Standard Summary and Additional Rail Calculations With Respect to Seismic Forces
Sep 23, 2023
“TS EN 81-77 Safety Rules for the Construction and Installation of Lifts — Particular Applications for Passenger and Goods Passenger Lifts — Part 77: Lifts Subject to Seismic Conditions”
“TS EN 81-77 Safety Rules for the Construction and Installation of Lifts — Particular Applications for Passenger and Goods Passenger Lifts — Part 77: Lifts Subject to Seismic Conditions” Standard was revised and implemented in 2020. Most of our country is located in high-grade earthquake zones. This constitutes an important risk that needs to be considered, especially in regions located in the first- and second-degree earthquake zones. Therefore, I think it would be useful to provide some preliminary information on this Standard. I have tried to explain the calculation method proposed according to this standard and to evaluate the formulas.
Another point I would like to emphasize is that our colleagues responsible for inspections should not undertake any additional tasks for themselves on the basis of this study. Authorized institutions in this regard are the Ministry of Industry and Technology and the Ministry of Environment and Urbanization, and as long as they do not implement or announce a decision on the implementation of this Standard, it would not be right for individuals and institutions to consider themselves authorized and to assign themselves special duties. The purpose of this study is to provide preliminary information. Unless the Ministries issue a communiqué on implementation, it would be wrong to introduce additional articles to the Lift Control Criteria or to conduct additional inspections. Personal, impromptu operations cause considerable damage to the sector.
TS EN 81-77 Standard Content
This study essentially aims to focus on the method of calculation. Therefore, I will try to give a very brief summary of the content of the standard. As this will be a short summary, it will obviously not cover the full content. These preliminary explanations are only intended to explain what is covered, and the relevant articles of the Standard should be examined for the full scope. It would be wrong to make implementations based on the explanations in this article. The Standard itself should be taken as a source for implementations. This article cannot be cited as a source in this context. The Standard starts with 0 Introduction, 1; Scope, 2; Normative References, 3 ; Terms and Definitions, 4; List of Significant Hazards and then moves on to 5; Safety Requirements and/or Protective Measures. In order to comprehend the standard, the first 4 articles should also be carefully examined. As this study will serve as a preliminary introduction, we have proceeded from Article 5 onwards.
In article 5.2 Lift Well, the precautions to be taken to prevent snagging, friction or interference between lift fixtures and moving parts of the lift due to oscillations that may occur during an earthquake in the lift well are explained. Lift well height is examined in 3 different cases. For the first case, for well height z ≤ 20 mt, no additional safety measures are proposed. For 20 < z ≤ 60 mt, distances between fixed and moving parts are defined. This height clause stipulates that there must be a horizontal clearance between the moving parts and the corners of the fixed parts where there may be snagging of more than 900 mm for travelling cables, more than 750 mm for Compensating Chains and ropes and counterweight regulator ropes, more than 500 mm for car regulator ropes and more than 300 mm for suspension ropes. In situations where this clearance requirement cannot be met, it is required to install protection measures for example a protection wire in the corner of the rail bracket or other snag points. In cases where the well height is z > 60 meters, it is stipulated that regardless of the distances, all protruding points must be protected throughout the well with protection wires or ropes against snagging during swinging. Article 5.3 stipulates that if the building is divided into independent blocks by dilatation joints (expansion joints), the lift must remain on the same side of the dilatation section with all its parts, including the entrance halls and the well.
Article 5.4 Car states that the possible design acceleration (ad) effect expected during an earthquake and the forces that may occur in the lift should be taken into account. (It would actually be more accurate to refer to (ad) as calculated or planned Acceleration, but since it is used as design acceleration in TS EN 1998-1 standard, the same term is used. For uniformity, attention has been paid to use the terms used by the TS EN 1998-1 Standard in other definitions, too). In order to calculate the additional force that may occur during an earthquake due to the design acceleration, 40% of the rated load in passenger lifts and 80% of the rated load in freight lifts should be added to the empty car mass to calculate the additional mass.
