.85; b = 0.68 + 0.21 1 at 1 > 0.85 but b must not exceed 1.0.


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5 EN 1993 DESIGN OF STEEL STRUCTURES

EN 1993 or as usually referred as Eurocode 3 applies to the design of buildings and

civil engineering works in steel. It complies with the principles presented in EN 1990

Basis of Structural Design.

EN1993 is intended to be used in conjunction with EN 1990 Basis of structural design

EN 1991 Actions on structures

ENs, ETAGs and ETAs for construction products relevant for steel structures

EN 1090 Execution of Steel Structures Technical requirements

EN 1992 to EN 1999 when steel structures or steel components are referred to

EN 1993-1-1 presents the basic rules of the design of steel structures with material

thicknesses t 3 mm. It also provides provisions for the structural design of steel

buildings. Note that for cold formed thin gauge members and plate thicknesses t < 3

mm one has to refer to EN 1993-1-3.

Nominal values of yield strength fy and ultimate tensile strength fu for hot rolled sections

are presented in Table 3.1 of the code. The same table is presented also below.


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Table 4: Nominal values of yield strength fy and ultimate tensile strength fu for hot rolled structural steel


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5.1 Partial Factors for Material The partial factors M as defined in 2.4.3 of the code should be applied to the various

characteristic values of resistance in this section as follows:

resistance of cross-sections whatever the class is: M0

resistance of members to instability assessed by member checks: M1

resistance of cross-sections in tension to fracture: M2

resistance of joints: see EN 1993-1-8

Note that the partial factors Mi for buildings may be defined in the National Annex of

the country of design. However, the following numerical values are also recommended

for buildings in the code:

M0 = 1,00

M1 = 1,00

M2 = 1,25

5.2 Tension in EN 1993


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5.3 Compression in EN 1993

5.4 Bending in EN 1993


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5.5 Compression Buckling in EN 1993


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5.6 Flexural Buckling in EN 1993


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6 DISCUSSIONS AND CONCLUSIONS

In accordance with the comparison presented in the previous sections of the report, the

following discussions are made.

1. The two codes follow a similar approach to the structural design which can be

called as load factor design, in which the actions on the structure are

multiplied by corresponding load factors in accordance with a probabilistic

approach.

2. Reliability factor for self weight of structural steel is 1.05 in SNIP, whereas

design value of permanent action in EN 1990 employs a partial factor of 1.10 in

the corresponding load combination as shown in Table 2 of this report.

3. The reliability factor of wind and snow load is 1.40 and corresponding factors

change between 0.90 and 0.95 for load combinations include more than one

sustained loads, whereas EN 1990 a partial load factor of 1.50 is employed as

shown in Table 2 of this report. However, factors used in accompanying

variable actions are less than the corresponding factors of SNIP as shown in

Table 1 of this report. Therefore, for load combinations with single variable

actions (e.g. only wind or only snow) SNIP would give less critical member

utilizations for the same amount of action considered, whereas for the

combined variable actions, Eurocode may give less critical results.

4. Both SNIP and EN consider material factors 1.0 to obtain design resistances.

5. Design resistance values obtained using EN are more than corresponding SNIP

values since the material factors m are 1.025 in SNIP and 1.0 for EN for the

yield strength structural members.

6. It is also noted that in the member checks in SNIP a factor of working condition

c is employed, which changes between the values of 0.80 and1.15 in

accordance with the type of the structural component. For solid beams and

compressed components of trusses the value of c is 0.90, for columns c is

0.95 and for solid beams with b < 1.0 c is 0.95. In

In accordance with the above discussions it is concluded that using SNIP and

Eurocode would give close results in terms of weight of structural steel used in a


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project. It is acknowledged that, SNIP codes employ less partial load factors than

European codes to be used in load combinations in general. However, it is noted also

that SNIP codes employs also less member resistance values compared with

European codes.

Based on the experience on the design with European and SNIP codes and the

comparison and discussions presented in this report, it is concluded that the structural

design with SNIP codes would yield very slightly economic solutions in terms of

material weight.

Therefore, it can be said that, based on above discussions it is acknowledged here that

Eurocode design gives slightly conservative results when compared against SNIP.

However it has to be noted that, the above conclusion is an estimate based on the

discussions presented in this report. It has to be also noted that, for a specific project,

the opposite of the above may be concluded in accordance with the local parameters

and requirements of the project. In order to have a better comparison a case study

would be recommended.

Eurocode vs SNIP_rev00

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