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Concrete Structures

Date: July 2017

Maximising the availability of existing bridges made of steel and concrete (2117005)
Structural maintenance measures on civil engineering structures usually require partial or complete closure and therefore traffic rerouting in most cases, which entails reduced capacities and higher risk of accidents. What is more, simultaneous construction and maintenance measures on several structures leads to a restriction to the performance of the federal trunk road network. The aim of the project is to maximise the availability of existing bridges made of steel and concrete during structural maintenance measures. For this purpose, findings, procedures and methods are provided which minimise the restriction of the availability and performance of maintenance measures. The investigations focus both on the planning and on the construction process at an object level. For typical structural measures, current construction methods and technologies are analysed in terms of the availability of existing structures and optimised under consideration of the modes of operation. Optimisation aspects through new approaches and coordinated planning of measures are also incorporated. Specific concepts in the form of handling instructions and auxiliary aids which take the entire planning and construction process into consideration are provided for practical situations.

Digital motorway test field – smart bridges – study programme (15.615)
By way of supplement to damage-based structural inspections which have been the norm so far, an adaptive system is developed under the heading of “Smart Bridges“ for the continuous provision of relevant information for a holistic assessment of condition using suitable sensor technology combined with analytical and evaluation methods. In the “Digital Motorway Test Field”, developments of new concepts and technologies are demonstrated and made accessible. The construction of a new four-field prestressed concrete box girder bridge in Bavaria serves as a pilot project for smart bridges. Sensor-controlled measurement and analysis technology has already been installed which records and analyses the impacts and structural reactions occurring in normal traffic conditions. The structure is calibrated for traffic approval. Focus is placed on heavy-traffic data. The structure serves as a monitoring system here that captures and processes bridge-specific parameters in free-flowing traffic. The findings obtained provide the basis for the evaluation and prediction of the condition as well as the reliability of the structure and its structural components. The captured and prepared information is provided to the operator online. The system is operated as part of a five-year investigation programme in collaboration with the motorway authority for Northern Bavaria - Autobahndirektion Nordbayern. The aim is to demonstrate the functioning and use of smart bridges for a reliability-based assessment of the condition of road bridges and therefore to provide a foundation to guarantee safety in holistic and sustainable maintenance planning.

Coordination and further development of the smart bridge project cluster (2116009)
The federal highway network is facing major challenges as a result of aging structures, increasing traffic loads, effects of climate change and a limited budget. Damage to structures is frequently only discovered once it has assumed considerable proportions. Adaptive systems to provide information in real time and facilitate a holistic approach have been developed as part of the “Smart Bridge” project cluster since 2011 in order to further develop the damage-based and reactive approach to maintenance. Numerous projects on intelligent sensors, structure and damage models and reliability-based assessment methods have been conducted within the project cluster. This project aims to coordinate and further develop the subject on the path to the demonstrator (www.intelligentebruecke.de).

Network of experts: permanent monitoring of existing bridges – quantification of reliability and use (2116014)
The development of strategies to guarantee the availability of civil engineering structures with the assistance of reliability-based methods and procedures is at the forefront of future research activities. The steep rise in traffic may cause shortcomings in the load-bearing capacities of bridge and engineering structures and restrict their residual serviceable life. Since a reinforcement and/or replacement of all structures concerned will not be possible in the short term, this project is intended to pinpoint concepts and approaches for the monitoring and reliability-based assessment of existing structures. The project will be conducted as part of the BMVI’s network of experts “Knowledge - Ability – Action" (Wissen – Können – Handeln) in the subject area 3 "Boosting the Reliability of the Transport Infrastructure".

Forecasting the serviceable life of concrete bridges (2116017)
According to the applicable regulations, bridge structures made of concrete should be capable of bearing loads, suitable for use and durable under consideration of economic aspects for around 100 years. Proof of durability against external effects is currently provided using descriptive concepts based on empirical values. Design and material-related requirements are outlined depending on the exposure classes assigned to the respective environment. A quantitative prediction of serviceable life is not possible. Computational verification or a design of durability is aspired to throughout the world and the methods are already contained in the regulations today. Concrete structures are based on physical and chemical damage models founded on experimentally determined model parameters. Models of this kind seek to provide computational verification for serviceable life under consideration of different impacts that reduce durability. However, no indications are provided for implementation in practical construction. The way in which the aspired-to serviceable life is achieved depends firstly on the design concept and secondly on considerations of economic efficiency. The aim of this project is to support procedures for durability design with bridge-specific coefficients. The results gained in this project will provide the foundation for further development and for methods which forecast the serviceable life of durable bridge structures made of concrete.

