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April 2009 | ELEVATOR WORLD | 95

Since the introduction of the first modern elevator in the 19th century, elevatorprofessionals likely have pondered ways that would allow them to accurately pre-dict how long various elevator components could be expected to last. Certainly onearea of fascination by many today involves efforts into trying to calculate thelongevity of one of the elevator’s more “active” elements – hoist ropes. The topic ofhoist rope longevity is more than an academic concern. In fact, the matter is criti-cal to the wellbeing of elevator installations in general, and to the future profitabil-ity of maintenance professionals in particular.

Many engineers and consultants already take the time to analyze and comparethe hardness of the metal present in hoisting components and then attempt toquantify the effect of various wear and fatigue factors on rope longevity. Althoughtedious and time consuming, the process of extrapolating rope life expectancy canbe accomplished through the use of mathematical calculations. This level of intro-spection and forethought is relatively complex, expensive and far from standard.Many who attempt such calculations stand daunted by the sheer complexity of themath and consequently choose to accept rough analyses, or life-expectancy prog-noses based on less than complete calculations. While better than nothing, deci-sions based on partial data are inherently flawed and lead to less than accurate, in-complete or erroneous conclusions.

The increased requirements and stresses of modern elevator designs impactworking components, especially hoist ropes, to varying degrees. It is critical thatprofessionals have ready access to complete empirical models using a comprehen-sive series of equations calculating results with a meaningful and useful degree ofaccuracy. Accuracy of such mathematical models can be further supported in com-bination with onsite observations of surrounding component machinery by experi-enced maintenance professionals.Physical examinations and testing,when combined with a complete seriesof mathematical calculations, can assistprofessionals in their efforts to decidewhich hoist rope is best for a particularinstallation and can, indeed, answerquestions about how long a particularrope should last. Continued

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Martin Rhiner and Kevin Heling of Brugg Wire

Rope offer more than 40 years of combined experience

in the elevator hoisting and parts-supply industry, with

their primary focus being in the area of ropes and ca-

bles. Rhiner led the RLP project and worked with vari-

ous individuals to develop Feyrer’s calculations into the

web-based application RLP.

UnderstandingElevator Rope

Performance, Endurance and Longevity

by Martin Rhiner and Kevin Heling

more sophisticated designs for rope. Today’s ropes arecrafted to more exacting tolerances and uses. Like the el-evator itself, hoist ropes have evolved. Technologically,they are far beyond yesterday’s simple sisal rope con-structions. In today’s elevator industry, it has becomemore essential than ever that rope design be closelymatched with the demands of elevator-system innovations.

When it comes to determining rope life, some profes-sionals seem to simply throw up their hands in confusionand walk away from the problem entirely. They have nei-ther the time nor the passion to delve into how variousfactors now present in today’s elevator designs have amultiplicatively destructive impact on the ropes them-selves. Some seek simple answers and solutions to theirquestions, which, to be fair, were not a real issue before.This failure to try to understand what’s behind the prob-lem has been a major factor for the oft-repeated storiesheard in the field that today’s rope is just not as good asit used to be. In reality, it only seems to be this way; ob-jective evidence shows the opposite. Of course, some ra-tionalize their lack of concern with the topic of rope lifeexpectancy by adopting an attitude that since it’s highlyunlikely they will have a serious long-term contract, theyneed not worry over the matter at all. It’s an economicdecision and someone else will pay; why should theycare? Still, some in the industry have identified the appar-ent contradiction of why better-made ropes seem to notlast as long as they did, and they want answers, which liein the answer to one major, seemingly obvious query:“How long should a hoist rope last on my elevator?”Why There Really Is No Simple Answer

Talk to a rope manufacturer and ask a “simple” ques-tion on how long the “average” rope will last, and you willlikely be met with a barrage of questions and details. Onegroup of questions concerns the actual elevator system,another the selection of specific rope designs, and yet an-other rope maintenance:

