Strategies to Reduce Lateral Forces on High-rise Buildings that Use Diagrid Structural System

                                                     Phage 1

Diagrid Structural System
Binh K. Nguyen and Hasim Altan
School of Architecture
The University of Sheffield

Abstract— The study focuses on strategies to enhance the performance of a building against lateral forces and earthquake. The strategies range from aerodynamic modifications to structure reinforcement to adopting auxiliary damping devices/systems. The study’s direction was toward Diagrid structural systems – the latest trend in high-rise projects.

Keywords-component; lateral forces; tall-buildings; high-rise;
diagrid, damping strategies.

INTRODUCTION
The evolution of tall-building structural systems, based on new structural concepts with newly adopted high-strength materials and construction methods, has been towards ‘stiffness’ and ‘lightness’. Structural systems are becoming stiffer and lighter. Diagrid1, acknowledged worldwide as a very light structure and one of the best when it comes to withstanding lateral forces, has been leading the trend. The lighter a structure is, the higher it can rise. On the other hand, it is also easier to blow away a light subject than a heavy one. Diagrid can save from 20% to 30% the amount of structural steel in a high-rise building. Moreover, high-strength material technology has come a long way since the invention of modern high-rise building in 1930s. Materials themselves are stronger and lighter. It is common knowledge that, rather than directly standing the forces, it is better to reduce them and dissipate the magnitude of vibrations. A high-rise structure needs both stiffness and damping characteristics. The strategies to enhance tall-buildings’ lateral performance can be divided into 3 categories: (1) Aerodynamic Modifications; (2) Structural Reinforcements; and
(3) Using Auxiliary Damping Devices/Systems. The strategies presented below are the ones that can be used for that use Diagrid structure. However, most of the strategies can be applied to other types of tall-building
structures.
Diagrid (or diagonal grid) is a design for constructing large buildings with steel that creates triangular structures with diagonal support beams. It requires less structural steel than a conventional steel frame. It also obviates the need for large corner columns and provides a better distribution of load in the case
of a compromised building.

AERODYNAMIC MODIFICATIONS

A) Aerodynamic Shapes
The form of a tall-building is usually limited to rectangular prisms. From geometrical point of view, this form is rather susceptible to lateral drift. Other building shape such as cylindrical, elliptical, crescent, triangular and like, offer better lateral performance due to inherent strength in their geometrical form. They provide higher structural efficiency and allow greater building height at lower cost. Building codes permit a reduction of the wind pressure design loads for circular or elliptical buildings by 20%-40% of the usual values for comparably sized rectangular building.

B) Corner Modification

Investigations have established that corner modifications such as chamfered corners, horizontal slots, and slotted corners can significantly reduce the along wind and across wind responses when compared to a basic perpendicular building shape.Chamfers of the order of 10% of the building width makes 40% reduction in the along wind response and 30% reduction in the across wind response. Excessive rounding of corners
of the cross section, approaching a circular shape in the cross section, significantly improves the response against wind. With a building of roughly 70 stories, peak deflection of the model in circular cross section was about half of the one with square cross section.

Fin     Vented Fin  Slotted Corners  Chamfered Corners  Stair-step Corners