Yoshimi Sonoda

A stabilized incompressible SPH method by relaxing the density invariance condition

A stabilized Incompressible Smoothed Particle Hydrodynamics (ISPH) is proposed to simulate free surface flow problems. In the ISPH, pressure is evaluated by solving pressure Poisson equation using a semi-implicit algorithm based on the projection method. Even if the pressure is evaluated implicitly, the unrealistic pressure fluctuations cannot be eliminated. In order to overcome this problem, there are several improvements. One is small compressibility approach, and the other is introduction of two kinds of pressure Poisson equation related to velocity divergence-free and density invariance conditions, respectively. In this paper, a stabilized formulation, which was originally proposed in the framework of Moving Particle Semi-implicit (MPS) method, is applied to ISPH in order to relax the density invariance condition. This formulation leads to a new pressure Poisson equation with a relaxation coefficient, which can be estimated by a preanalysis calculation. The efficiency of the proposed formulation is tested by a couple of numerical examples of dam-breaking problem, and its effects are discussed by using several resolution models with different particle initial distances. Also, the effect of eddy viscosity is briefly discussed in this paper.

Present status and future problems on the impact resistance performance design of civil engineering protective structures

There are many civil engineering structures that have different systems and required functions. Their design methods do not have consistent design concepts. Thus, it has been pointed out the necessity of universal concepts on assumed external actions and risk for various structures and on the required level of safety. In order to meet those demands, a research committee as part of Japan Society of Civil Engineers summarizing the basic concepts of impact resistance design. This paper introduces several design methods of structures subjected to impact loads, and presents the current status and remaining issues of establishing new performance-based design methods.

Evaluation of Cumulative Damage of RC Members under Repeated Impact Loading

In the civil and structural engineering field, there are so many problems regarding act of impact loading against some structures due to natural disaster. So it is important to evaluate the damage condition of them after impact loading, and to estimate the residual performance of them. This study is focused on a reinforced concrete (herein after called RC) structure such as caisson breakwater and rock-shed. In order to quantitatively evaluate the dynamic behavior and cumulative damage of RC members under low-velocity single and repeated impact loading, we conducted numerical approach by using the theory of Continuum Damage Mechanics (herein after called CDM). At the result, we clarified not only impact behavior of the members but also the relationship between cumulative kinetic energy of repeated impact loading and cumulative damage of the members. In addition, applicability limit of our model based on scalar damage modeling was clarified.

The effects of pressure dependent constitutive model to simulate concrete structures failure under impact loads

The main objective of this paper is to explore the effect of confining pressure in the compression and tension zone by simulating the behaviour of reinforced concrete/mortar structures subjected to the impact load. The analysis comprises the numerical simulation of the influences of high mass low speed impact weight dropping on concrete structures, where the analyses are incorporated with meshless method namely as Smoothed Particle Hydrodynamics (SPH) method. The derivation of the plastic stiffness matrix of Drucker-Prager (DP) that extended from Von-Mises (VM) yield criteria to simulate the concrete behaviour were presented in this paper. In which, the displacements for concrete/mortar structures are assumed to be infinitesimal. Furthermore, the influence of the different material model of DP and VM that used numerically for concrete and mortar structures are also discussed. Validation upon existing experimental test results is carried out to investigate the effect of confining pressure, it is found that VM criterion causes unreal impact failure (flexural cracking) of concrete structures.

Simulation of Shear and Bending Cracking in RC Beam: Material Model and its Application to Impact

This paper presents a simple and reliable non-linear numerical analysis incorporated with fully Lagrangian method namely Smoothed Particle Hydrodynamics (SPH) to predict the impact response of the reinforced concrete (RC) beam under impact loading. The analysis includes the simulation of the effects of high mass low-velocity impact load falling on beam structures. Three basic ideas to present the localized failure of structural elements are: (1) the accurate strength of concrete and steel reinforcement during the short period (dynamic), Dynamic Increase Factor (DIF) has been employed for the effect of strain rate on the compression and tensile strength (2) linear pressure-sensitive yield criteria (Drucker-Prager type) with a new volume dependent Plane-Cap (PC) hardening in the pre-peak regime is assumed for the concrete, meanwhile, shear-strain energy criterion (Von-Mises) is applied to steel reinforcement (3) two kinds of constitutive equation are introduced to simulate the crushing and bending cracking of the beam elements. Then, these numerical analysis results were compared with the experimental test results.

