Reinforced Concrete Pier Construction
AMERICAN SOCIETY OF CIVIL ENGINEERS
Paper No. 1176
REINFORCED CONCRETE PIER CONSTRUCTION.
By Eugene Klapp, M. Am. Soc. C.E.
With Discussion by Messrs. William Arthur Payne,
and Eugene Klapp.
A private yacht pier, built near Glen Cove, Long Island, has
brought out a few points which may be of interest. It is an example
of a small engineering structure, which, though of no great moment
in itself, illustrates the adoption of means to an end that may be
capable of very great extension.
The problem, as submitted to the writer, was to construct a yacht
landing at East Island, on the exposed south shore of Long Island
Sound, in connection with the construction at that point of an
elaborate country residence. The slope of the beach at this point is
very gradual, and it was specified that there should be a depth of at
least 4 ft. of water at low tide. Soundings indicated that this necessitated
a pier 300 ft. long. It was further specified that the pier should
be to some extent in keeping with the scale of the place being created
there, and that a wooden pile structure would not be acceptable.
Besides these esthetic conditions, wooden piles were rejected because
the teredo, in this part of the Sound, is very active. At the same
time, the owner did not care to incur the expense of a masonry pier
of the size involved. Also, it was desired to unload on the pier all
material for the house and grounds during construction, and coal and
other supplies thereafter, thus necessitating a pier wide enough to
allow access for a cart and horse and to provide room for turning at
the pier head.
Plate XXX.—Yacht Pier Near Glen Cove, N. Y.
Comparative designs and estimates were prepared for (a) a pier
of ordinary construction, but with creosoted piles; (b) a concrete pier
on concrete piles; and (c) for a series of concrete piers with wooden
bridge connections. The latter plan was very much the best in appearance,
and the calculated cost was less than that of the pier of concrete
piles, and only slightly more than that of creosoted piles, the latter
being only of a temporary nature in any case, as it has been found that
the protection afforded by creosote against the teredo is not permanent.
At this point on the Sound the mean range of the tide is about
8 ft., and it was determined that at least 5 ft. above mean high water
would be required to make the underside of the dock safe from wave
action. There is a northeast exposure, with a long reach across the
Sound, and the seas at times become quite heavy. These considerations,
together with 4 ft. of water at low tide and from 2 to 3 ft. of
toe-hold in the beach, required the outer caissons to be at least
20 ft. high.
To construct such piers in the ordinary manner behind coffer-dams,
and in such an exposed location, was to involve expenditure far beyond
that which the owner cared to incur. The writer's attention had shortly
before been called to the successful use of reinforced concrete caissons
on the Great Lakes for breakwater construction, by Major W.V.
Judson, M. Am. Soc. C.E., and under patents held by that officer. It
seemed that here was a solution of the problem. These caissons are
constructed on the shore, preferably immediately adjoining the work.
After thorough inspection and seasoning, they are usually launched
in a manner somewhat similar to a boat, are towed into position, sunk
in place, and then filled with rip-rap.
In this case what was needed was a structure that could be constructed
safely and cheaply in the air, could then be allowed to harden
thoroughly, and could finally be placed in accurate position. The
weights to be supported were not great, the beach was good gravel and
sand, fairly level, and, under favorable circumstances of good weather,
the placing of the caissons promised to be a simple matter. Therefore,
detailed plans were prepared for this structure.
An effort was made to preserve some element of the yachting idea
in the design, and bow-string trusses, being merely enlarged gang
planks, were used to connect the caissons.
The pier was originally laid out as a letter "L," with a main leg
of 300 ft. and a short leg of 36 ft. The pier head consisted of eight
caissons in close contact, and was intended to form a breakwater, in
the angle of which, and protected from the wave action, was to be
moored the float and boat landing. After the first bids were received,
the owner wished to reduce the cost, and every other caisson in the
pier head was omitted, so that, as built, the pier contains eight caissons
and five 53-ft. trusses. The caissons supporting the trusses are 8 ft.
wide and 12 ft. long, and those in the pier head are 12 by 12 ft. On
account of the shoal water and the great height of the outer caissons
in comparison with their cross-section, it seemed advisable to mould
them in two sections. The reinforcement in the side walls consisted of
round 1/2-in. rods horizontally, and 3/8-in. rods vertically, spaced as shown
on Fig. 1, together with cross-diaphragms as indicated.
