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

I - 19 http://www.njb-united.com/ncj/jpdfs/j1617.pdf

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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