ce 671 lect 4

Rivets, HS-bolts, and Rivets, HS-bolts, and Bolting SpecificationsBolting Specifications

CE671 – Lecture 4CE671 – Lecture 4

RivetsRivets

One of the oldest forms of fastener in One of the oldest forms of fastener in structural jointsstructural jointsCommon up until 1960’sCommon up until 1960’s– Used in buildings and bridgesUsed in buildings and bridges– Used in wrought iron and steelUsed in wrought iron and steel

Replaced by HS bolts and weldingReplaced by HS bolts and welding– Required 4-5 skilled laborersRequired 4-5 skilled laborers

FiremanFiremanToss manToss manCatcherCatcherRiveter (2)Riveter (2)

DiscussionDiscussion

RivetsRivets

A307 BoltsA307 Bolts

A325 HS-BoltsA325 HS-Bolts


Many Types of RivetsMany Types of Rivets

Rivet InstallationRivet Installation

Installed though multiple platesInstalled though multiple platesGenerally installed as “hot” rivetsGenerally installed as “hot” rivets– About 1,800 FAbout 1,800 F

Components drawn together with clamps or Components drawn together with clamps or boltsboltsRivet inserted into hole and the “driven”Rivet inserted into hole and the “driven”– Pressed or hammeredPressed or hammered

Head is formed by driving processHead is formed by driving processAs the rivet cools, it shrinks thereby introducing As the rivet cools, it shrinks thereby introducing precompression into the jointprecompression into the joint

Rivet CrewRivet Crew

HOT

Rivet InstallationRivet Installation

When rivet is driven it expands laterally into When rivet is driven it expands laterally into the holethe hole

Expansion “fills” the hole and reduced Expansion “fills” the hole and reduced likelihood of sliplikelihood of slip– M only occur on outer pliesM only occur on outer plies

When rivet cools, it will contract longitudinally When rivet cools, it will contract longitudinally andand diametrically diametrically– Diametric contraction which can increase Diametric contraction which can increase

clearance some small amountclearance some small amount–

3/4 7/8

1

Rivet PerformanceRivet Performance

Precompression depends on:Precompression depends on:– Joint stiffnessJoint stiffness– Driving and finishing temperatureDriving and finishing temperature– Driving pressure. Driving pressure.

Hot-driven rivets can develop clamping forces Hot-driven rivets can develop clamping forces that approach the yield load of a rivetthat approach the yield load of a rivetConsiderable variation in clamping forces is Considerable variation in clamping forces is generally observedgenerally observedAs the grip length is increased, the residual As the grip length is increased, the residual clamping force tends to increaseclamping force tends to increase

Effects of DrivingEffects of Driving

Driving generally increases the strength of rivets

For hot-driven rivets – machine driving increased the rivet tensile

strength by about 20%– Pneumatic hammer increases rivet tensile

strength about 10%

Hot working of the material

Rivet Strengths / TypesRivet Strengths / TypesThree structural rivet steels:Three structural rivet steels:– ASTM A502 grade 1, carbon rivet steel for general ASTM A502 grade 1, carbon rivet steel for general

purposespurposes– ASTM A502 grade 2, carbon-manganese rivet steelASTM A502 grade 2, carbon-manganese rivet steel

Suitable for use with high-strength carbon and high-strength Suitable for use with high-strength carbon and high-strength low-alloy structural steelslow-alloy structural steels

– ASTM A502 grade 3, ASTM A502 grade 3, Similar to grade 2 but with enhanced corrosion resistanceSimilar to grade 2 but with enhanced corrosion resistance

Rivet steel strength is specified in terms of Rivet steel strength is specified in terms of hardness requirementshardness requirements

There are no additional material requirements for There are no additional material requirements for strength or hardness in the driven conditionstrength or hardness in the driven condition

Rivets Material SpecificationsRivets Material Specifications

Strengths vary with type:Strengths vary with type:– ASTM A502 Grade 1 about 60 ksiASTM A502 Grade 1 about 60 ksi– ASTM A502 Grade 2 & 3 about 80 ksiASTM A502 Grade 2 & 3 about 80 ksi

Variations in driving temperature between Variations in driving temperature between 1,800 F and 2,300 F does not affect 1,800 F and 2,300 F does not affect strengthstrength

A307 BoltsA307 Bolts

A307 are low-carbon fastenersA307 are low-carbon fasteners

Typically available ¼ to 4 inch diameterTypically available ¼ to 4 inch diameter

Min. specified tensile strength of 60 ksiMin. specified tensile strength of 60 ksi

