The simplest type of staircase consists of an inclined, reinforced concrete slab. It is supported at its ends by beams, and steps are formed on its upper surface. A horizontal landing slab may be included at one or both ends. Under normal loading conditions, the effect of the angle crated by the landing can safely be disregarded. The staircase can then be designed as a simple slab with a span equal to the horizontal distance between supports. This design usually requires steel to be inserted in the longitudinal direction only. Transverse steel, normally at at the rate of one bar per tread, should also be included to assist load distribution and to provide temperature reinforcement. A spiral staircase can be constructed fairly easily by cantilevering precast, pie shaped step units from a central column. The units become monolithic through the action of the reinforcing steel and site cast concrete of the column. An alternative center support can be provided with a mild steel pipe of appropriate diameter or bar or cable pretensioned concrete. The construction of a concrete staircase follows the normal rules of good practice for placing, finishing, and curing. Normally, a 3,000 psi concrete is used for staircase concrete. Placing should begin at the bottom and work upwards. It is common practice to strip stair forms after the concrete has hardened for between 1 and 2 hours so the at the nosing, riser, and ends can be finished. Finishes for staircases requires some special care. The type of finish may be dictated by architectural or practical considerations. White or colored concrete is frequently used to improve appearance. Non-slip finishes can be provided by wire combing, brooming, sack rubbing, swirl troweling, or wood floating to a gritty surface, if architectural appearance is not of importance. Alternatively, abrasive grits of silicon carbide or aluminum oxide can be troweled into treads during finishing.