His background includes the structural design of stairways for a variety of uses with additional experience in industrial design, connection design, and construction engineering related to structural steel. Acknowledgments The author wishes to acknowledge the support provided by Computerized Structural Design S. He would also like to thank the following people for assistance in the review of this Design Guide.
Their comments and suggestions have been invaluable. Background information regarding stairways, code requirements, design methods, and design examples are presented. The goal of this Design Guide is to provide sufficient information for a structural engineer to complete the design of a steel-framed stairway or provide adequate guidance to delegate this work to another engineer or stair designer.
This Design Guide provides fabrication, erection and construction process related to steel information regarding tolerances for different con- stairways. Part of this effort involves providing guidance struction materials in Section 8. Code requirements for a stair dictate the functional Adjustment and flexibility can also be provided in the aspects of layout and design. It is imperative that design to accommodate changes to the stair layout accurate dimensions and clear requirements be pro- or construction tolerances.
Designers should provide vided by the architect to ensure the proper layout of stair connections that allow for adjustment through a stairway can be achieved. Chapter 3 of this Design the use of slotted holes or adjustable bearing details. Guide provides an overview of various code require- Refer to Figure for the use of an extended plate ments. These requirements should always be verified detail with horizontal slotted holes that allow for with the architect for each project.
This Design Guide provides several connection options in Chapter 6. For projects using delegated design submittals for structural engineering of stairways, code require- Designers can also provide a concrete slab edge angle ments should be confirmed with the architect before detail that allows for adjustment by the detailer when detailing work begins.
The architect should review the stair detailing is underway. Refer to Figure stair shop drawings for aesthetic elements and code for a detail that provides adjustment during detailing. Adequate time for the review process vide flexibility at opening locations by shipping the should be included. Chapter 9 of this Design Guide concrete slab edge angle as a loose piece to be field provides additional information related to delegated welded to the perimeter beams.
This allows for minor design. Final stair opening sizes should be coor- 3 Quality of design documents and information dinated with project team members. The design documents should clearly show the work Completing a field survey or creating an accurate set that is to be performed and should give sufficient of as-built drawings will help to avoid field modifi- dimensions and guidance to accurately convey the cations.
This can be especially important in existing design intent for the work to be constructed. It is most desirable to have throughout. To accomplish this, the main building struc- for stairways and guards. This level of information tural members must be present either at the level of often leads to conflicts between the design documents the landing or at a location that will permit the landing and project specifications. It also leads to unnecessary to be hung from the structure above or supported from delays and confusion that need to be resolved through below.
Design- Stair runs also require the same consideration. With a ers need to take care to provide accurate informa- fully supported landing, the stair run can be supported tion throughout their design documents or defer all by the intermediate landing and the lower or upper aspects of the design to another party.
Appendix A of floor framing. A review of Chapter 3 of this Design this Design Guide provides checklists that can help to Guide will aid designers in the framing layout to pro- ensure that designers have provided adequate infor- vide adequate support for stairways. These requirements will vary any portion of work that is part of a deferred submit- based on the stair type and stair class.
This Design tal, delegated design, or a design-build process. Each Guide covers general stair information in Chapter 2. Designers should clarify their ber types with advantages and disadvantages for each scope of work and expectations for project submittals type can also be found in Chapter 4, Chapter 5 and before entering into a contract.
Contractual guidance Chapter 7. Working with the project team to overcome and resolve 4 Coordination of structural support with stairway the issues presented here can help to avoid potential prob- support lems related to the design and construction of stairs.
Struc- An often overlooked aspect of stairway design is the tural engineers, detailers, fabricators and erectors can utilize requirement for structural support of the stair stringers this Design Guide along with years of experience to con- and landings.
Many times, stairs are shown pictorially tinue providing steel solutions for everything from simple on drawings without consideration of how they can egress stairs to unique feature stairs. This vertical access can be used to move from one This Design Guide illustrates methods for the layout and level to another and provides a means of egress in an emer- design of common stairway, handrail, guards and associated gency.
Stairways provide a safe and efficient option for trav- connections based on structural principles and presents the eling within a building. Handrails provide a graspable surface for 2 Tread and riser section occupants to hold while moving along a stairway.
Handrail is typically wall mounted or supported on the guard. Guards 3 Stringer design as a simple span are provided at or near the open side of an elevated walking 4 Stringer design with integrated landing surface and incorporate infill members or panels to minimize 5 Guard and handrail assembly the possibility of falling to a lower level.
