Lateral Stiffness Ratio Research Articles

The Research of United Energy Dissipated Design of Buckling Restrained Braces and Viscous Dampers for Frame Structure in High Seismic Region

In this paper, a series of computational analysis is carried out on the united energy dissipation design of the concrete frame structure with the buckling restrained brace and viscous dampers. The calculation results show that the value of the normal lateral stiffness ratio and the additional damping ratio provided the viscous dampers. The relation chart between the two damper matching rules is obtained, which avoids the inconvenience caused by multiple iterations based on the response spectrum design method. The accuracy and practicability of the relation chart for united energy dissipation design are verified by the engineering example. It is proved that the united energy dissipation structure can effectively improve the seismic performance of the whole structure, and has good theoretical research value and practical application value, which can provide some reference for the structure design in high seismic region.

High resolution lateral force-displacement measurements as a tool for the determination of lateral contact stiffness and Poisson's ratio

A Lateral Force Unit (LFU) as a second measuring head for nanoindenters is now available as a commercial tool with the necessary accuracy to investigate the elastic contact between a sphere and a flat surface with sub-nanometer resolution. The combination of normal and lateral load-displacement measurements at one and the same sample position gives two independent measurement results and can therefore be used to extract beside Young's modulus a second elastic constant. This can be shear modulus or Poisson's ratio for elastically isotropic materials. To realize that, it is necessary to determine all necessary corrections with high precision. This comprises normal and lateral instrument compliance, indenter area function, spring constant of the holding springs of the LFU and the surface slope. Two algorithms were developed and tested for the determination of the Poisson's ratio from fully elastic measurements with a spherical indenter. One is using the ratio of normal and lateral contact stiffness and the other the curvature of the lateral load-displacement curve at the turning points and the transition from sticking to sliding friction. By measuring six different materials it was shown that the ratio of normal and lateral contact stiffness results in relatively large errors for the Poisson's ratio of up to 50% against literature data while the other method had only an error (1σ) between 6% and 20%. The last method is restricted to hard and smooth materials to enable measurements in fully elastic regime but it can also be applied to coatings if they are about 2.5–4 times ticker than the contact radius during the measurement. This is nevertheless a progress against the current situation where the Poisson's ratio of coatings is mostly unknown.

Seismic risk assessment of steel frames equipped with steel panel wall

SummaryThis paper aims to conduct risk assessment on steel frame equipped with steel panel wall (SPWF) through probabilistic seismic demand analysis. First, cyclic test on a SPWF specimen with one‐third scale, one bay, and single story is performed, and the typical limit performance levels were determined in accordance with the test results and the stipulated in FEMA 356. Then, finite element models were built for a 12‐story steel frame and two 12‐story SPWF structures with different lateral stiffness ratio. The seismic performance of these models are investigated through nonlinear time–history analyses, and their limits capacities are determined from incremental dynamic analyses. Besides, fragility functions are developed for these models associated with 10%/50 years and 2%/50 years events, as defined in SAC project. Finally, the annual probabilities of each limits and the collapse probabilities in 50 years for the 3 models are calculated and analyzed, and the function associated with the collapse probability and lateral stiffness ratio is developed. The effectiveness of steel panel wall in reducing the seismic risk of the existing steel frame buildings is validated on the basis of the risk analyses.

Effects of pulse-like ground motions parameters on inter-story drift spectra of multi-story buildings

This article attempts to study the effect of various pulse-like ground motion parameters and local site conditions on the linear response of different multi-story buildings with special shear and flexural behaviour. The multi-story buildings are modelled using a combination of a shear and flexural beams with representative lateral stiffness ratios. A total of 61 near-fault pulse-like ground motions are selected for this study. The effects of peak ground velocity (PGV), PGV/PGA, rupture distance, Arias intensity, earthquake magnitude and local site conditions on maximum inter-story drift spectra (MIDS) and distribution of the inter-story drift ratio (IDR) along the height of the multi-story buildings are evaluated. It was observed that both the fundamental period of the structure and the lateral stiffness ratio can significantly change maximum inter-story drift demands in buildings subjected to pulse-like ground motions. The near-fault pulse-like ground motions are more dangerous for multi-story buildings with flexural behaviour than those with shear behaviour. The effects of peak ground velocity (PGV) and Arias intensity (I) on inter-story drift spectra is more obvious than others parameters.

