Stairs of Different Materials and Suitable Application

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Introduction

This article discusses staircases constructed from different materials, following our recent article on the various types of stairs. Staircases may be built using any of the following materials:

1. Timber
2. Stone
3. Bricks
4. Steel
5. R.C.C

Timber Stairs

Timber stairs are lightweight and easy to construct, but they offer very poor fire resistance. For this reason, they are generally used only in low-rise residential buildings and are unsuitable for high-rise or public buildings. To improve fire resistance, hardwoods such as oak or mahogany of adequate thickness may be used. All timber used for stair construction should be properly treated before installation.

In timber staircases, the strings serve as the primary supports for the steps, functioning as inclined beams spanning between the floor and the landing. Additional support can be provided by installing a bearer or carriage under the treads. Typically, one bearer is used; however, for stair widths of 90 cm, an additional bearer is recommended for every 40 cm of extra width. The strings are generally 3 to 5 cm thick, with depths ranging from 25 to 40 cm.

Stone Stair

Stone stairs are commonly used in regions where ashlar stone is readily available. Although stone is heavy, it is strong, rigid, and highly durable. Stones selected for stair construction should be hard, strong, and resistant to wear; they are also naturally fire-resistant.

The simplest type of stone staircase consists of steps supported at both ends. Open-well staircases can also be constructed using stone. Dog-legged staircases with cantilevered spandrel steps are often built using sandstone, such as that found in Jodhpur.

1. Rectangular steps with rebated joint
2. Spandril steps
3. Tread and rise steps
4. Cantilever tread steps
5. Built-up steps

Brick Stairs

Brick stars are not very common, except at the entrance. However, brick stairs of a single straight flight are often made in village houses. The stair consists of either a solid wall or also, arched openings may be left for obtaining storage space. Hence, these may be faced with stone slabs. Alternatively, these steps may be cement plastered at the top of treads and sides of rises.

Metal Stairs

Stairs of mild steel or cast iron are used only as emergency stairs. They are not common in residential and public buildings, though they are strong and fire-resistant. This is because they are not good-looking and also, they make a lot of noise when used by users. They are commonly used in factories, workshops, etc. In its simple form, a metal stair consists of rolled steel stringers (mostly channel section), to which angle irons are welded or riveted, and steel plates are used as treads. Another form of metal stairs commonly used is the spiral stairs.

Concrete Stairs

Reinforced cement concrete (RCC) stairs are widely used in residential, public, and industrial buildings. They are strong, durable, fire-resistant, and offer excellent resistance to wear. RCC stairs are typically cast in situ, and a wide range of finishes can be applied to suit functional and aesthetic requirements.

Based on the direction of spanning of the stair slab, concrete stairs may be classified into the following two categories:

1. Stair with slab spanning horizontally
2. Stair with slab spanning longitudinally.

1. Stair with a slab spanning horizontally

In this category, the slab is supported on one side by a side-wall or stringer beam and on the other side by a stringer beam. Sometimes, as in the case of stringer stair, the slab may be supported horizontally by the side-wall on one side of each flight and the common newel on the other side between backward and forward flights. In such a case, the effective span L is the horizontal distance between the centres of the supports.

Each step is designed to span horizontally with the bending moment equal to WL2/8, where W is the uniformly distributed load per unit area on the step, inclusive of the self-weight. Each step is considered equivalent to a rectangular beam of width b (measured parallel to the slope of the stair) and an effective depth equal to D/2 as shown below. Main reinforcement is provided in the direction of L, while distribution reinforcement is provided parallel to the flight direction. A waist of about 8 cm is provided.

2. Stair with a slab spanning longitudinally.

In this category, the slab is supported at the bottom and top of the flight and remains unsupported on the sides. Each flight of stairs is continuous and is supported on beams at the top and bottom or on landings. In the latter case, the landings also become part of the slab. Dog-legged stairs are a typical example of this type. The main reinforcement is provided parallel to the direction of the flight, and the distribution reinforcement is provided along the width of the slab.

Sometimes, especially for wider stairs, a central stringer beam, spanning between the end walls or columns, is provided on which the stairs’ slab (waist slab) is supported; the waist slab is designed as a slab cantilevering both sides of the stringer beam. The stringer beam itself is designed as a T-beam.

2.1 Precast Concrete Stairs

Precast concrete units are now a day available for the construction of concrete stairs of various shapes. The three common types of precast units are:

1. rectangular cantilever steps
2. Spandril cantilever steps
3. Sector-shaped cantilever units

2.2 R.C.C. Helical Stair

R.C.C. can be used in constructing stairs of any geometrical shape, such as helical stair, which is cast-in-situ. A large amount of steel reinforcement is used to resist bending moment, shear force and torsional moment. The continuous slab varies in thickness from top to bottom-less at the top and increasing at the bottom. There are two or three sets of reinforcement with top and bottom layers in each.

1. continuous bars running the length of the spiral
2. cross or radial bars
3. diagonal bars laid tangentially in two directions to the inner curve.

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