Displacement Moment Research Articles

Dynamic Analysis of Anchored Diaphragm Walls

Summary In this paper, the behavior of diaphragm walls with and without anchor have been studied. In addition to static loads, the walls were subjected to seismic load due to earthquake, using finite element program, PLAXIS 2D. Maximum displacement and bending moment of the wall were compared in different cases. Introduction Deep excavations in urban areas require not only the stability of retained soil, but also special attentions due to the nearby existing buildings. They must be designed in such a way that the requirements for both ultimate and serviceability limit state for supporting system and neighboring structures are satisfied. Anchored diaphragm walls are one of the safest lateral supports, which help in overall stability of the excavated areas. Diaphragm walls represent in general a considerably more complex problem than gravity or cantilever walls. Methodology and Approaches The wall displacement, maximum bending moment and anchor extreme force were calculated using a dynamic PLAXIS finite element program. The soil was considered as elasto-plastic material, using Mohr–Coulomb constitutive model. The wall and the anchor were considered to behave elastically. Considering the dynamic applied load, absorbent boundaries were assumed to prevent dynamic wave reflection. Three different historical strong motions namely, Tabas, Bam and Roodbar were applied to the wall. The following outputs were obtained for different excavation geometry and mechanical properties for soil. Results and Conclusions general results can be drawn as following: 1-Change in the soil stiffness (modulus of elasticity and cohesion) from soft to stiff has caused the maximum wall displacement and bending moment to increase by 76% and 20%, respectively. 2- Under dynamic load, the maximum lateral displacement of the wall is at its maximum value, while the static wall displacement is maximum at about one third the wall height measured from its toe. 3-Peak ground acceleration has direct effect on maximum wall displacement and bending moment, while earthquake frequency has inversely changed these output parameters. Based on the obtained results 30% increase in earthquake acceleration has caused the maximum wall displacement increase by 15%. 4- The maximum displacement and bending moments increased noticeably under earthquake load. Therefore, for diaphragm walls in earthquake prone area, dynamic case should be considered in design. Albeit, building codes, accept higher displacement and bending moments under exceptional loadings.

Seismic Response of a Base Isolated Cable-Stayed Bridge Under Near-Fault Ground Motion Excitations

Nowadays, development of cable-stayed bridges is increasing around the world. The mitigation of seismic forces to these bridges are obligatory to prevent damages or failure of its structural members. Herein, this paper aimed to determine the near-fault ground motion effect on an existing cable-stayed bridge equipped with lead-rubber bearing. In this context, Shipshaw cable-stayed bridge is selected as the case study. The selected bridge has a span of 183.2 m composite deck and 43 m height of steel tower. 2D finite element models of the non-isolated and base isolated bridges are modelled by using SAP2000. Three different near-fault ground motions which are Tabas 1978, Cape Mendocino 1992 and Kobe 1995 were subjected to the 2D FEM models in order to determine the seismic behaviour of the bridge. The near-fault ground motions were applied to the bridge in the longitudinal direction. Nonlinear dynamic analysis was performed to determine the dynamic responses of the bridge. Comparison of dynamic response of non-isolated and base isolated bridge under three different near-fault ground motions were conducted. The results obtained from numerical analyses of the bridge showed that the isolation system lengthened the period of bridge and minimised deck displacement, base shear and base moment of the bridge. It is concluded that the isolation system significantly reduced the destructive effects of near-fault ground motions on the bridge.

Dynamic Behavior of Curved Panels of Rectangular Planar Form: An Analytical Approach

The dynamic behavior of singly and doubly curved panels of the rectangular planar form subjected to different types of loadings is presented. The mathematical formulation is based on the higher order shear deformation theory, and the principle of virtual work is used to derive the equations of motion. The fast converging finite double Chebyshev series and Houbolt time-marching scheme are used for evaluating the dynamic response of the panel. The effect of the magnitude and duration of pulse loadings on the transverse central displacement and bending moment responses is evaluated for different parameters. The accuracy of the present solution methodology is established by the convergence study of non-dimensional central deflection and central moments and comparison of the present results with those available in the literature. Some new results are presented for the hyperboloid panels.

