Stairs - Exterior Steel Stairs

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A stairway, staircase, stairwell, flight of stairs, or simply stairs is a construction designed to bridge a large vertical distance by dividing it into smaller vertical distances, called steps. Stairs may be straight, round, or may consist of two or more straight pieces connected at angles.

Special types of stairs include escalators and ladders. Some alternatives to stairs are elevators (lifts in British English), stairlifts and inclined moving walkways as well as stationary inclined sidewalks (pavements in British English).

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Components and terms

A stair, or a stairstep is one step in a flight of stairs. In buildings, stairs is a term applied to a complete flight of steps between two floors. A stair flight is a run of stairs or steps between landings. A staircase or stairway is one or more flights of stairs leading from one floor to another, and includes landings, newel posts, handrails, balustrades and additional parts. A stairwell is a compartment extending vertically through a building in which stairs are placed. A stair hall is the stairs, landings, hallways, or other portions of the public hall through which it is necessary to pass when going from the entrance floor to the other floors of a building. Box stairs are stairs built between walls, usually with no support except the wall strings.

Stairs may be in a straight run, leading from one floor to another without a turn or change in direction. Stairs may change direction, commonly by two straight flights connected at a 90 degree angle landing. Stairs may also return onto themselves with 180 degree angle landings at each end of straight flights forming a vertical stairway commonly used in multistory and highrise buildings. Many variations of geometrical stairs may be formed of circular, elliptical and irregular constructions.

Stairs may be a required component of egress from structures and buildings. Stairs are also provided for convenience to access floors, roofs, levels and walking surfaces not accessible by other means. Stairs may also be a fanciful physical construct such as the stairs that go nowhere located at the Winchester Mystery House. Stairs are also a subject used in art to represent real or imaginary places built around impossible objects using geometric distortion, as in the work of artist M. C. Escher.

"Stairway" is also a common metaphor for achievement or loss of a position in the society; or as a metaphor of hierarchy (e.g. Jacob's Ladder, The Battleship Potemkin).

Step

Each step is composed of tread and riser.

The railing system

The balustrade is the system of railings and balusters that prevents people from falling over the edge.

Handrails may be continuous (sometimes called over-the-post) or post-to-post (or more accurately "newel-to-newel"). For continuous handrails on long balconies, there may be multiple newels and tandem caps to cover the newels. At corners, there are quarter-turn caps. For post-to-post systems, the newels project above the handrails.

Another, more classical, form of handrailing which is still in use is the tangent method. A variant of the Cylindric method of layout, it allows for continuous climbing and twisting rails and easings. It was defined from principles set down by architect Peter Nicholson in the 18th century.

The earliest spiral staircases appear in Temple A in the Greek colony Selinunte, Sicily, to both sides of the cella. The temple was constructed around 480-470 BC.

Other terms

Measurements

The measurements of a stair, in particular the rise height and going of the steps, should remain the same along the stairs.

The following stair measurements are important:

• The rise height or rise of each step is measured from the top of one tread to the next. It is not the physical height of the riser; the latter excludes the thickness of the tread. A person using the stairs would move this distance vertically for each step taken.
• The tread depth of a step is measured from the edge of the nosing to the vertical riser; if the steps have no nosing, it is the same as the going; otherwise it is the going plus the extent of one nosing.
• The going of a step is measured from the edge of the nosing to the edge of nosing in plan view. A person using the stairs would move this distance forward with each step they take.
• To avoid confusion, the number of steps in a set of stairs is always the number of risers, not the number of treads.
• The total run or total going of the stairs is the horizontal distance from the first riser to the last riser. It is often not simply the sum of the individual tread lengths due to the nosing overlapping between treads. If there are N steps, the total run equals N-1 times the going: the tread of the last step is part of a landing and is not counted.
• The total rise of the stairs is the height between floors (or landings) that the flight of stairs is spanning. If there are N steps, the total rise equals N times the rise of each step.

