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close this bookManufacture of Ceilings - Course: Timberwork techniques. Trainees' handbook of lessons (Institut für Berufliche Entwicklung, 22 p.)
View the document(introduction...)
View the document1. Purpose of Ceilings
View the document2. The Wooden Beam Ceiling
View the document3. The Framing
View the document4. The Attic and Collar-beam Framing
View the document5. The Pitch Size
View the document6. Load on Wooden Beams
View the document7. The List of Timber
View the document8. The Wall Plate
View the document9. Flooring Sleepers
View the document10. Special Constructional Recommendations

5. The Pitch Size

The wooden beams of a wooden beam ceiling should be placed at equal distances so as to equally distribute the load on all beams.

If the distances between the wooden beams are not shown in the drawing, the pitch size is to be calculated.


Figure 12

Determination of the pitch size

(1) bay 1, (2) bay 2, (3) bay 3

Lr length required for the calculation, BL length of wooden beam, T pitch size (beam spacing), B clear width of the room, L length to be distributed, a bearing length, b1, b2 width of wooden beams, c minimum distance of wooden beams from the wall, 1, 2, 3, 4 wooden beams

The pitch size depends on the thickness of the flooring and is calculated to formula (1).

T = pitch size (distance of wooden beams)
Lr = length required for the calculation
nF = number of bays

The number of bays is determined by means of formula (2).

Tzul = pitch size depending on the thickness of the flooring

20 mm thick flooring - - - pitch size Tzul = 600 mm
24 mm thick flooring - - - pitch size Tzul = 800 mm
30 mm thick flooring - - - pitch size Tzul = 1000 mm

If the resulting nF is a decimal fraction, it is to be rounded off to bring it up to the next integer number.

The rounded-off number of bays is provided with a superscript mark for identification.

For example: nF = 6.4; n’F = 7

The length to be distributed is determined by deducting the wooden beams’ minimum distance from the wall at both ends from the clear width of the room.

L= B - 2c (3)

L = length to be distributed
B = clear width of the room
c = minimum distance of the wooden beams from the wall, normally 20 mm

For the calculation of the pitch size, the arithmetical length is required. It results from formula (4):

b = wooden beam width

Formula (5) gives the number of wooden beams to be placed over a calculated distance:

nB = n’F + 1 (5)

The length of the wooden beams is calculated to formula (6):

BL = w + 2a (6)

BL = length of wooden beam

w = clear width of the room

(in straining direction of the beams)

a = bearing length

(a = at least 150 mm)

Why should the wooden beams have equal distances?

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Why should the wooden beams have equal distances?

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Why must the wooden beams have a distance of a least 20 mm from the wall?

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What does the formula nB = n’F + 1 say?

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Why must nF be rounded off to the next integer number?

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