Eugen Brühwiler

The wedge splitting test, a new method of performing stable fracture mechanics tests

Abstract The wedge splitting test is a new test method to perform stable fracture mechanics tests on concrete and concrete-like materials. Specific fracture energy G F as well as fracture toughness K Ic are determined using simple specimens like cubes or cylinders. The main features of the wedge splitting test are described and compared to other tests methods. Identical G F - values are found irrespective of the test method and the specimen shape. The significance of the interaction between the testing machine, the test controller, the test method and the material properties for the performance and interpretation of stable fracture tests is outlined.

Fracture energy and strain softening of concrete as determined by means of compact tension specimens

Fracture mechanics parameters of concrete are determined by means of the compact tension (CT) test. The effects of ligament length, rate of loading and concrete composition on the specific fracture energy GF and the strain-softening diagram are investigated. As a first approximation of the real softening behaviour of concrete, a bilinear strain softening diagram is used in a finite-element analysis. A parameter study shows that several bilinear diagrams can represent the real behaviour equally well. With the bilinear softening diagram, a good agreement between both calculated and measured load-displacement curves and GF-values is obtained. The determined strain-softening diagrams are transformed into a normalized presentation. For each investigated testing condition, characteristics shapes of this normalized strain-softening diagram are obtained.

Fatigue of existing reinforced concrete bridge deck slabs

Provisions for the fatigue safety evaluation of existing bridges rely on a narrow knowledge basis. The fatigue safety of existing reinforced concrete deck slabs often cannot be verified if current fatigue design provisions are applied. A brief discussion of fatigue models allows for the determination of their utility in a stepwise approach to fatigue examination of existing bridges. To enhance the knowledge for more realistic predictions of the remaining fatigue life of existing structures, results of an ongoing research with fatigue tests on slab-like concrete beams are presented and interpreted. First results indicate that current fatigue design provisions appear to be conservative and that the fatigue reliability of existing deck slabs is satisfactory if the principles of good fatigue design and construction practice have been respected.

Experimental Investigation of Composite Ultra-High-Performance Fiber-Reinforced Concrete and Conventional Concrete Members

Composite ultra-high-performance fiber-reinforced concrete (UHPFRC) and conventional reinforced concrete structural members are investigated to assess the rehabilitation potential for existing concrete structures. The composite structural response is determined by testing 12 full-sized flexural beams, loading the UHPFRC layer in tension. The results demonstrate that the exceptional material properties of UHPFRC significantly improve the composite member structural response, including the ultimate force, stiffness, and cracking behavior. An analytical model is developed to predict the composite UHPFRC and conventional reinforced concrete structural response, and is employed to further analyze the experimental test results.

Failure of Dam concrete subjected to seismic Loading Conditions

Abstract The numerical simulation of concrete dams subjected to earthquake loading requires realistic material laws which take into account seismic loading conditions. Dynamic tests were performed in order to examine the effect of initially applied compressive loading on material properties of a dam concrete at high tensile deformation rates. The test results show that no important fracture property is reduced at high deformation rates; the tensile strength and the specific fracture energy G F show a high rate sensitivity. However, dynamic compressive pre-loading leads to a reduction of the fracture properties at both quasi-static and high deformation rates.

Rehabilitation and Strengthening of Concrete Structures Using Ultra-High Performance Fibre Reinforced Concrete

Abstract An original concept is presented for the durable rehabilitation and strengthening of concrete structures. The main idea is to use ultra-high performance fibre reinforced concrete (UHPFRC) complemented with steel reinforcing bars to protect and strengthen those zones of the structure that are exposed to severe environmental influences and high mechanical loading. This concept efficiently combines the protection and resistance properties of UHPFRC and significantly improves the structural performance of the rehabilitated concrete structure in terms of durability. The concept has been validated by means of field applications, demonstrating that the technology of UHPFRC is now well developed for cast in situ and prefabrication using standard equipment for concrete manufacturing. This novel technology is a step forward towards more sustainable structures.

Risk-based approach to the determination of optimal interventions for bridges affected by multiple hazards

Abstract Decision makers use bridge management systems to determine the optimal allocation of available resources. These systems are currently focused on the structural condition of deteriorating bridges with respect to traffic loads. Bridges, however, are affected by multiple hazards, such as flooding and earthquakes, and not only traffic loading. These multiple hazards should be considered in these management systems when determining the optimal intervention. A risk-based approach can be used to determine the optimal intervention for a bridge subjected to multiple hazards. It requires the determination of the likely ‘levels of service’ to be provided by the bridge, (e.g. both lanes of traffic open, only one lane of traffic open or both lanes closed), the evaluation of the probability of having these levels of service due to the multiple hazards as well as the consequences of each of these levels of service, and selecting the interventions to minimise the risk of inadequate service. This article gives the methodology to be used when determining the optimal intervention for a bridge affected by multiple hazards. The risk-based approach is illustrated using a simple example in which the optimal intervention of two interventions is found.

Swiss Standards for Existing Structures

Abstract In January 2011, the Swiss Society of Engineers and Architects (SIA) published a series of standards for existing structures. The standard entitled ‘existing structures—bases for examination and interventions’ specifies the principles, the terminology and the appropriate methodology for dealing with existing structures. This standard is complemented by a series of standards which treat specific items regarding ‘actions on existing structures’, ‘existing concrete, steel, composite, timber and masonry structures’ as well as ‘geotechnical aspects of existing structures’. It is expected that these standards will provide effective solutions on questions such as higher live loads, accidental actions or the restoration and improvement of the durability of existing structures. This paper highlights major principles, in particular those related to risk-based safety, proportionality of interventions and updating of variables. Methodological aspects of the main activities, that is, examination of structures and intervention measures, are described.

Holographic interferometry for the determination of fracture process zone in concrete

Abstract Holographic interferometry is used to determine the fracture process zone of mortar and concrete. The tests reveal the presence of a significant fracture process zone prior to peak load of the specimen. The fracture process zone can be subdivided into an elliptical, continuous region and a narrow but long, disrupted band along which load is transferred due to aggregate interlock. The larger the aggregates, the more pronounced is this fracture process zone.

Thermal Effects on Physico-Mechanical Properties of Ultra-High-Performance Fiber-Reinforced Concrete

Material characterization tests of an Ultra High Performance Fiber Reinforced Concrete (UHPFRC) were performed at various ages. A linear relationship was obtained between the mechanical properties and the degree of hydration. In parallel, the influence of curing conditions on the physico-mechanical properties and the time dependent behavior of this UHPFRC was investigated. A temperature increase accelerated the hydration process at early age and therefore improved the material’s compressive strength and the carrying capacity in four point bending tests, but at a long term, a higher temperature had inverse effects on the mechanical properties. Moreover, at a 20 °C temperature cure, the UHPFRC exhibited autogenous shrinkage at long term comparable to normal concrete. An increase of curing temperature increased the autogenous shrinkage. This effect may be due to the hydration and the self-desiccation processes which are accelerated at high temperatures.