MEASUREMENT OF DYNAMIC STRESSES ON CARRIERS WITH DETACHABLE GRIP AT STATION ENTRANCE: LA.T.I.F. EXPERIENCES AND FUTURE PROSPECTS

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1 MEASUREMENT OF DYNAMIC STRESSES ON CARRIERS WITH DETACHABLE GRIP AT STATION ENTRANCE: LA.T.I.F. EXPERIENCES AND FUTURE PROSPECTS dott.ing. Fabio Degaperi Introduction The importance of dynamic tre effect of low temperature on fixed and mobile tructure i well known to engineer in thi field. Thee effect are even more important when ropeway car are conidered; all the more o a car deign mut provide for contained ize and weight. Dynamic tre effect on ropeway car are extremely variable and they depend on: - changing car loading condition - feature of the ropeway line - the poition of the car i modified by wind preure. It i then very important that the deigner i provided with the bet poible knowledge on dynamic tree and the relevant tatitic. Thee information can be obtained by meauring actual tree on different part of the car under different loading and peed condition. LA.T.I.F. (The Technological Laboratory on Ropeway in Trento - Italy) i a part of the local Control Authority (Service for Ropeway) and ha been in charge of tet on ropeway part ince Thi paper i intended to highlight the following ubject: "Meaurement of dynamic tree on carrier with detachable grip at tation entrance". Thi i not a new ubject for reearch and wa already dealt with more than ten year ago. We are pleaed to announce the reult of more than 1 tet on ropeway chair and gondola performed by LA.T.I.F. over the pat ix year. The tet were deigned a follow: - ame tet procedure; - ytematic data collection (number of meaurement point and ampling); - ame proceing method on all data (table and chart). We had an opportunity to draw up tatitic with a view to confirm running condition: tatitic are alo intended a a valuable bai for future development. According to Italian regulation, in ropeway car deign and in order that tree on crahworthy ection are within acceptable limit, deigner mut apply load allowance parameter to be identified experimentally. Thi i done to take Degaperi Fabio - LA.T.I.F. - via Provina, Ravina di Trento - ITALIA tel. +39.() fax +39.() labor.latif@provincia.tn.it

2 dynamic tre effect on board; whenever tet are not available, tree mut be increaed by at leat 5%. There i indeed a need to perform tet on dynamic tree to: - provide deigner with a erie of reult to calculate reliable allowance parameter; - provide deigner with data which help in the deign of prototype of new model with a view to ae the effect of buffer on joint and connection on different part of the car - when the ropeway i completed, to verify whether the deign reference value i conitent with that of the actual ropeway ytem and to allow for bet adjutment of guide roller height at tation entrance. Thi tudy doe not analye the conitency between deign tree and tree meaured under tatic condition. Meaurement method and gauge The wire train gauge method ha been ued in the tudy, with gauge having varying train force; thi i a imple, veratile, reliable and effective method. Any change in the train on the gauge can be meaured continually and dynamically: the gauge i cemented to the tructure under load. The change in trength i induced by any deformation of the part, which are induced by elatic tree. Single, grid-type train gauge are ued (3-6 mm grid, 12### trength, gage factor 2.) when the tre pattern i known; and train gauge roette compoed of 3 train gauge angled at 12 when the direction of ingle train gauge the main tree i unknown. When the ingle grid gauge wa ued the proportionality relationhip train gauge roette 12 i applied between meaured deformation and the correponding tre along the direction where tre i applied; with train roette, direction and main tree are calculated by the Ro-Eichinger relationhip. Meaurement train gauge were alway coupled with a train gauge mounted on an unloaded metal plate which i connected to a branch of the meaurement bridge to compenate for temperature change. The equipment ha 16 dynamic channel where data can be imultaneouly recorded through a remote detection ytem which provide for radio tranmiion of etting, balancing, a well a of collected data. The latet equipment we ued i very compact, olid and fully automated; it can tore data on a Memory Card which can be read with a P.C. Thi equipment i of the modular type and can be expanded up to 256 channel, and provide for radio tranmiion a well. Special care i devoted to cement train and roette gauge to the tructure and the cabling of connection. The help of aitant i of great value. 2

3 Selection of meaurement point Strain gauge were cemented to ection which had been checked during the deign tage a well a on the mot relevant point where experience had hown that the highet tre increment occur. On prototype, monitoring i performed on more point to identify any ection to be trengthened. A lower number of point i checked in cae of ma-produced equipment; the choice of point hall be uch to allow comparion with prototype meaurement. We were able to gather reliable tatitic a train gauge had alway and ytematically been applied to the very ame point. The chart which will be preented alway refer to tre pattern; however, what we actually meaured were deformation and hence correponding tree could be derived: in fact, we are dealing with elatic force and individual train gauge were only applied where the direction of the main tre wa known. 3

