沥青混合料的动荷载响应特征及沥青路面黏弹性力学研究

依托北京东六环改造项目的沥青路面工程,运用室内试验的方法,研究沥青混合料持续受到车辆活荷载作用的动力响应特征,以及受到车辆荷载与各种自然因素耦合作用的黏弹性力学变化规律。研究结果表明,沥青混合料的累积应变动力响应经历了2个阶段:在第Ⅰ阶段,沥青混合料的累积应变动力响应表现为逐步增加;在第Ⅱ阶段,沥青混合料累积应变量整体无明显变化,沥青混合料的应力受车辆循环动荷载的影响无明显变化。当荷载加载频率逐渐增加时,沥青混合料动态模量也呈对数上升的趋势,随着温度的升高,沥青混合料的动态模量也会逐渐降低,且降低幅度逐渐减小;混合料相位角在荷载加载频率小于等于10 Hz时呈对数增加的趋势,在加载频率大于10 Hz时呈线性降低的趋势,随着温度的增加,沥青混合料相位角不断减小,减小的幅度不断降低。

新岩滑坡地震与交通动荷载响应分析

为了研究动荷载对滑坡稳定性的影响,以吉林省在建汪延高速公路上的新岩滑坡为依托,借助GeoS-tudio软件建立有限元模型,输入不同峰值加速度的地震荷载与模拟交通震动荷载,通过滑坡稳定性系数的变化来研究2种动荷载对滑坡的影响。通过加荷前后的对比发现,施加动荷载后滑坡稳定性系数均大大降低,并且施加交通震动荷载后稳定性系数下降值略大于施加地震荷载后的下降值。由此可知,在该滑坡中这2种动荷载对滑坡内应力及稳定性影响较大,特别是交通震动荷载对其稳定性影响更大。研究结果可为公路滑坡在震动荷载作用下的稳定性评价及支护设计提供一定的参考依据。

重载车辆在不平整路面的动荷载响应分析

为更加准确的研究重载车辆在不平整路面上的振动响应情况,通过对四轴重载车辆建立七自由度(1+1+5)路面耦合动力学模型,并对该模型进行两个双自由度和一个三自由度的车载振动模型简化分解,借助MATLAB数学计算软件编写程序实现车辆动荷载的计算。研究结果表明:由于车辆在不平整路面上的振动响应,四轴重载车辆的拖车后轮产生的动荷载最大,挂车前轮、后轮动荷载相差较小,变化趋势相对平缓;车辆动荷载随着路面不平整度波长的增加出现两个峰值,当波长增加到一定程度时,最大动荷载趋近车辆振动系统的自重,此时可认为路面趋于平整;路面振幅对于动荷载的影响较大,最大动荷载与振幅呈现正相关;超载问题是影响道路使用寿命的主要"杀手",为了避免道路的进一步损坏,增长其使用寿命,有关部门应当严格控制车辆的超载现象。

地铁重叠隧道的列车动荷载响应分析

对深圳地铁一期工程单洞双层隧道列车动荷载响应进行了有限元模拟分析。分析结果表明,在列车动荷载作用下,隧道中将主要出现拉应力,在隧道底部内边缘、下洞边墙脚偏上内边缘、中隔板下边缘、上洞边墙脚偏上内边缘均将产生较大的拉应力,因此,需要采用加固措施,以确保隧道支护结构和周边建筑物的安全。同时,也应控制列车噪声,减小对周边环境的影响。

某水库新岩滑坡动荷载响应分析

以在建某水库上的新岩滑坡为例,借助GeoStudio软件中的部分软件模块,探究了地震与交通震动荷载对滑坡的影响。

大跨径钢桥面铺装层车辆动响应影响因素分析

从耦合振动的角度出发,研究大跨径钢桥面铺装层在车辆随机动荷载作用下的响应机制。将汽车等效为2自由度5参数模型,考虑桥梁表面不平顺产生的随机激励,建立车-钢桥面铺装耦合振动分析模型。利用模态分析与时变系数常微分方程求解方法,分析钢桥面铺装在车辆随机动荷载作用下的动力响应分布规律。定义由铺装层竖向位移、拉应力和拉应变表示的动力放大系数,研究车速、桥面不平度、铺装层开裂损伤和粘结层滑移等对动力放大系数的影响。结果表明,路面不平度、粘结层滑移是影响动力放大系数的主要因素,在进行大跨径钢桥面铺装结构设计时可考虑动力放大系数为1.5。

