Strength of Inseparable Joints

Knowing the distribution and values of external forces between board elements of the furniture body, the strength of appropriate connectors can be determined and the number of joints attributed to the length of the board’s edge can be therefore designed. Table 7.9 provides geometric examples, as well as the strength criteria for designing dowel joints connecting the side wall with the bottom (bottom flange) of the body of rack and flange structure. Considering this example seems to be the most effective, because in the whole construction of the furniture, this node is the most heavily loaded with all kinds of internal forces.

For design calculations, the following loads should be adopted:

• for internal vertical partitions only forces Pi,

• for horizontal partitions forces Pi and R,

• for top board forces Pi and Pk,

• for bottom board forces Pi, R and Pk and

• for side walls Pb.

Table 7.9 Strength conditions for the dowel joint connecting the side wall with the bottom (bottom flange)

Type

Scheme of distribution of forces

Strength conditions

Border conditions

Rack

construction

P,| 0,5P„ ^

4m (Pi + R)2+(0.5P* )2 n

nd2kf

g1 = 3/4.g, g2 = 1 – g1

kf—shearing strength of connector material, for beech wood kf = 6.5-18 MPa

R

— -1

19i

92 |

9

Pi

m(Pi + R) n

(2eg1 + ed)k-

k-—shearing strength of the board,

for particle board k- = 4-6 MPa

®t

R

t

19i

92 |

9

-tf+P/0

d,

^ 2m(Pi + R) n – ng2kw

k-—splitting strength of the slot material, for particle board

k – = 0.4-0.5 MPa

1

/ ~f

Pb

d.

mP6

ndgminkk

g1<g2, gmin = g1

kk—shearing strength of the glue, kk = 2.5-7 MPa

. 1

el

‘I ‘Pb t

191

92 |

9

Flange

construction

“E

0,5Pk

/

4m P + (0.5Pk )2 П – nd2kf

kf—shearing strength of connector material, for beech wood kf = 6.5-18 MPa

9i

9

n – mPb – (2eg1 + ed)k-

k-—shearing strength of the board, for particle board

k – = 4-6 MPa

9i

_^d

9

" d,

2mPb

n –

ng2k-

k-—splitting strength of the slot material, for particle board

k – = 0.4 – 0.5 MPa

I»»

02 j

9i

;|

‘1

m(Pi + R)

ndgminkk

kk—shearing strength of the glue, kk = 2.5-7 MPa

R

_,d

9

In the formulas: n means the number of individual connectors on half the length of the edge, m coefficient of safety determined experimentally, can be assumed m = 1.1-2