In article 5.4.2 Car retaining device, it is stipulated that additional support Emergency Guides to the Rails should be placed at the top and bottom of the car suspension in the 2nd and 3rd Class seismic lift category. (The term emergency rail guides is the term used in TS EN 81-21 article 5.2. It is also used here for the sake of uniformity, it is used to refer to rail retaining device). The description and dimensions of this device are given in Figure 1. The clearances d1, d2, d3 between them cannot be more than 5 mm. The depth of the Car retaining device or its proximity to the rails must be at a distance that would not cause braking or tripping. The Car retaining device must be calculated in such a way that it keeps the rail track within at least z3 > 5 mm as a result of the flexing of the rail during an earthquake. An additional amount of deflection in the rail, due to the introduction of new force, in addition to the normal amount of deflection should be evaluated. This case will be examined under the section on rail deflection in rail calculations. Again, in the car section and article 5.4.3, the car door locking device and its operation in Category 2 and 3 seismic lifts are explained by referring to TS EN 81-20 5.3.9.2.
Article 5.5 Counterweight and balancing weight stipulates that suspension and emergency retaining device should be resistant to the forces generated during an earthquake and that emergency retaining device should have the same specifications as those in the cars. Article 5.6 describes the precautions to be taken for the protection of suspension and compensating cables, traction sheaves and other sheaves, and Article 5.7 describes the precautions to be taken to prevent environmental damage in hydraulic lifts. Article 5.8 Guide rails specifies the values of stresses and deflections that are permissible during an earthquake. What is new in this article is the introduction of the equation “δperm = z1 — 2d3 – 5” as the maximum allowable amount of deflection during an earthquake. However, the deflection must remain below 40 mm under all circumstances. Article 5.9 describes the precautions related to the installation and fixing of machinery and other lift equipment.
Article 5.10 is on electric installations and electric appliances. Article 5.10.1 specifies that the electric equipment installation in the well should be protected against oscillations during an earthquake and withstand the forces caused by the design acceleration. In article 5.10.2, the behavior of the lift in case the main power supply is cut off during an earthquake is explained. Lifts in Categories 2 and 3 are mandated to have an additional energy source that will take the lift to the nearest floor even if the power is cut so as to prevent being trapped in the car. Article 5.10.3 specifies a Seismic Detector system and operating specifications for Category 3 lifts. The sensitivity, reaction times and re-commissioning conditions of seismic detectors are described in detail in this article. In article 5.10.4, the behavior of the lift in seismic mode is defined. Article 6 explains the inspection of safety requirements and protective devices and Article 7 explains the requirements for the provision of information for the user (instruction manual).
Note that these articles define the requirements based on lift categories. Not all conditions required are applicable for all categories. Each article specifies which requirements are necessary for which category. Attention should be paid to this in practice.
The category of a lift is also determined by the value of the (ad) design acceleration. Annex A Table A.1 shows how categories are determined after the design acceleration (ad) value is determined.
Annex B covers the determination of the Design acceleration (ad) value and general information. (ad) is defined as a function of the design acceleration, Sa is the seismic coefficient of a non-load-bearing element (adjoined to the building), ya is the importance factor of a non-load-bearing element (adjoined to the building), qa is the behavior factor of a non-load-bearing element and g is the acceleration of gravity and is expressed by the following formula.
In this formula, the seismic coefficient Sa of the lift, which is not a load-bearing element in the structure, must first be determined. Annex B proposes a formula for calculating Sa. This formula is as follows.
Where, according to EN 1998-1
ad is the design acceleration, in metres per square second;
g is the free fall accelaration (9,81), in meters per square second;
Sa is the seismic coefficient applicable to non- structural elements (non dimensional);
Ya is the importance factor of the element (shall e taken equal to 1. For lift used for special safety purposes the value shall be increased according to EN 1998-1. Ya is non dimensioal); lift used for special safety purposes are those installed in hospitals and the like for emergency services;
qa is the behaviour factor of the element (shall be taken equal to 2; qa is non dimensional);
a is the ratio of the design ground accelaration on type A ground (ag) as calculated in EN 1998-1, to the acceleration of gravity g (a=ag/g is non dimensiona);
S is the soil factor according to EN 1998-1 (non-dimensional);
Ta is the fundamental vibration period, expressed in seconds, of the non-structural element (Ta=0 if the lift does not affect the fundamental vibration period of the building. In other cases this value shall be increased according to calculation);
T1 is the fundamental vibration period, expressed in seconds, of the buuilding in the relevant direction;
However, instead of evaluations based on regions, new earthquake maps have recently been published and more precise values have been presented on the maps based on color charts. The new map and its values are presented below. The color equivalent value specified in the explanations section according to the color code should be considered as the α effective ground acceleration value.
