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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/275183566 Comparison between Eurocodes and North American and Main International Codes for Design of Bolted... Article in Journal of Bridge Engineering · December 2013 DOI: 10.1061/(ASCE)BE.1943-5592.0000512 CITATION 1 READS 511 2 authors: Some of the authors of this publication are also working on these related projects: Bond behavior of FRCM composites applied to masonry and concrete substrates View project Seismic vulnerability of networks and lifelines View project Emanuele Maiorana OMBA Impianti & Engineering SpA 18 PUBLICATIONS 173 CITATIONS SEE PROFILE Carlo Pellegrino University of Padova 162 PUBLICATIONS 1,620 CITATIONS SEE PROFILE All content following this page was uploaded by Carlo Pellegrino on 27 May 2015. The user has requested enhancement of the downloaded file.
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Seediscussions,stats,andauthorprofilesforthispublicationat:https://www.researchgate.net/publication/275183566

ComparisonbetweenEurocodesandNorthAmericanandMainInternationalCodesforDesignofBolted...

ArticleinJournalofBridgeEngineering·December2013

DOI:10.1061/(ASCE)BE.1943-5592.0000512

CITATION

1

READS

511

2authors:

Someoftheauthorsofthispublicationarealsoworkingontheserelatedprojects:

BondbehaviorofFRCMcompositesappliedtomasonryandconcretesubstratesViewproject

SeismicvulnerabilityofnetworksandlifelinesViewproject

EmanueleMaiorana

OMBAImpianti&EngineeringSpA

18PUBLICATIONS173CITATIONS

SEEPROFILE

CarloPellegrino

UniversityofPadova

162PUBLICATIONS1,620CITATIONS

SEEPROFILE

AllcontentfollowingthispagewasuploadedbyCarloPellegrinoon27May2015.

Theuserhasrequestedenhancementofthedownloadedfile.

Comparison between Eurocodes and North Americanand Main International Codes for Design of Bolted

Connections in Steel BridgesEmanuele Maiorana1 and Carlo Pellegrino2

Abstract: Bolted joints are broadly used for the connections of structural elements in steel bridges. Rules for design of bolted connections arecurrently under discussion in Europe for improving Part 1-8 of Eurocode 3, which deals with the sizing and structural design of joints. In thiswork, awide comparison ismade between the Eurocode and the codes of Italy, theUnited States, Canada, Australia, and Japan. General descrip-tions of the design criteria for typical connections in bridges related to materials, geometrical limitations, slip, shear, and bearing resistance arepresented. An illustrative example to compare the various code provisions is given to quantitatively show their performance for a practical case.DOI: 10.1061/(ASCE)BE.1943-5592.0000512. © 2013 American Society of Civil Engineers.

CE Database subject headings: Standards and codes; Bolted connections; Steel bridges; Comparative studies; Europe; North America.

Author keywords: Code; Design; Steel; Bolt; Connection; Bridge.

Introduction

This paper focuses on design rules for bolted joints in metal bridgesconsidering European [European Committee for Standardization(CEN 2005a, b, c, 2006, 2008)], American [(AASHTO 2002; AISC2000) and Research Council for Structural Connections (RCSC2009)], Canadian [the Canadian Standards Association (CSA 2010)],Australian [Standards Australia (AS 2012)], and Japanese [JapanSociety ofCivilEngineers (JSCE2007)] practices for evaluating somesimilarities and differences among them. General descriptions of thedesign criteria for typical connections in bridges related to materials,geometrical limitations, slip, shear, and bearing resistance will bepresented. The work to aims to compare design procedures in codesdeveloped in various countries for bolted connections.

Other authors have recently compared building codes for theUnited States and Europe (Topkaya and Sahin 2011), focusing theirattention on strength limit states related to basic materials only,without considering steel connections. In Xiao and Ishikawa (2005),McCarthy et al. (2005), and Cruz et al. (2012), experimental andfinite-element analyses have been developed to improve contem-porary practice pertaining to bolted joints used with high-strengthsteel or weathering steel plates. Cruz et al. (2012) obtained slip factorsequal to 0.50 for blasted surfaces without any additional surfacetreatment whereas they obtained a characteristic value of 0.40 forblasted surfaces with a painted coating of zinc-ethyl-silicate. Slipfactors equal to or smaller than 0.30were obtained for blasted surfaces

with a painted coating of zinc-epoxy. Concerning the specimensmadewith S355 weathering steel, the value of the slip factor increased withthe duration of environmental exposure, from 0.502 to 0.560. Inspecimensmadewith S275 steel and S690 high-strength steel, similarvalues of the slip factor were obtained with equivalent surfacetreatment. Cruz et al. (2012) concluded that the slip factor is stronglyinfluenced by the surface treatment and onlyweakly influenced by thesteel grade. Therefore, it seems that the classification system of theEuropean standard (EN) 1090-2 (CEN 2008) remains valid for slip-resistant joints with high-strength steel.

