Simplified Methods on Building Construction

TABLE 11 • 11 4PANELS

Truss Top Bottom A DIAGONA L VERTICA L
Spaci ng Chord Chord
in meters Bc 0 Xyz

. 6M SP AN Diam eter

mm

2.00 3x6 3x5 2x3 2x3 3x~ 3x3 12 12 12
2.50 3x6 3x5 2x3 2x3 3x3 3x3 12 12 16
3.00 3x6 3x6 2x3 3x3 3x3 3x3 12 12 16

7 M SP AN

2.50 3x6 3x6 ~·
3.00 3x8 3x8
3.50 3x8 3x8 3x3 3x3 3x4 3x3 12 12 16
3x3 3x3 3x4 3x3 12 12 16
3x3 3x4 3x4 3x4 12 16 19

2.4 0

TABLE 11· 12 5 PANELS Diagonal 0 Vertical y z
Truss Top Bottom
Spacing Chord Chord A Bc D wX
in meters
8M SPAN Diameter

3.00 3x8 3x8 2x3 3x3 3x3 3x4 3x4 12 mm 12 mm 16mm 16 mm
3.50 3x8 3x8 3x3 3x3·. 3x4 3x4 3x4 12mm 12mm 19mm 19mm
4.00 3x8 3x8 3x3 3x3 3x4 3x4 3x4 12 mm 16mm 19mm 22mm

9M SPAN

3.00 3x8 3x8 3x3 3x3 3x4 3x4 3x4 12 mm 12 mm 19mm 19mm

3.50 3x8 3x8 3x3 3x3 3x4 3x4 3x4 12mm 16mm 19mm 22mm
4.00 4x8 4x8 3x3 3x4 3x4 3x4 3x4 12 mm 16mm 19 mm 22mm

10M SPAN

3.00 3x8 3x8 3x3 3x4 3x4 3x4 3x3 12 mm 12 mm 16mm 19mm
3.50 4x8 4x8 3x3 3x4 3x4 4x4 4x4 12mm 16 mm 19mm 22mm
4.00 4x8 4x8 3x3 3x4 3x4 4x4 4x4 12mm 16mm 19mm 22mm

...,

~

12CHAPTER

ROOF AND ROOFING MATERIALS

12- 1 ROOFING MATERIALS

The term roof used here means the top covering of a building
that serves as a protective covering from the weather. Likewise.
roofing materials refers to the kind of materials used in the cons-
truction of the roof.

There are numerous forms of roofing which are classified
according to the materials used:

l. Fiber 5. Tiles
2. Wood 6. Reinforced Concrete
3. Metal 7. Plastics
8. Fiberglass
4. Slate

A Ftblr Roofing- Is a cheap kind of materials used for roofing
made out of tar felt or other materials, available in rolls made in

several varieties. Fiber roofing is laid on·an undersurface made of
tongue and groove (T & G) wood board preferably well-seasoned
or kiln-dried to prevent warping and splitting of wood due to
alternating temperature that causes tearing of the fiber.

Laying Procedure - The laying procedures in fastening fiber
roofing sheets are as follows:

a. Lay the T & G board on the roof frame as undersheating

well fastened by 8d common wire nails.
b. Mark the roofing surface with chalkline to insure a unt-

form laps and parallel widths in laying the fiber .materials.
c. Use galvanized nails with large head but short enough to

avoid penetration on the undersurface board.
d. Provide 15 em overlap and have it cemented .with coal

tar.
e. Do not pull a strip of roofing paper after it was unrolled

straight at the start of the work.

B Canvas Roofing - Is extensively used for deck roofing of

boats, cars, garage or shed etc. Canvas are usually treated .with

242

linseed oil and followed with a ~oat of paint 1fter laying or
maybe retreated with linseed oil after laying then fQIIowed by
paint.

Laying Procedure: -

1. Before laying, canvas should be dampened and drawn
evenly taut, raw edges are concealed and nailed with
2 em galvanized or copper tacks spaced at 2 em. apart.

2. One way of treating canvas is to apply a heavy coat of

raw linseed oil and allow to saturate, while it is still wet,
sprinkle all over with calcined plaster of paris evenly
spread with brush, thus removing superf uous plaster This
procedure prevents the contraction and expansion of the
canvas and at the same time increase the wear resistance
and provide a durable base for paint.

C - Wood Shing1es: - Is not popular and is not being used in

the Philippines although wood of the best quality are found in·the

entire archipelago. ·

D - Slate Roofing: - Is not recommended on roof of wooden
houses, because any vibration will readily crack off the shingles
if nailed rigidly or cemented..

E - Metal Roofing: - The materials used under this category
are classified as follows:

1. Galvanized Iron 5. Copper
2. Aluminum 6. Copper Bearing Steel
3. Tin {Terne .Plate) 7. Stainless Steel
8. Lead with 4% to 6% anti-
4. Titanium Copper Zinc
Alloy mony

12-2 GALVANIZED IRON SHEETS

Galvanized iron roofing is either plain or corrugated. The
thickness are measured in terms of "Gauge" from numbers 14 to
30. The sheet becomes thinner as the gauge number increases. for

instance. gauge 20 is thinner than gauge 18. The prices of G.l.

sheets varies per unit length depending upon the thickness.
The gauge number 26 is the most commonly use<.l for roof ing

243

1

although No. 24 is sometimes specified by those who could afford
the cost.

Statisticelly, most of the technocrats and laymen coosumers
have inadequate knowledge of how to dJstlnguish the difference
in thickness of G.I. sheets between the consecutive gauges 'kay, 24,
25, 26. to 30 which is difficult even with the aid of a caliper since
thickness will be measured in terms of hundreths or thouunths
of a centimeter. This is a matter of interest that one should kndW
in buying G. I. sheet because ~t is most likety to happen that one is
g;ven gauge 28 or 30 instead of the gauge 26 that was ordered and
bought from the supplier. Be it accidentally or Intentionally done,
it is to the disadvantage of the buyer In terms of cost and quality
of the materials.

The only way by which one could be sure of the right quaHty

required is by 'weight measure of the sheets which is presented in

the following Table. It would be logical to pay higher and obtain

the right gauge than pay lower without knowing that a th inner and
poorer quality.roofing sheet is obtained.

Corrupted G.l. Sheet:

Figure 12- 1

Among the metal roofing enumerated, galvanized iron sheet is
the most popular and commonly specified considering the advan-
tages that it offers to the builders and homeowners.

The standard commercial size width is (32" ) .80m with length
that ranges from (5 to 12') ' 1.50 to 3.60 m. Longer spans are also
available through special order and arrangement. Corrugated G.l.
sheet' is the most common and extensively used roofing materials
for residential, commercial; religious as well as industrial buildings.
The popularity of galvanized roofing is brought about by the ad-
vantages it offers such as cost. availability, durability and ease
of installation.·

TABLE 12- 1 STANDARD WE IGHT OF GALVANIZED IRON SH EET IN KILOGRAMS

GAGE Thickness Weight 1.50 1.80 2.10 2.40 2.70 3.00 3.30 3.60
(em.) per ft. (5') (6') (7') )8') (9') (10') {11') (1 2')

14 .203 1.49 22.36 26.84 31.31 35.78 40.26 44.72 49.20 53.6 7

15 .180 1.35 20.25 24.30 28.25 32.40 36.45 40.50 44.55 48.60

16 1.63 1.21 18.14 21.76 25.39 29.02 32.64 36.27 39.90 43.53

17 . .147 1.10 16.43 19. 72 23.00 26.29 29.58 32.86 36.15 39.44

18 .132 .98 14.73 17.67 20.62 23.56 26.51 29.45 32.40 35.35

19 . 117 .87 13.02 15.63 18.23 20.84 23.44 26.05 28.65 31.25

20 .102 .75 11.32 13.58 15.84 18.11 20.37 22.64 24.90 27.16

.21 .094 .69 10.43 12.52 14.60 16.69 18.78 20.86 22.95 25.04

22 .086 .64 9.61 11.54 13.46 15.38 17.30 19.23 21.15 23.07
23 . .079
.58 7.91 9.49 11.07 12.65 15.71 1,7.45 19.20 20.95

24 .071 .53 7.91 9.49 11.07 12.65 14.24 15.82 17.40 19.98

2,5 .064 .47 7.02 8.43 9.83 11.24 12.64 14.05 15.45 . 16.85

26 .056 .41 6.18 7.41 9.88 11.12 12.35 13.59 13.85 14.85

27 .051 .38 5.75 6.90 8.05 9.21 10.36 11.51 12.66 13.81

28 .048 .35 5.32 6.39 7.45 8.52 9.58 10.65 11.71 12.78

29 .043 .33 4.90 5.88 6.86 7.84 8.82 9.80 10.78 11.76

30 .041 .30 4.47 . 5.27 6.62 7.15 8 .05 8 .95 9.84 10.73

~

~

/

Plain G~l. Sheet:

Plain G.l. sheet commercial standard size is (36" x 8 ft.} .90

x 2.40 m. long; other sizes could be obtained through special order.
Plain G. I. sheet is also used for roofing, gutters, flashing, ridge, hip

and valley rolls, downspout, and straps for rivetting and many
more under the tinsmlthing field, to be discussed in the succeding
part of this chapter.