Modeling the behavior of FRP-confined concrete using dynamic harmony search algorithm

The accurate prediction of ultimate conditions for fiber reinforced polymer (FRP)-confined concrete is essential for the reliable structural analysis and design of resulting structural members. Nonlinear mathematical models can be used for accurate calibration of strength and strain enhancement ratios of FRP-confined concrete. In this paper, a new procedure is proposed to calibrate the nonlinear mathematical functions, which involved the use of a dynamic harmony search (DHS) algorithm. The harmony memory is dynamically adjusted based on a novel pitch generation scheme using a dynamic bandwidth and random number with normal standard distribution in DHS. A new design-oriented confinement model is proposed based on three influential factors of FRP area ratio ($$ \rho_{a} $$źa), lateral confinement stiffness ratio ($$ \rho_{E} $$źE), and strain ratio ($$ \rho_{\varepsilon } $$źź). Five nonlinear mathematical design-oriented models are regressed on approximately 1000 axial compression tests of FRP-confined concrete in circular sections based on the proposed DHS algorithm. The proposed models for the prediction of the ultimate axial stress and strain of FRP-confined concrete are compared with the existing models. It has been shown that the DHS algorithm offers the best performance in terms of both accuracy and fast convergence rate in comparison with the other modified versions of harmony search algorithms for optimization problems. The proposed design-oriented model provides improved accuracy over the existing models.

Load path dependence of strain and stress for confined concrete

The assumption of load-path independence of strain and stress has been widely adopted as the basis for building analysis-oriented models of fibre-reinforced polymer (FRP)-confined concrete. This assumption facilitates the application of stress–strain models to actively confined concrete in FRP-confined (or passively confined) concrete. However, consensus on the path independence of concrete has not yet been reached. In this study, an investigation into the influence of stress path on concrete mechanical behaviour was conducted by assessing the models of actively confined concrete and comparing the results of the most accurate active confinement model with the experimental results for FRP-confined concrete cylinders at the same confinement pressures. The influence of two confinement systems on strain and axial stress under the same lateral pressures was studied in detail. The results show that strain and axial stress are path dependent. The loading-path effect on both axial strain and stress is related to the lateral stiffness ratio. Based on the confirmation of the path dependence in the confined concrete, a modified analysis-oriented model is proposed. The model has good performance in predicting the stress–strain behaviour of FRP-confined concrete.

Seismic design of multistory tension-only concentrically braced beam-through frames aimed at uniform inter-story drift

In this paper, a seismic design procedure aimed at achieving uniform inter-story drift in multistory tension-only concentrically braced beam-through frames (TOCBBTFs) is presented. The TOCBBTF is designed so that the columns and beams would remain elastic for their negligible lateral stiffness while tension-only concentric braces resist all lateral loads as a reliable way of absorbing seismic energy under seismic loading. The hysteretic energy dissipation of the tension braces can be treated as supplemental damping ratio of the structure, and lateral stiffness ratio between braces and main structure exerts a significant impact on seismic behavior of the structure. Three performance objectives of seismic design procedure aiming for uniform inter-story drift along the building height are established first. From the perspective of supplemental viscous damping and proper lateral stiffness of the structure, the seismic design method is proposed and applied to 4- and 6- story model structures to demonstrate the design procedure. Time-history analyses are carried out to verify whether the pre-specified performance objectives are achieved or not. The analysis results show that the seismic performance of the 4- and 6-story model structure designed with the proposed design procedure agrees very well with the pre-specified design objectives.

Shaking table test and numerical analysis of a high‐rise building with steel reinforce concrete column and reinforce concrete core tube

SummaryThis paper assesses the seismic performance of a high‐rise building with steel reinforce concrete column and reinforce concrete core tube in Shanghai, China. This building has 54 floors above the ground and 4 basements, and it has two strengthened layers, which are composed of outrigger truss and belt truss. In order to validate the reliability and the safety of this structure, besides the conventional analysis, shaking table test of scale model was conducted. In the test, the maximum responses of acceleration and deformation were measured and evaluated, as well as the dynamic characteristics, crack pattern, and failure mechanism of the building. Meanwhile, elastic‐plastic time‐history analysis for prototype structure was carried out by the finite element analysis program, and the experimental data were compared with the analytical results to gain a better understanding of the seismic performance of the building.The conclusions are summarized below: Shaking table test of scale model is an effective method to understand the failure mechanisms and seismic performance of high‐rise building with steel reinforce concrete (SRC) column and reinforce concrete core tube. To high‐rise building, a whipping effect is remarkable. The stiffness and ductility of the stories closed to the roof should be paid more attention. In the strengthened layers, the outrigger truss and the belt truss are the main structures to resist a large part of seismic action. The stiffness of the stories between the strengthened layers is mutated, and the focus phenomenon of shear force on these stories is obviously serious. The lateral stiffness ratio of core tube to SRC columns should not be large. Well controlling of the size of these lateral resistance members can make them to give fully play to seismic capacity. Copyright © 2015 John Wiley & Sons, Ltd.

