Abstract.Diagrid system, which is the portmanteau of diagonal grid member, is an exterior lateral load resisting system for tall building that has gained a wide acceptance in the design of tall buildings. There is abundance of researches that studied the efficiency of diagrid systems, which are constructed from the ground level to the top of the buildings in resisting the lateral load. Nevertheless, no study had been performed on the effectiveness of the diagrid that is constructed above other tall building systems despite the existence of a few buildings in the world that employ such system. The objective of this research is to understand the behavior of the lateral displacement and shear lag effect due to wind load when the diagrid structure is constructed above a frame. Models of 60-story buildings with a footprint of 36m x 36m were analyzed by using Staad.Pro software. The level where the diagrid members started was altered. The lateral displacement was reduced to 60.6 percent and 41 percent of the lateral displacement of a building with full frame system when the combination of frame-diagrid that had the diagrid started at Level 1 and Level 45, respectively were employed. Furthermore, the shear lag ratio was reduced from 1.7 to 1.3 when the level where the diagrid started was increased from Level 1 to Level 45.

Abstract. Diagrid system has gained a wide acceptance in the design of tall buildings due to its many advantages including its high structural efficiency in resisting both gravity and lateral loads. Most diagrid structures that had been studied have full triangulated members from the ground level to the top of the buildings where comparison in the effectiveness in minimizing the lateral displacement was often made between structures with full diagrid, frame and outrigger system. Nevertheless, no study has been performed on the effectiveness of the diagrid that is constructed above a frame system. The objective of this research is to understand the behavior of the lateral displacement and shear lag effect due to wind load when the diagrid structure is constructed above a frame. Models of sixty storey buildings were analyzed by using Staad.Pro software. The level where the diagrid members started and the spacing of vertical base columns of the frame were altered. The lateral displacement and shear lag effect resembled closely of those of the model of full diagrid when the diagrid was started at level 3, and the vertical base columns were uniformly spaced at 6 metres.