• The slope or pitch of the stairs is the ratio between the rise and the going (not the tread depth, due to the nosing). It is sometimes called the rake of the stairs. The pitch line is the imaginary line along the tip of the nosing of the treads. In the UK, stair pitch is the angle the pitch line makes with the horizontal, measured in degrees. The value of the slope, as a ratio, is then the tangent of the pitch angle.
• Headroom is the height above the nosing of a tread to the ceiling above it.
• Walkline - for curved stairs, the inner radius of the curve may result in very narrow treads. The "walkline" is the imaginary line some distance away from the inner edge on which people are expected to walk. Building code will specify the distance. Building codes will then specify the minimum tread size at the walkline.

Exterior Steel Stairs Video

Forms

Stairs can take a large number of forms, combining winders and landings.

The simplest form is the straight flight of stairs, with neither winders nor landings. These types of stairs were commonly used in traditional homes as they are relatively easy to build and only need to be connected at the top and bottom; however, many modern properties may not choose straight flights of stairs because:

• the upstairs is directly visible from the bottom of a straight flight of stairs.
• it is potentially more dangerous in that a fall is not interrupted until the bottom of the stairs.
• a straight flight requires enough space for the entire run of the stairs.

Another form of straight staircase is the space saver staircase, also known as paddle stairs or alternating tread staircases, that can be used for a steeper rise, but these can only be used in certain circumstances and must comply with regulations.

However, a basic straight flight of stairs is easier to design and construct than one with landings or winders. Although the rhythm of stepping is not interrupted in a straight run, which may offset the increased fall risk by helping to prevent a misstep in the first place, many stairs will require landings or winders to comply with safety standards in the Building Regulations.

Straight stairs can have a mid-landing incorporated, but it's probably more common to see stairs that use a landing or winder to produce a bend in the stairs as a straight flight with a mid-landing will require a lot of linear space and is more commonly found in commercial buildings. "L" shaped stairways have one landing and usually change in direction by 90 degrees. "U" shaped stairs may employ a single wider landing for a change in direction of 180 degrees, or 2 landings for two changes in direction of 90 degrees each. A Z-shaped staircase incorporates two parallel 90° turns, creating a shape similar to that of the letter 'Z' if seen from above. Use of landings and a possible change of direction have the following effects:

• The upstairs is not directly visible from the bottom of the stairs, which can provide more privacy for the upper floor.
• A fall can be halted at the landing point, reducing the distance someone would fall to reduce risks.
• Though the landings consume total floor space, there is no requirement for a large single dimension, allowing more flexible floorplan designs.
• For larger stairs, particularly in exterior applications, a landing can provide a place to rest the legs.

Other forms include stairs with winders that curve or bend at an acute angle, three flight stairs that join at a landing to form a T-shape, and stairs with balconies and complex designs can be produced to suit individual properties.

A mono string staircase is a term used for a steel spine staircase with treads.

A Double string staircase has two steel beams on either side and treads in the center.

Spiral and helical stairs

Spiral stairs, sometimes referred to in architectural descriptions as vice, wind around a newel (also the central pole). They typically have a handrail on the outer side only, and on the inner side just the central pole. A squared spiral stair assumes a square stairwell and expands the steps and railing to a square, resulting in unequal steps (larger where they extend into a corner of the square). A pure spiral assumes a circular stairwell and the steps and handrail are equal and positioned screw-symmetrically. A tight spiral stair with a central pole is very space efficient in the use of floor area.

Spiral stairs have the disadvantage of being very steep - only if they are tight or are otherwise not supported by a center column. This is because of two reasons:

• The wider the spiral, the more steps can be accommodated per spiral. Therefore, if the spiral is large in diameter, via having a central support column that is strong (invariably large in diameter) and a special handrail that helps distributes the load, each step may be longer and therefore the rise between each step may be smaller, (equal to that of regular steps.) Otherwise, the circumference of the circle at the walk line will be so small that it will be impossible to maintain a normal tread depth and a normal rise height without compromising headroom before reaching the upper floor.

• To maintain headroom some spiral stairs have very high rises to support a very short diameter. These are typically cases where the stairwell must be a small diameter by design or must not have any center support by design or may not have any perimeter support.

