US1893491A - Concrete arch bridge - Google Patents

Description

Jan. 10, 1933. K. P. BILLNER 1,893,491

CONCRETE ARCH BRIDGE Filed Aug. 4. 1930 if. 1 ;s\

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G gv *www Patented Jan. 10, 1933 UNITED STATES PATENT oEFlcE KARL P. BILLNER, OF NEW YORK, N. Y., ASSIGNOR T THE AEROCRETE CORPORATION OF AMERICA, OF NEW YORK, N, Y., A CORPORATION 0F `TDELANAIE-E CONCRETE ARCH. BRIDGE Application led August 4, 1930. Serial No. 472,895.

My invention relates to various new and useful improvements in concrete arch bridges and my obj ect generally is to permit the construction of a bridge of this type at much less cost than has heretofore been possible.

In constructing these bridges at the present time, it is the practice to cast a concrete arch of proper form and resting solidly upon suitable foundations. yConcrete sides or panels are then formed so that the uncompleted bridge represents an open box-like structure, the bottom of which is the concrete arch. A suitable filling is now introduced into the hollow structure and closely packed or tamped. The character of this filling depends upon the locality of the bridge and is generally earth, gravel, sand, clay or .other available cheap material. After the filling has been firmly packed into place, the wearing surface of the bridge, generallyT reinforced concrete, is molded in position to complete the structure.

In designing lan arch bridge of this `type, generally known as a filled-in arch, it 1s desirable to give the arch such a shape that the center line between extrados and intrados of the arch closely follows the so-called pressure line, which means a curve composed of resultants of forces kdeveloped by theweight of the structure itself, before any load has been placed on the bridge. When the pressure line coincides with or closely follows the center line the stresses in the arch will be equally distributed throughout the same and the concrete will consequently be equally compressed throughout the whole arch. The same condition will obtain when an evenly distributed load is placed over the entire span'.

'If, however, the load is removed from one half of the span and covers only the other half of the span it will be found that a positive bending moment is developed in the part of the span that is loaded anda negative bending moment is developed in the unloaded part of the span. In designing the arch it will be necessary to give it so great thickness that it will withstand the maximum stresses developed under such uneven loading and not the maximum stresses developed under an evenly distributed load. Generally this will mean that the minimum thickness of the arch needed to support a certain load per square foot which only covers half the span will be twice as great as the thickness of theV arch needed to support the same load per square foot evenly distributed over the entire span.

The filling used in a bridge of this kind in no way contributes to the strength of the structure as a whole but merely offers support for the wearing surface, the latter being generally a continuation of the highway on either side. Therefore, the arch proper has to be designed to tak-e care of the weight of this load as well as the maximum superimposed load placed on half the span. For these reasons, the concrete arch has to be made very heavy and the cost of the construction of such an arch becomes high.

Furthermore, in many cases, the filling becomes saturated with water which leaks in so that hydrostatic stresses will be setup in the filling material, thus making it necessary for the sides or panels of the bridge to be of rigid, strong and therefore heavy construction.

By means of my present invention I am able to make a concrete arch bridge of not more than half the weight of that now required for equal strength, while at the same time it can be made much cheaper, and will resist practically indefinitely the deteriorating effects of weather.

To this end I utilize as a filling material in the construction of the concrete bridge porous concrete or so-called Aerocrete which I will later more definitely identify. This material is a form of concrete the major bulk of which is composed of pores or cells, so that the weight is less than half as much as earth, for example, for the same cubic contents. It is self-contained and practically non-absorbent to water, so that there are no hydrostatic stresses to be taken care of and in consequence, the usual side panels may be entirely omitted, thus further reducing the weight.

In order that my invention may be better understood attention is directed to the accompanying drawing, and in which is shown a concrete arch bridge construction in accordance with my present invent-ion, the left half being in elevation and the right half in longitudinal section.