4 Tet procedure - Preparation of the tet: cementing the train gauge; connection of cable; checking that train gauge are undamaged and correctly connected; loading and unloading the car to allow bonding of the gauge; checking that bridge are back to -etting. Static preliminary tet: the car hall undergo tatic preliminary tet to meaure tatic value, to confirm that the equipment i working correctly and that meaurement point are a intended. Similarly, the grip i opened and then cloed. Under tatic tet, reetting i performed with the car hanging on the line: under thi condition, the car tructure are ubject to the tree induced by the very weight of the part below the ection conidered: in order to meaure the relevant tre an additional weight hall alway be added equal to the weight of the above part. Stree are to be meaured a follow: - on an empty car: on the train gauge located on the upenion, with an additional weight equal to the weight of the whole car; on the other train gauge, with the weight minu the weight of the upenion; - on a loaded car: a above, plu the weight of paenger. Reetting for dynamic tet: before tarting the tet, train gauge bridge are balanced under the following condition: - on train gauge located on the upenion and the car frame: meaurement on the horizontal line ection outide the tation for ropeway car, with cloed grip and no contraint; - on train gauge located on the grip: car hall be on tation rail, with cloed grip on empty gondola, in the abence of tree exerted by the action of pring. Strain gauge located on the grip are reet under different condition a compared with the other train gauge and hence dynamic tre alo include the tatic tre; percentage increae hall be calculated on the difference between the two and hall then be referred to tatic tre. The remaining train gauge directly provide the magnitude of dynamic tre only. Note that on grip part under pring load the dynamic tre induced when the car i running along the line and at the entrance of the tation are negligible a compared with the tre exerted by the grip cloing force. 4

5 Available data and tatitical criteria. The reult of app. 1 tet performed between 1993 and 1998 have been included in the tatitic. Tet were performed on chairlift (4 and 6-eater) and gondola lif (6, 8, 12 and 15 pot) with detachable grip, and tation entry peed of m/ec. A large number of data i available upon completion of a dynamic tet with multi-channel data recording. Although meaurement were performed at tation entrance only, numerical data which are very ueful with a view to tatitic are obtained under the following circumtance and depend on: - number of tet performed; - number of train gauge ued, uually 7 or 8, and arranged a follow: - two on the grip (n. 2 and 3 on the drawing) - one on the carrying wheel pin ("third wheel" - n. 1 on the drawing) - two on the upenion (n. 4 and 5) - one/two on the upenion/car frame connection (n. 6) - two/three on the car frame, on mot relevant point (n. 7 and 8); the following meaurement were performed on each meaurement point: - preliminary tatic meaurement, with gradual increment in load; - dynamic meaurement, under four different loading condition (empty, full load, 1/2 load unbalanced either on the outer or inner ide) with car entering both top and valley tation. Data are proceed and continuouly tracked into chart; highet and lowet value are calculated for each curve: more than 1, data were collected. 5

6 The urvey and the relevant tatitic were confined to a ingle and ignificant meaurement point and quality performance wa provided for ome other meaurement point. The train gauge under the upenion head - inner ide of the line - wa the mot relevant meaurement point becaue it i undoubtedly under the effect of the impact againt the tation guide roller becaue of the ditance from the ytem centre of gravity and a there are no buffer uptream. Data proceing provide the following information: - dynamic tree a a percentage of tatic tree on the ame point, with empty, fully loaded and unbalanced 1/2 loaded car; - the highet tre, a a um of tatic and dynamic tree having the ame ign to confirm that the value are within acceptable limit (thi i not really important during thi tage; indeed, it i key to confirm that deign ize are correct). The following chart were obtained on a chairlift, at the entrance of a valley tation, at a peed of 5. m/ec, a follow: balanced full load: md 6 et4 openione in alto

7 1/2 load, 2 paenger on the inner ide: md 6 et4 openione in alto change at the beginning of the curve indicate that the car i paing on the roller before the tation. Reult Baed on the above reult the following table ha been made, which i divided a to include chairlift and gondola lift becaue: - the connection between upenion bar and gondola frame in gondola lift uually differ from connection in chairlift (where ingle or "double wivel" joint are ued) - in gondola, when the load i unbalanced, impact tree when gondola enter the tation entrance are lower; The table how that: - increment are much higher in the cae of chairlift: when a paenger i itting on a ide eat and there i a need to reduce ide-to-ide ocillation inide the tation, the connection between the upenion bar and the eat frame mut be tiffer to reit the effect of ide-to-ide movement; chairlift average increment gondola lift average increment empty 1/2 load unbalanced full load 189% 84% 1% 18% 31% 63% - increment when the tructure i empty are nearly double a compared a loaded car; however, a the tatic tre i lower, total tre i lower than tre induced when the car i fully loaded. 7

