In Part 6, a new design aid is included that provides the avai lable f1exural strength, available shear strength, avai lable compress ive strength, and available tensi le strength for W-shapes in one table. In Part 9, a new interaction eq uation is provided for connection design based on a plastic strength approach. In Part 9, a new approach to designing coped beams is presented based on recent studies.
In addition, many other improvements have been made throughout this Manual. Hol land , Chairman Gary C. Carter Harry A. Ferre ll , Emeritus Patrick J. Fortney Timothy P. Fraser Louis F. Geschwi ndner, Emeritus John L. Ha"is 11 I C hristopher M. Hew itt Wi ll iarn P. Meng Larry S. Mui r Thomas M. Murray James Neary Davis G.
Schl an y Cli fford W. Schwinge r Willi arn T. Thornton Michae l A. West Rona ld G. Yeage, Cynthi a J. Scott, Marc L. Sorenson , and Sriram ulu Vi nn akota. The Manual consists of seventeen parts addressing various topies related to steel building design and eonstruction. Part I provides the dirnensions and properties for structural products cornmon ly used. For the des ign of conneetions, see Parts 7 through Tables in the Manual that present available strengths are developed using the geometrie conditions indicated and the applieable limil states from the AISC Specificationfor Structural Steel Buildings.
Given the nature of the tables, and the possible goveming limit state for each table value, linear interpolation between tabulated values may or may not provide correct strengths. IlSS llot. RolledStructu",IS hape. Ul IV 'M IJl U1 5. I' DT 0. OO1 1M 1M MI s. OO42 4. SOO IO H2 UnbrnoroL""gth TabIc3. OO """SlrI. If you need assistance resetting your username or password, visit our login help page. Your digital Manual subscription is good for one year from the date of purchase.
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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. In many cases, the treads will be shop occupied areas. Connections of grating to support framing include treads and risers are supported on the top flange rather than bolting, grating clips or welding.
Grating is typically pur- attached to the side or member web. Typical details for chased from a manufacturer, but designers should determine HSS or wide-flange members running under the treads may grating thickness, span direction, edge banding require- require a built-up plate section to provide adequate tread ments, and other special features prior to ordering grating. Standard grating treads are made from in. Stringers are the members supporting treads and risers and span from floor level-to-floor level of the stair.
Typically, the 4. There are several different member types that can Refer to the appropriate design standard or use information be used for stringers. Stringer support conditions and design provided by the component supplier i. Tolerances and applied forces from nonsteel compo- nents should also be reviewed.
The most commonly used stringer members are channels, plate and rectangular HSS. In some cases, wide-flange mem- 4. The typical depth range for stringers is from 10 to 15 in. A mini- The connections for treads and risers will vary based on the mum in. The tread and layout of the treads and risers.
Deeper stringers are typically riser connections are important aspects of the stringer design used for longer spans to limit overall deflection.
Table as well. Tread and riser connections can be used to brace lists some of the advantages and disadvantages of common the stringer and can also provide diaphragm rigidity to the stringer types. This can be completed in the shop additional length related to the sloped member self-weight and is ideal when building stair flight assemblies. Disadvan- must be taken into account when using the projected length. Weld of the stringer beams can be completed using the sloping design is based on the American Welding Society AWS beam method or the horizontal plane method.
The values for required strength in shear and moment are based on the normal perpendicular component 4. In the horizontal plane method, the verti- can be welded to the stringers.
Integral pans, steel plate, cal loads are applied to the stringer beam with a span that and some nonsteel options are then supported on the car- is taken as the horizontal projection of the stringer. Both rier angle or plate. The supported element is then welded or methods are illustrated with the required shear and flexural bolted in the field or in the shop. The tributary width, W, for the stringer beam is 2 ft based on a 4-ft-wide stair. The sloping length, L, is Because the purpose of this example is to compare the loads obtained for the two different methods, service level unfactored loads are used.
Determination of required strengths: a sloping beam method; b horizontal plane method. The horizontal plane method is commonly used to determine the required shear and flexural strength for inclined beams. This approach is simpler and provides an equivalent required flexural strength and conservative available shear strength compared to the sloping beam method illustrated in Fig- ure a.
Both methods assume that the stringer is a simple span beam. Due to the additional length of a sloping member, actual vertical deflections will range from 1. Accurate deflections should be calculated using the sloping beam method to ensure the stair design meets the required serviceability criteria. Tread Riser Fig. Tread and riser layout. Deflections at sloping beams. Appropri- using some or all of the methods described previously.
Using support conditions associated with nections will be designed for both shear and axial forces, the a simple span beam with a pinned base at one end and a author recommends that stringer member design follow the roller base at the other end will produce reactions with shear, simple span method, and end-connection design including flexure and axial forces.
Vertical deflection will be highest at checks on the support structure is based on the reactions midspan, and the roller base will allow for lateral deflection produced from a frame analysis. This will provide conserva- typically a relatively small value due to live load. This will produce reactions with shear, flexure and 4. In this case, the beam will exhibit frame action behavior, thereby minimizing deflection but substantially An important aspect of stair stringer design is the determi- increasing the axial reactions at each end.
Both support con- nation of unbraced length. The type of tread and riser and ditions are illustrated in Figure Details allow- may not fully brace the stringer along the length. Alternatively, a situation where a stair is covering the majority of the stringer web depth are used, connected between thick concrete walls using thick end the stringer can typically be considered to be fully braced.
Configurations differ- reactions that must be considered in the design. The author recommends that designers use a b Fig. Figure illustrates bolted Landing support can be provided by several different means, grating treads to a stringer. Without detailed information several of which are described in this section. The support regarding the grating tread construction, connection layout, of landings can become complex when connecting into the and bolt information, the author recommends that stringers building structure based on the location of structural steel, with bolted grating treads be treated as unbraced.
