АНАЛІЗ НАПРУЖЕНО-ДЕФОРМОВАНОГО СТАНУ ФІТИНГОВОГО СТИКУ ПАНЕЛЕЙ ВІД'ЄМНОЇ ЧАСТИНИ КРИЛА ТА ЦЕНТРОПЛАНА ТРАНСПОРТНОГО ЛІТАКА

With the help of 3D modeling software and finite element analysis software, the force distribution of four rows of bolts in the aircraft fitting joint is obtained in this paper. In 3D modeling software, the solid model is segmented according to the area and height of the center of gravity of the cross-section. In finite element analysis software, the beam elements are used to replace the segmented model to obtain the internal force applied at the end of the segmented model and the stress-strain state of each segment is calculated according to the internal force applied at the end of each segment. Finally, the force distribution of the four rows of bolts is obtained according to the average force difference on the center section between the bolt rows. In order to ensure the validity of this step-by-step calculation result, it was compared with the entire calculation result. It can be concluded that the force distribution of the two calculations is consistent. Under the working conditions of the fitting joint (130 MPa), the force distribution coefficients of the four rows of bolts are 0.182, 0.215, 0.197, and 0.12. Therefore, it is feasible to use the step-by-step method to calculate the force distribution of the four rows of bolts in the fitting joint. Compared with the entire calculation, the step-by-step calculation has the advantages of less calculation amount and faster calculation speed.

Bolted connections are the most common method for joining thin-walled galvanized sheets at the site. For this purpose, small-diameter bolts (M8, M10 or M12) and the corresponding nuts are used. According to the standard BDS EN 1993-1-8, only for single-shear joints with one row of bolts, washers should be provided both under the bolt heads and under the nuts. That is, for two or more rows of bolts, it is not necessary to place washers under the bolt head. In connection with a failure of thin-walled steel silos, a test of single-shear connections with two rows of bolts without washers under the nuts was carried out in the laboratory of the University of Architecture, Civil Engineering and Geodesy (UACEG). Their load-bearing capacity turned out to be lower than the theoretically determined one. The initial explanation is that the lack of flat washers under the bolt heads leads to large rotations, and hence to reducing load-bearing capacity. To test this seemingly logical explanation, the authors conducted a series of laboratory and numerical tests on connections with two rows of bolts. The results show that the presence of washers under the bolt head and under the nut affects the load-bearing capacity of this type of connection.

Bolted connections are the most common method of joining thin-walled galvanized sheets on site. Small diameter bolts (M8, M10 or M12) and the corresponding nuts are used for this purpose. Washers should be provided both under the heads of the bolts and the nuts in case of a single shear connection with one row of bolts, according to the standard BDS EN 1993-1-8. I.e. it is unnecessary to place washers under the bolt head in case of two or more rows of bolts. In laboratory tests of bolted connections with two rows of bolts without washers under the nuts, is accounted bearing capacity lower than the theoretically determined one. The initial explanation is that the lack of flat washers results in high bolt rotations and hence reduced load resistance. To verify this seemingly logical explanation, the authors has conducted series of finite element analyses (FEA) on connections with two rows of bolts. It turned out that this was not the reason for the reduced bearing resistance. The presence of washers under the bolt head and the nut had a negligible effect.

This paper presents a model for the determination of the serviceability and ultimate moment capacities of bolted moment end plate connections utilizing rectangular hollow sections and two rows of bolts. One row of bolts is positioned above the top flange, and the other is positioned symmetrically below the bottom flange. The model considers the combined effects of prying action caused by flexible end plates and the formation of yield lines in the end plates. The model is calibrated and validated using experimental data from an associated test program. The design model constitutes a relatively simple method for predicting the serviceability and ultimate moment capacities for the particular type of bolted moment end plate connection described here. An example is given to illustrate how the design model can be applied to practical connection designs.

