Seismic Behaviour of Elevator Systems in Hospitals

Joana Isabel Freire Palha

Civil Engineering Department, Instituto Superior Técnico, Universidade Técnica de Lisboa, Portugal

Abstract

Elevator systems are a vital key regarding the functional quality of hospitals. The defective functioning of these systems

may cause the disruption of medical services, leading to the generalized suspension of medical care, a situation that may

reach critical proportions after a seismic event. This dissertation presents a description of the most important components of

elevator systems and makes a retrospective analysis of the observed performance of elevator in past earthquakes, thus

allowing drawing conclusions about the diversity and severe nature of the defective functioning reported. This leads to a

logical assessment of the importance of these systems and confirms their vulnerability in moments of seismic activity. The

derailment of counterweights stands as the most common failure here reported. A comprehensive review of the researches conducted to study the dynamic behaviour of the elevators, more specifically the rail-counterweight system, is also presented.

This work includes a retrospective of international regulations regarding the seismic design of non-structural elements, aimed

at standardizing the methodologies used. Among these, the standards and recommendations of the US, Japan and Europe

(still under development), are characterized by a higher specificity in the context of elevator systems. Portugal hasn’t so far

developed any regulations concerning the seismic design of the elements in the elevator systems and this is the reason why

the ICIST/IST, answering a request addressed by the ACSS, has implemented the study reported in this dissertation. The

study intends to analyse the seismic performance of the elevator systems as installed in hospitals, with the main purpose of

informing and alerting about the vulnerability of these elements, introducing the concept of seismic safety devices (seismic

switches and counterweight derail sensors) and the methodologies to deal successfully with the seismic design and instalment

of the components and their connections to the main structure. These measures aim at increasing the safety and the operative

functioning of the system after a seismic event. The methodologies here presented have been applied and confronted in the

context of a case study based on the recently built hospital in Cascais, in order to analyse the car and counterweight guide rails seismic response. The study mentions the involvement/participation of the representatives of well-known manufacturers

of elevator systems, such as KONE, OTIS, Schindler, SICMALEVA and Thyssenkrupp Elevators.

Keywords: Hospital, elevator, seismic response, seismic safety devices, NP EN 1998-1, prEN81-77, ASME A17.1.

1. Introduction

The increased demand for medical care after seismic events makes it imperative that hospital facilities keep their

capabilities and services fully active. In this context,

elevator systems are unquestionably important to the

successful operation of hospital in emergency situations.

The importance of elevator issues in seismic design and

performance evaluation is now well recognized by

researchers as well as engineers. The devastation resulting

from the earthquakes in San Fernando (1971) and Miyagi

(1978) raised the concern to collect and record in a

systematic and organized manner the quantitative and

qualitative information on the failures presented by elevators after the occurrence of strong earthquakes [15].

This process led the U.S. and Japan to introduce the first steps of design and installation, with the purpose to

mitigate elevator damage resulting from seismic events,

thus constituting the great pioneers in this field.

Experience shows that the acceleration and

deformation of the structure strongly affect the elevator

systems and is essential for its consideration in its design.

The constant concern to ensure the safety of the

occupants, limit the damage and reduce the systems out of

service led to the development and continuous refinement

of methodologies for seismic design of elevators,

especially the use of seismic switches and counterweight derail sensors. Given the high degree of

comprehensiveness and specificity, the American code

ASME A17.1 [2] and the prEN81-77 [11], still under

development, deserve a special attention.

INSTITUTO SUPERIOR TÉCNICO

Universidade Técnica de Lisboa

2 J. Palha

2. Description of Elevator Systems

The elevators are a complex structural, mechanical and electrical system [15]. Depending on their mechanism of

operation is possible to highlight the electrical traction and

hydraulic systems for its use on hospital facilities.

In general, the traction elevators essentially consist of a

car responsible for transporting passengers, balanced by a

counterweight through a system of cables that pass through

a traction sheave. These components, together with the

electric motor, the brakes and couplings are the power unit.

The vertical movement of the car and the counterweight is

guided by guide rails, usually made of steel, fixed to the

walls of the shaft by means of brackets. The components slide through guide shoes fixed to their frame.

The hydraulic elevators are typically used in buildings

up to seven floors, being composed essentially of a tank

that stores the hydraulic fluid, which, by means of a pump

system activated by an electric motor, is directed through

pipes to a cylinder that contains the piston. The piston

pushes directly or through cables (roped), the car. The

cylinder may or may not extend into the ground, being

referred to as in-ground or holeless respectively. Usually,

these systems do not have counterweight and can differ

depending on the number and location of the pistons in the shaft.

