Ch20-Site and Precast

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Concrete Construction II

Site
-
cast and precast framing systems

Chapter 20

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Elevated concrete floor systems


Beam supported


Beamless

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Beam
-
supported floor systems

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Load
-
transfer: one
-
way and two
-
way concrete slabs

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

One
-
way and two way slabs in same floor,

view from below

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Beam and girders with slab floors increase spans,
decrease economy

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

One
-
way and two
-
way slabs


Slabs become thicker as spans increase


Uneconomical when slab exceeds 8 inches


Dimensions maximized


One
-
way slab, 16 fts wide


Two
-
way, square slab 24 ft. wide


Beams and girders can be added to slabs to
increase spans & reduce slab thickness


Beam and girder sizes vary


Increase cost and complexity of formwork


Not commonly used due to lack of economy


Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Band beam floor

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Modular formwork creates economy


Constructing formwork with flat deck as base
creates economy


Simple, repetitive formwork


Easier working surface


Faster construction time


One
-
way and two way floors possible


Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

One
-
way joist floor viewed from below

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Standard module formwork with beam
reinforcement laid

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Standard module pan sizes

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Tapered pans, widened joist ends

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Wide
-
module pans

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Wide module floors, thicker slabs


Used when thicker slab is appropriate


Increase fire rating (1 hour or 2 hour floors)


Slabs accommodate electrical conduit

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Thick slab in one
-
way joist floor

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Wide module pans

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Two
-
way joist
floor (waffle slab)

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Beamless waffle
slab

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Glass fiber reinforced dome for waffle slab

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Flat plate slab:
light occupancies, lower ceiling
height, small, square bays

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Flat slab has round column and drop panels

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Post
-
tensioned elevated concrete floors


Reduces slab and beam dimensions


Reduces dead loads


Reduced seismic load


Reduced foundation requirements


Lower floor to floor height


Reduced cost of cladding

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Draped cables in reinforcement cage for prestressed
beams. Cage will be lowered into beam form

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Beam cage has been lowered and floor reinforcement
and bands of prestressing cables placed.

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Prestressed concrete frame. Ends of tensioned cables have
been flame cut on lower floors, still hanging above


Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Most economical site
-
cast floor systems


Flat plate


One
-
way joist floor

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Precast concrete


Prefabricated in plant and transported to site for
assembly


Good for climates where site
-
cast concrete difficult to use


Cost of formwork and shoring reduced


Permanent formwork


Cast at ground level


Greater quality control


Improved strength


Improved finishes


Disadvantages


Cost of transportation


Heavy hoisting equipment


Skilled workforce


Limitations on sculptability


Straight standard profiles


Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Precast types


Architectural precast
(not discussed here)


Concrete elements used as non
-
structural
elements


Typically cladding


Structural precast


All elements of a structural frame


Mixed precast construction


Some elements of structure precast


Most common use of structural precast


Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Precast structural floor and roof elements


Hollow
-
core slabs


Solid planks


Double
-
tee units


Inverted
-
tee beams

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Section through hollow core slab

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Precast concrete hollow core slabs rest on site
-
cast
concrete columns and beams

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Precast concrete hollow core slabs rest on steel
beams

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Connecting hollow core slabs to concrete beams

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Connecting hollow core slabs to steel beams

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Section through double
-
tee floor

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Double
-
tee units on precast inverted T
-
beams

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Double
-
tee meet at column and beam

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Double
-
tee meet at column and beam

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Casting double tee units

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Inverted T
-
beam

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Fire resistance of concrete members


Thickness of member


Type of course aggregate


Covering of reinforcement and prestressing
tendons

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Building separation joint: Single column, site cast

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Slip joint assembly

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Slip joint assembly

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Slip joint assembly

Mehta, Scarborough, and Armpriest : Building Construction: Principles,
Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.

Coefficient of Friction



=

F

P