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CONTENTS
Volume 9, Number 2, April 2020
 

Abstract
The reliability of structures is affected by various impacts that generally have a negative effect, from extreme weather conditions, due to climate change to natural or man-made hazards. In recent years, extreme loading has had an enormous impact on the resilience of structures as one of the most important characteristics of the sound design of structures, besides the structural integrity and robustness. Resilience can be defined as the ability of the structure to absorb or avoid damage without suffering complete failure, and it can be chosen as the main objective of design, maintenance and restoration for structures and infrastructure. The latter needs further clarification (which is done in this paper), to achieve the clarity of goals compared to robustness which is defined in Eurocode EN 1991-1-7 as: \"the ability of a structure to withstand events like fire, explosions, impact or the consequences of human error, without being damaged to an extent disproportionate to the original cause\". Many existing structures are more vulnerable to the natural or man-made hazards due to their material deterioration, and a further decrease of its loadbearing capacity, modifying the structural performance and functionality and, subsequently, the system resilience. Due to currently frequent extreme events, the design philosophy is shifting from Performance-Based Design to Resilience-Based Design and from unit to system (community) resilience. The paper provides an overview of such design evolution with indicative needs for Resilience-Based Design giving few conducted examples.

Key Words
resilience; extreme loads; Resilient-Based Design; earthquakes; Performance-Based Design

Address
Naida Ademovic: University of Sarajevo, Faculty of Civil Engineering, Patriotske lige 30, 71 000 Sarajevo, Bosnia and Herzegovina
Adnan Ibrahimbegovic: Laboratoire Roberval, Universite de Technologie de Compiegne/Sorbonne Universites, France

Abstract
Wastewater treatment plants (WWTPs) with activated sludge system are widely used throughout the most common technologies in the world. Most treatment plants require optimization of certain treatment processes using dynamic modeling. A lot of examples of dynamic simulations require reliable data base of diurnal variation of the inflow and typical concentrations of parameters such as Chemical Oxygen Demand (COD), Total Kjeldahl Nitrogen (TKN), etc. Such detailed data are not available, which leads to problems in the application of dynamic simulations. In many examples of plants, continuous flow measurements are only performed after the primary clarifier, whereas measurements from influent to the plant are missing, as is the case with the examples in this paper. In some cases, a simpler, faster and cheaper way can be applied to determine influent variations, such as the \"HSG-Sim\" method (\"Hochschulgruppe Simulation\"). \"Hochschulgruppe Simulation\" is a group of researchers from Germany, Austria, Switzerland, Luxembourg, Netherlands and Poland (see http://www.hsgsim.org). This paper presents a model for generating daily variations of inflow and concentration of municipal wastewater quality parameters, applied to several existing WWTPs in Bosnia and Herzegovina (B&H). The main goal of the applied method is to generate realistic influent data of the existing plants in B&H, in terms of flow and quality, without any prior comprehensive survey and measurements at the site. The examples of plants show the influence of overflow facilities on the dynamics of input flow and quality of wastewater, and a strong influence of the problems of the sewerage systems.

Key Words
municipal wastewater; input data; daily influent variation; HSG method; flow pattern generation; dynamic modeling

Address
Alma Dzubur and Amra Serdarevic: Department of Sanitary Engineering and Department of Environmental Engineering, Faculty of Civil Engineering, University of Sarajevo, Patriotske lige 30, Sarajevo, Bosnia and Herzegovina

Abstract
In this paper, we present a 3D thermo-hydro-mechanical coupled discrete beam lattice model of structure built of the nonisothermal saturated poro-plastic medium subjected to mechanical loads and nonstationary heat transfer conditions. The proposed model is based on Voronoi cell representation of the domain with cohesive links represented as inelastic Timoshenko beam finite elements enhanced with additional kinematics in terms of embedded strong discontinuities in axial and both transverse directions. The enhanced Timoshenko beam finite element is capable of modeling crack formation in mode I, mode II and mode III. Mode I relates to crack opening, mode II relates to in-plane crack sliding, and mode III relates to the out-of-plane shear sliding. The pore fluid flow and heat flow in the proposed model are governed by Darcy\'s law and Fourier\'s law for heat conduction, respectively. The pore pressure field and temperature field are approximated with linear tetrahedral finite elements. By exploiting nodal point quadrature rule for numerical integration on tetrahedral finite elements and duality property between Voronoi diagram and Delaunay tetrahedralization, the numerical implementation of the coupling results with additional pore pressure and temperature degrees of freedom placed at each node of a Timoshenko beam finite element. The results of several numerical simulations are presented and discussed.

Key Words
coupled discrete beam lattice model; saturated porous medium; pore pressure; temperature; coupling; localized failure; temperature dependent parameters

Address
Emina Hadzalic: Universite de Technologie de Compiegne, Laboratoire Roberval de Mecanique, Centre de Recherche Royallieu, 60200 Compiegne, France; Faculty of Civil Engineering, University of Sarajevo, Patriotske lige 30, Sarajevo 71000, Bosnia and Herzegovina
Adnan Ibrahimbegovic: Universite de Technologie de Compiegne, Laboratoire Roberval de Mecanique, Centre de Recherche Royallieu, 60200 Compiegne, France; Institut Universitaire de France, France
Samir Dolarevic: Faculty of Civil Engineering, University of Sarajevo, Patriotske lige 30, Sarajevo 71000, Bosnia and Herzegovina

