building construction_stair design

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Stairs35CHAPTER

CHAPTER OUTLINE

35.1 STAIRFUNDAMENTALS

35.2 WOODSTAIRS

35.3 STEELSTAIRS

35.4 CONCRETESTAIRS

35.5 FREESTANDINGCANTILEVEREDSTAIRS

A stair, defined as a series of ascending (or descending) steps, is an important element that

allows occupants to move vertically in a building. Architectural historians claim that thestair remained a purely functional element (without artistic overtones) until the end of thefifteenth century. The beginning of the sixteenth century, inspired by Leonardo da Vincissketches, however, signaled a new era of expression for the staircase [35.1]. From then on,the staircase played an increasingly important visual role, often becoming a sculptural fea-ture in a space, an imperial entrance to a public building or a significant facade element.

The birth of the elevatorand, subsequently, the escalatorreduced the importance ofthe stair. More recently, the requirement to make buildings accessible to persons with dis-abilities further eroded its significance.

Because a stair cannot be used by people in a wheelchair, it is no longer a mandatoryfeature of an entrance lobby. (Increasingly, entrance lobbies in contemporary public build-ings are designed without a stair.) Consequently, stairs are reverting to their purely func-

tional rolefulfilling the requirement as exit stair or standby vertical circulation in theevent of electrical outage or mechanical interruption.However, despite the stairs decreasing significance, in many contemporary buildings

the rhythm and repetitive features of a stair have been transformed into an importantaesthetic component of the interior space, as shown by the images in Figure 35.1. Thischapter begins with a general introduction to stairs, followed by the details of constructionof simple wood, steel, and concrete stairs.
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(a)

(b)

(c) .

FIGURE 35.1 Images showing theaesthetic potential of stairs; see alsoFigure 35.20. (a)An entrance lobbystair with structural steel beams(stringers) and concrete-filled sheet-steel tread pans (see Figure 35.13).(b)A highly transparent glass wallshowcasing the stair in the MadisonMuseum of Contemporary Art, Madi-son, Wisconsin. (c)Stair in the

entrance lobby of the MadisonMuseum of Contemporary Art, Madi-son, Wisconsin with structural steelbeams (stringers) and glass treads.Architect: Cesar Pelli and Associates.


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35.1 STAIR FUNDAMENTALS

Because a stair provides vertical transportation, it is part of the means-of-egress (exit) systemof a building. It is also a relatively hazardous element because injuries due to falls from stairsare not uncommon. For this reason, stair design is stringently controlled by building codes.

TREAD, RISER, ANDNOSING

There are two main components of a stair: treads and risers. A tread is the horizontal surfaceon which one walks. The riser is the vertical component that separates one tread fromanother. Generally, a stair has several treads and risers. For the sake of safety, the dimen-sions of treads and risers must be uniform in a stair. Building codes allow a small dimen-sional variation because perfect uniformity is unachievable.

In walking on a horizontal or an inclined surface, an average person can comfortablytraverse a distance of 24 to 25 in. in one step. Therefore, a rule of thumb generally used inproportioning the treads and risers of a stair is

2(riser

height) + tread

width = 24

to

25

in.Thus, if the risers in a stair are each 5 in. high, the tread width should lie between 14 and

15 in. The most commonly used dimensions for an interior public stair are 12- to 13-in.treads and 6-in. risers. Outdoor stairs generally have a smaller riser and hence a wider tread.Building codes generally require a riser height between 4 in. and 7 in. and a minimum tread

width of 11 in.In most stairs, the tread is a simple flat surface, and the riser is a solid vertical surface,

Figure 35.2(a). Where space is limited, the effective tread width can be increased somewhatby inclining the risers, Figure 35.2(b), or by projecting the front edge of the tread beyondthe riser, Figure 35.2(c). The front edge of a tread is referred to as the nosing.

When an inclined riser or a projected nosing is used, the code-required minimum widthof a tread does not change. In other words, the width of a tread is considered the horizontal

distance between the vertical planes of the foremost projections of adjacent treads, as shownin Figure 35.2(b) and (c).

The nosing of a tread is subjected to the maximum abrasion. In public stairs with heavytraffic, the treads should consist of a strong, dense material such as granite, high-strength concrete, or steel. Alternatively, a separate nosing (approximately 212in. wide)consisting of an abrasion-resistant and skid-resistant material is epoxied or embeddedinto the tread.

