--- title: "Stiffeners in plate girder: types and function" subject: "Design of Steel and Timber Structure" chapter: 7 key: "semester_6/design_of_steel_and_timber_structure:plate-girder-stiffeners" source: https://www.bctengineer.com/q/semester_6/design_of_steel_and_timber_structure/plate-girder-stiffeners site: BCT Engineering --- # Stiffeners in plate girder: types and function Design of Steel and Timber Structure · Chapter 7: Flexure Members - Asked in: 2073 Bhadra, 5 marks - Video: [Stiffeners | STEEL STRUCTURE Plate Girder](https://www.youtube.com/watch?v=Eibw7YWpsTI) — Adda247 Engineers - AE JE Exams - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/design_of_steel_and_timber_structure/plate-girder-stiffeners - Whole chapter: https://www.bctengineer.com/md/semester_6/design_of_steel_and_timber_structure/chapter-7 ## Question Describe use of stiffeners in plate girder with their 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. ## Answer **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 | ```text +-----------------------------+ | | | | | | | | = 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 $4t_w$. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What are stiffeners in a plate girder mainly used for? A. Increasing the flange width B. Preventing buckling of the thin web and carrying concentrated loads C. Reducing the bolt pitch D. Connecting the flange to the web Answer: B. Stiffeners keep the thin web from buckling and carry concentrated loads (IS 800 cl. 8.7). (Key point: Purpose of stiffeners) 2. Where is a longitudinal stiffener placed and why? A. At supports, to carry the reaction B. At the tension flange, to prevent yielding C. Across the web at spacing c, to allow tension-field action D. Along the span about 0.2d from the compression flange, to prevent bend-buckling of a very slender web Answer: D. A longitudinal stiffener near the compression flange is used when d/tw is very large, to stop bend-buckling of the web. (Key point: Longitudinal stiffener) 3. What does a load-carrying (bearing) stiffener do? A. Transfers a concentrated load or reaction into the web without crushing or buckling it B. Only increases shear buckling strength between supports C. Replaces the web D. Is checked only for welding Answer: A. It is checked as a column with a width of web up to 20tw each side, and for bearing on the flange. (Key point: Load-carrying stiffener) ## Related in Design of Steel and Timber Structure - [Size of web and flange plate in plate girder](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Aplate-girder-web-flange-size) — Design of Steel and Timber Structure, chapter 7, asked 2× - [Components of welded plate girder and selection](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Aplate-girder-components-selection) — Design of Steel and Timber Structure, chapter 7 - [What is plate girder? 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