Chapter 11 - Floor

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CMgt3350 Building Structures

Chapter 11
-

Floor
Systems

Objectives


List wood floor systems


Explain the advantages and
disadvantages of specifying precast
over sitecast concrete.


Explain why precast concrete structural
elements are usually cured with steam.


Explain the difference between a one
-
way and two
-
way concrete floor
system.


List and explain the different types of
one
-
way concrete floor systems.


List and explain the different types of
two
-
way concrete floor systems.

Wood Floors


1”x12” T&G sheet floor decking


Laminated 2”x4”’s or 2”x6”’s on edge at right
angles to the floor beams


Spiked together side by side


Wood Floors


Can be wood beam or steel beam with
wood nailer on top


Heavy planks, tongue and groove, spiked
to the beams

Concrete Floors


Slabs on grade


Durability depends on concrete strength
and finish


Strength of slab depends on reinforcing
and supporting subgrade


Structural slabs


Span between columns and beams


Strength depends on concrete strength
and the amount of reinforcing steel

5 Advantages of Choosing Precast


Able to control the quality of materials and workmanship
better than onsite (able to build in the rain, sleet, or snow).


Able to vibrate the concrete mechanically to achieve
maximum density and highest surface quality.


Able to reuse formwork more than onsite, thus reducing
formwork cost per unit.


Able to steam cure, thus accelerating curing with the
steam’s heat and adding moisture for full hydration.


Steam curing, coupled with the use of Type III cement
enables the plant to produce a fully cured structural
element in 24 hours.


(Allen, p. 518)

Disadvantages of using Precast


Although light compared to other building
elements, precast structural elements are
heavy to transport over the roads and
hoist into place.


This also restricts the size and proportions
of most precast elements (they can be
long, but they can only be as wide as the
maximum legal vehicle width of 12 to 14
feet.

One
-
Way Versus Two
-
Way
Floor Framing System


One
-
Way


Beams run in one direction, parallel
to one another, between
perpendicular girders that transfer
the load to columns.


Two
-
Way


Beams run in two directions, parallel
and perpendicular to one another.

One
-
Way Floor Systems


The One
-
Way Solid Slab System



Beams and girders are poured the
same time as the slab.


Economical when the slab does not
span very far between beams.


Slab depths are usually 4
-
10 inches.


Uneconomical on spans of more than
20’

The One
-
Way Solid Slab System

The One
-
Way Solid Slab System

One
-
Way Floor Systems


The One
-
Way Concrete Joist System


Longer one
-
way spans than solid slab systems.


Joists are formed with metal pans supported on
longitudinal strips of wood or on a plywood deck.


Distribution ribs are placed at mid
-
span to
distribute concentrated loads to more than one
joist.


When fire
-
resistance requirements of the building
code dictate a slab thickness of 4.5 inches or
more, the slab is capable of spanning a much
greater distance. This enables wide
-
module pans
that separate the joists by 4
-
6 feet.


See Figures: 11
-
30, 11
-
31, 11
-
32, 11
-
17, 11
-
18



One
-
Way Floor Systems

One
-
Way Floor Systems

One
-
Way Floor Systems

The One
-
Way Concrete Joist System

The One
-
Way Concrete Joist System

Two
-
way Floor Systems


Beams run in two directions, parallel
and perpendicular to one another.


“Generally, two way floor systems
are more economical than one
-
way
systems in buildings where columns
can be spaced in bays that are
square or nearly square in
proportion” (Allen, p 483).

Two
-
way Floor Systems (cont.)


The Two
-
Way Solid Flat Slab System


A system in which the slab is supported by a grid of beams
running in both directions over the columns.


Used for very heavily loaded industrial floors.


Slab depth = 4 to 12 inches


Maximum span = 34 feet


Most two
-
way floor systems are made without beams.
Instead, “the slab is reinforced in such a way that the
varying stresses in the different zones of the slab are
accommodated within a uniform thickness of concrete”
(Allen, p. 483).



Two
-
way Floor Systems (cont.)


The Two
-
Way Solid Flat Slab System (cont.)


Formwork is completely flat except for a thickening of the
concrete to resist the high shear forces around the top of
each column (drop panel). Historically the columns under
the drop panels also had mushroom capitals.


“Reinforcing is laid in both directions in half
-
bay
-
wide strips
of two fundamental types: column strips are designed to
carry the higher bending forces encountered in the zones of
the slab that cross the columns, and the middle strips have
a lighter reinforcing pattern” (Allen, p. 483).


The Two
-
Way Solid Flat Slab System

Allen, p. 482

Two
-
way Floor Systems (cont.)

Two
-
way Floor Systems (cont.)

Two
-
way Floor Systems (cont.)


