Uniaxial Spring Research Articles

Seismic displacement ratios for soil-pile-structure systems allowed to uplift

In this paper, the soil-pile-structure interaction effects on seismic displacement demands are investigated using various dimensionless parameters. The code prescribed procedures for estimating seismic displacement demands are built upon fixed-base structure assumption and neglect the effect of foundation uplift. Tensile index, the ratio of the summation of the tensile strength of all piles to the weight of the structure, is introduced as a novel dimensionless ratio for the seismic assessments. The seismic behavior of the structures with a small tensile index is close to the structures with uplift-allowed shallow foundations. Structures with a large tensile index behave like tied foundation structures. The tensile index paves the path to cover the interaction effects from the soil-structure to soil-pile-structure interaction. The considered simplified structure in this study is a single degree of freedom model with a rigid foundation mounted on a group of piles simulated using the Winkler springs. The piles are simulated using nonlinear uniaxial springs with asymmetrical behavior under tensile and compressive forces. The accuracy of the model is verified by calculating the displacement ratios for four cases; The first three cases representing high tensile index (tied foundation), are verified with the code results, and Case 4, which represents low tensile index (uplift-allowed foundation), is compared to the literature. More than 150,000 nonlinear response history dynamic analyses are conducted for several dimensionless parameters and 20 ground motion records with various intensities and for each analysis, the displacement of the structure, linear and nonlinear hinge plastic rotation, and the foundation rotation and uplift are collected. The results, including elastic and inelastic displacement ratios, are finally compared with those of ASCE41 for shallow fixed-base foundations. It is concluded that for the cases with no pile slippage, the code prediction is accurate enough. However, in cases with high soil-pile-structure interaction effects and low tensile index, the displacement ratios are up to twice the code predictions. • Tensile index is developed to assess the soil-pile-structure interaction effects. • Simplified uplift-allowed SDOF model with piles simulated using Winkler springs. • Elastic and inelastic displacement ratios are compared with the code predictions. • Foundation uplift, tensile index and aspect and periodic ratios are investigated.

Numerical Model of Cold Press-Formed Square Steel Tube Columns Considered with Degradation Behavior due to Local Buckling and/or Fracture

In steel building structures, local buckling and/or fracture of columns could occur during strong ground motions, furthermore complete collapse might be induced due to the column strength degradation. In this paper, cold press-formed square tube columns are targeted, and numerical model being able to trace precisely degradation behavior is proposed. In order to take account of both local buckling and fracture with low computational costs, multi-spring model which consists of some uni-axial springs is adopted. Axial force-deformation relationships of uni-axial springs are provided on flat area and corner area of square tube severally, and are separated into skeleton part and hysteresis part. All parameters on force-deformation relationship are identified based on finite element analysis results of short columns under monotonic or cyclic axial loading. Comparing between analysis results by multi-spring models and past cyclic loading test results or finite element analysis results, it is clarified that degradation behavior of cold press-formed square steel tube columns can be traced with high accuracy.

Analysis of RC slab–beam–column sub‐assemblages subjected to bidirectional lateral cyclic loading using a new 3D macroelement

SummaryAn existing two‐dimensional macroelement for reinforced concrete beam–column joints is extended to a three‐dimensional macroelement. The three‐dimensional macroelement for beam–column joints consists of six rigid interface plates and uniaxial springs for concrete, steel, and bond–slip, which model the inside of a beam–column joint. The mechanical models for the materials and the stiffness equation for the springs are also presented. To validate the model, we used test results from three slab–beam–column sub‐assemblages subjected to bi‐lateral cyclic load. It is revealed that the new joint model is capable of capturing the strength of beam–column joints and the bidirectional interaction in joint shear response, including the concentration of damage in the beam–column joint, the pinching nature in hysteretic behavior, the stiffness degradation, and strength deterioration resulting from cyclic and bidirectional loading. Copyright © 2017 John Wiley & Sons, Ltd.

Uniaxial Spring and Multi-Axial Spring Model for Structural Nonlinear Analysis

The paper includes the following models for nonlinear structural analysis purpose: (1) uniaxial spring mode (or one-component model);(2) multi-axial spring model (MS model). Moment-curvature relation model considers distributed nonlinearity as well. By specifying the relation of moment and curvature at critical sections, it is not a discretized-section but similar to the uniaxial model in including no interaction among bending and axial tension/compression. This paper describes the models and presents the related formula.

