US3577896A

US3577896A - Method for producing structure components of reinforced concrete subjected to tensile stress

Info

Publication number: US3577896A
Application number: US769478A
Authority: US
Inventors: Ulrich Finsterwalder; Klemens Finsterwalder
Original assignee: Dyckerhoff and Widmann AG
Current assignee: Walter Bau AG
Priority date: 1967-10-17
Filing date: 1968-10-17
Publication date: 1971-05-11
Anticipated expiration: 1988-05-11
Also published as: FR1584442A; AT298745B

Abstract

Method for making reinforced concrete structures or elements to be subjected to tensile stresses where pressure pads or casing presses are located in slots extending down from the surface at a predetermined distance from one another in parallel planes and splitting pressure is applied by hydraulic means through the presses in a direction perpendicular to the parallel planes.

Description

United States Patent [72] Inventors Ulrich Finsterwalder Munich-Obermenz; Klemens Finsterwalder, Socking near Starnberg, Germany 21 Appl. N0. 769,478

[22] Filed Oct. 17, 1968 [45] Patented May 11, 1971 [73] Assignee Dyckerholf & Widmann Kommanditgesellschalt Munich, Germany [32] Priority Oct. 17, 1967 [33] Oermany [54] METHOD FOR PRODUCING STRUCTURE COMPONENTS OF REINFORCED CONCRETE SUBJECTED TO TENSILE STRESS 5 Claims, 5 Drawing Figs.

[52] US. Cl 94/24, 94/ l 8 [51] Int. Cl. E0lc 7/10 [50] Field ofSearch 94/18, 22, 24, 8; 299/21; 52/2 [56] References Cited UNITED STATES PATENTS 1,900,446 3/1933 Joy 299/21 2,251,672 8/ 1941 Friberg 94/24 2,833,186 5/1958 Dobellw. 94/22X 2,852,991 9/1958 Dobell 94/22X 2,910,921 1 l/ 1959 Freyssinet 94/8 3,437,017 4/1969 Walz 94/18X Primary Examiner-Jacob L. Nackenoff Attorney-Robert H. Jacob ABSTRACT: Method for making reinforced concrete structures or elements to be subjected to tensile stresses where pressure pads or casing presses are located in slots extending down from the surface at a predetermined distance from one another in parallel planes and splitting pressure is applied by hydraulic means through the presses in a direction perpendicular to the parallel planes.

Patented May 11, 1971 3,577,896

Fe Fe 6 HUHiJIHHHI B I N VE N TOR.

Ulrich Fins I er walder Klemens F inslerwal der METHOD FOR PRODUCING STRUCTURE COMPONENTS or REINFORCED CONCRETE SUBJECTED T TENSILE STRESS BACKGROUND OF THE INVENTION The present invention relates to reinforced or prestressed concrete construction and is concerned with a method for producing structural components or other structures of reinforced concrete that are subject to tensile stresses and providing fissures in such structures.

The building material generally referred to as reinforced or steel concrete is a combination building material made of concrete and steel rods where the former absorbs the compression stresses and the latter the tensile stresses or strains. If this combination material is exclusively subjected to pressure as, for example, in Connection with columns loaded centrally by a compression force P, then the carrying capacities of both building materials, concrete and steel, are set up independently of one another in accordance with the theory of plasticity as a percentage of their wear resistance or breaking strength. In order to visualize these tension or stress relationships, three different conditions of tension are illustrated in FIGS. 1(a), 1(b) and 1(c) in connection with a cross section of a combination of concrete and steel. In this case FIG. 1(a) ap-' plies with a constant compressive stress 8,, and equal steel cross sections Fe at both borders or ends.

If due to an offcenter or eccentric force of compression P, different forces of compression 8,; and 6 arise at both edges or borders of a structural element subjected essentially to pressure, or one-sided tensile stresses of limited scope (FIG. lb) then one considers the cross section as a homogeneous concrete cross section in order to simplify the computation and computes it'in accordance with the theory of elasticity. For this purpose, it is assumed that the steel inserts Fe and Fe shall absorb stresses which in accordance with their elasticity module per unit of area are times as great as those absorbed by the concrete. It is presupposed for this, however, that no tension cracks or slits arise in the concrete. This condition is designated as tension condition If, however, a combination material cross section of concrete and steel is loaded in such a manner that pull slits can arise in the concrete (FIG. 10), then it is commonly assumed in computing, that the concrete does not participate in the absorption of the tensile stresses in the entire pull or tension zone, so that the total tensile stresses must be absorbed by the steel. This distribution of tension in the cross section is defined as condition ,II." It is used as the basis for the computation of compression of greater eccentricity for tension and for pure pull.