Stairs can also be constructed without risers, referred to as open-riser stairs,Figure 35.3.Because of safety concerns, open-riser stairs are subject to more stringent code restric-tions than stairs with solid risers. For example, open-riser stairs are generally notallowed as exit stairs. Additionally, the clear vertical distance between the treads ofopen-riser stairs cannot exceed 4 in.

STAIRSHAPESThe most commonly used stair shape is a U-shaped stair (in plan). It consists oftwo flights of stairs between floors with a midfloor landing (or simply a midlandingor

(a)

(b)

(c)

Tread width

Tread

Riser

Riserheight

Tread width

Inclined projection notto exced 1-1/4 in.

Tread width

Nosing projection notto exceed 1-1/4 in.

FIGURE 35.2 Tread, riser, and nosing configurations in a stair.

Treads and Risers of a Stair

The treads and risers of a stairmust meet the followingdimensional requirements:

Minimumtreadwidth = 11in.

Riserheight = 4to7in.

Residential Stair

Building codes are less restric-tive for a stair within a dwell-ing unit:

Minimumtreadwidth = 10in.

Riser

height =

4

to

7

3

4

in.A 10-in. tread is allowed in

a dwelling unit stair, providedthat a nosing projection of 34to114in.is used. If a nosing pro-

jection is not used, an 11-in.minimum tread width isrequired.

Some local building codesmay allow a riser height ofgreater than 734in.for a resi-dential basement stair.

NOTE

FIGURE 35.3 A stair with open risers.
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landing), Figure 35.4. In addition to the U-shaped stair, some of the othercommonly used stair shapes are

Straight-run stair with one or two flights, Figure 35.5: A straight-runstair with more than two flights can be used, but this is uncommon.

L-shaped stair,Figure 35.6(a): Where the space is limited, the landing ofan L-shaped stair can be used for steps, yielding trapezoidal (pie-shaped)treads, referred to as winders,Figure 35.6(b). Stairs with winders are notas safe as those with rectangular treads, and their use in an exit stair is

strictly controlled by building codes. Circular stair:A circular stair may consist of all winders and can take

many shapes. A spiral stair is a special type of circular stair in whichthe treads twist around a central column and are cantilevered from it,Figure 35.7. It is generally an open-riser stair. Again, building codeshave several restrictions on the use of a spiral stair. A helical stair is acircular stair without a central supporting column (see Section 35.5).

Floor level

Landing

Structural supportgenerally requiredunder landing.

Thus, each flight is supported at floorlevel and at landing level; see also thefreestanding stair in Figure 35.20.

Floor level

FIGURE 35.4 A U-shaped stair.

The rise of one flight of stairis generally limited by codesto a maximum of 12 ft.

Riseof

flight

Riseof

flight

Riseofflight

(a) A single-flight, straight-run stair (b) A two-flight, straight-run stair

FIGURE 35.5 Straight-run stairs; see Fig. 35.1(a).

Riseofflight

(a) (b)

Riseof

flight

Riseof

flight Pie-shaped treades

called winders

FIGURE 35.6 L-shaped stairs (a)without winders and (b)with winders.

OPENANDCLOSEDSTAIRS

Stairs are also described as either open or closed. An open stair is exposed to the area belowon one or more sides, whereas a closed stair is fully enclosed with a stair enclosure (stairshaft) and is usually accessed through a doorway.

WIDTHOF STAIR

The minimum width of a stair is determined by its purpose. When it is used as an exit stair,its width depends on the number of occupants it serves (occupant load) but is not less than44 in. clear (between handrail and handrail) for an open exit stair or 48 in. for an enclosedexit stair. An exit stair for an occupant load of less than 50, or a stair within a dwelling unit,has a minimum width of 36 in.


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HEADROOM

The headroom in a stair is the minimum clearance between a tread and a projection above,Figure 35.8. Building codes generally require the headroom to be a minimum of 80 in. atany point on the stair.

GUARDUNIT, HANDRAIL, BALUSTERS, ANDNEWELPOST

The edge of a stair exposed to a change in height (i.e., not protected by the wall of theenclosure) must have a guard unit to protect against falling. The minimum height of aguard unit is 42 in., Figure 35.9(a). The clear distance of openings in a guard unit must notexceed 4 in.

A spiral stair with a handrail on the

left allows a right-hand grip onthe handrail when walking down(preferred by some designers).

A spiral stair with a handrail on theright allows a right-hand grip on

the handrail when walking up.

FIGURE 35.7 A spiral stair.

Floor

Headroom80 in. minimum

Ceiling

Floor

FIGURE 35.8 Headroom in a stair.


