Pier with prestressed resiliant integral deck to absorb docking forces of ships

In a pier having a series of spaced-apart horizontal pile caps surmounting and connecting the supporting piles together transversely of said pier, there is an integrated one-piece deck supported atop the pile caps so that it can slide thereon. A series of prestressing tendons connect the deck to the pile caps so that when a wharf is struck by a ship, the lengthening and shortening of the tendons and the sliding friction between the deck and the pile caps absorbs the impact load.

This invention relates to an improved pier having a one-piece, integrated 
wharf deck which is connected to the supporting pier bents by 
post-tensioned tendons. As a result, the energy of approaching ships being 
docked can be absorbed by virtue of the internal work performed by the 
elongation and shortening of the prestressed tendons. 
BACKGROUND OF THE INVENTION 
A conventional wharf deck depends on timber and rubber fenders and flexible 
piles to absorb impact energy. These are often damaged and worn out in the 
course of time and have to be replaced, thus becoming difficult and 
expensive to maintain. 
SUMMARY OF THE INVENTION 
This deck of this invention absorbs part of the docking energy by 
distributing it to a number of pier bents, which are substantially fixed 
and are relatively unyielding. The distribution is done through 
prestressed, i.e., post-tensioned, tendons that are anchored to both the 
wharf deck and the pier bents. The post-tensioned tendons (which may be 
made of steel wires, bars, or strings), are elongated or shortened as the 
deck is moved sideways by the docking force of the ships. Both the 
elongation and shortening of these tendons perform internal work which 
(together with the frictional resistance at the sliding surface between 
the deck and the pier bents) absorb the major part or all of the impact 
loads produced by the moving ships as they are moored to the deck. 
These elongated cables and the pier bents all act within their elastic 
limit, so that they essentially regain their original position after 
having absorbed the energy imparted to them by the mooring ships. An 
adequate factor of safety insures proper behavior, as in most engineering 
designs. 
The wharf deck is integrated into one piece by any of various means, such 
as, by reinforcing it with steel rods, by prestressing it, or by welding 
and riveting of steel members and joints, so that the entire deck (of 
concrete or other suitable material) is integrated into one piece, (which 
may, for example, be about 100 feet wide and several hundred feet long). 
The wharf deck itself then acts as a horizontal diaphragm in the lateral 
(or transverse) direction and helps to distribute the mooring force to the 
majority of the bents supporting that wharf. The responses of the various 
bents to a mooring ship can be predicted and analyzed by basic mechanics 
and computer programs in order to determine the distribution of the dock 
force among the different bents. 
The entire deck is slidably mounted on top of the pile caps within limits 
imposed by the thickened edge of the pier, a sliding surface such as metal 
bearing plates being provided to minimize the friction between them and to 
provide a durable wearing surface. However, this frictional loss, as 
stated above, also helps in the absorption of energy. Since the frictional 
force may act in opposite directions, when the deck is moved laterally in 
one direction, frictional force may prevent it from returning to the exact 
original position. This change in position is small and can be predicted 
for a particular case. Later bumps against the opposite edge of the deck 
may restore it to or toward its original position; if not, when its 
limited permissible movement is achieved, the deck moves no farther. 
The main energy absorption is provided by the prestressing tendons, which 
are arranged in a suitable pattern, preferably a diagonal pattern, 
crisscrossing along the bottom of the deck or thereabout. The layouts and 
patterns of these tendons may differ for different cases and can be 
designed so that the tendons move within predicted limits. Some tendons 
are lengthened as a result of the mooring ships, while others are 
shortened thereby. In both cases, internal energy is absorbed by these 
tendons. 
In addition, certain small lateral movements of the supporting bents (which 
later spring back) also help to absorb the impact of energy of the mooring 
ships. These of course, have to be calculated for each case. 
The proper distribution of impact force by the concrete deck acting 
transversely depends on frictional forces between the deck and the bents, 
the lengthening and shortening of the tendons, and the lateral movements 
of each supporting pier bent. 
The tendons are protected and anchored to the wharf deck in a properly 
designed fashion. They are connected to or looped around verious pier 
bents at proper locations. The force created at such a point of turning is 
resisted by metallic or other sleeves. The tendons themselves are 
protected by plastic, steel, or other tubing, which is greased or grouted 
with plastic material inside to provide the necessary protection to the 
cables. 
