Simplified Methods on Building Construction

10CHAPTER

STEEL FRAMt·NG

10 -1 INTRODUCTION

Prefabrication of construction parts and the methods of erect-
ing and assembling to their designed form is not new in the field
of construction. Prefabrication of parts has originated as early as
the time of the Greek and Egyptian Architecture manifested in
the remains of the famous Parthenon of Greece and the Pyramid
of Egypt. The great Parthenon of the Greeks were built of post
and lintel. type of which solid marbles were made into cylindrical
form provided with enthasis and capitals plus other articulate
mouldings of various forms and designs. The entablature made
out from solid stone marbles enriched with carvings and decora-
tions were done first before .they were placed on top of the post.
Such fraction is similar to the modern day beam. On the other-
hand the pyramid of Egypt was built out from solid blocks of
stones which were fabricated off-site and assembled to its pre-
sent form.

Hannibal in his wars with the Romans carried along pre-
fabricated huts across the alps. The army uses prefabricated and
portable barracks and small field hospital as early as 1880 and
throughout the century from World War I to World War II. Pre-
fabricated constructions, became more popular not only for the
buildings but also for bridges that could be assembled and erected
in a couple ·of days.

As builders became more aware .of the value of time, the use
. of prefabricated building parts gained wide acceptance. Success-
ful companies in the field of construction produced factory made
homes relying on the conventional framing methods applying the
technique of mass production aimed at minim izing custom job
work without sacrificing the quality of thework. The recent pre-
fabricated construction of exper imental houses sponsored by the
National Association of Home Builders include:

. 1. Pre·cut steel post, beam and foundation system.

2. Combination of sheating and siding finished with poly-
vinyl flouride film.

•3. Vinyl finished interior wallboard

190

4. Combination of sub-flooring completely finished at the
factory.

5. Reinforced plastic shower stalls and roofing coated with
hy.palan that are fastened to rafters by a concealed nailing
strip.

Fabricate - means 1o put together. The combination of pre
to fabricate simply means that the parts of the structure are
assembled or put together before the erection.

Structural steel members in various shapes and sizes are avail-
able not only in its raw or un it fo rm but also available in pre-

fabricated form to any sizes, shapes, or spans required by the

designs.

10-2 STRUCTURAL SHAPES

The most common shapes of structural steel used in building
construction are the American Standard forms such as:

1. Square Bars 6. 1-Beam
2. Round Bars
3. Plate Bars 7. Tee Beam
4. Angle Bars 8. H-Column
5. Channels 9. Wide Flanges
10. Zee

0 wn *' . i •& &·•• L [

ROUND SQUARE Pl.ATE ANGULAR CHANNEL

IT H I Z

I-SEAM TEE H-COLUMN WIDE FLANGE ZEE

STRUCTURAL SHAPE

Figure 10- 1

191

Sections or Shapes: - Is the product of rolled mill used as
structural steel members represented by the shapes of their cross-
sections.

Regular Sections: - Refers to those commonty used with
higher demand.

Special Sections: - Are those frequently used and rolled only
upon demand or special arrangemen~.

PLATES AND BARS:

The plates and bars are generally available in various sizes
specified under ASTM A 7 or ASTM A36 for buildings and bridges.
Flat Steel is generally for structural use classified as:

a) Bars:
1. 15 em. (6") or less in width with 0.51 em. thickness
2. 15 em. to 20 em. width by .58 em. thick

b) Plates:
1. Over 20 em. wide by .58 em. thickness
2. Over 1.20 m. wide by .46 em. thick or more

STEEL BARS:

Steel bars are those specified at ( t) .64 em. wide by (1/8")

.32 em. thick which are the common practice. Plates on the other
hand. the preferred width and thickness are as follows:

1. Thickness: ( -f2 ) .8 up to ( t ) 12 mm.
( fe ) 1.6 mm up to over 12 mm to

5 em.

( f ) 6 mm. to over 15 em.

ANGLE BARS:

Angle bars are either :
1. Equal legs
2. Unequal legs

The Angle bar is desi.g:nated as L such as

L 10 x 10 x 12mm for angles of equal legs
L 15 x 10 x 12mm for angles of unequal legs

192

LL

tc} Equal leas tb) Unequal legs

ANGLES

Figure 10 • 2

STANDARD CHANNEL

The standard channel has the shape of unsymmetrical balance
consisting of ·two flanges on one side. It therefore requires lateral
support to prevent its tendency to b~Ackle. The standard channels
are generally used as elements of built-up sections for columns and
are also suitable for framing around floor openings, spandrels, and
lintels attributed to the absence of flange on the other side. The
channel section is identified as C 15 x 20 which means that the
channel has a depth of 20 em. and weights 15 kg. per meter length.

(e) (d)

STANDARD CHANNEL

Figure 10 • 3

WIDE FLANGE

Wide flange sections are designated as W 12 x 24 which means
that the flange has a depth of 24 em. and it weighs 12 kg. per
meter length. All wide flange sections are generally with paraUet

face flange except those with 5% slope inside face produced by
Betlehem Steel Company. Comparatively. wide flange sections
are more efficient than Standard I Beam with respect to bending
resistance.

193

trl~-~l! i!- ~~

W It!

WI DE-FLANGE SECTIONS

Figure 10-4

STANDARD I-BEAM

The use of 1-Beam as a column is uneconomical, because the
whirl or revolving action of the structure about an axis through
the centroid parallel to the web of the 1-Beam is comparatively

small.

STANDARD I-BEAM

Figure 10-5

H·BEARING PILES

H·Bearing piles although suitable for pile driving on deep exca-
vations is much more suitable than the 1-Beam for columns.

(f)

H-COLUMN

Figure 10- 6

194

ZEE SECTIONS

The Zee section is another structural form in a,letter Z which
is not frequently used in building construction except on the
fabrication of steel windows and other frames.

