Bolted Connections MCQ Quiz in বাংলা - Objective Question with Answer for Bolted Connections - বিনামূল্যে ডাউনলোড করুন [PDF]

Pitch: It’s the centre to centre spacing of bolts in a row, measured in the direction of the load.

Gauge: It is the distance between two adjacent bolt rows, measured right angle to the direction of load.

It should satisfy requirements specified in clause 10.2, IS 800: 2007, regarding spacing, such as

1) Pitch shall not be less than 2.5 × d (d is the diameter of bolt)

Critical section for Cover Plate:

The cross-sectional area of the plate through various sections.

Let the width of the plate be ‘b’, the thickness of plate ‘t’ and diameter of the hole be ‘d_h’

For section 1-1: A_{section 1-1} = (b – 3 d_h) × t

For section 2-2: A_{section 2-2} = (b – 2 d_h) × t

For section 3-3: A_{section 3-3} = (b – 1 d_h) × t

∴ Critical section for the cover plate is section 1-1 as the cross-sectional area is least.

Critical section for Main Plate:

Explanation:

Permissible tensile stresses in bolts used for column bases is 120 N/mm2. 

Additional Information

Concept:

Efficiency = (strength of bolt per pitch length / strength of plate per pitch length) x100 

Calculation:

Strength of bolt per pitch length = 55 kN

Strength of plate per pitch length is 120 kN

Efficiency = (strength of bolt per pitch length / strength of plate per pitch length) × 100 

η = (55 / 120) × 100 = 45.83 %

In the moment resisting connections, bolts will be required to transfer the load by direct tension. These are called prying forces and these are developed due to flexibility of end plate connections.

Shear lag is the non-uniform straining of member due to tension and it occurs when action and reaction do not pass through the centre of gravity of cross section.

If the steel is stressed into the inelastic range and then unloaded, then subjected to uniform compression in the opposite direction, it is found that and the stress-strain curve becomes nonlinear at a stress much lower than the initial yield strength. This is called Bauschinger effect.

It is assumed that bolts share applied axial load equally while designing bolted connection but in case of long joints, end bolts will take more load than inner bolts. So, failure of bolt in long joints is sequential (one after another), starting with outer bolts and progressing towards centre. This is called unbuttoning.

Explanation:

Pitch and gauge:

The distance between the centers of rivet holes measured along the applied stress is known as Pitch, whereas the distance the center of rivet holes measured perpendicular to the direction of the applied stress is known as Gauge.

As per IS 800, the minimum pitch specified is 2.5 times the nominal diameter of rivet.

Explanation:

Oversized holes:

1. The oversize hole shall not exceed 1.25 d or (d + 8) mm in diameter, where d is the nominal diameter of the bolt in mm.
2. A short slotted hole shall not exceed the appropriate hole size in width and 1.33 d in length, where d is the nominal diameter of the bolt in mm.
3. A long slotted hole shall not exceed the appropriate hole size in width and 2.5 d in length, where d is the nominal diameter of the bolt in mm.

Note:

1. The recommended size of Bolt/Rivet Hole diameter is given below:

Concept-

The design strength of a tension member is based on two limit states-

(a) Limit state based on the yield strength of the member due to its large elongation.

(b) Limit state based on the ultimate strength of the member.

The design strength of a tension member is the minimum of the following:

a) Design strength due to yielding of the gross section (Tdg)-

In this type of failure wherein yielding of the gross section occurs there a significant amount of deformation occurs before the material actually gets fractured. This significant amount of deformation makes the structure unserviceable.

b) Rupture strength of the critical section (Tdn)-

When the net section of the member reaches the ultimate stress, then rupture (or fracture) of the member takes place.

c) Block shear strength (Tdb)-

Here a segment of the block of the material at the corner of the connection shears out due to possible high bearing strength of steel and high strength of bolts.

In a steel plate with bolted connection, the rupture of the net section is a mode of failure under tension.

Additional Information

Concept:

Primary stresses are mainly force driven and are caused by imposed mechanical loading on the structure and excessive primary stress causes yielding and plastic deformation of the material. They are not self limiting. e.g Dead and Live load on a cantilever beam etc.

Secondary stresses are mainly displacement driven and are caused due to geometric discontinuity and stress concentration. They are self limiting and beyond a certain stage the stresses begin to decrease. e.g Thermal loads, Eccentric loads etc.

Eccentric connection: If the applied forces do not pass through the C.G of joint, it causes an additional moment about the C.G and these types of connections are called eccentric connections.

The stresses induced due to these eccentric connections are known as secondary stresses because they arise due to geometric dissimilarity.

Here eccentricity ‘e’ introduces a moment Pe and secondary stresses are generated consequently.'

Eccentric connection in lap joint

Here also secondary stresses are generated due to eccentricity in connections.

Concept:

Specification for the pitch of bolts or rivets

1. Minimum pitch and minimum gauge length

• P = 2.5 × nominal diameter of the bolt

2. Minimum end and edge distance

• emin = 1.5 × diameter of the bolt hole      ....... (for machine cut element)
• emin = 1.7 × diameter of the bolt hole      ....... (for hand-cut element)

3. Maximum end and edge distance

• emax = 12 × t × ϵ 
• Where, ϵ \(= \sqrt {\frac{{250}}{{{f_y}}}} \), fy = yield stress and t = thickness of thinner plate.

4. The maximum pitch of bolts or rivets or welds in the compression zone 

Pmax = minimum { 12 × t or 200 mm }     ....... (For compression zone)

Where, t = thickness of the thinner plate

5. The maximum pitch of bolts or rivets or welds in the tension zone

Pmax = minimum { 16 × t or 200 mm }     ....... (For tension zone)

Where, t = thickness of the thinner plate