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# Timber Engineering

What should be the Roof slope to prevent Ponding?

As per standards, the Roof beams should have a continuous upward slope equivalent to 1/4 in/ft ( 20.8 mm/m) between a drain and the high point of a roof, in addition to minimum recommended camber to avoid ponding.

What are Radial Stresses and Curvature Factor?

For a constant cross sectional the radial stress induced by a bending moment in a member is calculated by using this formula

fr=3M/2Rbd

What are the Adjustment Factors to be done in Design Values?

Their is always some variation in the design values calculated in timber. Therefore we need to apply the required adjustment to them.

Case- Extreme Fiber Bending
Fb‘=FbCDCMCtCLCFCVCfuCrCcCf

How to Check Timber Under both Bending and Axial Load?

The members which are under the combined effect of axial as well as bending load should satisfy the following equation

Pa/P +Ma /M < 1

What is the Allowable Unit Stress in Timber Columns?

Timber coloums are seldom used singly. Mostly they are a group of lumber which are stick together to form a single member. The allowable unit stress on timber is calculated by using the following formula

P/A=3.619E/(l/r)2

When the Columns have square or rectangular cross section
P/A=0.30E/(l/d)2

When the Columns have circular cross section
P/A=0.22E(l/d)2

What is the Stress in Timber Beams?

Extreme fiber stress in bending for a rectangular timber beam is calculated by the following
f=6M/bh2
=M/S
where
f= maximum fiber stress, lb/in2 (MPa)
M= bending moment, lb in (Nm)
h= depth of beam, in (mm)
b= width of beam, in (mm)
S= section modulus (bh2/6 for rectangular section), in3 (mm3)

What is the Bearing in Wood?

As per the guidelines, the allowable unit stresses for any given compression perpendicular to the grain is applied to any length bearings at the ends of beams. But when the length is more than 152.4mm or 6 inches, it is applied to all at other locations.

When we are calculating the bearing at the end of beams we should keep in mind that we don’t take into consideration the bending of beams and also that the pressure on inner edge is more than that at the outer edge.