1 Steel Construction 2 1 Architectural Structures III F2009abn ...faculty.arch.tamu.edu/media/cms_page_media/4350/notes21...Steel Beams connections ± welds ± bolts Steel Construction
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1
F2012abn
APPLIED ARCHITECTURAL STRUCTURES:
STRUCTURAL ANALYSIS AND SYSTEMS
ARCH 631
DR. ANNE NICHOLS
SPRING 2017
twenty one
steel construction
and designSteel Construction 1
Lecture 21
Applied Architectural Structures
ARCH 631
lecture
http://nisee.berkeley.edu/godden
F2009abn
Steel
• cast iron – wrought iron - steel
• cables
• columns
• beams
• trusses
• frames
Steel Construction 2
Lecture 21
Architectural Structures III
ARCH 631
http://nisee.berkeley.edu/godden
Steel Construction 3
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Steel Construction
• standard rolled shapes
• open web joists
• plate girders
• decking
F2012abn
Steel Construction
• welding
• bolts
Steel Construction 4
Lecture 21
Applied Architectural Structures
ARCH 631
AISC Education
2
Steel Construction 5
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Steel Construction
• fire proofing
– cementicious spray
– encasement in gypsum
– intumescent – expands
with heat
– sprinkler system
Steel Construction 6
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Steel Materials
• high strength to
weight ratio
• ductile
• beam size
often limited by
deflection
• column size
limited by
slenderness
F2007abnSteel Construction 7
Lecture 20
Architectural Structures III
ARCH 631
Steel Beams
• types
– manufactured shapes
castellated
http://nisee.berkeley.edu/godden
Steel Construction 8
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Steel Beams
• types
– wide flange
3
Steel Construction 9
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Steel Beams
• types
– open web joists
(manufactured
trusses)
Steel Construction 10
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Steel Beams
• types (more)
– plate girder
– decking
F2009abn
Steel Beams
Steel Construction 11
Lecture 21
Architectural Structures III
ARCH 631
http://nisee.berkeley.edu/godden
Steel Construction 12
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Steel Beams
• lateral stability - bracing
• local buckling - stiffen
4
Steel Construction 13
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Local Buckling
• steel I beams
• flange
– buckle in
direction of
smaller radius
of gyration
• web
– force
– “crippling”
Steel Construction 14
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Local Buckling
• flange
• web
Steel Construction 15
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Shear in Web
• panels in plate girders or webs with large shear
• buckling in compression direction
• add stiffeners
Steel Construction 16
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Steel Beams
• end conditions
• a) away from
connection - full
section effective
• b) high shear –
only web
effective
5
Steel Construction 17
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Steel Beams
• end conditions
• c) bolt holes –
less material
• d) local web
buckling
Steel Construction 18
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Steel Beams
• bearing
– provide
adequate
area
– prevent
local yield
of flange
and web
Steel Construction 19
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Steel Beams
• connections
– welds
– bolts
Steel Construction 20
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Steel Design – Open Web Joists
• SJI: www.steeljoist.com
• Vulcraft: www.vulcraft.com
– K Series (Standard)
• 8-30” deep, spans 8-50 ft
– LH Series (Long span)
• 18-48” deep, spans 25-96 ft
– DLH (Deep Long Spans)
• 52-72” deep, spans 89-144 ft
– SLH (Long spans with high strength steel)
• pitched top chord
• 80-120” deep, spans 111-240 ft
6
Steel Construction 21
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Steel Design – Open Web Joists
load for live load
deflection limit in RED
total in BLACK
Su2011abn
load for live load deflection
limit (L/360) in RED
total in BLACK
Steel Design – Open Web Joists
Steel Construction 22
Lecture 21
Applied Architectural Structures
ARCH 631
Steel Construction 22
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Steel Beam Design
• American Institute of Steel Construction
– steel grades
• ASTM A36 – carbon
– plates, angles
– Fy = 36 ksi & Fu = 58 ksi
• ASTM A572 – high strength low-alloy
– some beams
– Fy = 60 ksi & Fu = 75 ksi
• ASTM A992 – for building framing
– most beams
– Fy = 50 ksi & Fu = 65 ksi
F2012abn
Steel Beam Design
• AISC: 14th ed.