System inputs:◆ Car weight◆ Car capacity ◆ Percentage of capacity used◆ Car speed◆ Type of car guide (i.e., rollers or bushings)◆ Number of hoist ropes◆ Rope diameter◆ Drive sheave diameter◆ Groove profile of drive sheave◆ Type of wrap (single or double)◆ Number of deflector sheaves◆ Diameter of deflector sheaves◆ Number of reverse bends in the system◆ Type of suspension (1:1, 2:1, etc.)◆ Bending length◆ Angular offset between sheaves (if more than one

sheave)

The lack of a cost-efficient, easy-to-use process forprofessionals to mathematically use objective empiricaldata also leads them into using ropes that are suited nei-ther to their needs nor the building/property owner’s ex-pectations. Indeed, confusion or a simple lack of knowl-edge in this matter has led some professionals to rely onanecdotal evidence or base critical product decisions oncomparisons of how much time it took for a previous setof ropes to fail, then roughly extrapolate answers from that.

This present state of the industry also sometimes fails(or resists, due to a superficial or compartmentalized un-derstanding of cost) to consider maintenance issues,such as installation methods, the effects of poor (or no)load equalization, potential changing environmentswithin the installation or even the impact of significantlyincreased elevator use on hoist ropes (meaning moretrips on the elevator, more bends in the system or a com-bination of both). These are all real issues that create realheadaches for elevator service professionals bidding onnew maintenance contracts, or for architects or installa-tion designers who have to choose a product from amonga broad spectrum of rope manufacturers and distributors.Too often, the thinking is mainly about the machine duty,with far less thought given to such matters as rope designand the rope’s mechanical ability to perform. The Problem

For most of its early history, the typical elevator expe-rienced few real changes in overall design with respect tohoisting principles. Over the last 30 years, greater accel-eration and deceleration demands, increased repetitions(higher use), closer sheave placements and, even worse,reverse bends due to building limitations, have greatlyimpacted elevator designs and machinery. These factors,in addition to the implementation of smaller sheaves(which consequently requires the use of more demandingsheave-groove profiles) have created a major increase inthe demands placed on elevator hoisting systems. Thecombination of several of these factors has created somesurprising (and likely unanticipated) results in terms ofthe life expectancy of hoist ropes in some installations.Some severe instances of very short rope life may evenresult in a potential legal liability situation for elevatorcompanies, as maintenance attention and frequencymight not catch such aggressive wear and failure). Theindustry-wide adoption of machine-room-less (MRL) de-signs has made accurately predicting rope longevity a littlemore difficult – though far more necessary – than ever before.

To meet the challenge of more complex elevators,some rope manufacturers have already made the move to

96 | WWW.ELEVATOR-WORLD.COM | April 2009

UnderstandingElevator Rope Continued


Rope selection:◆ Lay direction of rope◆ Rope design (i.e., Seale, Warrington, filler, fiber core,

independent wire-rope core [IWRC], etc.)◆ Tensile strength of load-bearing wires◆ Number of strands

Rope and system maintenance:◆ Degree of rope lubrication (well lubricated, some lubri-

cation, dry, etc.)◆ Environment◆ New installation, replacement or modernization

Any of these parameters can be modified to optimizethe performance of the system and maximize the life ofthe rope, though to be sure, there are system design lim-itations. “What if” scenarios should be quick, accurateand easy to do. With existing systems, changing manyparameters may not be practical, but there is still the op-portunity for the substitution of different rope designsand finding the most appropriate improvement solution.After all these questions, the only answer offered willmost likely be that the life of a set of ropes depends onthe relative input and interactions of all these factors.

From this, one begins to understand the frustrationand the state of the industry today. This is not a smoke-screen from the manufacturer to limit discussion of thematter – only after obtaining this data can a rope manu-facturer or elevator-industry professional feel reasonablycertain enough to even begin to give an accurate rangedetailing rope life expectancy in a specific installation.Unfortunately, the calculations themselves take sometime to execute and understand. Your authors have seencases in which the results have been questioned or disre-garded entirely. Certainly, one can turn to engineers andconsultants (instead of rope manufacturers) to providesome analysis. But such a process can be expensive, andsometimes even their calculations will be found to be lessthan optimal, or their results will be described as “qualified.”

