Effects of Plan Geometry and Twisting Architectural Form on the Seismic Vulnerability of Tall Buildings’ Non-structural Components (NSCs)

Introduction
Earthquake is one of the most important risks in high seismic countries like Iran and, considering solutions to reduce the seismic vulnerability of buildings is one of priorities for designers, builders, and regulations in this area. Experiences of past earthquakes show that a significant part of the human injuries and financial loses is due to damage to NSCs in buildings - including architectural, mechanical and electrical components. Tall buildings are more important in reducing NSC’s seismic vulnerability due to their size, large number of residences and occupancies and the special characteristics of their structures. If earthquake happen,  even if it does not cause serious damage to the structural stability of tall buildings, any damage to their NSCs such as the facade, stairs, facilities, interior decoration, etc., in addition to the possibility of causing physical injuries and loss of life, It can leave significant costs for reconstruction. Managing these damages includes awareness, prevention and reduction of their vulnerability before the earthquake occurred and in the process of designing and constructing buildings.
Research Necessity
Tall buildings, due to their height and scale, have a considerable impact on the urban landscape, and for this reason, designers mostly like to use complex forms with complicated and impressive geometric in the design of these buildings. However, architectural forms play a major role in the seismic performance of tall buildings. This research explores the effect of the “Twisted forms” as a complex architectural form, with various plans and different heights on the seismic performance of tall buildings with steel diagrid structural system. The seismic performance indicators are drift and lateral displacement as indicators of measuring the vulnerability of NSCs and the weight per unit area of the structure as an indicator of the optimal structural design of buildings
Research Method
 This research is of a quantitative type and has been done by computer simulation and analysis method. For this purpose, first, the initial models with triangle, square, hexagon, and circle plans and with various heights including 160, 180, and 200 meters were made parametrically in Rhino software and the Grasshopper plugin. Then, twisted forms are made by twisting the floors of the primary models relative to each other by 1, 2, and 3 degrees. After that, the diagrid structural system has been designed for all of the architectural forms directly in the parametric design environment using the Karamba3D finite element analysis plugin. The linear static analysis for serviceability earthquake load has been used for designing and tuning the diagrid structures Finally, the seismic performance indicators including drift and lateral displacement as the indicators of measuring the vulnerability of NSCs and the weight per unit area of the structure as the indicator of the optimal structural design of tall buildings are extracted and analyzed using charts and tables.
Innovations and Results
The effects of simple various architectural forms on the seismic performance of tall buildings, have been studied in previous researches including taper, concave and convex forms. However, so far, complex forms have been less investigated. This research explores the effect of the “Twisting forms” as a complex architectural form, with various plans and different heights on the seismic performance of tall buildings with steel diagrid structural system. This issue has not been investigated in previous studies. The results show that in the diagrid structure with steel materials at the heights and plans investigated in this research, the twisting of the floors in the height increases the drift, lateral displacement, and weight per unit area of ​​the structure in the forms with triangular and quadrilateral plans in all 160,180 and 200 meters height. As a result, choosing these types of plans for twisting forms can reduce the lateral stability of tall buildings and increase the probability of damage to NSCs during an earthquake. On the other hand, by increasing the number of sides of the plan (forms with circular and hexagonal plans), the relative twist of the floors in terms of degrees (from zero to 3 degrees) has not cause significant changes in any of evaluated indicators. Resultantly, using plans with more sides for tall buildings with twisted forms would make it possible to avoid the adverse effects of twisting and to design optimal tall buildings from a seismic point of view.