Flexural behavior of segmental joint containing double rows of bolts: Experiment and simulation

The Songnen grassland is one of the grasslands in China characterized by concentrated heterogeneous patches of saline-alkaline soils. However, our understanding of how these patchy structures develop and how biochemical factors change within patches is limited. Thus, three representative semi-vegetated patches were selected and analyzed for soil electrical conductivity (EC), soil pH, soil organic matter (SOM), and soil nitrogen (N). Based on the different appearance and distribution of species, the patches were divided into a center, middle, and outer section. Our results showed that in contrast to EC, SOM significantly increased from the center to the outer section. Aboveground biomass and species distribution patterns were strongly associated with SOM and contrasted to EC. In the center section, the annual species Kochia scoparia (L.) Schrad represented more than 90% of the total biomass, whereas the perennial species Leymus chinensis (Trin.) Tzvel and Phragmites australis (Cav.) Trin. ex Steud were the most dominant species in the outer section with a contribution of more than 90% to the total biomass. In the middle section, most of the species achieved mutual coexistence and the perennial species appeared to benefit from the interspecific relationships with their neighbors. Our results suggest that a feasible means of restoration management for heterogeneous degraded grassland should be achievable through revegetation by species such as L. chinensis and P. australis, which improve soil organic matter and reduce EC.

According to the EN 1993-1-8 Standard, the moment resistance of end-plated connections can be calculated with the use of the component method. In this, a pair-of-force defines the moment resistance. The magnitude and the location of the compression force can be accurately identified. The tension force part is usually the resultant of parallel forces appearing in line with the bolt rows. Following the rules of manual calculation and using a mechanical finite element model, where each component is modelled with spring elements, in some—easily identifiable—cases, leads to different force distribution. The simplifications defined in the Standard provide a longer arm for the same force, and because of this, larger moment resistance at the expense of safety. In this work, an alternative calculation method will be presented that provides the same force values in each bolt row, as the mechanical model of the connection, without constructing the finite element model.

The results of the study of the influence of the harmonic components of non-circularity and non-cylindricity on the formation of the stress-strain state (SSS) of the surface layers of parts in interference fit joints are presented. It is determined, that in order to increase the reliability of fixed joints of parts in the shape errors of high-precision mounting surfaces, it is necessary to minimize the amplitudes of the harmonic components of the low-frequency range of the 2nd, 3rd and 4th orders and form an isotropic microrelief. Keywords interference fit joints, non-circularity of cross-sectional profiles, harmonic components, non-cylindricity, microtopography, microasperities, stress-strain state, shape deviation spectra. kaf-ts@stu.lipetsk.ru

Prefabricated modular steel (PFMS) construction is a more efficient and safe method of constructing a high-quality building with less waste material and labour dependency than traditional steel construction. It is indeed critical to have a precise and valuable intermodular joining system that allows for efficient load transfer, safe handling, and optimal use of modular units' strength. Thus, the purpose of this study was to develop joints using tension bolts and solid tenons welded into the gusset plate (GP). These joints ensured rigid and secure connectivity in both horizontal and vertical directions for the modular units. Using the three-dimensional (3D) finite element (FE) analysis software ABAQUS, the study investigated the nonlinear lateral structural performance of the joint and two-storey modular steel building (MSB). The solid element FE models of joints were then simplified by introducing connectors and beam elements to enhance computational efficiency. Numerous parameters indicated that column tenons were important in determining the joint's structural performance. Moreover, with a standard deviation (SD) of 0.025, the developed connectors and beam element models accurately predicted the structural behaviour of the joints. As a result of their simplification, these joints demonstrated effective load distribution, seismic performance, and ductility while reducing computational time, effort, and complexity. The validity of the FE analysis was then determined by comparing the results to the thirteen joint bending tests performed in the reference.

