Vertical Circulation 55536b

Vertical Circulation

Vertical circulations are those which furnish means for progress from one level to another. The position of any means of vertical circulation is a matter of great importance because such circulations not only control the plans of the various floors they connect but also condition the plan of each floor since they furnish the major approach to it. Vertical circulation of traffic in a multistory building is the key to successful functioning of the design, both in normal use and in emergencies. In fact, location of elevators or stairs strongly influences the floor plan. So in the design of a building, much thought should be given to the type of vertical circulation to be provided, number of units needed, and their location, arrangement, and design.

The simplest type of vertical circulation is the ramp, a slopping surface. Ramps vary in slope from 6 to 10%, although 8% should be considered the maximum in those to be used by the public. In a given period, ramps can accommodate huge numbers of people for their progress along them will be as direct and almost as swift as along a level floor. They are, therefore, especially suitable for buildings where crowds must at limited intervals. However, because they require a great deal of space, the use of ramps within buildings becomes practical only where great numbers of persons are to be handled or when special conditions make them necessary The second means of vertical circulation is the stair. Stairs are used for steeper slopes. The comfort of the climb depends on the number of steps in a single run between landings and on the proportion of the

tread width to the riser height. Interior stairs offer problems of great complexity. Types of stairs may vary from curving, spiral or ladder staircase in houses to monumental stairs in buildings. In interiors, the stair without any nosing has a standard 10-inch tread and a 7-inch riser. When nosing is used, the tread width is increased. When the risers are inclined, the length required is diminished and the angle of the stair is made steeper. Elevators An escalator resembles a powered ramp in construction (Art. 16.2). The major difference is that a powered ramp has a continuous treadway for carrying engers, whereas the treadway of an escalator consists of a series of moving steps. As for a powered ramp, the installation of powered stairs should conform with the requirements of the ‘‘American National Standard Safety Code for Elevators, Dumbwaiters, Escalators and Moving Walks,’’ ANSI A17.1. An escalator consists of articulated, grooved treads and risers attached to a continuous chain moved by a driving machine and ed by a steel truss framework (Fig. 16.6). The installation also includes a handrail on each side of the steps that moves at the same speed as the steps; balustrades, or guards, that enclose the steps on each side and the handrails; brakes; control devices; and threshold plates at the entrance to and the exit from the treadway. The purpose of the threshold plates is to facilitate smooth age of engers between the treadway and landing. The plates are equipped with a comb, or teeth, that mesh with and are set into grooves in the treadway in the direction of travel, so as to provide firm footing and to minimize the chance that items become trapped between treadway and the landing. Each step is formed by a grooved tread portion connected to a curved and grooved riser. The tread and riser assembly is either a single die-cast piece or is assembled to a frame. Both are suspended on resilient rollers whose axles are connected to the step chain that moves the steps. The step rollers ride on a set of tracks attached to the trussed framework. The tracks are shaped to allow the step tread to remain horizontal throughout its exposed travel.

An elevator (or lift in the Commonwealth excluding Canada) is a type of verticaltransport equipment that efficiently moves people or goods between floors (levels, decks) of a building, vessel or other structures. Elevators are generally powered by electric motors that either drive traction cables or counterweight systems like a hoist, or pump hydraulic fluid to raise a cylindrical piston like ajack.

For moving small packages or correspondence between floors, dumbwaiters, chutes, pneumatic tube systems, powered track conveyors, or vertical conveyors also may be installed. Ladders may be used for occasional access to

attics or roofs.