loading tests of existing concrete structures ...

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LOADING TESTS OF EXISTING CONCRETE STRUCTURES – HISTORICAL DEVELOPMENT AND PRESENT PRACTISE

Guido Bolle

Gregor Schacht

Steffen Marx

Abstract This paper gives an overview over the historical development of loading tests and describes the actual practise in Germany. The use of loading tests to prove the bearing capacity of structures is as old as the humankind and plays an important role in the historical development of reinforced concrete constructions. Loading tests proofed the bearing strength obviously for everybody and therefore they were likely used to convince the people of the bearing capability of floor slabs or bridges. With the development of static calculations and of acceptable design rules, load testing became unnecessary for new structures and by the mid 1960s it was deleted in almost all European codes. In the last decade of the 20th century the method of test loading was upgraded through big research projects and since 2000 a guideline for the execution and assessment of loading tests exists in Germany. Today there is a big amount of existing structures, which need to be evaluated in terms of their bearing capacity for future utilization. But the existing design codes and the lack of as-built information often don’t allow an appropriate analysis of the present bearing strength. With the help of loading tests, hidden bearing reserves can be detected and the structure can be preserved from demolition. Keywords:

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loading test, structural assessment, maintenance, existing structures

Introduction

Since prehistoric times people are striving to achieve the largest possible range of safety in all areas of their lives. For the construction industry this is important in a very special way, because the failure of structures is much less accepted in society, as for example the failure of motor vehicles or electronic devices. We especially feel a sense of security if we really „know” or „see” that structural components can withstand the appropriate loads. Civil engineering has its origin in the handcraft and especially in this, experiences, which have been gained by trial and error, were very important. This testing is therefore not only the literal, but also the historical origin of loading tests, and the first test, if something withstands a certain stress, like e.g. the test of the tensile strength of a liana or the bearing strength of a fallen log, already lays back some million years. Loading tests are thus as old as the humankind itself. They convinced the people that a construction is suitable for a certain load and established trust in cases of doubt. 1

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This confidence in the bearing capacity is the goal of all loading tests, which apparently prove the safety of a structure, visible for everybody. Particularly new construction methods or novel structural elements had and have to “earn” this confidence, first by passing a loading test. Especially, reinforced concrete could prevail in its early years only because its performance has been proven effective by a multitude of load tests to a wide public. Therefore loading tests have been the ultimate proof of a sufficient bearing capacity of components and structures till the 19th and 20th century.

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Loading tests of Bridges as proof of bearing capacity

Loading tests of bridges as part of the commissioning of a new bridge have a long tradition. This is on the one hand substantiated on the already described special character of a loading test to prove a sufficient load bearing capacity visibly even to laymen. On the other hand it was essential to compensate the deficits of the not fully developed calculation methods and to answer all open questions at the finished structure. Also material defects could often only be detected during the loading test. Commonly enormous efforts were accepted to perform a loading test. For example, at the loading test of the second Reichsbrücke in Vienna, which was undertaken from 1st to 3rd October 1937, altogether 84 trucks and 28 with stones loaded tramcars were deployed (Fig. 1). The test did not turn up any problems. As known, the bridge nevertheless collapsed in 1976 caused by the degradation of the column base. Usually the loading test was made during the opening ceremony and the public was included into the procedure of the testing to increase their confidence in the safety of the structure.

Fig. 1 Loading test of the second Reichsbrücke in Vienna in 1937, Picture: Austrian National Archive

To produce the partial considerably loads, always ballast masses were used and directly placed on the structures. Therefore, depending on the location and function of the bridge and the availability of the materials, different variations were chosen. For the loading test of the road bridge over the Thur near Oberbüren (Switzerland) in 1886 the water of the river was pumped up with firefightining, motor pumps into tanks, which were placed on the bridge [1]. For railway bridges, like the bridge near Tübingen (Fig. 2), the loading was realised with locomotives and heavily loaded freight cars. For the loading of the road bridge near Walsburg in 1895, sandbags were used to simulate the uniformly distributed loads and additionally two four-in-hands with a load of 5.3 t passed the bridge [2]. Often steamroller were used. Von Emperger reports in [3] of a loading test of

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a pedestrian bridge in Rotterdamm in 1901, for which trucks were hung up to the structure with chains and were loaded with sand from the street below. Figure 3 exemplarily shows the loading test of a road bridge (Altstädter bridge in Pforzheim [4]). It can be seen from the picture, that the full loading of the middle field is done with two steamrollers and six heavy trucks. To simulate the load by human crowd, steel rods were put on footpaths. As the essential reaction of the structure under load normally only the deflections were measured. If these were small enough or close to the calculated deflections, the proof of a sufficient load bearing capacity has been provided.

