An improved ISUM rectangular plate element taking account of post-ultimate strength behavior

Marine and offshore structures are subjected to dynamic loads during the lifetime. The values or directions of dynamic loads rapidly change in time, causing a significant rise of inertial forces in structural elements. Dynamic loads appear as result of ship’s movement at sea, wind and wave acting, machinery operation, hull vibration and sometimes even as result of collision or explosion. The corresponding dynamic forces and moments act on the ship hull provoking the appearance of stresses, often leading to buckling, plastic deformations or fatigue cracks of the structural members. To ensure the safety and reliability of structures under dynamic loading it is necessary to estimate the transient effects on the collapse behavior of plate panels. According to the Common Structural Rules (CSR) the safety of marine structures must be proved performing the hull girder ultimate strength check. As a possible tool for the ultimate strength analysis, the Finite Element Method (FEM) is widely spread among engineers. In spite of the great effectiveness, the transient Finite Element Analysis (FEA) remains very time consuming and sometimes difficult to accomplish well. Therefore, the formulation of the Idealized Structural Unit Method (ISUM) is extended for the dynamic collapse analysis of marine structures.

Dynamic ultimate strength analysis of stiffened plate based on Idealized Structural Unit Method

Aging effect for the ultimate strength of offshore structure is studied in this paper. A frame model of offshore structure is used, which is simplified from an actual offshore structure of jacket type. As an aging effect, corrosion due to wave, wind, current, tide, etc is considered. The history of collapse and the ultimate strength of the frame model are analyzed by using the idealized structural unit method (ISUM), for the concentrated load such as collision by a ship or an iceberg, changing the angle of collision. The analyses are performed for the initial state in which the pipe members of the frame model have the original sizes, and for the deteriorated condition in which the members are corroded and their thicknesses are reduced.The collapse behaviors (collapse modes) and the characteristics are clarified for the above various conditions. They are different depending on the angle of the collision even if the location of collision is the same. They change with the reduction of thickness of the members due to corrosion. The ultimate strength decreases proportionally to the reduction of strength of the member which is the cause of the collapse of the model, if the collapse mode does not change. But, it is possible that the ultimate strength decreased largely, if the collapse mode changes due to corrosion. The reduction of strength of the member is almost proportional to the reduction of thickness of the member. The maximum and minimum ultimate strengths of the frame model after corrosion can be estimated, using the maximum and the minimum of the ratio of reduced thickness to the original thickness of all the members in the frame model.The next second report, the frame model very close to an actual offshore structure of jacket type will be used to verify widely the characteristics and the estimating method of the ultimate strength obtained in this study.

It has been well known that exact closed-form solutions are not available for non-Levy-type plates. Thus, more accurate and efficient computational methods have been required for the plates subjected to arbitrary boundary conditions. This paper presents a frequency-domain spectral element model for the rectangular finite plate element. The spectral element model is developed by using two methods in combination: (1) the boundary splitting and (2) the super spectral element method in which the Kantorovich method-based finite strip element method and the frequency-domain waveguide method are utilized. The present spectral element model has nodes on four edges of the finite plate element, but no nodes inside. This can reduce the total number of degrees of freedom a lot to improve the computational efficiency significantly, when compared with the standard finite element method (FEM). The high solution accuracy and computational efficiency of the present spectral element model are evaluated by the comparison with exact solutions and the solutions by the standard FEM.

Ultimate strength characteristics and assessment of laser-welded web-core sandwich plates under combined biaxial compression and lateral pressure