The Two
-
Way Flat Plate System


“In more lightly loaded buildings, such as
hotels, hospitals, dormitories, and
apartment buildings, the slab need not be
thickened at all over the columns.”


“This allows some columns to be moved
off of the grid to facilitate a more efficient
floor plan (Allen, p. 483).


Slab depth = 5
-
10 inches.


Maximum span = 32 feet




Two
-
way Floor Systems


Flat
Plate

Two
-
way Floor Systems


The Two
-
Way Waffle Slab System


A.k.a. The two
-
way concrete joist system


Metal or plastic pans called domes are used to
eliminate the nonworking concrete from the slab,
allowing a greater economy in longer spans.
Domes now have a special fitting that allows one
to shoot compressed air between it and the
concrete to remove the dome.


Standard Domes form joists 6” wide on 36”
centers or 5” wide on 24” centers.


Solid concrete heads are created around the tops
of the columns by leaving the domes out of the
formwork. These serve the same function as the
drop panels in the two
-
way flat slab system.



The Two
-
Way Waffle Slab System

Allen, p. 485

The Two
-
Way Waffle Slab System

The Two
-
Way Waffle Slab System

The Two
-
Way Waffle Slab System

Introduction to Composite Construction


Composite

construction

refers

to

two

load
-
carrying

structural

members

that

are

integrally

connected

and

deflect

as

a

single

unit


An

example

of

this

is

composite

metal

deck

with

concrete

fill,

steel

filler

beams,

and

girders

made

composite

by

using

headed

stud

connectors

Adapted From (ASCE 2002)

Composite
Steel Deck

Shear
Connectors

Welded Wire
Fabric

Concrete


A steel beam which is made composite by using shear connectors,
composite metal decking and concrete is much stronger and stiffer than the
base beam alone


Composite floor systems are considered by many to be the highest quality
type of construction


This has become a standard type of construction selected by many
architects, engineers, and developers




(AISC 1991)

Introduction to Composite Construction

Advantages of Composite Construction

In

a

composite

floor

system

the

concrete

acts

together

with

the

steel

to

create

a

stiffer,

lighter,

less

expensive

structure





(Allen

1999
)

Advantages of Composite Construction

Connecting

the

concrete

to

the

steel

beams

can

have

several

advantages
:


It is typical to have a reduced
structural steel frame cost


Weight of the structural steel
frame may be decreased which
may reduce foundation costs


Reduced live load deflections


Shallower beams may be used
which might reduce building height


Increased span lengths are
possible


Stiffer floors


Puddle

welds

(above

right)

are

commonly

used

to

attach

the

decking

to

the

structural

steel

below


Daily

output

for

a

four

person

decking

crew

ranges

from

2700

S
.
F
.

to

3860

S
.
F
.

per

day

depending

on

the

depth

and

gauge

of

the

decking

(Means

2004
)

Installation of Decking


As

an

alternative

to

welding,

powder

actuated

tools

may

be

used

to

attach

metal

decking

to

structural

steel



Powder

actuated

tools

use

the

expanding

gases

from

a

powder

load,

or

booster,

to

drive

a

fastener


A

nail
-
like

fastener

is

driven

through

the

metal

deck

into

the

steel

beam


The

powder

actuated

tool,

powder

load,

and

fastener

must

be

matched

to

the

thickness

of

the

structural

steel

beam

flanges

Installation of Decking

Images courtesy of Hilti Corporation


Shear

connectors

are

commonly

referred

to

as

“studs”

or

“shear

studs”

in

the

trade


They

are

available

in

a

range

of

sizes,

materials,

and

grades


Headed

studs

(as

shown)

are

most

commonly

used


Other,

less

common

options

for

shear

connectors

include

hooked

studs

or

pieces

of

C
-
channel

Shear Connectors


Depending

on

the

welding

process

used,

the

tip

of

the

shear

connector

may

be

placed

in

a

ceramic

ferrule

(arc

shield)

during

welding

to

retain

the

weld


Shear

connectors

create

a

strong

bond

between

the

steel

beam

and

the

concrete

floor

slab

which

is

poured

on

top

of

the

metal

decking



This

bond

allows

the

concrete

slab

to

work

with

the

steel

beams

to

reduce

live

load

deflection

Shear Connectors


Shear

connectors

are

installed

after

the

decking

is

in

place


Shear

connectors

may

be

installed

by

the

steel

erection

contractor

or

a

specialty

shear

connector

installer


The

welding

equipment

required

for

installation

is

provided

by

the

shear

connector

installer


Daily

output

for

shear

connector

installation

averages

about

1000

per

day

depending

on

the

size

of

the

connectors

(Means

2004
)

