Concrete Hinge

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  • Steffen Marx, Gregor Schacht 3rd fib International Congress - 2010

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    CONCRETE HINGES HISTORICAL DEVELOPMENT AND CONTEMPORARY USE

    Steffen Marx, Prof. Dr.-Ing., Inst. of Concrete Structures, Techn. Univ. Dresden, Germany Gregor Schacht, Dipl.-Ing., Inst. of Concrete Structures, Techn. Univ. Dresden, Germany

    ABSTRACT

    Articulated connections consisting of concrete have existed since 1880, when Claus Kpcke first used saddle bearings in a natural stone-arched bridge. Further developments were made in France at the beginning of the 20th century. While Mesnager used reinforcement to carry the loads of his Mesnager hinges, Freyssinet developed an unreinforced hinge that transmits loads only through the concrete. All hinges work on the same principle the centering of compression stresses in a very small zone (the throat of the hinge). Concrete hinges have also been used in Germany, in the USA and, particularly, in Switzerland. In the 1960s, the work of Fritz Leonhardt (Germany), E.O. Fessler (Switzerland) and G.D. Base (Great-Britain), which define the international state-of-the-art until today, led to a renaissance of concrete hinges. The existing design rules are half-empirical and disallow the proper construction of concrete hinges up to the state-of-the-art. Investigations of the existing experiences and design rules were carried out. The design rules given by Leonhardt have been assigned to allow an appropriate design of unreinforced Freyssinet hinges which conform to current code.

    Keywords: concrete hinge, Freyssinet hinge, tri-axial compression stress state, Mesnager hinge, saddle bearing,

    INTRODUCTION

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    Concrete hinges are characterized by an enormous load-bearing capacity and deformability. They are nearly maintenance-free and have a high durability if designed and constructed properly. Concrete hinges are perfectly suited to control the flow of forces and to efficiently reduce constraints. The first massive hinges were developed by Claus Kpcke (Dresden) in 18801 and successfully used in several construction projects. The fabrication of these hinges was difficult since the contact-surfaces had to be extremely level. In an effort to correct this problem, von Leibbrand (Stuttgart) developed an alternative type of hinge by arranging thin plumb-plates between the adjacent concrete blocks2. The break-through in the development of durable and easily casted hinges was first accomplished by Augustin Mesnager in 19083. Inspired by his research on confined concrete columns, he developed a spring-hinge (semi-articulation), which was similarly used in steel construction. Adjacent concrete blocks are connected by intersecting steel bars. These steel bars transmit the entire force of the hinge-bodies. The concrete only serves to provide corrosion protection and together with the confining reinforcement to avoid the buckling of the steel bars. In 1910, Freyssinet was able to prove that reinforcement through the throat is unnecessary, and axial forces are only transmitted by the partially loaded area and an adequate confinement of the hinge4. The rotation of the hinge is secured by the elastic and plastic deformability of the concrete and with larger rotations a crack through the throat of the hinge occurs. In Germany these unreinforced concrete hinges are closely associated with Fritz Leonhardt who developed the commonly used design rules for this type of concrete hinge5. In the course of recent research, various existing design-models for unreinforced concrete hinges were analyzed and compared6. Figure 1 shows a classification of the different types of hinges.

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    Fig. 1: Classification of concrete hinges

    SADDLE BEARINGS SADDLE BEARINGS, HINGE-BODIES AND THEIR LOAD BEARING BEHAVIOUR Saddle bearings are two adjacent cubes of stone, comprised of either concrete or reinforced concrete with cylindrical surfaces that allow a rolling motion. In 1880, Kpcke first used these hinges for an arched stonebridge for the Pirna-Berggiehbler Eisenbahn near Langenhennersdorf (Germany) to avoid cracking during settling while stripping away the structures formwork1. The hinges were filled with concrete after removal of the formwork. The positive results from the use of these simple hinges led to a large number of saddle bearing hinges in practice. A considerable basis for the use of these hinges was increased knowledge in the material strength of partially loaded areas. By 1869, 12 years before Hertz published his Hertzian stress equations, Kpcke presented an initial theoretical solution to describe the contact between two cylinders7. The first experimental investigations on these saddle bearings were done by Krger in 1894 for the construction of the Marien Bridge in Dresden (Germany)8. Krger detected that the biggest tensile strains and stresses appeared in the middle of the hinge-bodies. These tensile stresses were distributed parabolically and the transverse tensile force was about 28% of the surcharge. The experiments of Bach with sandstone- and granite-hinges showed that the failure of the hinges was always caused by tensile stresses rectangular to the pressure. All hinge specimens failed with a big crack in the middle of the hinge-bodies. The detection of the actual cause of failure led to the use of reinforced concrete saddle