European Code for Design of Bolted Connections inSteel Bridges

Eurocode 3 EN 1993-1-8 (CEN 2005b) integrates the general part1-1 (CEN 2005a) dealing with verification procedures and require-ments for bolted and welded connections. The different classes ofbolts, with diameters measured in 12, 14, 16, 18, 20, 22, 24, 27, and30 mm, are known as Classes 4.6, 5.6, 6.8, 8.8, and 10.9, re-spectively. For each class, the yield stress fyb and the ultimate stressfub are given. In construction of bridges, the last two classes (Classes8.8 and 10.9) are typically used. Only bolt assemblies of Classes 8.8and 10.9 may be used as preloaded bolts with controlled tightening.The reference standard for the bolts in Europe is EN 14399-1 (CEN2005c).

Bolts with controlled tightening are very sensitive to differencesin manufacturing and lubrication. European regulations on boltswith controlled tightening have the aim to ensure that, with a giventorque, the required preload is obtained with a good reliability andsufficient safety margins to avoid excessive tightening of the screwand consequent plastic deformation. For this reason, a test method toverify the suitability of the components in controlled tightening isincluded in the Eurocode.

Design Procedure

The design procedures proposed in the Eurocode are consistent withthe Limit State Method (CEN 2005a, b, c, 2006, 2008).

1Ph.D. Research Assistant, Dept. of Civil, Environmental and Archi-tectural Engineering, Univ. of Padova, 35131 Padova, Italy.

2Assistant Professor, Dept. of Civil, Environmental and ArchitecturalEngineering, Univ. of Padova, 35131 Padova, Italy (corresponding author).E-mail: [email protected]

Note. This manuscript was submitted on August 29, 2012; approvedon May 20, 2013; published online on May 22, 2013. Discussion periodopen until May 1, 2014; separate discussions must be submitted forindividual papers. This paper is part of the Journal of Bridge Engineer-ing, Vol. 18, No. 12, December 1, 2013. ©ASCE, ISSN 1084-0702/2013/12-1298–1308/$25.00.

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The adopted safety factors are given in EN 1993-1-1 (CEN2005a) and EN 1993-2 (CEN 2006), respectively, for general rulesfor constructing buildings and bridges. The main safety factors aresummarized as• gM0 5 1:05, strength of gross cross-sections;• gM2 5 1:25, strength of net sections at the position of bolts;• gM2 5 1:25, strength of the bolts;• gM2 5 1:25, strength of the contact plates;• gM3 5 1:25, sliding resistance at the ultimate limit state; and• gM7 5 1:10, preload of high resistance bolts.

Geometric Limitations

In regard to the coupling of contact surfaces, the maximum differ-ence in height between adjacent surfaces cannot exceed 2 mm fornon-preloaded bolts and 1 mm for preloaded bolts. Alternatively,plates have to be used to ensure that the difference does not exceedthe specified limits.

Where bolts transmitting load in shear and bearing pass throughpacking plates of total thickness tp greater than one-third of thenominal diameter d, the shear resistance Fv,Rd of the design shouldbe multiplied by a reduction factor bp given by EN 1993-1-8 (CEN2005b)

bp ¼ 9d8d þ 3tp

# 1 (1)

This is a typical situation in connections of a beam with the nextbeam, each having a different thickness in bridge girders. Platethickness shall be chosen to limit the number of packing plates toa maximum of three (CEN 2008) (Fig. 1).

Furthermore, the length of the threaded portion of a fit bolt in-cluded in the bearing length should not exceed one-third of thethickness of the plate.

According to Eurocode 3 part 1-8 (CEN 2005b), minimum andmaximum spacing and end and edge distances for bolts are given inTable 1. The meaning of symbols is indicated in the following[further details can be found in Eurocode 3 (CEN 2005b)]:• e1 5 edge distance for bolts (measured in the direction of the load);• e2 5 edge distance for bolts (measured perpendicularly to the

load);• p1 5 bolt spacing (measured in the direction of the load);• p2 5 bolt spacing (measured perpendicularly to the load);• p1,0 5 bolt spacing for outer rows of staggered holes (measured

in the direction of the load);• p1,i 5 bolt spacing for inner rows of staggered holes (measured

in the direction of the load); and• L 5 diagonal bolt spacing for staggered holes.

The maximum values related to distance of bolts and edge dis-tances are included to avoid local instability problems for com-pressed elements and corrosion in aggressive environments.

Eurocode 3 part 1-8 (CEN 2005b) provides design equations forblock tearing, which consists of shearing failure at the row of bolts

Fig. 1. Typical joint in a bridge girder; arrows indicate the packing plates

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along the shear face of the hole group, accompanied by tensilerupture along the line of bolt holes on the tension face of the boltgroup.

For a symmetric bolt group subject to concentric loading, theblock tearing resistance for the design is given by

Veff,1,Rd ¼ fu Ant

gM2þ�1=

ffiffiffi3

p �fy Anv

gM0(2)

For a bolt group subject to eccentric loading, the block-shear tearingresistance for the design is given by

Veff,2,Rd ¼ 0:5 fu Ant

gM2þ�1=

ffiffiffi3

p �fy Anv

gM0(3)

where Ant 5 net area subject to tension; and Anv 5 net area subjectto shear.

