BOLTED JOINT.docx

8/18/2019 BOLTED JOINT.docx

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CHAPTER 1

1. Introduction

Bolted joints are one of the most common elements in construction and machine design. They

consist of fasteners that capture and join other parts, and are secured with the mating of screw.

There are two main types of bolted joint designs: tension joints and shear joints.

In the tension joint, the bolt and clamped components of the joint are designed to transfer the

external tension load through the joint by way of the clamped components through the design of

a proper balance of joint and bolt stiffness. The joint should be designed such that the clamp load

is never overcome by the external tension forces acting to separate the joint (and therefore the

joined parts see no relative motion.

The second type of bolted joint transfers the applied load in shear on the bolt shan! and relies on

the shear strength of the bolt. Tension loads on such a joint are only incidental. " preload is still

applied but is not as critical as in the case where loads are transmitted through the joint in

tension. #ther such shear joints do not employ a preload on the bolt as they allow rotation of the

joint about the bolt, but use other methods of maintaining bolt$joint integrity. This may

include clevis lin!ages, joints that can move, and joints that rely on a loc!ing mechanism (li!e

loc! washers, thread adhesives, and loc! nuts.

In both the tension and shear joint design cases, some level of tension preload in the bolt and

resulting compression preload in the clamped components is essential to the joint integrity. The

preload target can be achieved by applying a measured tor%ue to the bolt, measuring bolt

extension, heating to expand the bolt then turning the nut down, tor%uing the bolt to the yield

point, testing ultrasonically or by a certain number of degrees of relative rotation of the threaded

components. &ach method has a range of uncertainties associated with it, some of which are very

substantial.

http://en.wikipedia.org/wiki/Constructionhttp://en.wikipedia.org/wiki/Fastenerhttp://en.wikipedia.org/wiki/Fastenerhttp://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Shear_strengthhttp://en.wikipedia.org/wiki/Shear_strengthhttp://en.wikipedia.org/wiki/Clevis_pinhttp://en.wikipedia.org/wiki/Clevis_pinhttp://en.wikipedia.org/wiki/Lock_washerhttp://en.wikipedia.org/wiki/Lock_washerhttp://en.wikipedia.org/wiki/Adhesivehttp://en.wikipedia.org/wiki/Nut_(hardware)http://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Fastenerhttp://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Shear_strengthhttp://en.wikipedia.org/wiki/Clevis_pinhttp://en.wikipedia.org/wiki/Lock_washerhttp://en.wikipedia.org/wiki/Adhesivehttp://en.wikipedia.org/wiki/Nut_(hardware)http://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Construction


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CHAPTER 2

2. Bolted joints

The !ey feature of bolted joints is that they can be dismantled comparatively easily. 'owever

they are costly in that fre%uently additional parts are needed (washer, nut compared to riveted or

welded joints and they re%uire more s!ill $ effort to assemble. or these reasons they should only

be used where there is a strong possibility that the parts will at some stage re%uire to be

separated.

2.1 Types of bolted joint

(a Classification based on t!e type of resultant force transferred: The bolted connections are

referred to as concentric connections (force transfer in tension and compression member,

eccentric connections (in reaction transferring brac!ets or moment resisting connections (in

beam to column connections in frames. Ideal concentric connections should have only one bolt

passing through all the members meeting at a joint. 'owever, in practice, this is not usually


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ig: shear connections

(c Classification based on force transfer "ec!anis" by bolts: The bolted connections are

classified as bearing type (bolts bear against the holes to transfer the force or friction type (forcetransfer between the plates due to the clamping force generated by the pretensioning of the

bolts. The force transfer in either case is discussed in more detail later.

ig : (a Tension connection (b Tension plus shear connection


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2.2 Ad#anta$es and %isad#anta$es

• "dvantages

- They can be designed to ta!e tension loads, unli!e riveting (by tightening the bolt$nut to develop a

preload, you reduce the effects of fatigue due to cyclic loading, which you cant do with a rivet/ plus,

rivets can easily pull through a hole when loaded in tension.

0 *elds re%uire heating a metal, which can change the properties in the heat1affected 2one, and can

also create thermal stresses. Bolts avoid this problem. 3oure also not li!ely to start a fire (welds or

breathe toxic fumes (welds and adhesive joints when youre installing a bolt.

4 Bolted joints arent particularly sensitive to the condition of the parent material. *ith welds and

adhesive joints, the parent material needs to be clean, free of oils, etc (and obviously, it has to be

metal to weld.

5 3ou can put a bolt in a blind hole (one that doesnt go all the way through the material/ you cant

use a rivet.

6 Bolts are easy. *elding ta!es a lot of s!ill and a lot of time, particularly if youre going to inspect

the weld for flaws after its completed. But just about everybody has used a wrench.

7 Bolts offer much better joint %uality than a screw, mostly because the threads are more tightly

controlled.


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• 8isadvantage

- They re%uire access to both sides of the joint (although this can be overcome using

studs or special bolts li!e 'i19o!s. *elding, adhesive joints, and some types of riveting

can be done with access to only one side of the joint.

0 They can become loose over time as the nut bac!s off (this can be addressed to some

extent by using the proper preload and thread1loc!ing features or as the material creeps.

*elding and adhesive joints dont have this problem.

4 They re%uire holes, which introduce stress concentrations and more failure modes/

drilling the holes may create crac!s which will grow over time to cause failure. *elding

and adhesive joints dont re%uire holes. "lso, welds and adhesive joints are continuous, so

they dont concentrate load li!e a bolt does.

5 reload can be tough to measure accurately 1 it depends on the method of tightening,

the friction between the threads of the bolt and the nut, etc.

6 ;omplexity. " bolted joint adds to a part count 1 a bolt, a nut, washers, thread

lubricant, thread loc!ing compound. "nd the bolts, nuts, and washers come in specific

si2es with specific threads, with specific hole si2es and tolerances, for specific

applications 1 if you need a high %uality joint, youve got to !eep trac! of all that and

ma!e sure the right bolt is used in the right place and in the right way.

7 ;orrosion between a bolt and the parent material should be considered. This may not

be a problem with welding and adhesive joints if the parent materials being welded are

compatible.


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2.& Application

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BOLTED JOINT.docx