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Planning, design and construction of dock rubber fender equipment
Edit: Jiangsu Ahn Jin Rubber Co., Ltd.Date: 2018-10-04

The purpose of installing the wharf rubber fender system is to prevent the pier from colliding with the ship during berthing or mooring. Because when the ship berths to the dock, it has considerable kinetic energy. After hitting the dock, this function must be released. For small boats, the impact energy is lower and the action process is shorter, so the energy released is also very low. For larger ships, the dock designer needs to pay attention to the mooring impact force and provide a rubber that can absorb enough energy. Fender system to prevent damage to the terminal and the ship.

For small terminals, wooden fenders are the most widely used; of course, some large docks are also used: wood fenders are low in energy absorption due to wood fiber compression and even partial crushing to absorb energy. . When high-energy impulses occur, the wooden fenders are often damaged by the absorption of large additional energy, and thus the wooden fender system is often designed as a separate component for easy replacement. The earliest and most common method of increasing the energy of wooden fenders is to equip the traditional wooden fenders and wharf structures with a series of extruded rubber components. In fact, the current fender system is widely used, but its energy absorption capacity is still not large enough.

The large energy-absorbing rubber fender system originally studied led to the development of gravity fender systems. The theoretical basis for these rubber fender systems is the law of energy conversion, which converts the kinetic energy of a ship into potential energy by increasing the weight of the fender. However, gravity fenders cost a lot of money, and the maintenance work of the support system structure is also large. Twenty or thirty years ago, the use of steel springs as a means of absorbing energy was popular in fenders. At that time, it was of interest because of its high energy absorption and the need for expensive structures to support its weight. The main problem is that the components are prone to rust. With the continuous development of rubber fender components, steel springs have gradually been replaced and used instead.

The original rubber fender was a Leijin-type energy dissipating pad with high energy absorption. It works by absorbing energy by shearing the rubber members on the steel pad. Although a large number of areas in the 1960s were equipped with Rayin-type energy dissipating mats, most of them were replaced by rubber fenders that were cheap, high-capacity, and requiring no frequent maintenance by the 1970s.

First, the fender type

There are many types of rubber fenders on the market today, each with different characteristics and certain advantages and disadvantages. The types that are widely used in fenders are generally of the following types:

1. Buckling type;

2. Inflatable type;

3, foam type;

4, laterally loaded cylindrical type (drum type);

5. Docking V type {ie X type):

6, flexible pile type.

Figure 1 illustrates the above various types of reaction-invariant features. In the figure, all kinds of fenders have a corresponding energy absorption under the same design reaction force. That is to say, if the area under the reaction force-deformation curve is equal, the energy absorption is the same. As can be seen from the figure, the buckling rubber fender is for a given maximum reaction force. The deformation of its absorbed energy is much smaller than other types. Although it has some shortcomings, this small deformation characteristic still makes it quite widely used. Most of the ships within the design of the ship's tonnage will have the greatest reaction force during the mooring. Many buckling rubber fenders will exert considerable pressure on the hull. Therefore, it is often necessary to use a plate to reduce the pressure dispersion. The ability of the fender to absorb impact energy is greatly reduced when subjected to external forces that are not perpendicular to the fender surface.

Inflatable and foam rubber fenders have the same reaction force - deformation curve. As can be seen from the figure, they are obviously more deformed than the buckling fender, and therefore, the outreach of the assembly equipment is also required to be large. In this type, large circular suspended fenders have less contact pressure on the hull, so there is no need to apply panels between the hull and the fender. For small fenders that are directly mounted on the dock structure, panels must be attached. As for the inflated or foamed rubber fenders , there is little or no occurrence of the reaction force reaching or approaching the maximum design reaction force during use.

For places where energy absorption requirements are not too high, large-scale laterally loaded cylindrical (drum type) rubber fenders are commonly used. Although the contact pressure on the ship is quite large and the installation and fastening are difficult, the relatively low price makes it relatively inexpensive. It still has some competitiveness. V-type rubber fenders are also commercially available in the same conditions as above, and some V-type fenders are fitted with a unidirectional veneer to make the area of energy absorbed larger.

Flexible pile fenders are generally used where soil conditions are suitable because they combine the function of the fender with the ship's components. The suction energy of the pile depends on its length, so this type of collision avoidance system is particularly suitable for use in deep water.

Second, the design steps

To date, there is no uniform seaport (ship) protection system design specification. In 1978, the International Shipping Joint Standing Committee (PLANC) established an international committee to improve the design of fender systems with the aim of producing a document guiding the design of rubber fenders : members provided a variety of relevant fender designs. Important issues, a large number of different opinions were published in the literature and published in 1984. It serves as the most comprehensive and authoritative design guide for the design of fenders and recommends various aspects related to the design of fenders.

