1-16

0-16

1-15

DateSeptember, 2012

3 Design BasisGeneral design parameters for Norwegian bridges

RevisionC

Date2012-09-18

Rev date-

Made byJKD

Checked by-

Approved by-

DescriptionDesign of bridges in Norway

Contents

1.Introduction32.Design parameters42.1Codes and standards42.2Safety factors42.3Durability Requirements43.Software53.1Rambll, Bridge design system (BDS)53.1.1ECROSS & PRCOSS - Cross Sectional Analysis53.2LUSAS finite element analysis software54.Materials64.1Concrete64.2Mild steel65.Loads75.1Permanent loads75.2Temperature load75.3Traffic loads95.3.1Vertical traffic loads95.3.2Horizontal traffic loads105.3.3Traffic loads on filling105.3.4Other variable loads115.3.5Accidental loads116.Load Combinations116.1-factor for road bridges126.2ULS136.3ALS146.4SLS147.Design Checks157.1Minimum reinforcement157.2ULS157.3SLS - Concrete Structures157.3.1SLS Frequent Combinations158.References17

1. IntroductionThe purpose of this document is to highlight the general requirements, guidelines, design philosophies and parameters adopted for the design of a bridge structure. The basis for design gives descriptions on the following items:

Design parametersSoftwareMaterialsPrincipal loadsLoad combinationsDesign checks

Design parametersCodes and standardsThe structures shall be designed using the Eurocodes (including corrigendum and amendments) along with the Norwegian National Annexes. Table 21: Hierarchy for concrete designRoadway bridges: Norwegian handbook from the Norwegian road authorities Name: Bruporsjektering, Hndbok 185 fra Statens Vegvesen, nov. 2011

Eurocode for concrete bridges (EC2 part 2): NS-EN 1992-2:2005 + NA:2010

Eurocode for concrete structures (EC2 part 1-1): NS-EN 1992-1-1:2004 + NA:2008

Table 22: Hierarchy for load combinationsRoadway bridges: Norwegian handbook from the Norwegian road authorities Name: Bruporsjektering, Hndbok 185 fra Statens Vegvesen, nov. 2011

Eurocode for load combination (EC0), amendment A1 NS-EN 1990:2002/A1:2005+NA:2010

Eurocode for load combination (EC0): NS-EN 1990:2002 + NA:2008

Safety factorsFor all in-situ concrete structures the following partial safety factors shall be used when checking ULS load combinations:Table 23: Partial coefficients for ULS (Table 2.1N in NS-EN 1992-1-1 NA:2008)ULSALS

Reinforced concretec = 1,5c = 1,2

Reinforcement (mild and prestressed):s = 1,15s = 1,0

Partial safety factors for SLS combinations are given at the specific clauses of NA.2.4.2.4(2) in NS-EN 1992-1-1:2004/NA:2008 to be M = 1.0 for both concrete and reinforce, where nothing is specified in the standard.

Durability RequirementsThe structures are designed such that they meet the requirements on durability and sustainability as described in this document and in accordance with Norwegian tradition.

The wish for obtaining a service life of 100 years is met by abiding to the demands in this document. The service life of 100 years applies to all primary construction parts.

SoftwareA number of commercial and in-house software programs are used for calculating forces examining cross section stress distributions and for capacity checks.

Rambll, Bridge design system (BDS)Bridge design system (BDS) is an advanced Rambll in-house software package used for geometric and static analysis in bridge design. From this package the following programs are utilized: ECROSS PCROSS

ECROSS & PRCOSS - Cross Sectional AnalysisThe in- house software programs ECROSS and PCROSS are used for cross sectional analysis to determine the stress distributions.

ECROSSThe program ECROSS is used for elastic analysis on reinforced concrete cross-sections. The concrete and reinforcement are assumed to be linear elastic, i.e. Hook's law applies. Further the tensile strength of the concrete is taken as zero, and compression steel is taken into account.

The program can handle combined long-term and short-term load, taking into account the fact that for concrete the elastic modulus corresponding to sustained load has a lower value than the elastic modulus corresponding to instantaneous load.

PCROSSThe program PCROSS is used for plastic analysis on reinforced concrete cross-sections. The cross sections may be prestressed.

The program calculates the ultimate flexural capacity of a polygonal concrete cross-section under axial load combined with biaxial bending. The tensile strength of the concrete is taken as zero, and compression steel is taken into account.

For each user-defined value of the normal force and the angle for the declination of the neutral axis the program calculates the ultimate moments about the X and Y axis and the corresponding position of the normal force.

