BT3HeavyRCPrestressetc

8/11/2019 BT3HeavyRCPrestressetc.

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BUILDINGCONSTRUCTION

III

HEAVY REINFORCED CONCRETE, PRE-

STRESSED CONCRETE AND STEEL

CONSTRUCTION


2/106

3.0

3.1

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,

Basement

Construction, Cisterns

Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

3. HEAVY REINFORCED CONCRETE, PRE-

STRESSED CONCRETE AND STEEL CONSTRUCTION

3.1 FOUNDATION SYSTEMS (Deep and Shallow Foundation)

The foundation system transfers

the lateral loads on the

superstructure to the ground. The

horizontal component of these

lateral forces is transferred largely

through a combination of soil

friction on the bottom of footings

and the development of passive

soil pressure on the sides of

footings and foundation walls.

Foundation systems are classified

into two broad categories ---

shallow foundationsand deep

foundations.


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3.1

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,

Basement


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

3.1.1 SHALLOW FOUNDATIONS

Shallowor spread foundationsare employed when stable soil of

adequate bearing capacity occurs relatively near the ground surface. They

are placed directly below the lowest part of a superstructure and transferbuilding loads directly to the supporting soil by vertical pressure. The types

of shallow or spread footings are:

1. Individual or isolated footingsare spread footings supporting free-

standing columns and piers.

a. Block or square footings

b. Stepped footings

c. Slope or pyramidal footings


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STEPPED FOOTINGS

STRIP FOOTINGS

3.0

3.1

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,

Basement


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

2. Strip footingsare the continuous spread footings of foundation walls.

Stepped footingsare strip footings that change levels to accommodate a

sloping grade and maintain the required depth at all points around a building.

a. Combined footings. supporting two or more columns. This type of

footing is used where it is not possible to center the footing beneath itssupported column as in the case of columns located at or very near the

property line. In such case, the nearest interior column is selected and

a combined footing constructed under both columns.

3. Combined footings.


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3.1

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,

Basement


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

b. Cantilevered footings. This type

of footing may be used in place of a

combined footing under the same

conditions. In this type of

construction, the footings of the

exterior and interior columns are

connected by a tie-beam or strapwhich is so extended to support the

exterior column. The top of the beam

or strap is usually placed level with

the top of the footings.

The footing is so designed so that the

center of gravity of the combined

loads passes through the center of

gravity of the footing area. Combined

column footings are usuallyrectangularor trapezoidalin shape.


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Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,

Basement


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

c. Continuous footings.

These may be:

1. supporting a line of columns

2. supporting all of the columnsby strips at right angles to each

other.

They may beinvertedslab or

inverted tee continuous

footings.

L/5

L/4 L/4

L/5

L/4 L/4

4. Mat or Raft Foundations

Mat foundations, like continuous footings are used on soil of low bearing

power where there is a tendency towards unequal settlement due to unequal

loading of soil. In this type of foundation all parts of the foundation are so tied

together so that they will act as one and assist each other in keeping level

and plumb.


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3.0

3.1

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,

Basement


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

1. Flat slabs of plain or reinforced

concrete

Mat foundations may be divided into the following general classes:

2. Beams or girders with a slab

underneath

3. Beams or girders with a slab on top


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3.0

3.1

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,

Basement


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

4. STEEL GRILLAGE FOUNDATION

When it is desired to avoid the deep excavation required for concrete and

masonry footings, and when the load has to be distributed over a wide

area of support, steel rails or beams are used to give the required

moment of resistance with a minimum of depth.

For steel-grillage foundations the foundation

bed should first be covered with a layer of

concrete not less than 6 in thickness and so

mixed and compacted as to be nearly

impervious to moisture as possible. Thebeams are placed on this layer, the upper

surface brought to a line and the lower

flanges carefully grouted so as to secure an

even bearing. Subsequently, concrete should

be placed between and around the beams so

as to permanently protect them. The beam

must not be spaced so near as to prevent theplacing of concrete between them. The clear

space between the flanges of the top layer of

beams should not be less than 2 and should

be somewhat more for the lower layers.


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3.0

3.1

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,

Basement


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

3.1.2 DEEP FOUNDATIONS

Deep foundations are employed when the soil underlying a shallow

foundation is unstable or of inadequate soil bearing capacity. They extend

down through unsuitable soil to transfer building loads to a more

appropriate bearing stratum of rock or dense sand and gravel well below

the superstructure. The types of deep foundations are pileand caisson

foundations.

1. PILE FOUNDATIONS

A pile foundationis asystem of end bearing or

friction piles, pile caps,

and tie beams for

transferring building loads

down to a suitable bearing

stratum.

Pile Cap1. A slab or connecting beam which covers the heads of a group of piles, tying them together so that the structural load

is distributed and they act as a single unit. 2. A metal cap which is placed, as temporary protection, over the head of a

precast pile while it is being driven into the ground.