TTI
Structural tee Tee Zee

Tees lee

Figure 10- 7

10-3 STRUCTURALSTEEL

The early structural steel grade was mostly focused on the
ASTM A7 which concurrently is no longer considered as the basic
structural steel after the introduction of new types of structural
grade such as ASTM A36. However, the Code so provides that
structural steel t o be used in the construction shall conform to
any of the following specifications:

1. For steel bridges and buildings ASTM A7

2. Structural steel for welding ASTM A373

· 3. Structural steel ASTM A36

4. High strength structural steel ASTM A440

5. High strength low alloy structural manganese vanadium

steel ASTM A441 .

6. High strengt.h low alloy structural steel ASTM A242

The ASTM A36 is stronger with higher yielding point t han the
ASTM A7. The carbon content of ASTM A36 had been reduced
to improve weldabiljty, al~hough it could be connected by means
of bolts and rivets.

10-4 HIGH STRENGTH STEEL

. The three high-strength steels are the ASTM A440, ASTM
A441 and ASTM ·A242 which are of greater strength and higher
resistance to atmospheric corrosion.

195

The ASTM A440 is generally used in riveted and bolted cons--
truction. .It is not recommended by the AISC for welding connect-
ion. The ASTM A441 is suitable for welding connection and is
widely used in building constructions, because of its superiority in
quality, high resistance to corrosion and higher strength but lighter
in weight.

10-5 RIVETS AND BOLTS

The rivets and bolts used in build ing construct ion are of three
grades:

1. ASTM A141 structural rivet steel

2. ASTM Al95 high strength structural rivet steel
3. ASTM A406 high strength structural alloy rivet steel

Festanen is the term used for both rivets and bolts. The three
methods adopted in connecting structural steels ere rivets, bolts
and welds. The choice of any of the.above mtthods depends
upon the condition of fabrication and e'rtctlon, dttlll of arrange
ment and condition of service

10-6 RIVETING PROCEDURES

1. The steel metal to be connected are drilled and securely

held in such a manner that their holes are perfectly aligned.

2. Heated r ivets are inserted into the holes and a buckin~up
tool is pressed against the rivet head.

3. The projecting shank is then covered by the power riveter
which delivers rapid blows f illing the hole, deforming the shank
and form ing the head.

Since the rivets are heated when inserted into the hole, shrink-
age will occur on cooling that the two connected plates will be
drawn tightly together by the rivets. The size of the rivets depends
upon the types of work, the thickness of the materials to be con-
nected and the strength to be transmitted across the joints. The

most commonly used rivets are ( ! ) 19 mm diameter and
( t ) 22 mm. However, It is suggested that only one size of rivet

should be used.

196

TABLE 10-1 CONVENTIONAL SIGNS FOR RIVETS

t111o111tlveta Floldlt""""

.. ..... CountMWunk

f)

*""' CIIIIIIH'd

I"' ."..~

u .u l:r· d .... .. .. l ... ••~ .:.o...l. s: :.I i! :.;z..
fCof.&cdlett:UM i' f" i!flatton.,.to~F l , . t t. . .. . a t o f ' 11 Cottn.tettunlf
&'14 Rlwto !
Not over t.t«b RMts 8.nd ov•r z • ~!
'5
~~ s~~l
ll• .~.j l~;:s .:.c. f :~=I

l•tOl>l

10-7 CONDITIONS FOR PUNCHING AND ORI LLING

1. tf the thickness of the plate is not bigger than the dia·

meter of the rivets plus ( } ) 3 mm, the hole may be punch.
h )2. The hole should be (
l.S mm bigger than the dia·

meter of the rivets or the bolts for ease in inserting the bolts and

to avoid damages of the threads.

3. The materials adjacent to the holes are usually damaged

by the punching of the structural steel. Therefore, it is necessary

that the hole of the punch plate should be 3 mm greater than the

diamater of the rivet or bolt, thus punching 22 mm hole for. a

19 mm rivet or 25 mm for a 19 mm rivets are recommended.

4. All rivets shall be hot power driven, heated to a tempera·

ture not more than 1()650C and in no case shall be driven below

5370 c.

Rivet joint may fail in any among the following conditions:

1. By shearing of the rivets

2. By crushing of the rivet or metal on which it bear.

3. By tension in the sections of the connected members

4. By tearing at the edge..

GAGE LINE: - Is the line parallel with the length of a member
wherein the rivets are placed, or the· normal distance between the
gage line and the edge of a member

197

=-S-1 b = t + 1~~"
I Min. 2"

Figure 10-8

TABLE 10· 2 GAGE DIMENSIONS FOR ANGLES

(Centimeters)

Leg 20 18 15 13 10 9 8 65

g 11.5 10 9 7.5 6.5 5 4.5 3.5 3
5
gi 7.5 6.5 5.5
4.5
92 7.5 7.5 6.5

PITCH OF RIVETS:

The Pitch of rivet is the center to center distance between ad-
jacent rivets whether they fall on the same different Iines. The
accepted minimum pitch between the center of rivet holes shall
not be less than 9 em. for ( 1") 25 mm rivets; 7 em. for 22 mm;
6 em for 19 mm rivets; and 5 em. for 16 rivets. Pitch should not
be less than 3 times the diameter of the rivets.

Figure 10 - 8a

198.

TABLE 10 • 3 MINIMUM PITCH TO MAINTAIN 3 DfAMETERS
CENTER TO CENTER OF RIVETS

Diameter DISTANCE, g, centimeters em
of Rivet
M 2.5 - 3 4 4.5 5 5.5 6 7 7.5
mm.

16mm 5 4 3.5 3 1.5 0
22mm
22mm 6 5 5 4 3.5 2.5 0
25mm
6.5 6.5 6 5.5 5 4.5 3.5 2
7.5 7.5 7 6.5 6.5 6 5 4 3 0

EDGE DISTANCE OF RIVETS:

Rivets or bolts placed so close to the edge of the pJate have the
tendency to tear the adjacent thin metal. A standard' specification
requires a minimum edge distance of holes as shown on the follow-
ing Table 10-4. The maximum distance from the center of any
rivet or bolt to the nearest edge shall be 12 times the thickness of
the plate but shall not exceed 15 em.

STITCH RIVETS.

Truss members are usually built up of two angles provided

with gusset plate that separate the two angles. These angles act as
·one unit by the use of rivets connecting the members placed at

intervals between the ends of the members. This is called sti1Ch ·
rivets.

