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).