Simplified Methods on Building Construction

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.1,

2CHAPTER

WOOD

2.- 1 INTRODUCTIOI\.I

Wood is that fibrous substances which compose the trunk and
branches of the tree that lies between the pith and the bark.
Wood is the most common of the building materials.

The versatility of using wood in the constru ction has lifted it
to its present importance in the field of construction. Small houses
and even palatial homes used wood from its structure down to the
finishing and articulate carvings.

Even with the introduction and acceptance of new methods
and materials in construction, wood is evidently much in use. Con-
crete buildings used wood from the very start of its erection. Like-
wise, steel c.onstruction also use wood. Wood because of its
strength, light in weight, durability and ease of fastening has
become one of the most important bu ild ing materials.

Many Scientists and Engineers are engaged in the study and
research for the development of new methods of full utilization
of wood. New processes are being developed to reduce if not to
el iminate waste in the manufacturing of wood .

2-2 DEFrNITION OF TERMS:

1. Lumber = Is the term appl ied to wood after it is sawed or
sliced into boards, planks, timber etc.

2. Rough Lumber = Is the term applied to unplaned or un-

dressed lumber.

3. Surfaced o_r Dressed Lumber = Is a planed lumber having at
least one smooth side.

4. S2s; S4s ~ Are planed or dressed lumber of which the
number connotes the number of smooth sides; such as S2s is
· smooth on two sides.

5. Slab = Is a kind of rough lumber which is cut tangent to

the annual rings, running the full length ofthe fog and containing·

a-t fe-as-t o-ne-fla-t s-u·-rf·a·c-e.--

42

=6. Timber Is a piece of lumber five inches or 13 em. or larger

in its smallest dimension.

7. Plank= Is a wide piece of lumber from 4 to 13 em. thick.

8. Board = Is a piece of lumber less than Hz" or 4 em. thick

and at least 4 inches or 10 em. wide.

9. Flitch= Is a thick piece of lumber.

10. Fine Grained= When the annual rings are small, the grain
or marking which separates adjacent rings is said to be fine grained;
when large, it is called Coarse Grained.

11. Straight Grained = When the direction of the fibers are

nearly parallel with the sides and edges of the board, it is said to
be straight grained. When the lumber is taken from a crooked tree,
it is said to be crooked or cross·grained.

2-3 CLASSIFICATION OF WOOD:

Wood used in building construction are those wood which
grow larger by addition of layer on the outer surface each year
known to botanist as OXOGENS.

Wood are classified according to:

1. Mode of Growth:
a. Exogeneous = Are those outward growing trees which

are most preferred for lumbering.

b. Endogeneous = Are those inside growing trees and

are not preferred for lumbering because they produced a soft

center core.

2. Density= Density is either:

a. Soft
b. Hard

3. Leaves : The leaves of a tree is either:
a. Needle shape {conifers)
b. Broad shape

43

4. Shade or Color:
a. White
b. Yellow
c. Red
d. Brown
e. Black, etc.

5. Grain:
a. Straight
b. Cross
c. Fine
d. Coarse

6. Nature of the surface when sawed:
a. Plain

b. Grained
c. Figured or marked

.,:···;·

CROOKED GRAIN CROSS Ga.Anf STRAIGHr GRAIN

Cross Section of a Tree

Figure 2-1

2-4 PREPARATION OF WOOD

Lumbering is the term applied to the operations performed in
preparing wood for commercial purposes. It involves logging which
is the process or operation of felling or cutting of trees including
ib hauling and delivery to the sawmill for sawing.

Sawing on the otherhand, is the operation of preparing or cut-
ting the logs into its.commercial sizes.

The methods and manner of log ~wing are:
1. Plain or 811Stard Sawing: Is the cutting of the logs entire!.
through the diameter and parallel chords tangential to the annuc
rings.
2. Quarter or Rift Sawing

a. Radial

b. Tangential

c. Quarter Tangential

d. Combined Radial and Tangential

COMa!He!P 1\.\0\M. ~
TlMUtl'ftA\.

Figure 2·2

2-5 DEFECTS IN WOOD
Defects· are irregularities found in wood. The most common

defects in wood are:
1. Caused by Abnormal Growth

a. Heart Shakes = Are radial cracks originating at the

heart of the logs.

45

b. Wind Shakes or Cup Shakes = Are cracks or breaks

across the annual rings of timber during its growth
caused by excessive bending of the t ree due to wind.

c. Star Shakes = Composed of several heart shakes w-hich

radiate from the center of the log in a star-like

manner.
d. Knots = Occurs at the starting point of a limb or branch

of the wood.

2. Due to Deterioration:

a. Dry Rot = Is the presence of moisture caused by fungi
in seasoned wood.

b. Wet Rot = Takes place sometimes in the growth of the

tree caused by water saturation.

Figure 2-3

2 - 6 SEASONING OF LUMBER

Trees when fallen contains moistu re in their cell layer. These
moisture should be expelled thoroughly to preserve the .lumber
from shrinkage or decay. Experiments have proven that timber 'im·

mersed in water immediately after being fallen and squared is less

subject to splitting and decay. It reduces warping but'makes the
wood brittle and less elastic. Soaking timber into liquid is the
' method of seasoning practiced by the ancient Roman builders.
Sometimes wood are steeped in oil of cedar t o protect it from
worm attack.

...

Salt water makes wood harder, heavier and durable. However.
wood intended for use in buildings has the tendency to attract
moisture from the air.

The Two methods adopted in seasoning of lumber are:

as1. Natural or Air Seasoning= This is considered one of the

best method of seasoning lumber although the period involved is
relatively longer. The processes are:

a. Lumber is piled outside where its length'are sloped at
about 10 em. to the meter height. ·

b. Lumber is piled in a well.ventilated shed. Each piece
is properly and evenly spaced from each other for free
circulation of air around the lumber. ,

2. Artificial Seasoning = The lumber is stacked in a drying

kiln and then exposed to steam and hot air. Artifidal seasor.ing i.:;

resorted for quick drying but wood from this process is quite

inferior than that seasoned by the natural method. The different

artificial seasoning methods employed are: ·

a. Forced Air Drying = Fans are 'used to booster the cir·

culation of air preparatory process to kiln drying.
b. Kiln Drying= Lumber is dried in a specially built room

or chamber by which temperature and humidity as
well as the circulation of air is controlled.

c. Radio Frequency Dmlectric Drying = A very fast

method of drying lumber wherein the use of radio fre·
quency dielectric heat is employed. Drying through
this process may only take 24 hours as compared to
the other methods.

2 - 7 · CAUSES OF DECAY AND METHODS OF
PRESERVATION

Wood does not decay naturally through age, nor will it decay
if it is kept constantly dry or continuously submerged in water.

The common causes of decay in wood are:

1. Altern.:~te moisture. and dryness
2. Fungi and molds
3. Insects and worms
4. Heat and confined air

47

The essential requirement to achieve a successful preservation
of wood is good seasoning and the process of preserving wood are:

1. External = The wood is coated with a preservative coating

(as paint) which will penetrate the fibers.

2. Internal = A chemical compound is impregnated at a pres-

sure to permeate the wood thoroughly. The different processes are:

a. By impregnating the timber with a 2 percent zinc
chloride solution followed by an injection of about 45
kg of creosote oil per cubic meter of wood.

b. The cylindrical tank is filled from the charging tank
with creosote oil at a temperature of 930 C and pres·
sure is applied until the timber absorb oil to a pre·
determined amount.

c. A partially seasoned timber is run into the metal

cylinder 2.50 to 3.00 m. diameter by 50 meters long

and the doors or heads bolted. A pressure of 1.5 kg per

sq. em. steam is applied in 30 minutes and maintained
from 1 to 5 hours. A vacuum of 60 centimeters is
created and maintain for 11/z hour when creosote oil is
introduced at a temperature of about 70° C. A pressure
of about 12 to 14 kg. per cm2 is then applied until the
timber has absorbed 50 kg. of oil per cubic meter.

d. Another method is by emersing timber into 2 ·solution
of corrosive sublimate, 1 part of bichloride mercury to
99 parts of water for a period of 5 to 10 days sufficient
enough to insure thorough penetration o.f the preserva·
tive. The sublimate is insoluble in water/and remains in
timber for a longer time than salts like zinc chloride.

