DEVELOPMENT OF DESIGN OF SHIP-TO-SHORE CONTAINER CRANES: 1959-2004

Nenad Zrni ü University of Belgrade, Faculty of Mechanical Engineering, Dep. of Mechanization 11000 Belgrade, 27 marta 80, Serbia and Montenegro E-mail: [email protected] Klaus Hoffmann Vienna University of Technology, Faculty of Mechanical Engineering Inst. for Engineering Design and for Transport, Handling, and Conveying Systems A-1060 Wien, Getreidemarkt 9, Austria E-mail: [email protected]

ABSTRACT- The paper presents the historical development of mechanical and structural design of ship-to-shore (STS) container cranes, from 1959, when the first was built, up to now. The paper gives a short survey of the evolution of the container crane industry, the state of the art in modern container cranes, and focuses particular attention on mechanical design of trolleys and evaluation of the existing structures. The analysis of historical development and state of the art in modern container cranes enables us to analyze future trends in mechanical and structural design.

KEYWORDS: History of STS container cranes, design, trolley, construction

INTRODUCTION The method of handling ship cargo in the early 1950s was not very different from that used during the time of the Phoenicians, Figure 1 >6@. The time and labor required to load and unload ships increased substantially with the size of the ship, requiring more time in port than at sea, Figure 2 >6@. The problem “how to lift a load” is as old as humankind. From the earliest times people have faced this problem. The first written information on the use of hoisting mechanisms appeared around 530 BC, mainly concerning the construction of the first temple of Artemis in Ephesus >13@. The forerunners of modern cranes in the ports were the wooden slewing cranes developed in the middle Ages, Figure 3 >20@. The slewing level luffing crane was the main means of cargo loading and unloading between ship and shore up to the end of 1950s, Figure 4 >20@. Through the 1950s, general cargo continued to be handled as break-bulk (i.e. palleted) cargo. Pallets were moved, generally one at a time, onto a truck or rail car that carried them from the factory or warehouse to the docks. Each pallet was unloaded and hoisted, by cargo net and crane, off the dock onto the ship. Once the pallet was in the ship’s

229 230 hole, it had to be positioned precisely and braced to protect it from damage during the voyage. This process was then reversed at the other end, making the marine transport of general cargo a slow, labor-intensive, and expensive process. All this began to change in 1955. Believing that individual items of cargo needed to be handled only twice - at their origin when stored in a standardized container box and at their destination when unloaded, Malcolm McLean purchased a small tanker company, renamed it SeaLand, and adapted its ships to transport truck trailers. The first voyage of a SeaLand commenced on April 26, 1956 between Newark, New Jersey, and Puerto Rico. In the years that followed, standardized containers were constructed, generally twenty or forty feet long without wheels, having locking mechanisms at each corner that could be secured to truck chassis, a rail car, a crane, or to other containers inside a ship’s hole or on its deck. The idea of shipping cargo in locked containers has been widely accepted, resulting in an uninterrupted worldwide growth of about 8% a year at the beginning of this century >16@, >21@.

Fig.1: Beginnings of handling ship cargo. Fig.2: Past of handling ship cargo.

Fig.3: Wooden slewing crane. Fig.4: Development of slewing cranes 1856-1956. 231

One of the major problems facing the concept was that during the mid- Fifties most ports were not equipped to handle the heavy containers except by mobile revolving cranes and even then many of the cranes did not have the capacity to lift containers. These cranes were extremely inefficient, in that at least two to three minutes of loading cycle was lost due to poor control at the points of pickup and discharge. In July 1957 the engineering staff of Matson company, under the leadership of Mr. Les Harlander, commissioned a study of existing crane types, to determine the state of the art and identify the type which best met the general requirement for loading containers between ship and shore and keep turnaround time of container ships to a minimum. The study concluded that no crane then on the market satisfactorily filled this requirement, and that an ore-unloading type crane with a horizontal boom and through-leg trolley came closest to meet this requirement. Early in 1958, performance specifications were finalized and put out for bid >6@. PACECO, one of eleven biddres, pioneered the first container crane for Matson in 1958 >4@. PACECO philosophy was that the best design has the fewest number of pieces, and developed the conceptual drawings paying particular attention to aesthetics. Trusses, used at that time by most manufacturers, were replaced with all-welded box girders wherever possible. This resulted in unique and extremely clean-looking A-frame configuration. The A-frame takes its name from it’s “A”-shaped noticeable when observed from the bridge. On 7 January 1959 the world’s first container crane was put into service at the Encinal Terminals in Alameda, California, Figure 5. The original container crane set the standards for dozen of manufacturers around the world. Although there have been many significant improvements, all modern cranes are direct descendants of this first crane, and the design of later cranes has reminded relatively unchanged >6@. In the meantime, to keep up with the growth of container traffic, container ships and container cranes are getting bigger and bigger. During the first 45 years since the first container crane was designed, the size of container cranes and lifting capacity have more than doubled, Figure 6 >5@.

