Rivets, HS-bolts, and Bolting Specifications

1. Rivets, HS-bolts, and Bolting Specifications CE671 – Lecture 4

2. Rivets • One of the oldest forms of fastener in structural joints • Common up until 1960’s • Used in buildings and bridges • Used in wrought iron and steel • Replaced by HS bolts and welding • Required 4-5 skilled laborers • Fireman • Toss man • Catcher • Riveter (2)

3. Discussion • Rivets • A307 Bolts • A325 HS-Bolts • A490 HS-Bolts

4. Many Types of Rivets

5. Rivet Installation • Installed though multiple plates • Generally installed as “hot” rivets • About 1,800 F • Components drawn together with clamps or bolts • Rivet inserted into hole and the “driven” • Pressed or hammered • Head is formed by driving process • As the rivet cools, it shrinks thereby introducing precompression into the joint

6. Rivet Crew HOT

7. Rivet Installation • When rivet is driven it expands laterally into the hole • Expansion “fills” the hole and reduced likelihood of slip • M only occur on outer plies • When rivet cools, it will contract longitudinally and diametrically • Diametric contraction which can increase clearance some small amount

8. 3/4 7/8 1

9. Rivet Performance • Precompression depends on: • Joint stiffness • Driving and finishing temperature • Driving pressure. • Hot-driven rivets can develop clamping forces that approach the yield load of a rivet • Considerable variation in clamping forces is generally observed • As the grip length is increased, the residual clamping force tends to increase

10. Effects 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

11. Rivet Strengths / Types • Three structural rivet steels: • ASTM A502 grade 1, carbon rivet steel for general purposes • ASTM A502 grade 2, carbon-manganese rivet steel • Suitable for use with high-strength carbon and high-strength low-alloy structural steels • ASTM A502 grade 3, • Similar to grade 2 but with enhanced corrosion resistance • Rivet steel strength is specified in terms of hardness requirements • There are no additional material requirements for strength or hardness in the driven condition

12. Rivets Material Specifications • Strengths vary with type: • ASTM A502 Grade 1 about 60 ksi • ASTM A502 Grade 2 & 3 about 80 ksi • Variations in driving temperature between 1,800 F and 2,300 F does not affect strength

13. A307 Bolts • A307 are low-carbon fasteners • Typically available ¼ to 4 inch diameter • Min. specified tensile strength of 60 ksi • May be galvanized without concern • Will develop some pretension force • No specified tightening procedures • Relatively low strength • Hence, can’t design as friction connection

14. A325 HS-Bolts • A325 is a carbon steel bolt • Available in ½ to 1-½ inch diameters • Can be specified in two types • Used to be three • Head is heavy hex • Head must indicate bolt type • Minimum tensile strength • 120 ksi up to 1 inch • 105 ksi > 1 inch

15. Material Specification Underline if Type 3 bolt (weathering steel) Manufacturer (initials or abbreviation; here“Cordova Bolt”) Markings A325 Otherwise, Type 1 – standard (Type 2 discontinued) COR

16. A325 HS-Bolts • A325 used to be available in three types • Type 1 – Medium carbon steel (high temp) • Type 2 – Low carbon martensitic steel • Type 3 – Corrosion resistant for use with weathering steels • Type 2 was could only be used for “atmospheric” temperature conditions, but was discontinued since no need for it • If not specified, Type 1 or Type 3 can be provided by supplier • Usually Type 1 will be specified

17. A325 HS-Bolts • Can be reused as long as nut can be run up the threads by hand • Usually 1 or 2 times • If galvanized, reuse is not permitted • Can be hot-dipped or mechanically galvanized • Galvanized bolts and nuts must be thought of as an assembly • Can’t mix types of galvanizing • Galvanizing will affect tightening procedures

18. A490 HS-Bolts • A490 is a alloy steel bolt • Available in ½ to 1-½ inch diameters • Can be specified in two types • Used to be three • Head is heavy hex • Head must indicate bolt type • Minimum tensile strength • 150 min ksi all sizes • 170 ksi max (No upper limit on A325)

19. A490 HS-Bolts • A490 used to be available in three types • Type 1 – Medium carbon steel (high temp) • Type 2 – Low carbon martensitic steel • Type 3 – Corrosion resistant for use with weathering steels • Type 2 was discontinued since no need for it • If not specified, Type 1 or Type 3 can be provided by supplier • Usually Type 1 will be specified

20. A490 HS-Bolts • Galvanizing is prohibited • High strength steel is susceptible to hydrogen embitterment • Usually issue with steels with strengths over 200 ksi • But considered close enough to 170 ksi • A490 HS-Bolts CAN NOT BE REUSED • Insufficient ductility

21. Why Can’t We Reuse Some HS Bolts? • Pretension involves deformation of the bolt, primarily in the threads • Black A-325 bolts can tolerate multiple cycles of elongation • However, A490 and galvanized A325 are not consistently capable of undergoing more than one pretensioning cycles

22. Multiple Cycles on “Black” A325

23. Multiple Cycles on A490

24. Connect Plies • Can only apply specifications if: • All plies are steel • There are no compressible layers • i.e., no gaskets • Must only have steel to ensure precompression can be achieved • Compressible layers will result in loss of pre-tension

25. Installation Techniques • Generally four accepted procedures: • Turn-of-the nut • Calibrated wrench • Twist-off-type bolt • Direct-tension-indicator (DTI) • All have been researched and are acceptable for most applications • All require a minimum preload of 70% of specified minimum tensile strength

26. Minimum Bolt Preload

27. Turn-of-the Nut • After snugging the joint, the bolt shank and nut is marked and then a specific amount of rotation is induced between the nut and the bolt • Generally results in more uniform bolt pretensions than torque-controlled methods • Based on strain control • Deformation of bolt related to angle of thread • Requires joint is “compacted” prior to tightening (All plies in contact) • Current guidance on rotation requirements does not apply to bolts longer than 12db

28. Turn-of-the Nut

29. Calibrated Wrench • Representative sample of three bolts must be selected to calibrate a wrench • For each diameter, length, and grade • Tensioned in a Skidmore-Wilhelm on site • Wrench is then set to cut out at that torque • The wrench becomes "calibrated" • Rotation must be limited to a specific value • Calibration is required every day • Actual results of tension in bolts produced by this method are acknowledged to be highly variable • Not allowed in Canada

30. Calibrated Wrench Skidmore-Wilhelm

31. Twist-off-type Bolt • Covered by ASTM F1852 • Function by calibrating the torque needed to twist off a splined extension manufactured into the bolt shank • Made correctly, the "twist-off" will occur at a bolt tension above the minimum preload • Can be tightened from one side

32. Twist-off-type Bolt • Require special equipment • More expensive than regular bolts • But less labor • Hard to find in galvanized • Rumored

33. Direct-tension-indicator (DTI) • Covered by ASTM F959 • Can be thought of a load cell • Independent of torque • Issues with oversized holes • Issues with soft washers for galvanizing applications • ASTM F436 will be modified to ensure hard washers

34. Direct-tension-indicator (DTI)

35. Direct-tension-indicator (DTI)

36. Bolt Specifications • See www.boltcouncil.org • Research Council on Structural Connections • Established January 1947 • Provides general standards on bolting, bolts, installation, and inspection • Current specifications available for free on website

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