Modelling and Prediction of the Effects of Dynamic Responses of Tall Buildings on an Elevator System

Vibrations on a high rise building often influence all elevator components and affect the ride quality of the elevator car. The lateral and longitudinal vibrations of the suspension and compensating ropes can occur and the lateral and longitudinal vibrations at the elevator car may take place. The ropes in the elevator system can be characterized by low and high frequency modes and they are lightly damped. The elevator system in a high rise building is composed of suspension and compensating ropes, which are the pivotal components of the elevator system. An important feature of the ropes in the elevator system is that they have a time varying length. However, the rate in which the length changes can be considered as small and as a result dynamic characteristics of the system vary slowly during the elevator car travel. The design methodology of an elevator system requires a thorough dynamic analysis in order to predict the dynamic loads and to evaluate the response of the system during various operational modes. This response may be caused by a number of sources of excitation. The main source of excitation this study is focused on is the excitation coming from the wind loading on the high rise building. Wind loading on a building structure causes high displacements at the top of the building structure, exciting all of the components of the elevator system. The main excitation from the building structure to the suspension and compensating ropes are the displacements at the machine room level. The other sources of excitation are coming from the building interface which is used to guide the elevator car and counterweight along the elevator shaft during travel. The building interface consists of guide rails and roller guides. The lateral vibration of the elevator car can result from the roller guide vibrations or due to the guide rail segments being misaligned. These various sources of excitation may lead to an adverse dynamic behaviour of the elevator system due to its nonlinear and nonstationary nature. Due to the time varying length of the ropes in the elevator system the mass and the stiffness of the system change and consequently its dynamic characteristics such as frequencies, damping ratios and mode shapes are affected. The aim of this research is to develop and to validate a computer model of the elevator system to predict the dynamic responses of the ropes in an elevator system due to the vibrations of a high-rise building under wind loading, when the elevator system is stationary and in motion. The three objectives of this thesis are to develop a mathematical and computer model of the elevator system to understand the behaviour of the ropes in the elevator system under the influence of the building vibrations caused by wind action, to develop an experimental programme involving a lift testing tower facilities and/or alternative tall building sites, in order to validate the computer model through experimental testing, and to develop a computer software tool as an executable program on Windows operating system to predict the behaviour of the ropes in the elevator system based on the final mathematical models of a stationary and moving elevator system. The experimental testing was conducted at the National Lift Tower in Northampton using an experimental rig. A set of experiments were developed and various measurements were carried out. The equations that accurately describe the motion of the mass-rope suspension system in the rig were derived. The mathematical model takes into account the stationary and nonlinear nature of the mass rope suspension system in the rig. The linear and nonlinear resonance phenomena were predicted through simulation and they were compared with the experimental results. The equations of motion that describe the elevator system comprised of the elevator car, compensating sheave, and counterweight connected by the suspension and compensating ropes were derived. A method to account for the nonstationary and nonlinear nature of the elevator system was developed. The linear and nonlinear phenomena were observed. The nonstationary and nonlinear behaviour of the ropes in the elevator system was demonstrated through simulation. The results showed that nonlinear coupling in the lateral in plane and out of plane directions of the suspension and compensating ropes can generate modal interaction between the elevator car, compensating sheave, and counterweight. Thus, the displacements of the elevator car, compensating sheave, and counterweight can be predicted.