With the bridge shown, 1 is the concrete arch cast or molded by means of wooden forms in the usual way, and which may be reinforced if desired. The bases 2-2 of the arch are enlarged to the proper dimensions to give the desired support on the foundation used. 3 represents a filling in each spandrel of porous concrete or so-called Aerocrete. This material was invented by Aylsworth and Dyer, and is described in Patent No. 1,087,098, dated February 14, 1914. It consists of a mixture of Portland cement or other hydraulic cement, water and preferably an aggregate such as sand, to which is added a. finely powdered material, such as metallic aluminum, which in the presence of lime either inherent in the cement, or added thereto, results indissociation of the water and the generation of hydrogen bubbles. During the setting of the cement these bubbles are evolved and cause the mass to expand in somewhat the same way as the raising of ,l bread by the action of yeast. The resulting porous cement is very light, and is sufficiently strong for the purpose. Each of the bubbles within the mass is self-contained and does not connect with its neighbors so that the cement as a whole is practically watereproof.

It will be understood that substantially the same effect can be secured by aerating the cement prior to setting in other ways than by the use of powdered aluminum, as for example by blowing air into the mass.

By using expanded concrete or Aerocrete instead of the usual filling matter, I obtain a practically monolithic structure consisting of concrete part of which, namely the arch and wearing surface, is solidconcrete and part of which, namely the filling, is expanded concrete. For this reason I am able 4to utilize the filling material for reinforcement purposes. Formerly, when filling of gravel, earth or the like, was used, the reinforcement had to be confined to the concrete arches, otherwise, the part extending into the filling material would rapidly ccrrode. On the other hand, it would be economical to substitute concrete for the filling material and thus provide a base for reinforcement as in such a case the total weight of the bridge construction would be so considerably increased that the cost would be excessive.

Y By using expanded concrete or Aerocrete I am able to extend the reinforcement, in the form of tie rods 4 and 5 which are embedded in the arch when the same is cast, all the Way through the section of expanded concrete, above the upper level of the same and embed it in the concrete wearing surface that is placed on top of the filled-in section of eX- panded concrete.

When a bridge, constructed in the manner I have now described is subjected to a load which only covers half the span,the positive and negative bending moments resulting from the load are not taken up only by the arch proper but are resisted by the whole reinforced section of the bridge extending from the bottom of the arch through the expanded concreteup to the top of the wearing surface. As'will be seen the bending moments are absorbed in a section several times as thick as that, which would have been used if the bending moments had been resisted by the arch alone. For this reason I am able to design the arch to take care of an evenly distributed load only, and altogether disregard the stresses caused by a one-sided loading of the span as these stresses will be absorbed in the practically monolithic construction I obtain by .using expanded concrete as a filling. In other words, in designing a bridge of this kind I am able to decrease the thickness of the concrete arch to less than half of that which would have been needed, had the bridge been constructed according to methods heretofore in use.

The side panel 7 may be formed by the Aerocrete filler itself, or, in other words, no separate independent sides are required as with the present practice. For the sake of appearance these panels may be worked with a coating of neat cement in order to better resist weathering, or may be protected in some other suitable manner. n

I-Iaving now described my invention, what I claim is new therein and desire to secure by Letters Patent is as follows:

l. An improved concrete arch bridge comprising a solid concretev arch, a wearing surface of solid concrete above the arch and an interposed monolithic filling vof porous concrete.

2. An improved concrete arch bridge comprising a solid concrete arch, a solidv reinforced concrete wearing surface above the arch and an interposed monolithic filling of porous concrete.

3. An improved concrete arch bridge com prising a solid concrete arch, a solid concrete wearing surface above the arch, and a monolithic filling of reinforced porous concrete between the wearing surface and arch.

4. An improved concrete arch bridge comprising a concrete arch, a concrete wearing surface above the arch, vertical tie rods extending between the wearing surface and the arch and embedded in both, and an interposed filling of porous concrete between the wearing surface and arch.

5. An improved concrete arch bridge comprising a concrete arch, a concrete Wearing 5 surface above the arch, vertical and inclined tie rods between the Wearing surface and arch and embedded in both, and a filling of porous concrete between the Wearing surface and arch.

KARL P. BILL-NER.

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