An example of perimeter support is the Vatican stairwell shown in the next section or the gothic stairwell shown to the left. That stairwell is only tight because of its design in which the diameter must be small. Many spirals, however, have sufficient width for normal size treads (8 inches) by being supported by any combination of a center pole, perimeter supports attaching to or beneath the treads, and a helical handrail. In this manner, the treads may be wide enough to accommodate low rises. The photo on the right are self-supporting stairs. This means the spiral needs to be necessarily steep to allow the weight to distribute safely down the spiral in the most vertical manner possible. Spiral steps with center columns or perimeter support do not have this limitation. Building codes may limit the use of spiral stairs to small areas or secondary usage if their treads are not sufficiently wide or have risers above 9 and a half inches.

The term "spiral" has a more narrow definition in a mathematical context, as a mathematical spiral lies in a single plane and moves towards or away from a central point. The mathematical term for motion where the locus remains at a fixed distance from a fixed line whilst moving in a circular motion about it is "helical". The presence or otherwise of a central pole does not affect the terminology applied to the design of the structure.

Spiral stairs in medieval times were generally made of stone and typically wound in a clockwise direction (from the ascender's point of view), to place attacking swordsmen (who were most often right-handed) at a disadvantage. This asymmetry forces the right-handed swordsman to engage the central pike and degrade his mobility compared with the defender who is facing down the stairs. Extant 14th to 17th-century examples of these stairways can be seen at Muchalls Castle, Crathes Castle and Myres Castle in Scotland. Exceptions to the rule exist, however, as may be seen in the accompanying image of the Scala of the Palazzo Contarini del Bovolo, which winds up counter-clockwise.

Developments in manufacturing and design have led to the introduction of kit form spiral stairs. Steps and handrails can be bolted together to form a complete unit. These stairs can be made out of steel, timber, concrete or a combination of materials.

Helical or circular stairs do not have a central pole and there is a handrail on both sides. These have the advantage of a more uniform tread width when compared to the spiral staircase. Such stairs may also be built around an elliptical or oval planform.

Both double spiral and double helix staircases are possible, with two independent helical stairs in the same vertical space, allowing one person to ascend and another to descend, without ever meeting if they choose different helices. For examples, the Pozzo di S. Patrizio allows one-way traffic so that laden and unladen mules can ascend and descend without obstruction, while Château de Chambord, Château de Blois, and the Crédit Lyonnais headquarters ensure separation for social purposes. Fire escapes, though built with landings and straight runs of stairs, are often functionally double helices, with two separate stairs intertwined and occupying the same floor space. This is often in support of legal requirements to have two separate fire escapes.

Both spiral and helical stairs can be characterized by the number of turns that are made. A "quarter-turn" stair deposits the person facing 90 degrees from the starting orientation. Likewise, there are half-turn, three-quarters-turn and full-turn stairs. A continuous spiral may make many turns depending on the height. Very tall multi-turn spiral staircases are usually found in old stone towers within fortifications, churches and in lighthouses.

Winders may be used in combination with straight stairs to turn the direction of the stairs. This allows for a large number of permutations.

Alternating tread stairs

Where there is insufficient space for the full run length of normal stairs, alternating tread stairs may be used. Alternating tread stairs allow for a safe forward-facing descent of very steep stairs. The treads are designed such that they alternate between treads for each foot: one step is wide on the left side; the next step is wide on the right side. There is insufficient space on the narrow portion of the step for the other foot to stand, hence the person must always use the correct foot on the correct step. The slope of alternating tread stairs can be as high as 65 degrees as opposed to standard stairs which are almost always less than 45 degrees. The advantage of alternating tread stairs is that people can descend face forward. The only other alternative in such short spaces would be a ladder which requires backward-facing descent. Alternating tread stairs may not be safe for small children, the elderly or the physically challenged. Building codes typically classify them as ladders and will only allow them where ladders are allowed, usually basement or attic utility or storage areas not frequently accessed.

