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Technical Bulletin HSE-101-1

Noise and Vibration Control at High Speed Elevators

There are many sources of vibration capable ofproducing motion sufficient to be perceptible bythe occupants of a modern building. With buildingstructures getting lighter, mechanical equipmentrooms getting smaller, and equipment running athigher speeds, problems are on the rise. In addition,the public is increasingly aware of the effects ofnoise and has become more "noise conscious."Noise problems within buildings can no longer beneglected.

In view of noise and vibration control at elevator,the most appropriate lift should be hydraulicelevators. The hydraulically powered mechanismand modest operating speed of hydraulic elevatorsgenerated really little noise and vibration that nocontrol measures required. While it’s comparativelylow speed limits its application to low rise buildingsat height up to around five storeys and is rarely usefor city buildings.

New buildings in cities, not only commercial, buthotels and residential blocks are rising higher thanever. Architects are driven to design skyscrapersdue to expensive land cost. These buildings requireelevators run at super high speeds so as to savetravel times within the buildings. To meet thisrequirement, some elevator manufacturers have inrecent years developed technologies to allowelevators to achieve speed as high as 810m/min(13.5m/s). The increase in speed of elevator doesnot only lead to riding comfort problem forpassengers inside lift car while also caused a seriesof problems in regards to the generation andtransmission of noise and vibration within thebuilding.

Noise problems within building arise from vibrationintroduced by rotating mechanical equipmentmainly come from :

HVAC and other fluid pumping equipment vibrationcontrol are common and have already beenconsidered by almost all consulting engineers.Whilst the most annoying source normally beoverlooked by the design engineers is the elevatornoise. Elevator system severs the buildingoccupants all round the clock, and has never beenpossible to be controlled by means of operationalmeasures or long period suspension for remedialmeasures. When vibration problem arise, theimpact to users and building occupants could noteasily be solved.

The quality and functions of equipment in buildingshas already been improving day by day and theimprovements in building development demandthat elevator technology also keep up, in terms ofboth design and function. Today's elevatorsengineers have already put riding comfort of lift caras their major concern in design considerations.While it must also be addressed that elevatoroperation shall harmonized with the building bykeeping its noise and vibration generation atminimal to avoid possible complaints from buildingoccupants.

1 . Mason Industries (Hong Kong) Limited

In reducing the dynamic motion and to elevatedeflection of isolation mounting, a mass dampsystem is necessarily. It could be a “Mason” Jack-up Neoprene Floating Floor system (See Figure.2)designed with a large inertia block supported onjack-up neoprene resilient mounts.

▓ Traction Engine Vibration Control

Fig1. Typical Elevator Arrangement and Vibration Propagation Paths

Fig2. "MASON" Jack-up Neoprene Isolation System at Traction Engine Support

Vibration generated at traction engine during start-up, hoisting and breaking is the major cause ofnuisance. Since most traction engines are installedon steel channels base supported by four or sixpieces of so called vibration isolation pads with

Technical Bulletin HSE-101-1

Most nowadays elevators consist of an electrictraction engine pulling on wire ropes attached tothe top of the lift car. The motor unit is oftenlocated on top of the building in a dedicatedpenthouse lift room (see Figure 1). Air-borne noisefrom lifts has generally never been a problem.Typical noise levels inside lift plant rooms beingaround 70-80dB(A) for modern elevator machines.This noise level could easily be attenuated byconcrete slabs and walls which make up the liftmotor room.

static deflection in range of 1 to 2mm only. Thesepads are too hard and not efficiency in reducingvibration energy transmitted from the traction motorto the floor slab of the elevator plant room andonto lift shaft walls and connected structuralelements, then eventually reached occupantsinside building.

Solving this problem seems easy, as we could simplyreplace the “Hard” neoprene pads by a moreefficient spring vibration mounts. But there is alwaysa contradiction between the precision of lift carlanding control and achieving higher vibrationisolation by using softer springs at elevator base.Since the use of softer springs would inducedynamic motion problem when elevator inoperation and deteriorate the riding comfort as wellas the control of landing accuracy.

