Study of dynamic loads on metal structures of tower cranes during construction and installation works in conditions of dense urban development

Abstract

Urban densification alters the operating conditions of a tower crane more substantially than design schemes for verifying the load-bearing metal structure reflect: the mean component of wind pressure decreases, the pulsation component grows, and the load travel path is broken by coordinate protection into short segments with frequent starts of the slewing mechanism. The purpose of the work is to quantify the redistribution of dynamic load components acting on the metal structure of a tower crane when the site shifts to a restricted construction regime. An author's design model has been developed for a crane with a horizontal jib of 55 m radius and a free-standing tower 47.3 m high; dynamic factors are adopted according to GOST 32579.1-2013, load combinations according to GOST 32579.3-2013, and wind components are calculated according to SP 20.13330.2016 for terrain types A, B and C with allowance for the dynamic amplification factor at a first natural frequency of 0.278 Hz. In dense development the pulsation component of the wind load at the 40 m level exceeds the mean component by a factor of 1.74 and accounts for 63,4% of the total pressure, while the design bending moment at the tower base decreases by only 1,7% against ordinary urban terrain. Formal assignment of a restricted site to terrain type C underestimates the wind moment from the tower shaft by 5,0%. The sensitivity of the design moment to the hoisting class (21,0% over the range HC1-HC4) exceeds by an order of magnitude its sensitivity to the slewing acceleration time (1,8% over the range 4.0-10.5 s). The loading of the metal structure under restricted conditions is thus governed by the operating regime of the hoisting mechanism and by the accumulation of slewing starts, with the strength reserve of the tower cross-section remaining practically unchanged.