Vermeidung von Schäden an Schlitzrinnen

Prevention of Damages to Concrete Gutters – Considerations on the Design of Expansion Joints In the last few years at some airports cracking was observed in concrete gutters, which are implemented in large areas as drainage. In order to reveal the influences on this cracking both laboratory investigations as well as numerical analyses referring the expansion joints and the gutters were carried out. The main focus was on the stiffness of the joint filling materials. Due to seasonal variations in temperature concrete pavements casted in wintertime tend to expand by higher temperatures in summer, whereas the deformations of the free edges can amount up to 5 to 10 mm. Such deformations should be met without any restrain. If this can not be ensured, horizontal pressures on the side‐walls of the gutters are raised. These pressures mainly depend on the stiffness of the joint filling material. In the adequate laboratory tests the stress‐strain‐relations for various materials was determined. For the mostly used bituminous soft board a comparatively stiff behaviour was proved. Thus the observed cracking mostly can be correlated with restraint stresses raised by such joint filling material.     

Zur Ermittlung der rißbreitenbeschränkenden Bewehrung bei Zwang in erhärtenden Betonbauteilen: Die Problematik einer “ausreichenden” Mindestbewehrung

Determination of Crack Width limiting Reinforcement due to Constraint in Hardening Concrete If restraint‐induced tensile stresses can occur, for the guarantee of the serviceability and durability the appearing crack width has to be limited due to the purpose and the environmental conditions of the building up to now in accordance to DIN 1045 (Edition 7.88), section 17.6, and furthermore to DIN 1045‐1 (2001‐07), section 11.2. The control of a defaulted crack width has a key position within the standard for durability and serviceability of the structures. The parallel selection of constructive or concrete‐technological measures for the decrease of the restraint stresses is always reasonable, because the defaulted crack widths can be hold and in consideration of the minimum reinforcement und crack injection the building costs can be optimized. Although in the following only the limitation of crack width of early restraint stresses will be considered in the planning of bearing structure the development of further tension situation have to be included. For example, in external building members under winter conditions restraint strain can occur which lead to a crack force in connection with higher tensile strength, for which the minimum reinforcement is not sufficient.     

Detektion und Lokalisierung von strukturellen Schäden mit Hilfe von geführten Wellen

Detection and localization of structural damages by means of guided waves. The procedure presented serves for an automatic large‐area monitoring of steel structures by means of non‐destructive testing. Piezoceramic members are applied as a cluster to the structure under observation. These elements are used both as sensors and as actuators and initiate guided wave propagation in the structure. Damages are detected by the changed structural response. Beside other methods of signal processing the principle of beamforming is used with the sensor signals. The example of a 6 mm steel plate shows the sensitivity of the developed procedure for damage detection.     

Instandsetzung und Verstärkung von Stahlbrücken mit Kategorie‐2‐Schäden

Refurbishment of orthotropic steel bridge decks with damages of the category 2. Many of the steel bridges built in the 1960s to 1980s, which are still located within the network of German highways and federal roads, show severe damages often induced by the considerable increase of freight traffic in the last few years. In addition, the forecasts predict a further increase of the heavy‐load traffic. Furthermore and especially in the case of many orthotropic steel bridge decks, several details were realized being no longer state of the art. This paper focuses on the so‐called category 2 damages, which comprise all damages at the longitudinal stiffeners. For this type of damage, different examples of bridges and their solutions of refurbishment are presented. Above all, one possibility of a renovation by means of mechanical fasteners, like blind‐rivets, is considered in detail. This detail is also focused by the current research project ”Refurbishment of fatigue‐stressed longitudinal stiffeners of orthotropic steel bridge decks by means of screwed solutions“ conducted at the University of Stuttgart.     

Instandsetzung und Verstärkung von Stahlbrücken mit Kategorie‐1‐Schäden

Retrofitting methods for orthotropic steel deck plates with category‐1‐damages. Due to a high increase of traffic load during the last decades orthotropic steel deck plates show more and more fatigue damages in the welded connection between longitudinal stiffeners and steel deck plate (category‐1‐damages). This contribution gives an overview about existing retrofitting methods which have already been applied in pilot projects and currently investigates renovation techniques for retrofitting category‐1‐damages.     

Instandsetzung und Verstärkung von Stahlbrücken mit Kategorie‐3‐Schäden

Reinforcing steel bridges with category 3 damages – report on a BASt research project. In recent years, fatigue damages have been observed at the main supporting structure of steel bridges, the orthotropic decks, as well as the transverse structure of steel bridges (the so‐called category 3‐failure). The rapidly increasing road traffic intensifies the situation resulting in a huge amount of steel bridges affected by fatigue damages. Existing steel bridges with category 3‐fatigue cracks have been intensively investigated. Fatigue failure modes and general evaluation criteria have been summarized, analysed and categorized, in order to enable first fundamental and time‐efficient definition and classification of category 3‐damages. FE‐simulations of transversal steel bridge structures (with and without reinforcements) have been carried out to evaluate and review the structural bridge concepts. Based on these studies, a special way of the steel bridges' maintenance has been followed up, which is removing all possible transversal bracings. Finally, different options of maintenance and repair have been investigated both newly and successfully applied in the recent past. Appropriate actions for solving essential category 3‐fatigue problems are presented.     

Durchstanzversuche mit Bewehrung mit hochfestem Verbund,innovative Traganalysen und Bemessungsansätze

Slab Punching Tests with Reinforcement with High‐Strength Bond In this paper there is given an account of punching tests, in which the tested concrete slabs were reinforced against punching by reinforcement with high‐strength bond. The test results show that very good load capacities are obtainable. The pictures of the cracks, which were to be seen after the test slabs were cut up, gave interesting conclusions about the carrying behaviour of the system. Comparing these cracks with those of test slabs with double headed punching anchors clearly shows the differences of the carrying behaviours. The analysis of the test results also gives new knowledge about the carrying mechanisms at the critical punching zone of reinforced concrete slabs, which also build a basis for a proposal how to modify the existing design rules.     

Quantifizierung der Schäden infolge Hochwassereinwirkung: Fallstudie Eilenburg

Assessment of damage due to flood impact: the case study of Eilenburg. Estimating damage caused by flood impact is an important, yet scientifically and methodically insufficiently investigated task, which is necessary for preparing the management of catastrophes. Alluding to the procedure developed in the risk analysis of earthquakes it is checked, whether methodical fundamentals can be transferred or have to be modified, and which parameters must be derived from data surveys. As an essential improvement, in addition to the inundation level, the influence of the buildings' parameters are considered. Subsequently, the building types are sorted into vulnerability classes, to which characteristic structural damages, depending on the impact, or humidity penetration ratios can be assigned, which ultimately determine the extent of the damage and the resulting cost. As can be shown for the case study of Eilenburg, areas with unusually high vulnerability of the building stock can be identified by applying the chosen approach assuming a defined scenario, leading to recommendations for future decisions on building in the area. A key element of the procedure lies in the preparation of the required or, respectively, usable data, which must be linked by damage functions. The paper gives an overview of the approaches for observations on mesoscale and microscale. As can be shown on the example of the town Eilenburg, with the provided tools and data, the damages caused by the flood in August 2002 can be reinterpreted regarding their height and distribution.