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wt
 
Yesir-n and Construction
of

Mowe or “nzrlish xoof Truss

4A Thesis Submitted
to
The Fraoulty

Wehigan jgrioultural Colleze

by

Je Vhe Jarx Ae te 3roun

Caniidates for the e-ree of

B3achelor of calence

June 192
THEs.s

CO \ 4 \
 

 

102716
 
Preface

The problem preecentod in the followin: pres snows
tro method of procodure that «cs ecarrird ont in the de-
gi-n nnd oonstruction of nan “Enclish roof trucos”, some-
tines referred to na an “Hove so7f Truca’e The model
we oulit for the nurnove of nasistin: the future ine
struction in Cranhico Statice in the Civil Un-sineering
Departuent at tho ffehiznn Asrioultural Colle :e, and pere
haps mniy be found ugeful in any other «ork that deals

Vith etreeses in tru:3 members.

*rom a peycholovical otrnipoint, a student vill
more ren iily undorstanl the rrinoiples involved in the
oonstruction of mn roof truss, if he bas the truss itself
Glearly in mind. It is nlso honed by the authors thet
the model 111 be of e2me value to the eoallecrc snd the
Civil enctinecrin’ erhibits to cn-vect ta the vicitor the
scone of at least one branch of the olivil en:sinecring
Lurr Lon Lue A model is more attractive ts the averare
initivilinal, that is he onn nowitre more kK owle:-e in ree
vyerd to roof trusses in one -lnance at the model than

he oould by tryin: to utuly a dr-win’ or books.

All the work on the model such as nrkine Loop
roda for the lower chord, nll oarpenter -ork, otoe., ws

performed entirel; throu ch our own eflvorts, there? y
turnin, the ork into a practical problen in design
nnd conetrvnoetion,
The nuthors sre very much iniebted to Srovfacsoar
de 4, Vedler for the valuna:le sacsietance offercd durin:
the crdourse of the work, slno to the -lechanical Unvinceriiz

Jepartient for the nse of thechopae
Introduction,

A Bimple bent may he used for an rafter of a
common roof, but “hen the enan of 2 roof is Lon: it
heoones neaecanry t> join covernl membere torcther
end form a trucse A truss fy defined sa = jointed
structure whioh is arranved to onarry loade in such a
manner th:t each priscipnl member fe eubjeat to etrecs
only in the ifrection of ites len th, that fe, to a
tensile or . compreccive streso. Fionure I rorrerents

the aimplesat form of a roof trues.

C

a b

Fisnre I.

 

In order that ao truse may perfectly conform to
the above definition it ie negevonry that the loadsa
should be supported only at the joints, for flexural
streases VALL reunlt if they nre ninced at other pointe
on the ‘sombers. The elementnry fivurce ineluded bee-
taco n the truce members a-e trinn les, ns te noticei
in the model, beonurvs a trivn:le oannot chnnre the ennpe

without alterins the lenzth of its sides.
wombers «nioh area in esanreccion mre anlledl
"strecte", “soluans" or “poots” vwnile those “hich mre
in tension are enlled "‘tecon’, 410) Nre srietl os
referrei to ac "Ais comele” ani "“vertienle" in a roof
trusce In *ivnure I the upper menbers a C and C Dd are
in commprervsion and are eslled "upper chord”, while
tre lover mendber « b are in tenestion and are celled

the “lover qhord"”.

A simple truc: is one wiich ia supported at its
eniao nnd whieh under vertionl londe bri:.:c only ver=
tisal pressires on the eupnortere It must be revaem-
hored that in ga roof truss desicn, that all the forees

meetin: at any joint must be in eqiillibriunz,
 

 

Loads on hoof Trusses

There are four kinds of lovds to be considered
in roof trurs derizn: the welcht of the trugs itself,
the weirht of n roof eoverinz, the snow, and the wini,
The wetzht of roof coverin,: and trusa ie called the

"dead londi's

For the thooretical wet.cnt of the truse, the
followin. ompirical for’mla maz be uge.l