Fig. 2 Loading test of the railway bridge near Tübingen, [4]

Fig. 3 Loading test for commissioning the Altstädter bridge in Pforzheim, [4]

Otherwise the recognition of a loading test, because of small deflections, did not guarantee a permanent secure operation of the bridge. The steel-framework bridge over the Morawa near Ljubitschewo (Serbia) already showed some construction and material deficits before completion. The loading test was executed at the most carefully engineered opening of the bridge on September, 21st and 22nd 1892. Gravel from the river bed of the Morawa was used as ballast load. At the second day of testing the bridge suddenly collapsed caused by a buckling of the underdimensioned upper chord (Fig. 5). At that time the deflections were within the normal range and gave no sign of reaching a critical structure condition [5]. The road bridge near Salez (Kanton St. Gallen, Switzerland) collapsed during a loading test in 1884 at a measured elastic deformation of 10 mm, also caused by buckling of the upper chords because of a missing bracing and a poor construction of the junction plates. The bridge abruptly collapsed, even though the as acceptable declared maximum deflection was 17.5 mm [6].

Fig. 4 Collapsed road bridge over the Morawa near Ljubitschewo (Serbia), [5]

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A similarly sudden failure occurred at loading tests of suspension bridges. Thus, problems with the quality of the wire cables caused the collapse of the bridge in Maurin (France). The corroded cables had only partly been renewed and at the loading test for recommissioning, the bridge broke down [7]. Also the suspension bridge at Tonnay-Charente (France) was to be repaired, but at the loading test, which should determine the present load bearing capacity, the bridge collapsed [8]. Sometimes these collapses during a loading test were caused by imprudence or gross negligence. Thus, the Rhône bridge near Peney (Switzerland) with a span of 100 m passed the loading test with sandbags without any problems. But at lunchtime heavy rain started and the sandbags absorbed the water till the load was too much for the bridge and the anchorages broke. Also the 1873 tested bridge over the Broye near Payerne passed the loading test successfully. But it collapsed, when the worker began throwing the used water tanks over the bridge without any care, only to be able to take part at opening party quickly and therefore damaged a main girder [9]. Because of some spectacular bridge collapses, like e.g. the collapse of the Münchensteiner bridge 1891 [10], the Suisse railway department prescribed regular inspections for all railway bridges [9]. Within these inspections simple loading test had to be carried out, where the loading corresponded to the load assumptions of the calculation. Therewith loading tests became a standard procedure with all consequences, whereby the results of the tests often have not even been analysed. The bridge proved it sufficient load bearing capacity, if it did not collapse and if simply checkable criteria were fulfilled. These limit criteria have been derived from over centuries gained experiences and personal feelings and affected mainly the serviceability of the construction, namely deflections or vibrations. The limited significance of these criteria for proof of load bearing capacity led to general discussion about the value of loading tests of steel bridges. Despite all critics Ritter concludes: “Loading tests must always be done, particularly to calm the laymen” [11]. Therefore loading tests of bridges remain as the standard way of commissioning bridges even through the 19th and 20th century. In some countries they are still today carried out regularly.

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The importance of loading tests for the development of reinforced concrete

In 1884 Conrad Freytag purchased the patents of Monier, one of founders of reinforced concrete, after he first got in contact with this new construction method in Trier, Germany. He bought the patent rights for South Germany and gave his pre-emption rights for Northern Germany to G. A. Wayss. The business-minded Wayss went to Berlin, contacted Mathias Koenen (chief officer of Prussian Building Authority) and with very promising preliminary tests he gained his interest in this new construction method. Now it was the task to also convince building owners, the authorities and the public of the advantages of reinforced concrete as a construction material. Therefore Wayss invested a lot of money to manufacture test specimen to show the economic worth of the new construction method based on loading tests. The tests in February 1886 were successful and the results convinced even the greatest sceptics. Yet in the fall of 1886 Koenen published his calculation method, which he had derived directly from the test results and which showed sufficient agreements with these results [12]. However, the massive use of reinforced concrete did still not arrive. The strict patent regulations and the little knowledge of the calculation restricted the application. Next to the system of Monier, the monolithic system of Hennebique and many other individual developments were used. Because of the great amount of different construction types, all reinforced concrete structures were proven by loading tests. For special structures the loading test was mandatory by the authorities as a part of the commissioning. The execution of the testing was made according to the demands of the authority. The building contractors were satisfied with the acceptance of a special construction and were not interested in the development of general ideas of the load bearing behaviour out of the test results. For proving mass production elements often also tests to