Structural Design

Eurocode 3 part 1-8 (CEN 2005b) classifies bolted connections intwo categories: shear and tension connections. Each of them isdivided into subcategories.

The categories defined for shear connections are the following:• Category A: Bearing type. In this category, no preloading and

special provisions for contact surfaces are required. The ultimateshear load of the design should not exceed the design shearresistance nor the design bearing resistance.

• Category B: Slip-resistant at the serviceability limit state. In thiscategory, preloaded bolts should be used. Slip should not occur atthe serviceability limit state. The design’s serviceability shearload should not exceed the design’s slip resistance. The design’sultimate shear load should not exceed the shear resistance nor thebearing resistance of the design.

• Category C: Slip-resistant at ultimate limit state. In this category,preloaded bolts in accordance should be used. Slip should notoccur at the ultimate limit state. The design’s ultimate shear loadshould not exceed the slip resistance nor the bearing resistance ofthe design. In addition, for a connection in tension, the design’splastic resistance of the net cross-section at bolt holes should bechecked at the ultimate limit state.The categories defined for tension connections are the following:

• Category D: non-preloaded. This category should not be usedwhere the connections are frequently subjected to variations oftensile loading.

• Category E: preloaded. In this category, preloaded bolts withcontrolled tightening should be used.

Slip ResistanceIn bridges, friction often governs the design of the connection be-tween the main girder beams. Friction is mainly a function of thepreload force, the diameter and class of the bolt, and the coefficientof friction.

The design strength should be calculated using Eq. (4) (see CEN2005b), according to which Bolt Classes 8.8 and 10.9 have to beused

Fs,Rd ¼ ks nmFp,C

gM3(4)

whereks 5 specific hole geometry, with ks 5 1:00 for bolts in normalholes; ks 5 0:85 for bolts in either oversized holes or short slottedholes with the axis of the slot perpendicular to the direction of loadtransfer; ks 5 0:70 for bolts in long slotted holes with the axis of theslot perpendicular to the direction of load transfer; ks 5 0:76 for boltsin short slotted holes with the axis of the slot parallel to the directionof load transfer; ks 5 0:63 for bolts in long slotted holes with theaxis of the slot parallel to the direction of load transfer; n5 numberof friction surfaces; and m 5 slip factor, which also depends onthe treatment of the surfaces, as mA 5 0:5 for mechanically or grit-blasted surfaces free from rust and pitting, or with aluminum- andzinc-based painting; mA 5 0:4 for grit-blasted surfaces coated withzinc silicate and alkali with layer of 50e80mm thickness; mC 5 0:3for surfaces cleaned by brushing or flame and free from rust; andmD 5 0:2 for untreated surfaces.

The preload force is calculated by means of

Fp,c ¼ 0. 7 fu,b Ares (5)

If a slip-resistant connection is subjected to an applied tensile forcein addition to the shear force, the design’s slip resistance per boltshould be properly reduced (see CEN 2005b).

Shear ResistanceThe shear force at the ultimate limit state Fv,Ed, resulting from theanalysis of the connection, should be less than the ultimate shearresistance Fv,Rd

Fv,Ed #Fv,Rd ¼ av fu,b AgM2

(6)

where, if the shear plane passes through the threaded portion,av 5 0:6 for Classes 4.6, 5.6, and 8.8 and av 5 0:5 for Classes 4.8,5.8, 6.8, and 10.9; and if the shear plane passes through the non-threaded part of the bolt, av 5 0:6.

For combined action of shear and tension on the bolt, Eq. (7) hasto be satisfied

Fv,Ed

Fv,Rdþ Ft,Ed

1:4Ft,Rd# 1:0 (7)

Bearing ResistanceThe design’s bearing resistance is calculated by the followingrelationship:

Fb,Rd ¼ k1 ab fu dtgM2

(8)

whereab assumes the smallest value among the quantities ad, fu,b=fu,and 1.

Table 1. Minimum and Maximum Spacing and End and Edge Distancesfor Bolts According to Eurocode

Distance Note

1:5d0 # e1 # 4t1 40mm According to EN 1993-2a (1:2d0 isassumed in EN 1993-1-1b withreduced bearing resistance)

1:5d0 # e2 # 4t1 40mm

2:5d0 # p1 #minf14t; 200mmg According to EN 1993-2a (2:2d0 isassumed in EN 1993-1-1b withreduced bearing resistance)

2:5d0 # p1,0 #minf14t; 200mmg2:5d0 # p1,i #minf28t; 400mmg2:5d0 # p2 #minf14t; 200mmg1:2d0 # p2 #minf14t; 200mmg Staggered rows2:4d0 #LaCEN (2006).bCEN (2005a).

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Values ad and k1 depend on the geometry of the connection(diameter of the holes, distance between bolts, and distance betweenbolts and edges). For noncircular holes, the resistance is reduced bymeans of a factor equal to 0.8; for slotted holes perpendicular to theforce, the resistance is reduced by means of a factor equal to 0.6.

