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Volume 12, Number 6, December 2023

Over-coating is one of the most popular engineering practices to strengthen Reinforced Concrete (RC) structures, due to the relative quickness and ease of construction. It consists of an external coat bonded to the outer surface of the structural RC element, either by the use of chemical adhesives, mechanical anchor bolts or simply mortar injection. In contrast to these constructive advantages, the numerical estimation of the bearing capacity of the strengthened reinforced concrete element is still complicated, not only for the complexity of modelling a flexible membrane or plate attached to a quasi-rigid solid, but also for the difficulties that raise of simulating any potential delamination between both materials. For these reasons, the standard engineering calculations used in the practice remain very approximated and clumsy. In this work, we propose the formulation of a new 2D solid-layer finite element capable to link a solid body with a flexible thin layer, as it were the "skin" of the body, allowing the potential delamination between both materials. In numerical terms, this "skin" element is intended to work as a transitional region between a solid body (modelled with a classical formulation of a standard quadrilateral four-nodes element) and a flexible coat layer (modelled with cubic beam element), dealing with the incompatibility of Degrees-Of- Freedom between them (two DOF for the solid and three DOF for the beam). The aim of the solid-layer element is to simplify the mesh construction of the strengthened RC element being aware of two aspects: a) to prevent the inappropriate use of very small solid elements to simulate the coat; b) to improve the numerical estimation of the real bearing capacity of the strengthened element when the coat is attached or detached from the solid body.

Key Words
delamination; finite element formulation; solid-layer bonding

Arturo Suárez-Suárez, Orlando Susarrey-Huerta: Postgraduate Studies and Research Section, ESIME-UZ, Instituto Politécnico Nacional, Mexico
Norberto Domínguez-Ramírez: Postgraduate Studies and Research Section, ESIA-UZ, Instituto Politécnico Nacional, Mexico

Standard Digital Volume Correlation (DVC) approaches are based on pattern matching between two reconstructed volumes acquired at different stages. Such frameworks are limited by the number of scans (due to acquisition duration), and time-dependent phenomena can generally not be captured. Projection-based Digital Volume Correlation (P-DVC) measures displacement fields from series of 2D radiographs acquired at different angles and loadings, thus resulting in richer temporal sampling (compared to standard DVC). The sought displacement field is decomposed over a basis of separated variables, namely, temporal and spatial modes. This study utilizes an alternative route in which spatial modes are con-structed via scan-wise DVC, and thus only the temporal amplitudes are sought via P-DVC. This meth-od is applied to a glass fiber mat reinforced polymer specimen containing a machined notch, subjected to in-situ cyclic tension, and imaged via X-Ray Computed Tomography. Different temporal interpolations are exploited. It is shown that utilizing only one DVC displacement field (as spatial mode) was sufficient to properly capture the complex kinematics up to specimen failure.

Key Words
fiber reinforced polymer; in-situ tests; projection-based digital volume correlation; tomography

Ana Vrgoč: Laboratory of Experimental Mechanics, Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Ivana Lučića 5, 10002, Zagreb, Croatia; Université Paris-Saclay, CentraleSupélec, ENS Paris-Saclay, CNRS LMPS−Laboratorie de Mécanique Paris-Saclay, Gif-sur-Yvette, France
Viktor Kosin: Université Paris-Saclay, CentraleSupélec, ENS Paris-Saclay, CNRS LMPS−Laboratorie de Mécanique Paris-Saclay, Gif-sur-Yvette, France; Leibniz Universität Hannover, Institut für Angewandte Mathematik (IFAM), Hannover, Germany
Clément Jailin: GE HealthCare, Buc, France
Benjamin Smaniotto: Université Paris-Saclay, CentraleSupélec, ENS Paris-Saclay, CNRS LMPS−Laboratorie de Mécanique Paris-Saclay, Gif-sur-Yvette, France
Zvonimir Tomičević: Laboratory of Experimental Mechanics, Faculty of Mechanical Engineering and Naval Architecture,
University of Zagreb, Ivana Lučića 5, 10002, Zagreb, Croatia
François Hild: Université Paris-Saclay, CentraleSupélec, ENS Paris-Saclay, CNRS LMPS−Laboratorie de Mécanique Paris-Saclay, Gif-sur-Yvette, France

