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
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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TABLE OF CONTENTS
1 2
3
4
5
6
GENERAL ............................................................................................................... 3 1.1 Scope............................................................................................................... 3 1.2 Brief .................................................................................................................. 3 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 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 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 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 DISCUSSIONS AND CONCLUSIONS............................................................. 23
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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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
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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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.
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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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 γf. 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.
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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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 Ψ1 = 0.95, for instantaneous ones ψ2 = 0.9 In special combinations for sustained loads Ψ1 = 0.95, for instantaneous ones ψ2 = 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 γf are obtained from the code for a typical structural steel design and presented below for possible loadings. Weight of structural components
γf
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
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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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.
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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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 γf, where Frep can be found by multiplying the characteristic value of the action Fk with a coefficient ψ, where the coefficient is either 1.00, ψ0, ψ1 or ψ2.
3.4 Design Values of Material The design value Xd of a material is Xd = η Xk / γm where γm is the partial factor for the material and Xk is characteristic value of the material. For mean value of conversion factor η, please refer to Cl. 6.3.3. of the code EN 1990. Alternatively, the design resistance may be simplified to Rd = Rk / γm 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,
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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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 ψ factors for buildings are presented in Table A1.1 of the code and also presented below. Table 1: Recommended values of ψ factors for buildings
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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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)
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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Table 3: Design values of actions for use in accidental and seismic combinations of actions
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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4 SNIP II-23-81 STEEL STRUCTURES The design of steel structural systems of buildings is governed by this code SNIP II-2381. 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 γm. R = Rn / γm 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 γm 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 / γc where γc 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.
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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Stability analysis of the solid-wall components subject to central compression by force N shall be conducted by the following formula. N / (φ A) ≤ Ry / γc Numerical values of φ 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 φ.
4.3 Bending in SNIP The strength analysis of components subject to bending shall be conducted by the formula M / Wn,min ≤ Ry / γc The stability analysis of a component under bending is conducted by the formula below. M / (φb Wc) ≤ Ry / γc where Wc is determined using the compression chord and φb is a factor determined in accordance with Appendix 7 of the code. The calculation of φb in Appendix 7 is presented as below for a double-T section (I section). φ1 = ψ (Jy / Jx) (h / lef)2 (E / Ry) where ψ values are to be adopted from Tables 77 and 78 of the code. For rolled double-T sections α =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, φb = φ1 at φ1 ≤ 0.85; φb = 0.68 + 0.21 φ1 at φ1 > 0.85 but φb must not exceed 1.0.
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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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.
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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Table 4: Nominal values of yield strength fy and ultimate tensile strength fu for hot rolled structural steel
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SNIP vs. Eurocode
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Comparison of EN1991 and EN1993 against SNIP 2.01.07-85 and SNIP II-23-81
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5.1 Partial Factors for Material The partial factors γM 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:
γM0
resistance of members to instability assessed by member checks: γM1 resistance of cross-sections in tension to fracture: resistance of joints:
γM2 see EN 1993-1-8
Note that the partial factors γMi 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: γM0 = 1,00 γM1 = 1,00 γM2 = 1,25
5.2 Tension in EN 1993
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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5.3 Compression in EN 1993
5.4 Bending in EN 1993
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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5.5 Compression Buckling in EN 1993
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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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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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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5.6 Flexural Buckling in EN 1993
SUBJECT:
SNIP vs. Eurocode
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Comparison of EN1991 and EN1993 against SNIP 2.01.07-85 and SNIP II-23-81
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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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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 ψ 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, ψ factors used in accompanying variable actions are less than the corresponding ψ 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 γm 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 γc 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 γc is 0.90, for columns γc is 0.95 and for solid beams with φb < 1.0 γc 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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SNIP vs. Eurocode
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Comparison of EN1991 and EN1993 against SNIP 2.01.07-85 and SNIP II-23-81
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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.