The external non·pressure process of preserving wood is the
application of a penetrating nature as tar oils, carbolineum, spirit-
tine, solignum, etc. It may be applied on the surface of wood either
by brush, spray or by immersion. External preservatives could
only be effective if the wood to be treated is absolutely dry and ·
well seasoned in order to absorb a sufficient quantity of the pre·
servative.

All tar oil products should preferably be applied hot.

48

2-8 MEASURING WOOD

Although the System International (SI) has already superseded
the Engl1sh System of measure, the board foot as the unit measure
of lumber popularly and widely used is still presented for reference
in preparation for the transition from English to Metric approach.
A board foot is actually one square foot of wood one inch thick.
The formu la being used in com·puting board foot is:

= t x w x LBoard Foot -....;._...:..:.........;.;..-...:..;_...=._

12

Where t =thickness in inches

w =width in inches

L = Length in feet

This formula is being used for sawed wood of commercial
dimensions.
Example:

Compute the board foot of the following lumber :
5 pes- 2"x6"xl4'

Bd. ft. = 5 X 2 X 6 X 14'

12
== 70

Note* Under the English measure of lumber, the length
is always ordered at even·length.
The above formula could not beusedin finding the board foot
of.logs. Instead, the following formula is applied:

Board ft. =-{-0--.:4.)-2.x.-L-

16

Where 0 = smaller diameter of the logs in inches

L"" Length of iog in feet

4 and 16 =are slab deduction allowance which

are constant in the formula

.49..

1-. t8'

Figure 2·4

·Illustration:

From the above figure, find the total board foot that coul(j be
derived from the log for commercial purposes.

Solution:
{24 - 4)2 X 18ft.

Board Ft. -
16

(20) 2 X 18
16

= 450 bd. ft~

Sometimes lumber is computed by the linear foot method,

A PPl ied to lumbe.r hav ing a width and thickness of 2 inches or less.

The linear foot-method is simply mu.ltiplying its length in teet by
the unit price.

To convert linear foot to board foot

Linear foot of lumber size. divide length by to get

1 X 2" --·- -- - 6 - - - bd. ft.
2x2 --- -- - 3 bd. ft.

50

2-9 ENGLISH TO METRIC MEASURE OF WOOD

Lumber is customarily computed in terms of board foot which

simply means that one board foot is equivalent to 1 inch thick,·
one foot wide and one foot long wood. To find a board foot of a

piece of wood say 2'' x 6'' x 20' the thickness is multiplied by the

width and length divided by 12 thus:?. x 6 x 20'= 20 bd. ft. ·

12

Following such principle where one inch is the unit measure in

a foot, one centimeter is also the unit measure in a meter, the

above piece of lumber could be written as .5 x 15 x 6 m "' 4.5

board meter 100

where: 2""" 5 em;

6" = 15 em
20' =6 meters

From this example, we could then say that a board foot multi-

plied by .225 is converted to a Board Meter. Thus, 20 x .225 =4.5

Bd. m.
Most probably, the length of lumber under the Sl measure will

be at the intervals of .50 m phasing out the even length of lumber

in feet.
Example: 2" x 4" x 16' will be ordered 5 em x 10 em x 5 m.

2,-,10 MANUFACTURED BOARDS

Manufactured boards are made of wood but does not appear in
their natural state. This type of building materials can be classified
as a type of lumber as they are the by-product in the manufacture
of lumber. The complete utilization of wood has led to an ex-
panded field of manufactured boards.

·There are different types of manufactured boards available
such as:

1. Plywood = is made of an odd number of veneer sheets

glued together with the grains ruMing at right angle toeach other.
Forest laboratory test show that plywood shrinks less tnan Itt of

1% in drying from saturation to 6% moisture content which is less

than the shrinkage of solid wood of the same species under similar
conditions.

51

Plywood is light in weight and strong that screw or nail can be

driven dose to the edges without danger of splitting. Plywood

thickness varies from (1/8") 3.2 mm; 4. 7 mm {3/16"); 12.7 mm
(lk..} to 25 mm. available in 3 to 5 ply panels.

The different types of plywood are:

1. Soft Plywood =The most common for structural use.

2. Hardwood Plywood =Are used for panelling and finishing
where usually only one face is hard finished.

3. Exterior or Marine Plywood = Is made for external use,

sometimes used for construction of boats.

FoV£·Pl"t C~ti!IICTIOH
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Typical plywood construction
Figure 2~5

2. Hardboard = Hardboard or pressed wood is made from
wood chips which are exploded into fibers under steam of
high pressure.The lining in the wood itself binds pressed
wood together with no fillers or artificial adhesives ap·
plied. Pressed wood is equally strong in all directions but
very brittle. Its color varies from Iight to dark brown.

3. Particle Board: Is manufactured from wood chips, curls,
fibers, flakes. strands, shaving. slivers, strands etc.• bound

together and pressed into sheets and other molded shapes. ,

Particle board has equal strength in alt directions of a given
cross sectional area, it is not brittle and can resist warping.

52

3CHAPTER

LAYOUT AND EXCAVATIONS

3-1 DEFINITION

Layout is sometimes 01lled "Staking out" which means the
process of relocating the point of boundaries and property line of
the site where the building is to be constructed. It includes clear-
ing, staking, batter boards and establish ing the exact location of
the building foundation and wall line on the ground. For short
others define layout as the process of transferring the building
plan measurements to the 9round of the site.

Stake - are wooden sticks used as posts sharpened at one end
- driven int o the ground to serve as boundaries or support of t he

batter boa rds.

Batter board - wood stick or board nailed horizontally at the
stake which serves as the horizontal plane where the reference
point of bu ild ing measurements are established.

String - is either plastic chord or ga lvan ized wire across the
batter board used to indicate the outline of the building wall and
foundation.

3..2 LAYOUT METH.OOS AND PROCEDURES

Step 1. Before the construction begins see to it that a Building
Permit is first secured from the locaJ authorities concerned. Con-
structing a building without the necessary permit is considered as
malpractice and contrary to • existing laws punishable by f ine
or jmprisonment or both upon the discretion of the court. The
amount that you are supposed to sav.e from not paying the neces-
sary building permit fees Is comparatively less than the expenses
you will incur in seeking remedy to your problem.

Step 2..Relocate the ·boundaries of the construction site. It

is suggested that lhe relocation of the property line shall be done
by a Geodetic Engineer specially for those. lots without existing
reference points or adjoining structures. There were numerous
cases filed in court for·encroachment to adjoining property which
· all started f rom layouting and excavation without property relo-
cation by a competent surveyor.

53

Step 3. Clear the site of any existi ng structures, trees ana
other elements that will obstruct the construction work. Cutting
of trees shall be limited only to those that will hinder the progress
of the work but don't forget to consult the local forestry authority
. before the cutting to avoid further jusHfication, penalty or impri-
sonment.

GOMSaiiCT IOII lAYOUT

Figure 3 -1

Step 4. Construct and allocate a space for laborers' quarters,
construction office, bodega for the materials and working tools
and temporary waste disposal. These requirements could be pos-
sible if the construction site is' big enough to allocate ·space for
such a purpose. On the contrary, if the site is l imited to t he area
occupied by the structure, an off-site preparation, storaging and
batching of conc;:rete is inevitable.

Step 5. Apply for a temporary connections of electric and
water supply. Electric current is important for the power needs
of the tools and equipment and is necessary on overtime schedules
especially in the time of concreting. Water is also a prim& need in·
the construction, should there be no source of water along the
vi cinity of the project, undeground water pump is the alternative.

54

Step 6. Construct a temporary fence around the construction.

The fence will protect the materials from pilferage both from out·
side and inside.

Step 7. Order the construction materials that are sufficient for

the working force to accomplish in a week period. Insufficient
supply of construction materials increases the overhead cost.

