Type 2: Structures particularly sensitive to short duration gusts or flexible structures prone to respond with large displacements to the wind action. It includes structures with a slenderness ratio greater than 5 or natural period larger than 1s. It also includes towers, guyed or free standing antennas, elevated tanks, commercial signs and parapets and other type of structures having very short dimensions along the wind direction. It excludes structures explicitly classified as Type 3 or 4.