Design Of Steel Structures | Plate Girder

Design of Plate Girders

* Plate girder is a built up I-section beam with two flange plates connected to a web plate of required

depth.

* A plate girders need stiffeners to avoid buckling of web. Types of stiffeners used are:

(a) Transverse (vertical stiffeners)

(i) Bearing stiffeners

(ii) Intermediate stiffeners.

(b) Longitudinal (horizontal) Stiffeners

* If only one horizontal stiffener is provided, it will be at a depth 0.2d from compression flange. If

another horizontal stiffener is to be provided it will be at mid-depth of web.

* Self-weight of plate girder:

w = kN/m

where w = factored self-weight

W = total factored load on the girder.

* Economical depth: It is given by

where k = , M = factored maximum moment and fy = yield strength.

* Another practical guideline for selecting depth of plate girder is

= for girders in building

= for highway bridges

= for railway bridges.

* Flange thickness may be found by assuming that only flanges resist moment. Hence,

= M

To keep the section semi-compact should be 9.4 e to 13.6 e where e =

Hence, minimum is found from

13.6 t t

f

2 = Af

* If £ 67 e, design as ordinary beam

If ≥ 67 e, provide stiffeners.

* Shear buckling strength may be found by simple post-critical method or tension field method.

* End panel may be provided with a single stiffener at the end or with double stiffeners.

* Buckling resistance of stiffeners is found taking effective section is full area or core area of the

stiffener together with an effective length of 20 tw of web on each side.