Problem 4: Consider the following limit states in your design: : Siesur(ingeione

Question

Problem 4:

Consider the following limit states in your design: : Siesur(ingeiones . Shea . Serviceability Problem 4: An open-web joist roof framing system is to support a superimposed snow loading of 40 psf (no drifting) and a superimposed dead loading of 25 psf. The span of the joists is 40 feet and the span is simply supported. Select a K-series joist from the Vulcraft catalog available on the course D2L site for joists spaced at 6 feet on center. Vertical deflections under snow loading should be less than or equal to L/360 Use LRFD and ASD design philosophies.

Explanation / Answer

Joist spacing = 6 ft

Support type = Simply supported

Snow load = 40 psf = 40 x 6 lbf/ft = 240 lbf/ft

Superimposed dead load = 25 psf = 20 x 6 lbf/ft = 120 lbf/ft

'Vulcraft Steel Joists & Joist Girders 2007' is used for selecting appropriate K-series joist which has higher load carrying capacity than design load and also has the least self-weight.

LRFD approach :

Design load = Maximum (1.4 x DL, 1.2 x DL + 1.6 x LL ) = Maximum (1.4 x 120, 1.2 x 120 + 1.6 x 240) = 528 lbf/ft

Select 28K9 at 40 ft span.

SJI Load Table Load = 535 lbf/ft > 528 lbf/ft    ......OK

Deflection live load <= L/360

SJI Table Live Load = 241 lbf/ft > 240 lbf/ft    ......OK

ASD approach :

Design load = Maximum ( DL, DL + LL ) = Maximum (120, 120 + 240) = 360 lbf/ft

Select 30K9 at 40 ft span.

SJI Load Table Load = 384 lbf/ft > 360 lbf/ft    ......OK

Deflection live load <= L/360

SJI Table Live Load = 278 lbf/ft > 240 lbf/ft    ......OK

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