Abstract
Constructive merging of \"basic\" systems of different behavior creates hybrid systems. In doing so, the structural elements are grouped according to the behavior in carrying the load into a geometric order that provides sufficient load and structure functionality and optimization of the material consumption. Applicable in all materializations and logical geometric forms is a transparent system suitable for the optimization of load-bearing structures. Research by individual authors gave insight into suitable system constellations from the aspect of load capacity and the approximate method of estimating the participation of partial stiffness within the rigidity of the hybrid system. The obtained terms will continue to be the basis for our own research of the influence of variable parameters on the behavior of hybrid systems formed of glued laminated girder and cable of different geometric shapes. Previous research has shown that by applying the strut-type hybrid systems can increase the load capacity and reduce the deformability of the free girder. The implemented parametric analysis points to the basic parameter in the behavior of these systems - the rigidity of individual elements and the overall stiffness of the system. The basic idea of pre-stressing is that, in the load system or individual load-bearing element, prior to application of the exploitation load, artificially challenge the forces that should optimize the final system behavior in the overall load. Pre-stressing is possible only if the supporting system or system\'s element possess sufficient strength or stiffness, or reaction to the imposed forces of pre-stressing. In this paper will be presented own research of the relationship of partial stiffness of strut-type hybrid systems of different geometric forms. Conducted parametric analysis of hybrid systems with and without pre-stressing, and on the example of the glulam-steel strut-type hybrid system under realistic conditions of change in the moisture content of the wooden girder, resulted in accurate expressions and diagrams suitable for application in practice.

Key Words
optimization of load-bearing structures; hybrid system; pre-stressing of hybrid system; glued laminated timber; cable; effective force of pre-stressing; geometrical stiffness/rigidity, self- stiffness/rigidity

Address
Sladana Miljanovic: University of Sarajevo, Faculty of Architecture, Sarajevo, Bosnia and Herzegovina
Muhamed Zlatar: University of Sarajevo, Faculty of Civil Engineering, Sarajevo, Bosnia and Herzegovina

Abstract
Coupled thermo-mechanical analysis of reinforced concrete slab at elevated temperatures from a fire accounting for nonlinear thermal parameters is carried out. The main focus of the paper is put on a one-way continuous reinforced concrete slab exposed to fire from the single (bottom) side as the most typical working condition under fire loading. Although contemporary techniques alongside the fire protection measures are in constant development, in most cases it is not possible to avoid the material deterioration particularly nearby the exposed surface from a fire. Thereby the structural fire resistance of reinforced concrete slabs is mostly influenced by a relative distance between reinforcement and the exposed surface. A parametric study with variable concrete cover ranging from 15 mm to 35 mm is performed. As the first part of a one-way coupled thermo-mechanical analysis, transient nonlinear heat transfer analysis is performed by applying the net heat flux on the exposed surface. The solution of proposed heat analysis is obtained at certain time steps of interest by a-method using the explicit Euler time-integration scheme. Spatial discretization is done by the finite element method using a 1D 2-noded truss element with the temperature nodal values as unknowns. The obtained results in terms of temperature field inside the element are compared with available numerical and experimental results. A high level of agreement can be observed, implying the proposed model capable of describing the temperature field during a fire. Accompanying thermal analysis, mechanical analysis is performed in two ways. Firstly, using the guidelines given in Eurocode 2 - Part 1-2 resulting in the fire resistance rating for the aforementioned concrete cover values. The second way is a fully numerical coupled analysis carried out in generalpurpose finite element software DIANA FEA. Both approaches indicate structural fire behavior similar to those observed in large-scale fire tests.

Key Words
Thermo-mechanical analysis, reinforced concrete slab, fire loads, standard ISO 834 fire curve, parametric fire curves, structural fire resistance

Address
Samir Suljevic: Faculty of Civil Engineering, University of Sarajevo, Patriotske lige 30, 71000 Sarajevo,
Bosnia and Herzegovina; Université de Technologie de Compiègne/Sorbonne Universités, Laboratoire Roberval de Mécanique, Centre de Recherche Royallieu, 60200 Compiègne, France
Senad Medic, Mustafa Hrasnica: Faculty of Civil Engineering, University of Sarajevo, Patriotske lige 30, 71000 Sarajevo, Bosnia and Herzegovina

Abstract
Connection of adjacent buildings with stiff links is an efficient approach for seismic pounding mitigation. However, use of highly rigid links might alter the torsional response in asymmetric plans and although this was mentioned in the literature, no quantitative study has been done before to investigate the condition numerically. In this paper, the effect of rigid coupling on the elastic lateral-torsional response of two adjacent one-story column-type buildings has been studied by comparison to uncoupled structures. Three cases are considered, including two similar asymmetric structures, two adjacent asymmetric structures with different dynamic properties and a symmetric system adjacent to an adjacent asymmetric one. After an acceptable validation against the actual earthquake, the traditional random vibration method has been utilized for dynamic analysis under Ideal white noise input. Results demonstrate that rigid coupling may increase or decrease the rotational response, depending on eccentricities, torsional-to-lateral stiffness ratios and relative uncoupled lateral stiffness of adjacent buildings. Results are also discussed for the case of using identical cross section for all columns supporting each plan. In contrast to symmetric systems, base shear increase in the stiffer building may be avoided when the buildings lateral stiffness ratio is less than 2. However, the eccentricity increases the rotation of the plans for high rotational stiffness of the buildings.

Key Words
rigid link; random vibration; torsion; dynamic properties; response ratio

Address
Hamed Ahmadi Taleshian, Alireza Mirzagoltabar Roshan and Javad Vaseghi Amiri: Department of Civil Engineering, Noshirvani University of Technology, Babol, Iran


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