It is in the best interest of all in the industry (rope man-ufacturers, consultants, system designers and mainte-nance professionals alike) to have a simple, cost-effec-tive, usable way to accurately define and answerconcerns about rope life expectancy. Only in this way canmeaningful comparisons be made between rope (andother system) alternatives. Such work would requirelengthy articles/books full of exhaustive calculations toserve as a basis for such understanding. It would also de-mand years of testing and exacting validation to be con-densed to the essentials. Lastly, it would require combin-ing these calculations to create a system that professionalscould use by themselves. This is the very prescription ourindustry needs to answer the problem of predicting ropelife, and, fortunately, that prescription has been filled. The Answer: Predicting Rope Life

Why would a rope manufacturer provide a way to helpaccurately target rope life expectancy at all? Certainly, it

would be far more profitable to simply produce the samefamiliar standard sisal rope choices or simply keep sup-plying customers replacement rope. Your authors believethat in order to stay alive in the industry today, it is nec-essary for everyone to have access to as much informa-tion as possible. In today’s business world, it’s more thana courtesy – it’s a necessity.

If any one man’s work can be thought of as critical tothe field of calculating the life of ropes under strain andsubjected to motion, load, bending and tensile force, it isDr. Klaus Feyrer, former director of the Institute of Me-chanical Handling and Logistics (IFT) at the University ofStuttgart in Germany. Here, Feyrer researched the subjectand published his research in a variety of articles. Even-tually, his findings were combined into a single work ti-tled Wire Ropes: Tension, Endurance, Reliability. Over theyears, Feyrer continued his work in the field and becameone of the foremost names in rope technology.

Feyrer’s work is compre-hensive in scope, with hisbook serving as a treatisethat answers a vast numberof questions concerning theusage and lifespan of ropes.That the North American ele-vator industry as a whole isrelatively unaware of his ac-complishments can be attrib-uted to the fact that not onlydoes this field receive littlenotoriety in general, but thatalmost all of his work was,until recently, only availablein German.

Since Feyrer’s work usedmetric units, it was also more easily suited for immediateuse by European engineers, as opposed to North Ameri-can technicians who had to perform conversions to im-perial measurements. In addition, Feyrer’s work also re-quires the user to have both knowledge in and a facilityto understand complex mathematics. Thus, Feyrer’s workand its potential was just beyond the grasp of the profes-sional market that could best make use of it.

In late 2008, Brugg sought and received encourage-ment from Feyrer to present his calculations in a formatthat would increase their ease of use to the North Amer-ican marketplace. Now in final preparation, Brugg RopeLife Predictor (RLP) is to be released as a standaloneprognostic program accessible via the Internet. The sub-scriber must provide a password assigned by Brugg toenter a secure portal in order to access the program.From there, the user may enter data, handle calculations,adjust variables, contrast various scenarios and down-load results in PDF format. All data is automatically

Brugg RLP is based on Wire Ropes:Tension, Endurance, Reliability byKlaus Feyrer, which is available atwww.elevatorbooks.com.

Continued

deleted from the application after the user has logged out.The user can also copy work and send it to Brugg engi-neers for validation if desired. In addition to usingFeyrer’s calculations, RLP offers users a simple way toanalyze both the short- and long-term impact in installa-tion, maintenance and re-roping costs when using a va-riety of rope designs. RLP Basics

As with any researcher’s work, a large proportion isdedicated to analyzing various hypotheses, which arethen evaluated and explored. The end result of Feyrer’sWire Ropes: Tension, Endurance, Reliability is that one re-ceives a rounded view of the forces that affect hoist ropesand a relative understanding of how materials react tothem. RLP was fashioned by compartmentalizing, editingand, to a degree, reconfiguring Feyrer’s work. The finalresult is the creation of a prognostic program that calcu-lates the discarding number of bending cycles NA10where, with 95% certainty, not more than 10% of the wireropes have to be discarded because they have reachedthe maximum number of wire breaks. This is an objectiveand measurable criteria, which combines requisite safetywith rope inspection.