Torsional Design Method of Bottom Frame Structure with Irregular Plane

For the study of irregular plane adverse impacts on the bottom frame structure seismic performance, in this paper, a serious damaged bottom frame structure in Wenchuan earthquake is taken as the research object,and a comparative calculation model is designed and elasto-plastic time-history analysis is carried out on the use of ABAQUS finite element software. The calculation results show that: the stiffness center of floor with irregular plane does not coincide with the center of mass, this eccentricity will produce torsional response under horizontal earthquake action. Bottom frame shear layer has strong stiffness at the center, around the lack of lateral load resisting member will cause interlayer torsional rigidity insufficient, further increasing the torsional response of structures, aggravated the damage. The lateral stiffness ratio under the same conditions,the design method of the contrast model is more reasonable, and has lighter damage under the the same intensity grade, improve the seismic capability of the structure, and provides the ideas of design method of this kind of structure.

An analysis research of the stiffness characteristics of hospital building materials

This paper primarily aims to introduce different stiffness ratio requirements for hospital buildings of various structural styles, to achieve a new standard. The requirements of each stiffness ratio are analyzed, according to the specification formulas and illustrations. And whether the structural deformation situation complies with the code requirement or dissatisfies the specification requests can be intuitively reflected through the application of the chart form, respectively. The corresponding measures complying with the code requirement and the matters needing attention in the schematic design phase are proposed. The comparison analysis for the lateral rigidity and lateral stiffness ratios is performed by applying different methods for the project cases of shear wall, frame tube and partial frame shear wall structures. The proposed computing method may better reflect the stiffness characteristics of the component’s cross-section, with regard to vertical layer, storey height and materials, as well as the actual situation of the turning constraint on both ends. The result thus determined can better reflect the real lateral rigidity of the construction, which is available as a benchmark for engineers designing hospital building structures.

Discrete element modeling on fracture coalescence behavior of red sandstone containing two unparallel fissures under uniaxial compression

Particle flow code (PFC2D) was adopted to carry out a discrete element modeling (DEM) for the fracture coalescence behavior of red sandstone specimens containing two unparallel fissures under uniaxial compression. The numerical micro-parameters of red sandstone were firstly validated from the experimental results of intact specimen, and were then checked with the experimental results for red sandstone containing two unparallel fissures under uniaxial compression. Four key factors (i.e. the axial stress–axial strain curve, the peak strength and elastic modulus, the ultimate failure mode and the crack coalescence process) were put forward to discriminate the rightness and reasonability of numerical simulated results. A systematic simulation for red sandstone specimens was performed to compare quantitatively the numerical results with the experimental results, which showed that the numerical simulated results were in good agreement with the experimental results. Numerical simulated results showed that the peak strength and elastic modulus of red sandstone containing two unparallel fissures were increased at the fissure angle α2=90°, before decreasing up to our maximum fissure angle of 180°. However, the ratio of lateral stiffness of red sandstone containing two unparallel fissures firstly decreased and then increased with the increase of α2, and had a lowest value at α2=90°. The shear and tensile crack numbers of red sandstone reaching the peak strength with respect to α2 were also discussed. Through the numerical simulation, we made a detailed summarization for the crack initiation, propagation and coalescence in the entire deformation process of red sandstone, which was found to be dependent to α2. The simulated cracks replicated most of the phenomena observed during the experiment. Finally, the stress field in the red sandstone specimens containing two unparallel fissures was obtained, which revealed the fracture coalescence mechanism of flawed red sandstone under uniaxial compression.

Lateral Resisting Experiment of Prestressed-Tube Bolted Connection for Post-and-Beam Timber Construction

Connections are key elements and the weak points for timber structures. The most commonly used bolted timber connections with slotted in steel plate have low lateral stiffness and poor ductility in post-and-beam construction. This paper introduces the prestressed-tube bolted connection to alleviate this problem. To evaluate its lateral resisting performance, the failure mode, strength, lateral stiffness, ductility, hysteresis curve and equivalent viscous damping ratio of the ordinary and improved connections, as determined by the monotonic and reversed cyclic loading test, are compared. The results demonstrate that the lateral stiffness of the prestressed-tube bolted connection has been significantly improved, and its ductility is also better than the normal bolted connection with no decrease in the ultimate moment resisting capacity. It is believed that the semi-rigid prestressed-tube bolted connection, as an alternative to current bolted solutions, may provide reasonable lateral stiffness and has good potential for use in post-beam timber construction.