– combined ASD & LRFD
in one volume in 2005
Steel Construction 24
Lecture 21
Applied Architectural Structures
ARCH 631
7
Su2011abn
• ASD
– bending (braced) = 1.67
– bending (unbraced*) = 1.67
– shear = 1.5 or 1.67
– shear (bolts & welds) = 2.00
– shear (welds) = 2.00
* flanges in compression can buckle
Ra ≤ Rn
Unified Steel Design
Steel Construction 25
Lecture 21
Applied Architectural Structures
ARCH 631
F2012abn
Unified Steel Design
• braced vs.
unbraced
Steel Construction 26
Lecture 21
Applied Architectural Structures
ARCH 631
Su2011abn
LRFD Steel Beam Design
• limit state is yielding all across section
• outside elastic range
• load factors & resistance factors
Steel Construction 27
Lecture 21
Architectural Structures III
ARCH 631
E
1
fy = 50ksi
001724.0y
f
Steel Construction 27
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Load Types
• D = dead load
• L = live load
• Lr = live roof load
• W = wind load
• S = snow load
• E = earthquake load
• R = rainwater load or ice water load
• T = effect of material & temperature
8
F2012abn
LRFD Load Combinations
Steel Construction 29
Lecture 21
Applied Architectural Structures
ARCH 631
ASCE-7
(2010)
• 1.4D
• 1.2D + 1.6L + 0.5(Lr or S or R)
• 1.2D + 1.6(Lr or S or R) + (L or 0.5W)
• 1.2D + 1.0W + L + 0.5(Lr or S or R)
• 1.2D + 1.0E + L + 0.2S
• 0.9D + 1.0W
• 0.9D + 1.0E• F has same factor as D in 1-5 and 7
• H adds with 1.6 and resists with 0.9 (permanent)
Steel Construction 29
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Pure Flexure
Mu - maximum moment
b - resistance factor for bending = 0.9
Mn - nominal moment (ultimate capacity)
Fy - yield strength of the steel
Z - plastic section modulus*
ZFMMR ynbuii 9.0
Steel Construction 30
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Internal Moments - at yield
yyy fbh
fc
IM
6
2
• material hasn’t failed
y
2
y
2
f3
bc2f
6
c2b
Steel Construction 31
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Internal Moments - ALL at yield
• all parts reach yield
• plastic hinge forms
• ultimate moment
• Atension = Acompression
yyp MfbcM2
32
E
1
y = 50ksi
y = 0.001724
9
F2007abnSteel Construction 32
Lecture 20
Architectural Structures III
ARCH 631
n.a. of Section at Plastic Hinge
• cannot guarantee at
centroid
• fy·A1= fy·A2
• moment found from
yield stress times
moment area
1.
p y y i in a
M f A d f A d
Steel Construction 33
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Plastic Hinge Development
Steel Construction 34
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Plastic Hinge Examples
• stability can be effected
Steel Construction 35
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Plastic Section Modulus
• shape factor, k
= 3/2 for a rectangle
1.1 for an I
• plastic modulus, Z
y
p
M
Mk
y
p
f
MZ
SZk
10
F2007abnSteel Construction 36
Lecture 20
Architectural Structures III
ARCH 631
Shear
Vu - maximum shear
v - resistance factor for shear = 1.0
Vn - nominal shear
Fyw - yield strength of the steel in the web
Aw - area of the web = twd
iRi = Vu ≤ vVn = 1.0(0.6FywAw)
Su2011abn
Flexure Design
• limit states for beam failure
1. yielding
2. lateral-torsional buckling*
3. flange local buckling
4. web local buckling
• minimum Mn governs
Steel Construction 38
Lecture 21
Architectural Structures III
ARCH 631
1.76y
p y
FL r
E
i i u b nR M M
Su2011abn
Compact Sections
• plastic moment can form before any
buckling
• criteria
–
– and
Steel Construction 39
Lecture 21
Architectural Structures III
ARCH 631
0.382
f
f y
b E
t F
3.76c
w y
h E
t F
Su2011abn
Cb = modification factor
Mmax - |max moment|, unbraced segment
MA - |moment|, 1/4 point
MB = |moment|, center point
MC = |moment|, 3/4 point
Lateral Torsional Buckling
Steel Construction 40
Lecture 21
Architectural Structures III
ARCH 631
pbn MCM moment based on
lateral buckling
CBAmax
maxb
MMMM.