8 Statitical ditribution of dynamic tree (in percentage) During the tet, the gondola i driven to perform a round trip under all loading condition and, when entering the tation, condition might be affected by random parameter uch a lateral preure from wind, bay ocillation, etc. which may bring about unuual increment. Once the average value of dynamic tree are calculated, it i maybe worth checking the percentage range where highet tree occur. The ditribution i traced a follow: empty chair n % fully loaded chair n % 8

9 empty gondola 8 6 n % fully loaded gondola 8 6 n % Detailed analyi of tet with unbalanced load at tation entrance Tet are performed with 5% of rated load, to be arranged on the outer or inner ide of the car a to the direction of the carrying-haulage cable. The unbalanced load effect i uch that the ret car i tilted to the ide a to the vertical: upon entering the tation, the impact againt lide rail cannot be avoided. The following chart how the deformation/tree detected by the train gauge: - n. : on the bearing lever, the opening wheel providing data on the contact with the relevant guide: - n. 1: on the tabiliing wheel bearing pin; - n. 2: on the lever where the mobile jaw i mounted ; - n. 4: on the upenion head, which i the elected meaurement point; 9

10 1

11 et md 4 et leva mora md 8 et1 perno mora kmd.2 et2 leva apertura mora et md 4 et4 openione in alto Comment to chart: - on the firt chart we can ee the exact moment when the impact occur and the grip opening guide i detached: note that the bending tre decreae until the grip i fully open, which i then opened again once the cable ha detached: - econd chart: when the third wheel impact againt the upper guide, the train gauge on the pin i tenioned; compreion/tenion cycle follow which are due to ide-to-ide ocillation; 11

12 - the third chart repreent the dicharge of the mobile jaw, at the end of the opening guide rail; - the forth curve i like the econd one: however, here the highet tre i exerted when the firt impact occur (which i buffered by elatic guide); the highet tre i indicated by the econd peak when the car i already on fixed rail and it poition cannot be changed. Note the firt part of the fourth chart: it how the tre induced by the roller before the tation. In general, tre exerted when the gondola ha an unbalanced 1/2 load i lower than in cae of full load. Effect of roller guide height adjutment on dynamic tree During a tet performed on a 4-eater chairlift with wind hield, very high dynamic tree have been detected at tation entrance at a peed of 5. m/ec - chair with balanced full load - even though the chair wa in a perfectly vertical poition. The builder adjuted the height of elatic guide roller at the entrance and replaced the guide upporting buffer. Repone curve at three meaurement point (to be uperimpoed) are reported and comment are provided. Before adjutment: kmd 1. et1 et1 perno mora Chart 1 (train gauge located on the third wheel bearing pin - ee grip previou drawing): the pin i not loaded along the line; after impacting againt the upper ection of guide roller the pin i tenioned, and i ubject to alternate cycle - with decreaing intenity - of compreion and tenioning due to the ide-to-ide ocillation of the chair. In the tre cycle which follow the firt one, the average compreion value i below zero which i due to the vertical load exerted by the haulage wheel of guide roller. 12

13 kmd.2 et2 leva apertura mora Chart 2 (train gauge on the mobile jaw lever): thi element i only affected by the load exerted by the cloing force and i not due to impact occurring when the chair enter the tation; a a matter of fact, the tracing of the curve i unchanged: the peak value (lever unloading) are delayed if compared with the previou chart a the grip opening blade follow guide roller before the entrance of the tation. md 5 et4 openione in alto Chart 3 (train gauge on the upenion bar, upper ection): at the beginning of the curve, ignal change refer to the chair paing on the roller before the tation and then indicate the vertical ocillation of the bay and the impact againt the guide rail. 13

14 Guide roller height wa reet and the contraining buffer part were replaced: kmd 1. et1 perno mora kmd.2 et2 leva apertura mora md 5 et4 openione in alto et

15 dynamic tree on the upenion bar were then remarkably lower, from 214% to 113% increment, a compared with tatic tree. The ignal provided by the train gauge on the mobile jaw i unchanged. 15

16 Effect when replacing car component The tet i performed to ae the effect of replacing rubber buffer on the upenion bar/eat-bearing frame joint on the above chair. Softer rubber buffer were ued and located in a different poition. Chart - balanced full load - entry peed 5. m/ec original buffer train gauge 1 (grip pin) et1 kmd train gauge 4 (upenion bar) 16

17 et4 md

18 Same parameter with new buffer: train gauge 1 (grip pin) kmd 1. et1 perno mora et train gauge 4 (upenion bar) md 5 et4 openione in alto Dynamic tree decreae by 4-5%. 18