2 . Mason Industries (Hong Kong) Limited

Fig3. Noise Sensitive uses common with lift shaft

The neoprene mounting elements arecompounded to DuPont bridge bearingspecification and conform to the AASHO standardthat guarantee the longevity of use. Staticdeflection rating of mounting element at rated loadcould be around 8 to 10mm. This system hasproven to be not only effective for isolating motorand gear noise, but also be considerably alleviatethe start-up “thud” and in turns reduced thevibration transmission at lift shaft to adjoiningstructures and noise sensitive areas.

In contrary, hotel guest rooms and residentialbedrooms is a unique situation where occupanciesare conscious on the noise level, since these placesare designed for sleep with a noise criterion asstringent to NC30 to NC35, so that guide railvibration should be considered carefully in thedesign stage.

Nowadays, structure-borne vibrations from the liftcar rollers and guide rails has been substantiallytreated by elevator manufacturer by using ofrubber types at rollers and more precise guide railsat the elevator system. While sound re-radiatedfrom lift shaft walls caused due to the vibration fromguide rails is still a problem when passing speedexceeded 2.5m/s. Figure 4 shows a typical noisespectrum at close proximity to lift shaft walls.

Fig4. Typical Noise Spectrum in Octave Band Frequency close to Lift Shaft

The interaction between guide shoes and rails isanother major source of vibration when consideringhigh speed elevators. In most office buildings, rollernoise is not perceived as a problem at all due tohigher ambient noise level. However, in residentialbuildings and particularly hotel blocks, lift noise inbedrooms or guest rooms common with the lift shaftcan be a big problem (See Figure.3), re-radiatednoise levels at common shaft wall being in therange 40 to 45dB(A) from passing lift at speedhigher than 2.5m/s . At the same time, as thefrequency of excitation is determined as accordingto the speed of elevation and the rail bracketspacing that are at constant, the induced noiseproblem in most cases are tonal in nature whichmakes the transmitted noise more annoying.

Technical Bulletin HSE-101-1

▓ Guide Rails Vibration

3 . Mason Industries (Hong Kong) Limited

Technical Bulletin HSE-101-1

The combination of the above vibration controlsystem has proven to be successful in numbers ofjobs locally and overseas. As the actual situationvaries from case to case, our technical team is gladto provide sound advises at your request.

The fine cellular structure of Sylomer® allows for thenecessary deflection when loaded statically ordynamically. Materials with densities between150kg/m3 and 680kg/m3 are available for using atdifferent loading conditions (See Figure 6).

A load-deflection curve typical for Sylomer® is asshown in below figure (See Figure.7). At low loads,the deflection increases proportional to thepressure. When permanent static load is applied tothe material within this linear range, the long-termcreeping effective would be very small. Thematerial reacts “Soft”with progressive dynamic

loads and allows efficient vibration damping.When loads exceeded the degressive load range,the load deflection characteristic becomesprogressive, material at this load range becomesstiffer with increasing load that movements atoverloads are limited.

Fig7. Load Deflection Curve of Sylomer® M 25

Fig6. Sylomer® Standard Types: Load ranges,Identification Colours and Densities

To solve this problem, the simpliest way is to insert aresilient vibration isolation pad at support brackets.The isolation pad has to be soft in dynamicmovement for best vibration absorption andbecoming hard when at overload, so as to keepthe rail in position and guiding the verticalmovement of elevator cars properly. To facilitatethis, a quasi-linear load to deflection material calledSylomer® is used. Its non-linear deflection vs loadcharacteristics precisely controlled the “Soft” regionto cater the lift roller loads and maintaining bestpractical minimum movement when load isexcessive (See Figure. 5).

Fig5. Sylomer® Special PUR Pad at Lift Rail Brackets

4 . Mason Industries (Hong Kong) Limited