Experimental Study of Pore Pressure and Deformation of Suction Bucket Foundations Under Horizontal Dynamic Loading

Centrifuge experiments are carried out to investigate the responses of suction bucket foundations under horizontal dynamic loading. The effects of loading amplitude, the size of the bucket and the structural weight on the dynamic responses are investigated. It is shown that, when the loading amplitude is over a critical value, the sand at the upper part around the bucket softens or even liquefies. The liquefaction index （excess pore pressure divided by initial effective stress. In this paper, the developmental degree of excess pore pressure is described by liquefaction index） decreases from the upper part to the lower part of the sand foundation in the vertical direction and decreases from near to far away from the bucket＇s side wall in the horizontal direction, large settlements of the bucket and the sand around the bucket are induced by the horizontal dynamic loading. The dynamic responses of the bucket of a smaller height （when the diameter is the same） are heavier. A cyclic crack some distance near the bucket occurs in the sand.

Variational Solution of Coral Reef Stability Due to Horizontal Wave Loading

This paper proposes a theoretical method that can be used in calculating the stability of coral reefs or artificial islands.In this work,we employ the variational limiting equilibrium procedure to theoretically determine the slope stability of coral reefs covered with hard reef shells as a result of horizontal wave loads.A reasonable functional is proposed and its extremum is calculated based on the conservation of energy.Then,we deduce the stability factor Ns of coral reefs under combined vertical self-gravity and horizontal wave loads,which is consistent with the published results.We compare some classic examples of homogeneous slopes without hard shells in order to analyze the accuracy of results generated by this variational procedure.The variational results are accurate and reliable according to the results of a series of detailed calculations and comparisons.Simultaneously,some other influence parameters on the reef stability,including the top-layer tensile strength of coral reef,the amplitude of wave loading,and the tensile crack,are calculated and discussed in detail.The analysis results reveal that the existence of a hard reef shell could enhance the stability of reef slope and that there is a nonlinear relationship between the stability factor Ns,the shear strength,and the thickness Ds of the covered coral reef shell.Furthermore,the emergence of top-layer tensile cracks on the coral reefs reduces their stability,and the action of horizontal wave loads greatly decreases the stability of coral reefs.Thus,the hard shell strength and its thickness Ds,surface tensile crack,and wave loading require more careful attention in the field of practical engineering.

Optimization design of piles subjected to horizontal loads based on reliability theory

Based on reliability theory,a general method for the optimization design of piles subjected to horizontal loads is presented.This method takes into consideration various uncertainties caused by pile installation,variability of geotechnical materials from one location to another,and so on.It also deals with behavior and side constraints specified by standard specifications for piles.To more accurately solve the optimization design model,the first order reliability method is employed.The results from the numerical example indicate that the target reliability index has significant influence on design parameters.In addition,the optimization weight increases with the target reliability index.Especially when the target reliability index is relatively large,the target reliability index has significant influence on design weight of piles.

The Influence of Aerodynamic Unsteady Effect on Maneuver Load of Aircraft Horizontal Tail

In this paper, the unsteady effect of airflow is introduced into the calculation of aircraft maneuver load, and the results are compared with those obtained by quasi-steady method. Taking the steep pitch maneuver of an aircraft as an example, two methods are used to calculate the aircraft response after the rudder input is given according to the specifications. The calculation results show that if the peak overload of the aircraft is the same, the horizontal tail load increases by about 1% when the unsteady effect of the airflow is taken into account. If the rudder input of the two methods is the same, the unsteady calculation method will increase more. At the same time, the calculation shows that the bigger the deflection speed of rudder surface is, the bigger the difference between them is. Therefore, in order to improve the design quality of aircraft, it is necessary to introduce the unsteady effect into the calculation of loads in the detailed design stage of aircraft.

