Martin Herbrand

Structural Assessment of Concrete Bridges in Germany : Shear Resistance under Static and Fatigue Loading

Abstract The demands on the load-carrying capacity of bridges have increased over the last few decades because of the higher traffic volumes and weights. In the future, an even greater increase is expected. Since a large part of the existing bridges in Germany was built in the 1960s and 1970s, the assessment of these structures is deemed crucial. Therefore, the German Ministry of Transport introduced guidelines in 2011 allowing for a more accurate determination of the bearing capacity compared to the current German bridge design code. Nevertheless, many concrete bridges show deficits in shear and fatigue resistance. Consequently, a supplement to the guideline was published in 2015 to incorporate new research results. This paper describes the approaches for static and fatigue shear verification that consider the provided shear reinforcement. These methods refer to a truss model with variable compression strut inclination. Further, an application to a typical box-girder bridge in the road network is presented, demonstrating the potential for increasing the design value of the bearing capacity.

Strengthening of Existing Bridge Structures for Shear and Bending with Carbon Textile-Reinforced Mortar

Increasing traffic loads and changes in code provisions lead to deficits in shear and flexural capacity of many existing highway bridges. Therefore, a large number of structures are expected to require refurbishment and strengthening in the future. This projection is based on the current condition of many older road bridges. Different strengthening methods for bridges exist to extend their service life, all having specific advantages and disadvantages. By applying a thin layer of carbon textile-reinforced mortar (CTRM) to bridge deck slabs and the webs of pre-stressed concrete bridges, the fatigue and ultimate strength of these members can be increased significantly. The CTRM layer is a combination of a corrosion resistant carbon fiber reinforced polymer (CFRP) fabric and an efficient mortar. In this paper, the strengthening method and the experimental results obtained at RWTH Aachen University are presented.

Shear Strengthening with Textile Reinforced Concrete

Summary A large part of existing bridges in Germany exhibits deficits in the shear capacity under static and cyclic loading according to the current design rules. More structures are expected to demand refurbishment and strengthening within the next years especially due to the current conditions of many older road bridges. Since a reconstruction of the respective bridges is not feasible in many cases, the assessment and development of effective strengthening methods becomes more important. The use of textile reinforced concrete (TRC) offers an innovative alternative to existing strengthening measures by combining the advantages of lightweight glued CFRP-stripes (Carbon Fiber Reinforced Polymer) and additional concrete layers. For the above reasons, full scale tests on strengthened and non-strengthened I-shaped prestressed concrete beams (h = 0,7 m, l = 6,5 m) under cyclic shear loading as well as single span reinforced concrete slab strips (b = 0,5 m, h = 0,28 m) under static shear loading were carried out at the Institute of Structural Concrete at RWTH Aachen University. The paper presents the test results with regard to the effectiveness, advantages and possible fields of application of this innovative strengthening method. Keywords: shear; strengthening; bridges; testing; slabs; reinforced concrete; prestressed concrete; textile reinforced concrete; cyclic loading.

Processing ultrasonic data by coda wave interferometry to monitor load tests of concrete beams

Ultrasonic transmission measurements have been used for decades to monitor concrete elements, mostly on a laboratory scale. Recently, coda wave interferometry (CWI), a technique adapted from seismology, was introduced to civil engineering experiments. It can be used to reveal subtle changes in concrete laboratory samples and even large structural elements without having a transducer directly at the place where the change is taking place. Here, several load tests until failure on large posttensioned concrete beams have been monitored using networks of embedded transducers. To detect subtle effects at the beginning of the experiments and cope with severe changes due to cracking close to failure, the coda wave interferometry procedures had to be modified to an adapted step-wise approach. Using this methodology, we were able to monitor stress distribution and localize large cracks by a relatively simple technique. Implementation of this approach on selected real structures might help to make decisions in infrastructure asset management.

Improvement of Punching Shear Design Provisions According to Eurocode 2

The punching shear design of flat slabs and footings was revised with the introduction of Eurocode 2. While in many former codes the punching shear resistance was determined regardless of the type of member, in Eurocode 2 two different design equations for flat slabs and footings were introduced. Additionally, different control sections for flat slabs and footings were defined. The differentiation between flat slabs and footings and especially the iterative design procedure for the determination of the punching shear resistance of footings require great effort in daily engineering practice.

Investigations on the Strengthening of Existing Highway Bridges Under Shear and Flexural Loading with Textile Reinforced Mortar

Many existing highway bridges in Western countries have deficits in shear and flexural capacity under static and cyclic loading due to increasing traffic loads and changes in code provisions. Therefore, a lot of structures are expected to require refurbishment and strengthening within the next years, especially due to the current condition of many older road bridges. Different methods with specific advantages and disadvantages have proven to be suitable for the shear and flexural strengthening of bridges.

Experimental Investigations on the Shear Capacity of Prestressed Concrete Continuous Beams with Rectangular and I-Shaped Cross-Sections

Due to increased traffic loads and changes in the code provisions many bridges in Germany exhibit shear capacity deficits according to current codes. However, the shear capacity of prestressed concrete continuous beams might be underestimated according to recent test results. Also, the design procedures have usually been verified on the basis of single span beam tests so that additional tests on continuous beams seem appropriate. In order to extent the service life of existing bridges, the epistemic safety margins in the design procedures can in part be used by application of refined design approaches. For this reason, five shear tests on prestressed concrete continuous beams are performed at the Institute of Structural Concrete of RWTH Aachen University (Germany). Within these tests, the influence of the cross-section type (rectangular and I-shaped cross-section), the load distribution (concentrated and distributed loads) and the shear reinforcement ratio is investigated. In this paper, the preliminary test results of two beams under concentrated loads will be presented.

Experimental Studies on the Shear Capacity of Prestressed Concrete Continuous Beams

A large number of existing bridges of the German Federal Highways are built as prestressed concrete continuous beams. Because of rising traffic loads, the calculated shear capacity of some bridges is insufficient according to current codes. However, the calculated shear capacity might be underestimated by the design codes and the actual shear capacity may be increased, e.g. by using additional external tendons. This paper presents a research project that is carried out at the Institute of Structural Concrete at RWTH Aachen University. Six tests on three continuous beams with parabolic and additional external tendons were performed. The aim was to investigate whether the shear capacity is accurately predicted by the current bridge design code or if the shear capacity can be calculated more precisely by alternative approaches, especially regarding the influence of additional external tendons.