Plate Girder MCQ Quiz in తెలుగు - Objective Question with Answer for Plate Girder - ముఫ్త్ [PDF] డౌన్‌లోడ్ కరెన్

Explanation:

Plate girder: 

• A plate girder is a built-up I-beam section, used to carry heavy loads which cannot be carried economically by rolled I-sections.
• It is made by riveting or welding the steel plates in an I-beam shape.

The optimum thickness for the web (tw)

\( t_w = \left [ \frac{M_z{}}{f_y{k^{2}}} \right ]^{0.33}\)

Depth of web (d)

d = \(\left [ \frac{M_z{k}}{f_y{}} \right ]^{0.33}\)

Where, tw = Optimum thickness of the web, Mz = Moment applied to the flanges, fy = Design strength of the flanges, k = Slenderness ratio of the web = \(\frac{d}{t_w{}}\)

d = Depth of web

Concept:

Stiffeners

• When the web of the plate girder is not sufficient enough to carry the loads. In that case, stiffeners are provided which perform certain specific functions which are discussed below.

In general, there are only two types of stiffener viz. intermediate stiffener and bearing stiffener but as per IS 800:2007 the following types of stiffeners are identified based on the purpose for which a stiffener is being used:

(a) Intermediate and longitudinal stiffener:

• To improve the buckling strength of a slender web due to shear.

(b) Load carrying stiffener:

• To prevent web buckling due to concentrated load.

(c) Bearing stiffener:

• To prevent local crushing of the web due to concentrated loads or reactions.

(d) Torsional stiffener:

• To provide lateral restraint to beams and girders at support.

(e) Diagonal stiffener:

• To provide a sort of local reinforcement to web under shear and bearing.

(f) Tension stiffener:

• To transfer tensile forces applied to the web through a flange.

Concept:

Economical depth of Plate Girder as per Working Stress Method is given by

\(d = 1.1 \times \sqrt {\frac{M}{{\sigma \times {t_w}}}} \)

Note:

If the depth of girder is less than 750 mm, it is called shallow plate girder.

If the depth of girder is more than 750 mm, it is called deep plate girder.

Concept:

Design of End Bearing stiffner:

(i) They are designed as imaginary column with both ends fixed whose effective length is 0.7L.

(ii) Since they are designed as column, the ends of bearing stiffner should have tight bearing stiffner between the flange angle so they can act as a column.

(iii) The cross sectional area of the imaginary column is taken as the cross-sectional area of the outstand leg of bearinf stiffner and web area whose length is 40t_w as shown in figure.

A_g = 4 × outstand leg area + Web area = 4 × outstand leg area + (40t_w).t_w 

(iv) If flats are used as bearing stiffner, then the cross-sectional area of the imaginary column or effective area of bearing stiffner is given by.

A_g = 2 × flat area + web area = 2 × flat area + (40t_w).t_w

Calculation:

Here flats are used as bearing

So, A_g = 2 × flat area + web area = 2 × (100 × 5) + (40 × 10) × 10 = 5000 mm²

Explanation:

Horizontal stiffeners are to resist web compression buckling at a distance not greater than 1.5d and not less than 0.33d [d = depth of web].

Horizontal stiffeners are also called longitudinal stiffeners these increase buckling resistance and provided in the compression zone of the web. So for a cantilever plate girder, horizontal stiffeners are provided below the neutral axis.

Transverse Stiffeners/Vertical Stiffeners are provided to increase buckling resistance of the web due to shear; it is provided vertically along the span.

Note:

Horizontal Stiffener / Longitudinal Stiffener is designed to prevent web buckling due to bending compression.

Explanation:

The main purpose of stiffener in a plate girder is to prevent buckling of web. In which different type of stiffeners are used

According to IS 800: 2007, different type of stiffeners are:

1) Intermediate transverse stiffener:

To improve the buckling strength of slender web due to shear

2) Load carrying stiffener:

To prevent local buckling of the web due to concentrated loading

3) Bearing stiffener:

To prevent local crushing of the web due to concentrated loading

4) Torsion stiffener:

To provide torsional restrained to beams and girders at supports

5) Diagonal stiffeners:

To provide local reinforcement to web under shear and bending

Explanation:

• Intermediate transverse stiffeners or vertical stiffeners are provided to stiffen the web and prevent shear buckling.
• Longitudinal stiffeners or horizontal stiffeners are used to increase buckling resistance under bending.

Plate Girder: A plate girder is a built-up I-beam section, used to carry heavy loads which cannot be carried economically by rolled I-sections. It is made by riveting or welding the steel plates in the I-beam shape. It has only one web which is continuous throughout the length of a plate girder.

A box girder comprises two concrete slabs — top and bottom. The slabs are connected by an array of vertical bridge stems, also known as webs. These webs can be vertical or inclined, as per requirement. They are formed by joining two web plates by a common flange at both ends and they many intermediate web plates which makes a closed cell that has enough strength and torsional stiffness than that of an open section.

Gantry Girder:  Gantry Girder is similar to Plate girder in shape-wise but there capacities and usage are different according to the different elements connected. Gantry girders are laterally unsupported beams to carry heavy loads from place to place at the construction sites. The gantry girders are used to support the loads that are transmitted through the traveling wheels of the crane in factories and workshops

Explanation:

• Intermediate transverse stiffeners or vertical stiffeners are provided to stiffen the web and prevent shear buckling.
• Longitudinal stiffeners or horizontal stiffeners are used to increase buckling resistance under bending.