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destruction were carried out to determine a factor of safety compared to the calculated load capacity. Figures 5 shows as one example of the wide diversity of testing the ultimate test of so called Visintini-girders [13], which are prefabricated reinforced concrete girders for ceiling constructions and for which the advantages of steel framework girders were transferred to the reinforced concrete.

Fig. 5 Loading test of Visintini-beams, [13]

A remarkable technical development shows Figure 6. The engineer G. Hill developed a hydraulic testing machine for destructive testing of structural elements. The hydraulic loading ensured on the one hand the exact load and on the other hand made it possible to test many specimens in a short time. Also the exact loading and deformation was directly measured by the machine. But the special advantage of the hydraulic loading for the prevention of a collapse has not yet been recognised.

Fig. 6 Hydraulic testing machine of Hill, [14]

Normally the load was applied on the structure using ballast masses, mostly sandbags or railway rails. Despite the known poor significance of deflection measurements at steel bridges, the loading tests of reinforced concrete structures were assessed with the help of the same deflection measurements. Thus, the loading test of three concrete bridges system Hennebique in 1898 were assessed positively because the steamroller with a load of 18.1 t only cause elastic deflections of 1.2 mm and no plastic deformations at all [15]. While the above describe method of load testing was only used to prove a sufficient load bearing capacity of individual components or structures, in Stuttgart was worked on systematic testing to make reinforced concrete predictable. Emil Mörsch became the chief of the technical

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office of Wayss & Freytag AG in 1901 and was assigned to develop a scientific basis for the calculation of reinforced concrete structures. Also for him loading tests were the precondition for the development of theoretical basics and calculation models. The activities of Mörsch and several other scientists demonstrate the important role of loading test for the development of models about the load bearing behaviour of reinforced concrete. For a more detailed research of shell structures the company Dyckerhoff & Widmann AG constructed the shell shown in Figure 7 in 1931. The still today existing shell was also load tested to study the load bearing capacity. After the successful loading with sandbags, 50 employees were assembled on the only 1.5 cm thick shell. The shell structures stayed without any cracks during all tests. This loading test and the proof of the enormous load bearing capacity led to the construction of many reinforced concrete shell structures [16], [17].

Fig. 7 Test shell with uniform loading (left) and human crowd (right), [14]

But there have also been a lot of problems and inadequacies in the execution of loading tests. The patent claims of reinforced concrete systems, like the one of Monier or Hennebique, caused that every construction company developed own reinforced concrete constructions at the turn of the century. To convince the public of the safety and an adequate load bearing strength of their constructions, they used loading tests and the results for advertising purposes. But at that time there were no regulations on how the loading tests have to be done or who is allowed to carry out those tests. Every layman could do loading tests and sell his product as a safe construction. Answering a warning on these inadequate loading tests and the wrongly praised safety in 1895 [18] von Brestovsky first described important requirements of the loading apparatus. At that time von Bresztovsky is a trainee of Prof. Föppl in Munich and took part in the load testing of slabs and vaults, which were tested under uniformly distributed loads. The loading was applied with a loading frame, which was developed by Bauschinger and which ensured, by a statically determined construction with wooden beams, that the loading equipment did not take part in the load bearing (Figure 8). Therewith already 1895 the necessary and functional arrangement of the loading elements is known, but was not respected in many in-situ loading tests.

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Fig. 8 Loading system of Föppl, after [19]

An example of a wrong loading test is described in [20], a test of Monier-slabs reinforced on both sides in Vienna 1905 (Figure 9). The loading with railway rails was then an usual way, but is the loading itself not movable and therefore the rails are supporting each other while the deflection of the slab increases and so the load is carried over an arch directly to the supports. Figure 10 also shows a faulty loading test, where the sandbags act like an additional enlargement of the crosssection and a big part of the load is not carried by the beam but taken down to the support by arching action [21].