United States Code

Materials

Diameters and characteristics of bolts in American code (seeAASHTO 2002) are different from those in the Eurocode. Thestandard (AISC 2010) in the United States for the design of steelallows the types of structural steel included in the following ASTM(2012) specifications (AISC 2000):• ASTM A36/A36M;• A709/A709M;• A529/A529M;• A913/A913M;• 572/A572M;• A992/A992M;• A1043/A1043M; and• A588/A588M.

The most commonly used structural steels are• A36 ( fy 5 248 N=mm2, fu 5 400 N=mm2), and• A572 Gr50 or A992 ( fy 5 345 N=mm2, fu 5 448 N=mm2).

Screws, nuts, and washers are described in the 2010 AISCstandard (AISC 2010) having specific characteristics according toASTM (2012) specifications. The diameters are 15.88, 19.05, 22.23,28.58, 31.75, 34.93, and 38.10 mm (the smallest diameters ap-proximately correspond to the European 16, 20, 22, 27, and 30mm).ASTM Classes A325M ( fy 5 634 N=mm2 and fu 5 830 N=mm2)and ASTM A490M ( fy 5 940 N=mm2 and fu 5 1040 N=mm2) forbolts are similar to European Classes 8.8 and 10.9, respectively.

Under American code, manufacturer’s certification shall besufficient proof of compliance with the code standard.

The use of high-strength bolts according to 360-10 (AISC 2010)is described in the document Specification for structural joins usinghigh-strength bolts, which contains the requirements of the RCSC(2009). High-strength bolts are classified in this document accordingto the strength of the material as• Group A: ASTM A325, A325M, F1852, A354 Grade BC, and

A449; and• Group B: ASTM A490, A490M, F2280, and A354 Grade BD.

Geometric Limitations

The distinction between cut edge and oxygen-cut edge is introducedin AISC (2000), whereas in Europe only the second type is con-sidered (see CEN 2008).

For a long row of slotted holes, it is necessary to install contin-uous bars completely covering the slotted holes.

The distance between the centers of the holes must not be lessthan 3d0, where d0 is the diameter of the bolt. The distance from thecenter of a hole perpendicularly to the edge of the connecting platemust not be less than 1:4d.

The maximum distance between the hole and the edge is thesmallest between 12tmin (tmin is the minimum thickness of theconnecting plates) and 150mm, and the maximum distance betweenthe bolts is the smallest between 24tmin and 305mm.

All high-strength bolts that must be preloaded shall be tightenedwith a specific preload force5 0:73 the tensile strength of the bolt.

Bolts of Group A or B can be generally used according to theprovisions listed in Table 2.

Structural Design

Slip ResistanceThe design strength must be calculated using the following relation(see AASHTO 2002):

fRs ¼ fFs Ab Nb Ns (9)

wherefFs 5fTb m5 design friction resistance per unit area of thebolt depending on the type of hole, in which f5 1:00 for standardholes; f5 0:85 for oversized holes; f5 0:70 for slotted holesperpendicularly to the force direction; andf5 0:60 for slotted holesin the direction of the force. The value m assumes the followingvalues: mA 5 0:33;mB 5 0:50;mC 5 0:40; Ab 5 nominal area of thebolt;Nb 5 number of bolts;Ns 5 number of surfaces in contact; andTb 5 preload force.

Shear ResistanceThe design resistance fRn in [kN] for high-strength bolts subjectedto applied axial tension or shear is given by (see AASHTO 2002)

fRn ¼ fFn Ab (10)

wherefFn 5 design strength per unit of bolt area as given by norm(AASHTO 2002) for appropriate kind of load; Rn 5 nominal shearresistance of the bolt; and Ab 5 nominal area of the bolt.

For combined action of shear and tension on the bolt, Eq. (11)has to be satisfied �

TuðfRnÞt

�2þ�

Vu

ðfRnÞv

�2# 1 (11)

whereTu 5 tension on the bolt;Vu 5 shear acting on the bolt; ðfRnÞt5 design tension strength; and ðfRnÞv 5 design tension strength.

Bearing ResistanceThe design resistance for bearing failure fR is a function of edgedistance and geometry of the holes (see AASHTO 2002).

For standardholes, if thedistanceL from the edge, in the directionof force, is not less than 1:5d and the distance between the centers ofthe bolts of not less than 3d, then

fR ¼ 1:6 dt Fu (12)

For slotted holes aligned perpendicularly to the direction of the force

fR ¼ 1:4 dt Fu (13)

Table 2. Nominal Resistance of the Bolt or Threaded Parts

Group Characteristics Traction (N=mm2) Shear (N=mm2)

Bolts A307 310 188A Bolts A325 with threaded

part in the shear plane620 372

Bolts A325With threadedpart out of the shear plane

620 457

B Bolts B490 with threadedpart in the shear plane

780 457

Bolts B490 with threadedpart out of the shear plane

780 597

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If L is less than 1:5d, then

fR ¼ 0:68Lt Fu# 2:0 dt Fu (14)

where Fu 5minimum tensile strength in the joint; and f5 0:75 forjoints with standard holes, regardless of the direction of the load, orfor slotted holes in the direction of the force.