Purpose. To substantiate the parameters of formation of elements in the roof-bolting construction and to establish the dependence of displacements of the mine working contour on the technological parameters of mine working driving and supporting for development of the bearing-bolt supporting technology in the conditions of Ukrainian coal mines. Research methods. To study the process of changing the stress state of host rocks around the mine working during the technological cycle of setting of roof bolts, a mathematical elastoplastic model was developed. This model takes into account roof bolts parameters, mining parameters, rock properties, as well as the time and place of the start of roof bolting. The problem was solved using the finite element method. The methods of researching the state of the rock around the mine working with roof bolts, which were developed by the authors, were used during the calculations. Results. The mechanism of formation of a rock-bolt support and a reinforced arch in the mine roof was studied. The conditions and parameters of formation of the following elements in the roof-bolting construction are substantiated: load-bearing and backing-up parts of the arch, supports of the arch, a base of the structure and protective “bridges”. Numerical simulation of the stress-strain state of the host rocks was completed when various elements of the roof-bolting construction were used. Graphs of the relative heaving of the mine work floor were constructed. In order to study the influence of the speed of the mine working advance and the distance between the first row of bolts and the mine working face on the mine working stability, simulations were performed for various technological schemes. The dependence of changes in roof displacements on these technological parameters was obtained: decreasing the distance between the first row of bolts and the mine face and increasing the speed of the mine working advance lead to a decrease in rock displacements and an increase in the stability of the mine working. Scientific novelty. A new method of calculating the parameters of the stress state of the host rock and the roof-bolting construction during the technological cycles of bolts setting was developed. This method takes into account that during each cycle the host rock is unloading from the rock pressure and that the bolts start to work at a certain point in time. Methods of erecting roof-bolting constructions using various elements were developed and confirmed by patents. Practical significance. The use of roof-bolting constructions in 52 mines of Ukraine made it possible to achieve a stable state of mine workings in difficult mining and geological conditions and to obtain a great economic effect due to the reduction of costs for operation and repair of mine workings.

Appraising the methods accounting for 3D tunnelling effects in 2D plane strain FE analysis

The geometries and electronic properties of six polymers based on furo[3,4-b]pyridine-type heterocyclics were studied using density functional theory (DFT) at the B3LYP/6-31G(d) level. Bond lengths, bond critical point (BCP) properties, nucleus-independent chemical shift (NICS), and Wiberg bond indexes (WBIs) are analyzed and correlated with conduction properties. The changes of bond length, BCP properties, NICS, and WBIs all show that the conjugational degree is increased with main chain extension. The changes of NICS also show that the conjugation is stronger in the central section than in the outer section. And the HOMO–LUMO energy gap (Eg) is decreased steadily upon chain elongation. The results suggest that the six polymers all have lower energy gaps (in the range of 0.39–0.58 eV), which indicate that these proposed polymers are good candidates for the conductive materials.

Theoretical analysis on the electronic structures and properties of PPV fused with electron-withdrawing unit: Monomer, oligomer and polymer

The structures and electronic properties of furo[3,4‐b]pyridine‐based alternating donor and acceptor conjugated oligomers, in which furan and pyrrole are used as donors, and their periodic polymers were investigated using density functional theory at the B3LYP/6‐31G(d) level. The bond lengths, bond length alternation, bond critical point (BCP) properties, nucleus‐independent chemical shift (NICS) and Wiberg bond index (WBI) were analyzed and correlated with conduction properties. The changes of bond length, BCP properties, NICS and WBI all show that the degree of conjugation increases with main chain extension. The changes of NICS also show that the conjugation is stronger in the central section than in the outer section. Hydrogen bonding interactions and nitrogen atom substitution in the acceptors play very important roles in the geometries, electronic structures and energy gaps. The theoretical results suggest that pyrrole‐based polymers are good candidates for conducting materials, compared with furan‐based polymers. With an increase of nitrogen atom substitution in the acceptors in these polymers, the intermolecular charge transfers along the polymeric axes are enhanced, and the bond length alternations and HOMO–LUMO energy gap for these polymers are decreased. The results suggest that the six polymers studied all have lower energy gaps (in the range 0.81–1.26 eV), which indicate that these proposed polymers are good candidates for n‐doping conductive materials, especially poly(7‐(furan‐2‐yl)furo[3,4‐e][1,2,4]triazine) and poly(7‐(1H‐pyrrol‐2‐yl)furo[3,4‐e][1,2,4]triazine). Copyright © 2011 Society of Chemical Industry

Shock-free compressible vortex rings impinging on a stationary surface: Effects of surface angle variation