Seismic Response of a Base Isolated Cable-Stayed Bridge Under Near-Fault Ground Motion Excitations

Nowadays, development of cable-stayed bridges is increasing around the world. The mitigation of seismic forces to these bridges are obligatory to prevent damages or failure of its structural members. Herein, this paper aimed to determine the near-fault ground motion effect on an existing cablestayed bridge equipped with lead-rubber bearing. In this context, Shipshaw cable-stayed bridge is selected as the case study. The selected bridge has a span of 183.2 m composite deck and 43 m height of steel tower. 2D finite element models of the non-isolated and base isolated bridges are modelled by using SAP2000. Three different near-fault ground motions which are Tabas 1978, Cape Mendocino 1992 and Kobe 1995 were subjected to the 2D FEM models in order to determine the seismic behaviour of the bridge. The near-fault ground motions were applied to the bridge in the longitudinal direction. Nonlinear dynamic analysis was performed to determine the dynamic responses of the bridge. Comparison of dynamic response of nonisolated and base isolated bridge under three different near-fault ground motions were conducted. The results obtained from numerical analyses of the bridge showed that the isolation system lengthened the period of bridge and minimised deck displacement, base shear and base moment of the bridge. It is concluded that the isolation system significantly reduced the destructive effects of near-fault ground motions on the bridge.

Numerical research on the lateral global buckling characteristics of a high temperature and pressure pipeline with two initial imperfections.

With the exploitation of offshore oil and gas gradually moving to deep water, higher temperature differences and pressure differences are applied to the pipeline system, making the global buckling of the pipeline more serious. For unburied deep-water pipelines, the lateral buckling is the major buckling form. The initial imperfections widely exist in the pipeline system due to manufacture defects or the influence of uneven seabed, and the distribution and geometry features of initial imperfections are random. They can be divided into two kinds based on shape: single-arch imperfections and double-arch imperfections. This paper analyzed the global buckling process of a pipeline with 2 initial imperfections by using a numerical simulation method and revealed how the ratio of the initial imperfection’s space length to the imperfection’s wavelength and the combination of imperfections affects the buckling process. The results show that a pipeline with 2 initial imperfections may suffer the superposition of global buckling. The growth ratios of buckling displacement, axial force and bending moment in the superposition zone are several times larger than no buckling superposition pipeline. The ratio of the initial imperfection’s space length to the imperfection’s wavelength decides whether a pipeline suffers buckling superposition. The potential failure point of pipeline exhibiting buckling superposition is as same as the no buckling superposition pipeline, but the failure risk of pipeline exhibiting buckling superposition is much higher. The shape and direction of two nearby imperfections also affects the failure risk of pipeline exhibiting global buckling superposition. The failure risk of pipeline with two double-arch imperfections is higher than pipeline with two single-arch imperfections.

Redesigning layout in the palm oil tank plant to enhance the utility

Material transfer is one of the most important activities in the production process activities and has a close relationship with the design of the layout of production facilities. A manufacturing company engaged in the manufacture and assembly of machine spare parts at the oil palm plant constraints in terms of material handling so that the decline in utility of the production floor layout and the increasing cost of moving raw materials. To improve the utility on the production floor using group technology method that is Rank Order Clustering (ROC) and Similarity Coefficient (SC). From the result of matrix rank calculation in pairs or between machines then SC method is the best layout design with decreasing material displacement moment by 56,86%. And to improve the layout of facilities on the production floor using BLOCPLAN algorithm that is the value of the degree of Adjency Score of 0.5317. This proposed layout provides a smaller displacement moment so as to shorten the processing time of all parts by 338 minutes and increase utility on the production floor.

Response of thermoelastic microbeams to a periodic external transverse excitation based on MCS theory

In this paper, we investigated the dynamics vibration of clamped–clamped microbeams exposed to associate exterior cross excitation. The theory of modified couple stress (MCS) and thermoelasticity model based on replacing Fourier’s law (LS) are applied to the constructed model. In sight of on Laplace transform technique, an analytical method is utilized to get the deflection and therefore the temperature fields. The inverse of Laplace transforms are calculated numerically utilizing Fourier development methods. The effects of angular frequency of the external force and couple stress term on temperature, deflection, displacement and bending moment are taken into consideration. Numerical results we obtained are displayed in graphs and discussed.