“8 bal (1 + 1/10 1}

‘7 @ approximate weight of one truss in lba,
1 ®# span in fect

a ® dletnnoe between trusses
 

 

YELLE SY
= (oe 0) to lele AY,

IIWVIG LOVXZ

cathhilslelak Qiu bE HED LS

 
Conclusione

Jue t9 our inability to eceure the exact sizes
9° model materinls fro:n the cdllev’e or near-by BLOres
Gone slicht devarturce hai ts bo ‘inde fron tne intended
aanterilals and exact vonle rednuotirne ithe model should
be to one fifth ecale and as it stands -e think it

411 serve tne -urpose aleyuntely as inteniede

Solos ave ted skatehes showin: hat the exact sizes

ane

of members should be and what we made them,
Page 1

Yesgi-mn and Construction of a Howe s.sof Trusea,.

BAIS

Jeni

(3

eunelpe--8 10 Lect
liLgqgeu-=82)0 foet

Spaneo-ee80) feet

if 9 eis

¥rom “etchungs “Steel A4i11 Sulldinzsa", we
find that slate of 3/16" thickness is oon
monly used, the aizoe being 6” x 12".
Therefore ve will use this size *ivinz a
woleht of 7.25 Lbs. ner sanare foot. Voing
nm Slap 5.3 shin-vles are required for 190
grsunce Teate

Sheathin.:, purlins snd rafters will be made
of yellow pine which velvhts 4 lobe per
hoard foot.

For the weit.cht of the truss a formula from
derrimane “xoofe and Bridges” will ve used.

. « € AL (1+1/10 4).

' & the totnl weiszht of one truss in pounds.
A a the iLoetonce betvecn crijncent trusses in feot,
Le the enan of the truss in feot

The tension verticals ani the lover chord shall
be of stoel, Vee nn vallovable workinyz stress
of 1200 lbse per cymara inche

sherithin: and rrefters chnall be of short leaf
yOllow plc@e

Vinsonnle, purling ani tne upper chord shall

be of lon. lenf yellow pine.

ane etresges ueed shall be those reconnendiad

by the Acuwetehde For Hull@in s. (see Carne.-le
Handboon, parec53, )

fruesea are not space: levs than 10 feet apart,
anid for o trues of thie vpan 20 feet can be
considered an 290d enaain:. Jata collected
from "Ketohum's Steel 411 Buildi re".
22 2@ 2

=
ct

Accordin: to Verricen's 's2.0f8 cnd Bridres"
Vole 1, tho maximum sno. lod for this
Latitude shovld be rndout .f Los. per eruaro
foot on horisontal rrojeation 2% roof. The
mintnun ond lonwd woulli be about 10 1h,
ner sounre f90t on horizontal erofjection

on roof.

For a maxima vilne ase that ziven by sucheina,
Huttons or the Straicht Sine formulae.
2nrts shall be vronortioned for the -rentest
stress as viven by the follovin: con -inations.
(1) vend Lond Inaimiad Snow Gonde
(2) Jer Gord ind Goad finkawa Cnow Londe

xsenetions

Note:

Wor the ind “Sond the horizont:1 econponents of
the renetiona chall be taken eqnale

‘nar roofine folt chnll be Inid between elnte
ant shenthin: to aeelet tn mecing the roof
watorproofe
Cae TOAD Ig

Bo ATUL
Assume rafters <= 24" geca,
Deed Lond

 

wlnte “ 7.25 lbs. per sruirc Lodte

Shenthing <' 4 lbse per siunre fo0te
Slate Potal © 11625 lhe. per erwre £30t65e
heathing

rafter

     
  
  

Snoy Goad (max imun)

eS 2s 13.7 lbda,. MY D6 ft. (roof surface )

(rmindterza)
purtin O0.0 92 LJe Tee Yedd Lhee per oqe fte (roof surface)

truss

“ind Lond .
? « e 04 Ie 004 x 6400 w 2506 Lbe per Ete ft.
(vertical curfaoce)

Jn inclined surface voucheime 19 lss. per S846 fte
Hutton @ 14.8 lbs. per te Pte
Stroicht Lines 14.8 " " " "

Note: For Vi itn the forcmln above n vind v looity of
8) milee per hour is ssgunci. the w:lne of
the sind prec:sure on inolincd curface by the
three forvulee avove is obtnined from a craph
in JInlcobm's ‘“srepnio otaties” on prve 74.