In the PIANC academic report, three basic methods for calculating the energy absorption of the rubber fender system are described. That is, mathematical statistics methods; mathematical model methods; dynamic methods. Among them, the longest application time and the widest range is the dynamic method. Its theoretical basis is the kinetic energy equation, that is, the kinetic energy generated by the motion of an object {here, the mooring kinetic energy) is equal to half the product of the mass of the object and the square of its motion velocity (E=1/2mi). However, the full kinetic energy of the ship's movement cannot be absorbed by the fender system. Usually, when we calculate the energy absorption, we multiply the total kinetic energy of the ship by a coefficient fo. This coefficient consists of four parts, namely: the centrifugal factor C. : Additional quality factor Cm: compliance factor C. And the pier wall shape factor cc:f=C. ×Cm×Cs×Ce

The centrifugal factor is determined by the position of the ship's pressing force acting relative to the ship's center of gravity. The method for calculating Ce proposed about 20 years ago is very simple, that is, Ce is equal to the square of the ship's inertia radius divided by the square of the radius of inertia and the distance from the center of gravity of the ship to the point of impact. Of course, it can be calculated more accurately, but generally This is necessary. For a typical continuous fender system, Ce takes 0.5 to 0.6: for a single dock, Ce takes 0.7 to 0.8.

When the ship hits the rubber fender , not only the hull itself is decelerated, but also a part of the water moving with the ship is decelerated. Therefore, the additional mass factor Cm should be considered, and the Cm value determined by a large number of model tests and physical experiments. In typical cases, the designer can take 1.2 to 2.0. For the Cm method, there are nine different calculation formulas in the PIANC academic report. The additional quality factor is a water depth, a rich water depth under the keel, a distance to an obstacle or wall, a hull shape submerged under water, There are functions related to berthing speed, water flow, ship deceleration and hull clarity. Therefore, it is not surprising that there is no uniform numerical value and calculation formula. Under the keel, the depth of wealth is large, or the ratio of water depth to ship draft is 1.5 times, Cm can be 1.5, and the water depth is only 1.1 times the ship's draft. Cm can take 1.8.

The compliance factor C8 takes into account the relationship between the ship's and the fender's stiffness, usually for a "flexible" fender, and the C8 takes a 1.0 "rigid" fender for 0.9. However, for large new fenders, due to their large deflection, simple calculations show that the exact value of this coefficient is close to 1.O. Therefore, it is recommended that C8 often take 1.O.

Regarding the wharf shape system C8, considering the buffering effect of the squeeze water between the ship and the quay wall, when the ship is parked in parallel with the dock wall, the Ce value is about 0.8. For a permeable structure or only if the ship and the shoreline are at an angle of more than 5 degrees, Ce should take l.0.

Since the kinetic energy is proportional to the square of the speed of the ship, the choice of the speed of the ship is the key to the design. However, because it involves too many factors, there is no hard and fast rule for the choice of this value; for this reason, people have to choose this value by experienced engineers who are familiar with the field conditions. As a general reference, some common values are given below:

Under very good conditions 10 cm / sec

Under normal circumstances 15 cm / sec

Under very unfavorable conditions 25 cm / sec

When choosing the design berth speed, it is necessary to make a sound judgment, which is not overemphasized. To underestimate this, it often damages people’s lives and property.

As a guideline, larger ships are berthed at a lower speed than smaller ships. Since some berths are berthed by ships of a certain tonnage range, it is also possible that the berthing capacity of smaller ships is comparable to the berthing capacity of larger ships.

Third, the choice of fender

Now, the method of calculating the required energy absorption has been determined, and the designer must select a fender facility that can satisfy this energy absorption based on the calculated amount of energy absorbed. There are many factors to consider when selecting the best fender equipment for a given condition. There are usually a variety of fenders available. These devices generally meet the energy requirements, but the designer must compare them according to various other factors. Choose the best rubber fender . The main factors to consider are listed below:

1. The reaction force acting on the hull and the docking member;

2. The size of the deformation of the fender after absorbing the kinetic energy of the ship:

3. The deformation of the fender produces a reaction force acting on the hull:

4. Relative stiffness of the fender:

5. Effectiveness of the energy absorption of the fender during non-positive thrust:

6. The rate at which the rubber fenders slow down the ship's berthing speed;

7. Changes in environmental conditions during the berthing of the ship:

8. Coefficient of friction between the fender system and the hull:

9. Factors that cause the rubber fender or supporting the fender member to strike the ring;

10. Infrastructure investment and maintenance costs of fender systems and support members;

11. The tonnage range of the design vessel of the berthing dock;

12. Contact between the hull and the fender:

13. The range of water level changes;

14, the angle between the wave and the force.