Effect of thermal regime on the seismic response of a dry bridge in a permafrost region along the Qinghai-Tibet Railway

Dry bridges have been widely applied in the Qinghai-Tibet Railway (QTR) to minimize the thermal disturbance of engineering to the permafrost. However, because the Qinghai-Tibet Plateau is an area with a high potential occurrence of earthquakes, seismic action can easily destroy the dry bridges. Therefore, a three-dimensional numerical model, with consideration of the soil-pile interactions, is established to investigate the thermal characteristics and their impact on the seismic response of the dry bridge in permafrost region along the QTR. The numerical results indicate that there exist significant differences in the lateral displacement, shear force, and bending moment of the piles in different thermal conditions under seismic action. When the active layer become from unfrozen to frozen state, the maximum displacement of the bridge pile reduces, and the locations of the zero and peak values of the shear force and bending moment also change. It is found that although the higher stiffness of frozen soil confines the lateral displacement of the pile, compared with unfrozen soil, it has an adverse effect on the earthquake energy dissipation capacity.

Optimization of the bending stiffness of beam-to-column and column-to-foundation connections in precast concrete structures

Abstract This work involved the structural optimization of precast concrete rigid frames with semi-rigid beam-to-column connections. To this end, several frames were simulated numerically using the Finite Element Method. Beams and columns were modeled using bar elements and their connections were modeled using spring elements, with variable bending stiffness. The objective function was based on the search of the least stiff connection able to ensure the global stability of the building. Lastly, a connection model with optimal stiffness was adopted to design the frame. Semi-rigid beam-to-column connections with a constraint factors of 0.33 sufficed to ensure the maximum allowable horizontal displacement and bending moment of the connection, with a global stability parameter of 1.12. This confirms that even connections with low constraints generate significant gains from the structural standpoint, without affecting construction and assembly-related aspects.

Lateral cyclic response of an aluminum model pile in sand

ABSTRACTLateral cyclic load tests were performed on an aluminum model pile in dry sand. Two levels of loading were adopted to represent different service load conditions. The maximum number of loading cycles was 1,000. From the test results, it was found that the even though in the service load condition, the pile response was still affected by cyclic effects and a larger load level would produce more significant influence. In a global point of view, the lateral displacement and maximum moment increased with loading cycles, while the secant stiffness within a cycle decreased with cycles. The cyclic effect was more significant on the lateral displacement than on the moment. In a local point of view, cyclic loading would degrade the equivalent subgrade stiffness for the soil shallower than about seven times diameter. In addition, the secant subgrade stiffness within a cycle increased with loading cycles. Some experimental relationships of lateral pile response and loading cycles were built and compared with those in the literature.

A study of hydroelastic behavior of hinged VLFS

This paper introduces a new method to study the hydroelastic behavior of hinged Very Large Floating Structures (VLFSs). A hinged two-module structure is used to confirm the present approach. For each module, the hydroelasticity theory proposed by Lu et al. (2016) is adopted to consider the coupled effects of wave dynamics and structural deformation. The continuous condition at the connection position between two adjacent modules is also satisfied. Then the hydroelastic motion equation can be established and numerically solved to obtain the vertical displacement, force and bending moment of the hinged structure. The results calculated by the present new method are compared with those obtained using three-dimensional hydroelasticity theory (Fu et al., 2007), which shows rather good agreement.

A Combined EFEM–Discrete Element Method Dynamic Model of Rotor–Bearing–Housing System

In this paper, a model was developed to study the effects of rotor and support flexibilities on the performance of rotor–bearing–housing system. The system is composed of a flexible rotor and two supporting deep-groove ball bearings mounted in flexible bearing housings. The dynamics of the ball bearings were simulated using an existing dynamic bearing model, which was developed using the discrete element method (DEM). The explicit finite element method (EFEM) was used to model the flexibilities of the rotor and bearing support. In order to combine the dynamic bearing model with finite element rotor and support system, new contact algorithms were developed for the interactions between the various components in the system. The total Lagrangian formulation approach was applied to decrease the computational effort needed for modeling the rotor–bearing–housing system. The combined model was then used to investigate the effects of bearing clearances and housing clearances. And it was found that, as the rotor is deformed due to external loading, the clearances have a significant impact on the bearing varying compliance motion and reaction moments. Results also show that deformation of the flexible housing depends on the total force and moment generated within the bearing due to rotor deformation. The first critical speed of rotor was simulated to investigate the unbalance response of the rotor–bearing system. It was demonstrated that rotor critical speed has a significant effect on inner race displacement and reaction moment generated at bearing location.

