S355J0 is fairly normal for beams etc.
The S stands for structural, the 355 is the tensile strength and the J0 means that its hardness test has been done at 0° temperature.
Either side of J0 you have grades JR(20°) and J2 (-20°).
Flats and angle are most commonly S275JR, hollow sections are usually either S235JRH for general use or S355J2H for structural use. The H on these grades simply means its a hollow section.