Laura De Lorenzis

Bio: Laura De Lorenzis is an academic researcher from ETH Zurich. The author has contributed to research in topics: Isogeometric analysis & Finite element method. The author has an hindex of 35, co-authored 112 publications receiving 4965 citations. Previous affiliations of Laura De Lorenzis include University of Salento & Missouri University of Science and Technology.

A review on phase-field models of brittle fracture and a new fast hybrid formulation

Abstract: In this contribution we address the issue of efficient finite element treatment for phase-field modeling of brittle fracture. We start by providing an overview of the existing quasi-static and dynamic phase-field fracture formulations from the physics and the mechanics communities. Within the formulations stemming from Griffith's theory, we focus on quasi-static models featuring a tension-compression split, which prevent cracking in compression and interpenetration of the crack faces upon closure, and on the staggered algorithmic implementation due to its proved robustness. In this paper, we establish an appropriate stopping criterion for the staggered scheme. Moreover, we propose and test the so-called hybrid formulation, which leads within a staggered implementation to an incrementally linear problem. This enables a significant reduction of computational cost--about one order of magnitude--with respect to the available (non-linear) models. The conceptual and structural similarities of the hybrid formulation to gradient-enhanced continuum damage mechanics are outlined as well. Several benchmark problems are solved, including one with own experimental verification.

Comparative Study of Models on Confinement of Concrete Cylinders with Fiber-Reinforced Polymer Composites

Abstract: The use of fiber-reinforced polymer (FRP) composites for strengthening and/or rehabilitation of concrete structures is gaining increasing popularity in the civil engineering community. One of the most attractive applications of FRP materials is their use as confining devices for concrete columns, which may result in remarkable increases of strength and ductility as indicated by numerous published experimental results. Despite a large research effort, a proper analytical tool to predict the behavior of FRP-confined concrete has not yet been established. Most of the available models are empirical in nature and have been calibrated against their own sets of experimental data. On the other hand, the experimental results available in the literature encompass a wide range of values of the significant variables. The objective of this work is a systematic assessment of the performance of the existing models on confinement of concrete columns with FRP materials. The study is conducted in the following steps: the experimental data on confinement of concrete cylinders with FRP available in the technical literature are classified according to the values of the significant variables; the existing empirical and analytical models are reviewed, pointing out their distinct features; the whole set of available experimental results is compared with the whole set of analytical models; strengths and weaknesses of the various models are analyzed. Finally, a new equation is proposed to evaluate the axial strain at peak stress of FRP-confined concrete cylinders.

Shear Strengthening of Reinforced Concrete Beams with Near-Surface Mounted Fiber-Reinforced Polymer Rods

Abstract: The use of near-surface-mounted (NSM) fiber-reinforced polymer (FRP) rods is a promising technology for increasing flexural and shear strength of deficient reinforced concrete (RC) members. The structural behavior of RC elements strengthened with NSM FRP rods needs to be fully characterized. In this research, 8 full-size beams were tested. Carbon FRP deformed rods were used for shear strengthening. The variables examined in the shear tests were spacing of the rods, strengthening pattern, end anchorage of the rods, and presence of internal steel shear reinforcement. In this paper, performance of the tested beams and modes of failure are presented and discussed. Test results confirm that NSM FRP rods can be used to greatly increase the shear capacity of RC elements, with efficiency that varies depending on the tested variables. Results of the experimental tests are compared with the predictions of a simple model, showing reasonable agreement.

Bond of Fiber-Reinforced Polymer Laminates to Concrete

Abstract: Fiber-reinforced polymer (FRP) laminates are being successfully used for strengthening existing reinforced concrete structures. The bond of FRP reinforcement to the concrete substrate is of great importance for the effectiveness of this technique. In this research, flexural test specimens were prepared to address some of the factors expected to affect bond such as bonded length, concrete strength, number of plies (stiffness), ply width, and, to a lesser extent, surface preparation. Experimental results are presented and discussed. A linear bond stress-slip relationship, along with a simple shear model for the evaluation of the slip modulus, is used to predict the strain distribution at moderate load levels. Lastly, expressions of the peeling load and the effective bond length are provided. A design equation is proposed for calculating the effective FRP ultimate strain to be used in design to account for bond-controlled failure.

Bond between Near-Surface Mounted Fiber-Reinforced Polymer Rods and Concrete in Structural Strengthening

Abstract: Use of near-surface mounted (NSM) fiber-reinforced polymer (FRP) rods is a promising technology for increasing flexural and shear strength of reinforced concrete (RC) members. As this technology emerges, the structural behavior of RC elements strengthened with NSM FRP rods should be fully characterized, and bond is the first issue to be addressed. Bond is of primary importance as it is the means for the transfer of stress between the concrete and the FRP reinforcement to develop composite action. This research program aimed to investigate bond between NSM FRP rods and concrete. Some of the factors expected to affect bond performance are addressed here, namely: bonded length, diameter and surface configuration of the rod, type of FRP material, and size of the groove in which the rod is embedded. Results are presented and discussed.

Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures

Abstract: *Co-chairs of the subcommittee that prepared this document. Note: The committee acknowledges the contribution of associate member Paul Kelley. ACI encourages the development and appropriate use of new and emerging technologies through the publication of the Emerging Technology Series. This series presents information and recommendations based on available test data, technical reports, limited experience with field applications, and the opinions of committee members. The presented information and recommendations, and their basis, may be less fully developed and tested than those for more mature technologies. This report identifies areas in which information is believed to be less fully developed, and describes research needs. The professional using this document should understand the limitations of this document and exercise judgment as to the appropriate application of this emerging technology.