Riveted Joint MCQ Quiz - Objective Question with Answer for Riveted Joint - 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, \( \eta = \frac{P}{P_{solid}} \times 100 = \frac{31400}{75000} \times 100 = 41.86\% \)

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:

Efficiency of Riveted Joints

• In the context of riveted joints, the term "efficiency of the joint" refers to the ratio of the strength of the riveted joint to the strength of an unriveted plate of the same material and dimensions. This efficiency is an important measure as it indicates how much of the original strength of the plate is retained after riveting.

The efficiency of a riveted joint can be calculated using the formula:

Efficiency = (Strength of Riveted Joint / Strength of Unriveted Plate) × 100%

Where:

• Strength of Riveted Joint: This is the maximum load that the riveted joint can withstand without failing.
• Strength of Unriveted Plate: This is the maximum load that the original plate, without any rivets, can withstand.

The efficiency is usually expressed as a percentage and it helps in determining the effectiveness of the riveted joint in maintaining the structural integrity of the plate.

Factors Affecting Efficiency:

• Type of Rivet and Material: The type of rivet used and the material of both the rivet and the plate can significantly impact the joint's efficiency.
• Riveting Process: The method and quality of the riveting process, including factors like the precision of hole alignment and the degree of tightness, play a crucial role in joint efficiency.
• Configuration of Rivets: The arrangement and number of rivets, such as single row, double row, or zigzag patterns, affect the load distribution and thereby the efficiency.
• Plate Thickness: The thickness of the plate being riveted can also influence the joint's efficiency, with thicker plates potentially providing better load distribution.

Concept:

Strength of Rivet in Bearing

Pb = fb × d' × t

Where P_b = bearing strength of rivet, f_b = permissible bearing stress in rivet, d' = dia of hole or gross dia of rivet, and t = thickness of plate.

Calculation:

Given

Joint is a single riveted lap joint

Thickness of plate (t) = 10 mm

Diameter of rivet (d) = 20 mm

Bearing stress (f_b) = 150 MPa

Bearing strength of rivet (P_b) = f_b × d' × t

where d' = d + 1.5 mm (d = 20 mm < 25 mm)

d' = 21.5 mm

Bearing strength of rivet (Pb) = 150 × 21.5 × 10 = 32250 N or 32.25 kN

Bearing strength of rivet (Pb) = 32.25 kN

The calculated value of the bearing strength of the rivet is very close to the option (3) value. Hence option (3) is correct.

Explanation:

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:

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.

Explanation:

The Snap Heads are usually employed for structural work and machine riveting and for boiler shell.

The Counter sunk heads are mainly used for ship building where flush surface are necessary.

The Conical heads are mainly used in case of hand hammering.

Welding is the process of joining two pieces of metal by creating a strong metallurgical bond between them by heating or pressure or both. Generally welded joints are stronger than the base metal, thereby placing no restriction on the joints.