HIGH RISE STRUCTURES. INTRODUCTION

In the design of high-rise buildings, different sectors and specialists gather in workshops to sort out an optimum design in terms of aesthetics, creativity, built ability and economy. The main elements involved in the design are shear core, footings, beams, floors and columns. In terms of the total cost of HB, floor is 40% and core a 30%. Therefore, an economic design has to reduce the floor or wall thick, because just a couple of millimeters imply a huge decrease in the total cost. Designs can be improved learning of the other’s mistakes. First, the design of short beams cannot be analyzed thinking that its behavior is similar to a beam under bending moment, which implies a minimum reinforcement. The right design should be made considering a truss model. Second, when is required a construction joint, the grout should be a concern thus the strength should be rise at least the same strength resistant of the concrete. Third, pedestrian comfort is a topic usually not thought. High Rise Buildings modify the airflow, thus the wind force is moved not only to the sides, in fact is also spread downwards to the pedestrians. When this force increases could be quite uncomfortable for pedestrians who are walking in the ground floor. Also the design of buildings should be simple. In other words, the vertical loads should be transferred to the ground in a simple way. The lower levels cannot be weaker than the upper. Nowadays, our technology let us built buildings of 2km height, without problem. The fire control however is a limitation. The requirements lead to let escape to people in just a minutes. Lift can not be used, parachutes are not a safety solution, therefore we have to expect that someone who lives in the last floor escaped alive. High-rise design has three main characteristics that have to be considered: strength, stability and serviceability (deflections). Lateral loads, like wind and earthquake controlled the behavior of these structures, whereas short buildings are governed by strength of individual elements. Therefore the HR design has to be focus in to assess the magnitude of wind and earthquake loads and lateral displacements or drift to limit the formation of plastic hinges. The engineer has to be aware of the effects on non-structural elements, like dry walls, which cannot resist vertical loads. It is required a analysis of second order effects like P-D, creep movements and differential movements. A analysis of overall stability against overturning and sliding and the assessment of soil properties are also required. The optimum design has to be lead to reduce the core size, which is quite complex and require the participation of the all sectors, not only the structural engineer. The reason is that the core is not included in the net lettable area.