The design and layout of stairways is dependent on the 6 Typical connections intended use, occupant load and serviceability requirements. Although this Design Guide is primarily intended to assist Proper clearances and intuitive layout are important to the practicing engineer, it may also be a reference for archi- ensure occupants can easily and safely use a stairway.
Stairways, handrail and guards are a critical aspect of any Complex and custom stairway systems, independent building design, but they are often overlooked or deferred to stairways, nonsteel elements e.
This Design Guide will focus on steel- ing, aluminum, etc. A valuable resource for additional infor- odology, and delegated design considerations. Practical mation related to stairs and railings can be found in the design examples are included in Chapter 10 of this Guide.
Typical types of stair- 1. The Design Guide presents standard design are critical to the proper layout of these elements. The lay- methodologies for the design of steel elements for stairways, out is mandated by the appropriate code requirements and is handrail, guards and associated connections.
Additionally, determined based on the type and classification of the build- information regarding delegated design and recommended ing and the needs of the occupants.
The most commonly standard practices related to stairways is provided. When referring to and This Design Guide provides additional the use of post-installed anchors.
The decisions made dur- information, design methods and recommendations related ing design can have a major impact with regard to fabrica- to stairways, handrails and guards fabricated from steel. Designers should consult with local detailers and fabrica- However, the criteria for the design, fabrication and erection tors to determine preferred member sizes, ideal layout, and of steel members and steel connections that are part of a stair connection details for stairways, guards and handrail.
Utiliz- or handrail may be subject to the same provisions within the ing these preferences in the design phase can typically save AISC Code of Standard Practice, the AISC Steel Construc- time and money during detailing and fabrication. Using these standards cores, and freestanding self-supporting systems. The attach- as references along with professional judgment will provide ments and integration of a stairway to each of these elements a set of reasonable design criteria that can be applied to the presents concerns related to tolerances and fit-up that need structural design of steel members and connections used in to be evaluated.
All of these considerations need to be accounted for by the The level of occupant comfort is also a design consider- SSE to provide a stairway that meets the code requirements ation. Serviceability requirements for stairs are based on ver- for occupant use, provides the required level of strength and tical deflection limits per the applicable code requirements serviceability, provides an economical and constructible sys- or more stringent project requirements.
Additional guidance tem, and can be integrated into the main building structure. Vibration analysis may also be or design-build submittal, the SSE must also coordinate with required based on the size and configuration of a stairway. Activity Murray et al. Consists of either a single flight extending between This information is reproduced in this chapter with modifi- floors as shown in Figure or a series of two or cations, additional information and commentary pertaining more flights in the same line with intermediate plat- to common steel-framed stairways used for egress and main- forms between them as shown in Figure The Type des- Successive flights which are parallel to each other and ignation identifies the physical configuration or geometry of are separated by one or more intermediate platforms the stair, while the Class designation refers to its construc- as shown in Figure Successive flights placed at an angle to each other with an intermediate platform between each flight as 2.
The geometry, layout and finishes are based on the proj- the previous section. Several common stair types d Scissor are discussed herein, including straight stairs, circular stairs, A pair of straight run flights paralleling each other curved stairs, alternating tread devices, and ships ladders.
They may or in which the stringers are straight members. The slope of may not have intermediate platforms between floors. Straight stairs may to Figure Straight run stair. Straight run stair with integrated landing. Straight stair—parallel with intermediate landing. Straight stair—angled. Refer to Figure Curved stairs are stairs that, in plan view, have two or more centers of curvature, being oval, elliptical or some other 2. They also may or may not have one or more intermediate platforms between floors.
Refer In this type of stair the treads are flat, and handrails are typi- to Figure This type of stair is not acceptable as a path used for means of egress except for certain special situations. If In this type of stair, the treads are alternately mounted on the space permits, other stair types are typically preferred.
Ship left and right side of a center stringer. Because of this tread Ladders are more commonly used for maintenance access in construction and the use of handrails on each side, these areas not intended for access by the general public.
Refer to stairs permit safe descent facing outward from the stair. The Figure This type of stair is not acceptable as a path used for means of egress except for certain special The class designation of a stairway is indicative of the type situations. If space permits, other stair types are typically of construction; the quality of materials, details and finish; preferred.
