Influence of welding sequence on the mechanical properties of a latticed shell formed by orthogonal and oblique members

With the development of economy and the improvement of people’s aesthetic level, large-span latticed shells are increasingly used. Such structures are commonly large in volume and huge in welding. In order to select an optimum welding sequence and avoid correcting complex welding deformation, a latticed shell formed by orthogonal and oblique members was taken as the research object in this paper. The finite element models of single and whole latticed shells were established respectively, and according to the equal deformation principle, the influence of different welding sequence on the deformation and internal force of the structure in each construction stage was quantitatively analyzed. The results show that in the welding and assembling stage of small assembling units in the single latticed shell, welding sequence has the greatest impact on the longitudinal deformation, and the change rate of the longitudinal deformation is up to 83.63%; whereas in the tension, sliding and closure stages of each piece of the latticed shell, the transverse deformation is most affected by welding sequence, and the change rate is 33.05%; in different construction stages, the axial stress of the latticed shell is less vulnerable to welding sequence. Furthermore, it is feasible to control the welding shrinkage deformation by selecting a reasonable welding sequence, and the symmetrical welding sequence from both ends to the middle should be adopted during construction.

Operational control of rib pillar stability

In room-and-pillar mineral mining, rib pillars should support overlying rock mass for the specified time limit of production. Therefore, one of the mining safety components is monitoring of the behavior of rib pillars in the course of time. For the conditions of the room-andpillar method of mining, the authors propose a monitoring procedure for rib pillar deformation based on operational measurements of horizontal convergence in stopes. The theoretical and experimental research proves that transverse deformation of rib pillars is an informative parameter suitable for generalized assessment of pillar failure. The obtained ranges of critical transverse deformation rates (50–100 mm/m/yr) in rib pillars can tentatively be used as an indicator of the critical stability of load-bearing structures in room-and-pillar mining. In-situ determination of the integral transverse deformation rates in rib pillars is based on the ratio of the measured horizontal convergence in stopes to the width of pillars. Implementation of the proposed approach in the Upper Kama potash salt mines has proved its applicability to identification of rock mass areas where intense deformation is expected. The comparison of the monitoring data of the transverse deformation rates and their critical values determined makes it possible to predict service life of rib pillars, which is very important in terms of safety of mining operations. This study was supported by the Russian Science Foundation, Grant No. 19-77-30008.

An Improved Approach to Direct Simulation of an Actual Almen Shot Peening Intensity Test with a Large Number of Shots

In existing simulations of the Almen intensity test, arc height is indirectly obtained by an equivalent method including a representative cell, a few shots and equivalent loading. Most of these equivalent methods cannot consider the transverse deformation of the strip, the complex stress state of the plastic hardening layer and process parameters, resulting in deviation from the actual test. This paper introduces an improved and experimentally validated discrete element model (DEM)-finite element model (FEM) to predict the actual Almen intensity. The improvement of this model is mainly reflected in the large and real number of shots involved in the actual Almen intensity test, shot–shot interactions, and real-size solid finite element model of the Almen strip. A new method for calculating the shot stream is proposed based on the test and considering test process parameters such as the mass flowrate, nozzle movement speed and nozzle–workpiece distance. The shot stream impacting the strip with a fully restrained underside was first simulated in improved DEM-FEM to bring the forming energy. As a second step, an implicit solver of the Almen strip FEM calculates the spring-back to simulate strip removal from the holder. The results achieved by the present approach are compared with the results obtained by the experimental results and those in the literature. The results show that the arc height and Almen intensity obtained by the present approach match much better with the literature than the traditional method. Some new results obtained by the improved coupling DEM-FEM method are presented. The influences of the transverse deformation and surface plastic layer on the deformation of the Almen strip are discussed. This improved method provides an alternative characterization method for precision peen forming simulation.

ПОЛНЫЕ ДИАГРАММЫ РАЗВИТИЯ ДЕСТРУКЦИЙ ОДНОРОДНО И НЕОДНОРОДНО СЖАТОГО БЕТОНА ПРИ ОСЕВОМ И ВНЕЦЕНТРЕННОМ НАГРУЖЕНИИ БЕТОННЫХ КОРОТКИХ КОЛОНН