The next element that needs to be evaluated is the S soil factor. An explanation is given for this value in the article 3.1.2 Definition of soil types in TS EN 1998-1 standard. Descriptions of Stratigraphic profiles are provided in addition to soil types defined as A, B, C, D, E, S1, S2 types. According to these definitions, the lowest soil on which a building with a lift can be constructed is determined as C type soil.
In the event that deep geology is not taken into account, the recommended option is to use two types of spectra: Type 1 and Type 2. For the purposes of the probabilistic risk assessment, it is recommended to select the Type 2 spectrum if the earthquakes that contribute most to the seismic risk identified for the site have an Ms surface wave magnitude not greater than 5.5. However, in the B.2 section of the TS EN 81-77 standard where Type 1 values are provided for the S value, Chart 3.2 was used and the value S=1,15 was selected.
If we continue from the formula, we reach the next expression. Except in very exceptional cases, the well length (z) of the non-load-bearing lift attachment and the building height (H) (EN 1998-1 A 1.6.3) of the load-bearing building from the building foundation can be considered as equal to each other. For exceptional cases (lifts operating in various parts of the building) these values should be adjusted and calculated. For normal practices, the z/H ratio can be considered as 1. (if z=H case)
In lower expressions, the fundamental vibration period Ta of the extension lift can be considered as 0 since it is not in a structure that will affect the vibration period T1 of the stationary building. Again, in very exceptional cases, this must be taken into account and calculated separately. In this case, the second part of the formula for a normal lift can be slightly simplified.
We have determined that we will consider S = 1.15, in this case
Sa = 1,15*2,5* α
It can be calculated as Sa = 2,875 α
This value is valid for lifts that are subject to normal practices as mentioned above. For exceptional cases, the formula should be calculated in detail. By simplifying, we get an accurate value quite easily and with very little margin of error. Since we have determined the Sa value, we need to rewrite the design acceleration formula used at the beginning to find the ad value and continue the calculation. To obtain the ad value, we need to determine the 
and qa values used in this formula. These values are specified in article 4.3.5 Non-load bearing elements of TS EN 1998-1 standard.
ad= Sa*( ya/ qa)*g
Article 4.3.5.3 defines the ya Importance factor
“4.3.5.3 Importance factors
(1)P For the following non-structural elements the importance factor ya shall not be less than 1,5:
- anchorage elements of machinery and equipment required for life safety systems;
- tanks and vessels containing toxic or explosive substances considered to be hazardous to the safety of the general public.
(2) In all other cases the importance factor ya of non-structural elements may be
assumed to be ya = 1,0. “
According to this article, we can consider the ya value as 1 for extensions other than safety systems and explosive tanks. In specialized buildings (schools, congress buildings, cultural assets, hospitals, hospitals, high-rise buildings) listed in Class 3 and 4 categories, it may also be a good practice to consider this value as 1.2 as an additional safety measure. (It is a suggestion of the author and not a standard requirement. See TS EN 1998-1 article 4.2.5, Importance classes in buildings)
In ELA’s statement on seismic lifts, it is explained that “lifts used for special safety purposes are those used in hospitals or emergency services and ya shall be considered equal to 1.5 in these lifts”. For high-rise buildings, it is recommended to consider the ya value as 1.2. (Amended 25.09.2021)
The qa value, which is the other new value in the formula, is specified in TS EN 1998-1, 4.3.5.4 Behavioral factors article in Table 4.4. According to TS EN 1998-1 Table 4.4, we can also consider the qa value as 2 in lift extensions, as well (TS EN 81-77 Annex B.2).
The formula then becomes as shown below.
ad= Sa*( ya/ qa)*g
Sa = 2,875 α m/s2
ad= 2,875*α*( 1/ 2)*9,81 m/s2
ad= 14,1*α m/s2
I would like to remind you again that this method is valid for lifts that do not have any special features and are installed normally. In exceptional cases, calculations should be made by substituting the values for the specific installation.
According to this formula, if we know the value of the coefficient of effective ground acceleration α, it would be very easy to calculate ad Design acceleration and Sa Seismic coefficient of a non load-bearing element (extension). If we know the design ground seismic acceleration value for type A soil ag, we can easily calculate the α value from ag/g. This approach is also suitable for the calculation method of the standard.