TABLE 10 • 4 MINIMUM E[)GE DISTANCE FOR HOLES

Rivet or Bolt Minimum Edge Dist,ance for
Diameter Punched, Reamed or Drilled Holes
(m.m.)
(Centimeters}

At Sheared Edges At rolled Edges of

Plates, Shapes or Bars
or Gas Cut Edges

16mm 3 2.5
19mm
22mm 3.5 2.5
25mm 4 3
4.5
3.5

199

10-8 BOLTS

Bolts used t o con nect structur.al steel are either common bolts

or high strength bolts. '

Common bolts are not permitted in some Codes for building

construction for more than a prescribed height but rather limited

to field connections or to work of less importance not subject to

shock or vibration and those buildings containing machineries or

rolling loads that will cause loosening of the nuts which will subs-

tantially reduce the strength of the connections.

High Strength Bolts: - Are usually made of ASTM A325

steel which have been used for years in bu ild ing construction . High

strength bolts prov ide a resisting force. by friction between the
contacting surfaces of the plates, eliminating bend ing, shearing or

bearing stresses on the bolts. Bolts and rivets are called "fasteners:· :

Bolts are called "threaded fatteners".
Bearing Type Connection: - Where the end of the plates are •

in bearing against rivets and the shank of the rivets that resist

shear.

Friction Type Connection: When high strength bolts are used.

tensile stresses are set up in the shank of the bolts and the frict ion
between the plates which resist the tension and compression load .

TABLE 10-5 HIGH-STRENGTH BOLT TENSION

Nominal Minimum Bolt Tension
Bolt Diameter Klg. Newton

in mm.

16 mm 8,727 85,400
19mm 12,900 126,3 20
22mm 16,380 160,350
25 mm 21.470 210,160

10-9 CONNECTIONS OF STRUCTURAL MEMBERS

1. The Column Base Plate:- Spreads the column load over

the foundation in various sizes where the length in meter and
thickness of 2 mm increments. Rolled steel gearing plates should

200

be in absolute contact for proper ' distribution of load. Plates ot

more than 5 mm to 10 mm thick maybe straightened by pressing

or planning.

· Steel column should be properly anchored to the foundation

by steel bolts which passes through the plates and angles riveted

or welded to the flange of the column. Angles are sometimes

omitted for light columns, instead, the base plate is secured to the

column by means of fillet wel<1,. . ·

I

I.
I
,,~ b.
,·1 .

Welded connection for columns and base plates, the a(lgles are

shopwelded to the column and field welded to the base plate.
'

Figure 10- 9

· 2. Column Splices: - Are usually made at 60 em. or more

above the floor levels. Splices are generally made by riveting or
welding splice plates of 10 to 12 mm thickness to the flanges of
the columns. The splice plates does not resist compression load
but only serves to hold the column sections in the right position.
Where the upper column is smaller in width than the supporting
.column, filler plates are used. If the difference in width is so great,
a horizontal plate is used instead. ·

201

. ;: _ii_
....:1
tl ... .+..il:.......
: ...+++--:UI..:I.I~t-++.-..
+ll+
±-~L-!
..+.... !::::!+......
.++...!:!:;: ...
II . ii + II
II
..II II

II (c)

(aJ (b)

...• ~ I I !
'
I""""" J..4. ! _.I_
-..~
..~ T! T I·~ i_ • <I!· !

._. - I . I! I
I
(d) i i -•

I I

(e) (f)

(a) The splice plates are not design to resist compressive stresses
but only to hold the column sections in position. (b} and (c} A
horizontal plate is used to attain a full bearing area between the

column. (d) to (g) Auxilliary plates and angles are shop welded to

the column then bolted in the field before making the permanent
welds.

Figure 10-10

3. Beam Bearing Plate: - Beams to rest on masonry watls or
pier usually are provided with bearing plates to provide an angle
bearing area and to attain a uniform distribution of the beam load.
The bearing pcates are usually not riveted nor welded to the beam
flange.

202

I.

Figure 10-11

4. Beam Connections to Columns: - Beams connected to

columns has a great variety of condittons using rivets or weld an-

chorage. For large beams, seat connections with stiffeners are

commonly employer! which usually consists of shelf angle and
single or double angles. The filler should be the same in thickness

as the shelf angle. The top angle, or clip angle is used only to hold
the beam in its right position but not to assist in transferring the

beam load to the column.

. ! ..

I

I v

i
I.E~tH-B
M I C&J I (c)

t~ rr1r r~
oo w m

Figure 10-12

5. Seat Connection without stiffeners maybe used for beam

with smaller reactions.

203 .

t:;.. lbl (<}

:r

t:...
lol

(d) (•) lfl ~

(a), (b), .and (<:) Seated connections consist of a shelf angle filler
and single or double stiffener angles. The top angle or clip angle

only serve to hold the beam In position and does not help in tran,.

fering the load to the column. (d), (e) and (f) Beams for smaller

react ions. (g) A welded stiffened seate~ beam connection to

column. Figure 10 • 13

a.m6. to Girder Connections: -The methods commonly
adopted in connecting beams to girders is by attaching two angles

to the web of the beam connected either by rivets, bolts or weld.

GJ rn urn aJ

w~ ~

(a} Framing beam to a girder (b) Weld replace rivets or bolts in

securing the connection angles to the web of girder (c) Connection

angles welded to both beam and girder. '

Figure 10- 14

7. Rivetlld Framing: -The different types of riveted framing
are:

·a) When a beam is supported by another by placing on top of
it, rivets or bolts are used just to hold the beam.

T;

-.

Figure 10- 15
b) Frame connections using connecting angles commonly

used for beams and girders.

Figure 10 • 16
c) A seated connection without stiffener angle~ but only top

or side angles are used.
d) Flush top refers to the connections of two beams where

the upper surface. of the top are of the same level. This
could be done by cuttfng away a portion of the upper
flange known as coping or blocking.