If the deformation of the hole under service load is explicitlyconsidered in the project, then

Rn ¼ 1:2 lct Fu# 2:4 dt Fu (15)

If the deformation of the hole under service load is not explicitlyconsidered in the project, then

Rn ¼ 1:5 lct Fu# 3:0 dt Fu (16)

For slotted holes aligned perpendicularly to the direction of theforce, then

Rn ¼ 1:0 lct Fu# 2:0 dt Fu (17)

whereRn 5 nominal resistance; Fu 5 tensile resistance; d5 nominalbolt diameter; lc 5 distance between the edge of the hole and theadjacent hole or the edge in thedirection of the force; and t5 thicknessof the connected plates.

For combined tension and shear in bearing-type connections,bolts shall be proportioned so that the shear stress does not exceed

Fvc #

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiF2v 2 ð0:6 ftÞ2

q(18)

whereFv 5 shear strength of the fastener;fF5measurement givenby the norm from AASHTO (2002); and ft 5 tensile stress from theapplied load.

Canadian Code

Geometric Limitations

The minimum distance between the bolts required by CanadianstandardS16-09 (CSA 2010) is 2:7d and theminimum edge distanceis the diameter of the bolt. Themaximum distance to avoid problemsof instability is theminimumbetween 12 times of the thickness of theplate and 150 mm, as specified by AASHTO (2002). The nominaldiameter of the hole must be greater than 2 mm plus the diameter ofthe bolt.

Structural Design

Slip ResistanceThe slip resistance is given by

Vs ¼ 0:53 c1 ks nmAb Fu (19)

where c1 5 correction coefficient taking into account the initialstresses (see Table 3); ks 5 slip coefficient depending on the type ofsurface (see Table 3); n5 number of bolts; m5 number of contactplanes; Ab 5 effective area of the bolt; and Fu 5 tensile resistance ofthe plate.

If long slotted holes are used, the preceding value must be mul-tiplied by 0.75.

Shear ResistanceThe overall shear strength of the joint is calculated as follows:

Vs ¼ 0:6fb nmAb Fu (20)

wheren5 number of bolts;m5 number of shear planes;fb5 safetycoefficient equal to 0.80; and Ab 5 nominal area.

In the case where the threaded part of the screw intersects theshear planes, the shear resistance of the bolts must be assumed as0:70Vs.

Shear resistance should be compared with bearing resistance,assuming the minimum of two values as overall resistance of theconnection.

For combined action of shear and tension on the bolt, Eq. (21) hasto be satisfied

�Vs

Vr

�2þ�TsTr

�2# 1 (21)

whereTu 5 tension on the bolt;Vu 5 shear acting on the bolt; ðfRnÞt5 design tension strength; and ðfRnÞv 5 design tension strength.

Bearing ResistanceThe bearing resistance is

Br ¼ 3fbr tdn Fu (22)

where fbr 5 0:67; d 5 diameter of the bolt; t 5 thickness of theelement; n5 number of the bolts; andFu 5 ultimate resistance of theplate.

Australian Code

Geometric Limitations

The Standards Australia (AS) specification AS 4100 (AS 2012)refers to AS 1250 (AS 1981) and considers as structural steels thosesteels meeting the requirements specified in the U.S. ASTM (2012;AASHTO 2002) code standards. As for the bolts, nuts, and washers,they shall comply with AS 1110 (AS 1984), AS 1111 (AS 1980a),and AS 1112 (AS 1980b).

Structural Design

Slip ResistanceThe acting shear force has to be less than the resisting force

Table 3. Coefficient ks2c1

Contact surface c1

Class Description ks

A325 andA325M

A490 andA490M

F958 andF1852

A Surfaces treated by sandingor grit and painted withproducts of this class

0.33 0.82 0.78 0.72

B Surfaces cleaned withsandblasting and paintedwith products of this class

0.50 0.90 0.85 0.78

C Hot galvanized surfacesand cleaned with brushing

0.40 0.90 0.85 0.78

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Vsf ¼ mVpsf #fVsf (23)

with

Vsf ¼ mnei Nti kn (24)

where f 5 safety coefficient equal to 0.70; m 5 slip coefficient(see Table 4); nei 5 number of slip surfaces; Nti 5 preload forcedepending on the ultimate strength of the bolt; and kn 5 givennumber dependent upon the shape of the hole, inwhich kn 5 1:00 forstandard holes; kn 5 0:85 for slotted and oversized holes; andkn 5 0:70 for long slotted holes.

Shear ResistanceIt is required that

Vpf #fVf (25)

where

Vf ¼ 0:62 fuf krðnn Ac þ nx AoÞ (26)

and where Vpf 5 acting shear force; Vf 5 resisting shear force; fuf

5 ultimate strength of the bolt; kr 5 correction factor (see Table 5);nn 5 number of shear planes in the threaded part; Ac 5 resisting areaof the bolt; nx 5 number of shear planes out of the threaded part;Ao 5 nominal area of the bolt; and f5 0:8.

For combined action of shear and tension on the bolt, Eq. (27)has to be satisfied

"V pf

fVf

#2þ"N ptf

fNtf

#2# 1 (27)

where f5 0:9; Vf 5 design tension strength; and Ntf 5 designtension strength.