LUSAS finite element analysis softwareThe finite element analysis software, LUSAS, is used for structural analysis and structural design with use of Wood-Armer.

MaterialsConcreteThe concrete construction is designed for concrete strength class B45 in accordance with EC2 Table 3.1.

The following characteristics shall be used for concrete (see section 3.1 in EN 1992-1-1:2004)

Poissons ratioComment by LRP: Korttids E-modul??? = 0.23.1.3(4)

Mass density = 2548 kg/m3 (25kN/m3)

Thermal expansion10 x 10-6 / C3.1.3(5)

Long-term modulus of elasticityEc,eff = Ecm / (1+ (,t0))eq.7.20

Concrete classNvalid for all concrete grades and environmental classes

Table 41: Selected values from EN 1992-1-1:2004+NA:2008, table 3.1.Concrete gradefck (MPa)45

Max. compressive capacityfcm (MPa)53

Tension capacityfctm (MPa)3,8

Short term modulus of elasticityEcm (GPa)36.283

Furthermore the minimum requirements given as characteristic values listed in the table below shall be adopted for each individual structural part. Table 42: Minimum requirements for concrete grade, exposure and control classStrength(MPa)Control ClassNominal cover (mm)Max wk*(mm)

Areas exposed to water from traffic and river:Edge beams, wings, columns and abutments.45Extended6015 => 75mmwk < 0.3

other areas45Extended5015=> 65mmwk < 0.3

*wk is crack width for reinforced concrete for SLS QUASI-permanent (tilnrmet permanent)

Mild steelThe following characteristics shall be used for mild steel (See also Section 3.2 in EN 1992-1-1:2004).

Ribbed steel B500NC, Yield stress:fyk = 500 MPa Density = 7850kg/m3 (Section 3.2.7(3) in EN 1992-1-1:2004 )E-modulusEs = 200 GPa (Section 3.2.7(4) in EN 1992-1-1:2004)Comment by LRP: Brudvrdi samt trykstyrke angives

LoadsFor the purpose of computing internal forces and moments, the following shall, where applicable, be considered as per the relevant codes of practice given in section 2.1. The parameters in the designs are those specified in relevant codes with interpretations, modifications and additions as described in this section.

Permanent loadsDead load:Reinforced concrete: 25kN/m3

Asphalt : 25kN/m3

Fill masses (rock): 20kN/m3

Creep and shrinkage:

Temperature loadBridges are to be loaded with temperature loads in accordance with NS-EN 1991-1-5.

The geographical determined temperature values for Kobbervoll bridge fra figure NA.A1 and NA.A2 in the national annexs is:

Tmax=36C

Tmin=-40C

NS-EN 1991-1-5 p. 6.1.3.3 gives the values for evenly distributed temperature loads.

The initial temperature is set as 10C

Max temperature:Tmax = 36C(Figure NA.A1)Te,max = Tmax - 3C = 33C(Figure NA.6.1)TN,exp = Te,max - T0 = 33 C - 10C = 23C(6.2)Min temperature:Tmin = -40C(Figure NA.A2)Te,min = Tmin + 8C = -32C(Figure NA.6.1)TN,con = T0 - Te,min = 10 - (-32 C) = 42C(6.1)

NS-EN 1991-1-5 p. 6.1.4 gives the values for temperature differences over the crossection: (Table NA.6.1 and NA.6.2):

Specified variables: Superstructure Type 3, plate bridge. Asphalt 100mm

Overside warmer than underside:ksur = 0,7 TM,Heat = 0,7 x 15C = 10,5CUnderside warmer than overside:ksur = 1,0TM,Cool = 1,0 x -8C = -8C

The above loads are combined in accordance with p. 6.1.5. The combinations factors are and in accordance with NA.6.1.5.

The most unfavorable combination should be chosen.

Below is a clip-out from NS-EN 1991-1-5.

Traffic loadsTraffic loads on culvert top plate in accordance with NS-EN 1991-2 /8/, traffic on filling around culvert in accordance with HB185 /1/

Vertical traffic loadsRv 23 consists of two roadways of 3m with about 3m spacing between. The culvert is therefore only loaded by one roadway locally.

Loadmodel LM1:

NS-EN 1991-2 (4.3.2):

Where q1 have to be mutiplied with the factor 1. N.A.4.3.2: 1 = 0.6 => q1 = q1k*1 = 5.4kN/m2Contact surface is 0.4m x 0.4m with a distance of 1.2m along the roadway.For other lanes qn = qnk

Loadmodel, LM2 :section 4.3.3The axel load is 400kN => Two wheel loads of 200kN.Contact surface is 0.35m x 0.6m.