May be galvanized without concernMay be galvanized without concern

Will develop some pretension forceWill develop some pretension force– No specified tightening proceduresNo specified tightening procedures– Relatively low strengthRelatively low strength– Hence, can’t design as friction connectionHence, can’t design as friction connection


A325 is a carbon steel boltA325 is a carbon steel bolt

Available in ½ to 1-½ inch diametersAvailable in ½ to 1-½ inch diameters

Can be specified in two typesCan be specified in two types– Used to be threeUsed to be three

Head is heavy hex Head is heavy hex – Head must indicate bolt typeHead must indicate bolt type

Minimum tensile strengthMinimum tensile strength– 120 ksi up to 1 inch120 ksi up to 1 inch– 105 ksi > 1 inch105 ksi > 1 inch

MarkingsMarkings

COR

A325

Material Specification

Manufacturer(initials or abbreviation; here“Cordova Bolt”)

Underline if Type 3 bolt(weathering steel)

Otherwise, Type 1 – standard(Type 2 discontinued)


A325 used to be available in three typesA325 used to be available in three types– Type 1 – Medium carbon steel (high temp)Type 1 – Medium carbon steel (high temp)– Type 2 – Low carbon martensitic steelType 2 – Low carbon martensitic steel– Type 3 – Corrosion resistant for use with Type 3 – Corrosion resistant for use with

weathering steels weathering steels

Type 2 was could only be used for “atmospheric” Type 2 was could only be used for “atmospheric” temperature conditions, but was discontinued temperature conditions, but was discontinued since no need for itsince no need for itIf not specified, Type 1 or Type 3 can be If not specified, Type 1 or Type 3 can be provided by supplierprovided by supplier– Usually Type 1 will be specifiedUsually Type 1 will be specified


Can be reused as long as nut can be run up the Can be reused as long as nut can be run up the threads by handthreads by hand– Usually 1 or 2 timesUsually 1 or 2 times– If galvanized, reuse is not permittedIf galvanized, reuse is not permitted

Can be hot-dipped or mechanically galvanizedCan be hot-dipped or mechanically galvanized– Galvanized bolts and nuts must be thought of as an Galvanized bolts and nuts must be thought of as an

assemblyassembly– Can’t mix types of galvanizingCan’t mix types of galvanizing

Galvanizing will affect tightening proceduresGalvanizing will affect tightening procedures


A490 is a A490 is a alloyalloy steel bolt steel bolt

Available in ½ to 1-½ inch diametersAvailable in ½ to 1-½ inch diameters

Can be specified in two typesCan be specified in two types– Used to be threeUsed to be three

Head is heavy hex Head is heavy hex – Head must indicate bolt typeHead must indicate bolt type

Minimum tensile strengthMinimum tensile strength– 150 min ksi all sizes150 min ksi all sizes– 170 ksi 170 ksi max max (No upper limit on A325)(No upper limit on A325)


A490 used to be available in three typesA490 used to be available in three types– Type 1 – Medium carbon steel (high temp)Type 1 – Medium carbon steel (high temp)– Type 2 – Low carbon martensitic steelType 2 – Low carbon martensitic steel– Type 3 – Corrosion resistant for use with Type 3 – Corrosion resistant for use with

weathering steels weathering steels

Type 2 was discontinued since no need for itType 2 was discontinued since no need for it

If not specified, Type 1 or Type 3 can be If not specified, Type 1 or Type 3 can be provided by supplierprovided by supplier– Usually Type 1 will be specifiedUsually Type 1 will be specified


Galvanizing is Galvanizing is prohibitedprohibited– High strength steel is susceptible to High strength steel is susceptible to

hydrogen embittermenthydrogen embittermentUsually issue with steels with strengths Usually issue with steels with strengths

over 200 ksiover 200 ksi

But considered close enough to 170 ksiBut considered close enough to 170 ksi

A490 HS-Bolts A490 HS-Bolts CAN NOT BE REUSEDCAN NOT BE REUSED– Insufficient ductilityInsufficient ductility

Why Can’t We Reuse Why Can’t We Reuse Some HS Bolts?Some HS Bolts?