LOAD BEARING WAL

REINFORCED

CONCRETE GRADE o

TIE BEAM

REINFORCED CONCRETE

PILE CAP

COLUMN LOAD


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3.0

3.1

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,

BasementConstruction, Cisterns

Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

A. WOOD PILES

Wood-pile Foundations. When it is

required to build upon a compressible

soil saturated with water and of

considerable depth, the most

practicable method of obtaining a

solid and enduring foundation for

buildings of moderate height is by

driving wooden piles. Wooden piles

are made from the trunks of trees and

should be as straight as possible, and

not less than 5 in diameter at small

end for light buildings, or 8 for heavy

buildings.

The piles are driven by means of a drop-hammer or with a steam-

hammer, a succession of blows being given with a block of cast iron or

steel called the hammer, which slides up and down; the uprights of the

machine is placed over the pile-driver. The machine is placed over the

pile so that the hammer descends fairly on its head, the piles being driven

with the small end down.


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3.1

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

In driving wooden piles with

a drop-hammer, the hammer

is generally raised by steam-

power and is dropped either

automatically or by hand.

The weight of the hammers

used for driving piles for

building foundations is

usually from 1,500 to 2,500

lb., and fall varies from 5 to

20 ft., the last blows being

given with a short fall. Steam

hammers are to a

considerable extent taking

the place of the ordinary

drop-hammers as they will

drive more piles in a day,

and with less damage to the

piles.

The steam-hammer delivers quick, short blows, from 60 to 70 to the minute,

and seems to jar the piles down, the short interval between the blows not

giving time for the soil to settle around them.


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3.1

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

In driving piles care should be taken to

keep them plumb, and when the

penetration becomes small, the fall

should be reduced to about 5 ft., the

blows being given by rapidsuccession. Whenever a pile refuses

to sink under several blows before

reaching the average depth, it should

be cut off and another pile driven

beside it.

When several piles have been driven to a depth of 20 ft. or more orrefuse to sink more than in. under 5 blows of a 1200 lb. hammer falling

15 ft., it is useless to try them further, as the additional blows result only

in brooming and crushing the heads and points of the piles, and splitting

and crushing the intermediate portions to an unknown extent.

When the penetration is less than 6 in. at each blow the top of the pile

should be protected from brooming by putting on an iron pile ring, about 1

in. less in diameter than the head of the pile, and from 2-1/2 to 3 in. wide by

5/8 in. thick. The head should be chamfered to fit the ring.

Pile Ringalso called a drive band; a steel band which encircles the head of a timber pile to prevent it from splitting when being

driven.


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3.0

3.1

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

In driving in soft and silty soils, the piles drive better with a square point. When

driven into compact soil, such as sand, gravel, or stiff clay, the point of the

pile should be shod with iron or steel. This is usually in the form of a cast

conical point about 5 in. in dia., secured by a long dowel with a ring

around the end of the pile.

Piles that are driven in or exposed to salt water should be thoroughlyimpregnated with creosote, dead oil or coal-tar, or some mineral poison to

protect them from teredo or shipworm which will completely honeycomb

an ordinary pile in three or four years.

Piles should not be spaced less than 2 ft. on centers; usual spacing is from 2 to

3 ft. When long piles are driven closer than 2 ft. on centers, there is

danger that they may force each other up from their solid bed on bearing

stratum. Driving the piles close together also breaks up the ground and

diminishes the bearing power. Maximum allowable load on wood piles is

usually 20 tons.

The top of the piles should be cut off at or below the low water mark, otherwise

they will soon commence to decay. They should then be capped, either

with concrete, or with timber or steel grillage. The usual practice is to use

the reinforced-concrete cap, the method being to excavate 6 to 12 below

the tops and one foot outside of the piles. Concrete is then placed around

and above the piles. Approximately 3 above the top of the piles a layer or

reinforcement running in both directions is placed. Caps are usually 18 or

more in thickness.


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Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

Heavy timber grillages may also be used for capping. These are bolted to

the top of the piles and the concrete footings laid on top of it. The

timbers for the grillages should be at least 10 x 10 in cross-section,

and should have sufficient transverse strength to sustain the load

from center to center of piles. They should be laid longitudinally on

top of the piles and fastened to them by means of driftbolts. The

advantages of timber grillage are that it can be easily laid and

effectually holds the top of piles in place. It also tends to distribute the

pressure evenly over the piles, as the transverse strength of the

timber will help to carry the load over a single pile, which for some

reason, may not have the same bearing capacity as the others.

Where timber grillage is used, it should be kept entirely below the lowest

recorded water line, as otherwise it will rot and allow the building to

settle.

Steel beams embedded in concrete are also sometimes used to distribute

the weight over piles, but this is too expensive a method to becommonly used.

Driftbolta short rod or square bar driven into holes bored in timber, for attaching adjacent sticks to each other or to piles; varies

from 1 to 2 ft (300 x 600 mm) in length; often provided with a head or with a sharpened end; also called a drift or driftpin.


16/106

3.0

3.1

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

Concrete Piles.Concrete piles, either plain or reinforced, possess many

advantages over wooden piles and, in general, can be used in all places

where wooden piles can be driven. Concrete piles are generally used

where wooden piles would be subject to decay or deterioration by the

action of marine worms. They are especially advantageous for

foundations on land where the permanent ground water is at a

considerable depth. Wooden piles must cut of under water as, when

subjected to an atmosphere which is alternately wet and dry, they will

decay. This is unnecessary with concrete piles, and foundations under

such conditions need not start so low as would be the case if timber

piles were used.

