Preliminary design of high-rise shear wall with outriggers and basement fin walls on non-rigid foundation

This paper presents a graphical method for locating the optimum position of outriggers on shear walls with basement fin extensions for preliminary design of high-rise stuctures subjected to horizontal loading. This location for the outrigger will cause a maximum reduction in lateral deflection at the top of the building. The method requires the input of seven structural parameters: bending stiffnesses for the shear wall, outrigger and fin-walls, racking shear stiffness of the outrigger, an overall bending stiffness contribution from the exterior columns, and rotational stiffnesses for the shear wall and column foundations. These parameters allow the setting up of two compatibility equations for rotations at the intersections of the neutral lines of the shear wall with the outrigger and foundation structures. They yield expressions for the restraining moments at outrigger and foundation level that act in the opposing direction to the bending moment from the horizontal loading on the structure. Maximising the influence of the restraining moments on the horizontal deflections leads to the optimum location of the outrigger structure. Combining all stiffness parameters into two non-dimensional characteristic stuctural parameters allows the optimisation procedure for this type of structure to be represented by a single graph that directly gives the optimum level of the outrigger. It further allows a rapid assessment of the influence of the various structural components on the overall behaviour of a high-rise structure in the early stages of the design.