Let b» brendth
fotal Lond @ 11625 + 19.7 & 29.97
11.625 + 9.55 + 19 S 40.1
say 40 lLba,
Aceume b & 12”

hae 2 - (2 2 1650)

4° we 6x 40x 4x18 «© 0685
8x 12 x 1650

Q@e i ,26"

 

Try rafters epaced + 4 feet o-c,
dee 6x 49 x 16x 12 = 274
8x 12 x 1650
de .52"

 

SB OI GHUAGHING ON oBACH Lo A ° TO o.
 

Desicn rafters allowi>s2 1%" notch over purlin.
44.7 fect is the lengtn of roof from point to co.nice.

“pace purlins 44.7 . 11.2 feet nnd desivn rafters
4 nocordinzlye

Agsiuue ae” x 8" rafter

Joad Load
2 feet of shenthins on each side of rafter ives
4(7.23+4) + ste of 1 Poot of rafter
4(7.254 4) + 4,38 @ 52.33 lbs. S1SP 4 Li..enar LY) ote

Snow Lond
4x 17.9 » 71.6 lbs per linenr foot. (maxis)
50, Of 71.9 @ :5,3 loBe per Llinenr foot (ini:nnmn)

Wind Goad
4x 19 es 76 lbs. per Llinenr ft
05 = 7126 @ 164 lbs. ver line r foot

any 164 lbc. ver Linenr foot ne total load.

bi” = 6 x 164x122 x12 » 111.8
x 160

be 2
ies 05.9
ds 7,5"
7.0" 1.5" 2 yn
Try a 2" x 10" rafter

4(7.25+ 4) + 6.64 @ 64.6
54.6 t+ 7626 + [909 w 166.4

say 167 lobe. per linear fot os total load.

bd= » ? 0 2 2 113.5
3 x o

b.2 2"

d-a 56.7

4 @ 7,82"

7652"+ 1.5” 2 9,92"

" for RAST AS

 
a JGGIRS

design purlins nllowinz: }" notch over trucse
Span e 20 feet.

apap fe

 

 

 

 

 

 

a
b. 20-0"
aP 2P

Pw 166.4 x lif w= 184)
woment avont center a0 nurlin

‘oe FE x LO = Ge 82 ew LAL
Ma 12 x 1040 & 52100 ft. lbs.

assune a 6" x 12" for a nurlin
weiczht per foot e 24 Lbs.

ae os 24 x £0 12)0 lbse
22100 1200 x 6 212 a*
1930 x 6

d - 12
12 +1.5 @ 15,09"

fry sa 8" x 12" tinder
weizht per foot s S32 lbs.

 

USE 8" x 42" for cr uINs

 
“agzeé

vey @ a tye at os PT Wy
mwoil wba. 3 ae kh Sisk

wae eA (1+ 1/102)
we x 90 x 80 (1 2 )
we 800 x92 72)0 1Lbae

“elcht per panel = 900 Lbs.

LADS

See 8 ogee
a a ‘
A + 1d wa  2.4in fb

maa,

23) Ta DJAG
“eizht of slate sg 7.25 x 990 x 1162 o
“elcht of eherntning »© 4x20 x 112
“eight of rafters = llee xX OX Oeo7 &

Velrnt of purlins © 2 x PQ

“elrht of trues

LJ. eid wVJAD

ot °F ‘abag
af id J .

Jaximnum e 20 x 10 8 20 » 4000

16235 1bd8-
396 Lbs.
575 Lbse

3s 640 lbs.

ws 990 lbs,

we 44356 lba.

lbse

dinimum =» 10 x 10 x 20 » 2000 1lbe.