The designer of the rubber fender system, whose main task is to evaluate each factor to suit a particular situation and choose the best solution. The best fender system usually means the lowest investment and the longest service life, and should also take into account the capital investment and annual maintenance costs (including fenders, ship components and ship maintenance costs).

It should be emphasized here that the specific conditions for installing the rubber fender system vary greatly. There is no such thing as the most suitable fender in any place. Even under the same circumstances, different designers have different influences on the fender design. The factors are also different from the side, so the best fender system for the selection is not necessarily the same. Designers should continue to increase their understanding of fender design principles and use their knowledge and wisdom to develop fender systems that meet specific engineering needs.

four. Several reference examples

The following three recent designs by HPA (Ham- - Padron Associates) fully illustrate these points. HPA is a consulting services engineering firm based in New York City that is responsible for the planning and design of harbour terminals and waterway engineering buildings. The company is to meet different regulations

The pieces are designed with a wide range of fenders. In all cases, all projects specifically consider the interaction of the rubber fenders and their supporting structures, giving full play to creativity and adapting to the specific conditions with the best rubber fenders .

The South Terminal of the Plaquemines Parish Coal Transit Station at the International Maritime Terminal was built in 1982 and is located on the west bank of the Mississippi River, approximately 60 kilometers from New Orleans. The terminal can accommodate from 13,000 tons of ocean-going to 150,000-ton bulk carriers. In order to minimize the maintenance of the terminal, the superstructure of the wharf is made of prestressed concrete and the foundation is made of steel pipe piles. In view of the fact that only personnel are allowed to enter and exit the dock, the design uses a truss structure (ie, a blank structure) without a dock panel. This type of construction, the amount of concrete is small, and can be prefabricated in large quantities to minimize the constant load on the pile.

The berthing force of the ship mainly produces horizontal loads, and the high-performance buckling fenders installed at the front of the pier minimize this horizontal load. The rubber fenders are TTV-type components manufactured by Seibu. In order to make the reaction force transmitted to the single pile very small, the superstructure is designed as a horizontal truss, so that the horizontal force acting on the pile is shared by many piles: the slope of the inclined pile is controlled at 1:8, the pile The flexibility is quite good, which improves the transmission and distribution of the ship's thrust.

This slight tilt has little effect on the vertical bearing capacity of the pile. Naturally, the inclined pile is used to bear both the vertical load and the horizontal load because the pier does not have a straight pile.

The situation at the Exxon Bavtown refinery in Texas is quite different. Its first number was built in 1921, and by the time of expansion in 1947, a new type of steel elastic fender system was installed on the 20,000-ton wharf shore. By 1982, the rubber fender was dilapidated, and the terminal had to dock 47,000 tons of bulk carriers and barges. Due to the deepening of the frontier of the wharf and the increase in the constant load on the superstructure of the wharf in recent years, the basic condition is unknown, so that the new fender system cannot generate any load on the wharf.

Over the past 25 years, the land subsidence in Baytown has exceeded 3.0 meters, and the dock surface is closer to the water surface, making the vertical use of the fender system relatively smaller. The choice of new rubber fenders is also affected by the dock. The restrictions on the protruding distance of the waterway to the fendering facility and the need to ensure the normal operation of the terminal and the safe berthing of the ship are required when the fender is damaged.

The best solution identified by HPA is the use of a steel-sheathed steel frame structure that is placed along the entire length of the pier and mounted on the rubber fender. This buckling rubber fender is specially manufactured by Morse Rub-ber Products Co. It is supported in turn on a twisted bracket that is fixed to a new vertical steel pile, vertical steel. The pile is fixed with the newly hit diagonal pile. All straight piles are longitudinally coupled to a continuous fixed beam welded behind the twisted bracket so that the exact alignment of the piles is not required for installation.

Each pile group (including a straight pile and a diagonal pile) supports a set of four fenders, each of which has a longitudinal support spacing of 5m-5m-3m. The choice of this type of layout mainly considers three design factors: 1. Provide sufficient concentrated row piles for energy absorption; 2. Provide spatial types that are independent of the original dock support: 3. Provide typical ease of use. The size of the fender panel that is easy to handle for construction (12-meter-long veneer is selected), and Figure 2 is a cross-sectional view of the new fender system.

