Analysis of Guyed Mast Using Gust Factor and Patch Load Method

Guyed masts have unique structural behaviour among other civil engineering structures due to their height, slenderness, light weight and overall flexibility of mast. Wind is predominant on these structures, are very sensitive to dynamic excitation from gusty wind due to flexibility associated with both mast-slender and guy cables. As per IS 875 (Part 3)-2015, dynamic wind loading shall be considered for such flexible structure using gust factor (G) method which is based on spectral characteristics of wind velocities, first natural frequency and damping ratio of structure, assuming that dynamic response at every point is a simple multiple of its static response of steady winds. Gust factor method is valid for structures with one or two dominant vibration modes, and it is not appropriate for guyed mast where 15–20 vibration modes contribute significantly to the response of structure to turbulent wind. In lieu of dynamic analysis Sparling et al. (J Int Assoc Shell Spatial Struct 37(2):89–106, 1996, [6]) proposed patch load method of analysis that utilizes a series of static load pattern to replicate effects of wind gusts and systematically accounts for the characteristics of mast and wind using empirical scaling factors. In this paper, study of gust factor method and patch load method for 100 m high guyed mast is undertaken through load calculation using gust factor and patch load method with geometrically non-linear analysis using STAAD Pro Advanced Analysis software along with comparison statement presented. From the analysis, gust factor method heavily underestimate leg forces in upper spans and bracing forces in middle of each spans and concluded that patch load method gives better approximation compared to gust factor method for analysis of guyed mast.