8.6Design of Beams and Plate Girders with Solid Webs

8.6.1.1 Serviceability requirement

• a) When transverse stiffeners are not provided,

$\frac{d}{t_{w}} \leq 200 \epsilon$ (web connected to flanges along

both longitudinal edges)

$\frac{d}{t_{w}} \leq 90 \varepsilon$ (web connected to flanges along one longitudinal edge only),

• b) When only transverse stiffeners are provided (in webs connected to flanges along both

longitudinal edges),

1. when $3 d \geq c \geq d$

• $\frac{d}{t_{w}} \leq 200 \quad \varepsilon$

2. when $0.74 d \leq c<d$ $\frac{c}{t_{w}} \leq 200 \varepsilon_{w}$
3. when $c<d$

• $\frac{d}{t_{w}} \leq 270 \varepsilon_{\mathrm{v}}$

4. when $c>3 d$, the web shall be considered as unstiffened,

• c) When transverse stiffeners and longitudinal stiffeners at one level only are provided (0.2 d from compression flange) according to 8.7.13 (a)

1. when $2.4 d \geq c \geq d$ $\frac{d}{t_{w}} \leq 250 \varepsilon_{w}$
2. when $0.74 d \leq c \leq d$ $\frac{c}{\leq 250 \varepsilon_{\mathrm{w}}}$
3. when $c<0.74 d$ $\frac{d}{t_{w}} \leq 340 \epsilon_{w}$

• d) When a second longitudinal stiffener (located

at neutral axis is provided

$\frac{d}{r_{w}} \leq 400 \varepsilon_{w}$

where

$d \quad=$ depth of the web,

$t_{w} \quad=$ thickness of the web,

$\begin{aligned} c & =\text { spacing of transverse stiffener } \\ & \text { (see Fig. 12 and Fig. 13), }\end{aligned}$

$\begin{aligned} \varepsilon_{\mathrm{w}} & =\text { yield stress ratio of web }=\sqrt{\frac{250}{f_{y w}}} \\ \text { and }\end{aligned}$

$f_{\mathrm{yw}}=$ yield stress of the web.

8.6.1.2 Compression flange buckling requirement

In order to avoid buckling of the compression flange into

the web, the web thickness shall satisfy the following

• a) When transverse stiffeners are not provided:

• b) When transverse stiffeners are provided and

1. when $c \geq 1.5 d$ $\frac{d}{t_{w}} \leq 345 \epsilon_{f}^{2}$
2. when $c<1.5 d$ $\frac{d}{t_{\mathrm{w}}} \leq 345 \epsilon_{\mathrm{f}}$ where

$d \quad=$ depth of the web,

$t_{\mathrm{w}} \quad=$ thickness of the web,

c = spacing of transverse stiffener (see Fig. 12 and Fig. 13),

$\begin{aligned} \varepsilon_{\mathrm{r}} & =\text { yield stress ratio of web }=\sqrt[3]{\frac{250}{f_{\mathrm{y}}}} \\ \text { and }\end{aligned}$

$\begin{aligned} f_{y f} & =\text { yield stress of compressi } \\ & \text { flange. }\end{aligned}$

8.6.2.1

The effective sectional area of compression flanges shall be the gross area with deductions for excessive width of plates as specified for compression members (see Section 7) and for open holes occurring in a plane perpendicular to the direction of stress at the section being considered (see 8.2.1.4).

The effective sectional area of tension flanges shall be the gross sectional area with deductions for holes as specified in 8.2.1.4.

The effective sectional area for parts in shear shall be taken as specified in 8.4.1.1.

8.6.3.1

In riveted or bolted construction, flange angles shall form as large a part of the area of the flange as practicable (preferably not less than one-third) and the number of flange plates shall be kept to a minimum.

In exposed situations, where flange angles are used, at least one plate of the top flange shall extend over the full length of the girder, unless the top edge of the web is machined flush with the flange angles. Where two or more flange plates are used, tacking rivets shall be provided, if necessary to comply with the requirements of Section 10.

Each flange plate shall extend beyond its theoretical cut-off point, and the extension shall contain sufficient rivets, bolts or welds to develop in the plate, the load calculated for the bending moment on the girder section (taken to include the curtailed plate) at the theoretical cut-off point.

The outstand of flange plates, that is the projection beyond the outer line of connections to flange angles, channel or joist flanges or in the case of welded constructions their projection beyond the face of the web or tongue plate, shall not exceed the values given in 3.7.2 (see Table 2).

In the case of box girders, the thickness of any plate or the aggregate thickness of two or more plates, when these plates are tacked together to form the flange, shall satisfy the requirements given in 3.7.2 (see Table 2).

8.6.3.2 Flange splices

Flange splices should preferably, not be located at points of maximum stress. Where splice plates are used, their area shall be not less than 5 percent in excess of the area of the flange element spliced; their centre of gravity shall coincide, as nearly as possible, with that of the element spliced. There shall be enough bolts, rivets or welds on each side of the splice to develop

the load in the element spliced plus 5 percent but in no case should the strength developed be less than 50 percent of the effective strength of the material spliced. In welded construction, flange plates shall be joined by complete penetration butt welds, wherever possible. These butt welds shall develop the full strength of the plates.

8.6.3.3 Connection of flanges to web

The flanges of plate girders shall be connected to the web by sufficient rivets, bolts or welds to transmit the maximum horizontal shear force resulting from the bending moment gradient in the girder, combined with any vertical loads which are directly applied to the flange. If the web is designed using tension field method as given in 8.4.2.2 (b), the weld should be able to transfer the tension field stress, $f_{y w}$ acting on the web.

8.6.3.4 Bolted/Riveted construction

For girders in exposed situations and which do not have flange plates for their entire length, the top edge of the web plate shall be flush with or above the angles, and the bottom edge of the web plate shall be flush with or set back from the angles.

8.6.3.5 Welded construction

The gap between the web plates and flange plates shall be kept to a minimum and for fillet welds shall not exceed 1 mm at any point before welding.

8.6.4.1 Effective sectional area of web of plate girder

The effective cross-sectional area shall be taken as the full depth of the web plate multiplied by the thickness.

NOTE — Where webs are varied in thickness in the depth of the section by the use of tongue plates or the like, or where the proportion of the web included in the flange area is 25 percent or more of the overall depth, the above approximation is not permissible and the maximum shear stress shall be computed on theory.

8.6.4.2 Splices in webs

Splices and cutouts for service ducts in the webs should preferably not be located at points of maximum shear force and heavy concentrated loads.

Splices in the webs of the plate girders and rolled sections shall be designed to resist the shears and moments at the spliced section (see Annex F).

In riveted or bolted construction, splice plates shall be provided on each side of the web. In welded construction, web splices shall preferably be made with complete penetration butt welds.

8.6.4.3

Where additional plates are required to

augment the strength of the web, they shall be placed on each side of the web and shall be equal in thickness. The proportion of shear force assumed to be resisted by these plates shall be limited by the amount of horizontal shear which they can transmit to the flanges through their fastenings, and such reinforcing plates and their fastenings shall be carried up to the points at which the flange without the additional plates is adequate.