The caissons were reinforced for exterior pressures, which were to
be expected during the launching and towing into position, and also
for interior pressures, which were to be expected at low tide, when the
water pressure would be nothing, but the filling of the caissons would
be effective. The corners were reinforced and enlarged. In order to
secure a proper bedding into the sand foundation, a 12-in. lip was
allowed to project all around the caisson below the bottom. In the
bottom there was cast a 3-in. hole, and this was closed by a plug while
the lower section was being towed into place.
The question of the effect of sea water on the concrete was given
much thought. The writer is unable to find any authoritative opinions
on this subject which are not directly controverted by equally authoritative
opinions of a diametrically opposite nature. He thinks it is a
question that this Society might well undertake to investigate promptly
and thoroughly. There can be no question that there are many distressing
instances of failures due to the action of sea water and frost
on concrete, and that many able and experienced engineers in charge
of the engineering departments of the great transportation companies
have simply crossed concrete off their list of available materials when
it comes to marine construction. It is a subject too large in itself to
be discussed as subsidiary to a minor structure like the one herein
described, and though many have rejected concrete under these conditions,
other engineers equally conservative are using it freely and
The writer consulted with his partner and others at some length,
and, considering all the advantages to accrue by the use of these concrete
caissons, decided to do so after taking all known precautions.
These precautions consisted in:
First, the use of cement in which the chemical constituents were
limited as follows:
It was specified that the cement should not contain more than 1.75%
of anhydrous sulphuric acid (SO3) nor more than 3% of magnesia
(MgO); also that no addition greater than 3% should have been made
to the ingredients making up the cement subsequent to calcination.
Secondly, to secure by careful inspection the most completely
homogeneous mixture possible, with especial care in the density of
the outer skin of the caissons.
Thirdly, a prolonged seasoning process before the new concrete
should be immersed in the sea water.
In addition to these well-known precautions, it was decided to try
the addition to the cement of a chemical element that should make
with the free lime in the cement a more stable and indissoluble chemical
combination than is offered by the ordinary form of Portland
cement. This was furnished by the patent compound known as
"Toxement," which is claimed by the inventor to be a resinate of
calcium and silicate of alumina, which generates a resinate of lime and
a silicate of alumina in crystalline form. It is further claimed that
each of these materials is insoluble in sodium chloride and sodium
sulphate, 3% solution. It was used in all the caissons, excepting
Nos. 1 and 2, in the proportions of 2 lb. of Toxement to each 100 lb. of
cement. The first two caissons were not thus treated, and will be held
under close observation and comparison with the others, which were
treated with this compound.
The mixture used was one of cement (Pennsylvania brand), two of
sand, and four of gravel. The sand and gravel were from the nearby
Cow Bay supply, and screened and washed. None of the gravel was
larger than 1/2 in., grading down from that to very coarse sand. The
sand was also run-of-bank, and very well graded.
The caissons, after being placed, were filled with sand and gravel
from the adjoining beach up to about mean high-water mark, and
the edges outside all around were protected from tidal and wave
scour by rip-rap of "one man" stone.
The trusses were constructed on a radius of 34 ft., with 8 by 8-in.
chords, 6 by 6-in. posts, and 1-in. rods. The loading was figured
as a loaded coal cart plus 100 lb. per ft. All lumber was clear yellow
pine, except the floor, which was clear white oak. The pipe rail and
all bolts below the roadway level, and thus subject to frequent wettings
by salt water, were of galvanized iron. The trusses were set 9 ft. 9 in.
apart on centers, giving a clear opening of 8 ft. between the wheel
guards under the hand-rails. The fender piles were creosoted. The
float was 18 ft. long and 12 ft. wide.
A contract was let to the Snare and Triest Company, and work
was commenced early in August, 1909. The first caisson was poured
early in September, and the last about the beginning of October.