I' ~~j k--;--------------~

I 205
I

I

I
. II

1 lo I

~

fill er Bea"' Or a llped
to Avoid Cop lnq

Figure 10- 1/
COMMENT:

Coping or blocking method. is not a good practice, since it in-
volves additional expenses besides the reduction of the material
which may affect the strength of the beam.
10 • 10 PLATE GIRDERS

When a rolled steel sections are inadequate to meet the span
requirements built-up section plate or box girder is the solution. A
plate girder is a beam made up of steel plates and angles either
riveted or welded together forming an 1-section. When the web of I
section consists of two separated steel plates, the structure is
called box girder.

BOX GIRDER

BUILT UP PLATE GIRDER

Figure 10- 18

The axial vertical plate is called the "web plaW". Flange angles
are placed at the top and at t~e bottom of the web plate secured
by rivets. One or more plates are riveted to the outstanding legs of

the flange angle called mvar pletes and a stiffener m~de of angle

section riveted to its side to prevent buck ling of the web plates.
In welded plate girders, the flange angles are omitted since

the cover plate could be connected directly to the vertical plate.

The three principles involved In making built-up plates are:
1. Web plate is to resist shearing stresses

t2. The fla nge made-up angles cover plates and of the web

area, wil l resist tension and compre$sion stresses due to
bending.
3. The stiffeners serves to prevent buck ling of the web plates.

BUILT u ·p SECTIONS

Figure 10 · 19

10-11 WEB PLATES AND INTERMEDIATE STIFFENERS

The Code specifies a minimum thickness of web plate to be
10 mm for interior and 6 mm for exterior locations. In addition,

plate dirder web's thickness should not be less than 3~ of the

unsupported distance between the f lange angles. If full allowance
bending stress in the flange is used, the web plate thickness

should not be less than 1l~ of the unsupported distance: This

requirement apply to ASTM A36 steel. The intermediate stiffness

that prevent buckling is usually 6 x 6 em. x 6 mm angles placed
in pair at each end of the girder then at a distance not to exceed.

85 em as f irst pair of intermediate stiffness then at 2.25 m. there-
after.

207

m. . .=. ·ec- plate$

~--+--1..1

STIFFENE RS BEARING PLcA.T.EpiMn - · - ·
Figure 10- 20

An Open web Steel Joist is considered lightweight structure to

support floor and panels between main supports.

I - -- '""'i
I

l;.i
I!.i
j:.:,

TfL..

PLAN

STEEL BEAM SUPPORTING STEEL JOIST

Figure lO- 21
208

Y. • rivets

1~· holes
~ ~ auuet plates

All lln&les ion& less back to beck

W.b memben 2 L 2 ~ x 2 x Y..

Pur1ins 9 [ 13.4

209

WE \..t>€0 CONIU CT ION S

'o\IE.l.l>EO EN1> JOINTS

EN O JOINT WITHOU T SHOE .ANGLIES

OI!SIGN OF £NO J "OINT
WITH SHOE ANGLE·

210

10- 21 ROOF TRUSSES

Roof trusses is the most economical structure to cover a build-
ing having a wide span of supporting columns or walls. A truss is a
structural frame generally supported only at both ends by col-

umns, beams, or walls.

The different types of trusses are:

1. King post truss 7. Single span fink truss

2. Simple fh1k truss 8. Clipped truss

3. 'Fink truss 9. Rigid frame open-web clear

span truss

4. Howe truss 10. Rigid frame clear span
11. Single span slope beam
5. Pratt truss
6. Fan Truss · 12. Continuous Seam

~~

SIMPLE FllfK TIIUSS KIKG POST TIIUSII

"OWE TRUSS PRATT TRUSS

FAll TRUSS fiKK TRUSS

THR£E·IUN6£ ~!lAME

Figure 10- 22

21l

PURLINS:
Purlins is a beam placed on top of the rafters or top chord that

extends from truss to truss which carry and transfer the roof load

to the truss at the panel points.

Roof Panel: - Refers to the roof portion that Hes between
two adjacent joints of the upper chord, in short, roof panel is
that portion of the roof supported by each purl ins.

Sag rods: - Refers to a steel bar usually of 16 mm or 19 mm
diameter rod attached at the center or endpoints of the span of the
purlins. Sag rod is secured to the purl ins over the line of the ridge
truss usually placed at 7 em. below the top flange of the purl ins.

Root ?a"nal

~-

Figure 10 - 23
10-13 WELDED CONNECTIONS

The advantages of using welded connections are:
1. Minimal noise in the erection of structure
2. Savings on labor and materials
3: Rigidity of frame
4. Easy to correct new work to existing structure and also its

repair.
5. Simplicity of design

212

Arc Welding:- Although arc and gas welding are permitted in
the connection of structural steel members, arc welding is the one

most preferred.

Penebatlon: - Is the term used to indicate the depth from the
original surface of the base metal to the point ·at which fusion

ceases.

Partial penetration: - is the failure of the weld metal and base

metal to fuse at the root of the weld.

Welded Joints:- Are classified into three:
1. Butt joint
2. Tee Joint
3. Lap Joint

The selection of the type of weld to be employed depends
upon the magnitude of the load requirements, the manner in
which it is applied, and the cost of the preparation and welding
operation.

The weld that is commonly used in building construction is
the fillet weld which is somewhat triangular in cross section form·
ed between the intersecting surfaces of the joined members. The
minimum effective length of a fillet weld shall not be less than 4
times the weld size. The 5 mm fillet weld is considered the mini-
mum size and an 8 mm weld is the most economical size that ·
could be made by one pass of the electrode. A small size conti·
nuous weld is more economical than a bigger discontinuous weld.
Large size fillet w~ld requires two or more passes of the electrode.

f I +f I tf I t
(o) Squar• JI'OOVO joitlt (b) Sifl&le·vetlf'OC)Vtl joint (el Double-vee POCM joint

f ~+~~
(dl Sinlle bevel·- jllint ld Square 1M joint mDouble beveiltOO\Ie joint

f I ~~ f . • f f 9 f

(81 Sinale fillet lap joint fill Doubtt fitfet ''"joint til Sin.lt-U groove joint

WELC SYMBOLS 8 C:ONNECT10NS

Figure 10 • 24

213

Shop Weld: - Where the structural members are welded in
the shop before delivering at the site.

