Stair calculations: code requirements and best practices

In today's environment of delegated design, stair manufacturers must provide a complete design and engineering service for steel egress stair systems. Providing a complete design service requires a deep knowledge of stair engineering, stair codes, standards, and design guides. At Lapeyre Stair, our design and engineering team spends a lot of time keeping up with these requirements. In this post, we will review the code requirements, tools and guidelines for engineering of steel stair systems. 

Codes and guides for steel stair design and engineering 

outsourcesolutionLapeyre Stair performs steel stair design in accordance with IBC-2015 Section 2205.  This section defers by reference to the American Institute of Steel Construction (AISC) specification 360-10, Specification for Structural Steel buildings.

For seismic consideration, we engineer stairs in accordance with ASCE 7-16 Chapter 13, Seismic Design Requirements for Non-structural components.

We also use AISC guides and practices. We use the AISC Design Guide 34, Steel Framed Stairway Design as a design guide. And although stairs are classified as non-structural steel per AISC-360 Section A1 and AISC-303, Code of Standard Practice section 2.2, we also incorporate structural steel requirements into our steel stair designs.

Engineering load specifications for steel stairs

The 2015 edition of the International Building Code (IBC-2015) and the American Society of Civil Engineers (ASCE) standard 7-16 contain engineering load requirements for design of stairs, guards and handrails.

Stair tread load requirements

primed-stringerIBC-section 1607, Table 1607.1 and ASCE-7-16 Chapter 4 specify a uniform design Live Load (LL) for stairs of 100 psf, or a 300 lbs. concentrated load on a 4 in2 for stair treads.

 

 

Guardrail and handrail load requirements

rail-finish-primedIBC-2015 Section 1607.8 and ASCE-7-16 Chapter 4, specify that guards and handrails are designed for a uniform load of 50 pounds per linear foot (50 plf) or a 200 pound concentrated load at any location on the guard. This load must transfer through the entire guard structure. Additionally, fillers of the guard must be designed for a 50-pound concentrated load applied over one square foot.

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Stair load combinations specifications

IBC-2015 1605.3.1 and ASCE-7-16 Chapter 2 specify load combinations for stairs. Lapeyre Stair engineers typically uses the Allowable Stress Design (ASD) design method but can use the Load and Resistance Factor Design (LRFD) design method if requested.

For stairs that are indoors, we use load combinations with only Dead Load (D) and Live Load (L), unless other loads such as seismic are specifically required by the project specifications or drawings.

For stairs that are outdoors, we use load combinations with Dead Load (D), Live Load (L) and Wind Load (W), unless loads such as snow, etc. are required by location or loads such as seismic are specifically required by the project specifications or drawings.

Stair engineering tools

Typically, Lapeyre Stair engineers use PTC Math CAD software to perform stair analysis using the applicable load combinations. In the calculations, we check all the major stair components:

  • stair treads
  • stair stringers
  • landing front and rear headers
  • landing cross beam members which support the decking
  • landing support members which are typically columns, hangers, or shelf angles, and the
  • guard and handrail members

To determine appropriate member sizing, we perform both strength and deflection checks. Deflections are typically limited to L/360 unless otherwise specified in the project specifications. Templates for each of the members types allow for quick preparation of calculations. The Math CAD software allows for changes to stair system dimensions to also be performed quickly. For calculations which require more complex checks, such as for wind or seismic loads, we use STAAD Pro structural analysis software. For seismic designs, we use  “Slip” connections, which allow stair movement in a direction parallel to the stair. 

To ensure that our designers design stairs to pass calculations on first-pass, Lapeyre Stair's engineering team has performed engineering analysis on the vast majority of stair system configurations. We maintain a library of standard member sizes and profiles for each stair configuration. We use simple stair calculation tools to check that member sizes pass load requirements during the initial design. Using a pre-engineered stair system approach ensures that our stair system designs do not need to be revised upon final engineering analysis. This approach contributes to better coordination and turnaround times for stair submittals and reviews. 

 

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