parking garage - live loads and live load reductions

huangyhg

parking garage - live loads and live load reductions
just wanted to pass along a good concise article describing what has become quite a mess in the codes the past few years - parking garage live loads and live load reductions:
in cast insitu parking garages, and for that matter, any building where live load reduction has been used in the design of the horizontal members, has anyone ever checked the back propping requirements of the floors?
though the floor is theoretically designed to carry 50psf, some   
thanks
i am a new   
i've been involved in the design of several dozen parking structures and live load reduction shouldn't be an issue.  with typical cip concrete parking structures, a series of long beams at 15'+/- on centre pick up a concrete slab.  the ll red factor for the slab is 1, the ll red factor for the individual beams is calculated on the trib area of the beam and the supporting columns are designed based on the total trib area the column supports... pretty straight forward.
for alternating loads, for slab design and column moment determination, have considered using the 'real' live load for a parking structure.  a fully loaded parking structure if vehicles were parked side by side and in all the isles, etc. would be loaded to less than 20 psf and more likely 15 psf max.  this adds assurance about any live load reduction you undertake...
dik
brantlet
are these structures that are failing and being repaired prestressed flat plates or other structural systems?
if they are flat plates, a lot of the blame, in my humble opinion, can be attributed to the structural layout used in unbonded pt slabs and the design methodology being used by designers using aci and pti design methods for unbonded pt flat plates rather than the use of live load reduction by itself. obviously designing for a significantly reduced live load makes the problem worse.
regarding the point load, no it should not be reduced and the width of it's influence should be considered carefully.