In practice concrete piles are generally reinforced. Reinforced-concrete piles

are of two general types: those molded in place and those molded

before driving. Spacing for concrete piles usually from 2 6 to 4.

Concrete piles are extended at least 4 into the concrete of the footing,

and where a steel casing surrounds the pile, 3 to 4 in. of concrete is

required between the top of the piles and the footing reinforcement,

unless the casing is trimmed back at a distance, in which case the case

reinforcement is allowed to lie directly upon the butts of the piles.

B. CONCRETE PILES

H R i f d


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3.1

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

1. PRE-CAST PILES

Pre-cast Piles These are usually moulded

in a yard or at the site allowed to cure for 4

weeks before using. In driving, a pre-castpile is provided with a cast-iron point, and a

driving head is used in which a cushion of

sand, rope or other material is placed

between a driving block of wood and the

concrete in order to prevent the crushing of

the pile. Concrete piles are often sunk by

means of water-jet. This method is madepossibly by inserting an iron pipe in the

center of the pile.

H R i f d


18/106

3.0

3.1

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

2. CAST-IN-PLACE PILES

Cast-in-place Piles Cast in place piles are constructed in the ground in

the position they are to occupy, and are often reinforced. Practically all

cast in place piles are covered by patents.

Cast-in-place piles may be formed by any of the following methods:

a. A hollow cylindrical steel tube usually furnished with a tight-fittingcollapsible steel core or mandrel, is driven into the soil. The core is then

collapsed and removed, and the steel shell filled with concrete. Thus

there is a shell or form for every pile, e.g. McArthur piles, Raymond piles

(this uses a No. 24 gauge shell in which a spiral of No. 3 wire is

encased). This is also commonly called a cased pile.

Heavy Reinforced


19/106

3.0

3.1

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

A steel tube is fitted at the bottom with a driving point and is driven into the

ground to the required depth. Concrete is then poured into the hole thus

formed as the steel tube is gradually withdrawn. The driving point may be

either a conical cast-iron point that is left in place or a hinged cutting-edge

called an alligator point which opens as the tube is withdrawn, e.g.Simplex piles. This is called an uncased pile.

A steel pipe or shell is first driven into the ground. The steel driving core is

then removed and the bottom of the shell is filled with concrete to a height of

about 5 ft. from the bottom. Pressure is then applied to force out the concrete

into the surrounding soil as the core is withdrawn. These are known as

pedestal piles.

Heavy Reinforced


20/106

3.0

3.1

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

C. STEEL PILES

Steel-pipe Piles.These are concrete-

filled steel pipes which are made to bear

on rock or hard pan. The pipes are

generally 10 to 18 inches in diameter,

having a thickness of 3/8 to 5/8 inches.

The pipe is driven in sections with a

steam-hammer and, as additional sections

are required, these are attached to the

driven section by means of a cast-iron or

steel internal sleeve and re-driven.When the pipe has reached its bearing level it is cleaned out by blowing or

dug out by means of augers or similar tools. The pipe is then pumped out

and concreted.

Heavy Reinforced


21/106

3.0

3.1

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

D. COMPOSITE PILES

Composite Piles.

These are combination

timber and concrete or

steel and concrete piles.

They may be composed

of timber piles with

concrete coatings held

in position by steel

reinforcements in the

shape of expanded

metal or wire netting.

The latter are to be

considered as timber,

rather than concrete,

piles.

Heavy Reinforced


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3.0

3.1

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

2. CAISSON FOUNDATIONS

Caissonsare cast-in-place, plain or reinforced concrete piers formed by

boring with a large auger or excavating by hand a shaft in the earth to a

suitable bearing stratum and filling the shaft with concrete. For this reasonthey are also referred to as drilled piles or piers.

Heavy Reinforced


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3.2

3.0

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

3.2 FOUNDATION WALLS, BASEMENT

CONSTRUCTION, CISTERNS

Foundation walls

provide support for the

superstructure above

and enclose a

basement wall or crawl

space partly or wholly

below grade. In

addition to the verticalloads from the

superstructure,

foundation walls must

be designed and

constructed to resist

active earth pressure

and anchor thesuperstructure against

wind and seismic

forces.FOUNDATION WALLS

Heavy Reinforced


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3.2

3.0

y

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

BASEMENT WALLS

Heavy Reinforced


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3.2

3.0

y

Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

SECTION OF CISTERN

Heavy Reinforced


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3.3

3.0Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

There may be short columns or long columns.

Short columnsoccur when the unsupported height is not

greater than ten times the shortest lateral dimension of thecross section.

Long columnsoccur when the unsupported height is more

than ten times the shortest lateral dimension of the cross

section.

3.3.1 TYPES OF RC COLUMNS

Reinforced-concrete columns may be classified into five types:

1. Tied Columns. These are columns with longitudinal bars and lateral

ties. The ratio of the effective cross-sectional area of verticalreinforcement to the gross column area should not be less than 1% nor

more than 8%, and should consist of at least 4 bars of a minimum size

of #5.