Field Welding: - Welding done during t he erection of the

structural members.

Plug and Slot Welds: - In connecting two overlapping plates
by means of welding, holes are made in one of the two plates
then plug and slot welds are made at the entire area of the hole or

slot. The maximum and minimum diameters of the plug and slots
including its length are shown on the following illustration:

.a. ........ . .. . ,.,.,....

D. ~ ... ~'" """ '•

L ED 'Ille- L · !O • ~ D-ljMtotl llltt-
·thl ~ 't tl'tl:/'.i tl t I,

I[garI
! .I I D
t l_l
.t

I

t•J {<)
PLUG AI'I O SLOT WELOS

Note: Figure 10- 25

Since there is no st andard welding connections formu lated for

beams, the designer has to make the selection of the type of weld

which accord ing to his judgement will be most practical and eco-

nomical. Welding may be done either by shop weld, field welding

or both upon the discretion of the designer.

TABLE 10-6 BASIC WELD SYMBOLS

Plug Groove or 8 utt
or
Back Fillet v Bevel u J AireY f1lre
Slot SqiJare 8e¥el

v v v lr~ ~ CJ II y
' 'SUPPLEMENTARY WELD SYMBOLS
Weld aU Field Weld Contour
Around Flush Convex

0 • - ,.............,

2U

11CHAPTER

TIMBER ROOF FRAMING

11- L INTRODUCTION

The earl~ age constructions of house framing were built subs-
tantially strong and durable. Construction of houses by our. fore·
fathers have strictly observed the principle of durability and last-
ing quality of the materials. Only selected wood were used in the
construction.

Lately, the introduction of power tools, machines and saw·
mil-ls plus human greed has ruthlessly abused and destructed our
forests that the present construction has already precluded such
way of construction. Houses were built totally disregarding its
lasting quality, classification of lumber and its particular use in the
construction are no longer observed, the age of the tree. its falling
season including the proper drying and seasoning are totally dis-
regarded.

If builders are to be blamed, more so with the homeowners
who could not meet the expenses of a first class construction.

Nobody would like to own a house ·built from materials of poor

quality, but quality demands substantial appropriation that only
few could afford.

Under the present trend where house rental increases at an
average of 10 percent every year,prospective homeowners are being
forced to embrace the neck-deep agony and burden of long term
installments. To a family of average or below average income, a
house and lot is considered as a fulfillment of their aspiration
regardless of its quality and cost. Unfortunately, that fancy
house beautifully painted, deteriorate faster than the 20 to 25
year term to pay the monthly amortization of the loan.

Numerous homeowners were disappointed when their dream
house were blown up by typhoon because of poor quality and
under sized lumber used in the construction of the roof framing.

To · those who are planning to construct or own a house, it
would be better to reduce the floor area of the house rather than
.sacrifice the quality through the substitution of cheaper and poor
quality materials. It is therefore important to select good quality
of lumber for your house framework.

215

11 - 2 TYPES OF ROOF

There are several forms of roof and numerous variety of shapes

that one has to be familiar with:

1. Shed or Lean-to Roof 8. Gambrel Roof

2. Gable or Pitch Roof 9. Ogee Roof

3. Saw Tooth Roof 10. Mansard Roof

4. Double Gable Roof 11. French or Concave Mansard

Roof

5. Hip Roof 12. Conical Roof or Sphire

6. Hip and Valley Roof 13. Dome

7. Pyramid Roof 14. Butterfly Roof

Shed or Lean-to Roof- Is considered as the simplest form of
roof consisting of one single slope.

SH£1> OR LEA II - TO

Figure 11 - 1

Gable or Pitch Roof- The most common type and economic-
al form of roof made of triangular sections consisting of two
stapes meeting at the center of the ridge forming a gable.

GAll£

Figure 11 • 2

Saw Tooth Roof- Is the development of the shed made into

a series of lean-to roof covering one building. This is commonly .
used on factories where extra light is required through the window
on the vertical side.

216

$Alii l'OOTH

Figurell-3
Double Gable Roof: -Is a modification of a gabfe or a hip and
valley roof.

Figure 11· 4
Hip Roof: - Is also a common form used in modern houses

having straight sides all sloping toward the center of the building
terminating at the ridge.

HIP 11001'

Figure 11 • 5
Hip and Valley Roof:- ls a combination of a hip roof and an
intersecting gable roof forming aT or L shape.d building. This type
.of roof form however, has a variety of modification which are not
illustrated.

217

1+1" 4110 VAI.I.I't

Figure 11-6

Pyramid Roof: ts a modification of the hlp roof wherein the

four straight sides are sloping towards the center terminating at a
point.

P'tltAMtO

Figure 11 · 7
Gambrel Roof:- Is a modification of the gable roof with each
side having two slopes.

Figure 11-8

OGEE Roof: - Is a Pyramid form having steep sides sloping
to the center.

Figure 11 • 9

218 .

Mansard Roof: - Where the sides of the roof slope steeply
from each side of the building towards the center forming a flat
deck on top.

MAII$AIIO

Figure 11 • 10
French or Concave Mansard Roof: - Is a modification of the
Manzard Roof where the sides are concave.
Dome: -is a hemispherical form of roof usually used on ob-
servatories.
Conical Roof or Sphire: - Is a steep roof of circular section
that tapers uniformly from the circular base to a central point.

FR£NCH OR COMCAVE DOME
MAMSARD ROOF
Figure 11 • 12 .
Figure 11 • 11

Figure 11 · 13

219

Butterfly Roof: - Is 1 two shed roof where the slope meet at

the center of the building.

IUTTEit,LY

Figure 11 • 14

11 • 3 TYPES OF ROOF FRAME

The three types of roof frame commonly used are:
1. Rafters Type
2. Truss Type
3. Laminated Type

The various kinds of rafters for roof construction are:

1. Common Rafters
2. Hip Rafters
3. Valley Rafters
4. Octagon Rafters
5. Jack Rafters

Common. Rafters: - Are rafters extended at right angles from

the plate or girts to the ri~ge. ·

-Uf'IOI

Figure 11 • 15
220

Hip Raften: -Are rafters laid diagonally from the corner of a
plate or girts to the ridge.