混凝土桥梁桥面薄层铺装动态响应特性研究

从耦合振动理论的角度,对混凝土桥面薄层铺装在车辆随机动荷载作用下的动力响应规律进行研究。将汽车等效为两自由度五参数模型,将混凝土桥面薄层铺装等效为梁-板结构。考虑到桥面的路面不平度影响,建立车-桥面铺装耦合振动的仿真分析模型。基于状态空间法与模态叠加分析相结合的技术,给出耦合振动系统的动力响应求解新方法。进而研究车辆动荷载在混凝土桥面薄层铺装上作用的最不利位置和动力放大效应,并分析比较车速和桥面不平度对混凝土桥面薄层铺装车辆荷载动力响应的影响。结果表明,路面不平度是影响混凝土桥面薄层铺装车辆动荷载响应的主要因素。

Dynamic response of multi-scale structure in flexible pavement to moving load

In order to study the dynamic responses in the microstructures of the pavement structure, the multi-scale modeling subjected to moving load is analyzed using the discrete element method （DEM）. The macro-scale discrete element model of the flexible pavement structure is established. The stress and strain at the bottom of the asphalt concrete layer under moving load are calculated. The DEM model is validated through comparison between DEM predictions and the results from the classical program. Based on the validated macro-scale DEM model, the distribution and the volumetric fraction of coarse aggregate, mastics and air voids at the bottom of the asphalt layer are modeled, and then the multi-scale model is constructed. The dynamic response in the microstructures of the multi-scale model are calculated and compared with the results from the macro model. The influence of mastic stiffness on the distribution of dynamic response in the microstructures is also analyzed. Results show that the average values and the variation coefficient of the tensile stress at the aggregate-mastic interface are far more than those within the mastics. The dynamic response including stress and strain distributes non-uniformly in both mastics and the interface. An increase in mastic stiffness tends to a uniform distribution of tensile stress in asphalt concrete.

Dynamic Response of Stepped Beams Under Impulsive Loading

Aim To analyze dynamic failure of aerospace strutures subjected lateral impulsive loading. Methods Structures were modeled as rigid-perfectly plastic free-free stepped beams. Basic equations of motion un set up for analysis. Results Final pat deformation and rigid motion solutions were determined for a uniform impulsive loading. The critical rupture conditions for a space shuttle and a missile were obtained. Conclusion Failure is possible for aerospace structures under a uniform impulsive loading, but it is mere difficult in space.

Numerical Simulation of Dynamic Response and Collapse for Steel Frame Structures Subjected to Blast Load

The progressive collapse of steel frame structures under the blast load was investigated using LS-DYNA. The multi-material Eulerian and Lagrangian coupling algorithm was adopted. A flu-id-structure coupling finite element model was established which consists of Lagrange element for simulating steel frame structures and concrete ground, multiple ALE element for simulating air and TNT explosive material. Numerical simulations of the blast pressure wave propagation, struc-tural dynamic responses and deformation, and progressive collapse of a five-story steel frame structure in the event of an explosion near above ground were performed. The numerical analysis showed that the Lagrangian and Eulerian coupling algorithm gave good simulations of the shock wave propagation in the mediums and blast load effects on the structure. The columns subjected to blast load may collapse by shear yielding rather than by flexural deformation. The columns and joints of steel beam to column in the front steel frame structure generated enormous plastic defor-mation subjected to intensive blast waves, and columns lost carrying capacity, subsequently lead-ing to the collapse of the whole structure. The approach coupling influence between struc-tural deformation and fluid load well simulated the progressive collapse process of structures, and provided an effective tool for analyzing the collapse mechanism of the steel frame structure under blast load.

