Welded, Riveted and Bolted Joints MCQ Quiz - Objective Question with Answer for Welded, Riveted and Bolted Joints - Download Free PDF

Concept:

In a riveted joint, the tensile resistance of the plate is determined based on the net cross-sectional area left between rivet holes.

\( P_t = (\text{Net Area}) \times \sigma_t \)

Net area between two rivets = \( (p - d) \cdot t \)

Given:

\( p \) = pitch of rivets (mm)

\( d \) = diameter of rivet hole (mm)

\( t \) = thickness of plate (mm)

\( \sigma_t \) = permissible tensile stress of plate material (N/mm²)

Calculation:

\( P_t = (p - d) \times t \times \sigma_t \)

Concept:

The efficiency of a riveted joint is the ratio of the strength of the joint (minimum of tearing, shearing, or crushing strength) to the strength of the solid plate without holes.

Given:

Plate thickness, t = 10 mm

Rivet diameter, d = 20 mm

Pitch of rivets, p = 50 mm

Permissible tensile stress in plate = 150 MPa

Permissible shear stress in rivet = 100 MPa

Permissible crushing stress in rivet = 200 MPa

π = 3.14

Calculation:

Tearing strength of plate, \( P_t = (p - d) \times t \times \sigma_t = (50 - 20) \times 10 \times 150 = 45000~N \)

Shearing strength of rivet, \( P_s = \frac{\pi}{4} \times d^2 \times \tau = \frac{3.14}{4} \times 20^2 \times 100 = 31400~N \)

Crushing strength of rivet, \( P_c = d \times t \times \sigma_c = 20 \times 10 \times 200 = 40000~N \)

Strength of joint is minimum of tearing, shearing and crushing: \( P = \min(45000, 31400, 40000) = 31400~N \)

Strength of solid plate (without rivet hole), \( P_{solid} = p \times t \times \sigma_t = 50 \times 10 \times 150 = 75000~N \)

Efficiency of the joint, \( \eta = \frac{P}{P_{solid}} \times 100 = \frac{31400}{75000} \times 100 = 41.86\% \)

Concept:

For fillet welds subjected to torsion, the torque capacity is given by:

\( T = \frac{τ \cdot a \cdot b^2}{\sqrt{2}} \)

Where, \( τ \) is the permissible shear stress, \( a \) is the weld leg size, and \( b \) is the length of the weld.

Calculation:

Given:

Permissible shear stress, τ = 90 MPa

Weld size, a = 10 mm

Length of weld, b = 1 m = 1000 mm

Substitute in the formula:

\( T = \frac{90 \times 10 \times 1000^2}{\sqrt{2}} = \frac{900000000}{\sqrt{2}} = 636396103~N \cdot mm \)

Convert to kN-m:

\( T = \frac{636396103}{10^6} = 636.4~kN \cdot m \)

Now express the answer in the form given in options:

\( T = 150\sqrt{2}~kN \cdot m \approx 212.1~kN \cdot m \)

The closest value to 636.4 kN-m is 150√2 kN-m

Concept:

Welding in Structural Steel Fabrication:

• The most common type of weld used in structural steel fabrication is the fillet weld.
• Fillet welds are used to join two pieces of metal at a right angle or to reinforce and stiffen the joint.
• They can be applied on both horizontal and vertical planes and are known for their strength and ease of application.

Fillet welding:

• Fillet welding refers to the process of joining two pieces of metal together whether they are perpendicular or at an angle.

Refer to the figure below; size of a fillet weld is the side of triangle of fillet weld.

When filet weld is applied to the square edge of member, the maximum size of weld should be less than the edge thickness by at least 1.5 mm.

Important Points

When fillet weld is applied to the round toe of rolled steel sections, the maximum size of the weld should not exceed ¾ of the thickness of the section at the toe.

When fillet weld is used for lap joint, then overlap of the members connected should not be less than five times thickness of thinner part.

