The Mechanics of Bolted Joints - Preloaded Bolted Joint Analysis - Lesson 2

Q: What distinguishes tension joints from shear joints in a bolted connection?

Tension joints support tensile loads that tend to pull plates apart, with loads acting along the bolt axis. Shear joints experience loads perpendicular to the bolt axis and performance depends on friction and bolt shear strength.

Q: Why is bolt preload important for preventing joint separation?

A well-designed bolted joint maintains enough initial compression so the joint does not separate under external forces. This is achieved by applying a sufficient preload based on the bolt’s proof load.

Q: How does an external load change the force carried by the bolt and the joint?

An external load reduces clamp force by an amount related to bolt/joint stiffness and increases the load on the bolt by the complementary amount. The redistribution is governed by the relative stiffness between the bolt and the joint.

Oct 29, 2026

Upload by Oliver

December 2019 lesson material explaining how preloaded bolted joints behave under different loading conditions. Covers two common bolt thread types, tension versus shear joint behavior, and the role of preload in maintaining initial compression to prevent separation. Introduces force balance concepts using joint diagrams, links bolt and member stiffness to extension and compression, and derives how external loads redistribute force between bolt and clamped members, affecting joint separation and bolt fatigue life.

LanguageEnglish

CategoryTechnology

FormatPDF

Pages12

Reading Time30 min

AccessFree to download

Preloaded Bolted Joint Analysis - Lesson 2

Types of Bolted Joints

Tension Joints

Shear Joints

Force Balance in Bolted Joints

Joint Diagram

Bolt Stiffness

Member/Joint Stiffness

External Load Effects on Force Balance

• DECEMBER 2019 The Mechanics of Bolted Joints Preloaded Bolted Joint Analysis – Lesson 2 Types of Bolted Joints Bolted joints can support different load configurations. • Two commonly used bolts are partially and fully threaded bolts. • Choosing the wrong type of bolt can lead to joint failure. • There are two types of joints: -Tension joints -Shear joints Partially Threaded Bolt Fully Threaded Bolt Tension Joints In a tension joint the bolt is predominantly supporting tensile loads that pull the plates apart. • Applied loads 􀜨 act along the axis of the bolts. • Due to external tensile loads, the forces acting through the crosssection of the bolt increase by a fraction of the total applied force,∆􀜨􀮻 . • The clamp force (which is equal to the bolt preload 􀜲) should typically be selected to ensure there is no plastic deformation of the bolt. • A sufficiently high value of 􀜲 and member (or joint) stiffness ensures that only a small portion, ∆􀜨􀮻 , of the external load, 􀜨 , is carried by the bolts and the rest of the load, 􀜨 − ∆􀜨􀮻 = ∆􀜨􀯃 , is carried by the clamped members. • If the external load applied to the joint is large enough to overcome the initial compression in the joint achieved through the bolt preload, then the members will separate, and the entire load will be carried by the bolt, which can also greatly reduce the bolt fatigue life from repetitive loadings. • The bolt preload 􀜲 is chosen based upon the proof load of the bolt. 􀡼 + ∆􀡲 􀡮 􀡼 − ∆􀡲􀡶 ∆􀡲 􀡮 + ∆􀡲􀡶 = 􀡲 Shear Joints Shear joints experience loads in a direction perpendicular to the axis of the bolt. • Performance depends on the friction between the fastener and the component, as well as the shear strength of the bolt. • If the frictional force due to the preload is not sufficient to counter the external load, then the component slips, which is often undesirable. • In some cases, the bolt directly supports the external load and friction is not needed. Such loads are called bearing loads. ‐ Here, preload is not important, and the shear strength of the bolt determines the strength of joint. • Partially threaded bolts are suitable for these joints as they offer more shear resistance and better alignment. F P μP Force Balance in Bolted Joints • A well-designed bolted joint should establish and maintain enough initial compression in the joint so that the joint does not separate under external forces. • To achieve this, we need to apply a sufficient preload 􀜲 to the bolt such that: 􀜲 < Proof load 􀜲 = Factor × Proof strength × Tensile stress area of bolt 0.75 < Factor < 0.9 1 • To determine whether 􀜲 is sufficient to prevent joint separation when external force is applied, we determine the force balance in the joint using a Joint diagram 1-Budynas, Richard Gordon, and J. Keith Nisbett. Shigley's Mechanical Engineering Design. Eighth Edition. New York: McGraw-Hill, 2008. Force Balance in Bolted Joints – Joint Diagram Force • Joint diagrams are developed to help visualize the loading in bolted joints. • Static equilibrium dictates that the tensile force acting on the bolt is equal and opposite to the compressive clamp force on the joint. 􀜨􀯃0 = 􀜨􀮻 0 = 􀜲 (Bolt Preload) • The bolt extension and joint compression depend on their respective stiffnesses. The slopes of the two lines represent the respective stiffnesses. 􀝑􀯃0 = 􀯉 􀯄 􀲻 􀝑 􀮻0 = 􀯉 􀯄 􀲳 • The origin of the Joint compression line is moved such that points 􀜬0 and 􀜤0 coincide to form a triangle. This is the Joint diagram. J0 Compression Joint Diagram 􀝑􀯃0 (0,0) 􀝑 􀮻0 Extension Force (0,0) J0 B0 (0,0) Extension /Compression 􀜲 􀜭􀯃 􀜭􀮻 B0 Force Balance in Bolted Joints – Bolt Stiffness • Approximate bolt stiffness can be calculated as 􀜣 􀯗􀜣 􀯧􀜧 1 􀜭􀮻 = ~~ ~~􀜣 􀯗􀝈 􀯧 + 􀜣 􀯧􀝈 􀯗 􀜣 􀯧 -tensile-stress area 􀝈 􀯧 - length of threaded portion of grip 􀜣 􀯗 -major-diameter area 􀝈 􀯗 - length of unthreaded por

FAQs

What distinguishes tension joints from shear joints in a bolted connection?

Tension joints support tensile loads that tend to pull plates apart, with loads acting along the bolt axis. Shear joints experience loads perpendicular to the bolt axis and performance depends on friction and bolt shear strength.

Why is bolt preload important for preventing joint separation?

A well-designed bolted joint maintains enough initial compression so the joint does not separate under external forces. This is achieved by applying a sufficient preload based on the bolt’s proof load.

How does an external load change the force carried by the bolt and the joint?

An external load reduces clamp force by an amount related to bolt/joint stiffness and increases the load on the bolt by the complementary amount. The redistribution is governed by the relative stiffness between the bolt and the joint.

Oct 29, 2026

Upload by Oliver