It is certainly possible that one could further refine theprogram, but this advantage would be of limited utility inthe field and hinder its ease of use. There are also certainfactors, such as installation and maintenance techniques,that can be very difficult to empirically judge. The formu-las used in Brugg’s RLP are specific for the elevator indus-try and include the following constant key factors:◆ All ropes share a common drive sheave.◆ All hoist ropes are tensioned to within 25% from the

highest to the lowest.◆ Rollers are used to guide the car.◆ Rope efficiency due to loss of friction is 98%.◆ Rope wire tensile strengths and sheave hardness/mi-

crostructure are compatible. Once the system parameters are entered and the rope

is selected, the RLP shows their impact on the rope lifeexpectancy. The results include: ◆ Static load per rope◆ Dynamic load per rope◆ D:d ratio◆ Number of single bends (NA10corr)◆ Number of corrected single bends (NA10corr) using en-

durance factors◆ Number of reverse bends, where applicable◆ Total number of working cycles to discard ropes


Example A shows how the life of hoist ropes increases ordecreases by simply changing one parameter.

RLP can optimize rope performance for and provide anunderstanding of what to expect from a particular eleva-tor system. The following examples show the impactwhen changing the groove profile, the type of rope andthe number of ropes used in an elevator system, whilekeeping all other parameters the same.

Brugg RLP offers a series of multi-step screens that walks the user through theprocess of calculating rope life, approximates ropes’ impact on maintenance costsand offers users the ability to review and contrast alternative rope selections.

Undercut U- and V-groove profiles – the kind of groove configuration is an impor-tant factor in the choice of a hoist rope.


8x19 FC sisal rope

Example ACar weight: 4,500 lbs.Car capacity: 2000 lbs.Car speed: 400 fpmNumber of ropes: 5 or 6Rope diameter: 0.5 inchesDrive-sheave diameter: 20 inchesD/d ratio: 40:1Bending length: 40 inchesRoping: 2:1Type of wrap: SingleUndercut U-groove: 105° or 85°Rope constructions: 8x19 RRL fiber-core (FC) sisal

8x25F RRL IWRC8x25 RRL parallel wire rope core

(PWRC)Merely changing the amount of undercut by 20° (from

105° to 85°) increases the rope life (number of bendingcycles) about fourfold. Feyrer lists an endurance factor of0.066 for the 105° undercut, and 0.260 for the 85° under-cut. This means that as the contact area between sheavegroove and rope gets smaller, the specific radial force onthe rope (groove pressure) increases. A 0.066 factormeans a 93.4% reduction in endurance (life) due to the


groove profile. The rope life in-creases approximately 60% whenthe number of hoist ropes is in-creased from five to six. The dy-namic force on each rope is re-duced from 924 lbs. (set of fiveropes) to 770 lbs. (set of six ropes).This directly reduces the specificpressure per point of contact, thusextending the life of the ropes.

Let us look at the combined ef-fect of these two situations. A four-fold increase in rope life due to a20° change in undercut multipliedwith a 60% improvement by addingone more rope results in an over-all impact of about 6.4 times (4 x1.6 = 6.4). Comparing the 8x19RRL FC sisal rope with the 105°undercut groove and five ropesper set to the 85° undercut grooveand six ropes per set is 2,616,000/ 402,000 = 6.5 times better. In theextreme case, a comparison of the8x19 RRL FC sisal rope with the105° undercut groove and five ropesper set to the 8x25 RRL PWRC withthe 85° undercut groove and sixropes per set equals 4,742,000 /402,000 = 11.7 times better.

Example BCar weight: 4,500 lbs.Car capacity: 2000 lbs.Car speed: 400 fpmNumber of ropes: 5 and 6Rope diameter: 0.625 inchesDrive sheave diameter: 25 inchesD/d ratio: 40:1Bending length: 50 inchesRoping: 1:1Type of wrap: DoubleU-groove: r/d = 0.53Rope constructions: 8x19 RRL FC sisal

8x25F RRL IWRC8x25 RRL PWRC

When the car travels to or from the ground floor, therope section running over the sheaves gets bent fourtimes in the same direction (four simple bends). _∩_ indi-cates one simple bend. In a double-wrap installation, therope gets bent four times (4 x _∩_). The rope sees the fol-lowing sequence:1) Straight between car and drive sheave2) Bent on drive sheave _∩_3) Straight between drive sheave and secondary sheave

