General Design Principles MCQ Quiz - Objective Question with Answer for General Design Principles - Download Free PDF

Explanation:

1. Plate girders are beams fabricated using rolled plates that are welded or bolted together to form a beam.
2. These girders are often used in large structures like bridges or buildings where the span is long and the loads are significant.
3. The plates used in the fabrication of plate girders are usually made of steel and are shaped to form the web and flanges of the girder.

 Additional Information

1. Castellated beams: These are beams that are created by cutting a regular beam (usually an I-beam) in a pattern and then reassembling it to form a beam with an enlarged web, which helps reduce weight and increase the depth of the beam for larger spans.

2. Hybrid beams: Hybrid beams combine two or more materials, such as steel and concrete, to take advantage of the benefits of both materials.

3. Composite beams: These beams combine two materials, typically steel and concrete, where the concrete works in compression and the steel works in tension, offering better load distribution and efficiency.

Explanation:

As per IS 800:2007, for steel structures:

• When a column is subjected to axial compression and bending, the maximum permissible slenderness ratio is 180.

This limit ensures the stability and safety of compression members under combined stresses and helps to prevent buckling.

Additional InformationOther Slenderness Ratio Limits (for context):

• 250 – For members subjected to axial tension.

• 350 – For members under compression resulting from wind or earthquake forces only (temporary loads).

• 180 – For columns under combined axial compression and bending (as in this question).

Concept-

Beam, column, channel, and angle sections are classified as follows:

Beams

a) Indian Standard junior beams (ISJB)

b) Indian Standard light weight beams (ISLB)

c) Indian Standard medium weight beams (ISMB)

d) Indian Standard wide flange beams (ISWB)

Columns/Heavy Weight Beams

a) Indian Standard column sections (ISSC)

b) Indian Standard heavyweight beam (ISHB)

Channels

a) Indian Standard junior channels (ISJC)

b) Indian Standard lightweight channels (ISLC)

c) Indian Standard medium weight channels (ISMC)

d) Indian Standard medium weight parallel flange channels (ISMCP)

Angles

a) Indian Standard equal leg angles (ISA)

b) Indian Standard unequal leg angles (ISA)

Explanation:

Statement 1:

"The maximum slenderness ratio shall not exceed 350 for a member subjected to compression forces resulting only from combination with wind/earthquake..."

• IS 800:2007 Table 3, Sl. No. iii clearly states:
  ➤ Limit is 250, not 350.

Hence, this statement is INCORRECT.

Statement 2:

"Tension members, such as bracings, pre-tensioned to avoid sag, need not satisfy slenderness ratio limits."

• Confirmed by Note (1) below the table:
  ➤ Such members are exempted from the slenderness ratio limit.

Correct

Statement 3:

"The maximum slenderness ratio shall not exceed 300 for a compression flange of a beam against lateral torsional buckling."

• IS 800:2007 Table 3, Sl. No. iv
  ➤ Confirmed as 300.

Correct

Statement 4:

"The maximum slenderness ratio shall not exceed 180 for a member carrying compressive loads from dead and imposed loads."

• IS 800:2007 Table 3, Sl. No. i
  ➤ Value is 180.

Correct

Explanation:

As per IS 800

Table 17: Constants \( \alpha_1 \) and \( \alpha_2 \) (Clause 9.3.1.1)

NOTE: \( n = N/N_d \)

Concept:

According to clause no. 11.1.4 of IS 800: 2007, when the effect of wind or earthquake load is taken into account, the permissible stress as specified in rivets (or in anchor bolts) may be increased by 25%.

Confusion/Mistake Point:

Explanation:

As per IS 800:2007, Clause No. 5.6.1:

• Supported by elastic cladding, deflection is limited to Span/120.
• Supported by brittle cladding, deflection is limited to Span/150.