Pretension involves deformation of the Pretension involves deformation of the bolt, primarily in the threadsbolt, primarily in the threads

Black A-325 bolts can tolerate multiple Black A-325 bolts can tolerate multiple cycles of elongationcycles of elongation

However, A490 and galvanized A325 are However, A490 and galvanized A325 are not consistently capable of undergoing not consistently capable of undergoing more than one pretensioning cyclesmore than one pretensioning cycles

Multiple Cycles on “Black” A325Multiple Cycles on “Black” A325

Multiple Cycles on A490Multiple Cycles on A490

Connect PliesConnect Plies

Can only apply specifications if:Can only apply specifications if:– All plies are steelAll plies are steel– There are no compressible layersThere are no compressible layers

i.e., no gasketsi.e., no gaskets

Must only have steel to ensure Must only have steel to ensure precompression can be achievedprecompression can be achieved

Compressible layers will result in loss of Compressible layers will result in loss of pre-tensionpre-tension

Installation TechniquesInstallation Techniques

Generally four accepted procedures:Generally four accepted procedures:– Turn-of-the nutTurn-of-the nut– Calibrated wrenchCalibrated wrench– Twist-off-type boltTwist-off-type bolt– Direct-tension-indicator (DTI)Direct-tension-indicator (DTI)

All have been researched and are All have been researched and are acceptable for most applicationsacceptable for most applicationsAll require a minimum preload of 70% of All require a minimum preload of 70% of specified minimum tensile strengthspecified minimum tensile strength

Minimum Bolt PreloadMinimum Bolt Preload

Turn-of-the NutTurn-of-the Nut

After snugging the joint, the bolt shank and nut is After snugging the joint, the bolt shank and nut is marked and then a specific amount of rotation is marked and then a specific amount of rotation is induced between the nut and the boltinduced between the nut and the boltGenerally results in more uniform bolt Generally results in more uniform bolt pretensions than torque-controlled methodspretensions than torque-controlled methodsBased on strain controlBased on strain control– Deformation of bolt related to angle of threadDeformation of bolt related to angle of thread

Requires joint is “compacted” prior to tightening Requires joint is “compacted” prior to tightening (All plies in contact)(All plies in contact)Current guidance on rotation requirements does Current guidance on rotation requirements does not apply to bolts longer than 12dnot apply to bolts longer than 12dbb

Turn-of-the NutTurn-of-the Nut

Calibrated WrenchCalibrated WrenchRepresentative sample of three bolts must be Representative sample of three bolts must be selected to calibrate a wrenchselected to calibrate a wrench – For each diameter, length, and gradeFor each diameter, length, and grade

Tensioned in a Skidmore-Wilhelm on siteTensioned in a Skidmore-Wilhelm on siteWrench is then set to cut out at that torque Wrench is then set to cut out at that torque – The wrench becomes "calibrated"The wrench becomes "calibrated"– Rotation must be limited to a specific value Rotation must be limited to a specific value – Calibration is required every dayCalibration is required every day

Actual results of tension in bolts produced by Actual results of tension in bolts produced by this method are acknowledged to be highly this method are acknowledged to be highly variablevariable– Not allowed in CanadaNot allowed in Canada

Skidmore-Skidmore-WilhelmWilhelm

Calibrated WrenchCalibrated Wrench

Twist-off-type BoltTwist-off-type Bolt

Covered by ASTM F1852Covered by ASTM F1852

Function by calibrating the torque needed Function by calibrating the torque needed to twist off a splined extension to twist off a splined extension manufactured into the bolt shankmanufactured into the bolt shank

Made correctly, the "twist-off" will occur at Made correctly, the "twist-off" will occur at a bolt tension above the minimum preloada bolt tension above the minimum preload

Can be tightened from one sideCan be tightened from one side

Twist-off-type BoltTwist-off-type Bolt

Require special equipmentRequire special equipmentMore expensive than regular More expensive than regular boltsbolts– But less laborBut less labor

Hard to find in galvanizedHard to find in galvanized– RumoredRumored

Direct-tension-indicator (DTI)Direct-tension-indicator (DTI)

Covered by ASTM F959Covered by ASTM F959

Can be thought of a load cellCan be thought of a load cell

Independent of torqueIndependent of torque

Issues with oversized holesIssues with oversized holes

Issues with soft washers for galvanizing Issues with soft washers for galvanizing applicationsapplications– ASTM F436 will be modified to ensure hard ASTM F436 will be modified to ensure hard

washerswashers

Direct-tension-indicator (DTI)Direct-tension-indicator (DTI)

Bolt SpecificationsBolt Specifications

See See www.boltcouncil.orgwww.boltcouncil.org– Research Council on Structural ConnectionsResearch Council on Structural Connections– Established January 1947Established January 1947

Provides general standards on bolting, Provides general standards on bolting, bolts, installation, and inspectionbolts, installation, and inspection

Current specifications available for free on Current specifications available for free on websitewebsite

Also, the most important Also, the most important book on connections is book on connections is available for free from available for free from the RCSC websitethe RCSC website

ce 671 lect 4

Documents