Installation of Shear Connectors


Concrete

is

installed

by

a

concrete

contractor

on

top

of

the

composite

metal

decking,

shear

connectors,

and

welded

wire

fabric

or

rebar

grid

(crack

control

reinforcing)


Pumping

is

a

typical

installation

method

for

concrete

being

placed

on

metal

decking


10
,
000

to

15
,
000

sq
.

ft
.

of

concrete

slab

may

be

installed

per

day

depending

on

slab

thickness

and

crew

size

(Ruddy

1986
)

Installation of Concrete


There

is

an

art

to

the

placement

of

concrete

on

metal

deck

and

structural

steel


The

work,

unless

shoring

is

used,

must

be

executed

on

a

deflecting

surface


An

experienced

concrete

contractor

should

be

employed

for

this

work


Concrete

should

be

deposited

over

supporting

members

first,

then

spread

toward

the

deck

midspans


The

accumulation

of

a

deep

pile

of

concrete

must

be

avoided


(AISC

2003
,

ASCE

2002
)

Installation of Concrete


The

contractor

must

be

aware

of

camber

in

the

beams

and

the

expected

deflections


Consultation

with

the

structural

engineer

may

be

necessary


As

the

concrete

cures

it

forms

a

connection

with

the

composite

metal

decking

and

shear

studs


The

composite

floor

system

is

now

complete


(AISC

2003
)

Installation of Concrete

Floor Finish


1” Metallic Aggregate Mix


Terra
-
Cotta Tile (Ceramic)


Mastic Finish (Epoxy)


Resilient Tile (VCT)


Terrazzo


AISC
.

(
1991
)
.

Design

Guide

for

Low
-

and

Medium
-
Rise

Steel

Buildings
.

American

Institute

of

Steel

Construction,

Inc
.

Chicago,

IL
.

AISC. (1999).
Construction Management of Steel Construction
. American Institute
of Steel Construction, Inc. Chicago, IL.

AISC
.

(
2000
)
.

Code

of

Standard

Practice

for

Steel

Buildings

and

Bridges
.

American

Institute

of

Steel

Construction,

Inc
.

Chicago,

IL
.

AISC
.

(
2002
)
.

Designing

With

Structural

Steel



A

Guide

for

Architects
.

American

Institute

of

Steel

Construction,

Inc
.

Chicago,

IL

.


AISC
.

(
2003
)
.

Design

Guide

for

Serviceability

Design

Considerations

for

Steel

Buildings,

Second

Edition
.

American

Institute

of

Steel

Construction,

Inc
.

Chicago,

IL
.

Allen,

E
.

(
1999
)
.

Fundamentals

of

Building

Construction

Materials

and

Methods
.

John

Wiley

&

Sons,

Inc
.

New

York,

NY
.

ASCE
.

(
2002
)
.

“Construction

Considerations

for

Composite

Steel
-
and
-
Concrete

Floor

Systems
.


Journal

of

Structural

Engineering
,

Vol
.

128
,

No
.

9
,

1099
-
1110
.

American Welding Society, (AWS). (2004). “Structural Welding Code


Section 7:
Stud Welding.”
ANSI/AWS D1.1
-
98,

Miami, FL.


References


Larson, J. W., and Huzzard, R. K. (1990). “Economical Use of Cambered Steel
Beams.”
Proc. AISC Engineering Conference
, Chicago, IL. 3
-
21.

Means, R.S. (2004).
2004 Building Construction Cost Data.

R.S. Means Company,
Inc., Kingston, MA.

Occupational Safety & Health Administration, (OSHA). (1996). “Concrete and
Masonry Construction.” Available at:
http://www.osha.gov/doc/outreachtraining/htmlfiles/concrete.html
. Viewed June,
2004.

Ricker, Jr., D. T. (1989) . “Cambering Steel Beams.”
AISC Engineering Journal,

4,
136
-
142.

Richard Lees Steel Decking, (RLSD). (2002). “Composite Beams & Shear Studs


Information Sheet CB5.” Richard Lees Steel Decking. Available at:
http://www.rlsd.com/
. Viewed April, 2004.

Ruddy, J. L. (1986). “Ponding of Concrete Deck Floors.”
AISC Engineering Journal,

3, 107
-
115.

Steel Inspection News, (SIN). (1993). “Shear Connector Inspection


a Tutorial.”
Steel Structures Technology Center, Inc. Available at:
http://www.steelstructures.com/StlInspNews/NEWS%20index.htm
. Viewed April,
2004.

References Cont.

References Cont.



Allen, Edward. (1990)
Fundamentals
of Building Construction: Materials
and Methods

(2nd edition). Wiley &
Sons: New York.


Andres C. K. and Smith R. C. (2004)


Principles and Practices of
Commercial Construction
(Seventh
edition). Pearson: Upper Saddle
River, New York.