Failure Behavior and Numerical Simulation of the Local Damage of Ultra High Strength Fiber Reinforced Concrete Subjected to High Velocity Impact

This study presents the local damage of ultra high strength fiber reinforced concrete plates. Impact test of the reinforced concrete plates using two different short fibers are conducted to examine the failure behavior and impact resistant performance. Material models are discussed and proposed by simulating the high speed tri-compressive and uni-tensile tests. Numerical simulations of the impact tests are carried out. Numerical results show good agreements with the test results.

A Fundamental Study on the Shock Cushioning Characteristics of a Novel pin-Fixed Aseismatic Connector for Bridges

This paper presents a novel pin-fixed aseismatic connector for bridges. A feature of this device is that the anchorage areas of both ends are connected with hinges; thus, there are no restrictions with respect to their mounting angles. Additionally, the PC cable of this device is given an appropriate amount of sag; thus, within the range of the sag the structure is capable of absorbing the amount of displacement because of temperature changes and live loads. In addition, this device has a certain shock-cushioning effect because of the rubber material surrounding the hinge pins. However, there is no quantitative evaluation method on the shock-cushioning effect of this device. Therefore, in this study, the shock-cushioning effect of the novel pin-fixed aseismatic connector for bridges is investigated using impact load tests and numerical analysis. It is found that the shock-cushioning effect of this device is almost equal to similar aseismatic connectors. Furthermore, it is also confirmed that their effects can be quantitatively evaluated using impact response analysis.

A Numerical Study on Impact Damage Assessment and Dynamic Behaviour of Concrete Bridges by Pounding Effect

The South Hyogo prefecture earthquake indicated that various kind of damage was incurred under severe ground motion. Some of the reported damage cases are caused by pounding between bridge girders and between a superstructure and an abutment. To establish the reasonable and safe seismic design for bridges, it is necessary to evaluate the damage level of bridge abutment under impact of bridge girder and to clarify dynamic behaviour of whole bridge under pounding. So the main objective of this study is to evaluate the damage level of an abutment by pounding. To achieve this, impact response analyses of pounding effect were conducted by using 3-dimensional FEM. Furthermore, to clarify dynamic behavior of whole bridge under pounding, frame analyses were conducted.

Numerical studies on cumulative damage of RC members under repeated impact loading

We have tried to develop the simple FE analysis method based on continuum damage mechanics to quantitatively evaluate the impact behaviour and the cumulative damage of RC beam under repeated impact loading. As a result, it has been found that the cumulative damage and residual displacement of RC beam under repeated impact load can be properly evaluated, but the crack propagation cannot be evaluated by using the proposed method. This paper presents the following matters: (1) Numerical investigation on the impact behaviour and cumulative damage of RC beam under repeated impact loading by using the proposed method. (2) Numerical investigation of the relationship between cumulative kinetic energy of repeated impact loading and cumulative damage of RC members. (3) Investigation on improved points of our existing proposed method to evaluate the crack path of RC member under repeated impact.

A study on the estimation of failure mode in impact analysis using SPH method

This paper proposes an analysis algorithm that can appropriately distinguish shear failure from bending failure of an RC beam under impact load, by using the SPH method. As structural members, beams generally fail by one of two modes: bending failure caused by excessive bending deformation of the member, and shear failure caused by shear crack growth, leading to rapid destruction at an angle in the web. In this study, to calculate the failure behavior accurately in the local stress field in which shear stress prevails such as when a shear crack occurs, an orthotropic constitutive equation is used. This equation is derived by applying the integrity tensor proposed by Ignacio Carol, Egidio Rizzi and Kasper William, to the usual SPH method. This operation is also extended to the tensile softening characteristic of concrete material. The results confirm that the failure behavior of RC beams under a wide range of conditions can be analyzed accurately by using the proposed algorithm.