Reinforced concrete slabs supported on columns fail by punching when a conical plug of concrete perforates the slab above the column. This failure has been mostly investigated experimentally, so what can numerical simulation contribute to understand this phenomenon? To answer this question, a computational simulation tool based on the finite element method is developed. This numerical model is implemented into a computer code in applying the object-oriented programming concept. The requirements that the numerical model should fulfill are derived from a review of the experimental results published in the literature and obtained in our laboratory. The numerical model reproduces the non-linear material behavior characterizing reinforced concrete structures by decoupling the actions of steel reinforcement and concrete. The steel reinforcement is represented by uniaxial truss elements which follow a bi-linear stress-strain response. The concrete is modeled with continuum elements which are described at the constitutive level within the framework of the incremental flow theory of plasticity. The concrete triaxial strength is delimitated with a new failure criterion. A plastic flow rule is derived so as to reproduce the evolution of the plastic strain observed experimentally. Cracking induces strain-softening which refers to a gradual decrease in tensile strength with increasing deformations. The reduction of the tensile strength is controlled by an isotropic decohesion process which is monitored by constant fracture energy. The stiffness degradation due to cracking is reproduced with an isotropic elastic damage model. A perfect bond between concrete and steel is assumed. The capabilities of the numerical model are illustrated by simulating the localized shear failure in soil under a footing, the uniaxial tensile, and the confined compressive tests in plain and reinforced concrete specimens. The simulation of punching failure is investigated for three circular reinforced concrete slabs. The comparison with experimental results indicates that: (1) the punching failure mechanism –characterized by a localized inclined punching crack– is generated, (2) the value of the punching load is predicted, (3) the cracking sequence is reproduced, (4) the global response is slightly too stiff. For slabs with orthogonal reinforcement, the perfect bond hypothesis does not allow to capture the punching failure mechanism and the numerical model is improved by relaxing this hypothesis. The developed computational simulation tool reproduces the punching failure observed experimentally and is consequently used to investigate the failure mechanism. First, it is shown that the punching crack results from a crack coalescence phenomenon at the top of the slab followed by a crack propagation in the direction of the corner slab-column. Second, a condition for punching failure to occur is determined. Third, it is illustrated that the size-effect observed experimentally is reproduced and is reflected by a modification of the tensile stress distribution along the punching crack. Finally, a parametric study of the punching failure is performed revealing that punching failure is governed by the tensile strength of concrete. It is also shown that increasing the percentage of reinforcement raises the punching load and reduces the ductility of failure. Lastly, the computational simulation tool allows to demonstrate that in a circular slab, the applied bending moment is not determinant for the value of the punching load.

A simplified geometric stiffness in stability analysis of thin-walled structures by the finite element method

In this research, we explore the rectangular plate element employing Kirchhoff Theory, specifically focusing on a strain-based approach to examine linear static and free vibration behaviors under a range of boundary conditions. This element has demonstrated its efficiency in linear analysis, producing results that align closely with the analytical solutions. The primary aim of this study is to extend the application of this element to assess both static and free vibration responses under various and complex boundary conditions. Practical applications include isotropic plates with diverse boundary conditions and specific scenarios such as rectangular plates that are point-supported at a corner and clamped or simply supported at opposite edges. These examples demonstrate the real-world applicability of the findings, underscoring their relevance for engineering and design purposes. Our findings indicate that the results obtained from the current element closely approximate both analytical and exact solutions, with minimal differences in deflection values at various points along the plate. The present element method exhibits superior accuracy, computational efficiency, versatility in handling complex boundary conditions, and consistency across different sections of the plate. The results obtained from the current element show excellent convergence with analytical solutions and the Finite Element Method (FEM), even with significantly fewer mesh elements.

The finite element techniques is used for the forced vibration analysis of horizontally curved box girder bridges. Annular plates and cylindrical shell elements are used to discretize the slab, bottom flanges, and webs. Rectangular plate elements and pin-jointed bar elements are used for discretization of diaphragms. A vehicle, as the applied time varying forcing function, is simulated by two sets of concentrated forces, having components in the radial and transverse directions and moving with constant angular velocities on circumferential paths of the bridge. The effect of centrifugal forces is considered and the effect of damping of the bridge is neglected in the analysis. The mass condensation technique is used to reduce the number of coupled differential equations obtained from the finite element method. The resulting differential equations are solved by the linear acceleration method. A number of bridges with practical geometries are analyzed and impact factors are calcualted. /Author/

