vehicle on existing slab

huangyhg

vehicle on existing slab
when checking whether existing one way rc/pt slab could support vehicle load, can i just apply the load at midspan in each span (one at a time) to check the maximum moments (+ve and -ve) in each case.  say, there are 5 spans.
this seems simple as i only have to change the location of the point loads (front and back wheels) each time.
you must check the slab for the appropriate capacity at the critical location for live load, which may or may not be at midspan.
draw an influence line for moment at midspan, moment at intermediate support, and for shear at intermediate and end supports.  then apply your design vehicle axle loads to the influence lines in the positions which cause maximum effect.
you must ensure that the capacity exceeds the load at each of the four locations listed above, as a minimum.  theoretically, you could have a failure at another location, depending on detailing, but this is somewhat unlikely.
check structural analysis, a classical and matrix approach by mccormac & elling by harper and row, chapter 7, for an introduction to influence lines.
just one note.
in most cases the maximum long moments are at the and of the slab. so you will need to apply loading there. this is cause there is nothing at one side that can help to the slab section.
the loading placed at the center of the slab will give you moments to check transverse reinforcement, but no max ;omg moments.
zmei  
ooops,
forgot. deppending of your dead loads when placing vehicle at the end of the slab you may find that negative transverse moments wiil ocure in the midle of the slab.
few mounths ago we checked a bridge that was just before colapse because of cracks and corosion of the top transverse reinforcement. so be careful.
hope this helps
zmei