twenty two continuous beams no beams concrete construction: - - PowerPoint PPT Presentation

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S2009abn Concrete Slabs 1 Lecture 22 Elements of Architectural Structures ARCH 614

ELEMENTS OF ARCHITECTURAL STRUCTURES: FORM, BEHAVIOR, AND DESIGN

ARCH 614

• DR. ANNE NICHOLS

SPRING 2019 lecture

twenty two

concrete construction:

T-beams & slabs

Concrete Slabs 2 Lecture 22 Elements of Architectural Structures ARCH 614 S2007abn

Systems

• beams separate from slab
• beams integral with slab

– close spaced

• continuous beams
• no beams

Concrete Slabs 3 Lecture 22 Elements of Architectural Structures ARCH 614 S2007abn

T sections

• two areas of compression in moment

possible

• one-way joists
• effective flange width

Concrete Slabs 4 Lecture 22 Elements of Architectural Structures ARCH 614 S2007abn

T sections

• negative bending: min As, larger of:
• effective width (interior)

– L/4 – bw + 16t – center-to- center of beams

Cf Cw T

) ( 6 d b f f A

w y c s

  ) ( 3 d b f f A

f y c s

 

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S2007abn Concrete Slabs 5 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 C a=1x

Concrete Slabs 6 Lecture 22 Elements of Architectural Structures ARCH 614 S2007abn

One-way

• Joists

– standard stems – 2.5” to 4.5” slab – ~30” widths – reusable forms

Concrete Slabs 7 Lecture 22 Elements of Architectural Structures ARCH 614 S2007abn

One-way

• Joists

– wide pans – 5’, 6’ up – light loads & long spans – one-leg stirrups

Concrete Slabs 8 Lecture 22 Elements of Architectural Structures ARCH 614 S2009abn

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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S2007abn Concrete Slabs 9 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

) ' ( d d f M A

y u s

  

Concrete Slabs 10 Lecture 22 Elements of Architectural Structures ARCH 614 S2007abn

Slabs

• one way behavior – like beams
• two way behavior – more complex

Concrete Slabs 11 Lecture 22 Elements of Architectural Structures ARCH 614 S2007abn

Slab Design

• one unit wide “strip”
• with uniform loads

– like “wide” beams – moment / unit width – uniform curvature

• with point loads

– resisted by stiffness

• f adjacent strips

– more curvature in middle

Concrete Slabs 12 Lecture 22 Elements of Architectural Structures ARCH 614 S2007abn

Slab Design

• min thickness by code
• reinforcement

– bars, welded wire mesh – cover – minimum by steel grade

• 40-50:
• 60:

0018 .   bt As  002 .   bt As 

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Concrete Slabs 13 Lecture 22 Elements of Architectural Structures ARCH 614 S2007abn

One-way Slabs

• As tables
• max spacing*

–  3(t) and18” –  5(t) and18” – temp & shrinkage steel

• no room for stirrups

*not in note set