M.C
34352
512
11
Su2011abn
Beam Design Charts
Steel Construction 41
Lecture 21
Architectural Structures III
ARCH 631
F2007abnSteel Construction 40
Lecture 20
Architectural Structures III
ARCH 631
Deflection Limits
• based on service condition
• no “impairment” to serviceability
• avoid ponding
• L/360 due to live load for beams &
girders supporting plaster (service)
F2009abn
Steel Arches and Frames
• solid sections
or open web
Steel Construction 41
Lecture 21
Architectural Structures III
ARCH 631
http://nisee.berkeley.edu/godden
Steel Construction 42
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Steel Shell and Cable Structures
12
Steel Construction 43
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Approximate Depths
Su2011abn
Unified Column Design
• limit states for failure
1. yielding
2. buckling
Fe – elastic buckling stress (Euler)
Steel Construction 46
Lecture 21
Architectural Structures III
ARCH 631
ncu PP gcrnc AFP. 900
ye
y
F.ForF
E.
r
KL440714
ye
y
F.ForF
E.
r
KL440714
n
a
PP
Su2011abn
Unified Column Design
• Pn = FcrAg
– for
– for
– where
Steel Construction 47
Lecture 21
Architectural Structures III
ARCH 631
yF
E.
r
KL714 y
F
F
cr F.F e
y
6580
ecr F.F 8770
22
rKL
EFe
yF
E.
r
KL714
Su2011abn
Procedure for Analysis
1. calculate KL/r• biggest of KL/r with respect to x axes and y axis
2. find Fcr from appropriate equation• tables are available
3. compute Pn = FcrAg
• or find fc = Pa/A or Pu/A
4. is Pa Pn/ or Pu Pn?• yes: ok
• no: insufficient capacity and no good
Steel Construction 48
Lecture 21
Architectural Structures III
ARCH 631
13
Su2011abn
1. guess a size (pick a section)
2. calculate KL/r• biggest of KL/r with respect to x axes and y axis
3. find Fcr from appropriate equations• or find a table
4. compute Pn = FcrAg
• or find fc = Pa/A or Pu/A
Procedure for Design
Steel Construction 49
Lecture 21
Architectural Structures III
ARCH 631
Su2011abn
Procedure for Design (cont’d)
5. is Pa Pn/ or Pu Pn?• yes: ok
• no: pick a bigger section and go back to step 2.
6. check design efficiency
• percentage of stress =
• if between 90-100%: good
• if < 90%: pick a smaller section and
go back to step 2.
Steel Construction 50
Lecture 21
Architectural Structures III
ARCH 631
%P
P
c
r 100
Su2011abn
Column Tables
Steel Construction 51
Lecture 21
Architectural Structures III
ARCH 631
Su2011abn
Beam-Column Design
• moment magnification (P-)
Cm – modification factor for end conditions
= 0.6 – 0.4(M1/M2) or
0.85 restrained, 1.00 unrestrained
Pe1 – Euler buckling strength
Steel Construction 52
Lecture 21
Architectural Structures III
ARCH 631
factoredmaxu MBM 1 )PP(
CB
eu
m
1
11
22
1
rKl
EAPe
14
Su2011abn
Beam-Column Design
• LRFD (Unified) Steel
– for
– for
Pr is required, Pc is capacity
c - resistance factor for compression = 0.9
b - resistance factor for bending = 0.9
Steel Construction 53
Lecture 21
Architectural Structures III
ARCH 631
019
8.
M
M
M
M
P
P
nyb
uy
nxb
ux
nc
u
:.P
P
c
r 20
012
.M
M
M
M
P
P
nyb
uy
nxb
ux
nc
u
:.P
P
c
r 20
Steel Construction 57
Lecture 20
Architectural Structures III
ARCH 631
F2007abn
Construction Supervision
• proper grade material
– high strength bolts
• quality welds
• proper bolted
conditions (ex. sc)
• fabrication and erection
of steel frame
connection details
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