12-3 CORRUGATED G. I. ROOFING FASTENERS

Corrugated G.t. Sheets are fastened to the purlins either by:

1. Rivetting
2. Nailing

Riveting: - In the process of riveting, what is required are
plain G.I. straps, G.I. rivets, lead washers and G.l . washers. The G.l.

strap is folded 3 em at one end then a hole is punched therein
using a nail set with one rivet and G.l. washer inserted inside the

hole of the strap then punched to hold in position.
In the process of the final riveting, two tinsmiths do the job,

one underneath the roof and the other on top of the roof who
does the punching setting in the lead washers on the rivets followed
by the G. I. washer then the final riveting by the use of ball hammer.
The straps are then nailed on the purl ins for final anchorage of the
roofing sheets.

Figure 12-2

Nailing)- Fastening of G.i. sheets by nail is the simplest and'
most economical method where G.I. roofings are anchored to the
• purlins by the use of Roof Nails and a pair of G.l. and lead washer.

246

12-4 ADVANTAGESANDDISADVANTAGESOFG.l. RIVETS

Adv1nt1ge1:

of1. Rigidity - The entire roofing acts as one solid covering

on top the roof frame with all parts connected by rivets and
washers.

2. flexibility - The anchorage on the purlins by G.l.
straps allow free movement of the materials brought about by
the thermal expansion and contraction.

Disadvantages:

1. Expensive - due to the various accessories involved

aside from the high cost of labor
2. Difficulty of repair or replacement of defective parts

which include dismantling of the ceiling underneath to give
access to the tinsmithing activities.

3. Statistically, ' roof damage caused by typhoon are
mostly of the rivetted types. Any portion of the roof tha.t
fails and give way during typhoon is subjected to maximum
exposure to wind pressure. Other parts of the roof structure are
affected that usually results to a total destruction of the
entire roof including the roof framework.

12-5 ADVANTAGES AND DISADVANTAGES OF G.l. NAILS

Advantages:

1. Economical because only nail and washers are involved.
G.l. straps are totally eliminated and the labor cost is substan·
tially small.

2. Easy to repair or replace aefective parts without neces·
sarily affecting other parts of the building. ·
· 3. Failure of roof in case of typhoon will 1'\0t result to
total damage of the entire roof and framing structure because
roofing sheets usually blows up one at a time without being
rotted entirely affecting the whole structure. Roofing sheets
blown up by wind will not be totally damaged and could be
returned to its original position immediately after the calamity.

?47

DisadvantageS - :

1. Wat'er might leak into the nails if not provided with

roof cement during the fastening operation or when not pro·
perly driven down to attain rigid anchorage onthe purlins.

2. Loose nalls allow roof-play and movement which
usually invite water to penetrate into the holes. This usually
happens if nails missed the purlins and not corrected at once.

12-6 TECHNICAL SPECIFICATIONS:

1. Corrugated G. I. sheets shall extend not less than 8 em

beyond the outer face of the facia board.

2. Nails or Rivets shall be spaced at every other corruga-

tion along the gutter line, end lapping joints, ridge, hip and

valley rolls. Other's at every after two corrugations.

3. Nails shall be driven enough to hold the sheet firm to

the purlins. too tight might deform the corrugation: too loose

will cause movement that might cause water to leak. Avoid

· mishitting the purlins in driving nails. Always provide string

across the laid roofing sheet to insure the center fastening of

• nails to the purlins. ·

4. Always provide with string along the gutter Iine where

to start th e laying of roofing sheets to avoid misallignment of

corrugation of the.succeeding sheets.

Figure 12
Lapping: - In laying corrugated G. I. roofing sheets, there are
two kinds of lapping involved:

1. Side Lapping which is either ll/2 or 21/z corrugations
2. End Lappmg which ranges from 20 em to 30 em de-
pending upon the slope of the roof and the number of sheet in
a longitudinal row. As previously mentioned, the side lapping
is also affected by the above factors but the plan and specifi-
cations shall govern.

248

CommiM:

Different menufacturers of corrugated G.I. sheet has their own

standard mould of corrugations that differ from each other. It is
therefore suggested that In specifying or buying roofing sheets
always specify one brand throughout to avoid misalignment of
corrugations and unfitted end joints of the roof.

TABLE 12- 2 ROOF ACCESSORIES AND NUMBER
PER Kl LOGRAM

MATERIALS NUMBER OF PIECES

Galvanized Roofing Nails 102
Lead Washers
Galvanized Washers 75
Galvanized Rivets
126

180

,.. Quantity may vary a .little for different brand

TABLE 12-3 SIZES OF G.l. STRAP

Size of PurHns Strap Dimensions
{In) {em.) (em)

2x2 5x8 2.5 X 23

2X4 5 X 10 2.5 X 25
2X 5 5 X 12 2.5 X 28
2.5 X 30
2X6 5 X 15

12- 7 PLAIN G.l. SHEET

Plain G.l. sheet has numerous uses In roof construction aside

from the countless projects of tinsmithlng work. in building
construction, plain G. I. sheet could be used as:

1. Gutter 6. Anchor Strap
2. Flashing 7. Downspout
8. Roofing
3. Ridge rolf 9. Water Proofing-sheating
4. Hip Roll
5. Valley Roll

249

Roof Gutter:

Roof gutter using galvanized sheet usually specify gauge

No. 24. Gutter is either concealed or exposed type In various
forms and designs. It runs level in appearance but should be sloped
at 5 mm per meter run for effective drainage. G.I. gutter as much
as possible should be free from stagnant water and shaH be well

maintained with paint or rust protective coating.

- Outl e r$

Pur lin5---\-W\l..f.......,-"

- r o.c i a

Ex posed type Concealed type

Figure 12-4

Flashing:

Flashing makes intersections and other exposed parts of

the house watertight. It provides a smooth boarder line giving

beauty to the structure considering the unlimited variety of designs.

fPloin G.l. FIOS ~ ln9
oot
oc io

Figure 12-5

Ridge and Hip Roll .

Ridge and hip rolls are unlikely to leak because of the slope
that water tends to slide down. Because of its prominency in the
structure, it is important to have it well done.

Figure 12-6 ·
250

Valley Roll

It is always concealed underneath between the intersecting
angles of the roof. The design is limited to a semi-circular. U-~hape
or square type. This portion of the roof needs careful attentcon as
the gutter to avoid overflow or leak of water that create trouble
and embarassment.

.

Figure 12- 7

Downspout:

Downspout conveys the water from the gutter down to the
storm drain. Spout is either circular, square or rectangular cross
section or othl:!r geometrical form to suit the taste of the designer.

The size and location of the downspout is sometimes o matter
of hit and miss discretion of the builder. He would not usually
waste time to determine the accumulated rain water in the roof,
its flow inside the gutter and the required size of the downspout
th<,tt will convey the water down the drainage system. The most

common size of G.l downspout being used is the (2..x4") 5 x 10

em ready made commercial standard.
For residential work allow 6 square centimeters downspout

for every 10 square meter roof area with a minimun spacing of 6
meters apart and a maximum distance of 15 meters.

Comments and Observation:

In the field of actual construction work, it will be noted
that after the roof tinsmithing job, there are so many wastes of
scrap G.I. sheets.These are the result of indiscriminate and careless
cutting of plain G.l. sheet by the tinsmith due to lack

251

of foresight and planning of the work. These waste could have
been avoided if the cutting process were done from the largest to
the smallest piece of the accessories.The procedures and manner
of cutting G.I. sheet shall be as follows:

1. Prepare and cut into actuat sizes the gutter, hip valley
and ridge roll in accordance with the plan including the number of
pieces needed. Install them to their positions.

2. Layout the corrugated roof and make the necessary
diagonal cutting if there is any along the hip and valley roll.

3. Prepare and cut the flashing into 1ctual sizes and have
it moulded to its design form. Include in this preparation the cut
for the proposed downspout.

