New Steel Frame - clearance

[ajk1]

We are designing a supplementary support frame to an existing concrete girder in a parking garage.
The new supplementary support is a steel frame of HSS 12x12 members forming an arch comprising an inclined member at the left end, a horizontal member at the top, and an inclined member at the right end. This will be installed at the centreline of the central beam running the north-south length of the garage. This central beam spans 13 m and supports the east-west beams that span the 17 m width of the garage each side of the central girder. This new frame will be at the back of the parking stalls. The parking is "angled" parking only. We are going to pour a concrete sidewalk on the floor directly below the new frame (taking care to use styrofoam to lighten the sidealk and not overload the floor)to prevent cars from impacting the new steel frame when they drive into the stalls. Due to the angled parking, they drive in only, they do not back in. Question: Does anyone know how wide the sidewalk should be to prevent vehicles from impacting the steel when they drive into the angled parking stall? Please do not guess at the answer. We can guess too (it might be based on the distance to the front wheel or it might only have to be to the distance to the shroud below the chasis at the front of the vehicle, but in either case I don't know if there are measuremnts for this that should be used for such situations).

 

[EngJP]

Ajk1: A little curious as to why the existing girder needs the supplemental support. Is the girder damaged? If so, is it better to temporarily shore up the east west beams and recast the girder. I'd be concerned with overloading the girder below with the new steel frame assuming this is not at foundation level.

 

[ajk1]

The floor below can not take this additional load. That is precisely why we designed this system so that we are not imposing any additional loads whetever on the floor below. All the load is being taken by an new steel arch system, with the bottom portion of the arch bringing its load directly into the column so that the centroidal axes of the arch and the column and the beam coincide, thereby not inducing moment.

The beam is prestressed and a number of tendons have failed due to corrosion. To demolsih and recast the 40 foot span prestressed beaam which supports other prestressed beams spanning 56 feet is neither practical, as you can well imagine. Neither were any of the other solutions (such as but not limited to carbon fibre; external p.t., etc,) that we investigated over an extensive period.

Does anyone know the answer to the question that was asked?

 

[Screwman1]

There is no "standard" for front overhang. It varies from vehicle to vehicle. This will be a factor of the overhang, the tire diameter and the vehicle width. I would go to a parking lot with a couple tape measures and start checking different cars and trucks that are angle parked. Probably the worst case will be some sort of commercial box truck (delivery van) or a big old F350 pickup with a home made bumper from an old 4 X 12 oak beam.
Rather than go with a walkway, you could save weight by just using a parking stop the same height as you walkway.