The basic economy of this particular invention is due not only to the basic 
layout and design of the structure, but also to the extreme economy of 
highly stressed steel tendons acting in tension, as compared to 
conventional structure, thereby providing elastic movement of significant 
magnitude under large prestressing forces, so that a large internal work 
is done by these tendons. 
Many details are involved, such as the proper location and the placement of 
these tendons, the openings provided through the deck for the passage of 
the tendons, the anchorage to be provided for the tendons, the protection 
of the tendons, etc. All these require judgment, investigation with proper 
experimental and theoretical values to be determined, and consideration of 
the special conditions of each site. 
Other objects, advantages, and features of the invention will appear from 
the following description.

BRIEF DESCRIPTION OF SOME PREFERRED EMBODIMENTS 
The Embodiment of FIGS. 1-6 
FIGS. 1 to 6 show a pier 20 supported by a series of piles 21 and 22, which 
may be driven at an angle (see FIG. 5), as shown, meeting at their upper 
ends 23, or may be identical and vertical. The upper ends 23 of these 
piles 21 and 22 are joined by laterally extending horizontal pile caps 23 
extending across substantially the width of the pier 20. The pier 20 may, 
for example, be 100 feet wide and 600 feet long, with the pile caps 24 
spaced apart, typically, at twenty-foot intervals, resulting in a total of 
thirty-one lateral pile caps 24. The pile caps 24 thus serve as bents to 
support a deck. 
All these pile caps 24 may be made from reinforced or prestressed concrete, 
or they may be made from steel or other suitable materials. They have 
coplanar upper surfaces 25 and, if made of concrete, the upper surfaces 25 
are preferably provided with metal plate 26 thereupon to help lower the 
friction with the deck and to provide a durable wearing surface. Of 
course, other materials can be used for the plates 26. The plate 26 may be 
half-inch steel and may be substantially the same width as the beams 24 to 
which it is secured at intervals, as by counter sunk bolts 27. The metal 
plate 26 is corrosion resistant or coated to protect it against corrosion 
in the marine environment. 
These pile caps 24 support an integral deck 30, which is preferably made of 
concrete. It may be made of prestressed concrete or a reinforced concrete 
in such a way that the deck 30 is integral and functions as a single large 
slab. This reinforcing or prestressing is not shown in the drawings, being 
quite of the conventional types of reinforcing concrete. Two novel 
features, however, are that the deck 30 itself is not secured in any way 
to the pile caps 24 and that the deck 30 is, in effect, a single, 
integral, long slab. 
As shown in FIG. 1, the deck 30 has a continuous flat slab 31 with an upper 
surface 32 and, as shown in FIG. 3, the slab 31 is supported from below by 
depending lateral beams 33 and longitudinal struts 34. The beams 33 may be 
spaced apart at twenty-foot intervals, and the struts 34 may be located 
near each edge and about twenty-feet therefrom. The deck 30 also has 
depending thickened marginal portions 35 at each side and at its outboard 
end, extending down to about the bottom of the pile caps 24. The outer 
edges may be protected by conventional fenders 36, which may be rubber, 
for example, to prevent chipping away of the concrete. The deck's beams 53 
each have a flat lower surface 37 that rests on the steel plates 26. 
A very important feature of the invention is the use of prestressing 
tendons 40 and 41 which are arranged in such a manner as to resist 
movement of the deck 30 relative to the pile caps 24. For example, one end 
of a tendon may be anchored to the deck 30 at a strut 34 or at a margin 35 
and the other end may be anchored to a pile cap 24. Or, as shown in FIGS. 
4, 5, and 6, both ends 42 and 43 of a tendon 40 that describe a vee, the 
ends being anchored to the same strut 34, with the tendon 40 passing 
through an opening 42 in a pile cap 24 at a vertex 43 of the vee, to bear 
on that pile cap 24 at the vertex 43. The tendon 40, in such an example, 
passes freely through openings 44 or slots 45 in beams 33 and through 
slots 46 or other openings in either pile caps 24 (see FIGS. 6 and 10). 