In most cases, to be sure, this last assumption permits a practical computation of the combination structural material reinforced concrete. However, the actual carrying behavior of the combination building material is not sufficiently taken into account in this connection; inparticular, the tensile strength of the material steel concrete, which exists, even though minor, is not exploited in all cases. The tensile strength of the reinforced concrete may, however, not be included because with a structural element that is subjected to tensile pull neither thew'idth nor the spacing of the cracks that may arise can be accurately determined and thus no conclusion can be drawn about factors regarding the distribution of tension in the steelv and in the concrete, nor about the elasticity module of the Concrete for pull which would have to be set up.

SUMMARY OF THE INVENTION It is an object of the invention to provide a possibility to enable one also with pull members of reinforced concrete to include in the computations the tensile strength of the combination building substance; for this it has to be possible to draw a conclusion regarding the magnitude of the elasticity module of both construction materials.

It is'a particular object of the invention to impart strains or stresses in concrete slabs constructed without spacial gaps.

In accordance with the invention this problem is solved in the external loads to cause cracks or splits which extend at predetermined distances parallel to one another vertically with respect to the supporting direction of the structure, so that the concrete is elastically pressed apart in the plane of the splits or cracks to be produced by splitting forces acting perpendicularly to this plane.

In this manner, cracks are artificially produced at predetermined distances from one another in a reinforced concrete structural element that is subjected to tensile stress. If the distances of the cracks from one another are so adjusted to the entire supporting behavior of the structure, that between the given splits wild cracks or splits are avoided, then it is possible on the basis of the expansibility of the construction material steel concrete, between any two splits or cracks and the distribution of tension of the steel in the splits to make a prediction about the elasticity module for tension, so that the concrete can be made to participate in absorbing the tensile stresses within the limits of its strength.

Suitably, these splits or cracks are produced in that in the plane of the splits to be made, small pressure elements or pads are provided that extend merely across a part of the thickness of the structure which inorder to produce the splitting forces are charged with a hydraulic pressure agent. Advantageously, the pressure elements or pads are subsequently placed in wedges or grooves produced in the surface of the structural elements.

Suitably, the pressure pads are in the form of elongated, narrow casing presses of sheet steel, which casing presses may, in addition, be coated on the outside with a binding agent, for example, bitumen.

To be sure, it is known to cause in structural reinforced concrete components, particularly in runway covers, decreases in the cross section by inserting bodies of any configuration in order to obtain that the cross section of the concrete splits preferably at predetermined locations. However, these known measures have the considerably shortcoming that it cannot be dependably ascertained that cracks develop solely at predetermined locations, but that they also have a predetermined width. Only then can it be assured that individual splits will not open more than adjacent ones. In accordance with the invention these shortcomings are avoided, because in each location where a split or crack is to be produced a splitting force can be applied that can be accurately determined in relation to or depending on the thickness of the structure or structural component which, moreover, can be attuned to the elastic behavior of the concrete between two splits.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF PREFERRED EMBODIMENTS In the drawings the invention is illustrated in connection with a runway cover, without it being intended to limit the invention to runway covers. Although runway covers are a preferred field of application for the invention, it is also possible to apply the same to all desired tension members of reinforced concrete.

In the example illustrated grooves or slots 2 of approximately 4 mm. width are produced in a runway cover 1 poureduninterruptedly without gaps, after it is hardened at distances of,

for example, 3 m. These grooves or slots can be provided without difficulties, for example by scoring with a known groove cutter. These grooves or slots 2 extend transversely of the longitudinal extent of the runway plate 1. The depth of penetration of the slots is determined in relation to the total thickness of the concrete construction because it is necessary to insure that the split or crack that will be formed will also extend over the entire depth of the concrete construction. With a runway plate of 16 cm. thickness, for example, a penetration depth of 3 .5 cm. is sufficient for the groove or slot 2.

