Keywords: tall buildings, shearwall-frame, framed-tube, outrigger-braced, bundled-tube, diagonal-tube, preliminary design, optimisation, drift, acceleration, strength, serviceability.

The design of tall buildings from principles of behavior is described herein. The structural systems-shear wall-frame, framed tubes, outrigger braced tall buildings, bundled and diagonal trussed tubes are described based on their behavior due to gravity and lateral loadings. Displacement limits of H/500 and acceleration limits of 15-20 milli-g are used.

Approximate methods of analysis are described for shearwall-frame buildings, as shear-flexure cantilever beams. Framed tubes are modeled as equivalent orthotropic plates.

Exact solutions for these shear-flexure, equivalent orthotropic tubes, and cantilevers with rigid arms, as well as diagonal trussed tubes are derived using differential equations and stress-resultants are derived, which enable preliminary design and optimization. Software developed for these solutions are described. Real life examples of tall buildings designed by the author as a consultant to CBM Engineers Inc., Houston, Texas, are illustrated to show the usefulness of these methods of analysis and design. Research in tall buildings at WPI is focused on approximate methods of analysis and preliminary designs of tall buildings. This research was funded by NSF, Darpa and Army.

Preliminary design and optimization techniques are described for shear wall-frame buildings, using approximate methods of analysis and design. Detailed steps are shown on how to find stiffness of wall and frame separately for a three dimensional building. Torsion is included. Techniques of determining stiffness required for the shear wall as well as frame from the overall solution of a shear-flexure cantilever. Moments and shears carried by the wall and frame enable proportioning of them. Drift is optimized as well as strength and stability. Human comfort is insured by specifying threshold of perception of acceleration levels. This is met in preliminary design.

Preliminary design and optimization techniques are also illustrated for framed-tube buildings, outrigger-braced buildings and bundled and diagonal trussed tubes by using equivalent 10-story models. These could be accomplished using plane frame and space frame software systems. The optimization of these systems to match given drift and permissible stresses are illustrated using one story sub-assembly models. These are used at different levels of a tall building, and parametric variation of column, girder and brace stiffness is done, to meet specified drift. This allows weight/sq.ft calculations to be made for cost optimization, as well as construction drawings to be made, next. Some general design notes are made for the proportioning of floor systems, columns, girders, bracing systems and shear walls to be used in all tall buildings. These are based on past experience and heuristic rules, condensed from past practice in tall building design.

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