The elevator systems can have a machine room, which

is the compartment where the engine and command units

are installed.

3. Review of the Observed Performance of Elevators in

Past Earthquakes

Based on reports supported by inspections, surveys and

interviews with elevators companies, the main system

damages in major earthquakes recorded after the mid-

twentieth century, are identified in Table 1, such as the San

Fernando (1971), Northridge (1994) and Kobe (1995)

earthquakes. These results allow the identification of the

components most susceptible to earthquake-induced ground motions. It is noted that the operation of elevators

depends on the stability of the structure and conservation

of electrical power supply.

The notorious quantitative and qualitative discrepancy

of damage observed between both systems can recognize

and distinguish the vulnerability of traction systems, which

gives particular emphasis to the whole counterweight-rail

system. The counterweight, being the heaviest element of

the whole system, is subjected to high inertial forces

during the earthquake, inducing strong contacts with the

guide rails, damaging it, their supports, the frame and the guide shoes. This situation may result in counterweight

derailment or weights coming out from the frame. The

occurrence of derailment or the oscillation of the structure

itself are the main causes for the movement of the cables

out of the grooves, swaying in the shaft and being stuck by

fixed devices in the shaft as for example the guide fixing.

Tabela 1 - Summary of major elevator damage observed

in past earthquakes.

The hoses, machinery and main equipments in the

machine room may overturn and displace as a result of a

defective or inadequate anchorage.

The restoration of elevator service after being shut

down by triggered seismic switch, without conducting an

inspection by an elevator mechanic, can result in major

system damage, endangering the lives of passengers.

Hydraulic systems appear to be much less susceptible to seismic events, which may be due to a lack of a

counterweight system in most hydraulic models, the

smaller number of components, their applicability to low

and medium buildings, or the fact that the machine room is

located on the lower floors (where the accelerations are

usually smaller compared with the top floors). However,

on should recognize the scarcity of information on the

damage presented by hydraulic elevators in the various

consulted reports.

Electrical Traction Hydraulic

- counterweight derailment;

- car derrailment; - counterweight or weights collision with the car; - bent guide rails; - damage to guide rail anchorage; - machinery and electrical equipment in the machine room tipped or moved;

- hoist rope jumped from sheave grooves; - ropes damaged by hitching, colliding and wrapping with the protuberances in the hoistway; - damage to the landing and final limit switches resulting in the loss of spatial reference; - failure of the seismic safety

devices;

- leaks in the hydraulic line; - piston and cylinder tipped or moved; - hydraulic machine and tanks overturned or displaced; - hoses displaced;

- damage to the car and shaft doors; - damage to the shaft walls resulting from fallen debris; - damage to the guide shoes.

Fig. 1 – Elevator damage: counterweight derailment (left) and guide rail and bracket (right). [7]

J. Palha 3

4. Codes and Standards

Currently, there is a set of standards and recommendations for the determination of acceleration and

maximum inertia forces that develop in the components,

and the maximum allowable drift. However, ASME A17.1

[2] and prEN81-77 [11], go further, including sizing and

installation requirements to meet seismic action for the

various components that comprise the elevator system.

ASME A17.1 is the primary regulation used for the

design and installation of lifts1 located in 3 of the 4 seismic

zones that cover the U.S. territory (zone ≥ 2). The design

procedure is essentially based on an horizontal seismic

action defined by an acceleration of 0.25 g and 0.5 g for zone 2 and 3 (or higher) respectively. However, these

figures do not seem to consider the position of equipment

and importance of the building. The code presents a set of

seven graphs corresponding to a specified type of guide

rail, listing the maximum supported by the pair of guides

with the spacing between brackets, the number of

intermediate supports and seismic zoning, thus establishing

the equations. These graphics are intended to assess or

ensure the resistance of the guide rail system due to

seismic forces.

The prEN81-77, developed by CEN/TC, prescribes safety rules of construction and installation of new

electrical and hydraulic elevators subject to earthquakes

and should be used in conjunction with EN 81-1 [8] and

EN 81-2 [9]. A major feature that distinguishes prEN81-77

from ASME A17.1 is the definition of security

requirements based on the classification of the elevator

system, taking into account the design acceleration (ad), for

shaded classes identified in Table 1.

Table 1 – Seismic elevator categories.

