By: Prof Dr. Akhtar Naeem Khan chairciv@nwfpuet.edu.pk Lecture 04: Bolted Connections By: Prof Dr. Akhtar Naeem Khan chairciv@nwfpuet.edu.pk

Topics to be Addressed Types of connectors Tightening procedures Behavior of Bolted & Riveted connections Types of Bolted connections Types of connection failures Code Requirements Design Examples

Types of Connectors Components which make up the complete structure are fastened together by means of: RIVETS (older version) BOLTS (newer version) WELDS

Types of Connectors Rivets: They are made from rivet bar stock in a machine which forms one head and shears the rivet to desired length. Steel rivets are always heated before driving Most rivets are driven by pressure-type riveters which complete riveting in one stroke. Typical Round Head Rivet

Types of Connectors Rivets: Rivets are generally made from steel conforming to ASTM A502 and comes in 2 grades: Grade 1(carbon steel) Grade 2 (carbon-manganese steel)

Types of Connectors Rivets: Round Head Rivet Countersunk Rivet

Types of Connectors Rivets:

Types of Connectors Rivets: Riveting processes Rivet Heating Oven Rivet Heater

Types of Connectors Rivets: Riveting processes Earlier Riveting Gun Modern Riveting Gun

Types of Connectors Rivets: Characteristics of riveted connections In riveted connections magnitude of clamping is function of length of rivet and magnitude of shrinkage after the head is formed. Magnitude of slip depends on the extent to which rivet fills the hole.

Types of Connectors Rivets: Causes of rivet obsolescence Riveting required a crew of 4 to 5 experienced riveters Bolt installation is less labor intensive Riveting is time consuming operation requiring preheating, driving and finishing

Types of Connectors Rivets: Causes of rivet obsolescence Rivet strength is low compared to high strength bolts High strength bolts are now economical Riveting is still used in some industries and applications such as aircraft industry

Types of Connectors Bolts: Two common types of bolts are: Unfinished (A307) A307 is known by names unfinished, rough, common, ordinary and machine. They are made of low carbon steel having tensile strength of 60Ksi.

Types of Connections Bolts: Two common types of bolts are: High strength bolt (A325,A449,A490). A325 is made of medium carbon steel whose tensile strength decreases with increase in dia. High strength bolts can be tightened to large tensions.

Types of Connections Bolts: Typical High Strength Bolt

Tightening procedures Research Council on Structural Connections (RCSC) prescribes four tightening procedures. Turn of the nut method Calibrated-wrench tightening Installation of alternate design bolts Direct-tension-indicator tightening

Tightening procedures Torque Wrench

Tightening procedures Positive Tension Shear Bolt Bolt Installation Procedure

Tightening procedures Direct Tension Indicating Washers

Behavior of Bolted & Riveted connections T = Tensile Force on Connection ∆ = Joint Displacement

Behavior of Bolted & Riveted connections In riveted connections magnitude of clamping is function of length of rivet and magnitude of shrinkage after the head is formed. Magnitude of slip depends on the extent to which rivet fills the hole.

Types of Bolted connection Slip-Critical connections Connection transmits the force by friction produced between the faying surfaces by the clamping action of the bolts. Slip-critical connections are recommended for joints subjected to stress reversal, severe stress fluctuation, impact, vibration or where slip is objectionable

Types of Bolted connection Slip-Critical connections The clamping force applied to the bolt brings the two members close enough so that appreciable friction is produced between them which is then responsible for resisting the load. The more the clamping force the more is the friction and strong is the connection but the clamping force need not to be greater than tensile strength of the bolt. Slip critical connection becomes bearing type connection after the slip occurs so every slip critical connection is essentially a bearing type connection also.

Types of Bolted connection Bearing type connections Load is transferred by shearing and bearing on the bolt. Capacity in shear depends on whether shear plane intersects the body of bolt or threaded portion.

Types of Bolted connection Bearing type connections Bearing type connection is the most widely used general type connection in which the load is resisted by the bolt body without any friction between faying surfaces.

Type of connection Failures Shearing Failure of Bolts. Bearing Failure of plate. Tearing failure at edge of plate.

Type of connection Failures Shearing failure of bolts

Type of connection Failures Shearing failure of bolts

Type of connection Failures Bearing Failure of Plate

Type of connection Failures Shear & Bearing Area

Type of connection Failures Tearing Failure at edge of Plate Shearing Failure edge of plate Transverse Tension Failure

Type of connection Failures Tearing Failure at edge of Plate Tests showed, failure by tearing through free edge of material will not occur if Le measured parallel to line of applied force is not less diameter of bolt multiplied by ratio of bearing stress to tensile strength of connected part.

Type of connection Failures Tearing Failure at edge of Plate Force transmitted by the bolt P = fp D t ------------------------(A) Force to cause failure along two shear planes P = 2(Le – D / 2 ) t u u = 0.7 Fu P = 1.4DtFu(Le/D –1/2) -----(B) Equating (A) & (B)

Type of connection Failures Tearing Failure at edge of Plate ------- (C) Eqn (C) can be approximated as So Eqn becomes

Type of connection Failures Tearing Failure at edge of Plate LRFD ASD Tearing length or Edge distance  = 0.75 With FOS= 2

Type of connection Failures Tearing Failure at edge of Plate LRFD ASD Spacing between holes

Eccentricity of Applied Force Type of connection Failures Eccentricity of Applied Force Plates of lap joint tends to bend. Bending produces non uniform bearing of the fastener on the plates

Code Requirements Topic Ref. Text Book Ref. LRFD Code Minimum edge Distance Table 2-8 Table J3.4 Allowable Working Stress on Fasteners or Connected Material Table 2-9 Allowable Load for Slip-Critical Connections Table 2-10 Table J3.6 Allowable Stresses A502 Rivets Table 2-12 Design Strength of Fasteners Table 2-13 Table J3.2

Code Requirements AISC Minimum Edge Distance

Code Requirements Minimum installation tension

Code Requirements Allowable Stresses

Code Requirements Properties of structural bolts

Code Requirements Allowable load for Slip critical connection

Code Requirements Design strength of fasteners

Design Example No.1 (ASD Method)

Design Example No.1 (ASD Method)

Design Example No.1 (ASD Method)

Design Example No.1 (ASD Method)

Design Example No.1 (LRFD Method)

Design Example No.1 (LRFD Method)

Design Example No.1 (LRFD Method)

Design Example No.1 (LRFD Method)

Design Example No.2 (LRFD Method) W = 10 in t = .25in

Design Example No.2 (LRFD Method)

Design Example No.2 (LRFD Method) Fub

Design Example No.2 (LRFD Method) 2” 6” 3” P = 77 Kips

Thanks