Fig. 9 Loading test of Monier-slabs with railway rails, [20]

Despite the many experiences with loading tests, there have always been collapses. In 1908 the collapse of a warehouse during the loading test in Milan (Italy) is reported in [22]. While the lower floors passed the loading tests, the floor in the roof was only 14 days old and did not withstand the loading with sandbags. The collapsing of the upper floor also caused the breaking down of all lower levels until only a skeleton of columns and girders remained. This collapse caused 13 deaths and 12 heavily injured worker.

Fig. 10 Faulty loading tests with insufficient movable loading, [21]

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Such collapses during loading tests have been quite normal in the beginning of the construction with reinforced concrete. The considerable consequences provide evidence of the risk using ballast masses without any falling protection and also show that loading tests then have been carried out with less care and ignorance.

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Development of Guidelines and Standards

The planning and execution of these loading tests has often been done at one’s own discretion without any acknowledged rules of technology, often with the goal to prove a load bearing capacity as high as possible. Because of that or also caused by lack of knowledge many loading tests were not carried out properly, what sometimes even caused the collapse of the total structure. As a result many experts discussed the sense of loading tests already at the turn of century ([18], [23], [24], [25], [26]). However, they all agreed, that the planning and the execution of loading tests require a standardised regulation. One of the greatest critics was Robertson, the chief of the technical office of the Egyptian Railway. He reports in 1897 [26] about his bad experiences with the loading test of the Nil bridge of Embabek. Even though the loading test was passed without any problems, the web plate of one of the main steel girder cracked only a couple months later. After repairing this girder another loading test was executed. The bridge passed again, but some months later the web plate cracked again. Robertson concluded rigorously that “loading tests are not only useless, but even harmful, because they suggest a wrong safety.” First efforts for standardised regulations for loading tests of concrete structures were given by the “Vorläufige Leitsätze zur Vorbereitung, Ausführung und Prüfung von Eisenbetonbauten” in 1904 [27]. These advices were still very general. They recommended that loading tests should only be executed in cases with doubts in the load bearing capacity or a correct execution of the work. Also, the structure to be loaded should at least have been 45 days old and an upper load limit was defined. The structure was accounted as safe, if “significant residual deformations have not arised”. More detailed regulations are first given by the “Bestimmungen für Ausführung von Bauwerken aus Eisenbeton” of the DAfEB in 1916 [28], which remained only with little changes in the standards for many years. These guidelines now required that the loading equipment must be movable itself, so that an overestimation of the load bearing capacity due to an arching action is excluded. The maximum load had to be left on the structure for at least 12 hours. The main measurand was the deflection of the structure. The test was passed, if the residual deflection after unloading remained smaller than ¼ of the maximum measured deflection. These basic regulations of the application of loading tests, the requirements of the loading arrangement, of the limit and duration of the load and of the assessment of the maximum and residual deflection could also be found in the other foreign standards in that time. But in the different standards the limit of the load was different and varied between 1.0 times the service load (Austria, Netherlands, France, Belgium) and 1.5 times the service load (Germany, Denmark, Sweden, Norway) [29]. A continuing point of criticism was the simple assessment criteria of the ratio value of the residual to the maximum deflection, which was given in all standards. The limiting value was given to ¼ (Germany, Austria, Norway, Poland) or to 1/3 (Hungary, Czechoslovakia, Russia). In some standards an additional condition was given with the ratio of the maximum measured to the maximum calculated deflection – tacitly assuming that the deflection of reinforced concrete members can be calculated precisely. Permitted was an exceedance of the calculated deflection of 0% (Italy), 20% (Sweden, Poland) or 25% (Czechoslovakia, Norway) [29]. The ratio of the residual to the maximum measured deflection was examined more precisely by Graf and Bach in 1914 [30]. They showed with numerous test results, that the ratio of the deflections extremly depends on the loading history of a construction. They also showed that beams with and without an appropriate shear reinforcement have similar deflections under the permitted loads. They concluded therefore, that “the passing of a loading test because of not

