architectural structures: s analysis and systems …
TRANSCRIPT
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F2018abnConnections 1
Lecture 17
Applied Architectural Structures
ARCH 631
seventeen
connections
lecture
APPLIED ARCHITECTURAL STRUCTURES:
STRUCTURAL ANALYSIS AND SYSTEMS
ARCH 631
DR. ANNE NICHOLS
FALL 2018
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Lecture 17
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Connection Design Considerations
• joints often critical in design
– can influence choice of structural system
• types used influenced by:
– member behavior
– member geometry
• basic types join by:
– lapping
– deforming and interlocking
– butting
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Connectors
• “third-elements”
– bolts
– nails
– welds
– splice plates
• transfer load at a
point, line or surface
– generally more than a point due to stresses
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M = Td = CdT = CConnections 4
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Connector Rigidity
• pinned joints
– point type
• rigid joints
– line and surface types
– multiple “points”
separated by
distance resist
moment
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• connected members in tension cause
shear stress
• connected members in
compression cause
bearing stress
Point Connectors
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• seen when 2 members are connected
Single Shear
2
4
vd
P Pf
A
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• seen when 3 members are connected
Double Shear
0 2( )2
PF P
2
4
2 2
2v
d
P PP
fA A
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• compression & contact
• projected area
Bearing Stress
F=
p
projected
P Pf
A td
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Beam Stresses
• shear – horizontal & vertical
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Beam Stresses
• shear – horizontal & vertical
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• plates with
– nails
– rivets
– bolts
• splices
• V from beam load
related to Vlongitudinal
Connectors Resisting Beam Shear
x
y
ya
4”
2”
2”
12”
8” p
p p
4.43”
longitudinalV VQ
p I
connected area
connector
VQnF p
I
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Vertical Connectors
• isolate an area with vertical interfaces
p p
p connected area
connector
VQnF p
I
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Tension Members
• members with holes have reduced area
• increased tension stress
• Ae is effective net area t
e e
P Tf or
A A
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Effective Net Area
• likely path to “rip” across
• bolts divide transferred force too
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Wood Connectors
• adhesives
– used in a controlled environment
– can be used with nails
• mechanical
– nails
– bolts
– lag bolts or lag screws
– split ring and
shear plate connectors
– timber rivets
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Wood Connections
• mechanical
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Nails
• tension stress (pullout)
• shear stress
• nails presumed to share load by
distance from centroid of nail pattern
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Bolts
• bearing stress
– parallel to grain
– perpendicular to grain
• shear stress
• tension stress in member
• concerned with
end shear rupture
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Lag Screws
• tension stress (pullout)
– avoid parallel to grain
• shear stress
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Split Ring Connectors
• bearing stress
– parallel to grain
– perpendicular to grain
• shear stress
• tension stress in member
• concerned with
end shear rupture
• (like bolts)
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Plate Connections
• rigid
– bolts or nails
– plate
– continuous at
top & bottom
• shear
– metal plate with teeth
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Miscellaneous Connectors
• beam hangers
• frame anchors
• seats
• etc…
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Steel Connections
• needed to:
– support beams by columns
– connect truss members
– splice beams or columns
• transfer load
• subjected to
– tension or compression
– shear
– bending
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Bolts
• bolted steel connections
http://courses.civil.ualberta.ca
(AISC - Steel Structures of the Everyday)
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Welds
• welded steel connections
http://courses.civil.ualberta.ca
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Bolted Connection Design
• considerations
– bearing stress
• yielding
– shear stress
• single & double
– member
• rupture
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Bolts
• types
– materials
• high strength
– location of threads
• included - N
• excluded - X
– bearing or friction (SC)
• always tightened
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• Unified steel
– shear:
• bolt strengths
– bolt types
• A325-SC, A490-SC
• A325-N, A490-N
• A325-X, A490-X
2.00 0.75v
na
RR
u v nR R
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Bolted Connection Design
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Bolted Connection Design
• Unified steel
– bearing:
• bolts rarely
fail by bearing
• other part fails first
– slip critical
• tightened down
– holes are 1/16” larger
– effective hole widths
are 1/8” more
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n n bR F A 0.75
2n n bR F A
• single shear or tension
• double shear
• bolt area
– threads excluded
– threads included
Connections 30
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Bolted Connection Design
u nR R
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• bearing at bolt holes
– deformation is concern
– deformation isn’t concern
– long slotted holes
Lc – clear length to edge or next hole
1.2 2.4n c u uR L tF dtF
1.5 3.0n c u uR L tF dtF
1.0 2.0n c u uR L tF dtF
0.75
Connections 31
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Bolted Connection Design
u nR R
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Tension Members
• Ae = AnU
– An is actual net area
– U is shear lag factor by element type
4n g of all holes
sA A A t
g
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• limit states for failure
1. yielding
2. rupture*
Ag - gross area
Ae - effective net area
Fu = the tensile strength
of the steel (ultimate)
Connections 33
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Tension Members
u nR R
0.9 n y gR F A
0.75 n u eR F A
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Welded Connection Design
• considerations
– shear stress
– yielding
– rupture
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Welded Connection Design
• weld terms
– butt weld
– fillet weld
– plug weld
– throat
• weld materials
– E60XX
– E70XX
FEXX = 70 ksi
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Welded Connection Design
• shear failure assumed
• throat
– T =0.707 x weld size
• area
– A = T x length of weld
• weld metal generally
stronger than base
metal (ex. Fy = 50 ksi)
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Welded Connection Design
• minimum
– table
• maximum
– material thickness ( to ¼”)
– 1/16” less
• min. length
– 4 x size min.
– ≥ 1 ½”
163
165
83
167
85
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F2018abn
• shear
– table for S
0.6n EXXR F Tl Sl
u v nR R0.75
Welded Connection Design
area
Connections 38
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na
RR
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Framed Beam Connections
• angles
– bolted
– welded
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Framed Beam Connections
• terms
– coping
(AISC - Steel Structures of the Everyday)
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Framed Beam Connections
• tables for standard
bolt holes & spacings
• n = # bolts
• bolt diameter, angle
leg thickness
• bearing on
beam web
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Other Beam Connections
• seated beam
– unstiffened
– stiffened
• continuous
– beam to column
– beam to beam
http://courses.civil.ualberta.ca
http://www.steel-connections.com
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Other Connections
• rigid frame knees
• beam splice
• column splice
http://courses.civil.ualberta.ca
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Beam Connections
• LRFD provisions
– shear yielding
– shear rupture
– block shear rupture
– tension yielding
– tension rupture
– local web buckling
– lateral torsional buckling
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F2018abn
• LRFD design of connected elements
– shear yielding
– shear rupture
– block shear rupture
1.00 0.60n y gR F A
0.75 0.60n u nvR F A
0.7
0.6 0.6n u nv bs u nt y gv bs u ntR F A U F A F A U F A
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Beam Connections
where Ubs is 1 for uniform tensile stress
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– tension yielding
– tension rupture
– flexural yielding
– local web buckling
– lateral torsional buckling
Connections 46
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Beam Connections
http://aisc.org
n y gR F A0.90
n u eR F A0.75
n y netM F Z0.90b
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Beam Connections
• block shear rupture • tension rupture
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Beam Bearing
• design considerations
– web crippling
– base plate
bending
– bearing on
concrete, etc.
• load distributed
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Column Base Plates
• attached by anchor bolts
– usually 4
– 2 if no moment
• plate level
– by shims & grout
– leveling nuts
• considers
– bearing on steel
– bending of plate
http://courses.civil.ualberta.ca
http://www.steel-connections.com