CE479: An Introduction to the Design of Steel Joists and ...jliu/courses/CE479/extras/CE479... · I...
Transcript of CE479: An Introduction to the Design of Steel Joists and ...jliu/courses/CE479/extras/CE479... · I...
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CE479: An Introduction to the Design
of Steel Joists and Joist Girders
Part I
Based on slides from:
Perry S. Green, Ph.D.,
Technical Director, SJI
Fall 2012 – J. Liu
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Steel Joists and Joist Girders
Introduction
Specifications
Manufacturing
More on Steel Joists and Joist Girders
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Top Chord
Bottom Chord
Web Members
Seat
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Joist Basics
Co
lum
n
Joist Girder
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Joist Basics
Horizontal Bridging
Diagonal Bridging
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Steel Joist Institute
Background and Development
The Steel Joist Institute was founded in 1928 and produced its first Catalog and Specifications in 1932.
The 2005 Catalog is the 42nd Edition, the previous being published in 2002.
The K-Series, LH- and DLH-Series and Joist Girder Specifications are ANSI accredited and are part of the 2006 International Building Code Section 2206.
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2005 SJI Unified Specifications
Unified specifications for the K-Series, LH- and DLH-Series and Joist Girders similar to AISC and AISI allowing an ASD or LRFD approach to joist design have been developed.
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Rod (Round Bar) Web Members
Crimped Angle Web Members
Double Angle Web Members
Joist Web Types (not all inclusive)
Joist Manufacturing
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Crimped Angle
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Crimped Angle
Double Angle
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Joist Manufacturing
Shortspans
K-Series
KCS Joists
Joist
Subs
Longspans
LH-Series
DLH-Series
Joist Girders
G-Series
BG-Series
VG-Series
Joist Specification Types
Rod Web
Crimped Web
Double Web Members
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Joist Manufacturing
Usually Warren Web Configuration
K-Series, KCS Joists
• Typically, all designations 8 in. to 24 in. deep (may vary by manufacturer)
• 2 ½ in. to 5 in. deep seats OK for K-Series
• Finish Welding
Bundle of 3 joists in “Pit”
“Multiple” joist manufacturing
Rod (Round Bar) Web Members
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Joist Manufacturing
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Joist Manufacturing
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Joist Manufacturing
Usually Modified Warren Web Configuration
Crimped Angle Web Members
K-Series, KCS Joists, “Light” LH-Series
• Typically, LH-Series from 18 in. to 32 in. or 36 in. deep (may vary by manufacturer)
• Finish Welding
Bundle of 3 joists in “Pit”
“Multiple” joist manufacturing
(Similar process to Rod Web Manufacturing)
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Joist Manufacturing
“Heavy” LH-Series, DLH-Series, Joist Girders,
and Special Profile Joists including Barrel or
Arched, Bowstrings, Gables, etc.
“Single” Joist Manufacturing
Double Angle Web Members
Usually Modified Warren Web Configuration
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• Meant to minimize rust, not prevent rust
• Should not be considered a “Finish” Coat
• Provisional Coating: Dip applied and air dried
Joist Painting
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Available Steel Joist Choices
Joists Directly Supporting Roof or Floor
Loads:
• Open-Web Steel Joists, K-Series
KCS Joists
Joist Substitutes
• Long-Span Steel Joists, LH-Series
• Deep Long-Span Steel Joists, DLH-Series
Primary Members
• Joist Girders Supporting Other Joists
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K-Series Joists
Designations: 8K1 to 30K12
Depths: 8 to 30 in.
Standard Seat Depth (Height): 2.5 in.
Span Range: 8 to 60 ft.
ASD Load Range: 127 to 550 plf
LRFD Load Range: 190 to 825 plf
Maximum Span/Depth Ratio: 24
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KCS Joists
Designations: 10KCS1 to 30KCS5
Depths: 10 to 30 in.
Seat Depth (Height): 2.5 in.
Span Range: 10 to 60 ft.
Constant Moment Capacity
Constant Shear Capacity
Maximum Span/Depth: 24
Diagonals designed for stress
reversal, except end diagonal which
is designed for 100% tension only
KCS Joists
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Joist Substitutes
Joist substitutes are 2.5 inch deep sections intended for use in very short spans (less than 8 feet) where Open Web Steel Joists are impractical.
Typical 2 ½ in. deep Joist Substitutes
Hot-Rolled Cold-Formed
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LH-, DLH-Series Joists
Designations: 18LH02 to 72DLH19
Depths: 18 to 72 in.
Standard Seat Depth (Height): 5 in. up to #17 chords, 7.5 in. for #18 and #19 chords/section numbers
Span Range: 21 to 96 ft.; 61 to 144 ft.
ASD Load Range: 174 to 1068 plf; 208 to 706 plf
LRFD Load Range: 261 to 1602 plf; 312 to 1059 plf
Maximum Span/Depth Ratio: 24
Types: Parallel Chord, Single Pitch, Double Pitch; Underslung or Bottom Chord Bearing
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http://www.canadianjoist.com/joistproducts.html
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http://www.njb-united.com/ncj/jpdfs/j1617.pdf
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Joist Girders
Joist Girder Weight Tables
• Maximum chord angle size is 6 x 6 x ¾
Applicable to all joist manufacturers
• Some joist manufacturers will be able to go
up to a 8 x 8 chord angle, but that will be a
non-standard SJI product
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Joist Girders
Joist Girder Weight Tables
• The weight table can not cover every combination of span, panel spacing and kip loading
• A Joist Girder can be made to fit within any of the “gaps” in the weight table
• The weight table is provided as a design aid for the structural engineer to help provide an approximate value for the Joist Girder self weight
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Joist Girders
Depths: 16 to 120 in.
Standard Seat Depth (Height): 7.5 in.
Spans: 20 to 120 ft.
ASD Panel Point Loads: 4 to 100 kips
LRFD Panel Point Loads: 6 to 150 kips
Weights: 16 to 332 plf
Various Web Configurations: G, VG, BG
Designation: 48G8N9K; 48G8N13.5F
• 48G is the Depth in inches
• 8N is the Number of Joist Spaces
• 9K is the unfactored load at each panel point
• 13.5K is the factored load at each panel point
Joist Girders
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Joist Girders
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SJI Load Tables
Joist Series
Depth
(in.)
Span
(ft.)
Capacity
(lbs/ft.)
K 8 - 30 8 - 60 Varies w/ Span
KCS 10 - 30 10 - 60 In terms of Moment
and Shear
Substitutes 2.5 4 - 8 Varies w/ Span
LH 18 - 48 21 - 80 Varies w/ Span
DLH 52 - 72 61 - 120 Varies w/ Span
SLH 80 - 120 80 - 190 Varies w/ Span