Analysis and Design of a Complex⁃Shaped High⁃Rise Cantilevered Steel Structure

This project is a cast bronze statue with an overall shape of a high-rise cantilevered form， and its structural system is a special-shaped spatial truss structure. The statue is mainly divided into two parts： the vertical body section and the horizontal cantilevered cloak. The vertical body section has a height of 32 m and adopts a vertically stacked spatial steel truss with a story height of approximately 2 m. The cantilevered cloak has a length of 24 m and employs a horizontally arranged spatial steel truss with a width of approximately 2 m. Considering the stress characteristics and construction convenience of the members in each part， the upper and lower chords of the vertical section of the steel truss use I-shaped sections， the web members use round steel tubes， and the members of the cantilevered section of the steel truss also use round steel tubes. In view of the particularity of this structure， an overall structural analysis method combining seismic performance design and stability verification was adopted. A finite element analysis was carried out for critical joints to effectively ensure the safety of the structural design results. Firstly， the seismic performance objectives of the structure were determined according to its characteristics： the vertical members were designed to remain elastic under moderate earthquakes and non-yielding under major earthquakes， while the horizontal members were designed to remain elastic under minor earthquakes， non-yielding under moderate earthquakes， and partially yielding under major earthquakes. The results of the elastic analysis under minor earthquakes showed that the displacements of the structure met the code requirements when the effects of the cast aluminum cladding was fully considered. The equivalent elastic analysis results for moderate earthquakes showed that the stress ratios of vertical members were within 0.85， and those of most horizontal members were within 0.7， meeting the performance target for moderate earthquakes. The elastic-plastic time-history analysis results of the structure showed that the ductility coefficient of the members at the cloak reached 0.96， the maximum ductility coefficient of the body part members was 0.78， and the ductility coefficients of the bottom columns were all less than 0.2， which met the seismic performance objectives for major earthquakes. Then， the eigenvalue buckling analysis method and the dual nonlinear stability analysis method were used to carry out the stability check of the overall structure. The eigenvalue buckling analysis results showed that the first three buckling modes were concentrated in the vertical deformation buckling of the cantilevered cloak， and this buckling mode conformed to the structural characteristics of the cantilevered structure. The load cases of the dual nonlinear stability analysis were dead load + full live load （Case 1）， dead load + semi-distributed live load （Case 2）， and dead load + wind load （Case 3）， respectively. The calculation results showed that the critical load coefficients for the three cases were 2.1， 2.7， and 3.2， all of which exceeded the specification limit of 2.0. Some members in the span of the horizontal cloak and in the belly of the vertical body had entered the plastic stage， meaning that the members at the first yielding position would become the weak link in structural instability and failure. The design value of the elastic load for moderate earthquakes was adopted for the critical joints in the vertical part， while the design value of the non-yielding load for moderate earthquakes was adopted for the critical joints in the horizontal part. The finite element model of typical joints was established. Through finite element analysis， the stress state of critical joints under the design value of the fortification target load was obtained. The maximum stress of the critical joints in the vertical part was 270 MPa， and that of the critical joints in the horizontal part was 300 MPa. Both remained in the elastic stage， meeting the seismic performance objectives.