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The height of a handrail in a stair is generally required to lie between 34 in. and 38 in.The cross-sectional profile of a handrail is controlled by building codes to give it therequired graspability.

In some wood stairs, the first and/or the last vertical member of the guard unit (referredto as a baluster) is highlighted by using a more ornate design. Such a baluster is referred toas a newel post,Figure 35.9(b).

STAIRLAYOUTANDSTAIRPLAN

In preparing a stair layout, we first determine the floor-to-floor height and then calculatethe number of risers and treads. Assume that the floor-to-floor height in a building is 10 ft8 in., that is, 128 in. Assume further that we would like the riser height to be approximately6 in. Dividing 128 by 6 gives us the number of risers:

Numberofrisers =6

= 21.3

Because the number of risers must be a whole number, assume 21 risers. Dividing 128in. by 21 gives the exact riser height, 6.1 in. From the tread-riser relationship given earlier,the tread width is

24(or25) - 2(6.1) = 11.8to12.8in.

We will use a tread width of 12.0 in. Assume further that a U-shaped stair is desired and thewidth of the stair is 4 ft. By code, the minimum width of the landing must be the same as the

1. Tread depth and riser height must be dimensionally uniformthroughout.

2. Minimum tread width =11 in. Riser height =4 to 7 in. (SeeSection 35.1 for exceptions for residential stairs.)

3. Nosingprojection 114in.4. Stair width =function of the occupant load, but not less than

48 in. for an enclosed exit stair, 44 in. for an open exit stair,or 36 in. for a stair serving an occupant load of less than 50or a residential stair.

EXPAND YOUR KNOWLEDGESummary of Stair-Design Criteria

5. Width of landing stair width.6. Rise of one flight 12 ft.7. Headroom 80 in.8. Use of winders is restricted.9. Height of guardrail =42 in. minimum. Height of handrail =

34 to 38 in.

10. Handgrip portion of the handrail must have a circular crosssection between 114in.and 2

58in.Noncircular profiles must

provide equivalent graspability.

(b) Balusters and newel

post in a wood stair

Newel post

Baluster

Vertical members of a guard unit, called balusters

Guardrail

Handrail

34to38

in.

Handrailheight

42-in.min.

guardrailheight

A guard unit can be solid or open. A guard unit with an opening may consist ofhorizontal or vertical members or both. The clear dimension of an opening in a guardunit must be less than 4 in. Minimum guard unit height = 42 in.

(a) Guard unit and

handrail in a stair

FIGURE 35.9 Guard unit, handrail, balusters and newel post.


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width of the stair, that is, 4 ft. With these data, a plan of the stair can be drawn, as shown inFigure 35.10.

STAIR-DRAWINGCONVENTIONS

There are standard conventions for how stairs are shown in building plans. Figure 35.10 is

the plan at the second-floor level of a U-shaped stair that extends from the first to the sec-ond floor only. The plan of the same stair at the first-floor level is shown in Figure 35.11(a).If the same stair were to extend over several floors, then the plan of the stair at a typicalfloor would generally be drawn as shown in Figure 35.11(b).

Omitting a riser at mid-

landing and at a floorallows the handrail to turnwithout a pronouncedvertical step.

(a) Plan of the stair in Figure 35.10 at the

first-floor level

(b) Plan of a multifloor stair at a

typical floor

UP

DN

UP

FIGURE 35.11 Stair plans at different levels.

7

2

3

4

5

6

89

10

11

12

1

1314

15

16

17

18

19

20

21

LANDING

Stairenclosure wall

It is a good draftingpractice to number therisers in the plan of a stair.

UP Guard unit

Width of landing>

Width of stair

FIGURE 35.10 Plan of a U-shaped

stair (at the second floor level) thatextends only from the first floor tothe second floor.


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FIRE-RATEDSTAIR(SHAFT) ENCLOSURE

Because most stairs in a building are used as exit stairs, they need to be enclosed by verticalenclosures (also referred to as shaftsor shaft enclosures). Generally, a shaft enclosure isrequired to be 1-h rated for a building up to four stories tall and 2-h rated for a building

with five stories or more. Shafts are not required for individual single-family dwellings (upto four stories tall).

Building codes also contain several other exceptions to the requirement of shaft enclo-sures. For example, shafts are not required if the stair connects only two floors and is notused as an exit stair.

Each question has only one correct answer. Select the choice that bestanswers the question.