3.3 REINFORCED CONCRETE COLUMNS

Heavy Reinforced


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3.3

3.0Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

Lateral tiles shall be at least 3/8 (10 mm) diameter and shall be spaced

apart not over than 16 bar diameters, 48 tie diameters, or the least

dimension of the column. Where there are more than four vertical bars,

additional ties should be provided so that every longitudinal bar will be

firmly held in its designed position. The reinforcement for tied columnsshall be protected by a covering of concrete, cast monolithically with the

core, of at least 1-1/2 (38 mm) thickness.


28/106

Heavy Reinforced

C t P


29/106

3.3

3.0Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

2. Spiral Columns. These are columns with longitudinal bars and closely

spaced continuous spiral hooping. For spiral columns, the ratio of the

area of the vertical reinforcement to the gross column area shall not

less than 1% nor more than 8%. The minimum number of bars shall 6,

and the minimum bar size shall #5.

The spiral reinforcement, with min

size of 3/8 shall consist of evenly

spaced continuous spirals held

firmly in place by at least three

vertical spacer bars. The centerto center spacing of the spirals

shall not exceed 3 (75 mm) nor

be less than 1-3/8 (35 mm) or 1-

1/2 times the maximum size of

the coarse aggregate. Protective

covering for the column

reinforcement shall not be lessthan 1-1/2 (38 mm).

Heavy Reinforced

Concrete Pre


30/106

3.3

3.0Concrete, Pre-

Stressed Concrete &

Steel Construction

Foundations Systems

Foundation Walls,


Reinforced Concrete

Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

3. Composite Columnswhere structural steel columns are embedded

into the concrete core of a spiral column.

4.Combined Columnswhere structural steel is encased in concrete of

at least 7 cm thick, reinforced with wire mess surrounding the column

at a distance of 3 cm inside the outer face of the concrete cover.

5. Lally Columnsare fabricated steel pipes provided with flat steel

plates which holds a girder or girt, and is filled with grout or concrete

to prevent corrosion.

3.3.2 DOWEL BARS

Dowel barsare short bars used totransfer the stress at the bottom of

the columns to the footings. When

dowel bars are used, there should

be at least one dowel bar for each

column bar. The total cross-

sectional area of dowels should not

be less than the cross-sectionalarea of longitudinal reinforcement

in the column.

The dowels shall extend into the column and into the pedestal or footing not

less than 50 bars diameter for plain bars or 40 diameters for deformed bars.

Heavy Reinforced

Concrete Pre-


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Foundation Walls,


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Columns

Reinforced Concrete

Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

3.4 REINFORCED CONCRETE FLOOR SYSTEMS

3.4.1 SUSPENDED SLABS

In general, there are six types of reinforced-concrete floors systems:

1. One way solid slab and beam

2. One way joist slab or Ribbed slab

3. Two way solid slab and beam

4. Two way waffle slab

5. Two way flat plate

6. Two way flat slab

Each particular system has its distinct advantages, depending upon the

spacing, of columns, the magnitude of the loads to be supported, lengths

of spans, and the cost of construction. Although the arrangement of the

plan of a building frequently determines the column spacing,

approximately square bays are desirable. Column spacing of 20 ft., more

or less, has proved to be most economical, but this, of course, depends

on the type of floor construction to be used.

Heavy Reinforced

Concrete Pre-


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Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

1. ONE-WAY SLABS

Probably the most commonly used type or reinforced concrete

construction consists of a solid slab supported by two parallel beams,

the beams framing into girders, and the girders in turn framing into

columns. The reinforcement slabs runs in one direction only, from

beam to beam, hence the slab is known as one-way slab. The number

of beams in a panel depends upon the column spacing and the live

load to be supported. The beams are spaced uniformly and generally

frame into the girders at the center, third or quarter points.

This type of framing is called the beam-and-girder floor. It is readilyconstructed and the formwork is simple. The one-way slab is

economical for medium and heavy live loads for comparatively short

spans, 6 to 12 ft. For light live loads, 40 to 60 psf, the spans may be

increased, but long spans for one-way slabs results in comparatively

large dead loads.

Heavy Reinforced

Concrete, Pre-


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Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems

Building Protection

Systems

The main tensile reinforcement (running along the short direction) in fully

continuous slabs are alternately bent up, usually at an angle of 30 to

45 degrees, at the fifth points of the span and extend over the supports

to the quarter points of the adjoining span. The remaining bars are

straight, placed in the bottom of the slab. For single span slabs thebars are bent up at the quarter points.

Another method of placing the reinforcement is to place straight bars at the

bottom of the slab and the other straight bars at the top of the slab

over the supports. If the bent bars are used, bent bars from the

adjoining bars are extended over the supports, thus providing the

same amount of reinforcement over the supports as at mid-span.

In addition to the tensile reinforcement, temperature bars are also provided

running along the long direction. These serve to provide against the

effect of shrinkage and changes in temperature and also to distribute

possible load concentrations over larger areas. The size and spacing

of temperature bars depends upon the slab thickness.

Heavy Reinforced

Concrete, Pre-Mi i i i f l b i f i 20 ()


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Walls & Structural

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Systems

Minimum protective covering for slab reinforcement is 20mm ().