The maximum vertical deflection for simply supported beam:

• Supported by elastic cladding, deflection is limited to Span/240.
• Supported by brittle cladding, deflection is limited to Span/300.
• Max deflection < L/325 of the span in general

As per IS 456:2000, Clause 23.2:

The deflection shall generally be limited to the following:

• The final deflection due to all loads including the effects of temperature, creep, and shrinkage and measured from the as-cast level of the supports of floors, roofs, and all other horizontal members, should not normally exceed span/250.
• The deflection including the effects of temperature, creep and shrinkage occurring after the erection of partitions and the application of finishes should not normally exceed span/350 or 20 mm whichever is less.

Explanation:

Maximum permissible deflection in simply supported steel beam other than industrial building is given by = \(\frac{1}{{300}} \times {\bf{Span}}\)

Some of the reason for limiting deflection is:

• Excessive deflection may create problems for floor or roof drainage.
• Excessive deflection may lead to crack in the plaster of ceilings & may damage the material attached to or supported by the beam.
• There may cause undesirable twisting and distortion of connections and connected materials.

Confusion Points

325 is as per IS 800: 1984, Question is asking as per IS 800: 2007, according to which 300 is the correct answer.

Concept:

As per IS 800:2007, Clause No. 5.6.1

a) Supported by elastic cladding, deflection is limited to Span/120.

b) Supported by brittle cladding, deflection is limited to Span/150.

Calculation:

Span of beam = 5 m = 5000 mm

Vertical Deflection = 5000/150 =  33.33 mm

Additional InformationThe maximum vertical deflection for simply supported beam:

a) Supported by elastic cladding, deflection is limited to Span/240.

b) Supported by brittle cladding, deflection is limited to Span/300.

c) Max deflection < L/325 of the span in general

Vertical Deflection limits for industrial buildings as per IS 800:2007 are:

a) For Purlins and Girts subjected to live load/wind load supported on elastic cladding, maximum deflection is limited to span / 150.

b) For Purlins and Girts subjected to live load/wind load supported on Brittle cladding, maximum deflection is limited to span / 180.

Calculation:

∴ Permissible maximum deflection = Span/150 = 4500/150 = 30 mm

Explanation:

As per IS 800:2007, Table 5, Partial safety factors for materials are given as:

(i) When resistance is governed by ultimate stress, γ_m1 = 1.25

(ii) When resistance is governed by yielding, γ_mo = 1.1

(iii) Resistance of member to buckling,γmo = 1.1

(iv) Resistance of connection:

• Bolts-Friction Type or Rivets = 1.25
• Welds = 1.25 (shop fabrications) and 1.5 (Field fabrications)

Types of beam connection: Two or more beams at a junction are connected each other using either flange or web clips.

Framed Connection: Framed connection are usually connected through web cleats only as shown in the figure below:

Stiffened and unstiffened beam seated connections are depicted in the figure below:

It can be clearly observed, the unstiffened connection requires flange cleat only, and an additional connecting member is used for stiffened connection.

Concept:

As per IS 800: 2007 

1. Design strength due to yielding of Gross section.

2. Design strength due to Rupture of Net Section.

As per table 5 of IS 800:2007 partial safety for different mode of failure is given below-

Concept:

Factor of safety (FOS) = Ultimate stress / Working stress

Calculation:

Given,

Ultimate stress = 472 MN/m²

FOS = Ultimate stress / Working stress

Working stress = 472 / 5 = 94.4 MN/m²

Concept:

Following are the specifications for steel member exposed to weather:

• When the steelwork is directly exposed to weather and is fully accessible for cleaning and repainting the thickness shall not be less than 6 mm.
• When the steelwork directly exposed to weather and is not accessible for cleaning and repainting the thickness shall not be less than 8 mm.
• When the steelwork is not directly exposed to weather, the thickness of steel in main members shall not be less than 6 mm.
• When the steelwork is not directly exposed to weather, the thickness of steel in secondary members shall not be less than 6 mm.