Istraživanje ponašanja adhezionih spojeva metalnih konstrukcija pod dejstvom statičkog i cikličnog opterećenja

Adhesive joints offer many advantages compared to the traditional joining techniques in metallic structures. However, the lack of unified design standards and procedures limit their wider use in civil engineering industry. For the purpose of standardization, extensive experimental work has to be done on investigating their behavior under the service conditions. Besides the influence of the joint geometry, the manufacturing process and the temperature and humidity effects, type of the loading has the greatest influence on the behavior of adhesive joints. Main goal of this dissertation was to investigate behavior of adhesive joints in metallic structures under static and cyclic loading, using modern experimental and numerical methods. In order to achieve this the selection of proper adherent surface preparation procedure was necessary. Experimental investigation of the behavior of adhesive joints subjected to static and cyclic loading was conducted on two types of adhesive joints: galvanized steel façade joint and double lap shear joint. Based on the results of the experimental investigation, as well as the results from the literature, new models and methods were developed for modeling of the behavior and predicting the fatigue life of adhesive joints subjected to static and cyclic loading

Numerical Modelling of Y Joints of Trusses Made of Steel Hollow Sections

The use of welded structural hollow sections in civil engineering is relatively new. Constructing and dimensioning joints of steel trusses made of welded structural hollow sections requires a more specified approach, compared to traditional joints, achieved by gusset plates. Stress and local deformations at the contact between elements are non-linear and very complex. In this paper, the FEM modelling of the Y-joint was performed, accounting for the non-linear behaviour of steel. The ultimate bearing capacities of the joint were determined numerically, by applying different failure criteria. The results showed very good agreement with the experimental data

Global Analysis of Steel Constructions with Semi-Rigid Connections

In this paper, original extension of classic deformation method for global elastic analysis of steel construction with semi-rigid connections is developed. The original calculation for steel frame structures with semi-rigid connections as a function of rotational rigidity of connection, a realistic parameter for determination of both tension and deformation fields of connection as well as entire construction, has been derived in detail. Due to its generality, simplicity and straight-forward calculation, the method developed in this paper is convenient for both computational utilization and hand calculations. For introduced rotational rigidity of realistic connections, the expressions for determination of bending moments at ends of semi-rigidly connected elements have been derived as well as conditional equations for determination of deformation-unspecified values at static load by first-order theory. The obtained results are illustrated in detail on a numerical example. Their comparison with the results of FEM analysis was provided

Influence of used waste cathode ray tube glass on alkali silicate reaction and mechanical properties of mortar mixtures

Rapid transition of electronic device manufacturing industry has led towards the increase of glass waste quantities, which are still being speculated. This resulted in increasing research on the use of waste glass in many different industries. In this study, the impact of using grounded waste cathode ray tube (CRT) glass as aggregate replacement (AR) on the alkali-silica reaction (ASR), mechanical properties and structure and microscopy of mortar were examined and reported. Crushed waste CRT aggregate was used to replace natural limestone aggregate of 0, 25, 50, 75 and 100% in mortar bars. ASR expansion values of mortar with added waste glass were investigated and tested for observation period according to Ultra-accelerated mortar-bar test. The results showed that the increase of AR percentage resulted in higher susceptibility to ASR. Mechanical properties and microscopy of mortar mixtures showed the potential of using waste CRT glass, due to the small difference between tested mixtures

A Comparison of the Capacities of ZnMn2O4 and ZnCr0.15Mn1.85O4 in Aqueous Media

To protect the environment from potentially hazardous components from commercial Li-ion batteries (i.e., contain toxic and flammable electrolytes as well as Li is uneconomical and a rare earth metal), a viable alternative need to be found for the components of these batteries. Thus, our focus is on replacement of an organic electrolyte using an aqueous one. Additionally, the work also examines the replacement of Li with Zn as production of Zn-based cathode material is more economical compared to Li and less toxic. Due to occurrence of the Ian Teller effect in ZnMn2O4, Mn3+ ions are partially replaced with Cr3+ ions to diminish this phenomenon and to obtain a higher capacity. Namely, due to the Ian-Teller distortion, not all cations of Zn2+ ions may intercalate in the crystal lattice sites. When the Ian-Teller effect lowers, more Zn2+ ions may intercalate into sites; thus, a higher capacity may be obtained. The materials ZnMn2O4 and ZnCr0.15Mn1.85O4 were synthesized by glycine nitrate combustion method. The materials were characterized by XRPD, SEM, EDS and cyclic voltammetry. The aqueous solutions of ZnCl2 were used as electrolytes as potentially more ecological alternatives compared to the organic ones already commercially used. The cathode capacities obtained for the ZnMn2O4 under 5 mV s-1 and 20 mV s-1 ranged from 17.7 mA h g-1 to 6.9 mA h g-1. The cathode capacities obtained for ZnCr0.15Mn1.85O4 under 5mV s-1 and 20 mV s-1 ranged from 86.3 mA h g-1 and 24.6 mA h g-1, respectively. Over the intercalation and deintercalation process of the Zn2+ ions into the ZnCr0.15Mn1.85O4, a release of oxygen occurred. The stable capacity obtained for both rates (5 mV s-1 and 20 mV s-1) indicates that the ZnCr0.15Mn1.85O4 material is applicable for both rates used. Further examination of the ZnMn2O4 material must be conducted in terms of increasing the capacity through its doping with other ions or its use in an aqueous solution of other salts