While such concrete elements and walls. Coordination with the archi- a decision is likely conservative, the potential for racking tect and structural engineer of record SER is important to and discontinuities in the stair flight assembly are reasons ensure that proper support can be provided without adversely to consider stringers with bolted grating treads as laterally affecting the building design. In most cases, stairway support connections should be designed so as not to impose torsion on the supporting mem- 4.
The use of standard shear connections from the AISC A stair landing provides an area for occupants to stop or rest Manual can help to avoid this situation. Alternatively, addi- when ascending or descending a stairway. The applicable tional support framing may be required to provide concentric building code provides requirements regarding the size and support points for hangers, posts or stairway connections.
Based on these requirements, the stair designer can incorporate and support landings in multiple 4. Integrated landings are supported by the stair framing with- Depending on the architectural requirements, landings out any connection to the building structure. Using an inte- will typically be constructed based on one of the following: grated landing can greatly simplify the design, detailing and 1.
Cast-in-place concrete over metal deck on landing fabrication of stairs. The integrated landing provides support steel framing members and a floor system that does not require additional 2. Cast-in-place concrete over stiffened plate on landing support from posts or hangers; this type of landing typically steel framing results in the main stringers spanning the additional length of the landing to a support point.
Figure shows a layout 3. Checkered plate flooring on landing steel framing for a straight stair with an integrated landing, and Figure 4. Steel grating with clips or bolts on landing steel shows the framing layout for an integrated landing for a typi- framing cal parallel stair. Precast, masonry or nonsteel flooring on landing steel framing 4. This type of landing is similar to typi- design resources for nonsteel elements.
In many situations, cal steel-framed construction using columns, beams, and a the landing construction for stairways should be consistent floor system. It is important to ensure that the slab on grade with the design and layout of the building or structures ser- viced by the stairway. Stringer Grating tread with checkered plate nosing bolted to stringer, typical Fig. Stringer with welded metal pan for treads and risers. Stringer with bolted grating treads.
The masonry wall and beam Additional vertical bracing and utilization of a floor dia- pockets can then be built around the stair to provide perma- phragm may also be required to resist lateral loads. Another option is to use post-installed anchors with a steel 4.
Where stairways are supported by masonry A hanger-supported landing has similar framing to the post- core walls, coordination with the SER is critical because the supported landing but is connected by hangers to the support- stair connection details may require grouted cores, bond ing structure above. Various hanger members can be used, beams or other details that must be designed and specified in such as square or rectangular HSS, angles, pipe, and cables the design documents.
When using long hangers, cable or rod, additional lat- For concrete walls, landing framing can be supported by eral restraint should be provided to brace these elements and embed plates that are installed when casting the concrete ensure movement of the landing does not adversely affect wall.
Another option is to use post-installed anchors with a occupant comfort. Where stairways are supported by 4.
Core walls are typically constructed from masonry or specified in the design documents. For masonry walls, landing framing can be sup- For both masonry walls and concrete walls, stairs may be ported using beam pockets that need to be coordinated with shipped in individual pieces and assembled in the field to the masonry contractor during construction.
Alternately, the account for tolerances in the walls. This will require more stair can be temporarily supported with erection bracing time and effort during erection. General stability requirements crete over metal deck. Plate Shear Walls Sabelli and Bruneau, , for guidance related to diaphragm design for stiffened plate. For lateral forces, one option for design is to Checkered plate flooring can be used as a diaphragm based assume that each stringer resists one-half of the lateral forces on principles provided in AISC Design Guide 20, Steel Plate through weak axis shear and bending.
Refer to Chapter 4 for Shear Walls. Alternatively, when using welded tread and riser construc- 5. With thinner light gage material for the treads and ris- As an alternative to a landing diaphragm, horizontal brac- ers, it may be difficult to satisfy local buckling requirements.
This requires that a load path for Using thicker checkered plate, however, may allow for this lateral forces from the landing or stair assembly be provided type of analysis. If risers are omitted, it may be possible to back to the building structure for support. Table provides design the assembly as a horizontal Vierendeel truss. This is typically possible when 5. Using plate stringers cally for stairway design, bracing is designed using cable, requires careful analysis, design and detailing to ensure that rod, single angle or plate.
Improperly designed landings can number of connections and braces needed. Typical options create discontinuities in the stair with respect to resisting lat- include HSS members, single angle, double angle and pipe.
Creating a diaphragm at stair landings can pro- Follow the AISC Specification for slenderness limits and to vide an additional load path for resisting the lateral forces.
The AISC Specification should cast-in-place concrete over metal deck that is supported by be used to determine available strength. When using HSS the landing steel framing. Larger landings may require moment connections.
Using typical steel- AISC standard shear connections are detailed in AISC framed connections can simplify the design process, make Manual Part 10; they include double-angle connections, detailing and fabrication easier, and ensure the stairway shear end-plate connections, unstiffened seated connec- members are erectable in the field. Refer to the Purpose sec- tions, stiffened seated connections, single-plate connections, tion of this Design Guide in regard to connection adjustabil- single-angle connections, and tee connections.
For stairways ity and coordination of structural supports to avoid common designed as simple-span beams with only a shear end reac- issues that arise as part of the stairway design.
Refer to AISC Manual Part 10 for additional guid- Connecting the steel stair elements can be accomplished in ance and design requirements for each type of shear con- a variety of ways including embed plates, beam pockets, or nection. Figures and are, respectively, examples of post-installed anchors. Single-plate connections using the extended configura- support structures should utilize standard connections from tion can be used when adjustment is needed when connecting the AISC Manual AISC, to the largest extent pos- to existing structures or to provide additional flexibility dur- sible.
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