StepS. Verify the ·measurement in the plan if the distances

ind icated are from:

1. Center to center
2. Center to outer
3. Outer to outer
4. Inside to inside
these methods of indicating distances on the plan are commonly
overlooked by the foreman, hence, should be given attent ion before
the layout work.-

OUTEI! TO CENTER

lt4SIOE OUTSIOI!:

Figure 3-2

Step 9. Fix the batter board to its horizontal position with the

aid of a level instrument preferably plastic hose with.water. Usually,
the batter board is aligned with the ground floor elevation. The
important points in the plan such as post distances and wall cor- .
ners are indicated on the batter board by common wire nails
wherein the string is tied and laid across the opposite direction of
the batter board.

Most if not all building plans are parallel with the fronting
street, the setback of the building from the road is first verified
from the plan and is marked as the reference line where to start
the measurement. Establish the.corner to 900 angle with the aid
of plywood or stick made to a right triangle. The use of transit
instrument is preferred for a large construction but is seldom used
on small and medium projects. The use of small square in layouting
is not advisable because it will always result to big errors.

55

Figure 3 - 3

Step 10. ·Verify the measurement on the batt~r board. Some·
times the number 110 on the zig-zag rule is mistakably read as 100
by the measuring carpenter in the process of indicating the dis-
tances of post or column. The position of the stake should be well-
planned ·not to be affected by the excavation, otherwise, future
adjustment and correction of the batter board might displace the
right position of the reference points. ·

Step 11. · After establishing the reference point and line of t he
footing, transfer the intersecting points of the string on the ground
by the aid of plumb bob and indicate the size and width to be
ex cavated.

EXCAVATION

Excavation work in building construction is categor ized into
two types: the minor, and major excavation depending upon the
size .and nature of the foundation to be constructed. Excavation
for a small construction with independent wall. or combined
footing is classified under the minor excavation, while the rest
which requires sizable or total extraction of the earth fall under
the category of major construction.

'56

3-3 MINOR EXCAVATION

ExcavatiOI:'IS under this category are those constructions having
independent footing and hollow block wall footing where the dig·
ging of the soil for the footing extend to a depth from 1.00 to
l.SO meter and about half a meter depth for the wall footing.

Constructions involving minor excavations are common and
occupy the biggest percentage of works accomplished in the· field
of construction. Under this type of work, excavation is considered
as minor because it does not involve the difficulties·of sheeting,
bracing or underpinning except on rare cases where underground
soil are too· fluid or loose that small vibration creates erosion that
cause damage to the construction activities.

It is a common concept that excavation is simple as digging
the soil after the final marking of the building outIine has been
established on the ground. Unfortunately, there are factors that
should be considered in the process which when overlooked might
result to waste of materials and labor in the process of correcting
and adjusting the work.

The topographical condition of the ground plays an important
role in excavation work. For instance, when the· ground is level
or flat , laying out and excavation are simple and easy because the
problem of whate:ver depth is required could be readily verified
from the top of the ground so that a uniform depth could be as-
certained. Consequently, the succeeding work such as setting the
reinforcements, forms and concreting followed by the block laying
will meet no problem of adjustment and correction.

When the site is sloped' or a rolling ground, there are problems
that are most likely to arise:

1. What depth shall be excavated for each of the different
footings?

2. How deep shall the excavation be for the wall footing

and where shall the excavation depth be based?

It has been observed that most of. the building plans submitted
applying for a building permit shows a uniform height of footing,
. regardless ' of ·the ·topographical condition of the site, much more
of the footing detail that heights of the footing to the floor line is ·
measured not by the number of value but by word "verify". This
is an absolute manifestation of the planner's neglect either through
omission or commission of not obtaining the accurate and ·complete
information of the site condition before finalizing-the plan. ·

51

To handle the problems of excavation on sloped or rolling
ground, the following methods are presented:

1. For grounds with a minor slope condition, it is advis·

able to base the depth of the excavation from the horizontal
level of the batter board which is usually extended by the
layout string.

IIATTU tOAAO E•€VI'T10" AS Rt:H.R£NC£ LIME
f'OR EXCAVAYION

Figure 3 -4

2. The excavation depth of the wall footing from the
batter board elevation Is equal to the cumulative· sum of the

footing thickness plus the height o! hollow blocks and the

mortar.

i

s

.~

Ct:I'TM Of U<:olV.TIOM

lli!PTII or UCAVATION &A$£0 'RO.. TN£

COM..ULATIV£ NltOIIT 00 FOOTING1
loiOtn'AR AIIO Ck8

Figure 3-5

3. Another method is the use of stepped or sloped wall
footing where excavation follows gradually with the slope of
the ground. It is more economical to make adjustment in the
excavation of the ground than adjusting on the block laying
using masonry block or concrete mortar which are very ex·
pensive.

58

I l lI
l II I

J I II
I II I

I

II

I

STEPPED FOOTING SLOPED fOOTING

Figure 3-6

3 -4 MAJOR EXCAVAT ION

Building construction that requires wide excavation or total
extraction of the soil are classified into two categories depending
upon the condition or location of the site. Wh~n the area of the
construction site is big that there is enough space to accomodate
working activities, storaging of materials and dumping ground for
the excavated soil, problem is less due to the free movement of
construction equipment. Under this condition, the necessity of

providing lateral support to the excavation ground 'such as sheeting,

bracing or underpinn ing is not necessary since there is no adjoin-

i ng proper ty to be protected from damage that may be caused

by· digging, pile driving and other factors that may contribute

to the settlement of the existing structure. The constru'ction

progress could be seen immediately .due to the accessibility of the

construction materials, site fabrication of building parts and the

disposal of excavated soil within the premises which minimizes

overhead expenses of haul ing, rental and maint enance of heavy

e.qu ipment.

Bu ilding construction on a b.usy commerc ial center with

adjacent existing structure is considered to be the most complicated

among t he various construction works since this requires·careful

study and analysis of the right approach. Under this condition,

professionals and experienced bu ilders have also encountered t he

following problems: ·

1. The manner of excavation to be employed which will
not affect or damage the adjoining 'structure.

59

2. The kind of equipment to be used in digging and
extracting the ground may not be a problem but the place
where to station the equipment during the operation. Manual
digging Is very costly and time consuming, but sometimes could
not be avoided if the situation does not warrant the use of
power equipment.

3. How and where to dispose the extracted soil involves
the effective manner of maneuvering the payloader and dump: .
trucks in hau ling without obstructing the pedestrian and
vehicular traffic flow.

4. Where to dispose the underground water to be drained
by the water pump during the process of construction which
might cause muddy road and create inconvenience to traffic.

5. The kind of sheeting and bracing to be used in shoring
or under.pinning to protect the adjoining structure must be

considered~

·Comments

Shallow excavation can be done even w ithout supporting the
encloSure if there is enough space to establish a lower slope wh ich
the excavated earth could stand. The steepness of the stope de·
pends upon the character of the soil, climate and weather con·
dition and the duration of time the excavation will remain open.

Excavation that are extended below -the wa~_e_r .!~ble usually
demand drainage.of the;site priortoorduring the construction work
Erosion or sliding of the excavated soR is a problem not only
during the excavation stage but even during the installation of
steel bars and forms. The cost of removing·the materials affected
by the slide plus the additional excavation to provide a flat area
contributes largely to the cost aside from the delay of the work:
These problems should be anticipated and that necessary prevent-

theive measures should be made to prevent undue erosion. Sheeting

and bracing are solutions.

The Building .Code on the protection of adjo ining property

provides:

"Any person making or causing excavation to be made be-

low existing grade shall protect the excavation so that the soil

of adjoining property will not cave-in or settle and shall defray

the cost of underpinning or extending the foundation of

buildings on adjoining properties. ·Before commencing the

excavation, the person making or causing the excavation to be

made shall notify in writing the owner of the adjoining build~

ings not less than · 10 days before such excavation is to be

made and that the adjoining buflding will be protected by him.