3 0

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3 0

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Walls

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Building ProtectionSystems

2. ONE WAY JOIST OR RIBBED SLABS

For medium span lengths with light or

medium live loads, ribbed slabs have

proved to have an economical type offloor construction. They are not so

well suited to heavy concentrated

loads as the solid one or two-way

slabs. A one-way joist slab consists of

relatively small adjacent T-beams.

When the open spaces between the

webs or rings are filled with clay tile,gypsum tile, concrete filler block or

steel forms, the floor system is called

a ribbed slab.

3 0

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Pre-Cast Concrete

Floor Systems


Clay tile fillers are generally 12 x 12 in plan with depths of 4, 6, 8, 10, 12,

and 15 in. The usual practice is to place the tiles 16 o.c., thus

making the web 4 wide. The layer of concrete placed on top of the

tile is generally 2 or 2-1/2 in. thick. Reinforcement for this type of

construction may consist of two bars placed in the lower part of the

web, one bent and one straight, or of straight bars placed in the top

and bottom parts of the web.

3 0

Heavy Reinforced

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S C &


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Pre-Cast Concrete

Floor Systems


Metal tile fillers are frequently used for ribbed floors. This is commonly

known as tin-pan construction. The metal forms are usually 36 long,

with 6, 8, 10, 12, and 14 in. depths. They are placed on centers in

such a manner as to make the web 4 to 7 in. wide at the lowest point.

Form widths are generally 20 or 30 in.; a common condition is a form

20 in. wide, placed 25 in. on centers, to make a web 5 wide at the

bottom.

The metal forms may be removed or left in place after supporting

formwork has been taken down. To provide a greater web area near

the supports, where the shearing stresses may exceed the allowable,

special metal cores with the sides tapered in plan are used. The

degree of tapering generally is such that the web is increased 4 in

width. As in the case of clay-tile fillers, a 2, 2-1/2, or 3 in. slab is

placed over the metal tile forms, the slab and web forming a T-

section.

Gypsum-tile fillers have the advantage of providing a relatively lightweight

ribbed with a flush ceiling. Although they are made in various sizes, a

common width is 19, placed 24 o.c., with webs 5 wide. When block

12 wide are used, they are placed 16 o.c., thus forming 4 wide

webs.

3 0

Heavy Reinforced

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Floor Systems


3 0

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Pre-Cast Concrete

Floor Systems


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Pre-Cast Concrete

Floor Systems


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Heavy Reinforced

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Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems


3. TWO-WAY SLABS

When a floor panel is square or nearly so, having beams or walls on four

sides, it is generally economical to use two sets of reinforcing barsplaced at right angles to each other. These bars in two directions

transfer the loads to the four supporting beams or walls. Slabs thus

reinforced are known as two way slabs or slabs supported on four

sides.

For square panels, with supports of equal rigidity, the live and dead loads

are distributed equally in both directions and the reinforcements arethe same each way. When the panel is oblong or rectangular, the

greater part of the load is transmitted by the transverse or short

reinforcement. If the length of the slab exceeds 1.5 times its width,

the entire load is usually assumed to be carried by the short

reinforcement, and the long reinforcement used for shrinkage and

temperature reinforcement only; hence the slab would become a

one-way slab.

3.0

Heavy Reinforced

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Floor Systems

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Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems


In determining the reinforcement of two-way slabs two strips of floor are

considered. One is middle strip, one half of the panel in width,

symmetrical about the panel center line, and extending through the

length of the panel. The other is the column strip, one half of the

panel in width and occupying the two quarter-panel areas outside themiddle strip. In placing the reinforcement it is advantageous to place

the bars in the short direction, carrying the greater load, under the

longer bars. Bars are bent up at fifth points and extend over the

supports of the quarter points of the adjoining slabs as is done for

one-way slabs.

3.0

Heavy Reinforced

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Floor Systems

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Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems


4. TWO WAY WAFFLE SLAB

A waffle slab is a two way concrete slab reinforced by ribs in two

directions. Waffle slabs are able to carry heavier loads and span longer

distances than flat slabs.

3.0

Heavy Reinforced

Concrete, Pre-

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Floor Systems

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Walls & Structural

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Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems


5. TWO WAY FLAT PLATE.

A flat plate is a concrete slab of uniform thickness reinforced in two or

more directions and supported directly by columns without beams or

girders. Simplicity of forming, lower floor-to-floor heights, and someflexibility in column placement make flat plates practical for apartment and

hotel construction.

3.0

Heavy Reinforced

Concrete, Pre-

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Floor Systems

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Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems


6. TWO WAY FLAT SLABS.

A flat-slab is a flat plate thickened at its column supports to increase its

shear strength and moment-resisting capacity. The slab is commonly

reinforced with bars running in two directions. This area of increased

thickness is called a drop panel or drop. The columns are generally square

in cross section, but rectangular or circular cross sections are also used.

3.0

Heavy Reinforced

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Columns

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Floor Systems

Roof Decks

Walls & Structural

Walls

Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems


3.0

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

St l C t ti 3 4 2 REINFORCED CONCRETE BEAMS


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Columns

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Floor Systems

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Walls & Structural

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Pre-Stress Concrete

Pre-Cast Concrete

Floor Systems


3.4.2 REINFORCED CONCRETE BEAMS

A beammay be defined as a structural member, resting on supports

usually at its ends, which supports transverse loads. The loads that act on

the beam, as well as the weight of the beam itself, tend to bend ratherthan lengthen or shorten it. A girder is a term applied to a beam that

supports one or more smaller beams, as concentrated loads.