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exceeding a deflection limit, which would have been defined appropriate, in general doesn’t ensure a total robustness of a construction.” Despite all critics the determination of the ratio of residual to maximum deflection remained the only criterion for the assessment of a loading test for many years. To compensate the influence of a previous loading, some foreign standards allowed to repeat a failed loading test ones (provided that the construction did not collapse). Then the same (Great-Britain, USA) or a little more restrict demands (France, Austria) had to be used to assess the deflection ratio. These additional demands have never been taken over into the German standards. In the 1970s a strong development of the calculation methods began, which was particularly based on the increased use of computer technologies. Therewith it was possible to provide the proof of a sufficient load bearing capacity only by calculation. At the same time reinforced concrete has become an approved construction method and so the trust of the public existed, without having to prove it for every single structure. Therefore loading tests as the ultimate proof of load bearing capacity became unnecessary. This has to been seen positive, because this led to reduced efforts accompanied with a higher safety, because the always existing risk of a collapse during a loading test was omitted. In a nutshell, the trust of professionals and laymen prevailed, that the load bearing capacity of structural elements can be calculated with sufficient accuracy. As a result of this development and the shown discussion about the use of loading tests at all, no regulations about loading tests are given anymore since DIN 1045:1972 [31]. The calculation is for new structures usually the right and more sufficient approach. The more engineers had to deal with existing buildings and especially existing concrete structures, it became clear, that it was necessary to re-establish the method of loading tests for the assessment in the standards. But it was also clear, that this tool had to be brought up to the state of the art technically as well as theoretically.

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Theoretical and practical further development in the recent past

In Germany the necessary development took place almost simultaneously in both German states, but in different directions. In the former GDR Schmidt and Opitz [32] developed the theoretical basics for the planning and assessment of loading tests at the present level. For this purpose they developed a suitable safety concept based on the today, by default used partial safety factors, which ensures a similar safety level like the one used for computational analysis and which is also tailored to the specific constraints of loading tests. Furthermore they defined specific assessment criteria for the different expected failure modes, which allow an assessment of the load bearing condition during the test. All these guidelines were gathered in “TGL 33407/04 – Nachweis der Trag- und Nutzungsfähigkeit aufgrund experimenteller Erprobung“ [33], which allowed to execute loading tests again on a standardised base in the GDR since 1986. A considerable development of the testing technology was made in former West Germany under the supervision of Steffens [34]. He developed a mobile loading device of steel elements, which together with a hydraulic system made the use of ballast masses superfluous. Applying this loading device the produced test loads are anchored back close to the structure to be tested (Figure 11). The structure is therefore put under constraint, so that if a sufficient stiffness of the loading device and an adequate ductility of the structure are guaranteed, an automatic self securing effect is present. If the structure deforms, the hydraulic pressure is reduced and the overall system is transferred into a secure state of equilibrium. Therefore the collapse of a sufficient ductile construction can be precluded. The rapid development of the computer technology, practically combined with electrical measuring technology, allows the detection and analysis of the measured data online and thus a detailed assessment of the load bearing behaviour during the loading test.

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Fig. 11 Principle of load application with a loading framework

A considerable push was made, when both development directions were united with the Reunion of Germany. In a couple cooperative research programs the theoretical basics and functional loadingand measuring technologies have been developed and brought into practise. As a result of this development the Deutscher Ausschuss für Stahlbetonbau published the guideline “Belastungsversuche an Betonbauwerken” [35] in 2000. This guideline gives the base for the planning, the execution and the assessment of loading tests in Germany. Also should be noted, that in these research programs a mobile loading truck BELFA [36] was developed. This truck is equipped with a complete servo hydraulic system and was especially developed for loading tests of bridges with small and middle spans.

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Actual importance of loading tests and perspectives

Nowadays loading tests are used to determine the load bearing capacity especially of existing reinforced or prestressed concrete structures. Although sophisticated calculation methods are available, it is advised and useful if e.g. documents of the time of erection and therefore basic information for a realistic structural analysis are missing, or damages of the construction are present, whose influence on the load bearing capacity can’t be quantified. Also enhanced requirements due to a change of use are a common case for applying the method of load testing. Nevertheless a structural analysis play an important role for experimental investigations of the load bearing capacity, because a loading test should only be done if a preliminary calculation shows that a successful proof could be possible. For the execution of loading tests only the above described self secured loading device and online measuring and analysing technologies are used. Basis for the planning, execution and assessment is the already mentioned guideline of the DAfStb [35]. The criteria therein allow the determination of the load bearing capacity, without damaging the construction at all. In special cases, specific measuring technologies, like the acoustic emission analysis, is used to reliable determine a beginning cracking in the concrete. While Germany has had the “pole position” in loading tests in the last 20 years, other European countries (e.g. Netherlands, Luxembourg) endeavour to establish load testing as an accepted method for the determination of the load bearing capacity in special cases. The main focus for research and further development is today put on the examination of nonor low-ductile structures, which comprise a relative big amount of existing structures. Such constructions are currently excluded from loading tests because the existing assessment criteria aren’t yet sufficient to determine the ultimate load reliably and in time, so the examined construction is not damaged or even an abrupt collapse occurs. The authors are currently working in a research program “Zukunft Bau” on the development of sufficient criteria, so these constructions can be securely load tested. Because many old structures have no or not enough shear reinforcement to sufficiently withstand shear forces, these 10