Fig.5: First container crane. Fig.6: Growth of container cranes 1959-1995. 232

EVOLUTION OF CONTAINER CRANE INDUSTRY At these early 1960s a crane container purchaser could call up a PACECO (at that time a US company) representative in any part of the world and order STS cranes. Around the same time, European manufacturers entered the market, offering improved and standard design, good quality and competitive prices. The Japanese entry into the container crane industry in the late 1960s presented some opportunities and, for the first time, some challenges for the purchasers. Japanese consumer and industrial products were introduced to the world market at significantly lower prices. The first reaction in the Western world was “No such thing as a free lunch – you will pay for it one way or another” >4@. But, some large shipping lines saw opportunity in the new competition and decided to give the Japanese a try. The Japanese provided good quality cranes, and within a short time they were in the same category as the Americans and Europeans. With the growth of the economy and domestic demand increasing, Japanese cranes ceased to be a bargain. The concept of purchasing cranes with the “Tailor-Made” specification was born. The “Tailor-Made” philosophy requires the detailed performance specifications and very competitive bids. A larger number of cranes brings economy of scale and favors this concept. Tailor-made cranes require high expertise, whether in-house or through outside consultants >4@. Korean STS container cranes manufacturers were next with the lower-priced cranes, starting from 1970s. Now, at the beginning of 21st Century the Chinese manufacturer ZPMC, Shangai, has made the most significant impact on the container crane industry, and may further increase its share of the world market during the coming years. The actual situation is that PACECO could no longer compete with the overseas suppliers, some European suppliers have merged or quit manufacturing STS cranes, and the Japanese suppliers retracted from the international market and remained focused on their protected domestic market. To compete in the current market, established cranes builders have shifted fabrication and assembly to remote plants with cheaper labor, purchased electrical components and integrated them in-house, used standardized components and reduced profit margins. The use of standardized components favors the “Off-the-Shelf” approach in design of STS cranes. The aim of this strategy is to emulate the early purchasing strategy of issuing a brief technical outline and inviting proposals from two or more crane suppliers >4@.

DEVELOPMENT OF DESIGN OF STS CONTAINER CRANES The basic structural form of STS container cranes (A-frame) remains practically unchangeable compared with the first structure built in 1959. Of course some modifications are done. The basic structural shape of STS cranes can be divided into two groups:

1. Conventional or modified conventional cranes, Figure 7 >15@; 2. Low profile cranes, Figure 8 >1@.

Conventional STS cranes are used for servicing the following ships:

1. Panamax ships: III-generation ships with a beam of less than 32.3 m (width of Panama Canal) – their structure was developed from end of 1960s up to early 233

1980s, and they operate with up to 13 containers abeam on deck and with maximum capacity of 4,700/4,900 TEU (Twenty Equivalent Unit); 2. Post-Panamax ships: IV-generation ships, developed from 1984, whose beam is greater than the width of the Panama Canal – they operate with up to 20 containers abeam on deck and with a maximum capacity of 7,000 TEU; 3. Mega ships or Jumbo ships: Ships of the most recent generation, pioneered in the last years of the 1990s, they operate with more than 20 containers abeam on deck and with a capacity of more than 7,000 TEU.

Fig.7: Conventional Post-Panamax container crane.

Fig.8: Low profile container crane. 234

During this time there was an incredible growth of overall dimensions of STS cranes, and an increase in drive performances such as speed, acceleration, etc >21@. The outreach of the first container crane was 23.8 m (70 ft), and the gauge was 15.24 m (50 ft). The later Panamax cranes reached the gauge of 30.48 m (100 ft), maximum outreach 36/42 m, trolley travel 120/150 m/min, and hoisting with rated load 20/50 m/min. The state of the art of modern Post-Panamax and Mega cranes is given in Table 1 >15, 17, 18@.