Valley Raftan:- Rafters placed diagonally from the plate or
girts at the intersection of gable extension with the main roo"f.

Jack Rafters: -Any rafter which does not extend from the
plate or girts to the ridge.

Jack rafters are classified Into:
1. Hip Jacks
2. Valley Jacks
3. Cripple Jacks
Jack rafters framed between hip rafters and girts are called
Hip Jacks. The frame betwMn the ridge and valley rafters are
called Valley Jacka, while those frames between the hip and the
valtey rafters are called Cripple Jacka.

Figure 11 • 16
Octagonal Raflars: - Are rafters placed on an octagonal
shaped plate at the central apex or ridge pole.

221

OCTAGOHA~ RAFTERS

Figure 11 - 17

Trust: -Truss is a built-up frame commonly employed on a

long span roof unsupported by intermediate columns or partitions.

Truss is a design of a series of triangles used to distribute load,

stiffen the structure and flexibility for the interior spacing as welt
as strength and rigidity.

The different types of trusses are:

a) Light trusses {trussed rafters)
6. l! story frame
1. Pitched Truss

2. Howe Truss 7. Utility

3. Scissors Truss 8. Flat

4. Raised Chord Truss 9. Bowstring

5. Sawtooth Truss

b) Heavy Trusses 6. Cambered Fink
7. Saw Tooth
1. Howe Trusses
2. Belgian Truss 8. Flat Pratt
3. Fink Truss
9. Flat Howe
4. Pratt Truss
5. Scissors Truss 10. Warren

Gir1J- Is that structural member that supports the rafters or

trusses of the building.

Collar a..n - The ties between rafters on opposite sides of

the roof.

. LIGHT TRUSSES
~ ~

I'IT~M!D HOWE

S CISSORS IIA IS£0 CKOIIO

IJliLl TY

80WSTR IIIQ

HEAVY TRUSSES

~'·" · '-·~m. ~~
~9.00-2..,.0Qm .•

MOW£ TIIIISS at:LGIAM

~-mom ~
9 .00- 11·0011\ . ...

I' I IIX PRATT

~-"l.so-ao.oom.

~ 7.so-2.o.oom.

S~ISSORS CAMBER£0 FIMK

WAitllt:M FLAT HOWE
SAWTOOTH
-s.oo-ta .oom. ~

9 .00 -·2~.00 -l~--~-....;ll.-.....li<......---"~C;--.¥..--'

FLAT I'llAT T

Figure 11 18

223

Purlins - The structural member placed on top of a rafter or
top chord of a truss that supports the roof sheating.

TABLE 11·1 PURLINS SIZE AND SPACING

Span Size Length Spacing
of Roofing of Purlinslm}
2.00 2X3
3.00 2X4 6' .75
3.50 2X6 .60
4.50 2X6 7' .70
. 5.00 2X8 8' .60
9' .67
10•
.67
12'

TABLE 11-2 PURUNS SPACING IN METER

Length of Roofing Distance of End
· sheet Purlins Lap

1.50 .60 .30
2.00 .57 .30
2.50 .55 .30
3.00 .68 .30
M
1~ .62 ~
.60
4.00 .67 .30
4.50 .65 .30
5.00 .63 .30
5.50 .30
6.00 .30

Note:

The phasing- out of the English measure might affect the
present commercial width and length of the roofing materials
particularly the G.l. Sheets which are common and popularly
used in most construction work.

224

It is most likely that the length will be made to an increment of
.50m of which corrugated G.l. sheet will start from 1.50m to

6.00m long or more.
Consequently, this new length will govern the spacing of the ·

purlins. Table 11-2 is presented in anticipation of the new spacing
of the purlins if roofing sheets are manufactured in accordance
with the new Sl measure.

11 - 4 TIMBER FRAMING FASTENERS:

Nails -There are numerous variety of nails to meet the needs

of all kinds of constructin. They maybe clamped wit. : respect to

shape. Nails are either cut or wire. Cut nails are rectangular in
shape directly cut from a metal strip, likewise, w ire nails ~re com-
mon nails with circular cross sect ion which are cut directly from
wire.

With respect to service, nails are classified as common, flooring,
finishing, roofing, boat etc. Fasteners for timber framing usually
specify the use of common nails.

TABLE 11-3 COMMON NAILS FOR TIMBER FRAMING

.Desig"lat ion Length (em.) Lateral

6d 5.0 Diameter (mm) , Resistance per
10 d nail (kg.)
20 d 7.5
30 d .29 24
40 d 10.0 .37 40'
50 d 11.5 .52 45 - 75
60 d .56 68 - 88
12.5 .65 80 - 102
14.0 .66 113 - 121
15.0 .72 100 - 146

If nails are driven parallel with the grain, the lateral resistance
should be decreased by 25 to 33o/o.

Wood Screw - Are used to avoid splitting and injury to the

wood and to obtain better fitting and ease of disassembling when
necessary.

225

Screw should not be spaced less than 3 em. across the grain
and not less t han 5 em. parallel with the grain. For hard wood,
spacing should not be less than 4 em and 6 em respectively.

TABLE 11-4 SAFE LATERAL RESISTANCE·OF SCREW

Gage of Screw Safe Lateral
Diameter (mm) Resistance per screw (kg.)
•6
3.5 37
8
10 4.1 50
12 4.8 71
14
16 5.5 93
18 6.1 116
20 6.8 143
22 7.5 173
24 8.1 205
26 8.8 . 239
9.5 278
10.0 318

Lag Screw - Is used in fastening large pieces of t imber under
heavy stresses. The diameter of the lag screw vary from 6 mm to
25 mm and the length from 4 em. to 30 em. Lag screw is pre-
ferred where bolts are difficult to install.

drift bolts

CJ=;=Ot
. bolts
Figure 11- 19

Bolts -Are the rnost popu lar for fastening timber joints with
small or big stresses. Bolts in roof framing are classified as:

1. Common, Ordinary or Machine Bolts
2. Drift Bolts
3. Strap Bolts
.4. U-Bolts
5. Eye Bolts

226.

