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STRUCTURES ][
Steel Joist Institute (SJI)
Proprietary Products
Open-Web Joists
smallest and lightest
members
support
roof decks
floor decks
uniform load only
top chord - L shape
web - o rod
bottom chord - L shape
Identification of Open-Web Steel Joists 1. overall depth 12 2. series open web K long span LS deep long span DLS ca. 7'-0" deep ca. 150 ft span 3. class of size 1...12 higher number = heavier Table 9.5 P&A 304-305 1. first number = total load capacity 2. second number = load to produce l/360 deflection
Lateral Support floor decking roof decking ceiling bridging bracing to provide support for ducts lighting building equipment catwalks
Cost: Metal Joists 8" deep $ 2.10 /sq.ft. 16" o.c. 24" about same cost 40 psf 15' span add for larger spans 15' up to 25' 15% 30' 75% Metal Web Joists K series $9.50 - $12.50 / lf (50% M, 50% L) LH & LJ Series $26.30 - 34.35 / lf DLH & DLJ Series $24.45 - 31.00 / lf
Open-Web Steel Joists
Example Problem
Open-web steel joists are to be used to support a roof
with a unit live load of 20 psf
and a unit dead load of 15 psf
(not including the weight of the joists)
on an open span of 40 ft.
Joists are spaced 6 ft center to center.
Select the lightest joist
if deflection under live load is limited to L/360 of span.
A. Given:
=======
L = 20 psf
D = 15 psf
l = 40 ft
s = 6 ft
B. Asked:
=======
lightest open-web steel joist
C. Graph:
=======
L = 20 PSF
D = 15 PSF DOES NOT INCLUDE WEEIGHT OF JOIST
==================
v v
L= 40 ft
S= 6 ft
D. Calculations:
============
1. Live load
s x L
6 ft x 20 psf
L = 120 lb/ft
2. Dead Load
s x D
6 ft x 15 psf
L = 90 lb/ft
3. Total Load
T = L + D
T = 120 lb/ft + 90 lb/ft
T = 210 lb/ft
4. Table 9.5 P&A 304-305
( ) load in parentheses is load that produces a l/360 deflection
under live load only!
span = 40 ft
load = 210 lb/ft
5. select 22K9 overall capacity 278 joist weight 11.3 ---------------------------------------------- useable capacity 266.7 load for l/360 deflection 146 146 > 120 lb live load o.k.
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STEEL TRUSSES ============== Planar trusses ========== not a real truss very thin beam Joist Girder ======== Fig. 9.9 P&A 308 Designation: nominal girder depth weight spacing of members unit load to be carried
Three-Dimensional Truss =================== Space Frames
Design Guidelines: ============== 1. spacing of joists even number division of girder span 2. loads to be carried total design load unit concentrated load on 1 girder 3. span of girder 4. design table manufacturer's catalog girder span joist spacing joist load weight depth style span CUSTOM TRUSSES =============== link several small elements to form: arches bents bridge gable-form = roof truss flat-span = floor truss Parallel Chord Trusses ================ Warren Pratt Major Factor in Truss Design ===================== Joints simple pins fitted connections riveted joints welded shop connections high strength bolts field connections
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Ultra Span® Some
Examples Of
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| TRUSS TYPE | SIZE | GAUGE | |||||||
|---|---|---|---|---|---|---|---|---|---|
| 20 | 18 | 16 | 14 | ||||||
| CHORD | |||||||||
| TC | BC | TC | BC | TC | BC | TC | BC | ||
 |