The proposed procedure for determining the value of ad

is set out in Annex A of the document, which presents only

an informative nature. Thus, the described methodology is mainly based on the equations established in EC8 [10] for

non-structural elements (Art. 4.3.5.2):

Where Sa is the seismic coefficient applicable to non-

structural elements; γa the factor of the element (equal to

1.0, although it may be higher for lifts with special security

features); qa the behavior factor of a non-structural element

(equal to 2.0). Note that the quantification of these

——— 1 Applied to all elevators with counterweight or

direct-plunger hydraulic elevators

parameters does not consider the different sensitivities inherent in the various constituent components of various

models of existing elevator systems.

The seismic coefficient is determined by the following

equation:

(2)

Knowing that, α the ratio of the design ground

acceleration on type A ground (ag) to the acceleration of

gravity (g); S the soil factor; Ta and T1 the fundamental

vibration period of the non-structural element and of the

building, in the relevant direction, respectively; H building

height measured from the foundation or a rigid base; z

height of the non-structural element above the level of

application of the seismic action. As can be seen by the following figures, the seismic coefficient incorporates the

linear amplification of seismic acceleration with the

building height (Fig. 2), and the resonance effect

corresponding to peak showed in Fig. 3 (Ta = T1). There is

still that Sa contains values between αS and 5.5αS.

Thus, compared with the ASME A17.1, the proposed

approach for determining the seismic acceleration induced

at the elevator system seems to introduce a higher level of

accuracy, taking in account the following:

- seismic zoning;

- soil type;

- importance of structure;

- location of the elevator system in the building;

- amplification of acceleration with the building height;

- resonance effect.

However, this expression just considers the maximum

acceleration at ground level, discarding the spectral

accelerations associated with the relevant modes that

reflect the expected behaviour of the structure. In addition,

0

2

4

6

0 0,2 0,4 0,6 0,8 1

Sa/α

S

z/H

Ta=0Ta=T1

0

2

4

6

0 1 2 3 4

Sa/α

S

Ta/T1

z=0z=H

Classe ad

(m/s2) (g)

0 ad < 1,0 ad < 0,10

1 1,0 ≤ ad < 2,5 0,10 ≤ ad < 0,25

2 2,5 ≤ ad < 4,0 0,25 ≤ ad < 0,41

3 ad ≥ 4,0 ad ≥ 0,41

(1)

Fig. 3 - Sa/α.S depending on Ta/T1.

Fig. 2 - Sa/α.S depending on z/H.

4 J. Palha

this methodology does not consider the continued operation of the system to a seismic action corresponding

to the requirement of damage limitation.

Both methods impose limits of deflections and stresses.

Fig. 4 – Horizontal seismic forces induced by the car or

counterweight to the guide rails: scenario A (left); scenario B (right).

Based on the observed elevator damage during past

earthquakes and on seismic design methodologies

addressed in these regulations, it is presented a summary of

the requirements to several components of these systems

installed in hospitals with the introduction of new

recommendations [2] [5] [11]:

4.1. Guide Rail System

– Shall be design based on the seismic action imposed by the weight of the car plus part of its rated capacity

(and the weight of the plunger in the case of hydraulic

lifts) or counterweight and on deformation associated

with the movement of the floors.

Guide Rail:

– Shall be designed to resist to the flexural stresses and deformations generated by the seismic action.

Brackets and Supports:

– Shall be designed to resist to the flexural stress, shear forces and deformations generated by the seismic

action.

– Installation of intermediated supports to improve the seismic performance of the counterweight-rail system.

Fixings:

– Shall be designed to resist to the shear forces and deformations generated by the seismic action.

Fishplate (and fixings):

– The installation process and the geometric and resistant features shall be specified based on the type

of guide;

– Ensure the resistance to bending, shear stress and deflection induced by the weight of the car (and part

of its rated capacity) or counterweight, and also the

deformation associated with the movement of the floors.

4.2. Car and Counterweight

– The clearances between the components and the walls of the shaft shall be limited to prevent

collisions.

– The car and counterweight shall be provided with

position restraints able to hold the frame on its guide rails. The retaining devices shall be rated to

resist seismic action imposed by the weight of the

car or counterweight and positioned so as to avoid

contact with the guide, as well as its undocking.

The retaining device shall either be integrated or

mounted close to the guide shoes.

– Protective devices shall be installed on the counterweight frame to prevent the weights’

movement outside the frame.

4.2.1. Cables and Sheaves

– The sheaves shall be provided with cable retainers in order to avoid its displacement.

– The groove shall be designed to prevent the displacement of the cables during earthquakes;

– Clearances between cables and snag points located in the shaft shall be defined according to ;

– Control of induced vibrations of cables.