The sample presented in Annex B.2 of the standard demonstrates α =0,3262. Based on the calculation above:
Sa = 2,875 α =2,875*0,3262 = 0,9378
ad= 14,1 α =14,1*0,3262 =4,599 m/s2 would be achieved; and the standard also calculated the same values for α =0,3262.
Sa = 0,937 8
ad= 4,6 m/s2
For Türkiye, areas with effective ground acceleration coefficient α> 0.28 (lifts in earthquake zones 1 and 2) should be considered as category 3, those with values 0.177< α 0.28 (earthquake zone 3) as category 2, and those with values 0.07< α 0.177 (earthquake zone 4) as category 1 lifts. Zones withα 0.07 (5th earthquake zone) value are considered as category 0 lifts, and no additional measures are required for them. In the event that these calculations are required by the Ministry of Environment and Urbanization, each municipality should announce the effective ground acceleration coefficient for its borders.
Now that we have found the Design acceleration ad value, we can calculate the seismic force affecting the rails.
Annex D Proof of Guide Rails
Annex D describes the adjustments to be made in lift guide rail calculations specified in TS EN 81-20 article 5.7 and TS EN 81-50 article 5.10 according to the effect caused by ad seismic design acceleration. The rated load due to the seismic design acceleration during an earthquake should be calculated using the formula below (Annex D.2).
QSE = kSE*Q
The seismic force that would be generated by the earthquake design acceleration is specified by the standard as follows (Annex D.3)
FSE = ad*(PEC + kSE*Q) For car
FSE = ad*(PEC + q*Q) For counterweight and balancing weight,
QSE Mass of rated load to be considered under seismic conditions kg
kse Seismic load factor (0.4 for passenger lifts and 0.8 for freight lifts)
Q Rated load kg
FSE Additional force resulting from seismic design acceleration N
ad Seismic design acceleration m/s2
PEC Mass of empty cabin without taking into account control cable and balance chains kg
q Counterweight or balancing weight balance ratio value
Appendix D.4 describes the loads and forces to be taken into account in the seismic condition calculation. While calculations in TS EN 81-77 2014 standard are calculated under normal use travel condition, they are calculated as a separate condition in TS EN 81-77 2020 Standard. Seismic impact calculations include the calculation of rail bending and deflection while the lift is in motion (Annex D.4 Table D.1).
The calculation to be made for seismic conditions covers all the conditions specified in TS EN 81-20. Fp is the force exerted on the rails by the brackets due to the settling of the building or the shrinkage of the concrete, WL is the wind load on external lifts, Mg is the mass of the guide rails and Maux is the mass of the machinery or additional equipment attached to the rails, other than regulators and floor determining devices. The forces and torques consisting of these factors should be taken into consideration. For elevators with a travel distance of less than 40 m, the Fp force may be disregarded. Since the calculations are made for normal use travel conditions, k2=1.2 will be used as the impact factor (Annex D.5).
Another point to note is the values used as the permissible stress values of the rails. Despite the travel calculation, the 0.2% Tensile Strength value considered for the braking conditions of the rails should be utilized since earthquakes are not an event experienced regularly (TS EN 81-77 5.8.2.2).
A center of gravity misalignment of 5% in width and 10% in depth should be assumed for the counterweight or balancing weight if they are suspended from the center. Suspension system, balancing chain or ropes must also be taken into account in this calculation.
Regarding the direction of the acceleration that would affect the force that will occur as a result of the earthquake, since the ad value is not a directional value, it is essential to consider the ad value as the effective acceleration value in both directions for the additional force generated by the earthquake.
In the calculation of the bending force in the X axis direction ax = ad , ay = 0
In the calculation of the bending force in the Y axis direction ax = 0 , ay = ad values should be considered (Annex D.6).
Annex D.7 examines the vertical distribution of the loads. The distance between the car guide shoes or emergency guide rails is shown as h and the distance between the center of gravity and the ground is shown as ZSE.
XSE value represents the load ratio affecting the guide shoes or emergency guide rails and the greater of the following ratios should be used.
XSE = ZSE/h veya XSE = (h – ZSE)/h
This ratio is easy to determine in weights, but it is not so easy to know in the car beforehand. The center of gravity will change in the event of a levitating load or a distributed heavy load in the car. Since we will be using the larger ratio in this case, if we use the equation XSE = ZSE/h for the transfer load and XSE = (h-ZSE)/h for the distributed load, we will find a ratio of approximately 0.6. Therefore, it would be appropriate to use the value XSE = 0.6 for the car and for the weight group, unless it is a very exceptional design. Thus, we wouldn’t have to think too much, especially for a coefficient for the car, which can change in each travel.