Dynamic analysis of an axially moving finite-length beam with intermediate spring supports

This paper presents the analysis for the transverse vibration of an axially moving finite-length beam inside which two points are supported by rotating rollers. In this study, the rollers are modeled as uniaxial springs in the transverse direction. Hamilton׳s principle is applied to derive the equations of motion and boundary conditions of the system. The equations of motion include translational and rotational motions as well as flexible motion. These equations are discretized using Galerkin׳s method, and then the dynamic characteristics of a flexible beam with spring supports are studied by solving an eigenvalue problem. The veering phenomenon of natural frequency loci and mode exchanges are investigated for different positions of the springs and various values of the spring stiffness. In addition, the mode localization is also analyzed using the peak amplitude ratio. It is found in this study that the first mode is localized in one of the beam spans if an appropriate value of the spring constant is selected. Furthermore, it is shown that mode localization can be used to reduce the vibration transferred from one span to the other span while a beam moves axially.

비내진상세를 가지는 기존 저층 철근콘크리트 골조의 내진거동평가

In this paper, the a static experiment of on two reinforced concrete (RC) frame sub-assemblages was conducted to evaluate the seismic behaviors of existing RC frames that were not designed to support a seismic load. The specimens were a one span and actual-sized. One of them had two columns with the same stiffness, but the other had two columns with different stiffness values. As Regarding the test results, lots of many cracks occurred on the surfaces of the columns and beam-column joints for the two specimens, but the cover concrete splitting hardly occurred was minimal until the test ends. In the case of the specimen with the same stiffness offor the two columns, the flexural collapse of the left-side column occurred. However, in the case of the specimen with different stiffness values for of the two columns, the beam-column joint finally collapsed, even though the shear strength of the joint was designed to be strong enough to support the lateral collapse load. The nonlinear Nonlinear static analysis of the two specimens was also conducted using the uniaxial spring model, and the analytical results successfully simulated the nonlinear behaviour of the specimens in accordance with the test results.

선형 스프링모델을 이용한 전단벽식 부분구조의 비선형 정적해석

Domestic reinforced concrete (RC) apartments have a unique structural system that consists of shear walls and rink members of slabs and lintels. In this study, the nonlinear static analysis of two RC shear wall sub-assemblages, with and without lintels, was conducted using the uniaxial spring model to develop a method for accurately predicting the seismic behavior of domestic RC apartments. In the case of the specimen without lintels, the analytical result successfully represented a simulation of the nonlinear behavior of the specimen in accordance with the test result. On the other hand, in the case of the specimen with lintels, the analysis resulted in underestimating the nonlinear behavior of the specimen compared to the test result, because the coupling effect could not be predicted from the earlier loading cycle.

Nonlinear Analysis of Reinforced Concrete Core Walls Based on Three-Vertical-Line-Element Model

Three-vertical-line-element model and uniaxial spring model were adopted to simulate walls and beams. Based on the existing experiment data, numerical simulation is used to analysis the nonlinear behavior of reinforced concrete core walls. The analysis also considered the influence of relevant parameters on the elasto-plastic in core walls structure. Results from the simulation anlysis match well with those from the tests. It is shown that the higher axial compression ratio enhance the bearing capacity; the ratio of height to width has effect on the bearing capacity, deformation performance and the failure mode; the decrease of span-depth ratio of coupling beam reduce ductility and deformation ability of the core walls; the imposed horizontal angle has important effect on the overall space behavior of reinforced concrete core wall.

A new numerical method for dem¿block and particle model

As pointed out in Jing and Hudson’s 2002 review paper on numerical methods in rock mechanics, the distinct element method (DEM) is one of the important numerical methods for simulating the mechanical properties of rock masses. Many researchers have paid attention to block deformation and failure in DEM. The updated DEM can be classified into two types: one is the particle model; and the other is the block model. This paper describes the development of a new numerical model, the block and particle model (BPM), to simulate both continuous and discontinuous deformations of rock masses. Both elastic deformation and failure of blocks can be described in this model. The model assumes that a rock mass consists of blocks and each block is formed by particles arranged in a specific way (see Fig. 1), thus formulating a combination of a block model and a particle model. In this model, blocks and particles are connected by springs. Between blocks, there are three springs for adjacent particles: one is a uniaxial spring and the other two are transverse springs. One block has 25 particles. One of the particles is in the center of the cube and the other 24 particles lie in the midpoint between the face center and the four corner points. Spring groups connect these particles. This paper also describes the development of the forces in a block and between blocks and their spring stiffness. The rigidity coefficient of springs between blocks generates the mechanical characteristics of joints in the rock mass. They can be obtained by material tests or wave methods by means of the Goodman model. The rigidity coefficient of springs between particles depends on the characteristics of deformation and failure of a block. The block is cubic and uniform deformation is studied in this model. We assume that the displacement of each particle in a cube block is equal to the displacement of the same position point of the elastic block under the same and known loading; thus, nine equilibrium equations are obtained for each particle. Solving these equations, nine rigidity coefficients can be determined. These coefficients are the function for elastic modulus and Poisson’s ratio. Furthermore, a new failure criterion is suggested for the block failure. This model is verified by an example of rock masses under uniaxial loading. It is shown that numerical results agree well with theoretical ones and laboratory tests, not only for the deformation process but also for the failure process.