Freeze-Thaw-Resistance with the CDF-Method XF2: Ring Trial in Accordance with BASt Test Specifications (15.604)
In recent years, the “modified CDF-Method XF2” has been developed in order to assess the suitability of concretes for engineering constructions on the federal trunk road network in Germany in exposure class XF2. A follow-up project has validated the method, defined the precision data, suggested the acceptance requirement for the test and formulated the test specification. This project aims to carry out a supplementary ring trial and to verify the new test specification entitled “Recommendations for the Testing of the Freeze-Thaw-Resistance of Concretes in Exposure Class XF2” in practice, so that all instruments necessary for the adoption of the test into the ZTV-ING regulations can be made available.

Method for the Cost-Efficient Maintenance of Bridge Parapets (89.298)
Due to their particularly exposed position, bridge parapets are subject to increased freeze-thaw stresses. This can lead to a variety of damage profiles. The occurrence of these types of damage can be influenced by the type of cement and aggregates, production conditions, surface structure and follow-up treatment. In order to secure the fabric of these structures, it is necessary to document and/or suggest cost-efficient and highly durable maintenance methods relevant to the various damage profiles. In practice, the surface maintenance of damaged horizontal concrete surfaces which are exposed to the weather and passable for people to walk on involves a variety of methods and systems. These still contain a number of outstanding issues which must be clarified before recommendations for efficient and effective measures to protect the structures can be put forward.

Evaluation of concrete for civil engineering structures on federal highways using the XF2 CDF method (2114010)
The frost-thaw resistance is of key importance for the durability of concrete structures on federal highways. Against the background of changing bonding agents for concrete, a testing method to prove the equal value with the tried and tested bonding agents used on federal highways is of great significance. The new XF2 CDF method developed for this purpose has shown itself to be suitable for this application. This XF2 CDF method for testing concrete in the XF2 exposure class has been especially developed and validated for use on federal highways. The experience gained in the process as well as in the first round-robin trial with the new testing method has been transferred into a test specification. Before the adoption of the new CDF method in the set of regulations for bridges and civil engineering structures on federal highways, an improvement in the acceptance of the new XF2 CDF method is being sought. For this purpose, it is essential to undertake a second round-robin trial taking the new test specification into account and – complementing this – gather experience with the acceptance criteria by checking various concrete formulations.

Collaborative project: Intelligent, multifunctional reinforcement and protection system made from textile-reinforced, high-performance mortar for bridge constructions "SMART-DECK" – Sub-project: Requirements and assessment of the preventative maintenance concept SMART-DECK (2114021)
The durability and service life of road bridges is significantly limited due to water seepage through the waterproofing layer above the structural concrete and an inferior load-bearing capacity of existing structures to that which is required. In particular, corrosive damage resulting from chloride-induced corrosion can be detected neither reliably nor at an early stage with the sensors restricted to local measurement in use today or through the conduction of regular bridge inspections. Within the framework of the research project, an innovative, multifunctional and thin intermediate layer made from textile-reinforced concrete, which can be used for both new and existing constructions, is being developed. This intermediate layer combines three functions: ‘Real time monitoring system for the detection of moisture penetration across the entire road surface area on bridge constructions’, ‘Preventative cathodic corrosion protection (pKKS) across the entire road surface area with separately controlled sections’ and ‘Reinforcement function: Increasing load-bearing capacity’.
Within the framework of the current research project, the requirements of SMART-DECK will be defined and the developments to be achieved within the individual work packages of the cooperative partners, who encompass users and proprietors of the constructions, will be assessed. An initial demonstration will be executed on the grounds of the Federal Highway Research Institute (BASt) and a bridge construction will be obtained for a large-scale demonstration. Furthermore, BASt is contributing to the creation of design rules for utilisation and the support of a rapid implementation into practice.

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