Dynamic response of a beam on a Pasternak foundation and under a moving load

The dynamic response of an infinite beam placed on a Pasternak foundation when the system was subjected to a moving load was investigated.We used the double Fourier transform and its inversion to solve the formulations of the problem.A closed form analytic solution of the beam was obtained by the theorem of residues.We selected a numerical example to illustrate the dynamic response of the beam on Pasternak and Winkler foundations,respectively.We discuss the effect of the moving load velocity on the dynamic displacement response of the beam.The maximum deflection of the beam increases slightly with increased load velocity but increases significantly with reduced shear modulus of subgrade at a given velocity.The maximum deflection of a beam resting on a Pasternak foundation is much smaller than that of a beam on a Winkler foundation.

Finite Element Modeling and Parametric Analysis of Pavement Dynamic Responses under Moving Vehicle Load

This paper intends to develop finite element models that can simulate vehicle load moving on pavement system and reflect the pavement response of vehicle and pavement interaction.We conduct parametric analysis considering the influences of asphalt concrete layer modulus and thickness,base layer modulus and thickness,and subgrade modulus on pavement surface displacement,frequency,and strain response.The analysis findings are fruitful.Both the displacement basin width and maximum value of dynamic surface displacements are larger than those of static surface displacements.The frequency is positively correlated with the pavement structure moduli,and negatively correlated with the pavement structure thicknesses.The shape of dynamic and static tensile strain is similar along the depth of the pavement structure.The maximum value of dynamic tensile strain is larger than that of static tensile strain.The frequency of entire pavement structure holds more significant influence than the surface displacement and strain do.The subgrade modulus has a significant effect on surface displacement,frequency and strain.

Numerical Simulation of Dynamic Response of an Existing Subway Station Subjected to Internal Blast Loading

In order to design and retrofit a subway station to resist an internal blast, the distribution of blast loading and its effects on structures should be investigated firstly. In this paper, the behavior of a typical subway station subjected to different internal blast Ioadings was analyzed. It briefly introduced the geometric characteristics and material constitutive model of an existing two-layer and three-span frame subway station. Then three cases of different explosive charges were consid- ered to analyze the dynamic responses of the structure. Finally, the maximum principal stress, dis- placement and velocity of the columns in the three cases were obtained and discussed. It con- cluded that the responses of the columns are sensitive to the charge of explosive and the distance from the detonation. It＇s also found that the stairs between the two layers have significant effects on the distribution of the maximum principal stress of the columns in the upper layer. The explicit dynamic nonlinear finite element software ANSYS/LS-DYNA was used in this study.

Parallel Computing of the Underwater Explosion Cavitation Effects on Full-scale Ship Structures

As well as shock wave and bubble pulse loading, cavitation also has very significant influences on the dynamic response of surface ships and other near-surface marine structures to underwater explosive loadings. In this paper, the acoustic-structure coupling method embedded in ABAQUS is adopted to do numerical analysis of underwater explosion considering cavitation. Both the shape of bulk cavitation region and local cavitation region are obtained, and they are in good agreement with analytical results. The duration of reloading is several times longer than that of a shock wave. In the end, both the single computation and parallel computation of the cavitation effect on the dynamic responses of a full-scale ship are presented, which proved that reloading caused by cavitation is non-ignorable. All these results are helpful in understanding underwater explosion cavitation effects.

Dynamic Analysis of Structural Columns Subjected to Impulsive Loading

For a building structure subjected to impulsive loading, particularly shock and impact loading , the response of the critical columns is crucial to the behaviour of the entire system during and after the blast loading phase. Therefore, an appropriate evaluation of the column response and damage under short-duration impulsive loading is important in a comprehensive assessment of the performance of a building system. This paper reports a dynamic analysis approach for the response of RC columns subjected to impulsive loading. Considering that the dynamic response of a column in a frame structure can also be affected by the floor movement which relates to the global vibration of the frame system, a generic column-mass model is used, in which a concentrated mass is attached to the column top to simulate the effect of a global vibration. To take into account the high shear effect under impulsive load, the model is formulated using Timoshenko beam theory, and three main nonlinear mechanisms are considered. Two typical scenarios, one under a direct air blast loading, and another under a blast-induced ground excitation, are analyzed and the primary response features are highlighted.

