Transcript Designing with

Design of Lateral Load Resisting Frames
Using Steel Joists and Joist Girders
Authored by
James M. Fisher, Ph.D., P.E.
Perry S. Green, Ph.D.
Joseph J. Pote, P.E.
Presentation by:
James M. Fisher, Ph. D., P. E.
Vice President
Computerized Structural Design
Milwaukee, WI
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Technical Digest 11
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Technical Digest No. 11
• The purpose of TD No. 11 is to present
information to the EOR, and the joist
manufacturer, for the design of single
story moment resisting joist and Joist
Girder frames.
• Design considerations for both wind and
seismic lateral loads are presented.
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Technical Digest No. 11
• The digest has been limited to single story
frames, not because of wind requirements,
but because of current requirements for
seismic design; in particular, the use of
strong beam, weak column systems which
are typically necessary when using truss
construction in lieu of beams and girders.
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Technical Digest No. 11
• The Digest illustrates procedures to:
– Analyze,
– Design, and
– Specify joist and Joist Girder moment frames to resist
wind and seismic lateral loads.
• The reader is assumed to be familiar with:
– 2005 AISC Specification for Structural Steel Buildings
– 2005 AISC Seismic Provisions for Structural Steel
Buildings
– ASCE 7-05
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Technical Digest No. 11
• Designing joist and Joist Girder structures as rigid
frames is no more difficult than designing rigid
frames with wide flange beams and columns.
• To obtain a cost effective design the engineer must
be aware of the inter-relationships between framing
elements, i.e. joists, Joist Girders, columns, bracing
members and connections.
• In general, the most economical design is one
which minimizes manufacturing and erection costs,
and one which reduces the special requirements
(seat stiffeners, chord reinforcing, etc.) for the
joists, Joist Girders and columns.
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Design Methodology
• The first consideration relative to the design of
the structure is to determine if rigid frame action
is required.
• For single story structures the optimum framing
system generally consists of braced frames in
both directions, and the use of a roof diaphragm
system to transfer wind and seismic loads to the
vertical bracing elements.
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Design Methodology
• The specifying professional and the joist
manufacturer must communicate design data and
information to each other.
• The specifying professional must specify the
necessary loading and stiffness data to the joist
manufacturer.
• The specifying professional must indicate the
type of joist to column connections so that the
joist manufacturer can provide the joists with the
geometry that meets the design intent.
• Dialog must occur between all involved parties
prior to final pricing and design.
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Design Methodology
• The joist manufacturer must design
the joists in conformance with the SJI
Specifications and other contract
requirements specified by the
specifying professional.
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Analysis Requirements
• Forces and moments in single story joist rigid
frames are determined in a manner similar to
other Ordinary Moment Frames (OMF).
• The first step is to perform a preliminary analysis.
• In general, it is suggested that the OMF be
considered as a pinned based frame to eliminate
moment resisting foundations; however, for drift
control partially restrained or fixed bases can be
considered.
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Analysis Requirements
• After selecting trial member sizes for the columns
and joists, a computer analysis is performed to
determine forces, moments, and deflections (both
first-order and second-order) for the load
combinations prescribed by the Applicable
Building Code.
• Because a second-order analysis is a non-linear
problem, the analysis must be performed for each
required load combination.
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Frame Model
Model for IBC or ASCE Load Combinations
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Analysis
Trial joist stiffness can be obtained from the SJI
equations for the approximate moment of inertia
for a joist or a Joist Girder. The SJI equation for a
Joist Girder equals 0.018NPLd (LRFD),
and 0.027NPLd (ASD)
where:
N = number of panel points
P = panel point load (kips) at factored load level
for LRFD, and at nominal load level for ASD
L = girder length (ft.)
d = girder depth (inches)
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Analysis
The SJI equation for the approximate
moment of inertia for a joist equals
26.767(WLL)(L3)(10-6) for both LRFD and ASD.
where:
WLL = The RED figure in the K-, LH-, and
DLH-Series Load Tables
L = (Span – 0.33) in feet for K-Series joists
L = (Clear span + 0.67) in feet for LH- and
DLH-Series joists
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Analysis
Angle Size
Unbraced Length
feet
L=4 L=5 L=6 L=7
Area
in.2
2L6 x 6 x 1
939
911
879
842
22.0
2L6 x 6 x 7/8
828
809
781
749
19.5
2L6 x 6 x 3/4
705
698
678
650
16.9
2L2.5 x 2.5 x 3/16
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1.80
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Frame Model
Model for AISC-Strong Beam, Weak Column
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OMF Analysis
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Pseudo Columns
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Typical Connections
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Basic Connection
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Eccentricity Effect
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Added Reinforcing
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End Plate Type Connection
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Plate Connection-Sidewall
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Plate Connection-Interior
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Specification of Required
Forces and Moments
• IBC LRFD load combinations are used.
• Nominal loads:
 D = 15 psf
 L = 20 psf (reducible)
 S = 5 psf
 W (uplift gross) = 27.25 psf (windward roof)
= 17.3 psf (leeward roof)
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Specification of Required
Forces and Moments
• Seismic Criteria:
 R = 3.5 for OMF
 SDS = 0.9297g
 SD1 = 0.39g
 r = 1.0
 QE = 49 kips
• Imin = 6790 in.4 for the exterior girders and 4570 in.4
for the interior girder (analysis requirements).