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structures represent the main focus of the research. Therefore it is assumed that especially the combination of different measuring technologies, like the Photogrammetry and the acoustic emission analysis, more precise information about the actual structural condition can be obtained. In general loading tests today have the importance they deserve, namely as an accepted alternative method to prove the load bearing capacity of structures. Loading tests allow an economic and functional further use of existing and damaged concrete structures and helps to limit necessary renovation or strengthening to an extent required.

This outcome has been achieved with the financial support of the research project granted by the German Bundesamt für Bau- und Raumordnung, research programm “Zukunft Bau”. All support is gratefully acknowledged.

References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]

Bersinger: Die neue eiserne Straßenbrücke über die Thur bei Oberbüren, Canton St. Gallen, Schweizerische Bauzeitung, Vol. 8, Nr. 25, 18. Dezember 1886, S.147–150. Paul, W.: Straßenbrücke bei Walsburg a. d. Saale nach Monier-Bauweise und ihre Belastungsprobe, Centralblatt der Bauverwaltung (1895) S.32–33. von Emperger, F.: Handbuch für Eisenbeton, Band 3, Bauausführungen aus dem Ingenieurwesen, Berlin, Verlag von Wilhelm Ernst & Sohn (1908). Mörsch, E.: Der Eisenbetonbau – seine Theorie und Anwendung, 3. Auflage, Stuttgart, 1908. Tetmajer, L.: Ueber die Ursachen des Einsturzes der Morawa-Brücke bei Ljubitschewo, Schweizerische Bauzeitung, Vol. 21/22 (1893) S. 55–58. Zimmermann, H.: Einsturz einer Straßenbrücke bei Salez in der Schweiz, Centralblatt der Bauverwaltung (1884), S. 548–549. Zimmermann, H.: Ueber Unterhaltung und Dauer von Drahtseilhängebrücken, Centralblatt der Bauverwaltung (1881) S. 346–347. Sarrazin, O.: Brücken-Einsturz in Frankreich, Centralblatt der Bauverwaltung (1883) S. 308. Stamm: Brückeneinstürze und ihre Lehren, Mitteilungen aus dem Institut für Baustatik, ETH Zürich, Zürich, Verlag Leeman (1952). Waldner, A.: Das Eisenbahnunglück bei Mönchenstein, Schweizerische Bauzeitung, Vol.17, Nr. 25, 26 und Vol.18, Nr. 1, 2, 3 (1891). Ritter: Ueber den Werth der Belastungsproben eiserner Brücken, Schweizerische Bauzeitung, Vol. 20, Nr. 3, 16. Juli 1892, S.14–17. Koenen, M.: Für die Berechnung der Stärke von Monierschen Cementplatten, Centralblatt der Bauverwaltung, 20. November 1886, S. 462. G., O.: Weitere Versuche mit Gitterträger System Visintini, Beton und Eisen (1904) Heft 1, S. 42–44. von Emperger, F.: Handbuch für Eisenbeton, Band 1, Entwicklungsgeschichte und Theorie des Eisenbetons, Berlin, Verlag von Wilhelm Ernst & Sohn (1908). Waldner, A.: Probebelastung einer Cementbeton-Brücke, System Hennebique in Lausanne, Schweizerische Bauzeitung, Vol. 32, Nr. 4, 23. Juli 1898, S. 32. Stiller, M.: Entstehung und Rettung der Dischinger-Versuchsschale. In: Dischingerfestschrift (1987) S. 81–89. Petry, W.: Scheiben und Schalen im Eisenbetonbau; IABSE Congress Reports; Vol.1 (1932), S. 267–302. G.: Probebelastung von Decken und Gewölben, Centralblatt der Bauverwaltung, 7. August 1895, S. 339. von Bresztovszky: Antwort zu [18], Centralblatt der Bauverwaltung, 12. Oktober 1895, S. 433–434.