4. All the excesses from the above cuttingshal l be made
into small straps for riveting. Should it be inadequate, additional
cutting could be made out from the stock of plain G.l. sheets. This
will avoid excess or scrap galvanized sheet after the tinsmithing job.

.12-8 FLAT, STANDING SEAM AND BATTEN ROOFING

The materials which are usually used for this type of roofing
are :

1. Copper bearing steel Gauge 24
Gauge 19-20
2. Lead with 4% to 6% antimony Gauge 28
3. Tin (Tierne Plate) Gauge 24-25
4. .Titanium Copper Gauge 26
5. Galvantzed sheet Gauge·28-30

6. Stainless Steel

SLOPE OF ROOF

flat s..n of Flat lock -The minimum slope should be 5 em.

per meter run.

Standing Seam - The minimum slope should be 15 em. per
meter run.

A good pitch of the roof is advisable to prevent accumulation
of water and dirt in shallow puddles.

252

Flat Seam:

The roofing sheets are fastened to the sheating board by cleats

providing 3 pieces for every sheet. Two pieces along the larger side
and one on the shorter side. Fasten two pieces of 2.5 em. barbed
wire nails to each cleat. The cross beams are locked together and
soaked well with solder. ·

The sheets are edged 1 em. fastened to the roof with cleats
spaced at 20 em ·apart. The cleats are then locked into the seam
and fastened to the roof with nails to each cleats.

()

---~

Figure 12-8

Standing Sen Tin Roof:

The tin sheets are laid on a tongue and groove sheating or
underface board, well seasoned. dry lumber. narrow widths, free
from holes and should be even in thickness. A new tin sheet should
not be laid over otd tin sheet, rotten shingles or tar roof.

The sheets of this type of roofing are assembled together in
long length at the top. The cross seams are locked together and
are well-soldered. The sheets are laid and fastened with cleats
spaced at 30 em apart. One edge of the sheet is turned-up to 3 em
at right angle and the cleats are installed. The adjoining edge of the
next coarse is turned up 4 em and locked together: then turned
over and flattened to a round edge. Solder should sweat into all
seams and joints.

Roof sheets should be painted underneath before it is laid on
the roof sheating board. After laying, clean the surface then apply
.the first coat of pafnt. The second coat may be applied after two
weeks followed by a third coat after one year.

253

Figure 12-9
Batten Roofing:

Is made of plain sheets laid on a tongue and groove board, well-
seasoned, thoroughly over-lap and j oint to each other.

Figure 12 - 10

254

12-9 CLAV TILE ROOFING:

The different types of clay tile roofings art:

l. Span ish Type
2. Straight Barrel Mission Type
3. Roman Type
4. Greek Type
5. English lnterloc.king Tiles
6. , French Tiles
7. Shingle Flat Tiles

ePANI.H HI~ •COYtON ftOWA...

&:NO&..,.... AHa oa..oeco

IN T.IItt.OCKINO T•\.. &

l'"t \..1'
,_, D.C •ND DECK •CCYJOf'lil

Figure 12- 11

2.55

ASBESTOS ROOFING

lAYING Ol' IIIEilft

NOTI TH£ GAN 8ET'Wfi I ll
ntE SHIE'TIIF THE lAV·

lNG II MtOIIIQ.

ITMIERED LAYJNQ

Figure 1'.2t-12

256

prepainted steel ribbed tray roofing and walltng

,.,, ••" t)'J'I'fll'!)
~A•bW~JI

ftiOGf c..-PJHG prepainted steel roofing and welling

Position lap
over support.

-·FASCIA CAPPING

»'17110.-!C:...-
...... 1" c:ortv.-lent . . . . .

MI!TAIC ALLOIWAILILOAO CAI'ACITY fOR CONTINUOU$ '"AHI 1960 2100
2.0 1.7
-Span.,._ mm 1100 I OliO 1200 131i0 1!500 I 1860 1100 68
kl'• 8... 8.8 &.3 4.2 3.4 :u 2.3 1.3 1.1
atpporu
...... I 2 2 3 3 4 II
&-ledirtt!bolted
k"' 4.0 3.4 3.0 1.1 2.... 2.0 1.1
o.fltctlon undo<
obcmlood
Soft wlod
uplift

Figure 12·13

257

prepelrad llltel fOOting and walling

CREST fASTENING TO Tllo!etA:

-:-...:.....:...-=::-:-: For ...,..... wt ''h!IOl•'' TV~ 17

........-'f·-rm1ne --.1 ..... "-· 12 x 2:..

~IG t'IW'I'I~ '-twM,.., <Nith NtopftM

,., .,...... _. ~·· tU mm• to
"'""hol-''•w.

···.,.-·---~---

N•.''hkl" ttlf-dr.lllftCI tmtW: ~to 0.18"

(4.6 rnrn) Chick ....r NPI>O'b ...
to • &~&·· <tt mmt ~ witt.

Nt<~Prtt'l• .......,.

"BIIt!dt.w.. fyl)e 23: \tl,.<:t.mlng
~,.._: To .,..t euPCJIC!If'b 0.2•• ta rnm}
0t !nON t.l\k:l -HI>. (2 .. 4 .. C20 tftl'ft)
,..ahttcl ~~ ~ ..,_, Ordl
titr 13164'"15 MM),

CREST FASTENER LOCATION ""t .,.4

(Allou~l RIDGE CAPPING FASCIA CAPPING

· .....~---·-·- ,...,. . . ~rik l.-t.,..tt1r(.410,...).......,

. VALLEY fASTENER LOCATION
lAIItu_,.l

··-··~·-····

lhlstondard fl"91' ofPhilrtftl flo"'- Notleh and wrn down <tdflt of typo I
g~nt btltwwn rlbt. TRANSVERSE APflON fLASHING
iInnvuo...-.f1olclo.pwpinlv"''itcluapotbr.t-1i1oone&d:•• ,..,_
typo7 eo-,,...,,.,._
.,.s III'RON FLMHING
lft«o brfdc'411110rl( OfT !'*I.
TRANSVERSE FASCIA CAPPING Cov., f'-"iflt tttHtd
eo fono..., f•lt or toof.

A.·

METRIC ALlQWA8L£ LOADS- CONTINUOUS SPANS

$!Minbt-n ...... --1100 1!)50 I :ZOO 1350 1500 1650 I fiCO 1950 210Q 221!0 2400

~- kPo 8.14 4.S1 3.4S 2.73 2.21 1.83 1.54 1.31 1.13 0.98 o.ee

So'- dlttrlbutod
lold

Oofttctioft .,.,

. . . . loecl """ ·-3 3 6 8 1 & 10. 12 14 18 18
I
Solo-d kPe 3.7 3.2 :u 2.6 2.2 1.9 1.0 1.3 1.1 1.0 I 0.9
UCiift

Figure 12-:-14 /

258

13CHAPTER

STAIRS

13-1 INTRODUCTION

Not all carpenters possess the skill in building stairs. To those
who have tried to make one have found it to be an art in itself.

Many have tried but were frustrated, some made it successful,
and others won't dare being afraid of the circumstances involved
in case of error. ·

D if f iculties wi ll be encount ered in trying to frame-up a sta ir-
way if one does not know the uses and ma nipulation of t he "Steel
Square". The Steel Square play s a major role in sta irway framing,
know its functions and a satisfactory result will be obtained.

Before one makes an attempt to build a stairway, it is impor·

tant to know and be familiar with the terms used in stair design.

13 - 2 DEFINITIONS:

Beluster - A small post supporting the handrail or a coping.

Bal,ustnde- A series or row of balusters joined by a handrail

Bearen -or coping as the parapet of a balcony.
A support"_for winders wedged into the walls secured ·
by the stringers. ·

Carriage - That portion which supports the steps of a wooden

stairs.

Close String- A staircase without open newel in a dog stairs.
Cockel Stair- Is a term given to 'a winding staircase.
Circular Stair - A staircase with steps wif"!ding in a circle or

cylinder.
Curve out- A concave curve on the face of a front string.
Curtail Step - The first step by wh ich a stair is ascended,

terminating at the end in a f orm of a scroll following
the plan of a ·handrail. .
Elliptical . Stairs - Those ·elliptical in plan where each tread

assembly converging in an elliptical ring in plan.

Face Mould- A section produced on any enclined plane ver-

tically over a curved plan of a handrail. '

Flight of Stairs - Is the series of steps leading from one land·

ing to another.

Front String: - The string on the side of stairs where the hand-

ra il is placed.

259

Fillet - Is a band fastened to the face of a front string below
the curve and extending the width of a tread.

Flyers- Steps in a flight that are parallel with each other.

