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H-colouring revisited
Get PDFIn this paper we give a new, shortened proof of NP-completeness of CSP problem for undirected, non bipartite graphs, of interest for generalization to QCSP problem. We also give some illustrative examples
Potential and benefit of green roof energy renovation of existing residential buildings with a flat roof in Belgrade
Get PDFThis paper considers the phenomenon of the instability of steel plane frame structures in the elastic-plastic domain. The numerical analysis uses FEM, where the corresponding stiffness matrices are based upon the trigonometric and hyperbolic interpolation functions of normal forces. The tangent modulus concept is applied when buckling occurs in the plastic range. Thus, the stiffness matrices for nonlinear material behavior are also derived. The procedure for determining effective length factors of compressed columns, which implies a global stability analysis of entire frames, is established too. It means that the proposed approach is based on the assumption that the collapse of the structure occurs when the most loaded columns reach their stability limit. So, the presented procedure enables the calculation of the real critical load of plane frame structures in the elastic-plastic domain and determines the corresponding effective length factors
Poluautomatska predprojektna procena dinamike, troškova i rizika za stambene objekte
Get PDFZa obezbeđenje finansijskog uspeha projekta, ključno je da investitori izvrše pouzdane procene pre nego što se obavežu na projekat nabavkom građevinskog zemljišta. Ovaj rad prezentuje metodologiju i softversko rešenje za pred-projektnu polu-automatsku procenu dinamike, troškova i rizika za stambene objekte. Za automatsko planiranje, dizajniran je "Univerzalni ritmični ciklogram" na nivou glavnih tokova, koji je određen trajanjem prvog toka i zazorima. Umesto procene ukupnih troškova projekta, predloženi metod procenjuje količine za ključne aktivnosti omogućavajući korišćenje trenutnih tržišnih jediničnih cena u funkciji kvaliteta. Monte Carlo simulacije, primenjene na intervale prekoračenja na nivou aktivnosti, predviđaju vrednosti za ukupne troškove, prihode i trajanje projekta koje uključuju rizik. Ulazni podaci su: urbanistički parametri iz Informacije o lokaciji, broj podzemnih etaža, troškovi po aktivnostima, prodajne cene, parametri finansiranja, datum početka gradnje i granice intervala za rizik
Selection of wastewater treatment technology: AHP method in multi-criteria decision making
Get PDFWastewater treatment is a process that reduces pollution to those quantities and concentrations at which purified wastewater is no longer a threat to human and animal health and safety and does not cause unwanted changes in the environment. Municipal wastewater is classified as biodegradable water. Special importance should be given to wastewater with a high content of organic matter (COD), phosphorus (P) and nitrogen (N). MBBR technology, developed on the basis of the conventional activated sludge process and the bio filter process, does not take up much space and does not have problems with activated sludge, as in the case of conventional biological reactors, and has shown good results for the removal of organic matter, phosphorus and nitrogen. The aim of this paper is to optimize the wastewater treatment process in the municipality of Dojran, North Macedonia. Three alternative solutions for improving the capacity for wastewater treatment in the municipality of Dojran were analyzed. The shortlist of variants was made on the basis of several criteria, including: analysis of the system in the tourist season and beyond, assessment of the condition and efficiency of the existing wastewater treatment plant (WWTP) in combination with a new treatment plant, treatment efficiency when using different wastewater treatment technologies, the size of the site needed to accommodate the capacity, as well as the financial parameters for the proposed system. The selection of the most favorable solution for the improvement of the wastewater treatment system was made using the AHP (analytic hierarchy process) method. In order to select the optimal solution, a detailed analysis was conducted, considering several decision-making criteria, namely the initial investment, operating costs and management complexity. Based on the obtained results, Variant 3 was recommended, that is, the construction of a completely new station with MBBR technology, with a capacity for 6000 equivalent inhabitants
A Comparative Study of ML and FEM Models for the Prediction of Seismic Structural Behavior
No full textDuring the last several decades, the finite element method (FEM) is the most commonly used numerical method for performing seismic structural analysis. It requires careful structural modeling, but also the adjustment of small computation steps, especially for highly complex nonlinearities, which leads to significant time consumption, to ensure the stability and accuracy of the results. The development of new techniques based on machine learning (ML) models attracts considerable attention, due to the possibility to overcome the limitations of traditional techniques. This study presents an implementation of the long short-term memory (LSTM) deep-learning recurrent neural network (RNN) for the estimation of nonlinear seismic structural response. It is established in a data-driven manner. The LSTM model has shown considerable success in capturing structural response during nonlinear dynamic time-history (NDTH) analysis. Even in the case of an insufficient number of data, it shows better performance and greater adaptation to experimental results than the robust FEM model. In order to secure the consistency of the dataset for different ground motion records and increments, resampling and filtering of data is recommended. Such an innovative approach can enable the prevention of catastrophic consequences from devastating earthquakes. That can be achieved by fast and accurate pre-earthquake response prediction, damage state forecasting, and accelerated development of fragility curves based on previously conducted incremental dynamic analyses (IDA) or experimental tests. The predictive capabilities of the developed model were demonstrated through a comparative analysis of the behavior of two adjacent interacting unreinforced masonry structures (URM), tested on a shaking table. Even with the relative lack of experimental data, LSTM showed superiority over SAP2000 software. In all sequences of the time history records, the LSTM model gave closer results to the experimental ones than the SAP2000. The lack of a massive amount of data was observed as the main reason for the deviation of the results obtained by the LSTM model in certain time intervals, so the expansion of datasets is proposed for upcoming simulations. In future research, to model the dynamic response of different material and structural types, the formation of such models in a physics-driven fashion is recommended