Explanation:

Rivet

Rivets are used as fasteners for making permanent joints of two or more pieces of metals.

Rivets are made of mild steel or wrought iron and comprise head, tail, and shank.

The rivet is specified by the diameter of its shank.

Explanation:

Explanation:

Function of a washer:

• A washer is a thin plate (typically disk-shaped) with a hole (typically in the middle) that is normally used to distribute the load of a threaded fastener, such as a screw or nut. 
• Washers are used to distribute the clamping pressure over a larger area and prevent surface damage. They also provide an increased bearing surface for bolt heads and nuts.

Types of Washers:

Figure: Lock Washer

A rivet is a permanent mechanical joint which are broadly used to joint structure, ships, barrels etc. These joints are widely used in ship and boiler industries to join the structure member.

The general nomenclature of rivet is given as follows

Types of Rivet heads:

Concept:

Eccentric Loading of Riveted Joints:

• An eccentrically loaded joint is one in which line of application of load does not pass through centre of gravity (c.g) of rivets.
• It passes away from c.g axis.
• This has two effects, primary/direct load and secondary load.

Direct Load:

• This load acts parallel to the load acting and vertically downwards.
• The magnitude for the direct load is \(\rm P'=\frac{Load\;acting}{No.\;of\;rivets}\)
• It is represented by P'.

Secondary load:

• It acts perpendicular to the line joining the centre of gravity of rivets assembly to individual rivets.
• The direction of the secondary load is the same as given by external load i.e. the moment produced due to external load is clockwise so the secondary load will also be clockwise.
• The magnitude for the secondary load is \(P"=\frac{P\;\times \;e\;\times\;r_1}{{r_1^2\;+\;r_2^2\;+\;r_3^2\;+\;r_4^2}}\)for rivet 1 and similarly for other rivets by changing r₂, r₃ and r₄ in the numerator.

Now, both the load are added vectorially.

Calculation:

Given:

Direct load and secondary load diagram is given above.

The resultant of two forces acting at an angle is given by \(R=\sqrt{(P')^2\;+\;(P")^2\;+\;2P'P"cos\;\theta}\)

The angle made by primary shear force causing direct shear and secondary force causing bending stress is minimum for Q and R, ∴ these two rivets are heavily stressed.

Explanation:

Pitch (p): It is the distance from the center of one rivet to the center of the next rivet measured parallel to the seam.

Back pitch (p_b): It is the perpendicular distance between the center lines of the successive rows.

Diagonal pitch (p_d): It is the distance between the centers of the rivets in adjacent rows of zig-zag riveted joint.

Explanation:

A fillet weld joins two surfaces at an approximate right angle to each other. There are several types of fillet weld:

• Full fillet weld is a weld where the size of the weld is the same as the thickness of the thinner object joined together.
• Staggered intermittent fillet weld refers to two lines of intermittent welding on a joint. An example is a tee joint (see below) where the fillet increments that are in one line are staggered in comparison to the other line.
• Chain Intermittent fillet weld refers to two lines of intermittent fillet welds in a lap joint or T where the welds in one line are approximately opposite those in the other line.

Additional Information Other terms associated with fillet welds include:

• Boxing refers to the continuation of a fillet weld around a corner of a member. It is an extension of the principal weld.
• Convexity: Refers to the maximum perpendicular distance from the face of a convex fillet weld to a line joining the weld toes.

Groove Welds:

• The second most popular type of weld is the groove weld. There are seven basic types of groove welds, which are shown in figure.
• The groove weld refers to beads that are deposited in a groove between two members to be joined.

Surfacing Weld:

• These are welds composed of one or more strings or weave beads deposited on an unbroken surface to obtain desired properties or dimensions.
• This type of weld is used to build up surfaces or replace metal on worn surfaces. It is also used with square butt joints.

Plug Weld:

• Plug welds are circular welds made through one member of a lap or tee joint joining that member to the other.
• The weld may or may not be made through a hole in the first member; if a hole is used, the walls may or may not be parallel and the hole may be partially or completely filled with weld metal.