The prestressing tendons 40 and 41 are anchored by suitable conventional 
anchors 47, as shown in FIG. 7. FIG. 8 shows anchorage to a thickened 
marginal portion 35 of the deck 30, while FIG. 9 shows anchorage to a pile 
cap 24. The tendons 40 and 41 (see FIG. 10) may themselves be enclosed in 
tubing 48 of plastic, or steel, or other suitable material, which may be 
either greased or grouted inside with plastic 49 to provide the necessary 
protective cover to the cables 40 and 41 and to enable them to move 
relatively to the pile caps 24 or beams 33 through which the conduits 43, 
44, 45, 46 are provided. 
These tendons 40 and 41 may be arranged in various patterns, such as the 
one shown in FIG. 4, in which two series of tendon vees are used adjacent 
each longitudinal edge of the deck 30, with one series of tendons 40 being 
anchored to the strut 34 closest to the margin 35 and a second series of 
tendons 41 being anchored to the next strut 34 and the vee vertex 43 in a 
pile cap 24 very close to the margin 35. Two tendons 40 or 41 may be 
anchored at or near each such location, as shown in FIGS. 7-9, preferably 
with some overlap. The tendons 40 going in one basic direction are thus 
balanced by tendons 41 going in the other basic direction. 
These tendons 40 and 41 are brought up to the desired degree of 
post-tensioning by use of conventional post-tensioning means. Due to the 
fact that some go in one direction and some go in the other direction, 
impact against the deck 30 produces different kinds of reaction on them. 
This criss-crossing of the angles thus provides one good system. 
Efficiency can be obtained by using four one-half inch diameter strands 
initially stressed to about 50% of the effective or working prestress. For 
different sizes and different materials and in different instances 
different figures would apply, however, these are representative. Each 
time the tendon 40 or 41 passes through a pile cap 24 if it is free to 
move, as of course, it is where it simply lies free below the deck 30. 
The embodiments of FIG. 11 
The form of the invention shown in FIG. 11 comprises a pier 50 with 
transverse pile caps 51 that are spaced, for example, twenty feet apart. 
An integral deck 52 is provided as before, Tendons 53 and 54 are disposed 
in a V shape, with each end 55 and 56 of one set of tendons 53 being 
anchored to the rim or margin 57 of the deck 52, but extending over to and 
coming back from a vertex 58 at a pile cap 51 near the opposite deck 
margin 59. The other set of tendons 54 also has both ends 60 and 61 
anchored to the rim 57 and extending to and from a vertex 62 in a pile cap 
51 near the opposite side of the deck 52. No openings through the pile 
caps 51 are needed except at the vertices 58 and 62. Again, the 
prestressing may be brought up to about 50% of the full amount of which it 
is capable, meaning that it can be further prestressed under impact. The 
tendons 53 act in opposite direction to the tendons 54; so the tendons 53 
tend to move in one direction when the other tendons 54 tend to move in 
the other direction, thereby taking up the forces. 
Example of Calculations 
Assume: 
the pier deck is to be 100'.times.600'--absorbing 50% impact energy 
E.sub.i, 
the ship is to weight 30,000 long tons, and 
the approach velocity, V=0.75 ft/sec. 
Then: 
##EQU1## 
Assume that 50% energy is absorbed by the deck. Thus, E.sub.i /2=293,500 
ft. lbs. to be absorbed by the deck. 
Now assume that the tendons are to be stressed initially to 25% elongation, 
and under impact to 5%, i.e., moving a maximum of 3" under load; and 
assume that the coefficient of friction is 0.1 (static, then sliding, 
steel on steel). The pile rows are on 20-foot centerlines. 
The reaction Rf per pile row due to deadload (at 300 psf) 
=100.times.20.times.0.3.times.0.1=60 kips (a negligible amount). 
Equating E.sub.i to work done--E.sub.i /2=Fd/2=293,500 where d is the total 
lateral deflection of the deck, and F is the lateral force on the deck. 
(1) distance d=0.25' i.e.: 
##EQU2## 
(2)=0.5' i.e.: 
##EQU3## 
If the pile system is considered rigid or as reserve for purpose of energy 
absorption, and, assuming that the impact energy is absorbed by 6 rows of 
piles over 120'-0" of pier, then F per pile cap is reduced to 17%, or 
4.phi.1/2" strands. 
To those skilled in the art to which this invention relates, many changes 
in construction and widely differing embodiments and application of the 
invention will suggest themselves without departing from the spirit and 
scope of the invention. The disclosures and the descriptions herein are 
purely illustrative and are not intended to be in any sense limiting.