Drift Bolts and Dowels - Is a round or square iron or steel
with or without lead or point of specified length. Drift bolt is

driven into the hole of the timber with a diameter 80% smaller

than the bolts and the minimum diameter is 20 mm. This will
prevent the lateral .movement and separation parallel with the

axis. On the other hand. a dowel, which is thicker and shorter

than the drift bolt only prevents lateral displacement of the con

nected parts. Dowel is either iron or wood pin extended but

not through the members of the structure to be connected.

The disadvantages of dowels ara:

1. It does not provide a rigid joint
2. It is totally damaged if repair calls for defective lumber.
3. It is hard to replace.

Wooden Key - Is made of a piece of hard wood, rectangular ..

in cross section inserted between two lapping pieces of lumber
intended to prevent sliding of the adjacent members.

The keys are parallel or inclined as shown In the following
figures.

Inclined Key Split Ring

m

LIJ

Pins Shear Pins
Figure.ll-20

Shear Pins may be of hard wood, steel bars or G.J. Pipes.

227

1. (O$t 1ron robbed wo~hers 4. Cost iron O.G. woshtr5
2. Ma lleable i ron washers
3. Square steel plate washers 5. Bevelled cost iron washers
6. C irculor pressed steel wo~ers

Figure 11-21

Plate washers are used under the head and nuts of the bolts
to prevent the heads and nuts from damaging the timber when
tightening the bolts. The washer also provide sufficient bearing
area. The thickness of the washer should not be less than 1Jz of
the bolts's diameter plus 1.5 mm.

TABLE 11-S* BOLTS AND WASHERS THICKNESS AND
NlT lURING AREA NET BEARING

SIZEOF BOLTS DIA OF WASHERS THICKNESS AREA

Inches mm Inches mm Inches mm in' cm2

a! 12 e2 ~ 15.0 A 12 3.78 24.3
16 3 /.5 16 6.76 :34.6
50.6
i 19 3 ! 8.0 ~ 19 7.86 76.0
25 4 10.0 A 22 11.79 96.0
1,IA 28 4 ~ .11.5 1 A 28 ]4.91 118.5
~2 5 1~.0 1 l 171.0
32 18.41

1~ 38 6 ]5.0 1 i 38 26.50

* Materials ore wrought iron (W.I.l and Steel Rod

11- 5 INTERMEDIATE JOINTS

Joints must be within the center lines of the member meeting
on a common point so as to prevent rotation at the joints.

As much as possible, wood joint should not be used to coun·
ter act tension forces, unless, steel strap, g..~sset plates with bolts
are employed.

For structure with smaller stresses, wood connections shall
be provided with dapplng or notching the strut to the adjoining

member using dowels, lag screw or nails to keep the member in
the design position. On the otherhand, for structure with large

stresses, metal bear ing plate, or casting side plates, bolted con·
nect ions or bearing blo~ks shall be-specified.

228

Pocket jolntt that collect moisture should be avoided, all

joints 1h1ll be kept aligned as simple as possi ble for ease in the

carJ)4tntry work.

IIOTCHINO or 0APPING 8\JTT B\.OCIC

Figure 11-22

When. a strut is at right angle with the top chord, 1·19 mm.

dowel or 16 mm. lag screw is employed to hold the strut in
place. When the strut carries large stresses, the follow ing joints
can be used.

L Butt Block or A ngle Block.
2. Steel S-shaped Bearing Plate
3. Cast Iron angle solid bearing block
4. Cast Iron angle bearing block with a web

Butt Block - Is made of hard wood wit.h the same th ickness

as the top chord. The length of the block should be adjusted to
fit all possible conditions and interference with other connect ions.

Steel S-sheped Bearing Plate - The bearing plate should be

the same width as the top chord.

ST[EL S · Bf~AR IN G PLAf£ , .\•.•

Figure ll-23

229

C•t Iron Solid Bearing Block - The bearing -block is solid and

covers the whole width of the top chord casted at holes not less

than 16 mm thick provided with a lug into the top chord.

C. I . SOl.lO 8EARII'IG BLOCK

Figure 1 1 -25

Cast Iron Angle Bearing Block with a Web - Should have a
minimum thickness of 25 mm.

C.l . AMGLE 8EARII'IG &LOCK WITH A WEI

Figt,Jre 11-26

Center Joint of Howe Truss- This type of joint is provided
with a butt or angle block at the center intermediate joint.

•

Bull or
An gle 8 \ocll .

Figure 11- 27

Peak Joint- Has various types depending upon the design as

shown under tf1e following illustrations: ·

230

hollow cast
with collar plate solid cast Iron block Iron block is used

Figure 11-28

11 - 6 END JOINTS

There are five typas of end joints

1. Pinning the top chord into the bottom chord.
2. Notching the top chord into the lower chord w ith bolts.
3. Using bent strap or shoe plate with lugs or flats.
4. Using the side plat es with flats or tables.
5. Using malleable cast iron shoe.

1. Pinning the top chord into ·the bottom chord is the

simplest form of end joints employed on small structure.

. Bottom Chord
Machine. 'aoH"-

flg.fl-27

2. Notching the top chord into the lower dtord with bolts

are of the following types:
{1) Notching with bolts.
231

8 OIIOift Chord

2, Notching with bolts with wood key

3. By the use of bent strap with lugs or flats.

4. By the use of steeel side plate with flats or tables riveted
to the plates.

Figure 11-SO
232

5. By using Malleable cast iron shoe

Figure 11-31

11 - 7. SPLICING:

Splicing is the process of joining two pieces of timber in their
longitudinal direction in order to transmit stresses from one
membef to another. Splicing are of three different ways:

1. By Lapping

2. Fishing
3. Scarfing

Lapping- Is simply by joining one. member on the other.

Fishing - Is by joining two ends with the use of two side
blocks sometimes called splice pads.

Scarfing- Is by cutting away the opposite sides of two mem·

bers then lapped to obtain a continuous piece of uniform
thickness.