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Floor Systems


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Beams may be classified as:


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a. Simple beams. These are beams having a single span with a support

at each end, there being no restraint at the supports.

b. Cantilever beams. These are beams that are supported at one end

only, or they may be that portion of beams projecting beyond one of itssupports.

c. Continuous beams. These are beams resting on more than two

supports. The term semi-continuous is also frequently used in

reinforced-concrete. It refers to a beam having two spans with little or

no restraint at the two extreme ends of the beam. The end span of a

continuous beam, where little or restraint is provided at the end support,

is referred to as a semi-continuous beam.

When a beam is subjected to a given load, the beam is bent downwards at

the middle, the lower part of the beam being elongated while the upper

part is compressed. The lower part of the beam is said to be in tension,

while the upper part is in compression. In reinforced-concrete design, it is

assumed that the compressive stresses is resisted by the concrete andall tension resisted by the steel. Thus the reinforcement of a beam is

placed near the bottom of the section.

3.0

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

At the supports, however, the upper surface of the beam becomes concave

downward; that is there is a reversal of stresses. The upper portion of the

beam is now in tension ( or the bending moment is said to change from


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Pre-Cast Concrete

Floor Systems


( g g

positive to negative). The section of a beam at which the bending moment

changes from positive to negative is called the point of inflection. The

exact position of inflection points depends upon the position and

magnitudes of the loads as well as the end conditions of the beams. Forcontinuous beams having equal spans and uniformly distributed loads, the

inflection point is considered to be one-fifth the clear span between faces

of support.

At this point some of the reinforcing bars are bent up at an angle of from 30 to

45 degrees and extend over the supports into the adjacent spans. The bent

up bars serve to resist the tensile stresses over the supports. Thus for

continuous beams with uniformly distributed loads the bars would be bentup at one-fifth the clear span from the face of the supports and extend to

the quarter points of the adjacent span. Not more than half of the bears

should be bent up; the rest of the reinforcement extends straight through

the center of the supports.

Another method is to use separate straight bars in both the bottoms and tops

of the beams in place of bent bars. The slight cost in excess weight in thisarrangement over the combination of straight and bent bars is probably

balanced by the ease of preparing design and shop drawings, bill of

materials, and fabrication and placing of reinforcement. Bars not fabricated

according to drawings, or those lost and mislaid, are more easily replaced if

no bending is involved.

3.0

Heavy Reinforced

Concrete, Pre-

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Steel Construction


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Pre-Cast Concrete

Floor Systems


In addition to the tensile and compressive stresses in a beam subjected to

bending, there are also inclined tensile stresses. If a concrete beam is

reinforced with longitudinal steel only, these diagonal stresses tend o

produce cracks which are vertical at the center of the span and become

more inclined as they approach the support where they slope towards the

center at an angle of about 45. The stresses that cause these cracks are

known as diagonal tension. To prevent failure due to diagonal tension

additional reinforcing bars are used.

Sloping bars placed at right angles to the direction of these cracks would be

one method of reinforcing for diagonal tension, but, although this is

sometimes done, it is not the most economical method. The usualprocedure is to add #3 or #4 bars, bent in the shape of the letter U, in

vertical positions at those places in the beam at which the diagonal

tension stresses require their use. When the stresses are sufficiently

large. W-shaped bars are used. These bent reinforcing bars are called

stirrups. They should always have hooks at the ends to provide

anchorage to resist the tensile stresses.

3.0

Heavy Reinforced

Concrete, Pre-

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Floor Systems


Although it is occasionally necessary to put in two or more layers of steel,

particularly in large girders carrying heavy loads, it is usually more

economical to slightly widen a beam, thereby permitting all of the main

tensile reinforcement to lie in the same plane. Minimum clear distance

between bars should not be less than the nominal diameters of the bars,not less than 1 (25 mm), nor less than 1-1/3 times the maximum size of

the coarse aggregate. If more than one layer is used the clear vertical

distance between layers shall not be less than 1 (25 mm), and the bars in

the upper layer shall be placed directly above those in the bottom layer.

The following table is useful in selecting the proper width of beam given

number of reinforcing bars:

Reinforcement used to resist shearing stresses is known as web

reinforcement. Ties are frequently used for web reinforcement in place of

stirrups. A tie is generally made of #3 bars, but it completely encircles the

longitudinal tensile steel instead of being U-shaped with hooks.

3.0

Heavy Reinforced

Concrete, Pre-

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An allowance of 1-1/2 (38 mm) for fireproofing is made outside the

reinforcement on each side of the beam, and there is also allowance

for #3 stirrups. It should be noted that this Table gives the maximum

size of bars. Thus, for instance, the Table indicates that 4 - #9 bars may

be used in a beam 12 in width. Obviously, four smaller bars, e.g., 4-#7,

may also be used for the same beam width.

Fireproofing for beams and walls is 1-1/2 (40 mm).