The owners of the adjoining properties shall be given access

to the excavation for the purpose of verifying if their pl'o-

perties are sufficiently protected by the person making the

excavation. Likewise, the person causing such excavation shall

be given access to enter the adjoining property for the purpose

of physical examination of su<::h property. prior to the com-

mencement and at reasonable periods during the progress of

excavation. If the necessary consent is not accorded to the

person making the excavation, then it shall be the duty of the

person refusing such perm ission to protect his 'building or

structure, The person causing the excavation shall not be res-

ponsible for damages on account of such refusal by the adjoin-

aing owner to permit access for inSpection. In case there is

party wall along a lotline of the premises where an excavation

is being made, the person causing the excavation to be made

shall at his own expense, preserve such party wall in a safe

condition as it was before the· excavation was made and shall

when necessary, underpin and support the same by adequate

methods."· ·

3 - 5 SHEETING AND BRACING SHALLOW EXCAVATION

There are some legal cases filed in Court demanding damages
due to settlement of existing structure brought about by excava-
tion of adjoining property. Excavation involves the removal and
.disturbance of materials that consequently create changes in the
present concHtion of the soil or rock, such distu rbances occur

61

even if the sides of the cut is supported or not by sheeting and

bracing. Changes in stress is always associated with deformation
in the same manner as excavation is always accompanied by move-
ments which contribute to the tendency of settlement which
could be minimized by the proper application of sheeting and
bracing enumerated as follows:

1. The lateral pressure in the material adjacent to the excava-

tion could be reduced materially by means of a. proper design
and careful placement of sheeting and bracing, if the excavation
will not extend beyond the depth of 3.50 meters. The common
practice is to drive vertical planks called sheeting around the

property line of the proposed excavation.
2. The sheeting and bracing should be strong enough and

capable of resisting latera l pressure .
3. The depth of the sheeting shal l be maintained below the

bottom of the hole as the excavation progresses. Previous failure
is due to u nstrict observance of the proper sequence of excava-
tion and b~acing when excavation are permitted to advance too
far before the installation of the next set of support.

4. The sheeting shall be supported by horizontal beam
called wales supported by horizontal struts extending from side

to side of the excavation, if the excavation is too wide for the
struts. to be ex1ended ~cross the entire width, the wales shall be
supported by incIined struts called rakes or rakers.

llertico I WGie

wood . Slrul
t'lleetlnq - Vet lleol wood

BRACING SID£$ 01' SHALLOW £XCAVATt0tiS··

Figure 3 -7

62

5. There should b~ a close observation, frequent measure·
ments and recording of the·verticat and lateral movement and be·
haviour of the sheeting and bracing to provide early warning of
unfavorable development which might cauSe settl.ement of the
adjacen~ property or structure. .

6. If the work is under contract, a rigorous provisions regard·

ing the sheeting, bracing and excavation shall be incorporated in
the agreement to be strictly enforced during the execution of the
work.

7. The most effective way of prevent ing lateral movement of
the soil rs oy prestressing the bracing or struts.

Figure 3 -a

3 -6 SHEETING AND BRACING OF DEEP EXCAVATION

The methods of sheeting and bracing a deep excavation to
be discussed under this topic is not independent from that which
was previously explained under sheeting for shallow excavation
but rather a continuation and improvement of the methods, appli-
cation of new materials and approach. ·

1. The use of timber sheeting on excavation that exceeds 4 to
5 meters depth is generally uneconomical; instead, steel sheet
piles are driven along the property line of the excavation. The
wales and struts are inserted as the soil is removed from the site.

2. Steel sheet piles are driven down to a meter length below
the bed of the excavation to prevent local heaves, this embedment
of steel sheet below the excavation bed sometimes eliminate the
use of struts to support the lower portion of the sheeting.

63

3. The use of H pile is sometimes employed, driven along the

property line of the excavation spaced at 1.20 to 2.50 meters
eliminating the use of steel piles. The H piles are sometimes called

soldier pile, installed with their flange parallel with the side of the

excavation.

4. Horizontal wood board called lagging are inserted as the

soil next to the pile is removed. As excavation advances from one
level to another, wales and struts are inserted in the same manner

as that of the steel sheeting.

......,

.......,

f h.

··-~..,.,

. SECTIO" Z-Z _ /

Figure 3-9.

5. There are instances where the central portion of the site is
excavated to its final depth and then part of the permanent found-

ation is constructed. This structure then serves as the support for
the inclined bracing or rakers when the remaining soil is excavated.

"0~TIOM 0' lltllti'ORtt:O ••.eoo.C) "••cro "' Tllt:lltll
C.ONCitETE tAFT f OVNOo\TION
8trO~l (xeava1oott OJ II£·.

MAI"l"G .OIL

Figure 3-10

6. Ahother method that is sometimes employed is the cross-lot
bracing or inclined struts method called tieback.

fl""'l OltOUO lE .
LE VE1.

Figure · 3 - 11
3 - 7 SHEET PILES

The different types of sheet piles used in excavation are:

a. Flat web
b. Arch web·
c. Z piling

TABLE 3 - 1 AMERICAN STEEL SHEET PILES

Section Number -Width Weight Wall Interlock- Strength

US Steel Bethlehem in Per Kg. ing Lb./in. Kg.(Cm.

Meter Sa. Ft. Sa. m.

MZ 38 ZP38 .46 17 182 8,000 1.431
MZ32 ZP32
MZ27 · ZP 27 .53 14 150 8,000 1.431
M 110 DP 1
M 116 DP2 .46 12 129 8,000 1.431
M 115 AP3
M 112 SP4 .41 15 161 8,000 1..431
M 113 SP 5
SP 6a .41 12 129 8,000 1,43f
M 117 SP 7a
AP8 .50 10 107 8,000 1,431

.41 10.5 112 12,000 2,147

.41 13 139 12,000 2,147

.38 13 139 16,000 2,863

.38 15 161 16,000_ 2,863

.38 14 150 8,000 1,431

65

ZP·38 ZP-32

JL·· r-\\
,'l .1\,\

. ~--16"

!:lP-1 Df>·Z

·---19r---.-!

AP·3

Some tvoes &nd dim.euiou o! America ewe! thee' pilee. {From <OtGlog1u
of tfu Bethlehem &tel Co,)

Figure 3- 12

66

TABLE3-2 KRUPP STEEL SHEET PILES

SECTION b mm h mm K:awP 8nKL 8auT Pn.u ·
(Fl'OIIl' eatalope o( Rbeinhaueeu A. G.)

ksla 432 160
ksl 432

LI t1!Jkslb 432
160

160 ~·~ r
ksll 432 181 ....._.ICidon

kll 400 181 ~-cltMn(~
k'l 400 ·320 t = - .llllldiiiiiCIIIIdoliS
kvl -:..1
400 320

3-8 EXCAVATION IN SAND:

The Characteristic of sand above the water table possess the
quality of enough cohesion which facilitates the excavation work.
Tests have been conducted and results show that settlement of
the adjacent ground in large excavation does not exceed about
0.5% of the depth of the cut and that the influence thereof does
not extend farther than equal the depth from the edge of the cut,
when properly supported by sheeting and bracing called shoring.
Excavation of sand extended below water table is of different
approach , it is advisable to lower the water table before starting
the exc~vation to minimize if not to avoid subsidence which is the
usual nature of sand to sink down to lower level when springs are
permitted to form at or near the bottom of the excavation. The
water springs carry the materials into the excavation grain by
grain that might produce a tunnel beneath the slightly cohesive
layer that when sufficiently enlarged causes the roof to give way
and the water above subside to form into a sink hole that may
extend to a considerable distance from the edge of the excavation.
Ditches must be cut at the bottom leading the water to a sump pit
at a lower elevation than the rest ·of the excavation. The water
level in the sump should be maintained at the lowest elevation;
otherwise, wet sand becomes readily active in swallowing up any
heavy object resting on it. When springs sprout out, the sand will
start to boil; the slope will slough or drop off and the entire base

of the excavation might slope upward and the ditches around the
edge of the excavation that emerge near the toe of the slope will
cause the bank to collapse.

