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d1 - clear depth of web (depth of web between toes of flange angle 
Concepts :
1>  To ensure that web takes only shear force, a gap of 5mm will be provided between flange plate and web plate.
 (so that direct bearing action bet
ween flange plate and web plate is avoided .)

 2>  The flange angle must be unequal angles with larger legs connected  to flange plate to get more bearing area .

3>  The size of the flange angle should be such that they should form atleast one third  of the total flange area .

4> If d/tw> 90 ,vertical stiffeners are provided to prevent bucking of web due to diagonal compression .
Creadit IndiaMART

5> Vertical stiffeners are provided under point loads .they prevent web crippling or web crimpling or local bucking of web . These stiffeners are called load bearing stiffeners .(web crippling occurs due to excessive bearing stress at the toe of flange angle as shown in figure )

6> If d/w>200 horizontal stiffeners OR longitudinal stiffners are provided about neutral axis at a distance of.2dw form the compression flange .(they prevent bucking of web due to bending compressive stress.

7> if d/w> 250 additional horizontal stiffner is provided at neutral axis.this stiffner prevents buckling of web between stiffners due to shear force .

8> if d/w >400 then the section must be redesigned .

9> At the support ,to prevent bending of flange plate and buckling of web plate due to support reaction ,end bearing stiffeners are used .

10> If bearing stiffners are the only means of providing torsional restraint ,then they are also called torsional stiffeners .(The other means of providing torsional restraint is extending the plate girder into the wall)

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