architectural structures: s analysis and...

F2017abnConnections 1

Lecture 17

Applied Architectural Structures

ARCH 631

seventeen

connections

lecture

APPLIED ARCHITECTURAL STRUCTURES:

STRUCTURAL ANALYSIS AND SYSTEMS

ARCH 631

DR. ANNE NICHOLS

FALL 2017


Lecture 17


ARCH 631

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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• 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…


Lecture 17


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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



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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

Connections 28

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• 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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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



0.75

Connections 31

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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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• weld terms

– butt weld

– fillet weld

– plug weld

– throat

• weld materials

– E60XX

– E70XX

FEXX = 70 ksi


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ARCH 631


• 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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• minimum

– table

• maximum

– material thickness ( to ¼”)

– 1/16” less

• min. length

– 4 x size min.

– ≥ 1 ½”

163

165

83

167

85

Connections 37

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• shear

– table for S

0.6n EXXR F Tl Sl

u v nR R0.75


area

Connections 38

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na

RR


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Framed Beam Connections

• angles

– bolted

– welded

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• terms

– coping

(AISC - Steel Structures of the Everyday)


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• 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://www.steel-connections.com


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Other Connections

• rigid frame knees

• beam splice

• column splice



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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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• 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

Connections 45

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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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ARCH 631

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://www.steel-connections.com

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