The main objective of the research was to validate the method for determining the load capacity of GFRP composite lighting columns under horizontal loads according to the EN 40-3-3:2013 standard. The work involved developing a numerical model of GFRP composite columns with an inspection hole while accounting for the columns' nonlinear behaviour before the failure phase. The model was verified by testing 11 GFRP lighting columns on a natural scale and material testing of the composite. A calculation method was used in accordance with the standards EN 40-3-3:2013 and EN-40-7:2002 to determine their bending resistance. It was discovered that the load capacity estimated experimentally is two to three times less than the load capacity estimated using the standard's procedure. Also, the load capacity calculated based on the developed numerical model of the column is about 2.5 times lower than the characteristic load capacity calculated based on the currently applicable standard procedure. The analysis of the standard design procedure shows that the inspection opening is treated only as a local reduction of the cross-section, reducing the yield modulus. However, the possibility of buckling the walls in the inspection opening area is not taken into account. It means that the standard procedure for determining the bending resistance of composite columns has not been adapted to the actual behaviour of composite columns with inspection openings. Developed numerical model of a lighting pole with an unreinforced inspection opening accurately assesses the capacity of such poles for use in scientific and design practice.