New stress-strain model for concrete at high temperatures

Beton je jedan od najrasprostranjenijih materijala koji se koriste za izradu građevinskih objekata. Djelovanje visokih temperatura može ozbiljno oštetiti strukturu betona, što dovodi do degradacije njegovih mehaničkih karakteristika. Razmatranje glavnih karakteristika ponašanja građevinskih konstrukcija pri visokim temperaturama je povezano s djelovanjem požara, pri kojima se javljaju temperature u betonu i do 1000 °C. Za uporabu računarskih softvera za analizu armirano betonskih elemenata izloženih požarima neophodno je formulirati konstitutivne σ-ε modele kako čelika tako i betona, što se može postići fundamentalnim pristupom, ali i prilagodba krivulja prema eksperimentalno dobivenim podacima. U ovom radu predložen je novi dvoparametarski model za opisivanje krivulje naprezanje-deformacija. Novi model je potvrđen na eksperimentalnim podacima dostupnim u literaturi za temperature do 800 °C. Dana je njegova usporedba s drugim modelima dostupnim u literaturi. Rezultati pokazuju bolje poklapanje s eksperimentalnim podacima, posebice pri temperaturama većim od 500 °C.Concrete is one of the most widely used materials in civil engineering structures. Extremely high temperatures can seriously damage the concrete structure, leading to degradation of its mechanical properties. Considering high temperatures in civil engineering applications is strongly connected with the fire scenarios in which temperatures in concrete can reach 1000 °C. For using computer software for analysis of the reinforced concrete structures, it is essential to formulate constitutive stress-strain models of steel and concrete, which can be done using fundamental approach or by fitting curves to experimental data. In this paper, new stress-strain model was proposed using the two-parameter equation for fitting curves to experimental data. Verification of the model is done using experimental results available in the literature for temperatures up to 800 °C. Comparison with the models available in the literature was provided. The new model showed better agreement with experimental results, especially for the temperatures higher than 500 °C

Clinical and laboratory features in different immunologic type of multiple myeloma

Introduction: Multiple myeloma (MM) is a malignant blood disease, characterized by clonal proliferation of malignant plasma cells in the bone marrow and clinical manifestation of a disease that is heterogeneous and it's stratified by an internationally recognized Durie-Salmon classification (DS). Aim: The aim of this study was to determine whether the immune type of multiple myeloma affects the clinical and laboratory characteristics of the disease. Material and methods: The study included 45 newly diagnosed patients with MM (25 men and 20 women), the average age of 62.21 ± 8.62 years. A comparative analysis was performed between the class of M - protein and the mean value of the parameters contained in the DS classification. Results: The most common immune type was IgG MM. Considering gender, age, serum albumin values, total proteins, LDH, hemoglobin, beta 2 - MG, radiographic findings (number of osteolysis) and DS stages, there was no statistically significant difference in relation to individual immunological types MM. The IgD type was associated with a higher incidence of hypercalcemia than IgG and IgA type (p < 0.01) and with a higher incidence of renal insufficiency, compared to IgA MM (p < 0.01) and IgG MM (p < 0.05). Conclusion: Our findings exclude the association of Ig type of multiple myeloma with individual biochemical parameters, except for the increased incidence of hypercalcemia and renal insufficiency in IgD MM, which corresponds to literature data

Raspberry as a potential commodity exchange material in the Republic of Serbia

Commodity exchange has a very long tradition and in a modern business conditions. Serbia ranks among the world's largest producers of raspberries, exporting more than 90% of total production of this fruit. Considering that Serbia is among global leaders in the export of frozen raspberries and that the process of standardization of the quality and quantity of this type of fruit is relatively simple, the starting hypothesis is that Serbian raspberry can be traded at commodity exchange. The main objective of our research is to analyze the necessary conditions for formation and sustainable functioning of the raspberry commodity exchange, with the emphasis on testing the proposed model of the commodity exchange method of communication between primary raspberry producers (vendors), intermediaries (purchasers, raspberry dealers or exporters of raspberries) and end customers who buy raspberries. We surveyed 100 persons representing the key actors of the Serbian raspberry producers and proposed the model of raspberry trading through commodity exchange.Publishe

ZnMn2O4 as a Cathode Material in an Aqueous Solution of ZnCl2 and Mn(NO3)2 for Zn-ion Batteries

Due to Li-ion batteries having become the main power source of most portable electronic devices, their waste has also become a significant environmental problem. To find batteries that would be environmentally friendly, this work examines Zn-ion batteries in an aqueous solution of ZnCl2. The ZnMnO4 was synthesized by glycine nitrate combustion of Zn(NO3)2, Mn(NO3)2 and glycine as a chelating agent [1]. The structure of the material obtained was characterized by X-ray powder diffraction (XRPD) showing a spinel structure; the morphology was characterized by scanning electron microscopy (SEM) showing that nano-particles were obtained. The electrochemical characterization was done by cyclic voltammetry in an aqueous solution of ZnCl2. The mixture pasted on the glossy carbon electrode was prepared by mixing the cathode material, graphite and polyvinyl diene difluoride (PVDF) in a ratio 85:10:5 [2]. Due to the low discharge capacity obtained of ~14 mAh g-1 for 5 mV s-1 , further examination was done by adding 1 ml of 1M Mn(NO3)2 into 10ml of a saturated aqueous solution of ZnCl2. After adding the Mn(NO3)2 , the discharge capacity increased from ~14 mAh g-1 to ~65 mAh g-1 at the same polarization rate, making this additive a promising one for aqueous Zn-ion batteries. Further investigation needs to be directed to adding the same additive in larger amounts compared to 1ml to the same volume of the electrolyte. The results obtained suggest the aqueous Zn-ion battery described in this work to be a potentially promising “green” battery that may replace harmful commercial organic Li-ion batteries