An umbrella is formed of an elongated shaft having a first end and an opposite second end and a runner slidably disposed about the elongated shaft. The umbrella includes a rib assembly including a plurality of ribs that are attached to the runner by a plurality of struts that move between open and closed positions. In accordance with the present invention, the elongated shaft has a cross-sectional shape defined by a plurality of curved sections and a plurality of planar sections interspersed between the plurality of curved sections for providing increased torsional strength to the elongated shaft. At least one of the ribs can have a cross-sectional shape defined by a plurality of curved sections and a plurality of planar sections interspersed between the plurality of curved sections for providing increased torsional strength to the at least one rib.