Geometrical Stain- Is a flight of a stair supported by the wall

at the end of the steps.

Half Space - The Interval between two flights of steps in

staircase. ·

Han~rail - A rail ru nning parallel with the inclinat ion of the

. stairs that holds the baluster.

Hollow Newel - An opening in the middle of the staircase as

distinguished from solid newel wherein the ends of

steps are attached.

Ho..ing - The notches in the string board of a stair for the

reception of stairs.

Knee- Is the convex bend at the back of the handrail.

Unding - Is that horizontal floor as resting place in a flight.

. Newel - The central .column where the steps of a circular

staircase wind.

··"Nosing - The front edge of the step that project beyond

t he riser.

Pitching Piece - A horizonta l member one end is wedged into
the wall at the top of the flight of stairs that supports
the upper end of the rough stringer.

Pitch - The angle of inclination of the horizontal of the
stairs.

Ramp - A slope surface that rises and twists simultaneously.
Rise- The height of a flight of stairs frorn landing to landing.

The height between successive treads or stairs.
Riser- The vertical face of a stair step.
Run - The horizontal distance from the first to the last riser

of a stair flight.
Sp~ndril- The angle formed by a stairway.

Stain - The steps wherein t o ascend or descend from one

storey to another.
Staircase- Is the whole set of stairs; the structure containing

a flight of stairs.
Stair Builders Trusss - Crossed beams which support the

landing of a stair.
Stair Clip - A metal .clip used to hold a stair carpet in place.

260

llllrhlld - The initial stair at the top of 1 fUght of stair or

staircase.

· ltllr Headroom - The clear vertical height measured from the

nosing of a stair tread to any overhead. obstruction.

8tllr Turret - A building containing a winding stair wh~h

usually fills it entirely; A stair enclosure which pro-
jects beyond the building roof.

Stair well - The vertiCal shaft which contains a staircase.
Stn1ight flight of stairs - One having the steps parallel and

at right angle to the strings.

Steps- The assembly consisting of a tread and a riser.

Step - Stair unit which consists of one tread and one riser.

Scroll or wrtail l1lp - The bottom step with the front end

s1oped to receive.

String - The part of a flight of st<:tirs which forms its ceiling

or soffit.

String Board - The board next to the well hole which receives

the ends of the steps.

Soffit- The underneath of an arch or moulding.

T,_ - The horizontal part of. a step Including the nosing.

T,_. length - The d imension of a tread measured perpendi·
cular to the normal line of travel on a stair. · ·

Treld Plate - A metal fabricated floor plate.
Treed Return - In an open stair, the continuation of the hori-

zontal rounded edge of the tread beyond the stair

~tringer.

Treed run- The horizontal distance between two consecutive

risers or. on an open riser stair, the horizontal distance
between nosings or the outer edges of successive treads

all measured perpendicular to the front edges of the
nosing or tread.

Treed Width - The dimensions of a tread plus the projection
of the nosing if any.

Will String - The board placed against the wall to receive the

end of the step.

Well- The place occupied by the flight of stairs.
W•l Hole- The opening In floor at the top of a flight or stairs.
Well Staircase - A winding staircase enclosed by walls re-

sembling a well.
Wind. . - Steps not parallel with each other.

W.Nth- The whole of a helically curved hand rail.

261

lllf ll. HOL E

fl.OOR
CE ll.. l NG

RUN OF ST(P

:II
0

0cr

Q

r"'

SHP

1\\JN

F igure 13· 1

262

13-3 LAYINGOUTOFSTAIRS

The method of laying out stairs are:

1. Determine the clear height of the rise in meter. Ordinarily,

the rise per step is 17 to 18 em and the minimum tread width is

25 em.

2. Divide the rise (height in meter} by .17 or .18 to deter-

mine the number of steps.

3. Divide the run distance in meter by .25 or .30m ,

4. If the result.found in step 3 is less than the number found

in step 2, the run length has to be extended.

5. There should be no fractional value of a riser. Shoutd there

be from the result of step 2, adjust the fractional value in equal

proportion to the number of riser height, but in no case shall the

rise per step be greater than 19 em or less than 17 c.m otherwise,

the stairs will not be an ideal one.

It is important to make a cross sectional sketch of a stair

before making the final plan layout indicating the number of

steps to avoid adjustments of the run during the actual

construction. ·

Io.oe"'. ----------- ... •..
------ ___ 3·ii

Fl~or 11u/

Agure 13-2

13-4 LAYING OUT THE STRINGER
After determining the number of tread and the height per rise

of the steps follow the actual marking on the stringer by the aid
. of the steel square.

263

the length of the stringer could be determined by either the
use of the Pythagorian Formula L = rise2 + run2 or by actual
measurement using a meter rule or taptr;

Figure 13 - 3

TABLE 13~1 HEIGHT OF ·RISE AND LENGHT OF RUN

FOR A GIVEN NUMBER OF STEP ···-- --

Number Height of Rise Length ()f Run

of Step (in m.) (In m.)

Riser Tread ...- .
--·-·-·····
4 .68 .72
5. .85 .90 1.00 1.20
6 1.02 1.08 1.50
7 1.19 1.26 1.25 1.80
8 1.36 1.44 2.10
9 1.53 1.62 1.50 2.40
10 1.70 1.80 2.70
1.75
u 1.87 1.98 3.00
2.00 3.30
12 2;04 2.16 3.60
13 2.21 2.34 2.25 3.90
14 2.38 2.52 4.20
15 2.55 2.70 2.50 4.50
16 . 2.72 2.88 4.80
17 2.89 3.06 2.75
18 3.06 3.24 5.10
19 3.23 3.42 3.00 5.40
20 3.40 3.60 5.70
3.25 6.00

3.50

3.75

4.00

4.25

4.50

4.75

5.00

26.4

13-5 TYPE OF STRINGERS

Thero are several forms of stringers ·classified according to the

method of attaching the risers and the treads.
l. Cut
·

2. Cleated

3. Built-up

4. Rabbeted (Housed)

Cut Stringer - Are popularly employed in most modern and
contemporary house design.

Cleated Stringer- Is used for a very rough work.

Built·up Stringer - Is employed on the wi<le stairs that re-
quires a center stringer.

CUT STRING£R

CLEAT£0 STIWHitlt
8lO C Ita Cllt fr<ONI
o11tal O• atrlntor

8Uit.T·UP $"ff11HGER

Figure 13·4

265

Rabbeted Stringer - Is adopted on a fine work and usually
made at the mill. The risers and treads are held in the rabbets by
wedges set in by glue.

Figure 13·5
13- 6 HANDRAIL AND BALUSTERS

Handrail and balusters have multiplicity of dtslgn and forms
made of either wood or metal or the combination of both. In
either type and forms the best is prefabricated on tho mill or metal
craft for precision of the work to be assembled on site. Handrails
that presents difficulty to the carpenter is the curved portion
located at the end and the change of flight. These p<lrticular parts
should be prepared in the woodcraft or mill where band saw and
jig saw are best used to form the wreath or ramp. During the
early days when labor \Vas cheap, handrail and curves were ela·
borately made. but the present trend is toward a straight line plain
and simple curve but beautifully made.

It is impori:ant to select the materials for handrail from
straight grained wood thoroughly dried or kiln dried free from
defects.

13-7 REINFORCED CONCRETE STAIRWAYS

The simplest form of reinforced concrete stairway is the
inclined slab supported at the end by beams provided with steps
on Its uppper surface. Under this type. steel reinforcements are
placed only in one direction ~long the length of the slab. A trans-
verse steel consisting of one bar per tread is ~mployed to assist in
the distribution of the load and at the same instance serve as a
temperature reinforcement. As much as possible, the unsupported
span of a stair slab shall be reasonably short and no·break in the
flight between floors and intermediate beams supported by the

266

structural framework of the building shall be provided. Likewise,

if the stair between floor is divided into two or more flights, the

intermediate beams should be used to support the intermediate

landing.

Where conditions permit, the intermediate slab maybe sup-

ported directly by the walls of the building. .

The Building Code on stairs so requires that ·the maximum

distance from the farth~st point in the floor area to stairway,

the minimum width, the maximum height of any straight flight,

the maximum rise of a single step, the minimum distance of the

run between the vertical faces of the consecutive steps and the

' required relation of the rise and run shall be designed to give

safety and convenience in climbing.

The Code further specifies:

1) The minimum width of any stair slab and the minimum
dimensions of any landing should be about 1.10 m.

2) The maximum rise of a stair step is usually specified as
about 18 em. A rise less than 16 em. is general! not considered
satisfactory.

3) The minimum tread width exclusive of the nosing is
25cm.