– Snag points created by brackets, fixings, fishplates and similar devices shall be provided

with cable retainers to prevent snagging of the

cables in the shaft.

4.3. Electrical Equipment

– The electrical equipment e its anchorages shall be designed to ensure their stability and the internal and

external integrity.

Equipment:

– Shall be designed based on seismic force induced

by the weight of the equipment.

Anchorages:

– Shall be designed to resist the seismic action and strain imposed by the equipment in order to

prevent the displacement or overturning of the

equipment

– A seismic isolator shall be provided under the power unit to minimize the horizontal vibrations.

4.4. Shaft

– Shall be designed (position, configuration and material) based on actions and deformations

imposed by the system and structure.

– The shaft deformation shall be limited, in order to minimize the damage to the walls and equipment

that is fixed in the shaft (doors, brackets, etc.).

J. Palha 5

4.5. Emergency Modes

– Each building shall be provided with at least one seismic switch and each elevator system with a

counterweight derail sensor.

– The models and characteristics of the devices (trigger

level) shall be specified based on the dynamic properties of the structure.

– The seismic switch shall be designed to trigger below the damage threshold. The device shall comprise at

least two sensors. And it shall be activated when the

acceleration in one direction or the vector sum of these

is reached.

– Buildings placed in high seismic zones shall be provided with a seismic sensor that detects the first

vibrations, allowing the anticipation of the seismic

event or preventing, in case of false alarms, the

shutting down of the system by the seismic switch.

– The hospitals shall be provided with access and guidance for a non-elevator mechanic to safely restore

the reduced-speed service in case of critical

emergency, without an prior inspection by an elevator

mechanic due to the action of the seismic switch.

– Emergency generators shall be provided to allow, in case of power failure, the elevator to moves to the

nearest floor for the evacuation of the occupants.

– Emergency lighting in the car shall be provided in order to reduce the fear of the trapped passengers.

– The hydraulic elevators shall be provided with a rupture valve, to prevent leaks.

5. Presentation of the Case Study

Regarding the seismic design of

elevators, a case study is presented

corresponding to the system installed

in the central block of the new Cascais

Hospital.

This section is intended for the

comparative study of the dynamic

response of the guide rails based on a

modal analysis by design spectrum

[12]. This analysis consists on a

primary and secondary system corresponding to the structure and the

guide rail system respectively. The

results are used to compare with static

analyses performed according to the

ASME A17.1 code [2] and prEN81-77

[11]. The selection of guide rails as an

object of study arises from the fact

that during a seismic phenomenon,

being integral parts of the building, are

directly affected by actions associated

with structure interaction system

through the brackets and the contact between the rail and the guide shoe.

5.1. Presentation of the Structure and the Elevator System

The study case incorporate an hypothetical building based on the new Cascais Hospital, consisting on a

reticulated structure based on reinforced concrete frames,

calculated based on specifications in REBAP [13] for

structures of normal ductility, adopting where possible,

concepts related to improved ductility structures, and some

wall elements. The structure is composed by concrete of

C30/37 grade and presents a fundamental frequency of

0.90 Hz. The building has an irregular development in plan

and in height, comprising a total of total of 9 upper floors

and a semi-buried (floor 0).

The elevator consists on a traction MRL system, used for serving floors 1 to 7, with the exception of the 4th floor.

The metallic counterweight (T82A) and car (T125B)

T-guide rail (Fig. 8) have a yield strength of 370 MPa.

Both guide rails are composed of 14 spans, identified in

Fig. 5, with a total length of 30.0 m. The base of these

elements is located at a height of 3.3 m from the floor 0.

The car and counterweight move along the guide rails

by means of slide guide shoes. Table 2 indicates the

characteristics of these components.

Table 2 - Properties of the frame elements of the guide rail model

Property T125B T82A

Mass (kg/m) M 17,90 8,55

Area (cm2) A 22,83 10,9

Elasticity modulus (GPa) E 210.0

Poisson’s ratio ν 0.3

Moment of Inertia along x-x (cm4)

Ixx 151.0 49.4

Moment of Inertia along

y-y (cm4) Iyy 159.0 30.5

Vertical distance between guide shoes (m) L 3.74 2.14

5.2. Numerical Modelling of the Structure and the Elevator

System

5.2.1. Dynamic Analysis

The modal analysis by design spectrum is partly based

on three-dimensional finite element model of the hospital

structure fully developed by the program SAP2000. The

beams and columns are simulated with frame finite

elements, and the diaphragms at each floor with shell

elements.