• Minimum width of top chord = 7.0 in. (weld
requirements).
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Specification of Required
Forces and Moments
• Minimum thickness of bottom chord = 3/8 in.
(weld requirements).
• All top chord axial loads and end moments are
transmitted directly into the columns via the tie
plates. No horizontal forces are transferred
through the girder seats.
• Chord splices must conform to the requirements
of the 2005 AISC Seismic Provisions, Section
7.3a.
• Controlling IBC Load Combinations are given
below for Joist Girder Mark Numbers G1 and G2,
respectively:
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Controlling IBC Load
Combinations
+
Mark G1
LRFD
Load Combination:
+
Panel
Load
(kips)
Left End
Moment
(kip-ft.)
Right End
Moment
(kip-ft.)
TC
Force
(kips)
+
BC
Force
(kips)
Remarks
1.4D + 1.4C
1.2D + 1.2C + 1.6(Lr or S)
1.2D + 1.2C + 1.6W +
0.5(Lr or S)
1.2D + 1.2C + 1.0E +0.2S
(1.2 + 0.2SDS) (D+C) +
rQE + 0.2S
0.9D + 1.6W
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Main Wind Force Resisting
Pressure Table
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2005 AISC Seismic Provisions
Section 5.1
•
•
•
•
•
•
•
Designation of the seismic load resisting system
(SLRS)
Designation of the members and connections that
are a part of the SLRS
Configuration of the connections
Connection material specifications and sizes
Locations of demand critical welds
Locations and dimensions of protected zones
Welding requirements as specified in Appendix W,
Section W2.1
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Controlling IBC Load
Combinations
Mark G1
LRFD
Load Combination:
Panel
Load
(kips)
Left End
Moment
(kip-ft.)
Right End
Moment
(kip-ft.)
TC
Force
(kips)
BC
Force
(kips)
Remarks
(1.2 + 0.2SDS) (D+C) + rQE +
0.2S (L-R)
(1.2 + 0.2SDS) (D+C) + rQE +
0.2S (R-L)
(0.9 – 0.2SDS)D + rQE (L-R)
(0.9 – 0.2SDS)D + rQE (R-L)
Column Mp, (AISC OMF
Criteria)
Column Mp, (AISC OMF
Criteria)
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Bracing
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Examples 1 and 2
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Examples 1 and 2
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Example 1
• The building is located in Charleston,
South Carolina. The building code to be
used is 2006 International Building Code
(IBC 2006).
• The precast concrete shear walls at the
north and south ends of the building are
non-load bearing shear walls, and are
used to resist the forces between the first
interior rigid frame and the end wall.
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Example 1
Loading requirements are specified as:
Roof Loads:
Dead Load:
1 psf Membrane
2 psf Deck
2 psf Insulation
3 psf Joists and Bridging
2 psf Girder
10 psf Total
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Example 1
Collateral Load:
3 psf Sprinkler
2 psf Mechanical & Lighting
5 psf Total
Live Load:
20 psf Reducible per Code
(12 psf on Joist Girders)
Ground Snow Load = 5 psf
Roof Snow Load = 5 psf (ASCE 7, Section 7.3,
low slope roof criteria)
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Example 2
• Wind Load = 120 MPH – Exposure C
• Seismic Load: Charleston, South Carolina
• Serviceability Requirement:
– Maximum drift = H/100 (10 year wind)
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Examples 1 and 2 Comparison
• Example 1: Charleston, SC
– Wind Base Shear (120 mph)
• 22.9 kips per frame line (Factored by 1.6)
– Seismic Base Shear (R=3.5)
• 49.0 kips per frame line
• Example 2: Jackson, MS
– Wind Base Shear (120 mph)
• 22.9 kips per frame line (Factored by 1.6)
– Seismic Base Shear (R=3.0)
• 14.3 kips per frame line
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Example 1: Exterior Columns
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Example 1: Interior Columns
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Example 2: Exterior Columns
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Example 2: Interior Columns
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Examples 1 and 2 Comparison
• Example 1 (120 mph, SDC D)
–
–
–
–
Columns: Exterior W18x86, Interior W18x97
Total Column Weight = 12,200 lbs
Girder Weight = 6,300 lbs
Total Weight = 18,500 lbs per bay
• Example 2 (120 mph, SDC B)
–
–
–
–
Columns: Exterior W21x111, Interior HSS 8x8x3/16
Total Column Weight = 8700 lbs
Girder Weight = 3200 lbs
Total Weight = 11,900 lbs per bay
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Appendix A
• Appendix A contains a complete design of
the Joist Girders for Example 1
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Acknowledgement
• The authors of Technical Digest 11 would
like to thank:
– The Engineering Practice Committee and the
Research Committee of the Steel Joist Institute for
their review and contributions to the writing of this
document.
– John A. Rolfes, S.E., P.E. Vice President of
Computerized Structural Design for his assistance
in the preparation of the digest, and James O.
Malley, S.E. Senior Principal, Degenkolb
Engineers, for his insightful review of the digest.
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Thank you
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