What are stiffeners in a plate girder mainly used for?

Preventing buckling of the thin web and carrying concentrated loads

Connecting the flange to the web

Where is a longitudinal stiffener placed and why?

Along the span about 0.2d from the compression flange, to prevent bend-buckling of a very slender web

At supports, to carry the reaction

At the tension flange, to prevent yielding

Across the web at spacing c, to allow tension-field action

What does a load-carrying (bearing) stiffener do?

Transfers a concentrated load or reaction into the web without crushing or buckling it

Only increases shear buckling strength between supports

2073 Bhadra · 5 marks

Stiffeners in plate girder: types and function

Short answer

Stiffeners prevent web buckling and transfer loads. Intermediate transverse stiffeners increase shear buckling resistance; load-carrying stiffeners transfer concentrated loads/reactions; longitudinal stiffeners resist flexural compression buckling; end bearing stiffeners carry support reactions. Designed per IS 800 cl. 8.7.

Describe use of stiffeners in plate girder with their types and function.

Stiffeners are plates or angles welded or bolted to the web of a plate girder to prevent the thin web from buckling and to carry concentrated loads (IS 800:2007 cl. 8.7).

Types and functions

Type	Where placed	Function
Intermediate transverse stiffener	Across the web at spacing $c$	Raises the shear buckling strength (allows tension-field action) and reduces the effective slenderness of the web panel
Load-carrying (bearing) stiffener	Under concentrated loads and at supports	Transfers the reaction or load into the web without crushing or buckling of the web
Longitudinal stiffener	Along the span, about $0.2d$ from the compression flange	Prevents bend-buckling of a deep web under flexural compression; used when $d/t_w$ is very large
End (bearing) stiffener	At the support	Carries the end reaction, acting like a short column together with a part of the web
Torsion stiffener	At the supports	Provides torsional restraint and prevents distortion of the section

  +-----------------------------+
  |   |    |    |    |    |     |   | = intermediate stiffeners
  |   |    |    |    |    |     |
  +-----------------------------+
  ^ end bearing stiffeners at supports

Main design rules (IS 800:2007)

Outstand of a stiffener from the web $\le 20\varepsilon t_s$ (cl. 8.7.1.2); if it exceeds $14\varepsilon t_s$ , only a core section with an outstand of $14\varepsilon t_s$ is taken as effective. This prevents local buckling of the stiffener.
Spacing of intermediate stiffeners is limited by the web slenderness; the web needs no transverse stiffener where $d/t_w \le 200\varepsilon$ (with limits in cl. 8.6.1 for closer spacing).
Minimum moment of inertia (cl. 8.7.2.4): $I_s \ge 1.5d^3t_w^3/c^2$ when $c < \sqrt2d$ , and $I_s \ge 0.75dt_w^3$ when $c \ge \sqrt2d$ , taken about the web axis for stiffeners on one or both sides.
Load-carrying stiffeners must be checked for buckling resistance (curve c, effective length $0.7L$ if the flange is restrained against rotation) of the stiffener plus a width of web $\le 20t_w$ on each side, and for the bearing strength $F_{psd} = A_qf_y/(0.8\gamma_{m0})$ of the part of the stiffener in contact with the flange.
Connection to the web: intermediate stiffeners are welded for a shear of at least $t_w^2/(5b_s)$ kN/mm (cl. 8.7.2.6), with an added amount if they carry external loads.
Stiffeners are fitted tight to the compression flange and, for bearing stiffeners, to both flanges. Only intermediate stiffeners that carry no external load may stop short of the tension flange, by up to $4t_w$ .

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Stiffeners in plate girder: types and function

Types and functions

Main design rules (IS 800:2007)

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