The cross braces of the rubber fender frame are sized so that the adjacent fenders produce sufficient deflection when impacted at any location. Thus, when the ship is designed to kinetically impact the fender system, the four buckling fender members that are subjected to force can perform the equivalent of three fenders. The rubber fender frame is made of high-strength steel to reduce the weight of the buckling rubber fender support frame. These frames rely on the support of the buckling rubber fender to increase their flexibility and thus increase the energy absorption of the fender system. For fully prefabricated wood panels. These prefabricated members are bolted together with the rubber fender members supported on the piles. For the ease of installation of these fender members without affecting their energy absorption or carrying capacity, there are gaps of about 5 cm in all aspects of the members. The fender panels are connected to each other by pins or hinges. This type of connection is suitable for quick installation in the field, but it has a great limit on its curvature and is bent after the rubber fender panel is installed and used. Minimize its size and weight.

The third engineering design of the HPA requires a creative solution to the unique fenders of the US Connecticut Submarine Base. The No. 17 Jetty Pier of the base was built in 1946 as a berthing facility for two floating (ship) docks. Due to changes in the use requirements, the US Navy instructed to transfer its dock and change the side of the dock to a submarine. Service, the other is to repair another floating dock service. Reconstruction includes the restoration of piles and panels of the jetty and the renovation of the panel structure. At the same time, it adds some process trenches required for public installation, such as newly installed heating pipes, fire pipes, fresh water pipes and sewage pipes, and new power distribution. Lighting facilities, adding a unique rubber fender system to absorb the momentum of mooring submarines. However, the original jetty pier is not used to bear such a crushing force, and it is necessary to introduce a new concept to enable the project to be implemented. A lot of creative measures are used.

Before the widespread use of computers for design work, a conservative empirical estimation method was used to estimate the distribution of mooring forces along the length of the wharf. The calculation results show that each row of the pier must resist about 20% of the total impulse. The dock panel, like the horizontal beam, spreads the mooring impulse to many rows of piles. The exact distribution of this force depends on the pier panel structure and the relative stiffness of the pile. Through computer analysis, it is determined that the impulse of a row of piles only accounts for 8% of the total impulse. Obviously, the actual anti-squeezing force of the dock is 1.5 times different from the empirical calculation. The use of computers has made the installation of new rubber fenders more reasonable and has accelerated the progress of the project.

Providing a high-energy, low-maintenance submarine fender system is an extremely difficult problem to solve under conditions of limited investment. Due to the ship's hull characteristics, the pressing force is applied near the midpoint between the point where the pier panel supports the rubber fender to the bottom of the sea, so that the rubber fender pile is like a support traverse of about 15 meters long. When the submarine is pressed against the fender, the thrust has a lateral speed component and a longitudinal velocity component, and the lateral cantilever beam produces a large deflection in both directions.

To sum up, the problem is that the lateral load capacity of the original jetty is quite small, which limits the reconstruction project. In order to avoid overloading the pier's inclined piles, the choice of fenders is strictly limited.

The new fenders used by HPA's Pier No. 1 are second to none in meeting US Navy's overnight standards. Its equipment absorbs more than three times as much energy as other rubber fenders at the New London submarine base. The fender is manufactured by Morse Rubber Manufacturing, which uses a pair of curved rubber members to make it flexible. . It is then spliced with a high-strength elastic fender steel pile, and a wing-shaped rubber fender member is placed on the outer side surface of the fender .

The "butt V-shaped" rubber fender members are arranged in a pair of 3 m center-to-center spacing, and the V-shaped rubber fenders are butt-joined together to form an "X" shape. In this way, its energy absorption is twice that of a single "V" type fender, while the reaction force is equal to a single component. Each pair of fenders is fixed to the front edge of the dock deck and bolted together with the fender steel pile.

The rubber fender steel pile is "H" shaped and has a total length of 40 meters. 21 meters on the mud surface is a heavy-duty high-strength steel pile, and 19 meters below the mud surface is a light-duty soft steel pile. The mud surface is made of high-strength channel steel, and the pre-stress is fixed on the flange. The upper part of the pile uses slotted high-strength steel to prevent the instability of the long and unsupported steel pile due to bending, increase the bending strength, reduce the self-weight, increase the flexibility and enhance the energy absorption.

Where the submarine hull may impact, the outer section of the fender steel column is also fitted with airfoil rubber fenders . This fender protects the hull and steel pile and provides additional energy absorption. About 65% of the energy absorbed by the protection system is the most responsible for the "x' type fenders, 20% for the fenders and 15% for the airfoil members.

The construction of this rubber fender facility was completed in the second half of last year and the progress was quite fast. The fender steel piles are included, including brackets, brackets and wing fenders, which are shipped to the site for pre-production. The characteristics of the seabed soil are suitable for hitting the pile to a predetermined elevation, then holding the wooden facings in place and fixing them to the steel piles of each of the retaining boats with a single large bolt.