The methods and processes of pumping is a matter of impor-

tance. Sufficient equipment is necessary just from the beginning
of the work to guarantee the efficient removal of water without
the necessity of making additions or alterations during the pro-
cess. Inadequate pumping capacity wil! only lead to sand boils
and instability of the excavation base.

3-9 EXCAVATION IN CLAY .
·.

Large cut and deep excavation in soft clay develops lateral
forces in the subsoil due to the weight of the earth surrounding
the edge of the excavation which becomes a surcharge or addi-
tional pecuniary load, and if the depth of the cut becomes so great
that the bearing capacity of the soil below the sides is reached,
vibration and large movement become inevitable irrespective of
the care which the sides may be shored or braced. The movement
could only be decreased by driving piles around the cut braced by
struts or the use of metal sheeting. If the lateral pressure is so great
that metal sheeting could not withstand it. the use of steel piles is
the last recourse.

Shoring- is the process of providing temporary supports to
the. structure or ground during the excavation;"this is sometimes
called sheeting and bracing.

Heave- horizontal disp~acement of vein or stratum.

Subsidence- sinking down, or sink to lower level•

.Settlement - the sinking or lowering of materials or struc·

ture.

Underpinning - the operation of providing a permanent
foundation in place of an inadequate footing, for instance, r•
olacino a 41h"llnw fnotino bv,. nP.w fnntinn ;~~t a oreater deoth.

68

Comments and Observations:

The excavation work involved irf continuous footing is a con·
tinuous trench comparatively cheaper than that ofa series of sma.ll
pits for isolated footing, moreso, the excavation work for a raft

footing is not so much for it involved a simple broad shallow hole.

If the construction requires bracing of the excavations aside from
the forms necessary for the concrete work, less materials will be
needed for the continuous. or raft foundation than that of the in-
dividual ·footings. Records of cost comparison of several projects
show that a raft footing in some ways appears to be more econo·
mical than individual footings whose total area occupied exceed
50 to 75% gross area of the building.

.. 3- 10 FILLING

1. If the compressible materials is comparatively thin and is
just below the original surface, it can. in some instances be re-
moved economically thru excavatiors.

2. If it is very weak it is sometimes displaced by advancing
the fill from one direction to another so that a mud wave is
progressibly swept across the site.

3. The most suitable materials for filling on building sites are
well graded sand and gravel but it is considered costly.

4. Fills are placed in layers usually not thicker than .15 m.
(6") after compaction and compaction by equipment suitable to
the type of soil.

5. Filling materials are often dumped into the enclosure

. loosely and then flooded in an attempt to compact them. This

procedure although still widely used should not be permitted.. In
cohesive backfill, it inevitably leads to weakenina and softening
of the soil and to future loss ot support and subsidence

6. Clay with high swelling potential should be avoided as
fill beneath foundations or fill to support floors. If the soil dries.

69

differential shrinkage will most likely happen and irregula r subsi-
dence will develop. If the moistu re content increases, floors will
crack thereby creating lateral forces on foundation walls. If there
is no alternative material except the swelling clay for filling it is
better to compact the materials somewhat with more water than
at t he optimum moisture content because the effect of swelling
is more damaging than those of shrinkage.

7. Treatment is necessary. The addition of lime may also be
beneficial in improving the workability of clay and silts. The
principal effect of lime is to reduce the free ~ater in the soil by
hydration. It also reduces the plasticity of the d ay. The com-
pacted soil w ill develop an add it ional strength an~ stiffness w ith
time. Portland cement is seldom used fo r such a purpose because it
is less effective in reducing the free water content of the soil
although it may enhance strength in the clay later.

70

4CHAPTER

·c0NCR ETE

4 - 1 CONCRETE

Concrete is an artificial stone made out from the mixture of
cement, sand, gravel and water or other inert materials; this is

known as solid mass or plain concrete. Concrete in which rein-
forcement is embedded in sueh a manner that the two materials

act together in resisting forces is called Reinforced Concrete.

4 - 2 CEMENT

Of the various hydraulic cement which ha'-<e been developed,
Portland cement is by far the most extensively used in building
construction. The early strength portland cement is another type
of portland cement which is often recommended in constructions
that requires an early high strength such as road concreting or
building construction in time of lower temperature. This type of
cement is somewhat costly but reaches its strength in 3 to 7 days
compared to t he 7 to 28 days strength of ordinary portland
cement.

4-3 AGGREGATE

It is an inert granular materials such as natural sand, manufac-
tured sand, gravel, crushed gravel, crushed stone, pebbles, vermi-
culite, pert ite, cinders, slag, etc. Aggregates are classified as fine
and coarse that forms into concrete when bound together into a
conglomerate mass .by a matrix or cement paste.

Fine Aggregate - the materials smaller than 9 mm. in

diameter.

Coarse Aggregate- the materials over 9 mm. in diameter.

Coarse Aggregate vary In sizes from (l/4" to 3") 6 mm to

76 mm the maximum size for a reinforced concrete is (1") 25 _mm

71

or {1 lh'') .38 mm. When a concrete member is small and the
reinforcement spacings are close to each other, the coarse aggre-
gate shall be oroperly graded at {¥4.. to 13/4") 6 mm to 44 mm.

4-4 WATER

The water .intended for use in concrete mixing shall be clean
and free from injurious amounts of oils, acids, alkali, salts, or-
ganic materials or other substances that may be deleterious to con-
crete or steel. Water to be used for prestressed concrete or con-
crete which will contain aluminum embedments, shall be free
from deleterious amounts of chloride-ion.

Conditions for maximum size of coarse aggregate

1. It shall easily fit into the forms and in-between

reinforcing bars.

2. It should not be larger than 1/5 of the narrowest
dimension of the forms or 1/3 of the depth of the slab
nor lf4 of the minimum distance between the reinforcing

bars.

4- 5 TYPES OF CONCRETE AND THEIR WEIGHT

1. Ugh t weight concrete 3. Heavyweight concrete
2. Medium stone concrete

Lightweight concrete- is classified into three types depending

upon the kind of aggregates used in mixing, which predetermines
their weight.

a. Low density concrete- is employed for insulation
t-- purposes whose unit weight rarely exceeds 50 pounds per cubic

foot or 800 kgjm3

b. Moderate-strength concrete - with unit weight

from 960 to 360 kg. per cubic meter with a compressive strength

of 70 to 176 kg. per square <:f'ntimeter is usually used to fill

over light gage. steel floor panels. ·

c. Str~lWal concrete - has somewhat the same

characteristics as that of medium stone coocrete and weighs
from 90 to 120 pounds per cubic foot or 1440 to 1920 kg/

cu.m.

72

Med1um stone concrete ts a•so Known as structural concrete
weighing from 145 to 152 pounds per cubic foot generally assumed
to be 150 pounds per cubic foot or 3300 kg/cum

Heavyweight concrete - is used for shielding against gamma

and radiation in nuclear reactor and other s.imilar structure. This is
also used as counter weight·for a lift bridge. The contents. of heavy-

weight concrete are cement, heavy iron ores, crushed rock, steel
scraps, punchings or shot (as fine) is also used.

. WEIGHT OF HEAVYWEIGHT CONCRETE

The weight of the heavyweight concrete depends upon the
kind of aggregate used in mixing:

1. Heavy rock aggregate - weighs 200 to 300 pounds per
cu. ft. or 3,200 kg/cu. m.

2. Iron pa.1chings added to high density ores- 4,325 kg/
cum

3. Ores and steel - 330 lb/cu. ft or 5,300 kg/cum

4- 6 MIXING OF CONCRETE

The process of mixing concrete for building construction is
done in two different ways either on site job-mixing or ready mixed
concrete. The ACI Building Code so provides that:

"For job-mixed concrete, mixing shall be done i~ a batch
mixer of approved type. The mixer shall be rotated at a speed
recommended by the manufacturer and mixing shall be con-

tinued for at least 1Yz minutes after all materials are in the

. drum, unless a shorter time is shown to be satisfactory by the
criteria of "Specification for Ready-Mixed Concrete for cen"tral
mixers."
Mixing of concrete shall be done until after a uniform distrib-

ution of the materials has been attained· and that the mixture shall
be discharged completely before recharging the mixer.