To model the guide rails system it resorts to a

simplistic numerical model, capable of reproducing a realistic behaviour (Fig. 6). Thus, the rails are discretized

with frame elements with a cross section according to the

dimensions presented in Table 3. The brackets are

represented by rigid frame elements that connect each rail

to the frame element of the U-section core, freeing

rotations and longitudinal displacement of the guide. The

three translations are restricted at the lower end of the rail. Fig. 5 – Shaft cross

section (in millimetres).

6 J. Palha

Fig. 9 – Schematic representation of the two components

that integrates the guide rail seismic response.

Component 1 Component 2

Assuming that the elevator is stopped during the

earthquake, the car and counterweight were modelled by

mean of lumped masses applied separately in each horizontal direction at the level of the guide shoes (Fig. 7)

to evaluate its behaviour when subjected to the directional

component of the design spectrum. According to Fig. 4

and Fig. 7, it is assumed that the car and counterweight

make contact with the guide rail in one (scenario B – one

mass) or two levels (scenario A - two masses) in the y

direction. For the x direction, contact is established at both

levels (scenario A). To define the forces transmitted by

guide shoes, it is assumed that the mass centre of the car

and the counterweight is located 1/2 and 2/3 of the height

respectively. Table 4 presents the masses considered for car and counterweight modelling.

In order to cover the worst case, it’s considered a total

of 28 possible positions for the car and counterweight,

referenced by the location of the lower guide shoes, at the

floor, brackets and middle span level. These locations are

substantiated by the determination of the respective

influence lines.

The design spectrums for both types of seismic action

are established according to NP EN 1998: 2009 [12], assuming a behaviour factor (q) of 1.6.

Table 4 - Masses considered in the modelling of the car and

counterweight for scenario A. (tons).

The performance of the guide rails system can be

affected by the displacements between floors (component

1) and the local deformation of the guide rails due to

contact with the car or the counterweight (component 2),

schematized in Fig. 9. Based on a simplistic approach, it is

attempted to quantify both components through of two

distinct dynamics analysis. The first refers to a model of

individual guide rail not including the car or counterweight

to determine the effects associated with the deformation of

the building. In the second analysis is considered the

positioning of the car and counterweight in their guide rails, accounting for both components.

5.2.2. Static Analysis

To analyze the behaviour of the system due to the

actions defined in accordance with ASME A17.1 for zone

2 (Cascais could fit into that area), the rail are modelled as

a horizontal continuous beam with frame elements, whose characteristics are exactly identical to those used in

Direction Lower

Guide Shoes

Inferior

Upper

Guide Shoes

Inferior

Total

T125B x 0,454 0,454 0,907

y 0,907 0,907 1,814

T82A x 0,702 0,351 1,052

y 1,403 0,702 2,105

Table 3 - Properties of the guide rail cross section according ion according to Fig. 8.

Guia Dimension

(mm) A B C D E e

T82A 68,25 82,5 9,0 25,4 6,0 19,8

T125B 82,0 125 16,0 42,0 9,0 24,3

Fig. 7 – Schematic representation of the guide-rail system model.

Fig. 8 – Guide-rail cros section [2].

M2

M1 M1

Scenario A Scenario B

Guide Rail

T82A

T125B

Elevator shaft

Brackets

Fig. 6 - Representation of the guide-rail model.

e

J. Palha 7

Fig. 10 – Schematic representation of the moving loads.

dynamic analysis. The forces transmitted by guide shoes are defined as moving loads, as schematized in Fig. 10 in

which L is the distance between guide shoes.

The action established in accordance with the

prEN81-77, is set based on a maximum acceleration

corresponding to the higher share of the guide shoe. It is

also analysed the situation characterized by z max (25.1

m), assuming that the rigid base is located at floor 1, and

considering Ta zero.

5.3. Comparation of the Resuslts

In the following figures were exposed the envelope of

accelerations, bending moments and displacements

generated in each guide rail, obtained by dynamic analysis,

and according to the methodology proposed in the ASME

A17-1 code and prEN81-77. In this study are only exposed

the results related to the earthquake type 1, since it appears

as the most conditioning situation, and the scenario and

direction that results in a more severe guide rail response.

Fig. 11 – Envelope of accelerations in the car guide rail for

masses applied in x direction (scenario A).

Fig. 12 - Envelope of accelerations in the counterweight guide rail for

masses applied in x direction (scenario A).