4) The maximum height of a straight flight between landing
is generally 3.60 m. except those serving as an exit from place of
assembly where a maximum height of 2.40 m. is normally spe·
cified.

5) The number of stairway is governed by the number of
probable occupants per floor, width of stairway and the building
floor area. The distance from any point in an open floor area to
the nearest stairway shall not exceed 30 meters and that the
corresponding distance along corridors in a particular area shall
not exceed 38 meters.

6) The combined width of all the stairway in any floor shall
accommodate at one time the total number of persons occupying
the largest floor area under the condition that ~ne person for each
.33 sq. m. floor area on the landing and halls within the stairway
enclosure.

7) In buildings of more than 12 meters height and in all
· mercantile buildings regardless of height, the required stairways

267

must be completely enclosed by fireproof partitjons and at least

one stajrway shall continue to the roof.

The actual construction of stairways are usually boilt after the

completion of the main structural framework in which case re-

cesses should be left on the beam to support the stair slab inclu-

ding the provision of dowels in preparation for the necessary

anchorage. The steps of the stairways are usually poured mono-

lithically with the floor slab. '

Construction of reinforced concrete stairway is done from an

actual pattern made of plywood or other forms fixed on the site

to a rigid position supported by scaffolding or staging•

•

268

14CHAPTER

PRECAST AND PRESTRESSED
CONSTRUCTION

14 - 1 .INTRODUCTION

The introduction of precast-concrete construction was brought
about by building costs that has considerably increased faster than
most industrial products that are affected by the large amount of
on-site labor il1volved in the traditional methods of construction.

The demand for skilled workers on on-site building cons--
truction is increasingly outrunning the supply. The answer to
these problems· were brought about by the industrialization of
construction and substitution of site labor by factory produced
precast concrete structure which has rapidly developed and gained
importance.

The advantages of precast construction are achieved by mass-
production of standardized and repetitive units. less labor cost per
piece due to mechanized series of productions, use of unskilled
labor, less construction time, better quality control and higher
strength of concrete and construction free from the effects of
weather conditions.

14-2 TYPES OF PRECAST STRUCTURE

Wall Panels - This type of precast structure has numerous
designs depending upon the architectural. requirements. The
common. shapes produced for one to four story high structures

are sections having a width up to 2.40 m. They are used as curtain

walls attached to columns and beams or sometimes as bearing
walls.

The different types of wall panels are:

1. Flat Type 3. Ribbed Type
2. Double Tee Tyoe 4. Window or Mullion Type

To improve the therm~t insulation of the panel, foam glass,
glass fiber or expanded plastic is inserted between two layers of
lightweight concrete adequately bonded interconnecting the two
layers to act as one unit. Stresses in handling and erection of the
·member is more than that of the finished field structure, hence,
control of cracking is of great importance.

269

+'a+ewi 'I''P

2 3·

Figure 14-1

14- 3 ROOF AND FLOOR MEMBERS

Roof and f loor members are made in w ide variety to su it
the different conditions such as span, magnitude of load, fire
ratings and appearance.

1.11 0-2. 40111 .

• $S~5'"'·

.eo·.• "'·

Flat slab Hollow plan~ Double Tee .2)
Figure 14-2
Single Tee

Flat Slab - Is usually 10 em thick but sometimes as th in as

7 em when used on a continuous several span having a width that
ranges from 1.20 m to 2.40 m with a length up to 11.00 meters.

270

Hollow Plink - Is a lightweight member that covers a longer

span made by extrusion Jn speciat machine with a thickness that

ranges from 10 em to 20 em and the width ranges from .60 to
1.20 m used on roof having a span from 5.00 m to 10.00 m and
also on floor with 3.50 to 7.00 m span which could be augmented
to 9.00 m when 5 em topping is applied to act monolithically

with the hollow plank.

Double Tee- Are the most widely used shapes for longer
span having a depth from 4.00 to 6.50 m generally used on roof
having a span up to 18 m when a topping of at least 5 .em is
applied to act monolithically with the precast members. It could
be used on floor to a span up to 15 meters depending upon the

load and deflection ·requirements.

Single Tee - Are used for roofing having a span up to 30

meters and more. The flange of the Tee constitute the floor or
roof slab.

14- 4 PRECAST BEAMS

The shape of precast beams depends upon the manner of
framing. The various shapes are:

1. Rectangular Beam - Where the floor and roof members

are supported on top of the beam.

2. Ledger Beam - Is designed to reduce the height of the

floor and roof construction.

3. L·a.m - To provide bearing, the beam is designed in

a form of L. ;

4. AASHTO Bridge Girder - Named after the American

Association of State Highway and Transportation Officials.

Figure 14-3

271

·14- 5 PRECAST COLUMN

Precast column sizes are from .30 x .30m to .60 x .60 meters.
In a multi-story construction, the columns are made continuous
up to four stories where in corbels are used to provide bearing for
the beam. Tee column is sometimes used to support directly

double Tee floor members without tlie use of intermediate

members.

Column· bas e c onne c t i ons .Preca3 1 Columnr.. C orbel

column Figure 14- 4 Corbel

14 - 6 PRESTRESSED CONCRETE

The early concept of prestressing was suggested by P.H.
Jackson and G.R. Steiner of USA, J. Manli of Austria and J.
Koenen of Germany between the year 1886 and 1908. The use
of high strength steel wss through the suggestion of F Von Em-
perger of Austria in 1923 followed by R.H. Dell of USA who
proposed full prestressing to eliminate cracks completely but their
ideas only ended on papers.

The practical development of prestressed concrete was accre-
dited to E. Freesivet and Y. Guyon of France, E. Hoyer of
Germany and G. Magnet of Belgium.

In 1923 W.H. Hewitt has originated the circular prestressing of
cylindrical tank and pipes followed by the important contribu-
tions made by T.Y. Lin in the design of many types of prestressed
concrete structure in the United States since the year 1950.

272

14- 7 PRESTRESSING OF CONCRETE
There are several methods employed in applying prestressed

force to a concrete beam;
1. Precompressing Method - Is a proce$s of using jacks

reacting against abutment.

f4-8-rom-::,----~Ab~~~')

Figure 1~5
2. Self-Contained Method - The process is done by tying the
jack base together with wires or cables located on each side of
the beam. Usually the wires and cables are pressed through a
hollow conduit embedded in the concrete beam, One end of the
tendon is anchored and forces are applied at the other end. After
attaining the desired prestress force. the tendon is then ·wedged
against the concrete, removing the jack equipment.

Figure 1~6
3. Bond Friction ·- The prestressing s;rands are stretched
between massive abutment prior to casting of concrete in the
beam· forms. After the concrete has gained sufficient strength,
the jacks are then released transferring the prestressed force to
·the concrete by bond and friction along the strands.

27.3

t

4.. Th.,aJ Prestressing -The steel is preheated by means of
electric power which are anchored against the opposite end of the
concrete beam. The cooling process produces prestress force
through restrained contraction.

· ~"Anchorooe

~;--~-O-..m--=:,----CG-IMes= ;

Figure 14-7 '

5. Volumetric Expansion - The use of expanding cement

restrained by the steel strand or by a fixed abutments produces
prestressed force.

The Self Contained and the Bond and Friction methods can
generally be .classified as pre-tensioning or post-tensioning sys-

tem. These methods can be applied to mass production of casting
several meters long of structure and cutting the individual beam .
or post to the desired length out from the.long casting.

The .failure of early attempt In prestressing concrete was due
to the use of ordinary steel having low prestress strength capa·
bility which was rapidly lost due to shrinkage and creep in the
concrete.

Prestressing of concrete could be effective when a very high
strength steel are used. Experiments show that high strength has

only about 15% stress loss as compared to 100% loss in a beam

using ordinary steel. Prestressing steel is usually in the forrn of
individual wire strand cable made up of seven wires and alloy
steel bars.

t.HE CAUSES OF PRESTRESS LOSSES ARE:

1. Slip at Anchorage
2. Elastic shortening of concrete
3. Creep of concrete
4. Shrinkage of Concrete
5. Relaxation of steel stress
6. Frictional foss due to intended or unintended curvature

in the tendons.

27<4

14- 8 CONCRETE FOR PRESTRESSING

Concrete of higher compressive strength Is ultd for prestressed
structures. Most of the prestressed construction specify a com·

pressive strenath of concrete between (4,000 to 6,000 psi)
280-4.'?2 kg/em:~ becau;;t~ of the following advantages that it offers.

a) High strength concrete has a higher moduius of elasticity.
It minimize the reduction of prestress loss.
b) Increasing the compressive strength of the concrete meets
the problem of high bearing stresses at the ends of post and beam
where the prestressing force is transferred from the tendon to the
anchorage dowels which directly bears against the concrete.
c} High strength concrete develops stronger bond prestresses
to pretensioning construction.
d) High strength concrete gives higher strength to precast
construction when curing is carefully controlled.

