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Transcript of twenty two lecture - Facultyfaculty.arch.tamu.edu/media/cms_page_media/4211/lect22_fZx6LQ4.pdf ·...
S2017abnConcrete Slabs 1
Lecture 22
Elements of Architectural Structures
ARCH 614
ELEMENTS OF ARCHITECTURAL STRUCTURES:
FORM, BEHAVIOR, AND DESIGN
ARCH 614
DR. ANNE NICHOLS
SPRING 2017
lecture
twenty two
concrete construction:T-beams & slabs
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Lecture 22
Elements of Architectural Structures
ARCH 614
Systems
• beams separate from slab
• beams integral with slab
– close spaced
• continuous beams
• no beams
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Elements of Architectural StructuresARCH 614
T sections
• two areas of compression in moment
possible
• one-way joists
• effective flange width
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Elements of Architectural StructuresARCH 614
T sections
• negative bending: min As, larger of:
• effective width (interior)
– L/4
– bw + 16t
– center-to-center ofbeams
CfCw
T
)(6
dbf
fA w
y
c
s
′= )(
3db
f
fA f
y
c
s
′=
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Lecture 22
Elements of Architectural Structures
ARCH 614
T sections
• usual analysis steps
1. assume no compression in web
2. design like a
rectangular beam
3. needs reinforcement
in slab too
4. also analyze for negative
moment, if any
a/2
T
0.85f’c
Ca=1x
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Lecture 22
Elements of Architectural Structures
ARCH 614
One-way
• Joists
– standard
stems
– 2.5” to 4.5”
slab
– ~30” widths
– reusable
forms
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Lecture 22
Elements of Architectural Structures
ARCH 614
One-way
• Joists
– wide pans
– 5’, 6’ up
– light loads &
long spans
– one-leg
stirrups
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Lecture 22
Elements of Architectural Structures
ARCH 614
Compression Reinforcement
• doubly reinforced
• negative bending
• two compression forces
• T = Cc + Cs
• T = Asfy
• Cs = As’ fy
• Mn = T(d-a/2)+Cs(d-d’)
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Lecture 22
Elements of Architectural Structures
ARCH 614
Compression Reinforcement
• needs ties because of buckling
• simplified method in text assumes
– As’=0.3As
– Mn > Mu/
– f’s = ½fy
– a = 2d’
– so
)'( ddf
MA
y
us
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Lecture 22
Elements of Architectural Structures
ARCH 614
Slabs
• one way behavior – like beams
• two way behavior – more complex
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Lecture 22
Elements of Architectural Structures
ARCH 614
Slab Design
• one unit wide “strip”
• with uniform loads
– like “wide” beams
– moment / unit width
– uniform curvature
• with point loads
– resisted by stiffness
of adjacent strips
– more curvature in middle
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Lecture 22
Elements of Architectural Structures
ARCH 614
Slab Design
• min thickness by code
• reinforcement
– bars, welded wire mesh
– cover
– minimum by steel grade
• 40-50:
• 60:
0018.0bt
As
002.0bt
As
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Lecture 22
Elements of Architectural Structures
ARCH 614
One-way Slabs
• As tables
• max spacing
– 3(t) and18”
– 5(t) and18” – temp & shrinkage steel
• no room for stirrups