The image on the right illustrates the space efficiency gained by an alternating tread stair. The alternating tread stair appears in the image's center, with green-colored treads. The alternating stair requires one unit of space per step: the same as the half-width step on its left, and half as much as the full-width stair on its right. Thus, the horizontal distance between steps is in this case reduced by a factor of two, reducing the size of each step.

The horizontal distance between steps is reduced by a factor less than two if for construction reasons there are narrow "unused" steps.

There is often (here also) glide plane symmetry: the mirror image with respect to the vertical center plane corresponds to a shift by one step.

Alternating tread stairs have been in use since at least 1888.

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Ergonomics and building code requirements

Ergonomically and for safety reasons, stairs must have certain measurements so that people can comfortably use them. Building codes typically specify certain measurements so that the stairs are not too steep or narrow.

Nicolas-François Blondel in the last volume of his Cours d'architecture (1675-1683) was the first known person to establish the ergonomic relationship of tread and riser dimensions. He specified that 2 x riser + tread = step length.

It is estimated that a noticeable mis-step occurs once in 7,398 uses and a minor accident on a flight of stairs occurs once in 63,000 uses. Some people choose to live in residences without stairs so that they are protected from injury stairs can be a hazardous obstacle for some.

Stairs are not suitable for wheelchairs and other vehicles. A stairlift is a mechanical device for lifting wheelchairs up and down stairs. For sufficiently wide stairs, a rail is mounted to the treads of the stairs, or attached to the wall. A chair is attached to the rail and the person on the chair is lifted as the chair moves along the rail.

UK requirements

(overview of Approved document K - Stairs Ramps and Guards)

Approved document K categorises stairs as 'Private', 'Institutional or assembly' and 'other'

When considering stairs for private dwellings

Building regulations are required for stairs used where the difference of level is greater than 600 mm (23.6 in)

Steepness of stairs - Rise and Going - Any rise between 155 and 220 mm (6.1 and 8.7 in) used with any going (tread) between 245 and 260 mm (9.6 and 10.2 in) or any rise between 165 and 200 mm (6.5 and 7.9 in) used with any going between 223 and 300 mm (8.8 and 11.8 in)

Maximum Rise 220 mm (8.7 in) and Minimum Going 220 mm (8.7 in) remembering that the maximum pitch of private stairs is 42°. The normal relationship between dimensions of the rise and going is that twice the rise plus the going (2R + G) should be between 550 and 700 mm (21.7 and 27.6 in)

Construction of steps - Steps should have level treads, they may have open risers but if so treads should overlap at least 16 mm (0.6 in). Domestic private stairs are likely to be used by children under 5 years old so the handrail ballister spacing should be constructed so that a 100 mm (3.9 in) diameter sphere cannot pass though the opening in the risers in order to prevent children from sticking their heads through them and potentially getting stuck.

Headroom - A headroom of 2 m (78.7 in) is adequate. Special considerations can be made for loft conversions.

Width of flights - No recommendations are given for stair widths.

Length of flights - The approved document refers to 16 risers (steps) for stairs in shops or assembly building. There is no requirement for private stairs. In practice there will be fewer than 16 steps as 16 x 220 mm (8.7 in) gives over 3.5 m (137.8 in) total rise which is way above that in a domestic situation.

Landings - Level, unobstructed landings should be provided at the top and bottom of every flight. The width and length being at least that of the width of the stairs and can include part of the floor. A door may swing across the landing at the bottom of the flight but must leave a clear space of at least 400 mm (15.7 in) across the whole landing

Tapered steps - There are special rules for stairs with tapered steps as shown in the image Example of Winder Stairs above

Alternate tread stairs can be provide in space saving situations

Guarding - Flights and landings must be guarded at the sides where the drop is more than 600 mm (23.6 in). As domestic private stairs are likely to be used by children under 5 the guarding must be constructed so that a 100 mm (3.9 in) diameter sphere cannot pass through any opening or constructed so that children will not be able to climb the guarding. The height for internal private stairs should be at least 900 mm (35.4 in) and be able to withstand a horizontal force of 0.36 kN/m (2.1 lbf/in).