浅谈高层建筑结构嵌固端位置的选择

在实际工程设计中，多数结构工程设计人员并未重视高层建筑结构嵌固端的选择。这样往往会造成材料浪费，也会给高层建筑结构留下隐患。对于高层建筑结构嵌固端的定义，部分结构设计人员也存在误区，认为是力学嵌固，其实应为强度嵌固。规范对地下一层顶板作为嵌固端明确了要求。本文对三种地下室平面面积型式不同的高层建筑结构嵌固端做了初步的探讨，得出了一般情况下，不同地下室平面型式嵌固端的位置，并得出了地上一层与相关范围地下一层侧向刚度比是衡量地下一层顶板能否作为高层建筑结构嵌固端的关键。 In the practical engineering design, structural engineering staffs did not attach importance to fixed end of high-rise building structure. This will cause material waste, and will also leave hidden troubles to the high-rise building structure. Some of the structural designers have mistakes in the definition of fixed end of the tall building, who regard them as mechanics embedment, but in fact it should be strength-mounted. Specification makes requirements clearly about the roof of the underground layer as embedding end. In this paper, three basement flat area types of high-rise building structure embedded end have been studied. It comes to conclusions 1) there are different embedding positions in different basement flat forms under normal circumstances, and 2) the lateral stiffness ratio of ground floor with the relevant range of underground floor is the key to measure whether the basement roof can be used as a high-rise building structure embedded fixed end.

A Moment-Shear Story Model for the Design of Steel Frames with Semi-Rigid Connections

A moment-shear story model using the static condensation method is proposed for the steel frame with semi-rigid connections. Based on the superposition principle under small deformation, the story horizontal deflection can be divided into three parts, due to the action of story shears, the top story moment of column and the connection rotation of bottom story column, respectively. The formulas are derived for its lateral stiffness, horizontal deflection and height ratio of inflection point of column, taking into account the effect of semi-rigid connection. Numerical results indicate that this story model is reliable and can be used for preliminary design of this type of structures.

설계편심의 크기에 따른 비틀림 비정형 건물의 최종 정적편심 크기의 비교에 관한 연구

지진하중에 의해 발생하는 비정형 건물의 피해를 줄이기 위하여 내진설계기준에서는 비틀림 증폭계수를 도입하였다. 이 계수는 내진설계기준에 따라 다르게 적용되었으며 같은 시기의 설계기준에서조차 다르게 적용되었다. 본 연구에서는 서로 다른 설계편심으로 설계된 건물의 최종 정적편심의 크기, 연약단부의 횡강성과 비틀림 강성비를 비교하였다. 비틀림 증폭계수가 증가할수록 연약단부의 횡강성이 증가하여 건물의 최종 정적편심의 크기는 감소하였으나 이 계수가 최대값 3.0에 도달한 이후부터 건물의 최종 정적편심의 크기는 다시 증가하였다. 우발편심과 정적편심의 합에 비틀림 증폭계수를 곱하여 구한 설계편심으로 설계된 건물의 최종 정적편심의 크기는 수직부재의 위치에 따라 0 또는 음수로 측정되었다. To reduce the vulnerability of torsional irregular buildings caused by seismic loads, the torsional amplification factor was introduced by the seismic code. This factor has been applied differently in a variety of seismic codes. In this study, the final static eccentricity, and the lateral and torsional stiffness ratios of buildings designed with different design eccentricities were compared. The increment of the torsional amplification factor resulted in a decrement of the final static eccentricity of the building. However, after reaching the maximum value of this factor, the final static eccentricity of the building increased again. The final static eccentricity of the building designed by multiplying the sum of the inherent and accidental eccentricity by the torsional amplification factor was zero or had a minus value, depending to the position of the vertical element.

Study on Rational Ratios of Lateral Stiffness for Masonry Building with Frame Structure at First Two Stories

There are two typical seismic damage characteristics to the masonry building with frame shear wall structure at first two stories, and the lateral stiffness ratio of the third storey to the second storey is one of the key factors mostly affecting the seismic performance of this kind of building. However, some factors are not considered sufficiently in current Chinese seismic codes. According to the theory of performance-based seismic design, the seismic performance of this kind of structure is analyzed in this paper by taking time-history analysis on models which with different storey stiffness ratios. The results show that when the lateral stiffness ratio controlled in a reasonable range, the upper masonry deformation can be ensured in a range of elastic roughly, and the bottom frame can be guaranteed to have sufficient deformation and energy dissipation capacity. Finally, according to the seismic performance characteristics of masonry building with frame shear wall structure at first two stories, especially the characteristics under strong earthquakes, a method of simplified calculation model for the upper masonry is discussed in this paper.