Note that only the accelerations generated in the

isolated guide rails are comparable with the approaches

under consideration (Fig. 11 and Fig. 12). Interestingly, it

appears that, according to the elevators required in prEN81-77, the system belongs to Class 3, but the

acceleration defined by ASME A7.1 corresponds to a class

2 system. Indeed, the prEN81-77 imposes a seismic design

for the guide rail for both categories.

It appears that both guide rails have a similar behaviour

since they rely on vibrations induced by the building.

However, the maximum value defined by prEN81-77 is

exceeded at the top of the system, where is located the

traction and control.

For the U.S. code, assuming a nonlinear behaviour due

to the structure itself or the elevator system, it appears that

the value of 0.25 g is much lower than the results obtained by dynamic analysis for the top half of the rail, presenting

a less conservative compared to prEN81-77. Thus, the

acceleration seen in the top of the system goes far beyond

the value stipulated in ASME A17.1 sizing. This suggests

that the peak value of 0.25 g does not incorporate the effect

of amplification of the accelerations with the height of the

building.

The component of the accelerations associated with the

deformation of the guide rails due to its contact with the

car or counterweight, represented by the peaks of

acceleration corresponding to the points of location of the middle span guide shoes, shows fairly pronounced local

amplification, especially in T82A which is associated to

higher masses and lower stiffness. However, considering a

mass distribution of vertical cockpit identical to the note

balance is also high acceleration peaks, though less

significant.

This apparent amplification effect can be explained by

the existence of local vibration modes associated with the

positioning of concentrated masses on the model of the

0,0

5,0

10,0

15,0

20,0

25,0

30,0

35,0

0,00 0,10 0,20 0,30 0,40 0,50

Gu

ide

Rai

l(m

)

Acceleration(g)

0,0

5,0

10,0

15,0

20,0

25,0

30,0

35,0

0,00 0,20 0,40 0,60 0,80

Gu

ide

Rai

l(m

)

Acceleration(g)

L

8 J. Palha

guide rail. The observed peaks reach to exceed the rate of acceleration recorded at the top of the rail, which indicates

the importance of the building dynamic characteristics on

the guide seismic performance. Thus, these methodologies

do not consider the possible existence of local vibration

modes.

Despite that, the acceleration associated with the

position of the car/counterweight seems to be extremely

high, which may be the result of an unrealistic behaviour

of the system associated with the fact that it is subject to a

seismic action with a high period of return. However, these

results call for the need for further reflection and research on the behaviour of the system to be considered in the

design explained in the regulations.

It also raises the question of the reliability of the trigger

level of the seismic switch proposed by the various

regulations, highlighting the value of 0.3 g and 0.1 g of

ASME A17.1-77 and prEN81 respectively. The first

considers the sensor installed in the machine room (upper

floors) where 0.3 g accelerations are recorded, resulting in

the activation of the device. In pre-standard, the sensor is

placed at the lower floors, however it is observed that the

level of the first bracket are recorded accelerations in the value of 0.03 g in both systems, which is below the limit

recommended in the activation prEN81-77.

Fig. 13 - Envelope of the flexural moments generated in the car guide

rail for the masses applied in the x direction (scenario A).

The bending moments obtained by the dynamic

analysis also consider the effect associated to the local

deformation of the guide rail. Hereupon, the total bending

moment is given by the difference M2-M1, increased by

the effect of the building deformation (M1), which shall be

disused the behaviour factor. Thus, the represented

bending moments represented in Fig. 13 and Fig. 14 are given by the following equation:

Fig. 14 - Envelope of the bending moments generated in the

counterweight guide rail for the mass applied in y direction (scenario

B).

M2 is the bending moment generated in the model of

the guide rail with the car/counterweight.

Based on the joint efforts made by the dynamic

analysis it appears that most of the bending moments

derived from the local deformation of the guide rail. There

is a maximum occurrence of peaks along the guide rail,

particularly at the middle span of the guide, mostly due to

the application of concentrated masses and the associated

vibration modes.

In opposition to the acceleration values obtained by dynamic analysis, it appears that the worst case scenario in

terms of bending moments is associated to the masses

applied in y direction. This situation is justified by the fact

that this data incorporates the effects related to the contact

between the guide and the car/counterweight and the

movement between floors.

The values determined by the U.S. Code present

largely lower than those obtained by the prEN81-77 and

the dynamic analysis for the counterweight system. This

points to a rather non conservative approach.