Industry guidance on designing a staircase to UK Regulation and Standards.

US requirements

American building codes, while varying from State to State and County to County, generally specify the following parameters:

• Minimum tread length, typically 9 inches (229 mm) excluding the nosing for private residences. Some building codes also specify a minimum riser height, often 5 inches (127 mm).
• Riser-Tread formula: Sometimes the stair parameters will be something like riser plus tread equals 17-18 inches (432-457 mm); another formula is 2 times riser + tread equals 24.6 inches (625 mm), the length of a stride. Thus a 7 inches (178 mm) rise and a 10.6 inches (269 mm) tread exactly meets this code. If only a 2 inches (51 mm) rise is used then a 20.6 inches (523 mm) tread is required. This is based on the principle that a low rise is more like walking up a gentle incline and so the natural swing of the leg will be longer.
• Low rise stairs are very expensive in terms of the space consumed. Such low rise stairs were built into the Winchester Mystery House to accommodate the infirmities of the owner, Sarah Winchester, before the invention of the elevator. These stairways, called "Easy Risers" consist of five flights wrapped into a multi-turn arrangement with a total width equal to more than four times the individual flight width and a depth roughly equal to one flight's run plus this width. The flights have varying numbers of steps.
• Slope: A value for the rise-to-tread ratio of 17/29 ~ 0.59 is considered optimal; this corresponds to a pitch angle of about 30°.
• Variance on riser height and tread depth between steps on the same flight should be very low. Building codes require variances no larger than 0.1875 inches (4.76 mm) between depth of adjacent treads or the height of adjacent risers; within a flight, the tolerance between the largest and smallest riser or between the largest and smallest tread can not exceed 0.375 inches (9.5 mm). The reason is that on a continuous flight of stairs, people get used to a regular step and may trip if there is a step that is different, especially at night. The general rule is that all steps on the same flight must be identical. Hence, stairs are typically custom made to fit the particular floor to floor height and horizontal space available. Special care must be taken on the first and last risers. Stairs must be supported directly by the subfloor. If thick flooring (e.g. thick hardwood planks) are added on top of the subfloor, it will cover part of the first riser, reducing the effective height of the first step. Likewise at the top step, if the top riser simply reaches the subfloor and thick flooring is added, the last rise at the top may be higher than the last riser. The first and last riser heights of the rough stairs are modified to adjust for the addition of the finished floor.
• Maximum nosing protrusion, typically 1.25 inches (32 mm) to prevent people from tripping on the nosing.
• Height of the handrail. This is typically between 34 and 38 inches (864 and 965 mm), measured to the nose of the tread. The minimum height of the handrail for landings may be different and is typically 36 inches (914 mm).
• Handrail diameter. The size has to be comfortable for grasping and is typically between 1.25 and 2.675 inches (31.8 and 67.9 mm).
• Maximum space between the balusters of the handrail. This is typically 4 inches (102 mm).
• Openings (if they exist) between the bottom rail and treads are typically no bigger than 6 inches (152 mm).
• Headroom: At least 83 inches (211 cm).
• Maximum vertical height between floors or landings. This allows people to rest and limits the height of a fall.
• Mandate handrails if there is more than a certain number of steps (typically 2 risers)
• Minimum width of the stairway, with and without handrails
• Not allow doors to swing over steps; the arc of doors must be completely on the landing/floor.
• A stairwell may be designated as an area of refuge as well as a fire escape route, due to its fire-resistance rated design and fresh air supply.
• The American Disabilities Act and other accessibility standards by state (such as TAS) do not allow open risers on accessible or egress stairs.

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Stairs and art

As much as stairs are very functional, stairs are can be very decorative and an impressive part of a building. Especially at the entrance of a large building stairs play an important role in the first impression of a building. In large buildings such as banks this is very popular. Modern companies and construction utilize the opportunities of functional stairs to actually upgrade buildings. Large utilities such as banks as well as residential buildings such as penthouses (e.g. in St George Wharf Tower) have modern and luxurious installations.