NUMBER OF BARS IN BEAMS

Maximum number of bars for beams of various widths

Width 6 8 10 12

14

2- #5 2 - #11 2 - #11 3 - #11 4- #113 - #6 3 - #9 4 - #9

5 - #9

4 - #6 5 - #6

6 - #7

6 - #4

7 - #4

3.0

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

3.4.3 TYPES OF REINFORCED CONCRETE BEAMS


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Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

1. Rectangular beams

2 T b Wh i f d


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2. Tbeams. When a reinforced

concrete floor slab and its supporting

beam (or girder) are built at the same

time and thoroughly tied together, a

part of the slab may be considered to

act with upper part of the beam in

compression. This form of a beam is

called a T- beam.

3. Beam with Compression

Reinforcement. These are beams withreinforcement in the compression as

well as the tension side of the beam,

hence they are also called double

reinforced beams. In this type of beam

no bent up bars are required. Beams

with compression reinforcement are

used when the cross-sectionaldimensions of the beam are limited by

architectural or structural conditions so

that there is an insufficient concrete

area for the compressive stresses.

3.0

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction

4. Cantilever Beams. The tensile

reinforcement is located at top of the


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Floor Systems


beam and inverted U-stirrups are

provided.

5. Hollow box girders. These aredouble reinforced beams used for long

spans. In order to reduce the dead

load (the weight of the beam) it is

hollowed in the center of the section.

Diaphragms are provided at intervals

throughout the length of the beam.

3.0

Heavy Reinforced

Concrete, Pre-

Stressed Concrete &

Steel Construction6. Beam Brackets or Corbels. Short beam extensions from columns

used to support rafters or trusses.


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Heavy ReinforcedConcrete, Pre-

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Floor Systems


3.5

Reinforced concrete roof slabs (roof decks) are formed and sitecast in the

same manner as concrete floor systems. Roof decks are normally

covered with a type of membrane roofing for insulation and

waterproofing.

3.0


Stressed Concrete &

Steel Construction


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3.5

3.0


Stressed Concrete &

Steel Construction

3.6 WALLS AND STRUCTURAL WALLS

3.6.1 TYPES OF WALLS


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Floor Systems


1. Bearing wall. A wall on which either floor or roof constructionrests.

2. Curtain wall. The enclosing wall of an iron or steel framework

or the non-bearing portion of an enclosing wall between piers.

3. Foundation wall. That portion of an enclosing wall below the

first tier of joists.

4. Retaining wall. A subsurface wall built to resist the lateral

pressure of internal loads.

5. Spandrel wall. The space between any arch and the beam

over the same; or an exterior non-bearing wall in skeletonconstruction built between columns or piers and wholly

supported at each story.

3.6

3.0


Stressed Concrete &

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3.6

3.0


Stressed Concrete &

Steel Construction 3.6.2 CURTAIN WALLS


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Columns

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Pre-Cast Concrete

Floor Systems


3.6

1. Panel wallsare exterior non-load bearing walls whose outer surface

may or may not form the exterior facing of the building and whose

interior surface may or may not form the interior finish. It may rest on

the building structure or may be hung from the structure.

Masonry panel wallsare exterior non-load bearing walls whose outer

surface may form exterior building face or it may be used back of

panel curtain wall as back-up.

The two types of masonry panel walls are: the stone masonry panel

and the pre-cast masonrypanel wall units.

a. Stone masonry panelsare natural or artificial stone slabs which are

anchored to the building structure by masonry anchors.

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F d ti S t


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F d ti S t

b. Pre-cast masonrypanel wall units are ordinary reinforced or pre-

stressed concrete wall units which may span one floor or several floors.


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2. Panel curtain wallsare exterior non-load bearing walls made up of

panels attached directly to the building structure with an adjustable

attachment or mounted on supports (sub-frame) which in turn are


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3.6

attachment or mounted on supports (sub-frame), which in turn, are

attached to the building structure by adjustable attachments. Exterior

face of panels form the face of the building; interior face may or may

not form the interior finish. The panels which protect the building fromthe weather, may be one of the following types:

a. Window type panel. Transparent glass and frame incorporated in

panel curtain wall.

b. Skin type panel. Panel made up of one material.

c. Sandwich type panel. Panel made up of assembly of severalmaterials.

1. Open Sandwich type. Sandwich panel with top and bottom edges

closed.

2. Closed Sandwich type. Sandwich panel in which all edges of

panel are closed except for weep holes and vents.

d. Wall Units. Preassembly of several panels of any type. Units may be

one or several stories high.

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Panel curtain walls may be classified into the following types:


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3.6

Stick type. Refers to the method of installation where the mullions and

horizontal rails (gutter section and window sill section) are installed first

before installation of the window and wall panels.

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b. Unit and Mullion type. Supports (mullions) are clearly expressed.

Vertical lines dominant. Mullions are generally 4 4 max.; height, 8

0 i


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3.6

0 maximum.

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c. Grid type (or Unit type).Supports (vertical and horizontal

members) clearly expressed. Vertical and horizontal lines


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3.6

) y p

equally dominant. Area between support members, 32 sq. ft.

maximum. Width of panels, 4 4 max.; height, 8 0 max.