Features of Post-Panamax and Mega cranes 16 wide 18 wide 20 wide 22 wide Gantry rail gage (m) 30.48 30.48 30.48 30.48 Clear between legs (m) 18.3 18.3 18.3 18.3 Lift above rails (m) 34 34 36 t36 Total main hoist lift (m) 50 52 54 t60 Clear under portal (m) 12 12-15 15 12-18 Out-to-out bumpers (m) 27 24-27 24-27 24-27 Outreach from waterside rail 45-47 50-52 56 t60 Hoisting with rated load m/min 50 60 75 70-100 Hoisting with empty m/min 120 130 150 180

Trolley travel m/min 200 245 245 250

Tab.1: State of the art of Post-Panamax and Mega cranes.

The conventional and modified A-frame crane with single trolley and one operator is still the workhorse of container cranes industry >7@. In the last two decades there have been many attempts to improve the productivity of cranes by introducing the second hoist, or second trolley >23@. Dual hoist cranes have a second hoist located over the quay. They are conceived in the early 1980s, first by ECT (European Container Terminal) Rotterdam, and then by Virginia Port Authority >11@. These cranes can increase productivity by about 50%, but also increase the initial costs by 30 to 50%, require an additional operator, and increase operating costs. In practice they were not economic, but they may be making a comeback, as only one operator is needed on the ship trolley, and the second trolley may be fully automated. The newer solution of dual hoist crane combined the solution of dual hoist crane and elevating platform, Figure 9 >14@. Dual hoist elevating cranes are dual hoist single cranes, but the shuttle runway elevates to the ideal elevation. These cranes cost more than dual hoist cranes but have higher productivity >14@. The double trolley also boosts productivity of the crane, Figure 10 >8@. The suggestion is that two trolleys operate on the same runway. The SeaLand Ansaldo cranes in Taiwan are designed to carry two trolleys. For double trolley operations, the landside trolley transfer containers from the landside half of the ship to extreme landside lanes, and the waterside trolley operates from the waterside half of the ship to the waterside lanes. Boom deflections could cause problems when two trolleys are operating simultaneously over the ship. Since a trolley should not carry over the personnel, some of the transfer vehicles need to wait for the waterside trolley to pass. This reduces production, but not significantly. The second trolley requires a second operator. Nowadays, a dual hoist 235 crane will be more productive than a double trolley crane. The initial and operating costs of two cranes solutions are the same, so there is no apparent advantage in the double trolley crane >8@.

Fig.9: Dual hoist elevating cranes.

Fig.10: Double trolley cranes.

The first low profile cranes emerged in the late 1960s. The boom is supported by a hanger system including support truck and wheels; it rides on the wheels at all times. For the PACECO standard, all machinery and electrical equipment is on the boom. The machinery travels with the boom and causes significant increases in the wheel loadings >12@. Low profile cranes cost about 15% more than A-frame cranes and were used when it was necessary to restrict the height of the crane (under max. 46 m), i.e. because they have the advantage of keeping cranes profile below aircraft clearance lines, Figure 8. During the period 1970-1999 approximately 40 of these cranes were built, sized to 236 service vessels between 13 and 16 containers wide. Except for the US, they are now found only in Italy.

DEVELOPMENT OF MECHANICAL DESIGN OF TROLLEY The selection of a crane’s trolley system type is significant for the structure of crane, for wheel loads, and for maintenance considerations. The trolley can be rope towed (RTT) or machinery type (MOT). A hybrid of the two systems, commonly known as a fleet- through machinery trolley (or semi-rope trolley >9, 22@), was adopted by some manufacturers. For the fleet-through machinery trolley the main hoist machinery is placed on the gantry frame, but the trolley is self-driven >5@. Since the machinery in the machinery house tow the trolley and hoist the load by a system of wire ropes, this system is called a RTT system. The main hoist ropes run from the machinery house to the landside of the crane, through the trolley and head block, and usually dead end at the waterside tip of the boom, Figure 11 >2@.

Fig.11: Main hoist reeving, RTT system.

The trolley tow ropes run from the machinery house to the sheaves at the landside of the crane, through the trolley to the tip of the boom, and back to the house, Figure 12 >2@. This arrangement allows the trolley to be shallow and lightweight, permitting greater lift height and smaller loads on the crane structure and wharf >15@.