Alternating tread stairs are more commonly used and, in most cases, the relative cost. Stairs of all classes are built to meet the same standards of performance with respect Up Up Plan Elevation Fig. Straight stair—scissor. Up Up Plan Plan Fig. Circular stair. Curved stair. As such, these class dis- 2. Ser- rather in character and appearance. It is important to recog- vice stairs are usually located in enclosed stairwells and nize that where function is the prime concern and aesthet- provide a secondary or emergency means of travel between ics are of minor importance, significant economies can be floors.
In multi-story buildings, they are commonly used as achieved by specifying one of the less expensive classes. They may serve employees, tenants or the pub- The following descriptions indicate the general construc- lic and are generally used where economy is a consideration. It should be recognized Service stair stringers are generally the same type as those that because each manufacturer has its own preferred meth- used for industrial class.
Treads may be one of several stan- ods of fabrication, the details of construction vary somewhat dard types, either filled or formed of floor or tread plate, and throughout the industry. The four classes of stairs are listed risers are either exposed steel or open construction. Guards in the order of increasing cost as a general rule. Connections on the underside of the stairs are Stairs of this class are purely functional in character and, commonly made with hex head bolts, and only welds in the consequently, are generally the most economical.
They are travel area are ground smooth. This class does not include stairs that are Stairs for this class are usually for public use and are of integral parts of industrial equipment. They may be placed in an open location or may be construction. Hex head bolts are commonly used for most located in closed stairwells in public, institutional or com- connections. Welds, where used, are not ground to produce mercial buildings.
Stringers may be flat plate, open channels Stringers for this class of stairs are usually exposed open or hollow structural section HSS members; treads and plat- channel, plate sections, or HSS members.
Treads may be any forms are usually constructed of grating or floor plate; and of a number of standard types; risers are usually exposed risers are usually open, though in some cases, filled pan-type steel. Guards and handrail vary from ornamental bar or HSS treads and steel risers may be used. Guards and handrail are construction with metal handrail to simple pipe construction, usually constructed of pipe, tubing, angle or steel bar.
Exposed bolted con- When used for exterior applications, the details of con- nections in areas where appearance is critical are made with struction are similar, except that treads and platforms com- countersunk flat or oval head bolts; otherwise, hex head bolts monly utilize grating or perforated floor plate. For solid are used. Welds in conspicuous locations are smooth and all surfaces at treads and platforms, a slope to allow for drain- joints are closely fitted.
Side View Elevation Elevation Fig. Alternating tread device. Ship ladder. As a general rule, construction joints are made as inconspicuous as possible, exposed welds are This classification applies to more elaborate, and usually smooth, and soffits are covered with some surfacing material.
They may be wholly custom structural members enclosed in other materials. Guards and designed or may represent a combination of standard parts handrail are of an ornamental type and, like the treads and with specially designed elements such as stringers, guards, risers, will be dictated by architectural design requirements.
Usually this class of stair has a comparatively low pitch, with relatively low risers and cor- respondingly wider treads. Architectural metal stairs may be 2. This nomenclature is used The fabrication details and finishes used in architectural throughout the Design Guide. Nomenclature—plan views. Nomenclature—section views. Code require- acceptable regardless of the building use.
Stairways con- ments, including local amendments, are determined by the forming to OSHA standards may be acceptable only in cer- local authority having jurisdiction.
The most commonly tain situations or may be subject to modified requirements. Code requirements for residential stairs in one and These additional requirements may affect the recommenda- two family dwellings are based on the International Resi- tions and requirements given in this Design Guide. Designers should consider both erning code.
Designers should determine the applicable load the loading requirements in Section 3. The architect and structural engineer of record SER 3. The IBC, where adopted by the local authority having jurisdiction, applies to all types 3.
In most cases, stairways should be based on the requirements of the IBC Dead loads include self-weight of the steel framing and and any additional local amendments. These include stairs constructed in jurisdictions elements. In some cases, stair members may also support that do not use a model building code and stairs in a certain stud walls or partitions. Addi- C3. An allowance of 5 to 10 psf should also be consid- tionally, the authority having jurisdiction may grant a waiver ered when mechanical, electrical, plumbing, or fire protec- or exemption allowing stairways to conform to the OSHA tion components will be supported from the underside of the standards.
Table includes typical components that are additive It is critical that stair designers verify the applicable to the stairway self-weight. The designer should verify with the local authority having jurisdiction Live loads are specified by the governing building code. These live loads are summarized in handrail elements. Table with respect to stairway design.
