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Why are insulating washers installed between steel bolts and connecting aluminium plates?

Corrosion of aluminium can be triggered by putting it in contact with another metal in the presence of water. This is known as bimetallic corrosion or galvanic corrosion. The mechanism of such corrosion is the formation of a cell in moist condition so that an electric current is generated to flow between the two metals in direct contact. The degree of corrosion is influenced by the nature of connecting metals, their electrode potential, their areas, conductivity of fluid etc.

When aluminium plates are connected together by means of steel bolts, bimetallic corrosion may occur. Where there is presence of a good electrolyte like seawater, there may be local attack on aluminium. Therefore, some jointing compound or insulating insert and washer are adopted to insulate electrically the dissimilar metals from one another

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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What is the behaviour of internal force in preloaded fasteners?

The force in a bolt in a bolted joint depends on the preloading force applied to it during the tightening operation. For instance, when the preloaded bolt is tightened with a certain force, the bolts’ internal force will not increase significantly if the external applied force on the bolted joint does not exceed the preloading force. It looks like the bolt does not feel the external applied force and it is not until the external force has exceeded the preloading force when a substantial increase of internal force of the bolt will occur.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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Are washers necessary for proper operation of bolts?

“Fastener” is a general term used to describe something which is used as a restraint for holding things together or attaching them to other things.

The main physical distinction between screws and bolts is that screws are entirely full of threads while bolts contain shanks without threads. However, a better interpretation of the differences between the two is that bolts are always fitted with nuts. On the contrary, screws are normally used with tapped holes.

High friction grip bolts are commonly used in structural steelwork. They
normally consist of high tensile strength bolts and nuts with washers. The bolts are tightened to a shank tension so that the transverse load across the joint is resisted by the friction between the plates rather than the bolt shank’s shear strength.

Washer

The purpose of installing washers in a typical bolting system is to distribute the loads under bolt heads and nuts by providing a larger area under stress. Otherwise, the bearing stress of bolts may exceed the bearing strength of the connecting materials and this leads to the loss of preload of bolts and the creeping of materials. Alternatively, flanged fasteners instead of using washers could be adopted to achieve the same purpose.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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What is the difference between normal bolts and high friction grip bolts?

High friction grip bolts are commonly used in structural steelwork. They normally consist of high tensile strength bolts and nuts with washers. The bolts are tightened to a shank tension so that the transverse load across the joint is resisted by the friction between the plated rather than the bolt shank’s shear strength.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Filed under Steelworks | 2 Comments

What is the difference between fasteners, bolts and screws?

Fastener is a general term to describe something which is used as a restraint for holding things together or attaching to other things.

The main physical distinction between screws and bolts is that screws are entirely full of threads while bolts contain shanks without threads. However, a better interpretation of the differences between the two is that bolts are always fitted with nuts. On the contrary, screws are normally used with tapped holes.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Filed under Steelworks | 1 Comment