3-1/2" | 16'-4" | 20'-0" | 18'-4" | 20'-0" | 19'-6" | 24'-0" | 19'-6" | 24'-0" |
| 5-1/2" | 20'-0" | 24'-0" | 20'-0" | 24'-0" | 24'-0" | 31'-4" | 24'-0" | 31'-4" | |
| 7-1/4" | 24'-0" | 32'-0" | 28'-10" | 38'-5" | 28'-10" | 38'-5" | |||
 |
3-1/2" | 26'-10" | 30'-0" | 31'-5" | 30'-0" | 40'-0" | 36'-0" | 40'-0" | 36'-0" |
| 5-1/2" | 36'-0" | 36'-0" | 40'-0" | 36'-0" | 48'-0" | 46'-10" | 48'-0" | 46'-10" | |
| 7-1/4" | 48'-0" | 48'-0" | 57'-8" | 57'-8" | 57'-8" | 57'-8" | |||
 |
3-1/2" | 30'-0" | 44'-10" | 40'-8" | 44'-10" | 50'-0" | 48'-0" | 58'-10" | 48'-0" |
| 5-1/2" | 40'-0" | 52'-0" | 54'-6" | 48'-0" | 66'-0" | 62'-5" | 72'-0" | 62'-5" | |
| 7-1/4" | 58'-10" | 64'-0" | 73'-3" | 64'-0" | 80'-0" | 76'-10" | |||
 |
3-1/2" | 32'-0" | 45'-10" | 42'-8" | 59'-5" | 53'-5" | 70'-10" | 64'-3 | 72'-0" |
| 5-1/2" | 41'-4" | 72'-0" | 56'-3" | 80'-0" | 69'-10" | 80'-0" | 80'-0" | 80'-0" | |
| 7-1/4" | 60'-10" | 70'-0" | |||||||
 |
3-1/2" | 15'-0" | 20'-0" | 18'-4" | 20'-0" | 20'-0" | 24'-0" | ||
| 5-1/2" | 20'-10" | 24'-0" | 24'-0" | 24'-0" | |||||
| 7-1/4" | 24'-0" | 32'-0" | |||||||
 |
3-1/2" | 18'-8" | 28'-2" | 24'-0" | 36'-8" | 29'-0" | 45'-0" | 39'-0" | 48'-0" |
| 5-1/2" | 24'-0" | 43'-0" | 30'-5" | 48'-0" | 31'-3" | 62'-6" | 49'-0" | 62'-5" | |
| 7-1/4" | 35'-5" | 48'-0" | 44'-8" | 55'-10" | |||||
 |
3-1/2" | 19'-0" | 26'-5" | 25'-5" | 34'-3" | 31'-4" | 40'-3" | 38'-0" | 47'-5" |
| 5-1/2" | 31'-8" | 40'-0" | 40'-0" | 63'-3" | 52'-0" | 63'-3" | |||
| 7-1/4" | 34'-3" | 48'-10" | 47'-10" | 59'-0" | |||||
 |
3-1/2" | 8'-0" | 10'-0" | ||||||
| 5-1/2" | 10'-0" | 12'-0" | |||||||
| 7-1/4" | 12'-0" | ||||||||
 |
3-1/2" | 16'-0" | 20'-0" | ||||||
| 5-1/2" | 20'-0" | 24'-0" | |||||||
| 7-1/4" | 28'-10" | 38'-5" | |||||||
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3-1/2" | 23'-3" | 20'-0" | 28'-10" | 24'-0" | ||||
| 5-1/2" | 30'-0" | 24'-0" | |||||||
| 7-1/4" | 43'-10" | 57'-8" | |||||||
| |
3-1/2" | 26'-3" | 30'-0" | 33'-4" | 30'-0" | 38'-8" | 36'-0" | ||
| 5-1/2" | 34'-8" | 36'-0" | 40'-0" | 36'-0" | |||||
| 7-1/4" | 48'-4" | 48'-0" | |||||||
 Back
to Metal Truss |
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| This loadtable, and all contents, are Copyright © 1996 Metal Truss, L.L.C., Knoxville, Tennessee, USA | |
Cost: Steel Trusses 70% M, 30% L $ 1,450 - 2,425 / ton
Space Frames: =========== three-dimesnional truss whose linear members form a series of triangulated polyhedrons Grids: square grid triangular grid hexagon grid Supports: always at panel points column may disperse support points bearing wall offers support along a line equal spaced columns most efficient random support possible Connections: welded bolted screw-in Chord Members: structural pipe tubing channel tee w-shapes Enclosure: wood panel sheating metal decking cementitious planks slope or camber frame for drainage Modules 4' 5' 8' 12' Span 6 to 36 modules 200 ft with flat space frames 500 ft in faceted configurations Cantilevers 15% to 30% Depth-to-span ratio for roofs 1:18 if column-supported 1:20 if wall-supported Consult manufacturer for details, module size and allowable spans. Manufacturers: Mero Geometrica -Houston Starnet - Florida (Aluminum) OMNI HUB GEO HUB STAR DOME
Cost Space Frames 65% M, 35% L $ 25 / sq.ft.
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©Dr. Gruenwald 1996, 1997