1. An approximate formula generally used in determining the treaddimension (T) and riser dimension (R) in a stair isa. 2T +R =24 to 25 in. b. 2T +2R =24 to 25 in.c. 2R +T =24 to 25 in. d. R +T =24 to 25 in.e. none of the above.

2. The minimum tread width required by building codes for anonresidential stair isa. 11.0 in. b. 11.5 in.c. 12.0 in. d. 12.5 in.e. 13.0 in.

3. The minimum riser height required by building codes for anonresidential stair isa. 6.0 in. b. 5.5 in.c. 5.0 in. d. 4.5 in.e. 4.0 in.

4. The maximum nosing projection allowed for a stair isa. 3.0 in. b. 212in.c. 2 in. d. 112in.e. 114in.

5. A riser must be vertical. It cannot be inclined.

a. True b. False6. A U-shaped stair has been provided between the first floor and the

second floor of a building with a midlanding. This stair hasa. one flight. b. two flights.c. three flights. d. four flights.

7. The rise of one flight of stair is generally limited by building codes toa. 7 ft. b. 8 ft.c. 10 ft. d. 12 ft.

8. Given a multistory building with a floor-to-floor height of 10 ft andan optimal riser height of 7 in., how many treads would you use for aU-shaped stair with a midlanding between floors? (The landing is notcounted as a tread.)a. 15 b. 16c. 17 d. 18

e. None of the above9. A handrail and a guardrail in a stair are synonymous.

a. True b. False

10. The minimum height of a guardrail in a stair isa. 34 in. b. 36 in.c. 38 in. d. 40 in.e. none of the above.

11. A stair constructed without risers is generally called aa. no-riser stair. b. closed-riser stair.c. open-riser stair. d. hollow stair.

12. A stair with treads cantilevered from a central column is aa. circular stair. b. U-shaped stair.c. L-shaped stair. d. spiral stair.

e. helical stair.13. The minimum width of a stair in a dwelling unit is

a. 2 ft 6 in. b. 3 ft.c. 3 ft 6 in. d. 4 ft.e. none of the above.

PRACTICE QUIZ

35.2 WOOD STAIRS

The most important parts of a wood stair are the carriages(also called rough stringers). Car-riages are the structural elements of a stair (inclined beams) and are specially cut to support

the treads. Figure 35.12 shows a commonly used method of framing a wood stair.

PREFABRICATED WOODSTAIRS

There are several manufacturers who supply prefabricated wood stairs per the architectsdesign. Prefabricated wood stairs are usually transported in a knocked-down (KD) version,

where each part is uniquely numbered for assembly on site. They are commonly used formore ornate stairs requiring detailed millwork and craft, which are not usually possible atthe site.
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(a) Framing of a typical wood stair

(b) Detail of rough stringer and finish stringer

Floor frame Floor frame

Stringer (or finish stringer);see detail sketch below.

Gypsum wallboard

Wall frame

Wood ledger support for carriages.Alternatively, use joist hangers.

RiserTread

Carriage (rough stringer), generally of 2-by lumber (or equivalentLVL member). The number of carriages required depends on thewidth of the stair and the spanning capability of the material used forthe treads. For most residential stairs, three carriages are common.

Landing frame supported onstud walls.

Wood ledger support for carriages.Alternatively, use joist hangers.

Carriage

Thrust blcok

Stud wall

Gypsum board

Stringer (or finishstringer), generally of 1-by

finish lumber, nailed towall frame over gypsumdrywall

Space between finishstringer and roughstringer is covered overby treads and risers.

2-by nailer block nailedto wall frame alongthe slope of thecarriage

Carriage (roughstringer) nailed tonailer block

FIGURE 35.12 A commonly used framing system for a wood stair.


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35.3 STEEL STAIRS

Stairs in public buildings are generally constructed of steel or concrete. Because steel stairscan be shop fabricated and brought to the site ready for installation, they are far more com-monly used than concrete stairs. Another reason for the lack of use of concrete stairs is thattheir formwork is complicated and expensive.

Prefabricated steel stairs are used in all types of public buildings, that is, steel- and con-crete-frame buildings and load-bearing masonry buildings. They are particularly popular

for exit stairs.