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d. Panel type (or sheathed type).Supports not expressed. Non-

lineal pattern. Joints vertical and horizontal usually without trim.

I di id l l i idth 3 10 h i ht 8 0


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Individual panel size: max. width, 3 10; max. height, 8 0.

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e. Spandrel type (column cover and spandrel system).Supports are

not a primary element of expression in this type of wall. Horizontal

lines are dominant and the length of spandrel unlimited Width of


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3.6

lines are dominant and the length of spandrel unlimited. Width of

interlocking panels is 4 4 maximum; height is 8 0 maximum.

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Foundations Systems f. Sheathed type (Industrial).Supports not expressed. Non-lineal


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3.6

pattern. Joints vertical. Panel size: width, approx. 4; height, 60 max.

Assembly methods of panel curtain walls may be by:

1. Individual panels.

2. Wall units.Width, 6 max.; height, one several stories.

3.6.3 PRESSURE EQUALIZED DESIGN FOR CURTAIN WALLS.

Pressure differential between the outside atmosphere and an interior

environment can cause rainwater to migrate through even the smallest

openings in wall joints. Pressure-equalized design can significantly

reduce this cause of water leakage in wall construction by employing the

rain-screen principle.

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3.6

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3.6.4 RETAINING WALLS, BREAST WALLS, AND VAULT

WALLS.

A t i i ll i ll h i t i t th th t f


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3.6

A retaining wallis a wall whose purpose is to resist the thrust of a

bank of earth or other material. It is differentiated from breast walls

which is similar to the retaining wall, in that in the retaining the earth

or other filling is deposited behind it after it is built, while the breast

wall (or face wall) is built to prevent the fall of earth which is in its

undisturbed, natural position, but from which part has been

excavated, leaving a vertical or inclined face.

Retaining walls are of three types:

a. Gravity wall. This is a type of wall which is constructed of such

proportions that its weight alone resists the thrust of the earth. Low walls

are invariably gravity walls constructed of brick, stone masonry or

concrete.

b. Cantilever wall. The cantilever wall is constructed of reinforced concrete

and makes use of the weight of the earth in resisting the tendency tooverturn at the outer edge. The vertical wall, supported on a horizontal

base, serves as a cantilever beam in resisting the earth pressure. Walls of

intermediate height are generally of the cantilever type.

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3.6

C. Counterfort wall. It is similar to the cantilever wall with the exception

that the vertical wall is tied to the base at regular intervals with triangular-shaped walls called counterforts ( a counterfort is similar to a buttress, but

where a buttress is placed on the side of the wall opposite the pressure

acting on it, a counterfort is placed on the same side of the wall ). It is

usually more economical to use the counterfort wall for heights of 20 ft. or

over.

In large cities it is customary to utilize the space under the sidewalks forstorage or other purposes. This necessitates a wall at the curb line to hold

back the earth and the street pressures and also the weight of the

sidewalk. These are called vault walls.


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There are two methods of prestressed concrete, namely:

a. Pre-tensioning or bonded prestressing. In this method the


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3.7

g p g

reinforcing steel is first prestressed and then the concrete is poured.

When the concrete has developed strength, the stress in the steel is

released. The steel when stretched out becomes smaller in cross-section than when unstressed, and the concrete hardens around them

while they are still small. When their artificial tension is released after

the concrete hardens, they expand, reverting to their original shape,

grip the surrounding concrete. The bond between the concrete and

steel is sufficient to create compression in the concrete.

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b. Post-tensioning or unbonded pre-stressing. In this method, tubes,

conduits, or channels are inserted in the concrete where reinforcing

steel is required. After the concrete is adequately cured, steel

reinforcement is inserted in the tubes or channels, stretched to the


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3.7

,

proper tension, and anchored at the ends to put a squeeze on the

beam. Tensioning is done with hydraulic jacks.

The reinforcing for pre-stressed concrete is usually wire, strand, bar or rope

made of heat-treated steel. Concrete must meet strengths usually greater

than AA-type concrete which has a strength of 3750 psi in 28 days.

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The advantages of pre-stressed concrete are:

1. It is economical of materials due to the use of higher steel and concrete

stresses.


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3.7

2. It eliminates cracks because the concrete is always in compression.

3. It has remarkable elastic properties. For example, tests were made on a floor

slab only 1-5/s8 thick reinforced with not more than 1% steel. Although the

span was only 10 ft. the slab deflected 3 under a load of 1070lb. at its

center. When the load was removed it returned to its original level,

undamaged.

4. Beams do not have to be cast at the side in one form, but may be cast insmall sections or blocks at the factory with reinforcing wires threaded

through them. When the wires are stressed, the small units are brought

together like one large beam.

5. It develops remarkable resistance to shear stresses.

Pre-stressed concrete is used where spans and loads cannot be

adequately designed in reinforced-concrete, and for deckings, beams,girders and other prefabricated units where greater spans and loads with

thinner, stronger, and in some cases, lighter members are required.

The designing of pre-stressed concrete for structures is highly technical and

the architect should always work with a structural engineer, even when

using prefabricated pre-stressed concrete units.

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3.8 PRE-CAST CONCRETE FLOOR SYSTEMS


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Documents

BT3HeavyRCPrestressetc