73

Ready-mixed conaete. The concrete mixture from batching
plant is most preferred, because the proportion of the materials

such as cement and i!Qgregates are controlled by weight through
a manual or automatic scale connected to the hoppers. Water is
also batched either by a measuring tank or by water meter. The
use of Ready-Mix concrete is suitable and convenient for construc-

tions done in a congested city condition. Experienced builders

have proven the Ready-mixed concrete to be more economical
than the job-mixing processes. The Ready-mixed concrete is batched

in a stationary plant then hauled to the site in any of the following

manner:

1. Mixed completely then hauled by truck agitator.
2. Transit mixed-batched at the plant then mixed in a
truck mixer.
3. Partially mixed at plant and completed in a truck
mixer.

The Bui lding Code specifies - "Concrete shall be conveyed
from the mixer to the place of final deposit by methods
which will prevent the separation or loss of materials. Con-

veying equipment shall be capable of providing a supply of
concrete at the site of placement without separation of

ingredients and without interruptions sufficient to permit
loss of plasticity between successive increments."

Concrete shou ld be discharged from the truck mixer within 1%

hours after the water is poured to the batch. Conveying of concrete
mixture is done by either:

1. Bottom dump 4. Pumping through steel pipelines
2. Buckets
3. Wheelbarrows 5. Buggies

6. G. I. pail

Points to avoid in the placement of concrete to its final form :

1. Segregation of particles
2. Displacement of forms
3. Displacement of reinforcement in the form
4. Poor bond between successive layers of concrete

74

Preparatton of equipment and depositing:
Concrete mixing requires prior adequate preparation of equip-
ment and materials for the activities. Sec. 5.1 of the ACI Code
specifies:

"Before concrete is placed, all equipment for mixing and
transporting of concrete shall be cleaned, all debris and ice
shall be removed from the spaces to be occupied by the con-
crete, forms shall be properly coated, masonry filler units that
will be in contact with concrete shall be well drenched and the

ofreinforcement shall be thoroughly cleaned ice or other dele- .

ter ious coatings.''

'Water shall be removed from the place of deposit before
concrete is placed unless a tremie is to be used or unless other-
wise permitted by the Building Official."

Building construction in a place where ice fall is not known or
encountered. preparation of the site for pouring of concrete only
embraces the removal of water, debris, mud, dirts, laitance and
other unsound materials that will adversely affect the strength and
durability of concrete.

Depositing of Concrete. Depositing of concrete shall be made
as early as practicable in its final place to avoid segregation of par-
ticles due to rehandling or flowing. Concrete shall be carried at all
times in plastic form to flow re~dily into the spaces between the
reinforcing steel bars. Concrete that has partially hardened or that
has been contaminated by foreign materials shall not be deposited
in the structure or retampering or remixing of concrete shall be
made af~er the initial setti ng has started unless authorized by the
Supervising Engineer.

"After the concreting is started, it shall be carried on as a
continuous operation until the placing of the panel or section is
completed. All concrete shall be thoroughly consolidated by
suitable means during placement and shall be thoroughly worked
. around the reinforcement and ·embedded fixtures and into the
corners of the forms."

75

Where difficulties are encountered particularly in areas con-
gested with reinforcing bars, batches of mortar containing the
same proportion of cement, sand and water as used in the concrete,
shall be deposited first in the forms to a depth oH1 inch)25 mm.
then followed by the regular batch of concrete.

4 - 7 SEGREGATION

Is the separation of sand and stone from the matrix or paste
that causes inferior quality of concrete. The causes of separation
or segregatiQn of aggregates are:

1. Transferring of the concrete from the mixer to the
forms.

2. Dropping of the concrete mixture from a high elevation
3. Improper tamping and spading

4. The use of long chutes
5. Excess amount of tamping, vibrating or puddling in
the forms
6. Concrete particles tend to segregate because of their
· dissimilarity.
7. Gravel tends to settle and the lighter materials and
water also tend to rise inside a container when delayed in the
delivery to the forms.
8. Lateral movement such as the flow within the form
tends to separate the particles.

4 - 8 REOUI REMENTS FOR A GOOD QUALITY CONCRETE

A premium quality of concrete is not just attained by mixing
cement and aggregates, there are several considerations to be ob-
served in order to produce a good quality of concrete:

1. Strenth and Durability of concrete is attained from the
class of mixture or the right proportion of cement, aggregates
and water~

2. Workability - concrete mixture must be in plastic

form and could readily be P.lac.d in the form. ·

76

3. Dense. and Uniformity in Quality - concrete must be
compact with un,iform distribution of particles in order to be
water tight.

4. Curing - curing requires time, favorable temperature,
and continuous presence of water or moisture in concrete.
after pouring.

Factors that regutate the strength of concrete

1. Correct proportion
2. Suitability or quality of the materials
3. Proper methods in mixing
4. Proper placement or depositing of concrete inside the
form.
5. Adequate protection of concrete during the period of
curing.

4-9 CURING

The hardening of concrete depends upon the chemical reaction
between the cement and water. Hardening of concrete will continue
as long as moisture is present under a favorable temperature condi-
tion. The initial setting of concrete will start at about two or three
hours after the concrete has been mixed. At this stage, concrete
shall be properly protected to prevent craze due to rapid evapora·
tion of moisture; 70% of concrete strength is reached at the. end of
the 1st week and 30% could be lost by premature drying out of the
concrete. The protection of concrete from loss of surface moisture
is 7 days when ordinary portland cement is used and 3 days for an
early high strength portland cement.

The methods of ew-ing surface concrete are:

1. Covering of the surface with burlap continuously wet
for the required period.

2. Covering of the slab with a layer of wet sand or saw
dust l inch or 25 mm. thick.

77

3. Wet straw or hay on top of the slab continuously wet.
4. Continuous sprinkling of water on the slab surface.
5. Avoid early removal of forms; this will permit undue
evaporation of moisture in the concrete.

The Building Code on Curing so provides-"... concrete shal!
be maintained above lOOC temperature and in a moist
condition for at least the first 7 days after placing, except
that high-early strength concrete shall be so maintained for
at least the first 3 days....xx xxx Curing by high pressure
·steam at atmospheric pressure, heat and moisture or other
accepted processes, may be employed to accelerate strength
gain and reduce the time of curing."

4- 10 ADMIXTURE

Admixture is a material other than portland cement, aggregate,
or water added to concrete to modify its properties. All admixture
added to concrete serves as water repellent, coloring agent, increase
workability, accelerate or retard the setting, harden its surface etc.
The Code on admixture specifies "The admixture shall be shown

capable of maintaining essentially the same composition
and performance throughout the work as the product used
in establishing concrete proportions .. .xx .. Admixtures
containing chloride ions shall not be used in prestressed
concrete or in concrete containing aluminum embedments
if their use will produce a deleterious concentration of
chloride-ion in the mixing water."

4 --11 CONCRETE PROPORTION AND WATER CEMENT
RATIO

It has been mentioned that concrete proportion and water
cement ratio plays an important role in the strenth and durability
of concrete. There are two methods being adopted in proportion·
ing concrete mixture; it is either by volume or by weight measure.

7&

TABLE 4- 1 CONCRETE PROPORTION

Class of Cement Sand Gravel

Mixture Bag 40 kg. cu. ft. cu.m cu. ft. cu.m.
-----,.A---=A------=,.1---=---....,1:7% .043 3 .085
4 .113
A 1 2 .057 5 .142
B 1 2Ya .071 6 .170

c 1 3 .085

The philosophy behind in establishing the proportion of fine
and coarse aggregate is to create a solid mass where cement paste
enters the voids of the fine aggregate and in turn fill the void of
the coarse aggregate Theoretically, concrete proportion shows that
sand is always one half the volume of gravel, for instance, 1 : 2 :
4 means 1 bag cement, 2 parts sand, and 4 parts gravel is the
proportion for Class A concrete. Another way of expressing such
proportion is 1 : 6 which simply means that for every bag cement,
6 parts of fine and coarse aggregate forms a class A mixture. Such
idea does not necessarily fix the volume of the fine aggregate to be
always Y:r the volume of gravel.