14- 9 SHAPE OF PRESTRESSED STRUCTURE

The common shapes .of prestressed structural members are:

1. Double TEE - Is considered as the most widely used

section for prestressed construction with a flat surface having a
width that ranges from 1.20 to 2.40 'meters wide. The thickness

depends upon the requirements while the span can extend up to
18 meters.

iT

Figure 14·9

2. Single TEE - Is normally used for longer span up to 36

·meters with heavier loads. ·

275

cg

Figure 14-10
3. f·Sectlon -· Is widely used for bridges. roof, girders up to
36 meters span.

Figure 14-11
4, Channel Slab- Is used for floors in the intermediate span.

lf:..· ::::::::{{:-::::.·::-.~

.. .·.·
Figure 14-12

5. BoK Girder - Is used on bridges of intermediate and
major span.

Figure 14-13
276

lnwr1ed T• s.:tion - Provides a bearing ledge to carry the
precut deck members having a perpendiculer direction of span.

Figure 14-14

TABLE 14-1 AREAS, STRENGTH AND INITIAL TENSIONING
LOAD FOR PRESTRESSING STEEL

,...,il,Miru'"''~~"' NoJtli~te~l ' NorniMl Ultimate lr.iliol
orto, •trtrt{,tll
Tw• •lrtJt,C~ diomtlcr, in.' A~.f~·· ltlllicm
Gr-M•25o ill.
/,... bi lip• 0.70A_./,.,
MYeD-wire 250 0.250 0 .0356 kip•
mud 0.313 0 .0578 8 .9
270 0 .375 0 .0799 14.5 &.2
Gr-270 0.1089 20 .0 1Q. 2
250 . 0.437. O.IU8 27 .2
MVIlfl·wire 235 0.500 36 .0 u..o .
etrand 145 0.0356
0.250 0 .0578 9.6 19 .0
Strea--reliend 1&0 0 313 0 .0799 15 . 6 25.2
10lid wire 0 .375 0 . 1089 21 .6
- 0.437 0 . 1(38 29 .4 6.7
AJloy•teel 0.500 38.8 . 10.9
0 .0290 15.1
baN <recular> 0 . 192 0 .0598 7 . 25 20.6
0.276 14 .05 27 .2
AUDy«eel 0 .442
ban (•peeial) 0.750 0 .601 64 5 . 08
0.875 0 .7M 9.84
1.000 0 .994 87
1.125 1.227 114 46
1.250 1. 485' 61
1.375 Iff 80
0 ...2 178 101
0. 7.5(1 0 .601 215 125
0.875 0 . 785 15f
1.000 0 .994 71
1.125 1.:127. 50
1.250 1.485 ~ 67
1.375 88
126 111
159 137
196 167
238

277

. , ,.......

li.S.a~a~ SJ

NOIIIillll .,..,NOI'Irinal Nomillal Nominzl. Nominal Nominal
Bar diuwtet, wcitht, diameter. 111ea, mass,
la3 lb/fl mm mm' ki/m
...tile In
O.t1 0.376 9.S2.S 71 O.S60
..l .0.37.5 0.20 0.668 12.700 129 0.994
' G.W 0.31 1.043 13.87.5 200 U.52
0.44 1.»2 19.050 2&t 2.23.5
6 0.7,. 2.044 22.223 387 3.042
7 011.5 0.60 2.670 25.400 SIO 3.973
I 1.000 0.79 2!.651 645 .5,060
),~ 32.251 6,-404
' I.IZI LOO 3.5.814 119 7.907
4.303 43.00';' 11.385
to 1.270 1.27 .5..313 .57.328 1,()06 20.2'"1
1.$6 7.65G 1,452
II 1.410 2.25 13.600 2,-'111
4.00
14 U'J

II 2.m

WlnnW.-a

U.S. Cutonwy Sl

w.-osize Nomistal Nominal NOC!Iint.' Jl:ominal Nominal N0t11inal

s-odt Deformed diameter, area. wcjpt, dialheter, area. mAll.

in mz lb/ft mm mmz kt/m

Wll Dll 0/slS 0.310 1.0$4 15.951 200.0 1.'69
W10 D.JO 0.618 O.JOO I.C)lO 15.(6'1 193.6
W'lll DJ:8 0.597 0.280 1.5.164 !JIB
W26 D26 0.57.5 0.260 o.m )4.60$ ,,...110.7
Dl4 0.553 . 0.240 1.417
wu 0.934 14.046 167.7
022 0..529 0.220 0.816 1.)90
W22 Dlll 0.504 0.200 13.437 141 .9
W20 0.748 12.802 129.0 1.214
WII 018 0.478 0.180 12.141 116.1
W16 Dl6 OASI 0.160 0.680 11.45.5 103.2 1.11J
Wl4 014 0.422 0.140 6.612 10.719 9().)
0..544 1.012
Wll 012 0.390 0.120 0.476 9.906 n.4 0.911
Wit Dll 0.3?4 0.110 9..500 0 .8 10
6.408 9.296 7t.O 0.108
WIO.S . 0.366 0.10.5 0.374 9.042 67.7
DID 0.3.56 0.100 8.8)9 64..5 0.607
WIG 0.357 61.J 0.$57
W5U 0.348 0.051.5 0.)40 8.58.5 .58.1
W9 DP 0..338 0.0510 8.3.57 .s4A o.m
0.323 8. 103
Wl•.5 o.m o.oas 7.849 ."..·..'. 0.~
WI o.J06. 7•.569
Dl 0.319 0.080 4.5.2 0.4111
wu O.l09 0.01.5 0.219 7.31$ 41.9 6.4.55
0.0'10 7.010 38.7 0.430
·W? rY1 0.298 o.m 6.706 35.5
W6...5 0.288 0.06.5 6.401 32.3 0.40.5
W6 ' 0.060 0.25.5 6.096 29.0 0.380
D6 0.276 0.238 5.115 25.8 O.J.s4
wW'H 0.264 0.0.5.5 0 .22 1 0.)29
0.050 O.:!IW 0.304
W4.~ m 0.2-'l 0.04, 0.278
W.f 0.187 0.253
0.240 O.Oo6t 0.110
0.1$3 0 .22~
- .1)1 O.Z:!~
0.136 0.2(\"
-·-· - -· ...

278

TABLF. .14 2 MITAI. RIINPORCIMINT

w. ...........

U.S.cutc.mary Sl

'WIIIId Dll.ll No111inaJ -·NOIII6MI ......N-l"'l No111inaJ Nominal No111inal
dilflleter
SIIIOOth Deformed diuwler, ia1 "' " lttl, IIIUS.
in 111111
W3..5 0.0» Ul9 .nunz q.lm
W.l Ull 0.0)0 0. 102 .5.)59
W2.9 O. I.M 4.9S) 2,,2_.6. 0.177
W2..5 4.877 0. 152
W2 0. 192 O.Gl!J 0.0!11 4..'21 18.7 0. 146
W\.4 0.178 0,025 4,0)9 · 16.1 0.127
o.oas 12.9 0.101
.}.429 0.073
0. 159 0.020 0.061 9.0

..... ........O.tl.50.014OJNt

U.S.. cullloaWy Sl

Type NCIGiiul Nominal NoaUu1 NoaUMI NonriJIII ......NCIIIIiaal
diMietef, '!~~daM. ditalctec.
ill II'U, mm area. q.t,.
lb/fl mm'
in1 6.3-'0 t .l19
7.9-'0 %3.2
Seveo-win 0.250 . 0.4)6 0.12 9•.525 37.4 u•
strand O.OSI 0.10 11. 125 .51.6
(Onldc HO) o.m 12J'il0 69.7 0.402
o.oao o:21 U.240 92.9 0•.5.51
0.37.5 IJU
0.101 0.)7 9.52.5 o.m
0.431 0.144 11.125 .54.8
0.216 OAt 12.700 74.2 UOJ
o.soo· 15.2«1 98.7
uoo 0.01.5 0.74 ll8.7 O..Ul
0.11.5 4.877 0..59.5
Seven-wire o.:m 0.15) 0.29 4.978 18.7 0.789
$1Jaftd 0.215 0.40 6.)$0 19.4 1.101
(Grade 2?0} 0.4l8 0..5.} 7.010 :H.6
• 0.~ 0.74 31.7 0.146
19.0$0 0.149
0.600 22.22.5 283.9 0.25)
2.5.-Q} )17.1 0.2518
Prnttetatftl 0.192 0.029 0.098 21.$7.5 -'03.2
wire 0.196 0.0)0 0. 10 31.750 631.7 2.231
0.2'0 0.17 34.925 79).5
0.%76 0.049 0.20 954.1 ),0)6
0.060 1.5.875
19.0-'0 110.6 J.m
PrestreHU.. l 0.44 1.$0 2.5.400 271.0 !
lws 0.60 2.04 31.7-'0 548.4 '-030
(smooth) ,,•7 0.78 2.67 34.92.5 106•.5
1006..5 6.206
I 0.99 ).)1 7•.51.5
1.23 4.17
,I,! l ,q .5.0.5 1.4.18
2.217
Prestressina I 0.21 0.98 4AO
0.42 1.49 6.535
bus IJ 0.15 3.01 8.274
((lefonntd) tl 1.25 4.39
1..56 .5•.56