Since roro passenger ships have specific characteristics in handling cargo with the roll-on-roll-off loading and unloading system that must be equipped with a ramp door. Therefore, it is important to conduct the ultimate strength analysis by considering local loads and global loads to ensure the level of safety and reliability of the ship structure. The aim of this research is focused on the investigation of the structural response and the ultimate strength of the roro passenger ship using the non-linear finite element method. The dynamic explicit method is conducted to estimate the large displacement of the deformed structures such as the hull girders, deck girders and plates. In the structural response analysis, the results shows that maximum stress was occurred on the deck girders due to the sagging bending moment load. In the ultimate strength analysis, it is identified that hydrostatic load have reduced the ultimate strength about 33 %. Otherwise, the ultimate strength is increased about 1 %, in the sagging condition.
 HIGHLIGHTS
 
 The nonlinear behavior of the roro passenger ship ultimate strength due to the combined global and local load is presented
 On the hogging condition, the addition of local load (hydrostatic pressure) reduce the roro ship ultimate strength about 33 % compare to the pure global ultimate bending load
 On the sagging condition, the hydrostatic pressure have slightly increased the ultimate strength around 1 %
 
 GRAPHICAL ABSTRACT

Mechanical response analysis of asphalt microstructure under tensile and compressive loading based on finite element methods

The effect of elevated temperatures on the mechanical properties of laminated bamboo

Experimental investigation on the mechanical behaviour of air-entrained concrete under uniaxial compression, uniaxial tension, biaxial compression, biaxial tension–compression (T–C) and triaxial tension–compression–compression (T–C–C) loading conditions was carried out. The biaxial compression stress ratios α2=σ2/σ3=0·25, 0·5, 0·75, 1·0, biaxial tension–compression stress ratios α1 = σ1/σ3 = −0·05, −0·1, −0·3, −0·5 and triaxial tension–compression–compression stress ratios α=σ1:σ2:σ3= − 0·25:0·25: 1·0, − 0·25: 0·5:1·0, − 0·25:0·75:1·0, − 0·25:1·0:1·0 were selected as the major test variables. The failure characteristic of specimens and the direction of the crack are observed. Based on the test data, the biaxial ultimate strength envelopes and the failure criterion under triaxial T–C–C in principal stress space were proposed. The test results indicated that the strength of air-entrained concrete specimens under biaxial compression is higher than that under uniaxial compression and the maximum increase of ultimate strength occurred at a biaxial compression stress ratio of 0·5. The relationship between the ultimate compressive strength and stress ratio was given. It provides the experimental and theory foundations for strength analysis of air-entrained concrete structures.

In this study, the effect of wood powder and nanoclay particle content on composites’ mechanical behavior made with polyethylene matrix has been investigated. The wood flour as a reinforcer made of wood powder was at levels of 30, 40, and 50 wt.%, and additional reinforcement with nanoclay at 0, 1, 3, and 5 wt.%. Furthermore, to make a composite matrix, high-density polyethylene was used at levels of 70, 60, and 50% by weight. Wood-plastic composite (WPC) specimens were manufactured in injection molding. After preparing the specimens, tensile and bending tests were performed on samples. The mechanical properties such as tensile and flexural strength and flexural modulus were measured. Results showed that nanoclay particle content increases flexural modulus, flexural strength, modulus of elasticity, and tensile strength. The experimental test results show that Young’s moduli increased with the volume of wood flour. The biggest modulus of elasticity was achieved in the samples having 50 wt.% of wood powder. Furthermore, the highest value of tensile strength was achieved at the level of 30 wt.%. The highest flexural strength was for the sample containing 50% wood powder by weight. Additionally, a numerical model was made utilizing the Abaqus software using the finite element method (FEM). Comparing the numerical and experimental results, it was found that they are compatible in the linear-elastic and plastic state of the material. There are no crucial differences between experiment and FEM.

Assessment of the ultimate strength of stiffened panels of ships considering uncertainties in geometrical aspects: Finite element approach and simplified formula