at the link it says :
"The methods described below is based on the simple method of calculation of weld stress as identified in BS 5950- clause 6.7.8.2 . The other method identifed in BS 5950 - 1 clause 6.7.8.3 as the direction method uses the method of resolving the forces transmitted by unit thickness welds per unit length into traverse forces (FT ) and longitudinal forces (FL ). "