Bearing ResistanceThe following relationship shall be satisfied:

Vpb #fVb (28)

Vb ¼ min

�3:2 df tp fupae tp fup

�(29)

wheref5 0:9; df 5 diameter of the bolt; fup5 tensile strength of theplate; tp 5 thickness of the plate; and ae 5 minimum distance fromthe edge of the hole to the edge of the plate.

Japanese Code

Materials

Structural steels used for metal constructions in the JSCE code steelsare regulated by G3136 (JSCE 2007) according to the requirementsof the Japanese Industrial Standards Committee (JISC 2012, 2013).They are SN400 with fy 5 235 N=mm2 and SN490 withfy 5 325 N=mm2.

The screws, nuts, and washers used in bolted connections shallcomply with the provisions of JIS B1181 (JISC 2004). Classes andcharacteristics of normal bolts are• 4.6 ( fy 5 240 N=mm2; fu 5 400 N=mm2);• 8.8 ( fy 5 660 N=mm2; fu 5 830 N=mm2); and• 10.9 ( fy 5 940 N=mm2; fu 5 1040 N=mm2).

The high-strength bolted joints are divided into three categoriesaccording to their load transfer mechanism: friction, shear, andtraction.

The literature from the JSCE (2007) refers to the requirements ofJIS B1186 (JISC 2013), regarding high-strength bolts of types F8T(M16-M20-M22-M24with fy 5 640 N=mm2),F10T, andS10T (M16-M20-M22-M24 with fy 5 900 N=mm2).

Superhigh–strength bolts of the F15T class have a different shapecompared to ordinary bolts, with a resistance equal to 1.5 times thatof conventional high-strength bolts F10T and excellent resistanceto brittle fracture. Because of their specific microstructural char-acteristics, a specific method for the evaluation of their mechanicalproperties is needed.

Geometric Limitations

The size of the holes for bolts is determined according to load-transfer mechanism, type of connection, and workability.

In traction and friction connections, the diameter d of the hole isobtained by adding 2.5 mm to the nominal diameter of the bolt d0

d ¼ d0 þ 2:5mm

In shear connections, the diameter of the hole is obtained by adding1.5 mm to the nominal diameter of the bolt

d ¼ d0 þ 1:5mm

The minimum distance between the bolts must comply with thelimits given by the Honsh�u-Shikoku Bridge Authority (HSBA1995). This minimum distance is typically 3d0 whereas the maxi-mum distance must not exceed the minimum between 24t and300mm. The maximum and minimum distances from the edges areprovided by the JSCE (2007) and the Japan RoadAssociation (JRA)(JRA 2002).

Structural Design

The standard from the JSCE (2007) divides bolted connections intothree basic categories: friction, shear, and tensile connections.

Table 4. Slip Coefficient m

Surface type Surface treatment m

Uncoated As-rolled 0.35Hot-rolled and cleaned 0.48Sandblasted 0.53

Painted Zinc and chromium oxide 0.11Inorganic zinc silicate 0.50

Galvanized Zinc 0.18Sandblasted with lightly abrasive products 0.3–0.4

Table 5. Coefficient kr

lj ðmmÞ kr

lj # 300 1.00300# lj # 1300 1:0752lj=4000lj # 1300 0.75

Note: lj 5 length of the joint.

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In the case of frictional behavior, the following equation shallbe met:

gagbgiPs

Pu# 1:0 (30)

where ga 5 numerical value dependent upon the structural analysis;gb 5 numerical value dependent upon the structural elements;gi 5 numerical value dependent upon the structural importance;Ps5 force acting in the single rowof bolts;Pu5 slip resistance in theith row (Pu 5 nmPa=gm); n 5 number of bolts; Pa 5mN 5 char-acteristic value of the resistance to friction of the bolt per unit ofsurface; N5a fy Abe; m 5 slip factor depending on the type ofsurface (varying from 0.25 to 0.55);N 5 design axial force to whichthe bolt is subjected; fy 5 yield stress of the bolt; Abe 5 effectivecross-sectional area of the bolt; gm 5 safety factor for the material;and a5 0:75 for F8T bolts and 0.85 for F10T bolts.

For frictional behavior, design of joints has to satisfy the fol-lowing relations:

gagbgiPs

Pu# 1:0 (31)

wherePs 5 force applied to the bolts in the ith row; Pu 5 nm Pa=gm5 frictional resistance of the bolts in the ith row; ni 5 number ofbolts in the ith row; and Pa 5masy Abe 5 characteristic value offriction strength for unit area.

For combined action of shear and tension on the bolt, Eq. (32)has to be satisfied

ðgagbgiÞ2"

Pi

Pu

2

þVs

Vu

2## 1:0 (32)

where Vs 5 acting shear force and Vu 5 resistance to friction.For design against bearing failure, Eq. (31) has to be satisfied, in

which Pu 5 nmPa=gm and Pa 5 minimum value between shearresistance Psa 5 taAs and bearing resistance Pba 5sbAb, and whereta 5 characteristic value of shear strength of the bolt per unit area;sb 5 characteristic value of bearing strength of the bolt per unit area;As 5 cross-sectional area of the bolt; and Ab 5 effective area of thebolt.

