--- title: "Components of welded plate girder and selection" subject: "Design of Steel and Timber Structure" chapter: 7 key: "semester_6/design_of_steel_and_timber_structure:plate-girder-components-selection" source: https://www.bctengineer.com/q/semester_6/design_of_steel_and_timber_structure/plate-girder-components-selection site: BCT Engineering --- # Components of welded plate girder and selection Design of Steel and Timber Structure · Chapter 7: Flexure Members - Asked in: 2076 Baisakh, 4+4 marks - Video: [Steel Structures | Design of Plate Girder - 2 | RGPV | GATE | Steel-1 | Mohan Dangi](https://www.youtube.com/watch?v=4qtm87_9sJQ) — Digitech education - 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-components-selection - Whole chapter: https://www.bctengineer.com/md/semester_6/design_of_steel_and_timber_structure/chapter-7 ## Question Explain about the different components of welded plate girder with detail sketch. How can you select a section of welded plate girder. Give briefly design procedure. ## Short answer Welded plate girder components: flanges, web, bearing and intermediate stiffeners, longitudinal stiffener, welds, splices. Section selection: depth ≈ L/10–L/12, web thickness from d/t_w limits, flange area ≈ M/(f_y d). Design steps: compute factored M and V, choose dimensions, check moment and shear capacity, design stiffeners, check deflection and welds. ## Answer A **plate girder** is a built-up beam made of plates welded together (bolted or riveted in older work), used for large spans or heavy loads where a rolled section is not enough. #### Components of a welded plate girder Elevation: ```text +-----------------------------------------------+ top flange plate |B| |S| |S| |S| |S| |B| |B| |S| |S| |S| |S| |B| web plate |B| |S| |S| |S| |S| |B| +-----------------------------------------------+ bottom flange plate ^ ^ support support B = bearing stiffener S = intermediate transverse stiffener ``` Cross-section: ```text |<---- b_f ---->| +===============+ top flange (t_f) || <- fillet welds (flange to web) || || web (t_w), depth d || <- stiffener plates welded on one or both sides || +===============+ bottom flange (t_f) ``` 1. **Flange plates** (top and bottom): resist the bending moment as a couple, $M \approx F\times d$. 2. **Web plate**: resists the shear; its depth sets the lever arm. 3. **Bearing (load-carrying) stiffeners** at the supports and under concentrated loads: prevent web crushing and buckling. 4. **Intermediate transverse stiffeners**: raise the shear buckling strength of the web (and allow tension field action). 5. **Longitudinal stiffener** (for very deep webs): placed near the compression flange; controls web buckling in bending. 6. **Flange-to-web welds** (fillet welds): carry the horizontal shear flow $VA\bar y/I$. 7. **Splices** in the web and flanges (for transport lengths), and **end panels / bracing** for lateral stability. #### Selecting the section - Depth $d \approx L/10$ to $L/12$ (or use $d = (Mk/f)^{1/3}$ for minimum weight, with $k = d/t_w$). - Web thickness $t_w = d/k$, within the $d/t_w$ limits of IS 800:2007 cl. 8.6.1. - Flange area $A_f \approx M\gamma_{m0}/(f_yd)$; width $b_f \approx d/3$ to $d/5$; thickness $t_f = A_f/b_f$; outstand $b/t_f \le 13.6\varepsilon$ (welded, semi-compact) or $8.4\varepsilon$ for a plastic section. #### Brief design procedure 1. Find the factored $M$ and $V$ (add an assumed self-weight). 2. Choose $d$, $t_w$, $b_f$ and $t_f$ as above. 3. Compute $I_{zz}$ and $Z_{zz}$; check $M_d$ (including LTB if the compression flange is not restrained) against $M$. 4. Check the shear $V_d$ and web buckling; provide intermediate stiffeners as needed for the web slenderness (spacing $c$), and design the bearing stiffeners. 5. Check the deflection (Table 6: span/300 in general, span/360 where finishes are brittle or liable to crack). 6. Design the flange-to-web welds for the shear flow $q = VA\bar y/I$ and the splices; curtail the flange plates where the moment falls. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What do the flange plates and web plate of a plate girder resist? A. Flanges resist bending as a couple, web resists shear B. Flanges resist shear, web resists bending C. Both resist only torsion D. Web resists bending and flanges prevent buckling Answer: A. Moment is carried as a force couple M = F x d in the flanges, while the web, whose depth sets the lever arm, carries the shear. (Key point: Flange and web roles) 2. What is the function of intermediate transverse stiffeners? A. Raise the shear buckling strength of the web (tension field action) B. Carry the support reaction C. Resist bending in the flanges D. Join the flange to the web Answer: A. Intermediate stiffeners reduce web panel size; bearing stiffeners, by contrast, are at supports and concentrated loads to stop web crushing. (Key point: Stiffeners) 3. For what is the flange-to-web weld designed? A. The horizontal shear flow q = V A y-bar / I B. The axial load in the web C. The bearing pressure D. The torsional moment Answer: A. The weld must transfer the longitudinal shear between flange and web, given by the shear flow VAy/I. 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