Hanging belt carrier
The suspension belt carrier , also shortened belt carrier or Möller carrier , is a design principle that was developed from 1895 by the civil engineer Max Möller and a patent has been applied for. It is one of the earliest attempts to produce composite structures from concrete and metal . Bridges constructed according to this principle at various locations in Germany are known to this day as Möller bridges .
history
From 1895 Möller began empirical studies on the bond between iron and concrete. In addition to the series of experiments on cement ground anchors, he also began with experiments to create a ceiling construction , the belt girder ceiling. The development arose from the desire to combine the advantages of both materials. While concrete can withstand large compressive forces acting on the top of a girder , iron or the mild steel used is well suited to absorbing the tensile forces on the underside of the girder. The development took place primarily on the premises of the Drenckhahn & Sudhop construction company in Braunschweig at their expense. In return, the bridges were later primarily built by this company (all the way into Saarland) and its construction principle was protected by a patent. In Thuringia and Saxony, the Leipzig cement construction company Rudolf Wolle took over the construction of suspension girder bridges under license , and the Actien-Gesellschaft für Beton- und Monierbau also showed interest in it.
By 1920 over 500 bridges were built in Central Europe according to this system, but only a few of them have survived. Möller's idea was overtaken by the invention of reinforcement , which is widely used today. The bridge over the Uhlenbach near Silberhütte was only replaced by a new building a few years ago, after the railing had been renewed shortly before. The dilapidated Möller Bridge in Bernburg-Baalberge is also to be demolished. A few bridges were placed under monument protection due to their once innovative design , such as the Möller Bridge in Kämkerhorst near Calvörde ( Saxony-Anhalt ) and the Seffersbach Bridge , the last remaining suspension strap bridge in Saarland.
In the course of the necessary renovation of the two Möller bridges over the Pleißemühlgraben in Leipzig, a concept for the renovation and strengthening of the load-bearing capacity with the help of CFRP lamellas was developed by the Leipzig University in 2003 .
construction
Möller developed a T- beam construction, which consisted of concrete girders in combination with tension straps made of flat iron on the fish-belly-shaped or parabolic- shaped underside. They were anchored with steel brackets in the concrete and then plastered over - they were not in the sense of a reinforcement in the concrete. Several beams of this type were connected to the deck slab to form a T-beam. The connection of the individual straps was made using riveted angle irons ( chisels ). The transmission of the tensile forces into the camp took place in a similar way. The actual load-bearing capacity of the structure was difficult to calculate and had to be determined empirically . The suspension belt supports were inexpensive and quick to install, the pull bars were guaranteed to be in the right position and the formwork work was comparatively easy. The older buildings were still lacking transverse reinforcement, while those built later were mostly made of smaller rolled sections.
The suspension belt girders were the most economical variant for single span girder bridges with 5 to 20 m span. The 11 m long and 13 m wide bridge over the Pleißemühlgraben was completed within two days, and at 80,000 marks it was cheaper than the iron construction variants, which cost 100,000 marks each. The hanging belt girders were not only used for all types of bridges, but also as hanging belt girder ceilings for multi-storey residential and industrial buildings.
Since the sling girders only exerted vertical pressure and so did not load the abutments with sideshift, they could be dimensioned rather weakly, and the existing bank walls were often sufficient. A maximum of 1/20 of the span was necessary for the construction height. Möller was clearly wrong about the durability of his bridges. The construction of the carrier belts does not provide sufficient protection against corrosion, as Möller assumed. Despite a scientifically proven redevelopment concept, however, in many cases no redevelopment is carried out, since the municipalities' own financial contribution is lower in the case of demolition and new construction.
The sidewalks were mostly made of precast concrete or simply concreted, and the roadways were often paved with pavement . Occasionally, as with the Magdeburg Reyher Bridge , the curbs were edged with cast iron fittings. The bridge railings were made according to the client's wishes, the construction company Drenckhahn & Sudhop offered various options , from the simplest variant made up of commercially available gas pipes for 500 marks to cast parapet elements to the elaborate wrought iron version for 2,500 marks. The bridges usually got by without any major decorations, but individual bridges (e.g. the Reyher Bridge) were also decorated with ornaments.
Construction description
Möller described his construction in the journal for construction as follows:
- “The endeavor to compress all the iron of the supporting structure into a single lower chord subject to tensile stress, prompted the choice of the one shown in Figs. 2 beam ceiling shown. The upper straps of a row of fish-belly girders form a single panel. In order to gain load-bearing capacity, the curved tension belts, which are made of flat iron, are allowed to sag down as far as the local conditions allow. The space between the flat iron and the slab of each ceiling serving as pressure chord is to be filled with concrete for spans of up to 16 m, for bridges with larger spans with latticework. As the wall of a fish-belly girder, this web only absorbs relatively small forces. If the load is evenly distributed, the web only serves as a filling and to transfer the vertical pressure.