Fig.12: Trolley reeving, RTT system. 237

With the RTT design, there was concern that the rope would stretch and that catenary effect would reduce productivity. The auxiliary catenary trolley is the typical solution for reducing the catenary effect due to greater outreach of modern cranes and longer trolley travel, Figure 13 >2@. But even with the catenary trolley, the long runway will result in a significant catenary effect >3@.

Fig.13: Catenary trolley.

A machinery trolley (Figure 14, >10@) has the trolley and main hoist machinery on board. No trolley drive ropes are required, and the main hoist ropes (Figure 15, >2@) are shorter than for a rope-towed trolley >15@.

Fig.14: Construction of MOT. 238

Fig.15: Reeving diagram for MOT.

For the structural design, weight is the main difference between the two types of trolleys. The weight of the rope-towed trolley is approximately one-third that of a machinery trolley. The main disadvantage of the machinery trolley is the increase in crane weight and wheel loads on the wharf. The first dockside container handling crane, built by PACECO in 1959, utilized a RTT. This crane was conceptualized for operation on the existing wharf. This was common in 1959 >15@. The minimization of wharf loads was the primary factor favoring the RTT cranes for other existing facilities. This design became the model for the next generation of container handling cranes for most ports in the world, except for a few European ports. These RTT cranes have provided excellent service over the years and, with proper maintenance, have exhibited high reliability. However, the resulting maze of ropes, sheaves and trolleys has become complex. Some European crane manufacturers adopted the MOT design concept for most of their cranes. Kocks introduced the first European machinery trolley container crane in 1968 and have since used the same basic philosophy for most of their cranes worldwide. Another German manufacturer, Noell, later introduced their machinery trolley cranes >15@. Less than 10 years ago, American President Lines (APL) concluded negotiations with the Port of Los Angeles for construction of a new port facility. APL developed a new Post-Panamax crane specification written for the traditional RTT design. Bids were received from many international crane manufacturers. But one manufacturer, Noell, offered an MOT-type design. At first, APL did not consider changing from the traditional RTT – perhaps this was because the traditional design was familiar and worked well. But on second sight, the design began to intrigue the evaluation team. APL’s in-house evaluation team looked at it this way >2,5@: If no container cranes had ever been built and there were no dock wheel load constraints, would the team recommend a crane with a RTT system or as a MOT? Interestingly, the group was inclined toward the MOT. As a next step, APL invited a small group of crane experts to join the evaluation team. The team was asked to keep in 239 mind the basic criteria: that no container crane had ever been built, no design constraints exist, and the goal is to optimize efficiency, reliability and maintenance of the crane. The interesting result was how easily the group concluded that, with these criteria, the MOT design was the logical choice. Prior to making the final decision, the APL team visited sites where Noell had installed cranes of similar design. Why was the MOT system chosen?

1. Depending on the design, approximately 1,650 m of wire rope is eliminated from the main hoist, trolley drive, and catenary trolley. 2. Approximately 36 sheaves of various sizes are eliminated. 3. Hydraulic rope tensioning devices are eliminated. 4. The spare parts inventory is reduced. 5. The intensity of maintenance is reduced. 6. Up-time reliability is increased because of the reduced number of crane components. 7. Wire rope lubrication is reduced.

Table 2 >15, 22@, presents a comparison of both mechanical systems.

Rope-towed Trolley Machinery On Trolley Advantage RTT MOT Reeving Assemblies Main Hoist, Trolley Drive Main Hoist MOT Catenary Trolley Drive Trolley Positioning Movement due to trolley travel Movement due to skidding MOT rope stretch Festoon Spreader power only Power for main hoist RTT (including trim, list, skew, and snag device), trolley drive, and spreader Trolley Accelerations 0,6 m/s2 0,6 m/s2 --- Rope Lubricant Exposed to environment. Enclosed, spillage MOT Oil spillage on ground. contained

Tab.2: Comparison of mechanical systems of trolley.

