Basement slope specification for car
From 2006 IBC:
406.2.5 Ramps. Vehicle ramps shall not be considered as required exits unless pedestrian facilities are provided. Vehicle ramps that are utilized for vertical circulation as well as for parking shall not exceed a slope of 1:15 (6.67 percent).
Straight Ramp Slope
The recommended slope for straight ramps in situations such as:
· Half deck car parks where the vertical separation between decks is less than 1.5m, is 1:6. This relatively steep slope is only possible when using transition gradients top and bottom.
· Where vertical differences are greater than 1.5m, is not less than 1:10.
· Where ramps are curved, 1:10 or 1:12 depending on the separation.
Many modern cars have wheel bases that are ….. long and under-body clearances of less than… The effect of these specifications is that in any situation where a ramp of gradient steeper than 1:10 intersects with a flat slab that cars will bottom out on the transition line at the top of the ramp.
Three-Stage Ramp Structures
To address some of these issues, engineers have developed three stage ramp structures:
· The top and the bottom of the ramp are constructed to a gentle gradient say 1:16 or 1:20.
· The central section of the ramp is built to a steeper slope – 1:8 or 1:10.
Three additional issues with car park ramps include the:
· clear edge to edge width
· the turning circle on approach routes to the bottom or from the top of ramps.
· the location of ticket machines on ramps
Many drivers find ramps too narrow and scrape their bumpers along walls at the top or bottom of ramps. The recommended minimum width for a one-way ramp is 3.0m with an additional 0.3m for side clearance to the structure. The recommended width of the entry section for a turning approach to a ramp is 3.5m. Bearing in mind that very few cars are more than 1.8m wide these recommendations allow for a broad range of driver behaviour and skills.
Well-designed turning circles in car parks depend on the types of vehicles using them. Some modern cars have turning circles of radius 6.0m to 7.5m. If these have to be accommodated in a car park then it is prudent to design turning lanes on the basis of an outside kerb radius of 9.0m. It is highly desirable that there are no structural columns located at the turning pints onto or from ramps. They intimidate drivers and lead to damage to walls and vehicles.
It is undesirable to have ticket machines located on ramps, as drivers and vehicles experience difficulties. Practical experience suggests that ticket machines on down ramps can work well while those on up-ramps are generally unfriendly. On the down ramp the driver can see the barrier in front and can respond to any slippage. There is little risk of collision with another vehicle. On an up ramp the driver has very poor views of cars behind and will be nervous in case his car drifts back or the car behind gets too close. Handbrake starts on up ramps make many drivers nervous
Finally in designing ramps in car parks, it is vital that clear sight lines are maintained at the top and bottom of the ramps. These are essential to the safety of pedestrians and vehicles alike. The driver of a car on a ramp cannot readily see directly in front because the bonnet of the car intrudes, and as a consequence must depend on being able to see to the side to ensure he/she can proceed safely. Curtain walls on ramp sides have been built with large holes to provide very good sight lines.