279

14 - 10 ·. METAL REINFORCEMENT:

The ACI Code-on metal reinforcement for prestressed con
crete so provides: "Wire and strand for tendons in prestressed
concrete shall. conform to the specifications for Uncoated
Seven·Wire Stress-Relieved Strand for prest ressed concrete" ·

(ASTM A416) or specifications for Uncoated Stress--Relieved
Wire for Prestressed Concrete" ASTM A421). Strand or wire
not specifically itemized in ASTM A416 or A421 may be
used provided that they conform to the minium requirements
of these specifications and have no properties which make
them less satisfactory than those listed in ASTM A416 or

A421."
"High strength alloy steel bars for post tensioning tendons

shall be proof·stressed during manufacture to 85 percent of
the minimum guaranteed tensile strength. After proof-stressing,
bars shall be subj ected to a stress relieving heat treatment to
produce the prescribed physical properties. After processing,
the physical properties of the bars when tested on full sections,
shall conform to the follow ing min imum properties:

Yield strength (0.2 percent offset) . 0.85%

Elongation at rupture in 20 diameters: 4%

Reduction of Area at rupture:· 200/o

Minimum Bonded reinforcement requirements - "Some
bonded re inforcement shall be provided in the precompressed
tension zone of flexural members where the prestressing steel is
unbonded. Such bonded reinforcement shall be distributed uni-·
formly over the tension zone near the extreme tension fiber.

The minimum amount of bonded reinforcement As in beams

and one-way slabs shall be

or As = 0.004A

wh ichever is larger, where A '"' area of that part of t he cross
section between the flexural tension face and the center of gravity
of the gross section and Nc = ~ensile force in the concrete under
load of D + 1.2L and fv shall nqt exceed 60,ooo·psi or 413700
kPa."

280

End region•- "Reinforcement shall be provided when re-
quired in the anchorage zone to resist bursting, h()rizontal split·
ting, and spalling forces induced by the tendon anchorages.
Regions of abrupt change in section shall be adequately reinforced.

End blocks shall be provided when required for end bearing
or for distribution of concentrated prestressing forces.

Post-tensioning anchorages and the supporting concrete shall
be designed to support the maximum jacking load at the concrete
strength at time of prestressing and the end anchorage region shalt
be designed to develop the guaranteed ultimate tensile strength of
the tendons...

Continuous beans- "Shall be designed for adequate strength
and satisfactory behavior. Behavior shall be determined by elastic
analysis, taking into account the reactions, moments, shears, and
axial forces produced by prestressing, the effects of temperature,
creep, shrinkage, axial deformation, restrain of attached structural
elements, and foundation settlement."

Compression members-Combined axial load and bending-
..Pr.estressed concrete members under combined axial load and
bending,With or without nonprest.ressed reinforcement, shall be
proportioned by the strength design methods for members
without prestressing. The effects of prestress, shrinkage. and creep
shall also be included. The miniumum amounts of reinforcement
specified may be waived where average prestress is over 225 psi or
1551 kPa and a structural analysis shows adequate strength and
stability.

Lateral reinforcement excapt for walls ...... All prestressing steel
shall be enclosed by spirals or closed lateral ties at least 10 mm
diameter in size. The spacing of the ties shall not exceed 48 times
the tie diameters, o.r the least dimension of the column. Ties shall
be located vertically not more ttian one-half a tie spacing above
the floor or footing, and shall be spaced as provided herein to not
more than one-half a tie spacing below the lowest horizontal
reinforcement in the slab or drop panel above. Where beams or
brackets provide enClosure on all sides of the column, the ties
may be terminated not more than 7cm below the lowest rein·
forcement in such beams or brackets.

281

Corrosion protection for unbonded tendons - "Unbonded

tendons shal l be completely coated with suitable material to in5Ure
corrosion protection. Wrapping must be continuous over the entire
zone to be unbonded, and shall prevent intrusion or cement paste
or the loss of coating materials during casting operations."

"Burning or welding operations in the vicinity of prestressing
steel shall be carefully performed so that the prestressing steel
shall not be subject to excessive temperatures, welding sparks or
ground currents."

14 - 11 GROUT FOR BONDED TENDONS

The ACI code on grout for bonded tendons specif ies:

"Grout shall consist of portland cement and potable water.,
or portland cement, sand and potable water. Suitable admixtures
known to have no injurious effects on the steel or the concrete
may be used to ·increase workability and to reduce bleeding and
shrinkage. Calcium chloride shall not be used.

Sand if used shall conform to Specifications for Aggregate for
Masonry Mortar except that gradation may be mod ified as neces-
sary to obta in increased workabil it y.

The proportioning of the grouting materials shall be based on
the results of the tests on fresh and hardened grout prior to
beginning work. The water content shall be minimum necessary
for proper placement but in no case be more than 50% the content
of cement by weight. Grout shall be mixed in a high speed mecha-
nical mixer and then passed through a strainer into pumping
equipment which provides for recirculation. The temperature of
members at the time of grollting must be above 32° C and shall be
maintained at this temperature for at least 48 hours."

Ducts for grouted or unbonded tendons shall be mortar·
tight and nonreactive with concrete, tendons or the filler ma-
terials. To facilitate grout injection, the inside diameter of the
ducts shall be at least 7 mm larger than the diameter of the post-
tensioning tendon o.r large enough to produce an internal area at
least twice the gross area of the prestressing steel.

282

14- 12 MEASUREMENT OF PRESTRI.INQ PORCE

Prestressing force could be determined by:

1. Measuring the tendon elongation.
2. Either by checking jack pressure on a calibrated gage or

load cell or by the use of a calibrated dynamometer.

The cause of any· difference in determining the force which

exceed 5 percent could be ascertained and corrected. The elonga-
tion requirements shall be taken from the average load elongation
curves for the steel used. Where force trasmission from the bulk·
heads of the pretensioning bed to the concrete is made by flame
cutting the steel, the cutting points and cutting sequence shall be
predetermined to avoid undesired temporary stresses. Exposed
strands are cut near the member to minimize shock to the con-
crete. The total loss of prestress due to unreplaced broken tendons
shall not exceed 2 percent of the total prestress.

14- 13 POST TENSIONING ACHORAGE

The ACI Code on post tensioning anchorages and couplers so
provides:

..Anchorages for unbonded tendons and couplers shall develop
the specified ultimate capacity of the tendons without exceeding
anticipated set. Anchorages for bonded tendons shall develop at

least 90 percent of the specified ultimate capacity of the tendons,

when tested in an unbonded:condition, without exceeding anticipa-
ted set. However, 100 percent of the spec1fied ultimate capacity
of the tendons are bonded in the member. Coupler shall be placed

in areas approved by the Engineer ond enclosed in housings long
enough to permit the necessary movements. Anchorage and end
fittings shall be permanently protected against corrosion.

The anchor f~ttings for unbonded tendons shall be capable
of transferring to the concrete a load equal to the capacity of
the tendon under both static and cyclic loading conditions.

283

1SCHAPTER

FORM ,SCAFFOLDING &·STAGING

15-1 FORM

Form is a temporary boarding, sheating or pans used to

produce the desired shape and size of concrete. Forms are es

sential requirement in concrete construction. Structural members
of a building are built-up into its specified dimensions by the
use of forms that serves as mould for the mixed concrete.

Concrete mixture is generally semi-fluid that reproduces the
shape of anything into which it is poured'. Forms should be
watertight, rigid, and strong enough to sustain the weight of
concrete. It should be simple and economically designed to be
removed easily and reassembled without damage to themselves
or to the concrete.