For stair treads, It should be noted that factory, industrial and storage both the concentrated loading and uniform loading should be occupancies in areas that are not accessible to the public and checked. However, per IBC, these loads are nonconcurrent, that serve an occupant load not greater than 50 are excluded and the most severe loading should be used for design. For from the uniform live load for guards. The normal live load vides the required live loads to be used and these have been as required by OSHA standards should be based on project included in Table OSHA requires that stairs be designed specific requirements, but the author recommends using a for five times the normal live load or a minimum 1, minimum psf uniform live load nonconcurrent with con- pound concentrated load per Section Guard centrated load as an additional check for the stair design.
Toeboard loading require- sibility of unbalanced loading. Depending on the configura- ments are given in Section The total live load is lb over approx- been withdrawn as an active standard; however, it is still reg- imately 27 ft2.
Table sum- Per OSHA, this is the normal live load. The stair marizes these requirements. The normal live load should be based on expected usage 3. Stairs accessing certain maintenance platforms For exterior stairways, additional loadings should be con- may only be accessed by one worker in the infrequent event sidered, including wind loads, snow loads, rain loads and that a piece of equipment breaks down, resulting in a low ice loads.
Depending on the size and layout of the stairway, normal live load. On the other hand, stairs accessing an area environmental loads may control the design of individual that requires hourly checks of equipment by several employ- elements.
Due mic forces. Additionally, there are now multiple criteria for to the open nature of stair framing and attached guards, different components of the stairway. This includes general determining the force coefficient, Cf , is critical. Using the criteria for stairway components i.
The minimum wind load to be used is 16 psf bolts, welds, anchors. Snow may accumulate on the surface of purposes after an earthquake and are therefore required stairways with solid treads and landings. The minimum to use the higher component importance factor, Ip, of 1. Snow loading may The horizontal seismic design force, FP, is applied at the become more severe due to the effects of snow drifting. For center of gravity of the component and must be applied inde- stairways located in northern regions, load combinations pendently in at least two orthogonal horizontal directions.
Additional consideration should be made for drainage at the treads and landings when 0. Ice loads may become substantial in certain regions. For treads and landings when the ice melts. This table has 5 MSJC, for masonry. For concrete or masonry, the been reproduced with author commentary in Table and anchor selected for the project must also be prequalified for includes the applicable variables related to egress stairways.
Also note that redundancy and overstrength factors is permitted to be taken as 1. The requirements for these types of stairs are beyond the scope of this Design Guide.
Additional com- In many cases, stairway components are anchored to con- mentary and formulas to determine expansion joint spacing crete or masonry elements. Component anchorage design are provided in AISC Manual Part 2, in a section labeled involves additional requirements that must be followed. Excerpted from Table Reproduced with permission. All rights reserved.
By providing discrete lengths or expansion joints for guard 3. From historical experience, design for stairways, guards and handrail. In many cases, guards with lengths less than 50 ft have not typically pre- serviceability and occupant comfort will govern the design sented issues due to thermal loads. Assemblies with lengths of stairway members.
Stairs and other gravity members should also be reviewed 3. If the change in member length due to thermal serviceability requirements given in the IBC deflection lim- loads is a concern, care should be taken to provide connec- its of Table The tions that allow for thermal expansion and contraction using IBC does not explicitly provide requirements for deflection bearing type details.
Recommendations are pro- vided based on deflection limits for exterior walls with flex- 3. Additional requirements related to guards and handrails All structures are required to have a continuous load path are provided in Specification for Permanent Metal Rail- and a complete lateral force-resisting system. The appli- These limits are provided in Table At the time cation of notional loads is discussed as well as its use in of writing, ASTM E has been withdrawn as an active combination with dead and live loads.
The author recommends using the 7, Section 1. Lateral forces are determined using the following An additional serviceability requirement that should be equation: considered for the design of stairways is vibration. For dele- mental stairs can be more susceptible to vibration due to the gated design, the SER should provide this information to the movement of occupants.
Stair designers can then provide designs that al. In any case, Dp is not required to be taken as also consider the difference in lateral movements between greater than adjacent floors or seismic relative displacements due to earthquakes. Slip connections or sliding connec- point is attached, in.
Table Designers should apply the horizontal seis- of metal attachments. To ensure proper performance, mic forces at the center of gravity and use established meth- this connection type must: ods to determine lateral displacement values.
