Evaluation of collapse moment of pressurized 30°–180° bend pipes subjected to out-of-plane bending moment

The present paper determines collapse moments of pressurized 30°–180° pipe bends incorporated with initial geometric imperfection under out-of-plane bending moment. Extensive finite element analyses are carried out considering material as well as geometric nonlinearity. The twice-elastic-slope method is used to determine collapse moment. The results show that initial imperfection produces significant change in collapse moment for unpressurized pipe bends and pipe bends applied to higher internal pressure. The application of internal pressure produces stiffening effect to pipe bends which increases collapse moment up to a certain limit and with further increase in pressure, collapse moment decreases. The bend angle effect on collapse moment reduces with the increase in internal pressure and bend radius. Based on finite element results, collapse moment equations are formed as a function of the pipe bend geometry parameters, initial geometric imperfection, bend angle, and internal pressure for elastic-perfectly plastic material models.

Determination of collapse moment of different angled pipe bends with initial geometric imperfection subjected to in-plane bending moments

From the recent literature, it is revealed that pipe bend geometry deviates from the circular cross-section due to pipe bending process for any bend angle, and this deviation in the cross-section is defined as the initial geometric imperfection. This paper focuses on the determination of collapse moment of different angled pipe bends incorporated with initial geometric imperfection subjected to in-plane closing and opening bending moments. The three-dimensional finite element analysis is accounted for geometric as well as material nonlinearities. Python scripting is implemented for modeling the pipe bends with initial geometry imperfection. The twice-elastic-slope method is adopted to determine the collapse moments. From the results, it is observed that initial imperfection has significant impact on the collapse moment of pipe bends. It can be concluded that the effect of initial imperfection decreases with the decrease in bend angle from 150∘ to 45∘. Based on the finite element results, a simple collapse moment equation is proposed to predict the collapse moment for more accurate cross-section of the different angled pipe bends.

INITIAL GEOMETRIC IMPERFECTIONS AKIBAT TEKUK SINGLE CURVATURE MOMENT PADA BALOK BAJA SEDERHANA

ABSTRACTSteel beams are susceptible to initial geometric imperfections due to improper fabrication and installation processes. Consequently, long steel beams without stiffening are prone to bending due to lateral torsion. The purpose of this study is to determine the effect of variations in the initial geometric imperfections of Single Curvature-Moment (SCM) on the moment, total displacement, displacement in the X direction (U1), displacement in the Y direction (U2), and twist. This study used an RH profile with a compact wing and body. The boundary condition used is a simple beam with an initial geometric imperfection due to single moment-curvature (SCM) bending. The variations used are the initial geometric imperfections values of SCM 0 mm (without initial geometric imperfections), SR5 (with initial geometric imperfections of 5 mm), and SR10 (with initial geometric imperfections of 10 mm). Initial geometric imperfections of SCM in steel beam decreased moment capacities up to more than 2% in elastic conditions and 12% in plastic states. This SR10 beam is also a beam that has a displacement of the X-axis (U1 = -203,960 mm), a displacement of the Y-axis (U2 = -255,615 mm), and the most significant twist (28,179 °).Keywords: buckle, initial geometric imperfections, Single Curvature-MomentABSTRAKBalok baja rentan mengalami initial geometric imperfections akibat proses pabrikasi maupun pemasangan yang kurang tepat. Sementara balok baja yang panjang tanpa pengaku rentan mengalami tekuk akibat torsi lateral. Tujuan dari penelitian ini adalah untuk menentukan dampak variasi besarnya initial geometric imperfections Single Curvature-Moment (SCM) terhadap momen, displacement total, displacement arah X (U1), displacement arah Y (U2), dan twist. Penelitian ini menggunakan profil RH dengan sayap dan badan yang kompak. Boundary condition yang digunakan adalah balok sederhana dengan initial geometric imperfections akibat tekuk single momen curvature (SCM). Variasi yang digunakan adalah besarnya nilai initial geometric imperfections SCM 0 mm (tanpa initial geometric imperfections), SR5 (dengan initial geometric imperfections 5 mm), dan SR10 (dengan initial geometric imperfections 10 mm). Dari hasil penelitian diketahui bahwa pada kondisi elastis, leleh, maupun plastis, balok dengan initial geometric imperfections SCM menunjukkan penurunan kapasistas momen mengalami penurunan hingga mencapai lebih dari 2% pada kondisi elastis dan 12% pada kondisi plastis. Balok SR10 juga merupakan balok yang memiliki displacement arah sumbu X (U1=-203,960 mm), displacement arah sumbuY(U2=-255,615 mm), dan twist yang paling paling besar (28,179°).Kata kunci: tekuk, initial geometric imperfections, Single Curvature Moment