Adopting the concrete proportion as presented in Table 4·1
is theoretically right and also correct as far as the specification is
concerned. How if problems arise during the actual concreting
work when segregation of aggregate could not be avoided, specially
on portions where steel bars are crowded and closed to each
other? In a situation like this where workable plasticity of concrete
and other factors are adversely affected, correction and adjust·
ment should be made immediately to prevent further damages. In
this connection, the following solutions are suggested:

1. Verify the diameter .of the gravel, these might be bigger
than what is required by the specification, if so then, order the
right grade or have it passed the right screen.

2. Ascertain the thorough mixing of the concrete.
3. Verify if the proportion you are adopting, say 1 :2 : 4

79

mixture has enough paste to cover the gravel and the reinforcing
bars including the pipes and other materials.to be embedded in the
concrete. The paste of a concrete mixture should not only be
enough to cover the gravel mixed but also the steel bars and other
materials incorporated in the forms. This simple neglect will invite

a building of a honeycombed structure.
4. Aggregate proportion could be adjusted say from 1 : 2 ; 4

to 1 : 2% : 3lh which is also equivalent to 1 : 6 mixture, this will
reduce a little the gravel volume and at the same in~nce increase
the paste to cover both the gravel and the steel bars Testshave.been
con~ucted on such kind of adjusted proportion and the result was
equally satisfactory. It has also been proven that the adjusted pro·
portion is economical than the 1 : 2 : 4 mixture.

5. The concrete proportion where fine aggregate is always %

th~ volume of the coarse aggregate is effective on a massive struc-

ture with less reinforcement and also on concrete slabs with consi·

derable thickness like roads and the like.

TABLE 4 - 2 MAXIMUM PERMISSIBLE WATER- CEMENT RATIOS
FOR CONCRl:TE (when strength data from trial batches or field
experience are not available)

Maximum permissible water-cement ratio

Specified Non-air entrained Air entrained

Compressive Concrete Concrete

Strength

f's · Psi · kg/cm2 Absolute Liters. per Absolute : Liters. per

ratio by wt. bag cement ratio by wt. bag cement

2500 175 . 0.65 27.6 0.54 23.1
3000 25.0 0.46 19.7
3500 210 0.58 22.0 0.40 17.0
4000 245 0.51 19.0 15.1
4500 280 0.44 16.3 0.35 12.9
315 0.30 0.30

80

There is no definite rule or formula that could give the exact

amount of water per bag or batch of mixture to attain the desired

workable plasticity of concrete. The Code on water cement ratio

so provides. .

"If suitable data from trial batches or field experience

cannot be obtained, permission may be granted t o base concrete

proportions on the water cement ratio. limits as shown in Table

4-2".

..'When made with normal weight aggregate, concrete that

is intended to be watertight shall have a maximum water

cement ratio of 0.48 for exposure to fresh water and 0.44 for

exposure to sea water."

Air-entrained concrete is used extensively in the pavement of
road construction, it resists frost action and cycles of wetting or
freezing. It also provides higher immunity to surface scaling caused
by chemicals.

TABLE 4 - 3 CONCRETE AIR CONTENT FOR VARIOUS
SIZES OR COARSE AGGREGATE

Nominal maximum size of coarse: Total air content

aggregate percent by volume

inches mm percent by volume

3/8 9.5 6 to 10
lf2 12.7 5 to 9
lf4 19.0 4 to 8
1 25.4 3.5 to 6.5
fl/2 3 to 6
38.0 2.5 to 5.5
2
3 51.0 1.5 to 4.5
76.0
Comments and Observations

l. Concrete shall be of plastic and workab le form, hence, it
should neither be too dry nor too wet. Too dry concrete is dif·
ficult to place in the form, because it resists packing around the
reinforcement and corners of the form that honeycombing could
not be avoided.

81

2. Too wet concrete results to the segregation of the ingre-
dients. Water ratio is best determined by trial batch method to
determine the kind of mixture in obtaining the required strength
and consistency.

3. The water cement ratio shall be established during the first

hour of mixing operation and adjustment shall be made under the

following weather conditions: ·

a. On fair or cloudy weather
b. Sunny day
c. Rainy day

Fair or cloudy weather - at this weather conditio":~, adjust-

ment of water-cement ratio is sometimes negligible or Uf!necessary

because the moisture content of the aggregate will remain

constant throughout the mixing operation. ·

On Sunny day - the regular mixing operation follows after
the right water-cement ratio had been established in the first hour
through the trial batch · method. As the sun rises, temperature
increases which cause rapid evaporation· of aggregate moisture
dumped on the batching site; consequently, adjust ing gradually
t he water content per mixture batch is necessary. If m ixing will
continue until after sunset, adjustment by reducing the water
content ratio is sometime necessary to maintain a uniform mixture
of concrete.

On Rainy day - if rain occur any time after the water·cement
ratio has been established, an immediate readjustment of water
ratio is neccessary to maintain the uniformity of the mixture.
Under this situation, a reduction of water content per mixture
batch is inevitable. All conveying devices in de livering concrete
shall be free from rain water before use.

4-12 TESTS

<;:oncrete should undergo tests specially those made of various
proportions few days or weeks before the actual construction. The
Building Officials has the right to order the testing of any materials
used in concrete construction to determine if the concrete con-

82

forms wit.h the. quality specified. The c~mplete records of the
tests shall be maintained and made accessible for inspection during
the progress of the work and for a period of 2 years aner all and
shall be preserved by the inspecting Architect or Engineer for
re.ference purposes.

Consistency - refers to the state of f luidity of fn~shly mixed

concrete.
1. Slump Test ·- this method of test requires a fabricated

metal with the following dimensions:

lOtm

Figure 4- 1
Stump test procedures:

a. · Place the freshly mixed concrete inside the mould in
3 layers each rodded sepMately by 16 mm rod 25 times.

b. Level the mould and lift ·at once.
c. Measure the slump action immediately by getting the
difference in height between the height :.Jf the mould and fhe
top of the slumped concrete.
d. If the slump measure 10 em., It is said to be a 10 em.
slump.
• e. The degree of consistency of concrete could be as-
certained on the following table:

83

. TABLE 4-4 RECOMMENDED SLUMPS FOR VARIOUS
CONSTRUCTIONS

Types of construction Maximum Minimum
em em

Reinforced foundation wall and footing 13 5

Plain footings, caissons and sub- 2.5
7.5
structure walls 10 7.5
5
Slabs, beams and reinforced walls 15 2.5

Building colums 15

Pavement 7

Heavy mass construction 7

2. Compression Test: This type of test is the process

applied in determining the strength of concrete; the procedures

are as follows: ,

a) For a coarse aggregate not more than 5 em. dia·

meter, prepare a cylindrical specimen 15 em. diameter and

30 em. long

b) For a coarse aggregate more than 5 em. diameter

prepare a cylindrical specimen with a diameter 3 times the

maximum size of the aggregate and a height double its

diameter.

c) The mould should be made of metal placed on a

plane surface preferably 6 to 12 mm glass plate.

d) Place the fresh concrete inside the mould in 3

separate equal layers rodded separately with 16 mm rod 25

· strokes.

e) Level the surface with trowel and cover with a glass or

plane steel. ·

f) After 4 hours, cover the specimen with a thin layer

of cement paste and cover again with the planed metal or

glass.

·g) After 24 hours, curing shall be made in a moist

atmosphere at 21° C.

h) Test should be done at 7 and 28 days period.

i} Ascertain that both ends of the specimen are per·

fectly levelled.

84

j) Specimen is placed under a testing machine; then
a compressive load is applied until the specimen fails. The
load that makes the specimen fail is recorded.

k) The recorded load divided by the cross sectional
area of the cylinder gives the ultimate compressive unit
stress of the sample.