Optimization Design of Core Thickness of Exterior Frame and Core Hybrid Structures in High-Rise Buildings

Considering core thickness is important issue to performance of exterior frame and core hybrid structure in high-rise buildings, seismic response analysis is conducted by response spectrum method for finite element models with different core thickness. The optimization design of core thickness of hybrid Structures on the basis of the seismic response is studied, the core thicknesses are chosen as design variables, the objective function about core volume is adopted, some specification requirements such as deformation, the ratio of lateral stiffness to gravity, storey shear to gravity, storey shear of exterior frame, axial compression ratio of column and wall limb, bearing capacity of structural member and core construction are regarded as restricting conditions, the optimal mathematical model is established for reflecting integrity dynamic properties of hybrid structure. The ANSYS software is used for optimizing tool, the hybrid structures optimization design are made through different initial values for verifying convergence of optimization method, the optimal result show that the performances of hybrid structure are improved, the internal forces are reduced and the ratios of inner force born by exterior frames are increased in the optimal scheme.

Single aerosol trapping with an annular beam: improved particle localisation

In this paper we explore the trapping of aerosol droplets using an annular beam, formed by blocking the central portion of a Gaussian beam, and quantify the improvements over conventional Gaussian beam traps. Recent work on the modelling of single aerosol dynamics within an optical tweezer trap [Burnham et al., Journal of the Optical Society of America B, 2011, 28, 2856-2864] has indicated that the use of annular beams can allow smaller droplets to be trapped, which we experimentally verify. We also demonstrate that annular beams allow droplets to be trapped at higher powers, and with reduced axial displacement with increasing power, than Gaussian beams. We confirm these results, due to a reduction in the axial scattering forces, using this theoretical model. Finally back focal plane interferometry is used to determine the axial and lateral trap stiffnesses for a series of droplets, showing a significant increase in the axial : lateral trap stiffness ratio from 0.79 ± 0.04 to 1.15 ± 0.04 when an annular beam is used.

Nonlinear Seismic Analysis of Masonry Infilled RC Frame Structures

Many RC frame structures were severely damaged or collapsed in some layer. The phenomenon was significantly different from the expected failure mode in seismic design code. This paper comprehensively sums up the earthquake characteristics of masonry infilled RC frame structures. Based on an investigation of a masonry infilled RC frame structure damaged in the earthquake area, conduct the research on frail-layer caused by infill walls uneven decorated. On the hypothesis of keeping the main load-bearing component invariant, two models were considered, i. e. frame with floor slab, and frame with both floor slab and infill wall. Furthermore, divide them into groups of the bottom, the middle and the top frail-layer to discuss by changing the arrange of infill wall. Time history analyses using three-dimensional sophisticated finite element method were conducted. The major findings are: 1)infill walls may significantly alter the failure mechanism of the RC frames. 2)controlling the initial interlayers lateral stiffness ratio in a reasonable range is an effective method to avoid frail-layer damage. These findings suggest that the effects of infill wall should be considered in seismic design, keep the initial interlayers lateral stiffness ratio less than the paper suggested, and the structural elasto-plastic analysis model should take slabs and infill walls into account.

Application of Drucker-Prager Plasticity Model for Stress-Strain Modeling of FRP Confined Concrete Columns

Existing research works have identified that Drucker-Prager (DP) plasticity model is capable of modeling the stressstrain behavior of confined concrete. However, the accuracy of the model largely depends on the adequate evaluation of its parameters that determine the yield criterion, hardening/softening rule and flow rule. Up to date, most research works mainly focus on the first two criteria. The plastic dilation angle is the major parameter that governs the DP flow rule. This paper addresses the plastic dilation properties of concrete for FRP confined circular concrete columns under the theoretical framework of DP model in the commercial software ABAQUS. Through careful analyses of test results for FRP confined concrete columns, it is found that the plastic dilation angle is a function of axial plastic strain and the lateral stiffness ratio. A simple model for the plastic dilation angle is subsequently developed. With the implementation of this model, the finite element analysis results fit well with the experimental stress-strain curves for columns with both low and high confinement.