enhancement program timber design

7/23/2019 Enhancement Program TIMBER DESIGN

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TIMBER DESIGN

NSCP Specs:

Compression at Angle to Grain:

The allowable unit stress in compression at an angle of load to grain between 0 to 90 shall be

computed from theHankinson Formulaas follows:

2 2sin cos

pa pe

n

pa pe

F FF

F F =

+

In which Fnis the allowable unit stress acting perpendicular to the incline surface, Fpais the allowable

unit stress in compression parallel to the grain, Fpeis the allowable unit stress in compression perpendicular to

the grain and

is the angle between the direction of the load and the direction of grain.

1. (CE Board May 2012)The truss shown in is made from Guijo 100mm x 150mm.The load on the truss is 20 kN. Neglect friction.

Allowable stresses for Guijo!om"ression "arallel to grain # 11

$%a!om"ression "er"endicular to grain

# 5 $%a&hear "arallel to grain # 1 $%a&hear longitudinal for joints # 1.'5

$%a

a. (etermine the minimum )alue of x.b. (etermine the minimum )alue of * in mm.c. +hat is the axial stress on the member A! in $%a,

NSCP Specs:

SEC. 3.3 SIZE OF STRUCTURAL MEMBER

Sies of lumber and structural glued!laminated timber refered to in this code are normal sies.

"omputations to determine the re#uired sies of member shall be based on the net dimensions $actual sies%

and not the nominal sies. The rough sie of lumber shall not be less than the nominal sie and the reduction in

face dimensions of dressed lumber shall not more than &mm of the nominal sie.

2. A timber beam ha)ing a sim"le s"an of 'm carries a total load including its ownweight of 10 kN-m. t has a width of 200mm and a de"th of 2/0mmm used dresseddimensions b* reducing its dimensions b* 10mm. The wooden section is made u" of0 grade A"itong. (Use table on fgure TM-6)

3. A beam is to be loaded with a uniforml* distributed load kN-m throughout the 5ms"an the following data are gi)en

Allowable bending stress # 2' $"a

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Allowable shear stress # 1.2' $%aAllowable de3ection # 1-2'0 of s"an$odulus of elasticit* # 1/00 $"a+t. of wood # kN-m4

f the width of the section is 100mm determine

a. The de"th considering bending stress.b. The de"th considering shear stress.c. The de"th considering de3ection.

4. (CE board November 2011 !e"ember 201#)To retain the backll as shown treatedtimber "iles braced b* hori6ontal struts with a de"th of 400mm are anchored to bedro""ed at 4m s"acing. The "iles are considered hinged at the base. Allowablebending stress and shear stress are 1'.7 $%a and 1.' $%a res"ecti)el*.

a. +hat is the design moment of the struts,b. +hat is the )alue of struts width 8b9 based on bending,c. +hat is the )alue of struts width 8b9 based on shear,

5. (CE Board November 2012 May 201$ !e"ember 201#) The 50mm x 75mm timbercolumn shown is subjected to a load % # 200 kN. The "lane A:A makes an angle 15;with the x:axis.

a. +hat is the normal stress on "lane A:Ab. +hat is the shearing stress on "lane A:Ac.


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' 0.()c c

F F= when

*)eL

d

' *&0

ec c

L dF F

=

when

*) )0eL

d<

7.


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column could su""ort if the allowable com"ression "arallel to grain is < c#7.50$%a.

TIMBER CONNECTORS AND FASTENERS

10. Two "iece of 75mm x '00mm @acal 0 stress gradeB members under tensionare connected together b* means of a la" s"lice with C "cs of 25 mm diameter boltsarrange in three rows as shown. (re/er to TM-6 /or allo+able loads)

a. (etermine the net area of a timber member. !onsiderhoe diameter to be 2mm larger than the boltdiameter.

b. (etermine the safe )alue of % considering thenet area of the member timber.

c. (etermine the safe )alue of % considering thebearing of the bolts on the timber.

11. Two 75mm x 250mm secondar* A"itong members are connected to a 100 mmthick main A"itong member b* means of six bolts as shown. f the secondar*member carries a combined axial tension of '' kN determine(re/er toTM- /or %,e"s)

a.


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hen the slenderness factor "sis greater than *0 but does not e/ceed " -the allowable unit stress in bending

F4bshall be determined from the following formula:

+

*' *,

S

B B

K

CF F

C

=

where

0.5**k

B

ECF

=

In no case shall

sC

e/ceed )0.

hen the slenderness factor "sis greater than "-but less than )0 allowable unit stress in bending F46shall be

determined from the formula:

2

0.+,5'

$ %B

S

EF

C=

12. A timber wall is 50 mm wide 150 mm dee" and ha)ing a height of 4.50m isassumed to be hinged at to" and bottom use k#1.0B. t is subjected to uniforml*distributed load of 400 N-m acting along the weaker axis of its entire height. The wallis made:u" of A"itong wood stresses are shown in the T$:/ use 0 stress gradeB.

To be safe the actual stresses should not exceed the allowable stresses. Also thewall must be checked using the formula

NSCP Specs:

3.).* Fle+u$e #nd A+i#l Comp$eion

7ember sub8ected to both fle/ure and a/ial compression shall be proportioned such that

*.0' '

C B

C B c

f f

F F Jf+

where

**

**

eL dJk

=

e/pect that

J

shall not be less than ero or greater thanone.

a. (etermine the allowable com"ressi)e stress.b. (etermine the )alue of allowable bending stress.c. +hat is the maximum axial load,

UNSYMMETRICAL BENDING (DESIGN OF URLINS!

A wooden "urlin is used on the truss with a to" chord inclined at 40; with the hori6ontal.The "urlin is 50mm x 100mm and has length of 4.5m s"aced b* 0.'5m on center. t

carries a li)e load of 750 %a weight of roong is 120 %a and ceiling load eDual to 1'0 %a.>sing A"itong.

a. (etermine the uniform load carries b* the "urlin in N-m.b. (etermine the maximum 3exural stress.c. +hat is the )ertical de3ection of the "urlin,

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Working Stresses for Visually Stress-Graded Unseasoned Structural

Timber of Philippine Woods

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enhancement program timber design

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