In the small grooves or slots 2 thus produced, pressure elements or pads in the form of casing presses 3 are inserted. These casing presses may be made from a tube of steel sheet metal of about 0.5 mm. thickness which has been pressed flat, or also from one or two correspondingly thick small sheet metal strips which are welded together at the longitudinal edges or brazed, or otherwise connected. These casing presses extend over the entire width of the roadway cover. At one end of the casing presses a small tube is provided to which an injection nozzle can be connected. The other end may be provided with an air escape tube, but it may also be closed.

After placing the casing presses 3 into the grooves or slots 2 that extend transversely of the runway a pressure agent, for example water or an emulsion of oil and water, is forced into the interior of the press under high pressure. Since the hollow space to be filled is only small and the quantity of the pressure agent is small, it is possible to obtain the required high pressure in a very simple manner. As the pressure agent is forced in, first the outer surface of the casing press is forced against the walls of the slot while the outer surface adjusts itself plasti-' cally to minor defects in surface flatness. Then the splitting forces S which act vertically on the slot 2 produce a widening of the slot that reliably leads to the development of a split 4 below the groove or slot. The widening of the slot and consequently also the width of the crack or split corresponds to the elastic compression of the concrete between two successive splits and to the elastic expansion of the steel inserts 5 by the width of the split. This elastic deforming recedes after the pressure has been released, so that the slot is filled by the pressure pad which remains therein in a manner that in a sense it is resiliently filled. The slot and the split 4 that begins at the lower edge thereof are thus simultaneously protected against the penetration of dust, moisture or the like.

In order to further improve the sealing of the slot it is possible to coat the outer surface of the casing press prior to installation with a binding agent, for example bitumen. This results, within limits, in elastic adhesion of the outer surface of the pressure pads with the walls of the slot, which may yield to the changes in form of the runway cover that are caused by changes in temperature. Furthermore, the casing presses are protected against rust.

The casing presses used in accordance with the invention for producing artificial slits in the concrete parts as described in the example explained above must not be laid in the slots produced subsequently in the concrete, but they can already be laid into the concrete from the start as it is poured into the frame. In this connection it is only necessary to ascertain that the plane of the pressure pads is always exactly in the plane of the slits or gaps to be produced.

In this manner it is then possible to produce any desired reinforced concrete elements or structures in accordance with the method of the invention. This not only includes the runway covers or slabs described above but, for example, also pure tension members, supports in the form of walls, structural components which are connected to tension members, and the like.

Having now described our invention with reference to the embodiments illustrated in the accompanying drawings, what we desire to protect by Letters Patent of the United States is set forth in the following claims.

We claim: I

1. Method of producing a plurality of spaced cracks in reinforcedconcrete structures or structural com nents sub'ect to tensile stress, said cracks extending paralle to one ano er in a direction perpendicular to the carrying direction of the structure at predetermined distances from one another, said method including the steps of providing slots at predetermined locations, placing pressure pads into said slots and pressing apart the concrete by pressure forces applied by said pads against the walls of said slots in the plane of the splits to be produced and effective perpendicularly to said plane.

2. Method in accordance with claim 1 comprising the steps of placing small pressure pads in the plane of the splits to be produced over a part only of the thickness of the structure and charging said pads with a hydraulic pressure agent in order to produce splitting forces.

3. Method in accordance with claim 2, including the step of producing said slots in the surface of the structures or components after the concrete has been poured and placing the pressure pads therein.

4. Method in accordance with claim 2, where said pressure pads are in the form of elongated casing presses of sheet steel metal.

5. Method in accordance with claim 4, where said casing presses are coated with bitumen prior to being placed.

Claims

2. Method in accordance with claim 1 comprising the steps of placing small pressure pads in the plane of the splits to be produced over a part only of the thickness of the structure and charging said pads with a hydraulic pressure agent in order to produce splitting forces.
3. Method in accordance with claim 2, including the step of producing said slots in the surface of the structures or components after the concrete has been poured and placing the pressure pads therein.
4. Method in accordance with claim 2, where said pressure pads are in the form of elongated casing presses of sheet steel metal.
5. Method in accordance with claim 4, where said casing presses are coated with bitumen prior to being placed.