Eugen Brühwiler

Bio: Eugen Brühwiler is an academic researcher from École Polytechnique Fédérale de Lausanne. The author has contributed to research in topics: Ultimate tensile strength & Slab. The author has an hindex of 33, co-authored 289 publications receiving 4284 citations. Previous affiliations of Eugen Brühwiler include École Polytechnique.

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

Abstract: 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.

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) complemen...

Rehabilitation of concrete structures using Ultra-High Performance Fibre Reinforced Concrete

Abstract: An original concept is presented for the rehabilitation of concrete structures. The main idea is to use Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) to “harden” those zones where the structure is exposed to severe environmental and high mechanical loading. All other parts of the structure remain in conventional structural concrete as these parts are subjected to relatively moderate exposure. This conceptual idea combines efficiently protection and resis-tance properties of UHPFRC and significantly improves the structural performance in terms of durability and life-cycle costs of the rehabilitated concrete structure. The concept is validated by means of four applications demonstrating that the technology of UHPFRC is mature for cast in-situ and prefabrication using standard equipment for concrete manufacturing.

Cohesive Zone Models: A Critical Review of Traction-Separation Relationships Across Fracture Surfaces

Abstract: One of the fundamental aspects in cohesive zone modeling is the definition of the traction-separation relationship across fracture surfaces, which approximates the nonlinear fracture process. Cohesive traction-separation relationships may be classified as either nonpotential-based models or potential-based models. Potential-based models are of special interest in the present review article. Several potential-based models display limitations, especially for mixed-mode problems, because of the boundary conditions associated with cohesive fracture. In addition, this paper shows that most effective displacement-based models can be formulated under a single framework. These models lead to positive stiffness under certain separation paths, contrary to general cohesive fracture phenomena wherein the increase of separation generally results in the decrease of failure resistance across the fracture surface (i.e., negative stiffness). To this end, the constitutive relationship of mixed-mode cohesive fracture should be selected with great caution.

Properties of strain hardening ultra high performance fiber reinforced concrete (UHP-FRC) under direct tensile loading

Abstract: Enhanced matrix packing density and tailored fiber-to-matrix interface bond properties have led to the recent development of ultra-high performance fiber reinforced concrete (UHP-FRC) with improved material tensile performance in terms of strength, ductility and energy absorption capacity. The objective of this research is to experimentally investigate and analyze the uniaxial tensile behavior of the new material. The paper reviews and categorizes a variety of tensile test setups used by other researchers and presents a revised tensile set up tailored to obtain reliable results with minimal preparation effort. The experimental investigation considers three types of steel fibers, each in three different volume fractions. Elastic, strain hardening and softening tensile parameters, such as first cracking stress and strain, elastic and strain hardening modulus, composite strength and energy dissipation capacity, of the UHP-FRCs are characterized, analyzed and linked to the crack pattern observed by microscopic analysis. Models are proposed for representing the tensile stress–strain response of the material.

Mechanical properties of ultra-high-performance fiber-reinforced concrete: A review

Abstract: A comprehensive investigation into the mechanical properties of ultra-high-performance fiber-reinforced concrete (UHPFRC), considering various influential factors, is imperative in order to obtain fundamental information for its practical utilization. Therefore, this paper reviewed the early-age strength (or setting) development and mechanical properties of hardened UHPFRC. In connection with the latter, the effects of the curing conditions, coarse aggregate, mineral admixtures, fiber properties, specimen size, and strain-rate on the mechanical performance of UHPFRC were specifically investigated. It was obvious that (1) heat treatment accelerates the hydration process, leading to higher strength; (2) a portion of the silica fume can be replaced by fly ash, slag, and rice husk ash in mechanical perspective; (3) the use of deformed (hooked and twisted) or long straight steel fibers improves the mechanical properties at a static rate; and (4) high rate loading provides a noticeable increase in the mechanical properties. Alternatively, there are some disagreements between the results from various ‘size effect’ tests and the effectiveness of using twisted steel fibers at static and high rate loadings. Further research to reduce the production cost of UHPFRC is also addressed in an attempt to make its widespread use more practical.