Analysis on Dynamic Response of Hard-Soft-Hard Sandwich Panel Under Blast Loading

Surface contact explosion experiments have been performed for the study of dynamic response of the hard-soft-hard sandwich panel under blast loading. Experimental results have shown that there are four damage modes, including explosion cratering, scabbing of the backside, radial cracking induced failure and circumferential cracking induced failure. It also illustrates that the foam material sandwiched in the multi-layered media has an important effect on damage patterns. The phenomena encountered have been analyzed by the calculation with ALE method. Meanwhile, the optimal analysis of foam material thickness and position in the sandwich panel were performed in terms of experimental and numerical analysis. The proper thickness proportion of the soft layer is about 2.0% to the thickness of sandwich panel and the thickness of the upper hard layer and lower hard layer is in the ratio of ？ to 3 under the condition in this paper when the total thickness of soft layer remains constant.

Dynamic response of cylindrical cavity to anti-plane impact load by using analytical approach

The transient response of an unlimited cylindrical cavity buried in the infinite elastic soil subjected to an anti-plane impact load along the cavern axis direction was studied.Using Laplace transform combining with contour integral of the Laplace inverse transform specifically,the general analytical expressions of the soil displacement and stress are obtained in the time domain,respectively.And the numerical solutions of the problem computed by analytical expressions are presented.In the time domain,the dynamic responses of the infinite elastic soil are analyzed,and the calculation results are compared with those from numerical inversion proposed by Durbin and the static results.One observes good agreement between analytical and numerical inversion results,lending the further support to the method presented.Finally,some valuable shear wave propagation laws are gained: the displacement of the soil remains zero before the wave arrival,and after the shear wave arrival,the stress and the displacement at this point increase abruptly,then reduce and tend to the static value gradually at last.The wave attenuates along the radial,therefore the farther the wave is from the source,the smaller the stress and the displacement are,and the stress and the displacement are just functions of the radial distance from the axis.

Wind-induced responses of super-large cooling towers

Traditional gust load factor(GLF)method,inertial wind load(IWL)method and tri-component method(LRC+IWL)cannot accurately analyze the wind-induced responses of super-large cooling towers,so the real combination formulas of fluctuating wind-induced responses and equivalent static wind loads(ESWLSs)were derived based on structural dynamics and random vibration theory.The consistent coupled method(CCM)was presented to compensate the coupled term between background and resonant response.Taking the super-large cooling tower(H=215 m)of nuclear power plant in Jiangxi Province,China,which is the highest and largest in China,as the example,based on modified equivalent beam-net design method,the aero-elastic model for simultaneous pressure and vibration measurement of super-large cooling tower is firstly carried out.Then,combining wind tunnel test and CCM,the effects of self-excited force on the surface pressures and wind-induced responses are discussed,and the wind-induced response characteristics of background component,resonant component,coupled term between background and resonant response,fluctuating responses,and wind vibration coefficients are discussed.It can be concluded that wind-induced response mechanism must be understood to direct the wind resistant design for super-large cooling towers.

Simulation of the Response of Glass Window Under Blast Load

In the investigation of accidental explosion scene, the damage on the glass is one of the typi-cal traces which can be used to decide the characteristic of the explosion source. To analyze the re-sponse of glass under the blast load, a numerical model was developed. In the model, the brittleness glass model was adopted. A‘node release’method, which had some special merits compared with the erosion method was used to simulate the rupture of the glass In the calculation, several problems which play major role in the response of the glass were discussed. The velocity and the displacement of the glass fragment were two major factors. The numerical results are very helpful for the design and hazard assessment.

Dynamic Behavior of a New Hydraulic Steel Gate

A new style of hydraulic steel gate based on the principle of bionics is proposed in this paper. It has a fish-like shape and consists of right arches, invert arches, connection components and a face plate. It would be first applied in the project of Caoe River Sluice, used as both tidal barrage and flood gate. Compared with conventional hydraulic steel gate of beam grids, this new style of hydraulic steel gate can save up to 30%-50% of steel consumption. The dynamic behavior of the new gate under the impact load of tidal bore is investigated. The impact load of tidal bore is considered by a load spectrum obtained by field observation over a long period of time. Then a numerical analysis of the gate under the load spectrum is carried out by finite element method. The fluid-structure interaction is considered in the analysis. And a comparison between the response of the gate under the impact load and the response of the gate under the corresponding static load is conducted and indicates that the gate has a dynamic magnification factor of 1.2.