An Integrated Approach to Landslides Risk Management for Local and National Authorities
Get PDFThe University of Belgrade, Faculty of Mining and Geology has been involved in landslide risk reduction activities at the national, regional, and site-specific levels in Serbia for decades. Since 2011 the Faculty has had several activities closely connected with the International Consortium on Landslides, including the International Programme on Landslides Projects 181, 210 and 248, as well as World Centre of Excellency (WCoE) from 2017. In the past decade the Faculty of Mining and Geology was involved in several national, regional and local projects funded by the People of Japan, UNDP and The World Bank on landslide risk reduction in Serbia, Bosnia and Herzegovina and North Macedonia. They all closely involved many stakeholders from national to local authorities including Ministries, Local Self Governments, Public Enterprises, Emergency Offices and Civil Protec-tion units. In this report, the activities of WCoE for national and local authorities on landslide risk reduction will be presented
Design procedures for cold-formed stainless steel built-up columns assembled from equal-leg angles
No full textIn this paper, the structural behaviour of cold-formed stainless steel (CFSS) built-up T- and cruciform-section columns is studied experimentally and numerically, and the effect of discrete fasteners on their flexural and torsional rigidity is considered. To build the singly symmetrical built-up T-section columns, two equal-leg angle sections made of lean-duplex grade EN 1.4162 were assembled back-to-back. The doubly symmetrical built-up cruciform-section columns were composed of four star-oriented equal-leg angle sections made of austenitic grade EN 1.4301. They were connected using M8 bolts of class 8.8. Two pin-ended built-up T-section columns with length of 1000 mm, and four built-up cruciform-section columns with lengths of 600 mm and 2400 mm with semi-rigid support conditions, were tested under pure axial compression. As observed in the tests, built-up T-section columns experienced flexural-torsional buckling failure, whereas built-up cruciform-section columns failed in torsional buckling mode. Finite element models were validated against the conducted experiments and used to perform a parametric study of the structural behaviour of CFSS built-up T- and cruciform-section columns. The study included the column length, cross-sectional dimensions and bolt spacing as variables. The experimental and numerical data, i.e., the column strengths and failure modes, were compared against the results obtained based on the European and North American Specifications alongside a recent method established for cold-formed carbon steel equivalents and based on the Direct Strength Method (DSM). It is shown that the DSM-based approach predicts the ultimate buckling resistances of the considered built-up columns more accurately than the available codified design methods
Possibilities for Application of Modified Solidified Water Treatment Sludge as Supplementary Cementitious Material
No full textThe increased number of water treatment plants induces intensified production of water treatment sludge (WTS) that needs to be stabilized and reused. One of the possible stabilization processes is solidification, which involves the reaction of wastes with additives based on calcium-oxide and calcium-hydroxide. The final product of these reactions (solidified water treatment sludge - SWTS) is an inert material that can be used as a filler, but not as a supplementary cementitious mate-rial (SCM) - due to its insufficient pozzolanic activity. The paper presents the possibilities of application of modified SWTS (MSWTS) as a SCM when mixed with aluminium-oxide and magnesium-silicate. In order to achieve this, mortar mixtures were prepared with partial replacement of cement by using MSWTS in amounts of 10%, 20% and 30%. Flexural and compressive strength tests, togeth-er with ultrasonic pulse velocity, as well as with capillary water absorption and freeze-thaw resistance were performed. The obtained results point to the conclu-sion that the increase in the percentage content of MSWTS consequently led to a decrease in the mechanical properties of the tested samples, which limits the pos-sible cement percentage replacement in plasters. The decrease in flexural strength ranged between 3% and 8% and in compressive strength between 8% and 19%
The Impact on Karst Aquifer Regimes Induced by a Surface Reservoir in Karst through Multiparametric Analyses (Reservoir Bileća—Herzegovina)
Get PDFThe results of long-term groundwater monitoring in the Bileća reservoir adjacent (eastern Herzegovina, Bosnia and Herzegovina) indicate that there is a good hydraulic connection between the reservoir and the karst aquifer located in the right bank of the reservoir. In remote parts of the right-bank karst aquifer, due to complex lithostratigraphic characteristics and a tectonic structure, the influence of the reservoir is very variable and has been insufficiently studied up until now. This paper presents the analysis and synthesis of new, relevant hydrogeological data, as a basis for the creation of a 3D spatial model, i.e., the analysis of the karst system’s behaviour, both under regular and artificial hydrological conditions of surface reservoir construction and its continuous use (filling and emptying). The interactive connection of the model and complex surface and groundwater time series monitoring data of this system is presented through the analysis of its hydrodynamic characteristics, which completes the spatial model of the karst regime caused by low and high groundwater levels and low and high reservoir water levels. The integration of all the data into one model and further multiparametric analyses revealed the different types of hydrodynamic conditions prevailing in the karst aquifer with regard to the influence of the high or low waters of the reservoir
Augmented state estimation of urban settings using intrusive sequential Data Assimilation
Get PDFA data-driven investigation of the flow around a high-rise building is per- formed combining heterogeneous experimental samples and RANS CFD. The coupling is performed using techniques based on the Ensemble Kalman Filter (EnKF), including advanced manipulations such as localization and inflation. The augmented state estimation obtained via EnKF has also been employed to improve the predictive features of the model via an optimization of the five free global model constant of the K − ε turbulence model used to close the equations. The optimized values are very far from the classical values prescribed as general recommendations and implemented in codes, but also different from other data-driven analyses reported in the literature. The re- sults obtained with this new optimized parametric description show a global improvement for both the velocity field and the pressure field. In addition, some topological improvement for the flow organization are observed down- stream, far from the location of the sensors