Lato LOAD

10 x lle2 x 20 = 4200 1bdae
ae DD ie 2

a OPM MP yee tt . - yy TF Th t rps
oD) 1h, ius o~ D's I ein Sis bee woe » . \ re

lez The strece is zero but we vill uso m2 1" upeet rouni bar,
with eye at one end to connect t29 Lower onorde

S@-4 Lax, stress 54/0). 2438 = e403 8qe ine
£90
Jge a 1" unsot round bar tie srme nz for verticenl l-2,

om-6 cing, Btrecs LL. L135) 2 eJER eq. ine
12309

Ise al 1/8" upset rovusid bar with eve at one ende

£0 v0 = eel Bde ine
LED

Tse a 2?" upset round bar with eye nt one end.
for symnetry the corrernondin.: ‘nembors gn the other half
of truss wlll havo the er316e sl2e semnberd.e

7-8 «tax. Stress 261v).;¢

   

 

 

We enn ke)
Jax, stress 6990.6 PY _ 900
A
A ._ 69950 — 77.7 s:.ine gay 3 x 10%.
~ 30
2? . 1980 (1 ~ 43 — ) = 1950 x 2724 = 1410 allowable,
a 60 x 8
2200 = 825 actual
30
Assume 2 . 1200
AwdSe2 say 3" x 8"
B < 1950(1 -les_ ) = 1410 allowsble
A x
69950 = 1999 actual
4
Use 5" x 8" plus 2" for .dtonin., «ances {t a B" x 10%,
GO) 2.33 CH bw
Wix, etress 66050#. Length o-o of aya 1f0",
360609 = ed 8 le ine
2)

Use 2 loop bare fre e9ine- 7/8"
dembere Yl, Y2, Yl, Y14

Aembers Y4,6,%,11 use 2" loop bara.
Diameter of pin 1 1/38 "
Page 8
WLAG Qa dG JjaP
Jax, stress 12600 ven.th 11° 2"

ASEUNG + = L209

As 6)0 . Wed 8 teins eny 3” x 4".
120%

BY 2 lyc0(lelto) 2 vod x 285 = 507 allowndle
A 6UXS

12609 = 10590 actual
2

Assume _«< . 900
“A

 

Ao1?P650 2. 14 oqeine say 4" x 4"
YQ

Po 21950 (1 - = 1950 x 245 = 875 allo-inble
“4

£690 e 738 setual Jce 4% x §"

1

DIAGORAL 4@5

4nx, eatrees 15433 Lenzth 14° 3"

Assume 2 = 70

A
A~J]89985 = 2208 Soe ine say 4" x 6”
790
@oe lyod (1-169 ). 575 allovndle
nN , 249 :
389 = 665 notunl
2

Agsume ¢ — oO

A = 10535 = we BY. ine GNn77 4" xX 23"
030
2 = 1990 (1- 469) 975
A 240

$9985 = 500 actual
Oe
Use 4" x 8",

OITA aJTAQ 6-7

 

Jax. stress 20125 Len th 13!
Arvsume 2 = 600
A
A PO1L§ Jed B9eLNe gsnv 6" x 6"
= “G00
poe 10d (12 oe 6) = 600 allovable
A 60%
£20125 s duy actual
36 ‘J
 

8Gi ds ba a

£2 verticnla 1" 6° y” 32 1bse
2 " Ll" 41’ 2" 60 "
2 " 11” 16° Oo" 108 "*
2 " Ye" of 9" S53"
& dinsonals 4" x 5" x 15%" 23 "
p " 4" x 4" x 1O'y" 115—"”
2. " 6" x 6" x 17°6" 464 "
Urner chord 3" x 10" coekQ. ©”
Lover chord .°" loop bara lza "
7/8" loop bars 195 "*
Srlices 4 "
An-’le Irons 70 ="
Bolts, pins, ~. shere nnd hlocks 175”

Total woicht of truss 4507 1lbda.

Theoretianl weirvht -= ZJ0 lbae
   
Py
- we —
Oe EAS SR

 

 
Use

mS) PI AAS