Gaga

.....:..·...·:..:

.• '.-:_t•

Figure 4-2

5CHAPTER

METAL. REINFORCEMENT

5-1 STEEL REINFORCEMENT

Steel is the most widely used reinforcing materials in most
constructions. It is an excellent partner of concrete in resisting
both tension and compression stresses.

Comparativeiy, steel is ten times stronger than concrete in

resisting compression load and 100 times stronger in tensile stress.
The design of reinforced concrete assumes· that concrete and steel
reinforcements act together in resisting load and likewise to be in

the state of simultaneous deformation, otherwise due to excessive
load, steel bars might slip from the concrete in the absence of suf·
ficient bond.

Und.er this assumption, the load between the concrete and steel

should be sufficiently strong to prevent any relative movements of

steel bars and the surrounding concrete. In order to provide a high

degree of interlocking between the two materials, a steel reinforc·.
ing bar with a surface deformation in various sizes in diameters

were introduced.

Type's of deformed bars

Figure 5-1

The combtnation of concrete and steel shows the following
satisfactory joint performance:

1. There is a negligible difference in thermal expansion
coefficient that makes it safe from undue effects of differen-
tial thermal deformation.

2. The concrete that surrounds the steel reinforcement is

86

considered an excellent protective covering that retards corro-
sion in steel.

3. The strength of steel when exposed to high temperature
substantially decreases, but concrete covering provides a suffi·
cient thermal insulation.

4. While concrete is weak in tension force, steel has that
property in resisting high tensile stresses

Steel could be used in two different ways:

~,As reinforcing steel, it is placed in the forms before the

pourin of fresh concrete. .

~ As prestressed steel, heavy tension forces are applied to

the steel reinforcement before the casting of concrete.

5-2 STEEL BARS FROM ENGLISH TO METRIC MEASURE

Steel bar diameters have been standardized from '14" to 2114"
and the length varies from 20', 25', 30', 35' and 40' long. Aside
from these standard diameter measurements. a corresponding
number were introduced and designated to each diameter size for
convenience and proper identification. For instance, a number 2
bar is 114'' f/J No. 3 is 3/8''¢J bars etc. From these examples one could
easily determine the diameter of bars by dividing the designated
number by 8. In short, the diameter of bars differ from the con·
secutive numbering by 1/8".

TABLE 5-l DESIGNATIONS, AREAS, PER.IMt;TER$ &

WEIGI.ITS OF STANDARD BARS

Bar No. Diameter, in. Croes- Perimeter, Unit weight
in. ·pet foot, lb
sectional

area, •m. t

2 i- 0.250 0.05. 0.79 0.167

3 1- o.a75 0.11 1.18 0.376

" -t- 0.500 0.20 1.57 0.668

5 i- 0.625 0.31 1.96 1.043

6 f-0.750 0.44 2.36 1.502

1 f .. 0.875 0.60 2.75 2.044--

8 1 - 1.000 0.79 3.14 2.. 670

9 Ii- 1.128 1.00 3.54 3.400

10 It,. 1.270 1.27 3.99 4.303

11 lf- 1.410 1.56 4.43 5.313

14 lf- 1.693 2.25 5.32 1.650

18 2f ... 2 257 4.00 7.09 13.600

87

TABLE 5-2 AREAS OF GROUPS OF STANDARD BARS,
IN SQUARE INCHES

NvMkr o/.&oN

B'lr ---• ---- ----2 3
No. 5 6 7 8 t 10 11 12 13 14.
-~ - - ---- --
4 0.39 0.58 0.78 0.98 118 1.37 1.57 1.77 1.96 2.16 2.38 2.$5 2.75

s 0.61 0.91 1.23 1.53 1.84 2.15 2.45 2.76 3.07 3.37 3.6~ 3.09 4.30

6 0.88 1.32 1.11 2.21 2.65 3.09 3.53 3.98 4.42 4.86 5.3C 6.74 6.19
7
8 1.20 1.80 2.61 3.01 3.61 4 21 4.81 5.<41 6.01 6.61 7.22 7.82 8.4.2
9 1.57 2.35 3.H 3.93 4.71 s.so 6.·28 7.07 7.85 8.64 9.43 10.21 11.00
10
2.00 3.00 4.00 500 6.00 7.00 8 00 9.00 10.00 11.00 12.00 13.00 14.00
11
14 2!13 3.79 5.06 6 33 7.59 8.86 10.12 11.39 12.66 13 92 15.19 16.4.5 17.72
18
3.12 ' 68 6 25 7 81 9 37 10 94 12..'i0 14.00 15.62 17,19 18.75 20.31 21.87
4.50 6.75 900 11.25 l.'J50 15.75 18.00 20.2.') 22.50 24.75 27.00 29.25 31.50
8.00 12 00 16 00 20 00 24.00f2s.oo 32.00 36.00 40.00 44.00 48.00 52.00 56.00

Recently the great confusion arose after the intoduction of the
Sl Metric System in all kinds of measure. Steel bar manufacturers
in the guise of conforming with the international movement as
emphasized through a presidential decree produced steel bars that
slightly differ by millimeter. Manufacturers produced steel bars
with their own standard under the millimeter diameter and was
allegedly referreq to as "standard" (that which refer to the English
measure); below standard; oversize; undersize; mm; etc. which
created confusion even among technical men. The production of

steel bars that slightly differ by a millimeter in diameter was pur·

posely designed to cater on the buyers who in these time of eco·
nomic crisis prefer the cheaper steel bars. As a result. customers·
disregard the diameter size whether the materials that they are
buying are smaller than what is specified. As an outcome, there is
a total sacrifice in the strength of the structure.

COMMENTS AND ANALYSIS

1. How could one distinguish the difference between 10 mm
from 11 mm steel bars through the naked eye without the aid o;
a caliper? Even with the aid of'a caliper, one could not effectively
measure a steel bar with perforations and elliptical cross-sectional
diameter.

88

2. The former measure that differ by 1/8" could be easily
noticed and distinguished by anybody even without the aid of a
caliper.

To be able to buy the right diameter of steel bar:

a· Verify the weight per meter or weight per bar length

with the aid of Table 5-3 and 5-4
b. Order of steel bars shall be specific according to the

millime.ter sizes such as 12 mm. Avoid the '112" </J or other measure

in inches because they are no longer under production unless on
special orders.

c. Do not insist on bigger discount in buying steel bars,

because you will most likely get steel bars a millimeter or more
smaller than what you actually need which in turn might be
more costly and damaging to your construction.

3. The knowledge and training of the recent crop of Engineers
are centered on the English measure particularly on the structural
design as the textbooks and references in circulation are all based
from the English system of measure. The shifting from English to
Metric System needs time for adjustments and revision of most
if not all of the technical books and manuals of instructions.

4. The different steel bar manufacturers must be compelled

to strictly follow a standard of measurement of steel bars through
a more specific order. Guideline must be provided in the manufac6

ture of standard steel bars for protection of the public from un-
scrupulous manufacturers and suppliers.

TABLE 5-3 STANOARD WEIGHT OF REINFORCING BARS

NOM UNIT Near AS T M 6M 7.5M 9M 10.5M 12M

Dia. wt (19.68') 24.6') -(29.52') (34,44') (39.36')

(mrn) Kg.- (M) Designation Kg . Kg. Kg. Kg. Kg.

6 .222 No.2 1.332 1.665 2.000 2.331 2.664
10 .616 3.696 4.620
12 .888 No.3 5.328 6.660 5.544 6.468 7.392
16 1.579 No.4 9.474 7.992 9.324 10.656
20 2.466 No.5 14.796 11.843
25 3.854 . No.6 18.495 14.211 16.580 18.948
28 4.833 23.124 22.194 25.893 29.592
No.8 28.998 28.905 34.686 40.467 46.248
32 6.313 No.9 37.878 36.248 43.497 50.747 57.996
No. 10 47.946 56.817 66.286 75.756
36 7.991 No.ll 47.348
59.933 71.919 83.906 95.892

89