AUTOMATION OF STS CONTAINER CRANES

The development of efficient, automated, high-technology loading/unloading equipment has the potential of considerably improving the performance of terminal operations. The construction industry is relatively still slow in implementing advanced technology to improve safety. Current practice requires that control of the STS cranes dynamic behavior is the responsibility of a skilled operator. The operator applies corrective measures based on experience when any undesirable swaying is detected. The absence of automated sensing and control not only leave room for accidents arising because of human error and/or delayed response of the operator, but also can greatly reduced the productivity of the crane’s operation, also as the productivity of a whole port terminal. There is also a potential danger of an exaggerated response, which will lead to an uncontrollable load swing. The biggest source of dynamic forces is the pendulum motion of the loaded spreader suspended by cables. Advances in STS container cranes 240 technologies have a significant effect on the efficiency of port terminal operations once properly implemented. Precise control of the spreader and load is only possible using mathematically correct algorithms, and properly implemented sensor systems. For the years many authors have been researching and developing ways to make STS cranes transfer containers faster and more safely through computerized anti-sway and automatic controls. Automation continues to evolve and will continue to improve productivity of STS cranes. The fact that the cranes should be quicker, larger and more efficient, force both the manufacturer and terminal operator to incorporate to the equipment some automation for the repetitive process of handling containers. Automation is also another important aspect of container crane becoming a conglomerate of sophisticated elements of high added value consisting of specialized software and hardware. The pressure on the port terminal by the shipping companies to release vessels as fast as possible is used by port operators to specify that the cranes shall be supplied with an antisway system. The behavior of the crane with antisway device is completely different from that the cranes without it. The outline of the classification of existing STS cranes due to their degree of automation is shown in Figure 16.

STS container cranes

Conventional cranes manually - operated cranes, majority of today's quay cranes, performances mainly depend on a human factor, i.e. capabilities of operator

Semi - automated cranes equipped with advanced control systems and sensors, the role of control system is to enhance the human operator's decision in order to achieve better performances (e.g. control system controls the speed of the crane's components for sway avoidance and fine - positioning of the spreader, because about 30% of each manual crane move is spent in eliminating sway and fine - positioning of spreader)

Automated cranes Cranes of the future, equipped with advanced and intelligent control and measurement systems, do not require human operation

Fig.16: Classification of STS container cranes by their degree of automation. 241

CONCLUSION The future of STS cranes starts today and will last until 2030, what is the reasonable life of a container crane. The analysis of the past and state of the art of STS container cranes may help us to predict the future trends in their development. New cranes should be designed that are big and fast enough to keep up with the demands of new larger ships. Some expected performances of future cranes are as follows >10,19@:

1. Crane rail gage: 30,48 m (100 feet); although there are some good arguments for increasing the gage to as much as 45,72 m (150 feet), the cost of shipping the erected crane will be much greater. 2. Lift above rail: 39,92 m (131 feet) now, 47,55 m (156 feet) future. The higher the trolley is above the wharf, the more difficult is to control the load. Therefore, the current height should be kept to a minimum. 3. Outreach: 64/69,2 m (210/227) feet; the increase of the outreach will follow the increase in the size of ships. Current New Standard Maersk crane orders provide for vessels with 22 containers on deck. Ships with 23 containers on deck are referred to as Suezmax, and with 24 containers across as Malacca- max. 4. Trolley travel speed: 250/300 m/min, or even more. In 2002 ZPMC made fundamental improvement on the trolley starting up, braking and traveling, and the trolley speed has successfully reached 350 m/min, instead of previous 240 m/min. This crane is now undergoing industrial tests. 5. Trolley tipe: Both types of trolley systems, RTT and MOT have beneficial site-specific applications, and are viable. For each crane purchase, the owner have to evaluate each design and then choose the design which best suits the site and the all-round operational needs. For large super productive cranes, the MOT will be the choice of the future.

An effective crane must be designed to suit the present and future needs of the end user. But if today’s crane is built large enough to serve tomorrow’s ships using future technology, the crane will not perform well on today’s ship with today’s technology. For years design team members - mechanical, structural, automation, and electrical engineers have worked together to produce economical design that meet operational demands and that can be efficiently fabricated and erected. As always, the “best” (“optimum”) design requires balance. The cost and benefits of each alternative should be considered in respect of the specific case.

REFERENCES 1. Bhimani, A. K., Low Profile Cranes - New Applications, AAPA Facilities Engineering Seminar, American Association of Port Authorities, Baltimore, Maryland, USA, April 28-30, 2003. 2. Bhimani, A. K., Hoite, S., Machinery trolley cranes, Proceedings of the Conference "PORTS ’98", American Society of Civil Engineers, Long Beach, CA, USA, 1998, pp. 603-613. 3. Bhimani, A. K., Hsieh, J. K., Cranes to serve ship in the slip Ceres Paragon terminal Amsterdam, Proc. of the Conference "PORTS ’01", ASCE, section 30, chapter 3, Norfolk, VA, USA, 2001. 4. Bhimani, A. K., Jordan, M. A., Crane Purchase Specifications: Tailor-Made or Off-The-Shelf, Terminal Operations Conference "TOC'01", Lisbon, Portugal, June 20, 2001. 242

