Numerical investigation of factors influencing the experimental determination of concrete fracture energy

The fracture energy is one of the most crucial parameters for the numerical investigation of damage propagation and failure in reinforced concrete members. The correct characterization of concrete fracture properties can be compromised by different laboratory limitations, such as specimens size, mode of control, loading rate and the test apparatus. Nowadays limited recommendations exist concerning the experimental evaluation of fracture energy for normal and high strength concrete. In order to investigate the differences between different specimen sizes, evaluate the effect of mode of control and analyze the influence of different set-up on the fracture test, a numerical analysis supported by an experimental campaign is presented. The Lattice Discrete Particle Model (LDPM) has been used to simulate concrete and to provide realistic crack patterns and crack widths. In the first part of the study the position of the traveling crack tip is identified with two approaches and then used to investigate the strain rate distribution along the ligament. It is well-known that concrete is a visco-elastic material with strain-rate dependent fracture properties. For this reason in the second part of the study the potential influence of differences in loading rate on the effective fracture energy determined by the work of fracture method is investigated with simulated three-point bending tests of differently sized specimens and two notch depths

Interfacial bond behavior of steel-FRCM composites applied to a masonry substrate

In the last decades the theme of structural rehabilitation has acquired great importance and the adoption of composite materials in civil engineering applications has been a turning point in this field. The cement-based matrix of FRCM composites presents many advantages for their application to historical buildings. This dissertation presents a study of the influence of composite bonded length and width on the load response and failure mode. Two types of mortar matrix and two different steel densities were employed. The classical push pull configuration is adopted where fibers are pulled while the masonry block is restrained. Based on the experimental results and through a fracture mechanics approach, the cohesive material laws for mode II was obtained. For the completeness of the work, the characterization of each material involved in the single-lap shear test has been achieved

An Investigation of the Debonding Mechanism between FRCM Composites and a Masonry Substrate

Fiber reinforced cementitious matrix (FRCM) composites have recently become a hot topic in Europe as an alternative to traditional fiber reinforced polymer (FRP) composites for several strengthening applications of existing masonry buildings. The terrific success of this new retrofitting system is mainly due to some advantages that it offers when compared to FRP, such as the possibility of application of the composite to wet surfaces and the vapor permeability featured by the inorganic matrix. In this work, the stress transfer between FRCM composites and a masonry substrate is investigated. FRCM strips comprised of ultra-high-strength steel fibers embedded in a cementitious grout are externally bonded to masonry blocks. Single-lap direct shear tests are performed. Parameters studied are bonded length and density of the steel fibers. Load responses are presented and failure modes are discussed. Change in the bond behavior and load carrying capacity with increasing bonded length is analyzed to determine the effective bond length

Cure Kinetics and Inverse Analysis of Epoxy-Amine Based Adhesive Used for Fastening Systems

Thermosetting polymers are used in building materials, for example adhesives in fastening systems. They harden in environmental conditions with a daily temperature depending on the season and location. This curing process takes hours or even days effected by the relatively low ambient temperature necessary for a fast and complete curing. As material properties depend on the degree of cure, its accurate estimation is of paramount interest and the main objective in this work. Thus, we develop an approach for modeling the curing process for epoxy based thermosetting polymers. Specifically, we perform experiments and demonstrate an inverse analysis for determining parameters in the curing model. By using calorimetry measurements and implementing an inverse analysis algorithm by using open-source packages, we obtain 10 material parameters describing the curing process. We present the methodology for two commercial, epoxy based products, where a statistical analysis provides independence of material parameters leading to the conclusion that the material equation is adequately describing the material response