This paper presents a mathematical model suitable for the calculation of laminated glass, i.e. glass plates combined with an interlayer material. The model is based on a beam differential equation for each glass plate and a separate differential equation for the slip in the interlayer. In addition to slip, the model takes into account prestressing force in the interlayer. It is possible to combine the two contributions arbitrarily, which is important because the glass sheet fabrication process changes the stiffness of the interlayer in ways that are not easily predictable and could introduce prestressing of varying magnitude. The model is suitable for reformulation into an inverse procedure for calculation of the relevant parameters. Model consisting of a system of differential-algebraic equations, proved too stiff for cases with the thin interlayer. This novel approach covers the full range of possible stiffnesses of layered glass sheets, i.e., from zero to infinite stiffness of the interlayer. The comparison of numerical and experimental results contributes to the validation of the model.

Key Words
differential equations; force-coupled structures; glazing; interlayer slip; laminated glass experiments; laminated glass model

Ivica Kožar: Faculty of Civil Engineering, University of Rijeka, Rijeka, Croatia
Goran Šuran: KFK d.o.o., Dugo Selo-Rugvica, Croatia

Municipal solid waste landfills are unpredictable bioreactors which in cases of mishandling and bad supervision presents numerous risks. The key to municipal waste landfills is to approach them from the point of prevention of the possible consequences, which means using methods of organized waste disposal, and also utilizing landfill gas, as an unavoidable consequence with disposal of municipal solid waste with a high share of biodegradable organic matter. This paper presents an overview about problems of solid municipal waste management, type and composition of waste, and an overview of waste management condition. Further, the problem of landfill and landfill gasses is described with the calculation models of landfill production, as well as the use of the SWM GHG Calculator and LandGEM software on a specific example of gas production for the central zone at Sarajevo landfill "Smiljevici". Main focus of this thesis is the analysis of potentials of greenhouse gas emission reduction measures from the waste management. Overview of the best available techniques in waste management is presented as well as the methodology used for calculations. Scenarios of greenhouse gas emission reduction in waste management were defined so that emissions were calculated using the appropriate model. In the final section of the paper, its description of the problem of collection and utilization the landfill gas at the sanitary landfill "Smiljevici", and implementation of the system for landfill gas collection and solution suggestion for the gasification and exploitation of gas. Energy, environmental and economic benefits can be accomplished by utilizing municipal solid waste as fuel in industry and energy and moreover by utilizing energy generation from landfill gas, which this thesis emphasizes.

Key Words
benefits; costs; Landfill; landfill gas; landfill gas collection; landfill gas energy projects; waste greenhouse gas emissions

Dzevad Imamovic and Amra Serdarevic: Faculty of Civil Engineering, University of Sarajevo, Patriotske lige 30, Bosnia and Herzegovina

Although some prediction models have successfully developed for ultra-high performance concrete (UHPC), they do not provide insights and explicit relations between all constituents and its consistency, and compressive strength. In the present study, based on the experimental results, several mathematical models have been evaluated to predict the consistency and the 28-day compressive strength of UHPC. The models used were Linear, Logarithmic, Inverse, Power, Compound, Quadratic, Cubic, Mixed, Sinusoidal and Cosine equations. The applicability and accuracy of these models were investigated using experimental data, which were collected from literature. The comparisons between the models and the experimental results confirm that the majority of models give acceptable prediction with a high accuracy and trivial error rates, except Linear, Mixed, Sinusoidal and Cosine equations. The assessment of the models using numerical methods revealed that the Quadratic and Inverse equations based models provide the highest predictability of the compressive strength at 28 days and consistency, respectively. Hence, they can be used as a reliable tool in mixture design of the UHPC.

Key Words
compressive strength; consistency; mathematical model; ultra high performance concrete

Alireza Habibi: Department of Civil Engineering, Shahed University, Tehran, Iran
Meysam Mollazadeh: Department of Civil Engineering, Kurdistan University, Sanandaj, Iran
Aryan Bazrafkan: Department of Civil Engineering, Bijar Branch, Islamic Azad University, Bijar, Iran
Naida Ademovic: Faculty of Civil Engineering Sarajevo, University of Sarajevo, Bosnia and Herzegovina

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