Continued

4) Bent on secondary sheave _∩_5) Straight between secondary sheave and drive sheave6) Bent on drive sheave _∩_7) Straight between drive sheave and secondary sheave8) Bent on secondary sheave _∩_9) Straight between secondary sheave and counterweight

Depending on the type of rope selected, the number ofworking cycles (NA10) is more than doubled. In the aboveexample, the 8x19 RRL FC Sisal rope achieves only

719,000 working cycles, compared to the8x25 RRL PWRC rope, which achieves1,427,000 working cycles, or about twicethe rope life.

As in Example A, the rope life increasesalmost 60% when the number of hoistropes is increased from five to six. The dy-namic force on each rope is reduced from8,218 lbs. (set of five ropes) to 6,852 lbs.(set of six ropes). The combination of ahigh-performance rope with the additionof one more hoist rope results in an over-all impact of about three times (2 x 1.6 =3.2). Example B compares these numbers:2,267,000 / 719,000 = 3.1 times.Explanations

The discard number of wire breaks isachieved when the number of bending cy-cles NA10 is reached. This number is basedon the assumption that the same sectionof rope is running over the sheave duringevery trip. In reality, this is not always thecase. It depends on the usage of thebuilding and may be adjusted accord-ingly. For example, if only 80% of the tripsgo to the lobby (or ground floor), then theactual number of bending cycles isgreater and can be calculated by NA10 /0.80 to arrive at the installation-specificnumber of working cycles.

The calculations in both examples arebased on a 75% capacity for each trip.This number may be adjusted for installa-tion-specific calculations. All factors, for-mulas and definitions are based onFeyrer’s book. The same approach ap-plies to predicting rope life for differentinstallations including reverse bends, de-flector sheaves, etc.

After inputting the required data, youcan accurately quantify the total numberof working bends that a rope may be ex-pected to reach before it must be dis-carded. As with earlier analyses per-formed by engineers, consultants or a fewselect rope manufacturers, a host of criti-


Table 2: Factors for the bending equation to calculate NA10

Table 1: Wire Rope Tension Factors fs


cal factors must be obtained andentered. However, RLP signifi-cantly minimizes the amount ofinformation necessary requiredto do the job. After the entry ofspecific rope data, all calcula-tions are performed automati-cally for you.Why Determining Rope LifeExpectancy Matters

Being able to accurately fore-cast how long a rope should beable to perform in a particular installation and selecting theright rope needed using perform-ance and cost as a guide shouldbe of interest not only to industrydesigners, but also to all who estimate, adjust and install hoistropes. Any meaningful calculationof rope endurance must, by ne-cessity, account for the qualityand frequency of care providedfor the ropes themselves, and RLPalso considers in its calculations.

We hope that professionalswill see this new program as asource of information and a wayto help them overcome industrybias toward the unfamiliar. Wehave some concern that the ele-vator industry has become overlycontent with the old and familiar,and this is mainly due to a lack ofinformation about what is possi-ble. By understanding the manyvariables that affect hoist ropes,and by seeing for themselveshow a rope that is cheaper in theshort term can prove to be costprohibitive in the long run, webelieve that professionals willcome to demand elevator ropesoffering true innovation and de-livering real cost benefits.

Lastly, being able to accurately gauge rope life permitsthe entire industry to make another move toward being alittle “greener” in its use of resources, where replacementof ropes is concerned. We feel that an informed buyer,when weighing the choice between cheap, less efficientand less productive rope, versus an initially more expen-sive rope that delivers greater performance, increased lifeexpectancy and a better return due to reduced mainte-nance, will make the smarter buy.

Table 3: Endurance factors fN

A product that lasts longer means less waste and de-lays the use of energy in the creation of a new product.We believe this is a direction that the entire industryshould accept and adopt, and it is our job to make thismore attractive. In this way, RLP becomes a wise choicefor those wanting to profit from increased rope life. It isalso an essential choice for all who have an interest inpreserving resources for future generations. �


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