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    bearings (Friedrich-August-Bridge in Dresden, bridge in Rothenburg, Emsbridge Rheda all Germany) (Fig. 2).

    Fig. 2: Reinforced saddle bearings9

    In 1924, Mrsch developed the first theoretical solution for hinge-bodies10. He used the conditions of distortion as a simple mechanical model to deduce the orthogonal tensile stresses and simplified the representation of these stress fields into a strut-and-tie-model that allowed the determination of the size of the tensile force depending on the surcharge (Fig. 3).

    Fig. 3: Strut-and-tie-model of Mrsch10

    Almost half a century after Kpcke first successfully used his saddle bearings, Bortsch published his solution to calculating the stresses in hinge-bodies11. For a cut out slice of a hinge-body Bortsch used an approximation of a cosine function for the load and applied it to a

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    cross-section of a hinge-body before breaking down the cosine function into three separate components and solving the Airy stress function. He subsequently superposed the three resulting ratios and provided a solution for different geometric variations of the hinge-bodies. These theoretical solutions provided a means by which to calculate the stresses within these hinge-bodies. SPECIAL SADDLE BEARINGS The primary problem with using saddle bearings was the difficulty of creating accurate convex and concave surfaces. The smallest amount of unevenness from processing led to large stress-concentrations. Hence von Leibbrand (Stuttgart) developed a different type of hinged connection by placing small plumb-plates between the cubes allowing rotation from plumb deformation2. These plates also provided an equalizing layer between the cube surfaces. Plumb hinges have been used successfully for a long time. Even so, in the 1960s, engineers stopped using them since they had discovered that the plumb plates were worn down after numerous rotations even if the angles of rotation were small12. In 1933, Burkhardt presented a new development, concrete saddle bearings armored with steel plates13. It was thought that these would abolish the disadvantage of the uneven concrete surfaces. The first bridge with these hinges was built over the shipping channel near Oberelingen (Germany). Experimental investigations at the MPA Stuttgart (Testing Laboratories Stuttgart) proved the enhanced bearing capacity of the armored saddle bearings.

    DEFORMATION HINGES SPRING HINGES ACCORDING TO MESNAGER AND CONSIDRE At the beginning of the 20th century, French engineers intensively researched the new material, reinforced concrete. At the cole des Ponts et Chausses Augustin Mesnager and Armand Considre carried out investigations on confined concrete columns. Based on these experiments, Mesnager developed a semi-articulation for reinforced concrete similar to the spring hinges used in steel construction. In 1908, Mesnager described experimental investigations he had made that proved his theoretical ideas3 (Fig. 4).

    Fig. 4: Specimen of Mesnagers experimental investigations3

    The concrete in the throat of the hinge was only used for corrosion protection of the intersecting steel bars. In experiments, the failure of the hinges always occurred through concrete spalling at the hinge blocks near the throat followed by buckling or slipping of the steel bars. The intersecting bars must be rigidly confined, as close as possible to the throat of the hinge, to avoid this failure. Mesnagers hinges have been used successfully in many projects such as the arching of the channel Saint-Martin in Paris, the Amlie-les-Bains Bridge

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    (Fig. 5), the Carnon Bridge over the Canal du Midi in Montpellier, a suspended deck arch bridge in Mestre (Italy), the Pont sur la Noce and several airship hangars that were constructed as three-hinged arches.

    Fig. 5: Three-hinged arch-bridge Amlie-les-Bains6

    The Swiss engineer, Robert Maillart, is particularly known for his use of Mesnager hinges. For instance, he used these hinges in: his famous bridge over the Salginatobel (Fig. 6), the Rossgraben Bridge, the T