Analysis of laterally loaded short and long piles in multilayered heterogeneous elastic soil

A continuum-based method is developed for the analysis of laterally loaded piles in multilayered, heterogeneous elastic soil. The analysis considers the soil as a layered elastic continuum in which the modulus varies linearly or non-linearly with depth within each layer. Rational soil displacement fields are assumed and differential equations describing the pile and soil displacements are obtained using the principle of minimum potential energy. The differential equations describing the pile and soil displacements are solved using the Ritz method and the finite difference method, respectively, following an iterative numerical scheme. The analysis is used to study different pile geometries embedded in layered soil deposits with heterogeneity in each layer. The pile displacement, rotation, and maximum bending moment obtained from the analysis were found to be in good agreement with those obtained from an equivalent three-dimensional finite element analysis and from other studies available in the literature. The analysis can be used to obtain the pile head displacement, rotation, and maximum bending moment that can then be used in design.

Analysis of the Hydroelastic Performance of Very Large Floating Structures Based on Multimodules Beam Theory

The hydroelastic behavior of very large floating structures (VLFSs) is investigated based on the proposed multimodules beam theory (MBT). To carry out the analysis, the VLFS is first divided into multiple submodules that are connected through their gravity center by a spatial beam with specific stiffness. The external force exerted on the submodules includes the wave hydrodynamic force as well as the beam bending force due to the relative displacements of different submodules. The wave hydrodynamic force is computed based on three-dimensional potential theory. The beam bending force is expressed in the form of a stiffness matrix. The motion response defined at the gravity center of the submodules is solved by the multibody hydrodynamic control equations; then both the displacement and the structure bending moment of the VLFS are determined from the stiffness matrix equations. To account for the moving point mass effects, the proposed method is extended to the time domain based on impulse response function (IRF) theory. The method is verified by comparison with existing results. Detailed results through the displacement and bending moment of the VLFS are provided to show the influence of the number of the submodules and the influence of the moving point mass.

Vibrations of fluid-conveying inclined single-walled carbon nanotubes acted upon by a longitudinal magnetic field

This work deals with the influence of the longitudinal magnetic field on vibrations of inclined single-walled carbon nanotubes (SWCNTs) subjected to an inside fluid flow. Using an equivalent continuum structure model for the SWCNT and a plug-like model for the moving inside fluid flow, the nonlocal longitudinal and transverse equations of motion of magnetically affected SWCNTs are obtained in the context of small deformations. By application of the assumed-mode methodology, the displacements are discretized in terms of vibration mode shapes, and by exploiting generalized Newmark-β scheme, their corresponding time-dependent parameters are determined at each time. In the presence of the longitudinal magnetic field, the effects of the small-scale parameter, fluid flow velocity, and inclination angle on both longitudinal and transverse vibrations of SWCNTs are addressed. The obtained results reveal that the longitudinal magnetic field has fairly no effect on the longitudinal dynamic behavior of the nanostructure. However, maximum values of both transverse displacement and nonlocal bending moment of the fluid-conveying SWCNT would reduce as the strength of the magnetic field grows. Such a fact becomes more highlighted for high levels of the fluid flow velocity. The obtained results indicate that the longitudinal magnetic field can be exploited as an efficient way to control transverse vibrations of SWCNTs conveying fluids.

Effects of Near-Fault Motions and Artificial Pulse-Type Ground Motions on Super-Span Cable-Stayed Bridge Systems

AbstractThis paper evaluates the seismic responses of a super-span cable-stayed bridge subjected to near-fault ground motions. A new method, record-decomposition incorporation (RDI), is proposed to synthesize the artificial near-fault pulse-type ground motions by combining the high-frequency background record (BGR) with simple equivalent pulses. The effects of forward-directivity pulses and fling-step pulses on the responses are assessed for the Sutong cable-stayed bridge (with a main span of 1,088 m) in China. The results show that the near-fault pulse-type ground motions generate larger displacement and internal force to the bridge compared with the nonpulse ground motions, and the fling-step ground motions are more damaging to the bridge than those of the forward-directivity ground motions. The high-frequency components of near-fault records have a significant effect on the responses of the bridge. Subsequently, the longitudinal displacement and bending moment of the tower induced by artificial ground ...