Table 5 indicates that the minimum and maximum inertia and spacing brackets respectively, determined in

accordance with ASME A17.1, considering the total mass

of the component, are respected. Thus, the U.S.

methodology ensures that the system under study is

sufficiently secure to withstand the seismic action

considered. However, this statement does not comply with

the dynamic behaviour of the system to the present case

study. This raises questions concerning the effectiveness

0,0

5,0

10,0

15,0

20,0

25,0

30,0

35,0

0,0 0,2 0,4 0,6 0,8 1,0

Gu

ide

Rai

l(m

)

Mx(kNm)

0,0

5,0

10,0

15,0

20,0

25,0

30,0

35,0

0,0 2,0 4,0 6,0G

uid

e R

ail

(m)

My(kNm)

(3)

J. Palha 9

and appropriateness of applying the methodology of seismic design guides, which can compromise system

security.

Table 5 - Maximum and minimum length of the span and moments of

inertia of the guide rail cross section respectively in accordance with

the provisions of ASME A17.1 (without intermediate supports).

Fig. 15 - Envelope of the displacements generated in the car guide rail

in y direction (scenario A).

Fig. 16 - Envelope of the displacements generated in the

counterweight guide rail in y direction (senario B).

The Fig. 15 and Fig. 16 are exposed the envelopment of the displacements resulting from contact of the

car/counterweight with the guide rail, for the worst

scenario and direction. It appears that the evolution of

deformations along the guide does not show a linear trend,

as derived from the accelerations induced by the contact of

the cab/counterweight to the guide, which are associated

with the existence of local vibration modes, as already

mentioned. Therefore, these values are not maximum for

the highest positions.

In general, the guide rail displacements obtained by the

dynamic analysis are higher than those determined by the ASME A17.1.

The counterweight guide rail displacements exceed the

maximum value determined according to the prEN81-77,

but in the car guide rail the maximum values are very

close. However, the graphics above displayed should be

increased with the strong effect associated with

displacement of the floors. Hereupon, it appears to be an

unfeasible approach.

This parameter should play an important role in seismic

design of elevator systems, since the deformation of the

shaft walls significantly interferes with the maintenance of the system operation, as such, the results point to the fact

that prEN81-77 does not ensure the elevator safety.

However, based on a proper structural design of the

building is possible to reduce the impact that the

movement of the floor has in the elevator seismic response.

It was also analyzed the response of the car guide rails

considering a mass distribution identical to that of

counterweight, resulting in deterioration of system

behaviour.

6. Conclusions

In general, given the low number of fatalities recorded

in the analyzed earthquakes, it appears that the elevator

systems play a favourable role in the protection of human life. However, the severity of damage observed in the

various components contributes to the interruption of

system operation, affecting the vertical access to the

buildings. This leads to alarming social and economic

consequences, as it may significantly affect the

responsiveness of hospital facilities. However, the use of

seismic switches and counterweight derail sensor appears

to play a leading role in mitigating seismic damage,

promoting the security of these systems. Nevertheless,

restoring the system operation after the seismic switch

activation entails the completion of an inspection by an elevator mechanic, which, in a scenario earthquake, may

prove to be quite lengthy, affecting the operation of

hospitals.

There is a need for a comprehensive collection of the

resulting damage and the causes of earthquakes,

particularly in hydraulic elevators, and also the

characterization of the respective buildings.

0,0

5,0

10,0

15,0

20,0

25,0

30,0

35,0

0,0 1,0 2,0 3,0

Gu

ide

Rai

il(m

)

dy(mm)

0,0

5,0

10,0

15,0

20,0

25,0

30,0

35,0

0,0 5,0 10,0 15,0 20,0

Gu

ide

Rai

l(m

)

dy(mm)

lmax

(m) Imin

(cm4) x y x y

T125B 14,55 28,29 37,75 39,75

T82A 4,89 7,09 12,40 3,80

10 J. Palha

Based on the results of the case study, the counterweight system seems to be severely affected by the

seismic action mainly due to high masses and its vertical

distribution.

It was found that the behaviour of the system depends

on the following aspects:

seismic vibrations induced by the various brackets that

attach the guide rail to the structure, comprising the

amplification effect associated with the dynamic

characteristics of the structure and the soil type;

position of the car/counterweight, which affect the

dynamic properties of the system, including the positions at the middle span, and there is the

occurrence of local vibration modes .

The values determined in accordance with ASME A17.1,

point to a non-conservative behaviour associated with the

failure to consider the complexities inherent in the system.

Thus, the code does not appear to be valid to the seismic

design of the case study.