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[20] Sanders, L. A.: Belastungsproben mit doppelt armierten Monierplatten, Beton & Eisen (1902) 5. Heft, S.16–22. [21] von Emperger, F.: Die Durchbiegung und Einspannung von armierten Betonbalken und Platten, Beton & Eisen (1902) 4. Theil, S. 21–35. [22] B., G.: Einsturz eines Eisenbetongebäudes in Mailand, Schweizerische Bauzeitung, Vol. 51, Nr. 18, 2. Mai 1908, S. 235–236. [23] Ritter: Ueber den Werth der Belastungsproben eiserner Brücken, Schweizerische Bauzeitung, Vol. 20, Nr. 3, 16. Juli 1892, S. 14–17. [24] Von Bresztovszky: Antwort zu [3], Centralblatt der Bauverwaltung, 12. Oktober 1895, S. 433-434 [25] Waldner, A.: Ueber den Wert der Belastungsproben eiserner Brücken, Schweizerische Bauzeitung, 15. 05. 1892. [26] Robertson, J. R.: Die Nutzlosigkeit der Probebelastungen eiserner Brücken, Bulletin de la Commission internationale du Congrès des chemins de fer, Nov. 1897. [27] Vorläufige Leitsätze zur Vorbereitung, Ausführung und Prüfung von Eisenbetonbauten von 1904, aufgestellt vom Verbande Deutscher Architekten- und Ingenieur-Vereine und dem Deutschen Beton-Verein. [28] Bestimmungen für Ausführung von Bauwerken aus Eisenbeton, Bestimmungen des DAfEb, 1916. [29] von Emperger, F.: Handbuch für Eisenbetonbau, Band 9 – Die in- und ausländischen Eisenbetonbestimmungen, Verlag von Wilhelm Ernst & Sohn, Berlin, 3. Auflage, 1928 [30] Bach, C., Graf, O.: Gesamte und bleibende Einsenkungen von Eisenbetonbalken. Verhältnis der bleibenden zu den gesamten Einsenkungen, Berlin, Deutscher Ausschuss für Eisenbeton, Heft 27 (1914). [31] DIN 1045 – Beton und Stahlbetonbau, Bemessung und Ausführung (Ausgabe 01.1972) [32] Schmidt, H., Opitz, H.: Experimentelle Erprobung von Stahlbetonbauwerken in situ, 13. Kongress des IVBH in Helsinki, 6.–10.6.1988. [33] TGL 33407/04 – Nachweis der Trag- und Nutzungsfähigkeit aufgrund experimenteller Erprobung, Fachbereichsstandard, November 1986. [34] Steffens, K.: Experimentelle Traglastermittlung an Bauwerken – Grundlagen, Technik, Anwendungen; Schriftenreihe des Fachbereiches Bauingenieurwesen der Hochschule Bremen (1988), Heft 1. [35] DAfStb-Richtlinie Belastungsversuche an Betonbauwerken, Ausgabe September 2000, Beuth Verlag GmbH, Berlin und Köln. [36] Steffens, K. et al.: Entwicklung, Bau und Erprobung eines Belastungsfahrzeuges (BELFA), Kooperatives Forschungsbericht 01RA 9901/0, Abschlussbericht, Hochschule Bremen, Eigenverlag (2002).

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Prof. Dr.-Ing. Guido Bolle

Dipl.-Ing. Gregor Schacht

University of Applied Science Wismar Section Civil Engineering

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Philipp-Müller-Straße 14 23966 Wismar, Germany +49 3841 753 290 +49 3841 753 383 [email protected] http://www.bau.hs-wismar.de/

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Technical University of Dresden Faculty of Civil Engineering Department of Concrete Structures George-Bähr-Straße 1 01062 Dresden, Germany +49 351 463 32317 +49 351 463 37289 [email protected] http://www.tu-dresden.de/biwitb/mbau/

Prof. Dr.-Ing. Steffen Marx

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Leibniz-University Hannover Faculty of Civil Engineering and Geodesy Department of Concrete Structures Appelstraße 9a 30167 Hannover, Germany +49 511 762 3352 +49 511 762 2175 [email protected] http://www.ifma.uni-hannover.de/8.html

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