An Engineering Insight authored by SK&A Associate Monika Crandall, PE, LEED AP. Follow Monika on Linked In.
Preventing Deck Buckling: An Engineer’s Checklist
Despite there being multiple manufacturers on the market, the process of specifying the topping thickness and gauge of composite metal floor deck follows a similar flow every time.
Why is it called “composite”? (Not to be confused with composite steel beams). Composite metal floor deck has embossments designed to interlock with the concrete slab. The result: a slab that serves the dual purpose of permanent form during the pour and positive reinforcement in service.
Unless there are particular circumstances—such as slab thickness limitations (weight or clearance issues)—the unshored deck is the preferred construction model. An unshored deck spans between beams during the pour; it must carry wet concrete + construction loads and control deflection. It also eliminates the need for shoring, often resulting in cost and schedule savings.
One of the first determinations is the fire-rating requirement. That alone can lock us into a slab/deck assembly thickness and concrete type (lightweight vs. normal weight). Next is the number of deck spans. Catalogs provide information for 1- to 3-span conditions, with the 1-span condition resulting in the shortest spans and the 3-span condition allowing the longest spans—this is the most common in new construction. Once that is determined, we verify that the span length is adequate for the superimposed load and deflection criteria we’re designing for.
Let’s follow an example with 100 psf superimposed load requirement (per CSM Metal Deck Catalog) :
- Let’s assume that fire rating drives a 2″ deep composite metal deck with 2″ normal weight topping.
- We determine that a 22 ga deck can span 9′-3″ unshored.
- The table shows an allowable superimposed load of 148 psf at 10′-0″.
- Because we do not want to shore the deck, we limit the span to 9′-3″ despite the higher capacity at 10′-0″.
The selection is straightforward—one of those engineering tasks that can be completed in minutes. But diligence is still the engineer’s utmost priority. The cautionary photo above depicts what happens when a deck intended to be shored is not – buckling under wet concrete is an expensive reminder that sequence and temporary work are part of the design.
This insight was originally published by Monika Crandall, PE, LEED AP, on Linked In. View the original post and add your own comments.