For the global analysis only LM1 is considered. LM2 is considered for local calculations.

For LM1:

Horizontal traffic loadsHorizontal loads is defined as accelerations-, break- and centrifugal loads.

Break load:(EN 1991-2 pkt. 4.4.1):

The tranverse break force:

Qtrk = 0,25 x Qlk = 0,25*406 = 101kN

Centrifugal force:For bridges with radius, r>1500m the centrifugal force equal nill (NS-EN 1991-2 pkt. 4.4.2):

Traffic loads on fillingFrom HB185 (2011) traffic loads on filling next to the bridge structure is defined as:

qQk = 25kN/m2

qk = 5kN/m2

K = 0,35

Other variable loadsSnow load:Snow loads are neglected

Wind load:Wind loads are neglected

Accidental loadsCollision force on rail: In accordance with EN 1991-2 and HB231 the culvert is to be designed for a collision force of 100kN (class A) acting over 0,5m.

Earth quake loads are not applicable

Load CombinationsThe limit states to be considered for the design are:

Ultimate limit state, ULSAccident limit state, ALSServiceability limit state, SLS (Quasi-permanent, frequent and characteristic combinations)

-factor for road bridges

ULSThe load combinations given below shall be used for determining the combined stresses in the ULS.

ALS

SLS The load combinations given below shall be used for determining the combined stresses in SLS.

Design ChecksThe structural elements are investigated through different design checks against the resulting forces and moments found from the load combinations given in section 6. All parts of the structure must be checked in the ultimate limit state (ULS) and serviceability state (SLS), using requirements mentioned in this section with partial coefficients on materials as given in section 2.2.

Minimum reinforcementFormulas for minimum reinforcement are given in the following. The formulas are taken from NS-EN 1992-1-1:2004/NA:2008.

Beams and plates

is the width

WallsVertical reinforcement:

Horizontal reinforcement:The largest of

ULSDesign check of section capacities against various actions should be carried out according to:

Concrete structuresMoment capacity:NS-EN 1992-1-1:2004+NA:2008 cl. 6.1 and NS-EN 1992-2:2005+NA:2010 cl. 6.1 (In-house Program PCROSS)

Shear capacity:NS-EN 1992-1-1:2004+NA:2008 cl. 6.2 and NS-EN 1992-2:2005+NA:2010 cl. 6.2

0.1 SLS - Concrete Structures

0.1.1 SLS Frequent CombinationsRefering to table NA.7.1.N in NS-EN 1992-1-1:2004, the crack width limits are 0.3*kc for reinforced concrete in the load combination Quasi-permanent. kc is assumed 1.

Design check of crack widths shall be carried out according to table 7.3N in NS-EN 1992-1-1:2004 where the tension in the steel is limited to: 7Centre distance of rebar : 150mm (preferred rebar spacing)=> Steel tension for .

Deflection under short term loads (traffic load only) should not exceed span/350 (section 5.1.2 in HB185)

References

/1/ Bruprosjektering, Hndbok 185 fra Statens Vegvesen, nov. 2011.

/2/ Geoteknikk i vegbyggning, Hndbok 016 fra Statens Vegvesen, mai. 2009.

/3/ Eurokode: Grunnlag for prosjektering av konstruksjoner", NS-EN 1990:2002+NA:2008

/4/ Endringsblad A1, Eurokode: Grunnlag for prosjektering av konstruksjoner", NS-EN 1990:2002/A1:2005+NA:2010

/5/ Eurokode 1: Laster p konstruksjoner, Del 1-1: Allmenne laster. Tetthet, egenvekt, nyttelaster i bygninger" NS-EN 1991-1-1_2002 + NA:2008

/6/ Eurokode 1: Laster p konstruksjoner, Del 1-6: Allmenne laster. Laster under utfrelse", NS-EN 1991-1-6:2005 + NA:2008

/7/ Eurokode 1: Laster p konstruksjoner, Del 1-7: Allmenne laster. Ulykkeslaster", NS-EN 1991-1-7:2006 + NA:2008

/8/ Eurokode 1: Laster p konstruksjoner, Del 2: Trafikklast p bruer", NS-EN 1991-2:2003 + NA:2010

/9/ Eurokode 2: Prosjektering av betongkonstruksjoner, Del 1-1: Allmenne regler og regler for bygninger", NS-EN 1992-1-1:2004 + NA:2008

/10/ Eurokode 2: Prosjektering av betongkonstruksjoner, Del 2: Bruer, NS-EN 1992-2:2005 + NA:2010

/11/ Rekkverk og vegens sideomrder, Hndbok 231 fra Statens Vegvesen, des. 2011.