The factors considered in the selection of forms are:

1. Cost of materials
2. The construction and assembling cost
3. The number of times it could be used.
4. Strength and resistance to pressure and the tear and wear.

Wood board and Plywood forms

Wood is the most common andwidely used forms in minor or
major constructions. The introduction and satisfactory result
brought about by plywood forms almost absolutely resulted in
the limited used of tongue and groove (T & G) wood board due
to the following advantages offered by the laminated wood board.

l. Plywood as form is generally economical both in materials

and labor. .

2. Plywood has plain, even surface with uniform thickness.
3. It offers fitted joints, eliminate dressing. planing of the
surface which is normal to wooden board forms.

4. The laminated cross-grained of plywood has made the
board stronger and free from warping.

5. Plywood is light-weight, handy and fast to work on.

6. Produce · smooth finishe of concrete that sometimes
need little or no plastering at all.

284

Mml Forms-· Metal forms are seldom uMd In building cons-
truction becauM of the varied designs and shapes of the structures.

Althouoh metal forms are extensively used on road construction,

It Is also adopted on precast and prestressing plant 11 mould for
tho• flat and wider mem~rs such as floor slabt, wells, beams,

columns and those that require mass produCtion with similar
dimensions that calls for a repetitive use. Metal forms are generally
made out of G.l. sheet. or black iron sheet, supported by flat and
angle bars designed to be assembled and · Jacked by means of
clamp, bolts and nuts etc.

15 - 2 CONSTRUCTION OF FORMS

Concrete weighs about 2,200 to 2,400 kg./m3 Forms shall be
guarded against bulging and sagging failure that occur during
the process of pouring. Smatl cracks develop between joints
that gradually w i.dens and cause deforma.tion of the structure
that reduce the desired strength. Forms shall be substantially
strong to resist the weight and horizontal pressure of fresh
concrete. The thickness of the form and the sizes of the frame and
ribs depends upon t he nature of the structure t o be su pported
classified as small, medium or massive structure.

Ord inarily, small structure consisting of smal l footings,
columns and beam for one or two story building wherein (3/16)
- 6 mm. thick plywood is satisfactorily used supported by 2 x 2
wood frame and ribs.

Medium size cons1:ructions are those having concrete column,
beams, and concrete floor slab generally of 2 to 3 story high.

Forms are made out of (lf• or lfz) 6 or 12 mm thick plywood is
employed as form supported by 2 x 2 and 2 x 3 wood fr~me

and ribs.

Those construction having massive structures uses forms
of various thickness th!tt range from 6 mm to 19 mm thick
plywood ('I• to 314") support.ed by lumber of sizes from 2 x 2
to 2 x 4 . The design of the forms depends upon the degree of

the work and specifications as to whet thickness is to be used
for a certain structure including its frame and sizes. or dimen-

. sions of supports.

285

The term Cost being the principal consideration in build ing

construction connotes that all phases of the work shall be prog-
rammed to contribute to the reduction of cost without sacrificing
the strength and quality of the work. Form is not an exception to
' this objective,more so that it falls under the category of the major
item in building construction that requires substantial appropria-
tion. Form requires frame and ribs. 2 x 2 lumber is widely used
for this purpose regardless of the classification of the structure be
it small, medium or massive. The resisting capability of the form
depends upon the manner how it will be supported by the frame-
work called scaffolding or staging which will be discussed later.

There are two types of framing adopted in ma'king plywood
form : the longitudinal and the perpendicular rib type. So far, the
most economical and preferred one is the longitudinal type
because the cutting of lumber is controlled minimizing short
pieces and preserving the length for future use. On the contrary.
the perpendicular rib type cutting of lumber into short pieces
could not be avoided. After the femoval of forms, they finally
become waste to be turned into firewood.

Plywood torms -

- -2" 2 Frome -

perpendicular ribs Longitudinal ribs
Figure 15-1

Column forms - Square and rectangular colu mn forms consist
of two pieces having the same width with that of one side of the
column placed opposite to each other which will be closed with
another pair of form having wider width usually 10 em. wider
than the former. Circular column has only two pieces of semi-
circular forms usually made of metal sheet supported by wood
frame. Forms for column of various geometrical cross sectional
shape are cut according to de-sign.

286

Opposltt form tu••d '· <'~;nJ
'-. In riQtlt po•ltton
,../
-.... foiiOWid bY tl\t
col/'er Metol "heet
·Wood frome

Square Circular Rectan~ular

Figure 15·2

Beam Forms - The form of a beam consist of one bottom

forn1 having a width of 10 to 15 em. wider than the beam width

and a pair of side forms having a width equal the depth of the

beam. ') .': '
1
~ r ~"' ll} "' .· .

r

II '

1: ~ t :;1-=r:] ~.

Co) ~··

(o.) BoHoM form -the sne is .
wi d1h of beam pi ~s 4 in. or
'fj:.::::-~ :·
. 10111. .
.,
(b} ~ide cover .i~sto'oled qHer

stttiftO the reinforeemenl. beom .J.
form
It's widfh i$ e quo I tne deptll

of tile beam.

Figure 15-3

<

15- 3 ERECTION AND SECURING OF FORMS

Forms are properly secured in position by means of cleats,
braces. twisted tie ·wire, bolts, clamps or nails. Ordinarily for
small structure, forms are erected and secured by means of
common wire nails not totally driven down leaving a protroding
head for pulling off. by the aid of hammer or wrecking bar. Some-
times this method is not sufficient when the structure is massive
· that the employment of those above mentioned accessories are
necessary to prevent bulging or sagging of the forms.

297

When tie wire is used, they are twisted to tighten the forms
and the projecting end are cut when forms are taken down
leaving the other portion of the wire embedded inside the con-
crete. If bolts are used, they maybe greased before the con-
creting so that they could be driven out of the concrete easiiy
when forms are removed. After 24 hours from the time of
pouring, the bond of concrete around the bolts are disturbed
by merely tapping them with hammer, so that it could be easily
withdrawn when forms are removed.

15-4 .WALL FORMS

· Wall forms above the ground or f loor level is usually in pa ir
strong enough to resist the lateral pressure of concrete. Wall forms
should be guarded against bulging which is the usual failure, the
most effective way of securing wall form is the use of bolts and
knots.

Wall form~ are classified as:

1. Continuous

2. Full Unit
3. Layer Unit

a) Continuous
b) Sectional

The layer unit is considered economical as far as the form is
concerned, because the same forms are being used on different
section although there is delay in the progress of the work and
extra cost of labor.

15 - 5 GREASING OF FORMS

The purpose of greasing the form is to make the wood water
proof, thus preventing absorption of water in the concrete which
causes swelling and warping. Grease also prevents adherence of
concn~te to the pores of the wood.

Crude oil is the cheapest and most satisfactory materials for
this purpose. The oil is mixed with No. 40 motor oil proportioned
at 1:3 mixture varying according to the temperature where more
oil is necessary on warm wuther. Greasing of form should not be
done after the steel bars have been:set to its position.

288

. 15- 6 COMPARATIVE ANALYSIS BETWEEN THE T & G

AND PLYWOOD AS FORM

This comparative anatysls was made in 1982 when the price of

V.. x 4 ' x 8' plywood cost .,.45.00; lb." ·thick at ~85.00 while

T & G lumber cost ~.50 per board foot. The analysis could be

usefuI even If ttle prices change at any time because prices wiU

definitely increase but the quantity of the materials herein pre-
sented wilt remain constant. Hence, this will serve as· a guide in

determining the recent cost of materials which will be used as
forms in your construction whichever is less in cost.

PLYWOOD FORM T 8t G LUMBER FORM

a) Thickness -liz (12 mm) a) Thickness :Y." (19 mm)
Width- 4' {1.20 m) effective width - 3Yz"
Length - 8' (2.40 m)
( 9 em)
Length - 8' (2.40 m)

Effective Number of board ft.
equivalent to 2.88 sq. m.
coverage- 2..88 sq. m.
area of plywood is 40 bd. ft.

b) Cost: b) Cost:

Y, plywood@ .,.85.00 40 bd. ft@ .,.3~50 ""'~140.00 .

48 in. ft. 2 x 2 lumber 52 in. ft. 2 x 2 lumber

Fig15-4 Fig 15-41

c) 93 pes 1" cwnaiJ @ .15 o.c. c) 151 pes 2•. (5 em.) cw nail

10-4.. (10 em.) cw nail 18 pes 4" (10 em.) cw nail

d) Labor: !-carpenter to d) Labor: 2-carpenters to

do the assembling In 1 hr. assemble In 2 hours/ with

fitted T & G joir.ts.

289