Building Construction Handbook, Eighth Edition

Design calculations reference previous page.

Timber strength class C22, See page 115 for data.

BM =WL 4 =^393004 ¾^3000 = 29475000 Nmm

MR = stress¾section modulus = fZ = fbd

2

6

assume b = 300 mm and f = 6.8 N/mm^2

then 29475000 =^6 :^8 ¾^300 ¾d

2

6

d=

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

(^29475000) ¾ 6
6 : (^8) ¾ 300
s
= 294 mm
use 300¾300 timber section or 2 No. 150¾300 sections bolted
together with timber connectors.
Props to Needle Design:-
area =stressload =^196507 : 5 = 2620 mm^2
\minimum timber size =
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2620
q
=52¾52 mm
check slenderness ratio:
slenderness ratio =effective lengthbreadth =^450052 =86„5
the 52¾52 mm section is impractically small with a very high
slenderness ratio, therefore a more stable section of say,
(^300) ¾225 mm would be selected giving a slenderness ratio of
4500/225 = 20 (stability check, next page)
Check crushing at point of loading on needle:-
wall loading on needle = 3930 kg = 39300 N = 39„3 kN
area of contact = width of wall¾width of needle
=215¾300 = 64500 mm^2
safe compressive stress perpendicular to grain = 2„3 N/mm^2
\safe load =^645001000 ¾2„3= 148„3 kN which is > 39„3 kN
Determination of Temporary Support Members