19 Tet at tation entrance under fixed lateral inclination The reult reported o far were collected under tet condition where the car had a "natural" poition when entering the tation, i.e. it poition wa determined by loading condition and line-induced ocillation only. In order to take thrut effect on board, which are due to lateral preure from wind equal to the highet value under ervice condition, tet were performed where the car wa in a fixed laterally inclined poition before entering the tation Builder were requeted to provide lateral inclination value due to wind preure effect on each loading condition to define the following tet parameter (angle to be achieved): - empty car: 12 ; - 1/2 unbalanced load: the natural angle plu the value correponding to the highet lateral preure from wind; - full load: 6. Thi tet i rather dangerou o it wa performed on a limited number of car model only. The car wa driven outide the tation at a ditance that it could be fully tarted and could enter the tation at the maximum running peed; at the ame time, the car wa wung laterally o that it reached the deired angle when impact occur. Tet were performed with the car at deired angle, inward and outward the line. A recording channel line wa connected to a pitch indicator mounted on the head of the upenion to meaure the lateral inclination. 19

20 aa2 gradi 5 aa1 inclinometro (gradi) kmd 1. et1 perno mora kmd 1.4 et2 leva apertura mora aa md 5 et4 openione in alto aa

21 A comparion between the percentage dynamic increment meaured on a 4-eater chair with wind hield and a 6-pot gondola i provided, under normal condition and under lateral inclination, which were meaured on the train gauge on the upenion head. dynamic increment. a to tatic tre empty 1/2 unbalanced load full load chair gondola chair gondola chair gondola fixed lateral incl. tet 428% 513% - 31% 151% 225% dynamic 111% 167% - 23% 48% 81% tet ratio between the two incr. 3, ,34 3,1 2,77 The lat row how the ratio between the magnitude of the impact force in the preence of lateral preure from wind and the impact force with no wind, when entering the tation. Thee are clearly two completely different phenomena; in the hardet ituation the minimum level of afety degree mandated by regulation i not complied with (3 a to the unit yield point of the material and 4 a to the unit breaking trength, meaured under tandard loading condition and with a 5% increae). We therein provide a table comparing: - deign tre value (tatic + dynamic equal to 5%) - tre value (tatic + dynamic) meaured under a "natural" angle - tre value (tatic + dynamic) meaured under a "fixed" angle including the relevant degree of afety a to the unit breaking trength of the upenion material (teel Fe51D UNI 786) (Stree in N/mm 2 ) - 4-eater chair with wind hield deign tre afety degree afety degree meaured tre (natural angle) meaured tre (fixed angle) minimum afety degree before failure minimum afety degree before yielding point empty full load Lower value of afety degree were meaured on other ropeway ytem, which were however alway higher than 1.5. Baed on the following: 21

22 - low incidence of thi event, which a uch cannot be evaluated in the framework of the fatigue effect, - extremely rare event, o that lower degree of afety can be adopted; under uch circumtance, the Control Authority ha accepted that the minimum degree of afety can be reduced to 1.5 a to the unit yield point of the material. Dynamic tree on other point of the carrier Whenever tatic tree are known, we can confidently peak of a dynamic increment, i.e. the magnitude of the thrut effect. Whenever the car/chair i empty, under tatic condition, abolute tre value - generated by impact - i meaured (ee tabiliing pin, known a the "third wheel"). Signal coming from the train gauge on the eat frame, below buffer, may be remarkably out-of-phae - under pecific loading and peed condition - a to ignal ent by the train gauge on the upenion, epecially when the frame pae under the guide roller before the tation entrance. It may well be that the highet tree are induced at peed lower that the top peed. It mut be noted that on tructure below buffering part, dynamic tree are coniderably decreaed and afety degree are largely repected even at remarkable lateral inclination. Concluion The wire train gauge method to meaure dynamic tree proved of value a it i reliable, it provide reliable impact curve and i eay to ue. Whenever timely and exhautive information on tree are available: - builder can eaily undertake type approval procedure of a car type, with improvement of production procee (no need to continuouly modify the model erie) - deigner can elect the bet and mot uitable crahworthy ection, technical olution for part connection and joint; - builder and intaller can adopt bet olution for tation part touching car part; - the Control Authority i provided with an effective control method to monitor compliance of deign and erected tructure and a a valuable data bae to any amendment of the regulation in force. Future propect We advocate that teting procedure are harmonied in different countrie and in thoe on the Alp mountain range in particular. Having confirmed the value of uch method, we foreee further development in the future owing to technology development of intrument o that we could: - perform wider monitoring, with more point of meaurement to be thoroughly controlled; - have compact equipment to monitor the performance of part touching the car and which are at preent not eaily reached (line roller, tation cable pulley); 22

23 - wider data collection and proceing. A more thorough knowledge on tree and the ue of fatigue tet performed under actual tree condition will enable to confidently reduce degree of afety. Car will then be lighter, with le trong impact and a lower live load a to the pay-load available. LA.T.I.F. i fully committed to purue further tet to include meaurement of ree along ropeway line. 23