Impact Buckling and Post-Buckling of Elasto-Viscoplastic Cylindrical Shell Under Torsion

The dynamic torsional buckling and post-buckling of elasto-plastic circular cylindrical shell is studied. By the usage of the Bodner-Partom constitutive relation, the present visco-plastic problem is treated as an orthotropic elastic problem. Based on the nonlinear large deflection shell therory, the governing dynamic buckling equation is solved by the Runge-Kutta method, and the critical buckling stress is determined by the B-R criterion. The present paper is mainly focused on the imperfection sensitivity, the strain rate sensitivity, and the dynamic post-buckling characters for the shell loaded dynamically with a constant shear strain rate. Numerical results show that the critical shear stress and imperfection sensitivity will increase with the increase of strain rate. It is found that the elastic buckling stress is more sensitive to imperfection than the visco-plastic buckling. The present research also reveals some dynamic post-buckling characters for the cylindrical shell, and it is shown that the shell will vibrate with the amplitude proportional to the strain rate in elastic buckling but improportional to the strain rate in visco-plastic buckling. An interesting phenomenon is found that when the strain rate is sufficiently high, there is no dynamic visco-plastic buckling occurrence and the shell produces a harmonic oscillation with a very small amplitude.

THE IMPACT TORSIONAL BUCKLING OF ELASTIC CYLINDRICAL SHELLS WITH ARBITRARY FORM IMPERFECTION

A perturbation analysis for the impact torsional buckling of imperfective elastic cylindrical shells subjected to a step torque is given The imperfection is supposed to be small and has arbitrary form. It is shown that only the imperfection which has the shape of static torsional buckling mode could influence the critical step torque. Finally a formula is presented for the critical step torque.

Viscoplastic Torsional Buckling of Cylindrical Shell

The Bodner-Partom constitutive equation is used to study the viscoplastic torsional buckling of perfect cylindrical shell. By treating the viscoplastic shell as an orthotropic shell at each moment and neglecting the inertia term, the critical torque is determined from a set of homogeneous linear equations. The strain rate sensitivity is mainly discussed in the present paper.

STUDIES ON THE TORSIONAL BUCKLING OF ELASTIC CYLINDRICAL SHELLS

The experimental phenomenon and theoretical analysis are given for the torsional buckling of elastic cylindrical shells. From the experiment, it is found that the postbuckling deformation doesn't occupy the whole length when the shell is longer. In the theoretical calculation, only the normal displacement boundary condition is taken into account. By comparing the present calculation results with the accurate result of Yamakis theory and the results of the present experiment, it is shown that the influence of the axial and circumference boundary condition is less important.

An Inelastic Material Model for Lateral Torsional Buckling and Biaxial Bending of Steel W-Shapes

A new material model for beam elements was developed for use as normalized tangent modulus expressions when performing 3-dimensional second-order inelastic analyses of steel I-section beams.The stiffness matrix of a 14 degree-of-freedom beam element was updated to include the effects of yielding on St.Venant’s torsion and bimoment stiffness at the initial and terminal nodes.A validation study compared the new model’s results with those from published detailed finite element analyses and was found to be in very close agreement.A biaxial end-moment study with two different depth-to-flange-width ratios provided expected and consistent results over a range of moment conditions.

Effect of Web Opening on Buckling Instability of Simply Supported Steel I-Beam

The lateral torsional buckling phenomenon often governs design of steel I-beams. Although web opening is often used to accommodate the required mechanical and piping works in buildings, its effect on the buckling instability is not considered in the design codes. In this paper, the effect of web opening on both lateral torsional buckling and local buckling behaviors has been investigated. A simply supported steel I-beam has been studied under uniform bending moment around the major axis. Buckling analysis has been performed using the finite element method. Linear regression analysis has been conducted for output data to formulate an equation for the critical moment including web opening effect. The results have shown a limited reduction in the lateral torsional buckling capacity and a significant reduction in the local buckling capacity.

Model of the Bearing Capacity of Concrete Little Eccentric Compressive Flexural Members Affected by Rebar Corrosion

The assessment for bearing capacity of corroded RC members is one of the main component of durability study on RC structure. But few researches had been developed for the study of corroded RC eccentric especially little eccentric compressive members. By discussing the effect of factors, such as decrease of concrete strength in biaxial stress condition during pre-cracking stage and torsion buckling of local cracking concrete during post-cracking stage, on the bearing capacity of little eccentric RC members, the model of bearing capacity is established respectively, which the cracking damage coefficient of concrete k is suggested to be 0.15 in post-cracking stage. The experimental certification shows: model calculation fits well with experimental result, which proves the effectiveness of the model in this paper.

Evaluation of the remaining lateral torsional buckling capacity in corroded steel members

Corrosion is one of the main causes of deterioration in steel structures. Loss of thickness in flanges and web of corroded steel beams leads to reduction in section properties which can reduce the lateral torsional buckling capacity of the member. In this paper, thickness loss data were compiled from four samples of corrosion damaged I-beams removed from a petro-chemical plant. Visual examination of the four corroded beams showed that they were corroded uniformly. To improve the accuracy of the results, a large number of measurements for surface roughness were taken for each beam, totally 770 values to obtain the average thickness of flanges and web of each beam. The data was used to develop a corrosion decay model in order to calculate the percentage remaining lateral torsional buckling capacity of long and short span beams which are laterally unrestrained. To estimate the percentage of remaining lateral torsional buckling capacity in the corroded damaged I-beams, the readily available minimum curves for different types of universal beams in conjunction with information on the thickness loss were used. The results can be used by practicing engineers for better estimation on the service life of deteriorated steel structures.

AN IMPROVED M-C METHOD AND ITS APPLICATION TO STRUCTURAL RELIABILITY

An improved Monte-Carlo method for the failure calculation of structure is proposed.The present method can determine whether some sample points are in the safe region without doing structural analysis,so the calculation work is greatly reduced compared with the ordinary M-C method.Finally,the new M-C method is applied to reliability analysis of frame and the torsional buckling reliability analysis of cylindrical shells.