- In the case of one-sided loading, the inclined compressive forces D occur. The transverse angles are only used for constructions of more than 5 in span. Mr. Koenen, Director of the Actien-Gesellschaft für Beton und Monier-Bauten, has suggested that vertical tie rods Z (cf.Text-Fig. 2) be attached to the angle W for larger designs , which are fastened to the concrete ceiling with cotter pins S. are. It should be added here, however, that even if the above small transverse angles W are completely absent and if, furthermore, the adhesion between concrete and iron should be disturbed, the carrier is not yet likely to be destroyed. Then the horizontal thrust of the diagonal force D is passed over to the anchoring present on the support through the compressive forces d . The belt irons are anchored in their stalls in the upper solid ceiling by transverse angles in such a way that they transfer their tensile stress there to the panel forming the pressure belt. With regard to the level of safety achieved, this has gone too far so far by not taking into account the adhesion of the cushion to the concrete in the calculation.
- Advantages of the belt girder blankets: The amount of iron required is limited to a minimum. When the heat exchange occurs, the belt girder ceiling only shows as much length movement as corresponds to a change in shape of the solid ceiling. When the heat rises, the Bisen does not exert any thrust against the surrounding walls, it bends a little downwards for me. In the event of a fire, the iron stays cool for a long time, as it rests on one side of the massive concrete bridge and is plastered from below using a wire mesh covering. The beams lie in the same plane that is used for the cross beams; This saves on construction height (Fig. 1). The cross beams are also embedded in concrete and thus protected from attack by the flames. Since the webs are made of concrete, I-beams of larger dimensions can be conveniently installed across the chords in order to distribute individual loads over several chords. The ease of production required that the straps G1 and G2 (see the plan Fig. 4) were laid separately on the beam. They are united by wrapping two transverse angles of the two belts five to ten times by means of 4 to 5 mm thick wire (cf. the ring R thus formed ). Like any solid ceiling, these concrete ceilings are also completely safe against the penetration of fire and smoke from top to bottom and also relatively safe against fire acting from bottom to top. "
Stress tests
Möller always carried out test loads before each bridge inspection. The bridges were loaded up to the intended load-bearing capacity, sometimes beyond, mostly using steam rollers to apply the load. Unusual at the time, it also carried out extensive experiments to improve and test its design. In the absence of government support, he worked closely with the Drenckhahn & Sudhop construction companies in Braunschweig and the Rud cement construction business. Wool together in Leipzig.
In a handover protocol from the ducal district director of Ballenstedt , it said:
“After a thorough inspection of the bridge on the spot, a 20,000 kg steam road roller owned by the machine manufacturer Friedrich Dehne zu Halberstadt was led over the bridge. The fluctuation that appears with this load, respectively. The deflection of the bridge was controlled as described in the annex. The route of the steam road roller over the bridge was carried out in two ways, first of all in such a way that the roller was guided at a slow pace to the middle of the bridge and stopped at various points on the bridge for a long time. Then the roller drove over the bridge with the greatest possible speed over and over again. The result of the deflection of the bridge was that a deflection on the device attached under the bridge was not at all visible to the eye of the beholder. The device was approximately 0.4 millimeters. The endurance test exceeded all expectations ... "
From the test loading of the Reyher Bridge in Magdeburg carried out in 1900, it has been handed down that it was not completely uncomplicated. On the day before the test, a 40 cm thick layer of gravel had been applied to the road . The gravel layer on the sidewalks was 32 cm thick. It rained heavily during the night, so that the load from gravel and rainwater was already around 1.8 t . The bridge was only calculated for 500 or 400 kg / m², including the steam roller, however, resulting in a load of 720 kg / m² for the roadway and 580 for the sidewalks. The bridge was inspected 24 hours after the load was applied.
The construction only showed small cracks on the supports, which were to be expected with the high load and which almost completely closed again after the load was removed. The deflection of the bridge proved to be elastic enough and the bridge had passed the load test despite being overloaded. However, the bridge collapsed during the renovation in 1994, subsequently it was rebuilt in a modern design, but with a replica of the original shape.
literature
- Max Möller: Belt girder ceilings, Möller system. In: Zeitschrift für Bauwesen , Volume 47, 1897, Issue I – III ( digitized version), Columns 143–148.
Web links
- Möllerträger at LKG - engineering office for construction technology
- Möller bridges in Saxony-Anhalt
Individual evidence
- ↑ a b Strengthening for the Pleiße bridges. The renovation of Möllerträger ( Memento of the original from February 15, 2005 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ^ Carl Kersten: Bridges in reinforced concrete. Plate and girder bridges . 6. rework. Edition. Ernst & Son, Berlin 1928.
- ↑ The majority votes for a new bridge
