Steel deck (gravity)

A bare fluted steel deck panel, per foot of width, on one to six equal spans with an optional cantilever at the right end: strength by AISI S100-16 (with S2-20) from the section properties in the manufacturer's table, and deflection, with its construction stage. It is a check of a deck you have chosen. It takes no section properties of its own, since a deck's effective properties are its manufacturer's. Diaphragm shear is not checked here. Composite deck-slab strength is not checked: use the manufacturer's tables.

What the SDI items rest on. ANSI/SDI SD-2022, the current steel deck standard, was not read for this calculation. Construction loads and the concreting deflection limit come from the sources named beside each input, are marked (to confirm against the code text) and are all inputs. Confirm them against the standard.

Inputs of the steel deck #

• Use: roof deck, or form or composite deck during concreting. On form or composite deck only the bare deck under wet concrete is meaningful here; clear the area loads, or enter what the bare deck carries.
• Deck name, equal spans, span, cantilever: spans center to center. The cantilever is at the right end, at most one span.
• From the manufacturer's table: base steel thickness, yield stress (the grade the properties were computed at), weight, effective section moduli Se+ and Se-, and the deflection moments of inertia for a single span and for continuous spans. Manufacturers name these differently: Id+ or Idn for a single span; Idm, or Id- where a table has no multi-span value. Use the values for your deck: properties differ between manufacturers.
• Web shear and crippling: computed from the web's geometry (webs per foot, flat depth, inside radius, web angle, fastened at 18 in. or closer, bearing lengths), or typed from the manufacturer's tables at your bearing length. A manufacturer who prints no radius or web angle needs the second way.
• Loads: area loads by type, uplift negative, and line loads across the flutes per foot of width. A point load must be spread across the flutes by you: this calculation does not do it.
• Pattern live, roof live and snow span by span: on by default, ASCE 7-22 4.3.3. Manufacturers' load tables load all spans at once, so their tables give less moment at midspan than this. Turning it off is your decision.
• Deflection limits: span / n, from IBC Table 1604.3; a cantilever is on twice its length. Enter 0 to skip.
• Construction stage: on by default.
  • Concentrated load on a 1 ft width at each midspan and at the tip: 200 lb prefilled for roof deck, from a manufacturer's table note citing ANSI/SDI RD-2017, and 150 lb on form deck, from SDI's 2006 Manual of Construction, Figure 16. A Nucor / Vulcraft lecture also shows 150 lb on a roof deck: the prefilled 200 lb is the larger. (to confirm against the code text)
  • Uniform load: 20 psf on form deck, same manual. On roof deck, 10 psf, added at a cantilever's tip load as that table note says. That lecture also lists 50 psf: enter it if your standard calls for it. (to confirm against the code text)
  • Deck weight: on by default. The construction span table compared below leaves it out on simple and continuous spans, so the published cases clear it. Leaving it on is on the safe side.
  • Wet concrete weight and a factor on a single span, 1.5, because SDI's manual adds half the concrete weight where a single span is hard to pour under control.
  • LRFD factors: 1.2 on deck, 1.6 on concrete, 1.6 on construction loads. These are not read from the standard. ASD uses 1.0. (to confirm against the code text)
  • Concreting deflection: span / 180 and at most 3/4 in., from an SJI / SDI webinar slide. (to confirm against the code text)

Auto-design is not offered: the calculation checks one deck against table values you type, so there is nothing for it to size.

Checks performed #

The key results also give the uniform load the deck can carry on all spans, by stress and at your live deflection limit, directly comparable with a manufacturer's table.

Limitations of the steel deck #

• Equal spans only; one cantilever, at the right end.
• Section properties are entered. Perforated and acoustic webs are not handled: enter table values for them where the manufacturer prints them.
• One-flange web crippling only. A line load between supports, or one directly over a support, may be a two-flange case: check it yourself.
• Not designed: a point load's spread across the flutes, fasteners, side laps, uplift at the connections, diaphragm shear, ponding (use Rain load), the slab.
• The construction stage places its concentrated load at midspan, as the published table does. A position slightly off midspan gives about 2 % more moment on two spans.
• ANSI/SDI SD-2022, its roof design manual and its construction load wording were not read. See the top of this chapter.

Verification examples #

Verification status: 38 values compared in 17 examples (17 published, 0 hand calculations from the cited equations): 35 within tolerance, 3 recorded deviations. Code basis: partial. Only some provisions were read in the target edition; the rest rests on older editions, examples or summaries.

The Vulcraft catalog prints no radius or web angle, so the worked example's allowable reactions and shear use those of Verco's PLB-36, 22 gage. Where that leaves a difference it is listed on the Verification page. All published comparisons are ASD: LRFD uses the same nominal strengths and factors, and is checked by hand in the behaviour tests.