Crane Wheel Load Eccentricity

W h e e l l o a d e c ce c e n t r i ci ci t y

Due to w heel load eccentr eccentr icity we used to assum assum e that 60% of to tal wh eel load load w ill act act on on e side side of rail and 40% of t he same same w ill act act on ot her side side of rail.( In In th is ass assum ption , w e w ere not aware of actual value value o f “ ey” ). The disribution disribution of w heel load due t o its eccentrici eccentricity ty is consi considered dered as show show n b elow.

Now torsional torsional mom ent due t o uneven distribut distribut ion of wh eel load at centerline centerline of c r a n e r a i l will be as below; Tm1 = 0.6Fz X 0.5b b – 0 .4Fz X 0.5bb = Fz X (0.6 X 0.5 – 0.4 X 0.5) X bb = Fz X 0.1 X bb R a i l Ec Ec c e n t r i c i t y

The value of rail eccentricity eccentricity w e used to consider consider 0.5 t imes w eb th ickness ickness or 10mm wh ichever ichever is less less. And the to rsional rsional mo m ent at centr centr eline eline of c r a n e g i r d e r w ill be as below below . Tm 2 = Fz x e

Hence the to tal tor sional mo m ent Tm = Tm1 + Tm Tm 2. This This is is background background of th e calc calculation ulation wh ich I have sent.

This was the concept w e used t o fo llow . Due to poor wor kmanship rail eccentricity can be mo re than tw /2 or even m ore t han that . But w hy tw / 2, that is th e question. I think, if Rail eccn is less than tw / 2, in that case it is very difficult t o d iscard t he rail alignment by visual inspection . So w e m ust have to consider atleast t his amo unt (tw/ 2) of eccentricity in ou r design. And if rail eccn is m ore t han tw / 2 or mo re, then th at alignm ent m ight be dicarded b y inspecton team very easily. So w e don’t have to consider any unreasonable value o f rail eccent ricity. But fo r being in con servative side w e consider rail eccn as smaller of tw / 2 or 10m m . To some extent th is explanat ion is ok fo r any kind of rail fiixing, I th ink. The amo unt of rail eccentricity should also depend o n t he rail fixing detail. The amo unt of movem ent, wh ich w e will allow in th e adopt ed detail for rail fixing, that amoun t should be considered as rail eccentricity in our d esign calculat ion. Note th at in t he above explanation r a i l e c ce n t r i ci t y h a s a r e l at i o n w i t h w e b t h ic k n e ss o f ga n t r y g i r d e r . If w e don’t want t o follow euronorms, then the above explanat ion can be used fo r design of gant ry girder . In eurocode we get w heel load eccetricity as 0.25 times the head w idth of rail (not the base w idth) w hich is quite h igh. And its min imum value restricted t o t w/ 2. This m eans, here w h e e l l o ad e cc n h a s a r e l at i o n w i t h w e b t h ic k n e ss o f ga n t r y g i r d e r . Here you can see that th e value of br/ 4 is quite high. And eurocode n ever says anyth ing about rail eccentr icity. So if w e follow eurono rm s only t hen, w e can use wh eel load eccentr icity and ignore rail eccentr icity. You can see that th e value of to tal eccentr icity in bo th t he cases (dco practise & eur ono rm s) will be almo st same . Ofcourse that w ill also dep end on geom etry of crane rail.