In principle, the connections subjected to tensile forces are notallowed in presence of fatigue (typically in bridges).

Discussion

Regarding the geometric arrangement of the bolts, geometric limi-tations are mainly introduced for solving practical problems (posi-tioning and application of torque). Furthermore, the upper limitsensure that the bolts are not too far apart, allowing for any possibleinstability of the plates. Instead, the lower limits are mainly intro-duced to avoid stress concentrations.

Comparing the geometrical requirements provided by the variouscodes, Eurocode 3 (CEN 2005a, b, c, 2006, 2008) provides maxi-mum and minimum distances typically smaller than the other codes,regarding both distance from the edges and distance between bolts.Furthermore, according to Eurocode 3 (CEN 2005a, b, c, 2006,2008), maximum values for spacing, edge, and end distances areunlimited, except for compression members to avoid local bucklingand to prevent corrosion in exposed members and exposed tensionmembers to prevent corrosion, whereas the practice in the UnitedStates distinguishes between steel subjected to corrosion and weath-ering steel only for limitations on the maximum values of spacing.Japanese code distinguishes normally cut edges and oxygen-cut edgesonly for the minimum distances from the edges.

For example, considering a typical plate thickness t5 10 mmand bolts with diameter d5 24 mm, maximum and minimum dis-tances in the various standards are given in Figs. 2 and 3.

Regarding the slip resistance, Eurocode, American, andAustralianstandards adopt various coefficients depending on the type of hole [ksin Eurocode 3 (CEN 2005a, b, c, 2006, 2008), f in AISC 360-10(AISC 2010), and kn in AS 4100 (AS 2012)] whereas the Japanesecode does not introduce such a coefficient. However, the coefficientsthat depend upon the typeof hole, and the slip factors to beused, are alldifferent among the various codes that break them down this way.

As a general observation, Eurocode expressions include safetyfactors g allowing the user to obtain design values starting fromcharacteristic values, whereas the American approach, to which theCanadian and Australian approaches are similar, does not alwaysadopt safety coefficients that are immediately detectable.

In all the standards, shear strength is typically considered as givenby the product of the nominal resistance of each bolt and the resistingarea of the bolt, but each standard proposes different coefficients.

The Japanese procedure uses a resistance tu already includingreduction coefficients according to the type of the bolt, whereasEurocode and American procedures adopt specific coefficients infunction of the bolt. American code proposes a coefficient f5 0:75and Eurocode adopts the coefficientsan 5 0:5 and 0:6 depending onthe type of bolt and the position of threaded part with respect to shear

Fig. 2. Comparison of minimum and maximum distances between hole and plate edge (mm)

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surface. Australian standards also take into account the position ofthe threaded part with respect to shear surfaces and use significantlydifferent coefficients, one of which, kr, is a function of the length ofthe joint. Eurocode also takes into account the effect of the lengthof the connection by means of a specific coefficient similar to theAustralian one.

Regarding the combination of shear and tensile forces, Japaneseand American codes provide similar elliptical expressions whereasEurocode provides a linear relationship with explicit safety coef-ficient gM2 5 1:25.

Japanese, Canadian, and Eurocode standards deal with bearingfailure in a similar way from a conceptual point of view. Theyconsider the ultimate stress of the platemultiplied by the thickness ofthe plate and the diameter of the bolt. The American standard has thepeculiarity of taking into account that the deformation of the hole isconsidered in the project. Eurocode takes into account the influenceof the distance between holes and between the hole and the edges onbearing strength. The Australian procedure considers bearing re-sistance to correspond to the final hole of the connection, close to theedge of the plate. Eurocode 3 considers the value of 2.5 as maximumbearing factor k1. AISC 360-10 (AISC 2010) proposes 2.4 or 3.0 asmaximum limit for that factor.

These procedures are better compared by means of the followingnumerical example:

It is assumed steel S355 ( fyk 5 355N=mm2 and fuk 5 490N=mm2)for the plates and a thickness t5 40mm. The bolts are M24 Class10.9 [according to EN 14399-1 (CEN 2005c)], A490M [accordingto ASTM (2012)], or F10T [according to Japanese IndustrialStandard 1186 (JISC 2013)]. Figs. 4–7 show the results in terms ofslip, shear, bearing, and combined shear and tension resistances,respectively.

In the following, some issues related to the comparisons amongthe codes considered in this work are described regarding slip, shear,and bearing resistance and combined shear and tension strength.

Regarding the proposed numerical example, Fig. 4 shows thatEurocode is more conservative in predicting a slip-resisting force of∼10% less than that predicted by AISC (2000, 2010) and CSA(2010). For the same slip coefficient, this difference mainly derivesfrom the adopted values of the safety factor related to bolt ultimateresistance and the coefficient, taking into account the various kinds ofholes (standard, oversized, slotted) because all the basic formulationsare derived from the Coulomb friction law. Furthermore, Eurocodeand Australian code distinguish the basic safety factor from the co-efficient depending on the hole size and shape whereas US code givea unique f-coefficient depending on the characteristics of the hole.The safety factor can be eventually reduced if the level of knowledgeof bolt failure mechanisms increases and the quality control processduring bolt production is improved.