Experimental study on the dynamic responses of a freestanding bridge tower subjected to coupled actions of wind and wave loads

This work presents an experimental investigation of the dynamic responses of a freestanding bridge tower model under coupled wave and wind actions. A test model with a geometric scaling of 1:100 was manufactured, and the test was performed in a wind tunnel and wave flume. The dynamic responses of the test model were measured under three cases of wind, wave and wind-wave coupled actions. The displacement, acceleration and bending moment were analyzed for the model with different wind speeds and wave exposures. The test results indicated that the coupled wind-wave effects are clear for lower wind speed with regular waves when the wave period is in the resonant region of the structures. When the wave period is far from the resonant frequency of the structure or the wind speed is much higher, the coupled wind-wave action does not significantly affect the dynamic responses of the bridge tower.

Self-sensing and strengthening effects of reinforced concrete structures with near-surfaced mounted smart basalt fibre–reinforced polymer bars

A new retrofitting system is proposed for reinforced concrete structures with application of near-surfaced mounted smart basalt fibre–reinforced polymer bar. The distributed optical fibre sensing technology, namely pre-pump pulse Brillouin optical time-domain analysis, is applied as the sensing technology for the smart bar. Then the proposed system is explained in detail from both self-sensing and strengthening. Finally, some experiments were implemented with reinforced concrete beams to verify the actual effects. From the results, it is concluded that the ultimate strength and the stiffness after steel rebar yielding can be increased obviously due to the high strength and ultimate strain of the smart basalt fibre–reinforced polymer bar. Meanwhile, the structure strain distribution can be measured with the smart basalt fibre–reinforced polymer bar, with which some key parameters can be well assessed, such as crack location, crack width, displacement and bending moment. However, the self-sensing effects indeed have been obviously influenced by the strain measurement accuracy especially after concrete cracking. Therefore, it is meaningful to improve the sensing accuracy especially for complicated strain. Additionally, some prestress upon the smart basalt fibre–reinforced polymer bar can improve both sensing and strengthening performance.

Sliding mode boundary control for vibration suppression in a pinned-pinned Euler–Bernoulli beam with disturbances

This work addresses the control of a pinned-pinned beam represented by the fourth order partial differential equation commonly known as the Euler–Bernoulli beam model. The system under consideration has pinned boundary conditions on one end (displacement and bending moment fixed at zero) and controlled boundary conditions on the other end (displacement and bending moment are prescribed by control functions). There are also unknown bounded disturbances included on the controlled boundary. A backstepping control technique which introduces arbitrary damping into the system is discussed, and a method for applying this control in the presence of unknown disturbances is developed using sliding mode control theory. Sliding mode controllers are developed in a way that does not create a chattering effect, which is a common issue with sliding mode control. Simulation results are presented to show how the system dampens out vibrations at an arbitrarily determined rate and how the control functions respond to unmodeled disturbances.

Predicting the Bounds of Vehicle-Induced Bridge Responses Using the Interval Analysis Method

AbstractA method for predicting the bounds of vehicle-induced bridge responses with uncertain bridge and vehicle parameters is presented. The uncertainties in the parameters of the bridge and vehicle are represented with interval variables instead of conventional random variables with known probability distributions. First, a three-dimensional vehicle–bridge interaction (VBI) system, which has no closed-form solution and can account for road roughness, is established. Then, by introducing the interval analysis method (IAM) based on the first-order Taylor series expansion, the expressions of the bridge responses, including displacement and bending moment at the midspan, can be explicitly given as functions of the interval parameters, and the lower and upper bounds of the bridge responses are determined by the particle swarm algorithm instead of direct interval arithmetic to avoid excessive overestimation of the responses. The subinterval technique can also be adopted to improve the accuracy of the IAM. A n...