A Method to Estimate Dynamic Buckling Response of an Unstiffened Plate Elastically Restrained Along all Edges Under In-Plane Impact

Unstiffened plates in structures are usually welded or fastened to supporting members, providing rotational restraint stiffness to the plate. Previous studies have shown that neglect of rotational restraint stiffness at the edges of a plate in a structure can introduce deviations in the analysis of dynamic elastic buckling. In this study, the in-plane impact-induced dynamic elastic buckling responses of isotropic imperfect unstiffened plates with four elastically restrained edges are analytically investigated, based on the large-deflection theory of thin plate. The evolution of the peak deflection predicted by the proposed analytical method is found to be consistent with the responses available from the literature. Then the method is further used to estimate the deformation map of an unstiffened plate with four elastically restrained edges, and the effects of rotational restraint stiffness, initial geometric imperfection and shock duration on the dynamic buckling response of the plate are examined. The results show that the critical dynamic buckling load and the maximum deflection response of the plates are significantly influenced by the rotational restraint stiffness as well as the first-order initial geometric imperfection, and thus cannot be neglected in the analysis of dynamic buckling.

Nonlinear Dynamic Behavior of Porous and Imperfect Bernoulli-Euler Functionally Graded Nanobeams Resting on Winkler Elastic Foundation

Nonlinear free vibrations of functionally graded porous Bernoulli–Euler nano-beams resting on an elastic foundation through a stress-driven nonlocal elasticity model are studied taking into account von Kármán type nonlinearity and initial geometric imperfection. By using the Galerkin method, the governing equations are reduced to a nonlinear ordinary differential equation. The closed form analytical solution of the nonlinear natural flexural frequency is then established using the Hamiltonian approach to nonlinear oscillators. Several comparisons with existing models in the literature are performed to validate the accuracy and reliability of the proposed approach. Finally, a numerical investigation is developed in order to analyze the effects of the gradient index coefficient, porosity volume fraction, initial geometric imperfection, and the Winkler elastic foundation coefficient, on the nonlinear flexural vibrations of metal–ceramic FG porous Bernoulli–Euler nano-beams.

Stability of cable-supported spherical reticulated shell with tension members

The suspendome has been widely employed in large-span space structures in recent years, and it has stronger structural stiffness and higher load-carrying capacity than single-layer spherical reticulated shell. In general, it is negligible for enhancement of load-carrying capacity to integrate cables and struts into the inner ring of reticulated shell. Based on the suspendome structure, a new hybrid space structure system, namely, cable-supported reticulated shell with tension member, is proposed in this study. To elucidate and verify its feasibility, the buckling mode and buckling form are obtained by the eigenvalue buckling analysis and nonlinear buckling analysis using ANSYS package, respectively. Furthermore, to determine the optimal structural form, this article investigates the effect of the main ribbed strut length, the initial geometric imperfection, asymmetric load, pretension in cables, and the material nonlinearity on its stability. The result shows that the proposed new structural system is of high load-carrying capacity. Tension member integrated to cable-supported reticulated shell can effectively improve the overall stiffness and greatly reduce the deformation of spherical reticulated shell. The plastic failure shape occurs with the similar pattern. The instable region mainly occurs on the main ribs with tension members, and each main rib only has one local failure dimple. The load-carrying capacity is remarkably affected by the asymmetric load, the initial geometric imperfection, and material nonlinearity. Based on the parametric analyses, Type C is the optimal choice, that is, appending cables and struts to the outermost ring of single-layer spherical reticulated shell, and arranging out-of-plane tension members under the four main ribs.