1234

5

678

910

1112

13

14

15

Guard unit

Stud wall Handrail

A

A

Omitting a riser at the landing(as shown here) allows theguardrail to turn without apronounced vertical step

UP

Finished wood flooring appliedover rough treads and risers

Finished wood tread

Finished wood riser

Rough riser

Rough tread

Rough stringer

Finished wood tread

Finishedwood riser

Finished wood treads andrisers applied directly overrough stringers

Stud wall

Nailer blockbetween studs tosupport handrail

Finished stringer heightto match wall base

Handrail

P

(c) Plan of stair

(d) Section A-A

Carpet applied over roughtreads and risers

Chamfer front edges of

rough treads to allowcarpet to wrap over neatly

(e) Three alternative detailsat P

FIGURE 35.12 (continued) A commonly used framing system for a wood stair.
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A typical prefabricated flight of a steel stair consists of two stringer beams (stringers) towhich tread-riser units made of sheet steel are welded, Figure 35.13.

The tread pan is generally site filled with concrete, Figure 35.14 . For good wear resist-ance, a concrete strength of 5,000 psi is generally specified. Other tread finishes include aprecast-concrete drop-in treadwith a slip-resistant broom finish, Figure 35.15(a), and sheetsteel with a raised, diamond-shaped checkered pattern, Figure 35.15(b). Factory-installedepoxy-aggregate fill or wear- and slip-resistant coatings can also be used.

STRINGERS

Stringers in a steel stair function as inclined beams, spanning from the floor to the landingand from the landing to the next floor. They generally consist of a structural-steel channel

One-piece, sheet steel bentto form a tread-riser unit

Tread pan (in a thread-riserunit) to be site-filled withconcrete

Stringer. In this case, astructural steel channel sectionhas been used, but the use of asteel plate is also common

FIGURE 35.13 A typical prefabricated steel stair consists of two stringer beams (stringers) towhich tread-riser units made from sheet steel are welded; see Figure 35.14 for details. (In thisstair, the guard unit and handrail have not yet been installed.)

Site-filled concrete in treadpan; 1-1/2-in.-thick concrete

fill is typical

Sheet steel bent toform tread-riser unit.Sheet thickness is afunction of stair width

WeldSite-filledconcrete intread pan

SectionA-A

Stringer (generally a steel channel; asteel plate may also be used); depth ofstringer is a function of stringer spanA

A

FIGURE 35.14 Typical detail of tread-riser units welded to stringers. In this detail, tread pans are site-filled with concrete;see Figure 35.15 for alternatives.


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Precast concrete tread (5,000-psi concrete with broom finishfor slip resistance, wire meshreinforcing) adhered to steeltread with epoxy cement

Sheet steel with checkered orraised diamond pattern for slipresistance, bent to form tread-riser combination

Stringer

(a) (b)

FIGURE 35.15 Two alternative details of tread-riser units in a steel stair (precast concrete treads and checkered steel treads); another detail isshown in Figure 35.14.

or steel plate (16in. or14in. thick is typical). The depth of stringers is a function of the

stringer span and the structural loads required by codes. The tread-riser units span betweenthe stringers. Figures 35.16 and 35.17 show typical details of support connections between

the stringers and the floor of the building.

LANDINGFRAME

The landing of a steel stair is generally framed with structural steel members as a unit,called a landing frame. Typical details of connections between stringers and landings areshown in Figure 35.18. The finish on the landing is generally the same as that on thetreads. Thus, where site-cast concrete is used on treads, the landing is also topped withconcrete.

The landing frame may be supported on a beam (specially introduced for the pur-pose) between the upper and lower floors of the building, on (masonry or concrete)stair-enclosure walls, or on columns independent of the structural frame of the build-ing. In most buildings, however, the landing frame for a prefabricated steel stair is

supported by suspending it from the upper-level floor beams with steel hanger bars,Figure 35.19.

A major advantage of a suspended landing is that it allows adjustment of the height ofthe landing with a few turns of the nuts. Additionally, the entire stair can be erected beforeconstructing the walls of the stair enclosure.

35.4 CONCRETE STAIRS

Although concrete stairs can be precast and prefabricated, their use is limited because theyare heavy, which increases the cost of transportation and installation. Most concrete stairsare site cast. As previously stated, the formwork for concrete stairs is intricate, whichincreases the cost and causes construction delays. Their use is, therefore, infrequent, even in

buildings with a reinforced-concrete structural frame.
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Block-out in floor beam to be filledwith concrete after installing stair

Steel angle end support welded tostringers

Stringer

Block-out in floor

beam to be filled withconcrete afterinstalling stair

Steel angle

embedded inreinforced-concrete floorbeam

(a) Connection between stairstringer and upped reinforced-concrete floor beam

Stringer

Steel angle end supportwelded to stringers

Steel angle embeddedin reinforced-concretefloor beam(b) Connection betwen stair

stringer and lower reinforced-concrete floor beam

FIGURE 35.16 Typical details of the connection between stringers and a reinforced-concrete floor.

