Test: Steel Design- 2 - SSC JE MCQ

The effective length of the weld is the length of the weld for which specified size and throat thickness exist. In drawings only effective length is shown, while welding length made equal to effective length plus twice the size of the weld.

Effective length should not be less than 4 times the size of weld.

According to Unwin’s formula,

The nominal diameter (ɸ) of rivet is given by:

ɸ = 6.01√t

where,

t = thickness of plate in “mm”

As per I.S: 800-1984, the thickness of the web plate should not be less than the following as appropriate:

 for unstiffened web.

(ii) 1/180 of smallest clear panel dimension and   for vertically stiffened web.

(iii) 1/180 of the smaller dimension in each panel and   for webs stiffened both vertically and horizontally with a horizontal stiffener at a distance from the compression flange equal to 2/5^th of the distance from the compression flange to the neutral axis.

(iv) 1/180 smaller clear panel dimension and   when there is also a horizontal stiffener at the neutral axis, where d₂ is twice the clear distance from the compression flange angles, or plate or tongue plate to the neutral axis.

Followings are the assumptions in the design of riveted connections:

i) Load is assumed to be uniformly distributed among all the rivets.

ii) Stress in plate is assumed to be uniform.

iii) Shear stress is assumed to be uniformly distributed over the gross area of rivets.

iv) Bearing stress is assumed to be uniform between the contact surfaces of plate and rivet.

v) Bending stress in rivet is neglected.

vi) Rivet hole is assumed to be completely filled by the rivet.

vii) Friction between plates is neglected.

Two rolled steel sections are connected to each other by lacing, battening, tie plates etc. Lacings (and even battens) are not the load carrying members, they are basically provided so that two columns which they attach work as single entity.

i) Lacing is generally preferred in case of eccentric loads. Flat bars are generally used for lacing. Angles, channels and tubular sections are also used for lacing of very heavily columns.

ii) Battening is normally used for axially loaded columns and in sections where the components are not far apart. Plates are used for battens.

According to IS 875: Part 3

Buildings with medium and large openings - Buildings with medium and large openings may also exhibit either positive or negative internal pressure depending upon the direction of wind.

Buildings with medium openings between about 5 to 20 percent of wall area shall be examined for an internal pressure coefficient of +0.5 and later with an internal pressure coefficient of -0.5, and the analysis which produces greater distress of the members shall be adopted.

Buildings with large openings, that is, openings larger than 20 percent of the wall area shall be examined once with an internal pressure coefficient of -0.7 and again with an internal pressure coefficient of -0.7, and the analysis which produces greater distress on the members shall be adopted.

Impact factor is given by:

Where,

L = span

i.e, Impact factor lies between 0.5 and 1.0

Moment of inertia of Built-up plate girder is given by:

Where,

I_b = is the moment of the inertia of the rolled beam section

A_p = is the area of the cover plates in one flange

h = is the distance between the centroid of the top and bottom flange plates

Fillet weld is provided to square edges, the weld size should be at least 1.5 mm less than the edge thickness (i.e Thickness of thinner member – 1.5 mm)

For the rounded toe of a rolled section, the weld size should not exceed ¾ thickness of the section at the toe (i.e = 3/4^th thickness of rolled section at toe)

(i) Total transverse shear (V) = 2.5% axial load.

(ii) Slenderness ration of lacing bars ≯ 145

(iii) For both single lacing and double lacing, effective length of lacing is taken as the distance between inner rivets.

The minimum radius of gyration, 

As per IS 800:2007, clause 11.3.3 the permissible bending stress in column base is 0.66 f_y.

So, permissible bending stress is 0.66 x 415= 273.9 MPa

High concentrated loads create large bearing stress concentration at the junction of web and flange. The web near the portion of stress concentration tends to fold over the flange. This type of local buckling phenomenon is called as web crippling. The rot of the fillet weld is critical section for web crippling.