В статье приведены результаты выполненных исследований механизма интенсивности развития деструкций, псевдопластического деформирования и разрушения однородно и неоднородно сжатого тяжелого бетона призменной прочностью в диапазоне fc1522,265,6 МПа при мягком и жестком режиме нагружения одноосно и внецентренно сжатых бетонных колонн. Выполнен анализ литературных источников с исследованиями изменения упруго-пластических характеристик vc, Еcsek тяжелого бетона с учетом влияния значимых факторов и их изменение с увеличением уровня нагрузки при описании зависимости c-cх и c,е - cх,е. Установлено, что рекомендованные Строительными Нормами vcи и Ес одноосно сжатого бетона количественно и качественно не отражают характер изменения упруго-пластических свойств неоднородно сжатого бетона с ростом уровня нагрузки. Предложены аналитические выражения зависимости изменения коэффициентов упругости (vc, vc,е), секущих модулей упругости (Еcsek, Еc,еsek) и коэффициентов интенсивности развития деструкций (KD, KD,е) однородно и неоднородно сжатого бетона с ростом уровня нагрузки при мягком и жестком режиме нагружения исследованных серий тяжелого бетона с использованием сlx сlx,е Ес Nc,e/Ncu,e сu и сu,е, отражающих процесс изменения упруго-пластических свойств бетона на восходящих и нисходящих участках полных диаграмм деформирования бетона и их существенное отличие при центральном и внецентренном сжатии. Исследованиями отмечено, что интенсивность развития деструкций в структуре неоднородно нагруженного бетона существенно ниже, чем в одноосно сжатом. Экспериментами установлено характерное изменение по высоте сечения внецентренно сжатых бетонных элементов коэффициента поперечных деформаций , свидетельствующее о том, что с увеличением уровня нагрузки коэффициент наиболее сжатой фибры на всех уровнях нагрузки, значительно (в 1,21,5 раза) меньше волокон менее нагруженных фибр. Отмеченное свойство обусловлено изменением внутреннего напряженного состояния с ростом нагрузки и перераспределением напряжений силовыми связями структуры неоднородно сжатого бетона с субмикро- и микроуровней волокон наиболее нагруженной грани по высоте сечения внецентренно сжатых элементов на менее нагруженные волокна. Этот процесс перераспределения напряжений по высоте сечения бетонных колонн как свойство проявляется на изменении поперечной деформации cу,е и, как следствие изменения коэффициента поперечной деформации , влияющего на напряженное состояние сжатой зоны подобно внутренним силовым связям, обеспечивающим существенное повышение максимальных напряжений и деформаций в неоднородно сжатом бетоне.The article presents the results of studies of the intensity of development of destructions, pseudoplastic deformation and destruction of uniformly and non-uniformly compressed heavy concrete with prism strength in the range of fc1522,265,6 MPa in the soft and hard loading mode of uniaxially and eccentrically compressed concrete columns. The analysis of literary sources with studies of changes in the elastic-plastic characteristics of vc, Еcsek heavy concrete, taking into account the influence of significant factors and their change with increasing load level when describing the dependence c-cх and c,е - cх,е . It has been established that the vcu and Ес recommended by the Building Norms of uniaxially compressed concrete do not quantitatively and qualitatively reflect the nature of the change in the elastic-plastic properties of non-uniformly compressed concrete with increasing load levels. Analytical expressions are proposed for the dependence of the change in elasticity coefficients (vc, vc,е), cross-section elastic modulus (Еcsek, Еc,еsek) and the intensity factors for the development of destructions (KD, KD,е) of uniformly and non-uniformly compressed concrete and hard loading mode of the studied series of heavy concrete using: сlx сlx,е Ес Nc,e/Ncu,e сu and сu,е , reflecting the process of changing the elastic-plastic properties of concrete in the ascending and descending parts of the complete concrete deformation diagrams and their significant difference under uniaxial and eccentrically compression. Studies have noted that the intensity of the development of destructions in the structure of non-uniformly loaded concrete is significantly lower than in uniaxially compressed. Experiments established a characteristic change in the height of the cross section of eccentrically compressed concrete elements of the transverse strain coefficient , indicating that with an increase in the load level, the coefficient of the most compressed fiber at all load levels is significant (1,2-1,5 times) less fibers, less loaded fibers. This property is caused by the change in the internal stress state with increasing load and stress redistribution by force bonds of the structure in non-uniformly compressed concrete from submicro- and microlevels of the fibers of the most loaded face along the height of the cross section of eccentrically compressed elements to less loaded fibers. This process of stress redistribution along the height of the cross section of concrete columns as a property manifests itself in a change in transverse deformation cу,е and, as a result, a change in the transverse deformation coefficient , affecting the stress state of the compressed zone, similar to internal force connections, providing a significant increase in maximum stresses and strains in non-uniformly compressed concrete.

Mechanical Characteristics of Fully Grouted and Antiseismic Bolts considering Transverse Deformation in Underground Caverns

The load transfer control equations under bolt-surrounding rock interaction are established on the basis of classical beam theory and the trilinear shear slip model. The axial stress and transverse shear force distributions of the anchorage body are obtained by solving the equations. The equivalent forces obtained by the transverse force and axial shear stress of the bolts are applied to rock mass elements to simulate the support effect. A new dynamic algorithm for bolts is proposed in considering of the axial and transverse deformation of the anchorage body. The rationality of the algorithm is verified by comparing with laboratory pullout and shear tests of bolts. A dynamic time-history case study of underground caverns is conducted using this algorithm. Results indicate that (1) the algorithm may reflect the stress and deformation characteristics of bolts during an earthquake; (2) for the antiseismic support effect of the surrounding rock at fault, the bolt algorithm in this study is more valid than the algorithm that considered only the axial deformation of bolts; (3) in the support force of the bolt to the surrounding rock, transverse force is the key to limit fault dislocation and reduce the dynamic damage of the rock at fault.