The common types of splicing tension memben are:

1. Bolted wooden fish plate splice
2. Bolted steel fish plate
3. Wooden tabled fish plate splice
4. Shear pin splice
5. Steel tabled fish plate
6. Tension bar splice
7. Timber connector splice

233

BOLTED WOODEN FISH PLATE SHEAR PIN SPLICE

BOLTED STEEL FISH PLATE STEEL TAB.LEO FISH PLATE

WOODEN TABLED FISl11'LATE 1:: ~~~ ~:1~

llt...:tJ =+ll

TIMBER CONNECTOR SPL\CE

A

....._.< g. ....!L:

2

~ ~d
-.....4 II
~ ~ ..d...

2.

...~.-...._.d.__.....,, I 1 -~ .I
HALF LAP
BUTT JOINT 08Lf0UE ICARF.

SPLICING COMPRESSION MEMBER

Figaue 11-32
234

11-8 OLUED LAMINATED LUMBER

Structurally glued laminated wood is a stress rated product of
timber produced in laminating plant from selected wood securely
laminated and bonded together with adhesive. The grain of the
wood are mostly longitudinally parallel with each other forming
any length and bent to curved shapes during the process of gluing

the lamination. Thickness should not exceed 5 tm. net. When
bending radius that is too sharp to permit the use of 5 em. thick
lamination, a nominal thickness of 2.5 em. lumber is usually used.

the various forms of laminated structures are:

1. A-Frame 7. Tudor Three Hinged Arc
2. Gothic 8. Single Tapered Straight
3. Parabolic 9. Double Tapered Straight
4. Radial 10. Double Tapered Curve
5. Three Centered 11. Pitched
12. Double Tapered Pitched
6. Straight 13. Curved

n GOT HIC TUOO ~ s-Mo K~ O UCII.
ST U IGHT
r: 1

OOUet.£ TA'EUO • $TAAIOT

tltACtA L.

Figure .11-36

23.5

WOODEN HOWE ROOF TRUSSES
(sizes of members)

TABLE 11-6 4 PANELS

TRUSS TOP CHORD BOTTOM CHORD DIAG. VERTICAL
cB.C. A 8
SPACING T.C.

in meters

1.50 3x4 5M SPAN 12 mm 12 mm
2.00 3x5 12mm 12 mm
2.50 3x5 Jx4 2x2 12mm 16 mm
3.00 3x6 3x4 2x2 12 mm 16mm
3x5 2x3
3x5 2x3

6M SPAN

2.00 3x 6 3x5 2x3 12 rnm 12mm
2.50 3x6 3x5 2x3 12 mrn 16 mm
3.00 3 x6 3x6 2x3 12mm 16mm
3.50 3x8 3x6 3x3 12mm 16mm

7M SPAN

2.50 3x8 3x6 2x3 12mm 16mm
3.00 3x8 3x6 3x3 12mm l.6mm
3.50 3x8 3x6 3x3 12mm 19mm
4.00 . 3x8 3x6 3x3 12mm 19mm

236

TABLE 11·7 6 PANELS

TRUSS TOP BOTTOM DIAGONAL VERTICAL
SPACING CHORD AB
in meters c DE

mm mm mm

2.50 3x8 3x6 2x3 3x3 12 12 19
3.00 3x8 3x6 2x 3 3x3 12 12 19
3.50 3x8 3x8 2x3 3x3 12 12 22
4.00 3x8 3x8 2x3 .3x 3 12 12 22

9M SPAN .

3.00 3x8 3x6 2x3 3x3 12 12 19
3x8 3x3 12 mm 12 12 . 22
3.50 3x8 3x8 3x3 3x3 12 12 25
4.00 3x8 3x8 3x3 3x3 12 12 25
4.50 3x8
12 19
10M SPAN 12 22
16 22.
3.00 3x8 3x8 3x3 3x3 12
3 X 3. 3x3 12
3.50 3x8 3x8 12
4.50 4x8 4x8 3x3 3x3

237

TABLE 11-8 B PANELS

TRUSS TOP BOTTOM DIAGONAL VERTICAL

SPACING CHORD CHORD A Bc DIAMETER mm

in meters X y z0

12M SPAN

4.00 4x8 4x8 3x3 3x3 3x4 12 16 19 28
4.50 6x6 6x6 3x4 3x4 4x4 12 16 19 28
5.00 6x8 6x6 3'x4 3x4 4x4 12 16 19 31
5.50 6x8 6x6 3x4 3x4 4x4
12 16 22 31

13M SPAN

4.00 4x8 4x8 3x3 3x3 3x4 12 Hi 19 28
4.50 6x8 6x6 3x4 3x4 4x4 12 16 19 28
5.00 6x8 6x8 3x4 3x4 4x4
5.50 6x8 6x8 3x4 3x4 4x4 12 16 22 31
12 16 22 31
4.00
4.50 14M SPAN
5.00
5.50 6x8 6x6 .3 X 3 3 X 3 3x4 12 16 19 28
6x8 6x8 3x4 3x4 4x4 12 16 19 31
6x8 3x4 3x4 12 16 22 31
6x8. 6x8 3x4 3x4 4x4 16 19 22 41
6x8 4x4

238

TABLE 11· 9 2 PANELS

TRUSS TOP BOTTOM DIAGONAL VERTICAL
SPACING CHORD CHORD A
in meters Xy

Diameter

1..50 3x5 3x5 2X 3 2x3 12mm
2x3 2x3 12mm
2.00 3x6 3x5 3X'3 3x3 12mm

2.50 3x6 3x5

TABLE 11-10 3 PANELS

TRUSS TOP BOT:T'OM DIAGONAL VERTICAL z

SPACING CHORD CHORD A B Xy

(in meters) Diameter

4M SPAN

1.50 3..x4 3x4 2x3 2x 3 2x3 12mm 12mm
2.00 3x5 3x4 2x3 2x3 12 12
2.50 3x5 3x4 2x3 2x3 2x3 12 12
2x3
2.00
2.50 5M SPAN
3.00
3x6 3x5 2x3 2x3 2x3 12mm 12 m!_n
3x6 3x5 2x3 2x3 2x3 12 12
3x5 2x3 12 12
3x6 2x3 2x3

239