The results concerning the methodology recommended

in prEN81-77 suggest insufficient strength to ensure the

safety of the guide rail systems when subjected to a high

return period earthquake. Thus, the results suggest that the methodology advocated in prEN81-77 has no applicability

to the case study.

The invalidations can be justified by the fact that the

system behaviour is strongly affected by its local

deformation of the guide rail associated with the

occurrence of local vibration modes, which are not

considered in any of the addressed codes and normatives.

One must not forget the fact that it is considered different

values of behaviour factors, which reflect the nonlinear

response of the structure or elevator. Also the excessive

movement of the floors can compromise the operation of

elevators, which apparently is not always approached in the European methodology. However, based on an

appropriate structural design it can limit the deformation of

the shaft. This underlines the need to combine the efforts

of civil engineers and elevator companies, which involves

the optimization of elevator seismic response, in order to

ensure the safety and operational maintenance of these

systems, particularly in hospitals when subjected to a

seismic event.

However, optimization of seismic behaviour of the

building and vertical distribution of its mass appears to

favourably affect the guide rail system, which may make feasible the design seismic pre-defined in European

standard. Any of these general conclusions may be

regarded as provisional since these were based in a single

case, requiring confirmation in other situations.

7. References

[1] AN-EC8. Anexo Nacional da NP EN1998-1:2009

(Versão Provisória). Eurocódigo 8: Projecto de

estruturas para resistência aos sismos. Parte 1:

Regras gerais, acções sísmicas e regras para

edifícios. Comissão Técnica Portuguesa de

Normalização CT 115, 2009.

[2] ASME A17.1. Safety Code for Elevators and

Escalators. American Society of Mechanical

Engineers, New York, 2004.

[3] Ayres, J., Sun, T. e Brown, F. (1973a)

Nonstructural Damage to Buildings, in The Great

Alaska Earthquake of 1964: Engineering, Division of

Earth Sciences, National Research Council, National

Academy of Sciences, Washington, DC, 346-456.

[4] Boroschek, R. e Muñoz, E. Comportamiento

Sísmico de Ascensores. Boletín de Información

Tecnológica (BIT), 7(17) (2000), 26-29.

[5] Boroschek, R. e Muñoz, E. Diseño sísmico de

ascensores de tracción. Anales del Instituto de

Ingenieros de Chile, 114 (3) (Dezembro 2002), 107-

116.

[6] Ding, D. e Arnold, C. Architecture, building

contents, and building systems, Chapter 9 in

Supplement to Volume 6: Loma Prieta Earthquake

Reconnaissance Report. Earthquake Spectra (1990),

339-377.

[7] Du, P. Wenchuan Seism: Statistics & Analysis of

Elevator Dameges in Xi’an; Elevator World,

November (2008), 114-117.

[8] EN 81-1:1998. Safety rules for the construction

and installation of lifts — Part 1: Electric lifts.

European Committee for Standardization (CEN),

Brussels, 1998.

[9] EN 81-2:1998. Safety rules for the construction

and installation of lifts — Part 2: Hydraulic lifts.

European Committee for Standardization (CEN),

Brussels, 1998.

[10] Eurocode 8. Design of structures for earthquake

resistance - Part 1: General rules, seismic actions

and rules for buildings. European Committee for

Standardization (CEN), Brussels, 2004.

[11] prEN81-77:2010 (still under development). Safety

rules for the construction and installations of lifts —

Particular applications for passenger and good

passengers lifts — Part 77: Lifts subject to seismic

conditions. CEN/TC 10, 2010.

[12] NP EN 1998-1 2009. Eurocódigo 8: Projecto de

estruturas para resistência aos sismos, Parte 1:

Regras gerais, acções sísmicas e regras para

edifícios. CEN, 2009.

[13] REBAP. Regulamento de Estruturas de Betão

Armado e Pré-Esforçado. Decreto-Lei nº349-C/83,

Decreto-Lei nº Imprensa Nacional - Casa da Moeda,

Lisboa, 1984.

[14] Schiff, A. J. The Whittier Narrows, California

J. Palha 11

earthquake of October 1, 1987-Response of elevators.

Earthquake Spectra, 4(2) (1988), 367-375.

[15] Suarez, L. e Singh, M. Review of Earthquake

Performance, Seismic Codes, and Dynamic Analysis

of Elevators. Earthquake Spectra, 16 (4) (2000), 853-

878.

[16] Yao, G.C. Seismic Performance of Passenger

Elevators in Taiwan. International Journal of

Earthquake Engineering and Engineering Seismology

(2000).