35.5 FREESTANDING CANTILEVERED STAIRS

In the various stair types discussed so far, each flight is supported at the floor and landinglevels. The use of steel and reinforced concrete, however, allows the stairs to be constructed

without any supports at the landings (designed as cantilevers and supported only at thefloors). Cantilevered stairs, also referred to as self-supporting stairs,can either be U-shapedor circular in plan.

A cantilevered, self-supporting, U-shaped reinforced stair is shown in Figure 35.20(a).Figure 35.20(b) shows a cantilevered steel stair. In this stair, the stringers (of structural-steelchannels) function as continuous spatially bent beams that are rigidly connected to thefloor beams at both floors. Tread-riser units that span between stringer beams are made ofstructural-steel plate.

Self-supporting circular steel or concrete stairs can be constructed with or without land-ings. Called helical (or helicoidal) stairs, they are fairly common in steel, concrete, and

wood. A helical stair is similar to a spiral stair but has no central column support.
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Stringer

Steel angle endsupport weldedto stringers

Steel angle end supportwelded to stringers

Floor beam

Stringer

Floor beam

(a) Connection between stairstringer and upper structural steel

floor beam

(b) Connection betwen stairstringer and lower structural steel

floor beam

FIGURE 35.17 Typical details of the connection between stringers and a steel-framed floor.

Metal deck supported by landingframe and topped with concrete(2-1/2-in. concrete fill typical)

Structural steel channelas front header oflanding frame

Landing frameheaded by structuralsteel channel

Stinger

Stinger

Structural steelchannel as front headerof landing frame

Landing frame headed bystructural steel channels

Metal deck

supported bylanding frame andtopped withconcrete (2-1/2-in.concrete filltypical)

FIGURE 35.18 Typical details of the connection between stringers and the landing frame.


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Hangerbar forlanding

support

Landingframe

Stringer

FIGURE 35.19 A typical steel stair with a suspended landing a commonly used landing support system for exit stairs in concrete and steel-frame buildings. (Guard units and handrail have not yet been installed.)

(a)

(b)

FIGURE 35.20 Two examples ofcantilevered freestanding stairs,

which are supported onthe upper and lower floor structures,with no supports provided at mid-landing levels.


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Each question has only one correct answer. Select the choice that bestanswers the question.

14. In a typical wood stair, inclined beams that are cut to allow for thesupport of treads are calleda. rough stringers. b. finish stringers.c. balusters. d. all of the above.e. none of the above.

15. In a typical wood stair, the number of stringers required isdetermined by thea. width of the stair.b. spanning capacity of the carriage material.c. floor-to-floor height.d. thickness of the treads.e. all of the above.

16. In a prefabricated steel stair, treads and risers are generally twoseparate components.a. True b. False

17. In a typical prefabricated steel stair, the number of stringers requiredis determined by thea. width of the stair.b. spanning capacity of the stringers.

c. floor-to-floor height.d. spanning capacity of the tread-riser units.e. all of the above.

18. In a typical prefabricated steel stair, the stringers are cut toaccommodate treads and risers.a. True b. False

19. The stringers in a typical prefabricated steel stair are generally

made ofa. wide-flange sections. b. channel sections.c. plates. d. (a) and (b).e. (b) and (c).

20. The landing frame in a typical prefabricated steel stair is generallyhung from the buildings structural frame.a. True b. False

21. A self-supporting cantilevered stair is supported on intermediatelandings only.a. True b. False

22. A self-supporting cantilevered stair can be made only of reinforcedconcrete.a. True b. False

PRACTICE QUIZ

1. Provide the approximate expression used in proportioning the dimensions of the treads and risers of a stair. What isthe basis for this expression? List building codes restrictions on the dimensions of treads and risers.

2. With the help of at least two sketches, explain what a flight of stairs implies. What is the code-mandated maximumheight of a flight of stairs?

3. Using a sketch, explain the difference between a handrail and guardrail of a stair, and give their code-mandatedheights.

4. List the factors that determine the width of a stair.

5. Using sketches, explain how a steel stairs landing frame can be supported. Which one of these support methods ismost commonly used?

6. Explain why a prefabricated steel stair is most commonly used even in buildings that are built with a reinforced-concrete frame structure.

7. Using a sketch, describe a cantilevered freestanding stair.

REVIEW QUESTIONS

building construction_stair design

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