5. Bhimani, A. K., Kerenyi, J., Rope towed or machinery trolley – which is better?, AAPA Facilities Engineering Seminar, American Association of Port Authorities, San Pedro, CA, USA, November 15- 17, 1995. 6. 12th International Historic Mechanical Engineering Landmark: PACECO Container Crane - The World's First High Speed, Dockside, Container Handling crane, American Society of Mechanical Engineers, Encinal Terminals - Alameda, California, USA, May 5th, 1983. 7. Jordan, M. A., Dockside container cranes, Proceedings of the Conference "PORTS ’95", American Society of Civil Engineers, Tampa, Florida, USA, 1995, pp. 826-837. 8. Jordan, M. A., Super productive cranes, Terminal Operations Conference "TOC ’97", Barcelona, Spain, June 3-5, 1997. 9. Jordan, M. A., Purchasing cranes in a changing world, Proceedings of the Conference "PORTS ’98", American Society of Civil Engineers, Long Beach, CA, USA, 1998, pp. 591-602. 10. Jordan, M. A., Future-Proof Your Crane, Terminal Operations Conference "TOC Americas ’01", Miami, FL, USA, October, 2001. 11. Jordan, M. A., Quay crane productivity, Terminal Operations Conference "TOC Americas ’02", Miami, FL, USA, November, 2002. 12. Jordan, M. A., Davis Rudolf III, C., New container crane concepts, AAPA Facilities Engineering Seminar, American Association of Port Authorities, Savannah, Georgia, USA, April 14-16, 1993. 13. Lazos, C. D., Engineering and Technology in Ancient Greece, Laboratory for Automation and Robotics, University of Patras, Greece, 1998. 14. Morris, C. A., Hoite, S., The future of quayside container cranes, China Ports ’97, Post Conference Workshop, China, March 26, 1997. 15. Morris, C. A., Mc Carthy. P. W., The impact of jumbo cranes on wharves, Proceedings of the Conference "PORTS ’01", ASCE, section 30, chapter 4, Norfolk, VA, USA, 2001. 16. Payer, H. G., Technological and Economic Implications of Mega-Container Carriers, SNAME Annual Meeting, Society of Naval Architects and Marine Engineers, Orlando, USA, October 24-27, 2001. 17. Petkovi ü Z., Zrni ü N., Last trends in design of ship-to-shore container cranes, Proc. of the 4th Inter. Conf. on Heavy Machinery, Faculty of Mechanical Engineering Kraljevo, Kraljevo, 2002, pp. A.51-A.54. 18. Petkovi ü Z., Zrni ü N., State of the art of Post-Panamax ship to shore conventional and modified A-frame container cranes, Proceedings of the XVII International Conference on Material Flow, Machines and Devices in Industry, Faculty of Mechanical Engineering Belgrade, Belgrade, 2002, pp. 1.78-1.81. 19. Petkovi ü Z., Zrni ü N., The expectations in the trend of development of container cranes for the XXI century, Proceedings of the II Yugoslav Conference - Water transportation in 21st century, University of Belgrade, Beograd, 2002, pp. 121-128. 20. Verschoof, J., Cranes - Design, Practice, and Maintenance, 2nd edition, Professional Engineering Publishing Limited, London and Bury St Edmund, UK, 2002. 21. Zrni ü, N., The influence of some container cranes design characteristics on terminal system performances, In: Modelling and Optimisation of Logistic Systems (edited by T. Banayai and J. Cselenyi), University of Miskolc, Hungary, 2001, pp. 159-171. 22. Zrni ü, N., Petkovi ü, Z., Evaluation of design solutions for trolley of quayside container cranes, Proc. of the Conf. "IRMES 2002", University of Srpsko Sarajevo, Bosnia and Herzegovina, 2002, pp. 99-104. 23. Zrni ü, N., Dragovi ü, B., Petkovi ü, Z., Survey of some new concepts that increase STS container cranes productivity, Seminarband zu den Neuesten Ergebenisse auf dem Gebiet Foerdertechnik und Logistic ''Miskolcer Gespraeche 2003'', University of Miskolc, Miskolc, Hungary, 2003, pp. 133-138. 本文献由“学霸图书馆-文献云下载”收集自网络，仅供学习交流使用。

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