The layout of stairways, guards and handrails is presented Refer to Figures and for examples of this here as a guide only. The actual requirements for stairways, type of connection. To ensure proper per- is presented in Table If any of these Refer to Figure for an example of this type of elements were installed before January 17, , then they connection. Actual framing, connections and layout horizontal direction.
Refer to Figure for a plan view, elevation and cross sec- tion showing minimum code requirements per OSHA for a Additionally, all fasteners and attachments must be stairway. Careful analysis, design having jurisdiction. This may also include coordination with and detailing are required to ensure acceptable performance. Special attention must also be paid when working with Stairs must also be checked for lateral displacement due architectural class stairs due to the use of floor and wall to seismic forces to ensure the stair components are within finishes.
Group F:Factory and industrial. Group S: Storage. Group H: High Hazard. Solid required openings up to 2-in. Egress stairway based on IBC requirements.
Stairway based on OSHA regulations. The layout and construction of walls can present several challenges to the stair designer. The following sections provide door location and swing. Projections may reduce this width for IBC stairways. Determination of stairway opening dimensions. Coordinate with the on connection geometry, if required. Providing a half tread allows for space to include stan- These equations are provided as a recommendation dur- dard shear connections from the AISC Manual at the stringer ing the design phase to ensure proper fit-up of stairs during to support beam location.
It also allows additional space so detailing, erection and construction. When using deferred that the stair riser and nosing can be set back from the walk- submittals, establishing and providing the clear dimensions ing path on the landing. The author recommends that space for stair openings is critical.
Changing openings or fabricat- is provided to accommodate bolted connections for easier ing nonstandard stairs can lead to additional costs and proj- steel erection and fit-up in the field. Welded connections may ect delays. Once an overall shape and profile are established, the b if specified on the project. The American Concrete Institute ACI b list the maximum uniformly distributed service load Building Code Requirements for Structural Concrete and for deflection-controlled applications and the maximum Commentary ACI, can be used for the design of con- uniformly distributed load for flexural strength-controlled crete and precast concrete elements incorporated into steel- applications, respectively, for various thicknesses and spans framed stairways.
Table b presents the recommended maximum design criteria that can be applied to the structural design uniformly distributed load based on the stress limit of 24 ksi of steel members and connections used in stairways, guards in LRFD and 16 ksi in ASD, including the required safety and handrails.
Designers should verify with the fabricator or sup- Specification. Alternative design methods may also be used plier the actual material grade to be purchased for checkered based on historical evidence, engineering judgment, previ- plate or use the minimum values provided in the tables in ous experience or appropriate testing. For an IBC project, the checkered plate should be checked for the deflection limits previously dis- 4.
There are several options for the con- engineering judgment and expected usage. In most cases, struction of treads and risers, but the following are primarily the checkered plate will act as a multi-span beam, and using used: integral light gauge steel tread and riser, steel check- appropriate beam formulas for these conditions will help ered plate, prefabricated steel grating treads, and nonsteel to reduce overall thickness.
Designers should specify span options e. For non-walking surfaces, flat plate may be used to support 4. Additional stiffening elements may be provided to achieve the required design strength and Light-gauge steel can easily be bent and shaped to the stiffness. Depending on shop preferences, flat plate may be required geometry for treads and risers.
It can be directly used instead of metal deck. Concrete fill can then be poured into the formed pan tread. The thickness of settings, industrial settings, and around equipment platforms. Grating 4. This publication reviews good practice in Steel Deck Construction and serves as a safety primer for Contractors, Erectors, Architects, Engineers and Inspectors who are responsible for safe and proper field installation of steel deck.
June This publication replaces our current edition — COSP , and provides the latest industry standard information regarding the sale, manufacture, and installation of steel deck. The version provides the latest industry standard information as to the sale, manufacture and installation of steel deck. May This publication provides updated industry standard information as to the sale, manufacture and installation of steel deck.
The manual is based on research, testing, and analysis sponsored by the Steel Deck Institute and its member and associate member companies, under the direction of Dr. Larry D. The manual explains the method developed to calculate the capacity of diaphragms using steel roof decks or composite steel floor decks and the use of the diaphragm load tables. Details on the design of members—beams, columns, and tension components—and of bolted and welded connections are also covered.
Featuring contributions from renowned engineering experts, this is an invaluable working tool for structural steel designers. Roger Brockenbrough, P. He was a senior research consultant for U. Steel, where he worked for 30 years until retiring. Frederick S. Merritt, P.
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