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Notable sets of stairs

• The longest stairway is listed by Guinness Book of Records as the service stairway for the Niesenbahn funicular railway near Spiez, Switzerland, with 11,674 steps and a height of 1,669 m (5,476 ft). The stairs are usually employee-only, but there is a public run called "Niesenlauf" once a year.
• Mount Girnar, one of the holiest of sacred places for Hindu, Jain, and Buddhist followers, and also for some Muslims is located in Junagadh district in the Indian state of Gujarat in Saurashtrian peninsula. At a height of 1100 metres, with five summits, each adorned with several sacred places are accessed on foot by soaring close to 10,000 steps along a rugged terrain and deciduous forest that is also the last home for Asiatic lions. It is the longest completely stone-made stairway in the world.
• A flight of 7,200 steps (including inner temple Steps), with 6,293 Official Mountain Walkway Steps, leads up the East Peak of Mount Tai in China.
• The Ha?iku Stairs, on the island of O?ahu, Hawai?i, are approximately 4,000 steps which climb nearly ¹/₂ mile (0.8 km). Originally used to access longwire radio radio antennas which were strung high above the Ha?iku Valley, between Honolulu and Kane?ohe, they are closed to hikers.
• The Flørli stairs, in Lysefjorden, Norway, have 4,444 wooden steps which climb from sea level to 740 metres (2,428 feet). It is a maintenance stairway for the water pipeline to the old Flørli hydro plant. The hydro plant is now closed down, and the stairs are open to the public. The stairway is claimed to be the longest wooden stairway in the world.
• The CN Tower's staircase reaches the main deck level after 1,776 steps and the Sky Pod above after 2,579 steps; it is the tallest metal staircase on Earth.
• The Penrose stairs, devised by Lionel and Roger Penrose, are a famous impossible object. The image distorts perspective in such a manner that the stairs appear to be never-ending, a physical impossibility. The image was adopted by M. C. Escher in his iconic lithograph Ascending and Descending.
• The World Trade Center Survivors' Staircase is the last visible structure above ground level at the World Trade Center site. It was originally two outdoor flights of granite-clad stairs and an escalator that connected Vesey Street to the World Trade Center's Austin J. Tobin Plaza. During the September 11, 2001, attacks, the stairs served as an escape route for hundreds of evacuees from 5 World Trade Center, a 9-floor building adjacent to the 110-story towers.
• Stairwell A was the lone stairway left intact after the second plane hit the South Tower of the World Trade Center during the September 11 attacks. It was believed to have remained intact until the South Tower collapsed at 9:59 am. 14 people were able to escape the floors located at the impact zone (including one man who saw the plane coming at him), and 4 people from the floors above the impact zone. Numerous 911 operators who received calls from individuals inside the South Tower were not well informed of the situation as it rapidly unfolded in the South Tower. Many operators told callers not to descend the tower on their own, even though it is now believed that Stairwell A was most likely passable at and above the point of impact.
• In London, England a notable staircase is that to The Monument to the Great Fire of London, more commonly known simply as "the Monument". This is a column in the City of London, near the northern end of London Bridge, which commemorates the Great Fire of London. The top of the Monument is reached by a narrow winding staircase of 311 steps. Constructed between 1671 and 1677, it is the tallest isolated stone column in the world.
• The Spanish Steps in Rome are a monument of late Italian Baroque architecture connecting the Piazza di Spagna with the Trinità dei Monti up the side of the Pincian Hill. Designed by Francesco De Sanctis and constructed 1723-1725, the 135 steps form a wide vista looking down toward the Tiber. The steps are adorned with garden terraces blooming with azaleas and have been widely celebrated in cultural work.
• The Loretto Chapel in Santa Fe, New Mexico is well known for its helix-shaped spiral staircase, which has been nicknamed "Miraculous Stair". It has been the subject of legend and rumor, and the circumstances surrounding its construction and its builder are considered miraculous by the Sisters of Loretto and many visitors.

Source of the article : Wikipedia