The caissons were all cast standing on parallel skids at about
mean high water. It was first intended to construct a small marine
railroad and launch the caissons in that manner, rolling them along
the skids to the head of the marine railway. This plan was abandoned,
however, and by sending in at high tide a powerful derrick scow, many
of the caissons were lifted bodily from their position and set down
in the water, towed to place and sunk in position, while the others,
mostly the upper sections, were lifted to the deck of the scow and
placed directly from there in their final position. There was not much
difficulty in getting them to settle down to a proper bearing. Provision
had been made for jetting, if necessary, but it was not used. In
setting Caisson No. 2 a nest of boulders was encountered, and a diver
was employed to clear away and level up the foundation. The spacing
was accomplished by a float consisting of two 12 by 12-in. timbers,
latticed apart, and of just sufficient length to cover the clear distance
between the caissons. The first caissons being properly set inshore,
the float was sent out, guyed back to the shore, and brought up against
the outer edge of the set caisson. The next caisson was then towed
out, set against the floating spacer, and sunk in position. There was
some little trouble in plumbing the caissons, but, by excavating with
an orange-peel bucket close to the high side and depositing the
material against the low side, they were all readily brought to a
sufficiently vertical and level position to be unnoticed by sighting
along the edge from the shore.
The trusses were all constructed in the contractor's yard at Bridgeport,
and were towed across the Sound on a scow. They were set up
and braced temporarily by the derrick boat, and then the floor and deck
were constructed in place.
On December 26th, 1909, a storm of unusual violence—unequaled
in fact for many years—swept over the Sound from the northeast; the
waves beat over the pier and broke loose some floor planks which had
been only tacked in position, but otherwise did no damage, and did
not shift the caissons in the least. The same storm partly destroyed
a pier of substantial construction less than a mile from the one in
Unfortunately, the work was let so late in the summer, and the
restrictions as to seasoning the concrete were enforced so rigidly, that
the work of setting the caissons could not be commenced until
November 11th, thus the entire construction was forced into the very
bad weather of the late fall and early winter. As this involved very
rough water and much snow and wind, the work was greatly delayed,
and was not completed until the middle of January. The cost of the
entire dock was about $14,000.
The writer believes that the cost was much less than for masonry
piers by any other method of construction, under the existing circumstances
of wind, tide, and exposure.
It would seem that for many highway bridges of short span, causeways,
and similar structures, the use of similar caissons would prove
economical and permanent, and that they might be used very largely
to the exclusion of cribwork, which, after a decade or so, becomes a
source of constant maintenance charges, besides never presenting an
attractive appearance. Finally, in bridges requiring the most rigid
foundations, these caissons might readily be used as substitutes for
open wooden caissons, sunk on a prepared foundation of whatever
nature, and still be capable of incorporation into the finished structure.
William Arthur Payne, M. Am. Soc. C. E. (by letter).—On the
arrival of the first barge load of brick, to be used in building a residence
on the estate to which this pier belongs, a severe northwest wind
blew for two days, after the boat was moored alongside, directly against
the head of the pier and the side of the boat. The effect on the pier was
to crush the fender piles and cause a settlement of one of the caissons
at the pier head on the west end. The caisson was knocked slightly
out of alignment, and a settlement toward the west was observable.
The writer believes that this was caused by the pounding of the
brick barge on the sand bottom on which the caissons rest, during half
tide, the boat being raised from the bottom on a roller, and striking
when the roller had passed. In order to protect the pier and avoid the
bumping of barges against it, three groups of piles were driven about
8 ft. beyond the end, a secondary platform was built between these and
the stringer of the pier, and arranged so that it would slide on the
stringer in case of movement of the piles. This secondary platform
is particularly advantageous in the handling of material, as the height
of the dock was found to be excessive for passing up brick and cement.
For handling material after it is deposited on the dock, an industrial
railroad has been built. At the shore end of this railroad, brick and
cement are dumped into wagons, in which they are carried up the hill
to the house.
Eugene Klapp, M. Am. Soc. C. E. (by letter).—The injury done to
the piers, as reported by Mr. Payne, is not to be wondered at. The pier
was primarily built for a yacht landing, and, on account of the shoal
water conditions, excepting at extreme high tide, it was mostly to
be used by tenders and launches from larger yachts. It was thought
that at high water the large steam yachts might be able to come alongside.
Provision was not made for tying up to the dock a heavily loaded
brick scow and allowing it to remain there through rough weather.
The building of the secondary fender piles, during the temporary
use of the dock for unloading building material, will doubtless prevent