Eugen Brühwiler

Biography

birth date: 19.11.1958 nationality: Swiss (native from Dussnang, Canton of Thurgau) Education : - July 1988 : doctoral degree from the Swiss Federal Institute of Technology in Lausanne (EPFL), Switzerland with a thesis entitled Fracture mechanics of dam concrete subjected to quasi-static and seismic loading conditions - December 1983 : civil engineering diploma (university degree) from the Swiss Federal Institute of Technology (ETH) in Zurich, Switzerland Professional Experience : - Since 1st April 1995 : Professor of Structural Engineering at EPFL and Head of the Laboratory of Maintenance, Construction and Safety for Civil Structures (MCS) (often considered being the first chair worldwide devoted exclusively to existing civil structures). - 1991-94 Project Manager and structural engineer with the Swiss Federal Railways (SBB), Division of Bridges and Structures, Zurich: Monitoring and maintenance of bridges and structures, Project manager and checking engineer for the construction of new bridges and rehabilitation of existing bridges. - 1989/90 Research associate at the Department of Civil Engineering, University of Colorado, Boulder, USA : Fracture mechanics of concrete and fracture of concrete dams. - 1986-88 Doctoral student at EPFL-LMC (Building Materials, Prof. Wittmann) : Fracture mechanics of concrete, fracture of concrete dams under seismic loading - 1984/85 Research engineer at EPFL-ICOM (Steel Structures, Prof. Badoux and Prof. Hirt) : Fatigue behaviour and fracture mechanics of riveted bridges

Official source

https://people.epfl.ch/eugen.bruehwiler

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Assessment of the information gain of several monitoring techniques for bridge structural examination

Numa Joy Bertola, Eugen Brühwiler

2023

Combined Passive and Active Ultrasonic Stress Wave Monitoring of UHPFRC Properties on a Structural Level

Numa Joy Bertola, Eugen Brühwiler

Ultra-High-Performance Fiber-Reinforced Cementitious Composite (UHPFRC) is becoming popular in designing lightweight and durable structures. UHPFRC structural elements remain crack-free and waterproof under service conditions, significantly improving durability compared to designs made of conventional reinforced concrete. Due to its unique composition, UHPFRC has specific mechanical properties. In particular, the early-age development of UHPFRC properties, such as the elastic modulus, is difficult to monitor as it occurs while elements are in the formwork. Monitoring of the very early-age behavior of UHPFRC is thus challenging, which is why the hydration process of UHPFRC on a structural level is still not yet fully understood. This paper proposes a novel combined passive and active ultrasonic stress wave monitoring (USW) approach involving a network of ultrasonic transducers and thermocouples. The scheme was applied to a laboratory beam with a span length of 4.0 meters. The monitoring network consisted of 24 embedded ultrasonic transducers and 15 thermocouples and allowed data recording from the beginning of the UHPFRC hardening process. From the beginning, a set of ultrasonic pulses were emitted every 30 minutes and recorded (active USW monitoring), while acoustic emissions (AE) were recorded continuously (passive USW monitoring). After 28 days, the beam was moved into a load frame and tested under four-point bending. Continuous monitoring using this unique passive and active monitoring approach enabled accurate characterization of the evolution of material properties during the very early age of UHPFRC, as well as the structural behavior and degradation processes of the beam during structural load testing.

2023

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This paper discusses the influence of fiber orientation on elastic limit tensile stress of ultra-high performance fiber reinforced cementitious composites (UHPFRC). An original model relating elastic limit tensile stress to fiber orientation is proposed, and three determination methods of the elastic limit are compared. Five specimens are tested under uniaxial tension and characterized with digital image correlation, acoustic emission and displacement transducers. Before testing, the fiber distribution (local dosage and orientation) of each specimen is determined using a magnetic probe. After testing, three methods (offset with 2 different threshold values, and deformation modulus drop) are applied to determine the elastic limit tensile stress. The test results show that the proposed model estimates well the elastic limit tensile stress on the basis of fiber orientation. The modulus-drop method yields the most representative value for the elastic limit considering the underlying physical phenomena. It may be taken as definition of elastic limit tensile stress of UHPFRC.

2023