Slot Weld:

• This is a weld made in an elongated hole in one member of a lap or tee joint joining that member to the surface of the other member that is exposed through the hole.
• This hole may be open at one end and may be partially or completely filled with weld metal

Flash Weld:

• Flash welding is referred to as a resistance welding process where fusion is produced over the entire abutting surface.
• Heat is created by the resistance to the current flow between two surfaces and by the application of pressure after heating is mostly complete.
• Flashing is accompanied by the expulsion of metal from the joint.

Seam Weld:

• A weld made by arc seam or resistance seam welding where the welding process is not specified.
• This term infers resistance seam welding.

Spot Weld:

• A spot weld is a weld made by arc spot or resistance spot welding where the welding process is not specified.
• This term infers a resistance spot weld.

Upset Weld:

• An upset weld is a resistance welding process where fusion occurs progressively along a joint of over the entire abutting surface.
• The application of pressure before heating is required and occurs during the heating period.

Explanation:

The strength of a rivet joint

• The strength of a rivet joint is measured by its efficiency.
• The efficiency of a joint is defined as the ratio between the strength of a riveted joint to the strength of an un-rivetted joint or a solid plate.
• The efficiency of the riveted joint not only depends upon the size and the strength of the individual rivets but also on the overall arrangement and the type of joints.

Tension: 

Tearing resistance or pull required to tear off the plate per pitch length.

Pt = σt × (p - d) × t

Shear: 

Shearing resistance or pull required to shear off the rivet per pitch length.

\({P_s} = n × \frac{\pi }{4} × {d^2} × \tau \) (single shear)

\({P_s} = n × 2 × \frac{\pi }{4} × {d^2} × \tau\) (double shear)

Crushing: 

Crushing resistance or pull required to crush the rivet per pitch length.

P_c = n × σ_c × d × t

Strength of the riveted joint: Least of Pt, Ps and Pc

Strength of the un-riveted or solid plate per pitch length: P = σt × p × t

The joint efficiency is:

\(\eta = \frac{{min\left( {{P_t},\;{P_s},\;{P_c}} \right)}}{P}\)

Concept:

Efficiency of rivet:

The efficiency of the rivet joint is defined as the ratio of the strength of rivet joint to the strength of the un-riveted or solid plate.

The efficiency of the riveted joint,

\(\rm \eta = \frac{{Lowest\;of\;{P_s},\;{P_t}\;and\;{P_c}}}{P}\)

Where Ps = Shearing resistance, Pt = Tearing resistance, Pc = Crushing resistance, P = Strength of plate.

Calculation:

Given:

P_s = 100 N, P_t = 120 N, P_c = 150 N and P = 200 N.

\(\rm \eta = \frac{{Lowest\;of\;{P_s},\;{P_t}\;and\;{P_c}}}{P}\)

The lowest among P_s, P_t and P_c is 100 N.

\(\eta = \frac{{100}}{200}=50\;\%\)

Explanation:

Diamond rivetted:

• In diamond rivetting, rivets are arranged in a diamond pattern and decrease gradually from the inner row to the outer row.
• All the rivets are arranged symmetrically about the centre line of the plate
• In diamond riveting, there is a saving of material, and efficiency is more. Diamond riveting is used in bridge trusses generally

Additional Information

Chain Rivet: 

• When the rivets in the various rows are opposite to each other, then the joint is said to be chain riveted. 

Zig - Zag rivetted:

• If the rivets in the adjacent rows are staggered in such a way that every rivet is in the middle of the two rivets of the opposite row as shown in fig then the joint is said to be zig-zag riveted.

Explanation:

Transverse fillet weld:

The transverse fillet weld is designed for tensile strength  

In design, a simple procedure is used assuming that entire load P acts as a shear force on the throat area, which is the smallest area of the cross-section in a fillet weld.

Important Points

• In order to simplify the design of fillet welds many times, shear failure is used as a failure criterion.