Vibration isolation

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Vibration isolation and seismic restraint for mechanical equipment in Chile

Conference Paper · September 2016

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Structural Acoustics and Vibration (others): Paper ICA2016-78

Vibration isolation and seismic restraint for mechanical equipment in Chile

Nicolás A. Bastián-Monarca(a), Ian Azrak(b)

(a) Silentium, Chile, nbastian@silentium.cl

(b) Mason Industries, United States, iazrak@mason-ind.com

Abstract

Vibration control of mechanical equipment in seismic countries is a subject that should be addressed with some caution. One of the most utilized elements in controlling vibration is a spring isolator, one that has high deflection (relative to neoprene isolators). The problem is that the resonant frequency can coincide with the disturbing frequency of an earthquake, which means that in an earthquake the spring will begin to ‘jump’, causing the displacement of the mechanical equipment. The displacement of the equipment, beyond generating high costs (damage, loss of use, flooding, etc.), also creates the risk of personal injury and even death. Due to the aforementioned risks, it is necessary to consider the seismic ‘variable’ when doing a proper vibration control design in a seismic country or region. Criteria, designs and recommendations are presented in this report in order to perform proper vibration isolation in conjunction with seismic restraint for mechanical equipment and systems in Chile. In addition, you will be shown some failures from the M8.8 earthquake on February 27, 2010 in Chile.

Keywords: Vibration isolation, seismic restraint

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1. Introduction

The control of vibration transmission has received much attention in recent years due to its effect on the functionality of systems involved [1] and health. Vibration transmission can cause instability or even failure, as in the case in buildings subject to earthquakes [2]. Thus, vibration isolation is a vital requirement throughout much of engineering [3], particularly when there is a strong source of vibration such as a motor [4]. In this sense, technical or mechanical floors in any building project are a strong source of vibration due to the high density of equipment. In these scenarios, the direct radiation of a vibrating machine is usually not as serious as the radiation from the floor structure as a result of the structure-borne sound transmission from the machine to the floor structure [5]. In the past decade the use of active or semi-active vibration isolators had been a new trend for the designs of anti-vibration systems [6-11]. However, the advantage of the passive anti-vibration method are that they are stable and easy to set up [12]. Moreover, passive vibration isolators are the most simple, inexpensive and reliable means of protecting sensitive equipment from environmental shock and vibration [13]. Therefore, vibration isolation using passive isolators is very cost effective and hence is widely used in the engineering industry [14]. Thus, the passive isolation and seismic restraint of a structure from mechanical equipment is studied in this paper.

The use of vibration isolators (simply isolators from this point forward) in order to isolate mechanical equipment is a typical solution that engineers or acousticians always recommend. In the large range of isolators, neoprene and spring isolators are the most utilized, the reason being the static deflections that they offer. Spring isolators normally are offered between one inch and five inches of static deflection, which neoprene isolators are normally offered in a range between 0.15 inches and 0.55 inches [15]. Based on that, it is clear that when high deflection is required, springs be offered as the best solution. The problem with spring isolators is that they have a natural frequency that can potentially coincide with the frequency of an earthquake, which means that during an earthquake, the spring isolator can enter into resonance and being to jump violently. If the spring isolator does not have a seismic housing, the excitation of the spring will cause the equipment that it is supporting to being to move and fall over. If the machine is a fan or other airside type of HVAC equipment the danger is that it could fall over and pull down the ductwork, but if the equipment is wetside HVAC equipment it could fall over and bring down the piping with it, causing flooding within the building. Furthermore, if the equipment is located outdoors or on a roof, the possibility exists that the equipment could fall off the building.

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