Fig. 3. Comparison of minimum and maximum distance between the holes (mm)

Fig. 4. Slip-resistance comparison (kN)

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Fig. 5. Shear-resistance comparison (kN)

Fig. 6. Bearing-resistance comparison (kN)

Fig. 7. Combined shear- and tension-resistance comparison

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This result can be further traduced in adopting fewer bolts in steelbridges where slip resistance governs the ultimate failure of theconnection and AISC (2000, 2010) or CSA (2010) are used. JSCE(2007) gives intermediate results among AISC (2000, 2010), CSA(2010), and Eurocode (CEN 2005a, b, c, 2006, 2008), whereas AS4100 (AS 2012) seems even more conservative than Eurocode.

The comparison related to shear resistance shows fewer differ-ences than the previous case but Eurocode still seems to give moreconservative results than the others (see Fig. 5). Instead, AISC codeis that giving the highest values of the shear strength. The formu-lations are very similar and the differences are again resulting fromthe various factors adopted, e.g., Eurocode proposed both a reduc-tion factor related to the class of the bolt and a basic safety coefficient(equal for all the classes) whereas U.S. code proposes only onef-coefficient.

For bearing resistance (see Fig. 6), the possibility of consideringthread deformation can show significantly higher resistance in AISC(2000, 2010) predictions than the others. Furthermore, there aresignificant differences in the reduction coefficients taking into ac-count the geometry of the connection (diameter and shape of theholes, distance between bolts, distance between bolts and edges,etc.). The various formulations of these coefficients significantlyinfluence the final bearing strength and illuminate the discrepanciesfound between the predictions of the bearing resistance provided bythe various codes.

The comparison for connections in which there is an acting com-bination of shear and tension (see Fig. 7) shows that the Eurocodeseems, once again, the most conservative.While in the previous casesthe value of predicted strength is given for comparing the perform-ances of the codes, in this last case the comparison is developed interms of combination of ratios between acting and resisting shear andtensile forces in the bolts (as proposedbyall the codes). Consequently,the final result should be , 1. The comparison shown in Fig. 7 isconsistent with those of Figs. 4–6 showing even more percentagedifferences between the results provided by the codes. Eurocode is themost conservative when a combination of shear and tension actsbecause, for the same material strength, the sum of the ratios betweenacting and resisting shear and tensile forces is closer to 1 for Eurocodethan for the other codes. On the other hand,U.S. code shows the resultfarthest from 1 in terms of combination of ratios between acting andresisting shear and tensile forces. As stated previously in this paper,this result is also influenced by the different way of combining theratios between shear and tensile forces (linear for the Eurocode andelliptical for the others).

Hence, as general comment, the graphs of Figs. 4–7 showed thatEurocode on steel constructions and connections seem to be typi-cally the most conservative. This could be explained by observingthat contemporary Eurocode is actually a synthesis of design andconstruction practices from various European countries possessingdifferent design and building traditions and experiences. Probablythe homogenization process among the various design rules ofEuropean countries led to more detailed and conservative for-mulations than in those countries in whichmore consolidated designformulations are adopted.

Conclusions

This paper focuses on design rules for bolted joints in metal bridgesconsideringEuropean,American, Canadian,Australian, and Japanesepractices. General descriptions of the design criteria for typical con-nections in bridges related to materials, geometrical limitations, slip,shear, and bearing resistance are presented. The work was conductedto compare design procedures in codes developed in various countriesas pertains to bolted connections.

Upon comparing the requirements provided by the various codes,the following differences and similarities were noted:• Regarding general safety factors, European expressions include

safety factorsg allowing designvalues to beobtained starting fromcharacteristic values. The American approach, to which the Ca-nadian and theAustralian are similar, does not clearly highlight thetransition between characteristic and design values; instead, itsimplifies, as much as possible, their expressions for practitionersusing f-coefficients to ensure reasonable safety margins.

• Regarding both the distance from the edges and the distancebetween bolts, Eurocode 3 provides maximum and minimumdistances that are typically smaller than the other codes.

• Regarding slip resistance, Eurocode, American, and Australianstandards adopt various coefficients depending on the type ofhole, whereas the Japanese code does not introduce such a co-efficient; however, for the coefficients that did depend on the typeof hole, the slip factors were calculated differently for each of thevarious codes.

• Regarding thecombinationof shear and tensile forces, theAmerican,Canadian, Australian, and Japanese codes provide similar ellipticalexpressions, whereas Eurocode provides a linear relationship.

• Regarding bearing resistance, the American standard has thepeculiarity of taking into account the deformation of the hole forthe given project.A numerical example to compare the various code provisions is

presented to quantitatively show their performance for a practicalcase. Eurocode seemed to be the most conservative for the typicalcase studied in terms of shear, bearing, and combined shear andtension resistance.

Acknowledgments

The authors acknowledge Chiara Magnani for her contribution de-veloped during her B.Sc. thesis.

References

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