Course · lesson 2 of 6

Timber beams in practice

What decides real timber beams beyond the plain bending check: notches and holes, bearing, the lateral stability of deep joists, uplift, built-up and engineered members, moisture and durability, and connections in outline, with the STATIX timber beam calculator.

1. Learning outcomes

After this lesson you can:

check a notched end and decide about holes;
check bearing across the grain;
restrain deep joists against lateral-torsional buckling;
check a roof member under uplift and its hold-down;
use built-up, glulam and LVL members, and set moisture and durability right.

2. Before you start

Lesson 1 (grades, k_mod, the two routes) and Loads 1, lesson 5 (roof suction).
The free timber beam calculator.
A pocket calculator and about 50 minutes.

3. Cutting into a beam

Notched ends. Cutting the bottom of a joist at its support so it sits lower leaves a sharp corner where the timber splits along the grain. EN 1995-1-1 6.5.2 reduces the shear capacity by k_v, which falls fast as the notch deepens; a notch on the top edge is checked without that reduction. The calculator takes the remaining depth, the side, the distance to the support and any taper.

Holes. Pipes and cables through joists remove timber where it may be needed. The calculator does not check holes, so treat them as a design decision, not a site one: small, near mid-depth, away from the supports where shear is high and the mid-span where bending is high, and check what remains.

Bearing. The reaction crushes the timber across its grain, its weakest direction. A short bearing on a narrow wall plate can govern a heavily loaded short beam; the calculator checks it over the bearing length plus the spread EN 1995-1-1 6.1.5 allows.

4. Stability and uplift

Lateral-torsional buckling of deep joists. A joist much deeper than it is wide can twist and buckle sideways long before it reaches its bending strength, unless its compression edge is held. Boards nailed on top, blocking or bridging between joists, or a fixed ceiling give that restraint; the calculator takes their spacing.

Where the load is applied matters. A load on the compression edge rides with the twist and makes buckling worse (L_ef + 2h, EN 1995-1-1 Table 6.1 note); a load hung from the tension edge helps (−0.5h). The calculator has the three cases.

Uplift. On a light roof wind suction can exceed the weight, reversing the bending: the bottom edge goes into compression, usually with nothing holding it, and the ends lift. The calculator checks the uplift case with its own restraint and load edge, and gives the hold-down force at each support.

5. Members and materials

Built-up members. Two or three plies fastened together make a trimmer or lintel from standard stock. The calculator treats n plies as one section n × b wide, which is only true if the nails or bolts tie them well along the length; the fixing design is the detailer’s.

Engineered timber. Glulam and LVL are more uniform than sawn timber, so EN 1995-1-1 gives them lower partial factors and its own size and notch factors; the calculator applies them by material. Their strengths come from the manufacturer: the page asserts no default for SA glulam.

Moisture and durability. Timber shrinks as it dries and swells when wet, loses strength and creeps more in wetter service classes, and decays if it stays wet. Use treated timber where the hazard calls for it, keep it off the ground and away from trapped water, and set the service class honestly.

Connections, in outline. Timber is usually joined with nails, screws, bolts or punched metal plates; their strength depends on the timber density, the fastener and the edge and end distances. The timber beam calculator has one bolted end connection check (SANS 10163-1 13.11); the rest is beyond this course.

One route at a time. This lesson works in the EN 1995-1-1 route with the SANS load combinations. The SANS 10163-1 route has its own notch (13.4.2), bearing and lateral stability rules; if your project uses it, run the whole beam in it.