Appendix D.8 and Appendix D.9 present the formulation of the bending forces acting on the Car and Weight rails. However, the following three considerations should be noted.
1. There was a displacement in the formulas given for the Fx and Fy forces and some multipliers appeared as if they were subscripts of the QSE load. These should be taken as multipliers.
2. The formulation is not continued for all of the calculations given in Annex D.4. Therefore, all calculations required to be performed by TS EN 81-20 and TS EN 81-50 in normal use travel calculations should also be performed completely based on the new Fx and Fy forces that will be determined for the TS EN 81-77 Annex D.4 earthquake condition.
3. Deflection calculation should also be made for the maximum rail deflection value specified in Article 5.8.2.2 under earthquake condition.
We can write the force formulas for the X and Y axes and proceed with the calculations. Perm values to be used in all formulas listed below should be taken from the values specified in TS EN 81-77 5.8.2.2 Table 4.
The section marked in yellow should be calculated as written below.
FY= k2*gn*[QSE*(yQ-yS)+ PEC*(yP-yS)] / (h*n/2) +[ay*( PEC+ QSE)*XSE]/(n/2)
MX= (3* FY* LK) / 16 , x= Mx / Wx
Total Bending stress =m= x + y perm
B. Buckling stress
For buckling stress, the effects from auxiliary equipment, the weight of the rails and the thrust effect of the brackets must be taken into account. With the incorporation of rail weights into buckling calculations in TS EN 81-20, buckling calculations must also be made for each operating condition. However, it should be noted that the value of “ω” is not used in the stress formula under this condition. Since there is no safety gear operation, only rail weight and FP forces are analyzed. Equipment attached to rails must be taken into account.
FV = (Mg*gn)+ FP
k = (FV + k3*MAux)/ A
C. Combined stress
Bending stresses
Bending and compression/tension stresses
=m= x + y perm
=m +(Fv+k3.MAux)/A perm
D. Flange bending stress
For roller (rolling-wheel) guide shoes
F =(1,85 * Fx) / c2 perm
For sliding guide shoes
F =(Fx*(h1-b-f)*6)/(c2*(L+2*(h1-f)) perm
The value used here should be the newly calculated force Fx.
E. Deflection amounts
Emergency guide rail measurements should be taken into account. The deflection caused by Fx and Fy forces cannot be more than 40 mm and the z3 value cannot be less than 5 mm.
δy = (0,7 * FY * L3) / (48 * * IX)+ δ str-y y-y düzleminde δperm
δx = (0,7 * FX * L3) / (48 * * IY) +δ str-x x-x düzleminde δperm
Counterweight or balancing weight calculations
Bending stress
Center of gravity misalignment should always be considered on the opposite side for negative conditions
FX = [k2*gn*(PEC+ q*Q)*ex*Dx] / n*h +[ax*( PEC+q*Q)*XSE]/n
MY= 3*FX*L /16 , Y = MY / WY
FY = (k2*gn*(PEC+ q*Q)*ey*Dy) 2 / n*h +[ay*( PEC+q* Q)*XSE]/(n/2)
MX= 3*FY*L /16 , X = MX / WX
Buckling stress
FV = (Mg*gn)+ FP
k = (FV + k3.MAux)/ A
Bending and pressure stresses
Bending stress =m= x + y perm
Bending and compression/tension stresses =M+(FV+ k3.MAux)/ A perm
Flange bending
For roller (rolling-wheel) guide shoes
F =(1,85 * FX) / c2 perm
For sliding guide shoes
F =(FX*(h1-b-f)*6)/(c2*(L+2*(h1-f)) perm
Deflection control on rail
δy = (0,7 . FY . L3) / (48 . . IX)+ δ str-y y-y düzleminde δperm
δx = (0,7 . FX . L3) / (48 . . IY) +δ str-x x-x düzleminde δperm
δperm = δ1 – 2d3 -5
but never more than 40 mm.
This study has been prepared to help with the understanding of the TS EN 81-77 standard, but it is the standard itself that should be taken as a basis for project work. It would not be correct to perform any operations on the basis of this article, and the author declares in advance that he will not be held responsible in this regard. I hope that the paper will be useful and that it will help you in using these calculations. Best regards.
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