Assessment of natural frequency of installed offshore wind turbines using nonlinear finite element model considering soil-monopile interaction

A nonlinear finite element model is developed to examine the lateral behaviors of monopiles, which support offshore wind turbines(OWTs) chosen from five different offshore wind farms in Europe. The simulation is using this model to accurately estimate the natural frequency of these slender structures, as a function of the interaction of the foundations with the subsoil. After a brief introduction to the wind power energy as a reliable alternative in comparison to fossil fuel, the paper focuses on concept of natural frequency as a primary indicator in designing the foundations of OWTs. Then the range of natural frequencies is provided for a safe design purpose. Next, an analytical expression of an OWT natural frequency is presented as a function of soil-monopile interaction through monopile head springs characterized by lateral stiffness KL, rotational stiffness KRand cross-coupling stiffness KLRof which the differences are discussed. The nonlinear pseudo three-dimensional finite element vertical slices model has been used to analyze the lateral behaviors of monopiles supporting the OWTs of different wind farm sites considered. Through the monopiles head movements(displacements and rotations), the values of KL, KRand KLRwere obtained and substituted in the analytical expression of natural frequency for comparison. The comparison results between computed and measured natural frequencies showed an excellent agreement for most cases. This confirms the convenience of the finite element model used for the accurate estimation of the monopile head stiffness.

Finite element analysis of road structure containing top-down crack within asphalt concrete layer

In this paper, a four-layered road structure containing a top-down crack is investigated by performing finite element analyses in ABAQUS. In this study, in addition to the vertical load of a vehicle wheel, the horizontal load as well as its position with respect to the crack is also considered in the analyses, and the crack tip parameters including stress intensity factors(SIFs) and T-stress are then calculated. Moreover, influence of elastic modulus and thickness of the pavement layers on the crack tip parameters is studied. Results show that the horizontal and vertical loads along with their position with respect to the crack, elastic modulus and thickness of the road layers influence the crack tip parameters(KⅠ, KⅡ and T-stress) significantly. It was also found that for the cases that the vehicle wheel is positioned near the crack plane, only the shear deformation mode is observed at the crack tip;while, for the vehicle wheel positions far from the crack, only the opening mode is observed, and between these positions, both the opening and shear deformation modes(i.e., mixed mode Ⅰ/Ⅱ) are observed at the crack tip.

Bilateral shear strength of rectangular frame column based on simplified space truss-arch model

To investigate the bilateral shear strength of rectangular frame column subjected to oblique horizontal load, we presented a simplified space truss-arch model developed from unilateral truss-arch model. Main parameters in the new model were the cross-sectional area, transverse reinforcement raito, axial load, and material strength of the column. The reduction coefficient of concrete sterength owing to the severe cracking of column was also introduced in the model. Finally, 14 specimens under oblique horizontal load were tested to verified the feasibility and applicability of the space truss-arch model.

Earthquake-resistant behavior of short-limbed wall

The seismic resistance properties of the structures of short-limbed walls (SLW) were explored by horizontal cyclic loading experiments on 6 SLW specimens including 3 flanged and 3 non-flanged. The ratios of the depth to the width of the 3 specimens in each group were 5, 6.5 and 8, respectively. For non-flanged SLW structures with a small depth-to-width ratio, longitudinal bars in the limb yield first;and for those with a large depth-to-width ratio, stirrups in a linking beam yield first. For a structure with different depth-to-width ratio varying from 5 to 8, the failure mode is different. Correspondingly, different calculation model should be used in the design and engineering of the structure. For flanged SLW structures with whatever depth-to-width ratio, longitudinal bars in a flange or limb yield first. The SLW structures with a depth-to-width ratio of 6.5 exhibit the best comprehensive seismic resistant property and flanged walls have a better ductility than non-flanged ones.

Numerical analysis of bearing behaviors of single batter piles under horizontal loads in various directions

The horizontal bearing behavior of a single batter pile(SBP)is vital to its application in practical engineering;however,the horizontal responses of SBPs change with the directions of horizontal loads,and this phenomenon is rarely investigated.Therefore,the directional differences in the horizontal bearing behaviors of SBPs are investigated in this study.Four model tests are conducted to preliminarily examine the effects of the skew angle of horizontal loads on the horizontal bearing capacities and distributions of the bending moments of the SBPs.Subsequently,the differences in the responses of the SBPs under horizontal loads in various directions at full scale are analyzed comprehensively via finite-element(FE)analysis.The effects of the skew angle on SBP-soil interaction are discussed.Moreover,an empirical design method is proposed based on the FE analysis results to predict the bearing ratios of SBPs in medium-dense and dense sand while considering the effects of the skew angle,batter angle,and pile diameter.The method is confirmed to be effective,as confirmed by the close agreement between the predicting results with the model test(reported in this study)and centrifuge model test results(reported in the literature).

Performance comparisons between cellular-only and cellularfWLAN integrated systems based on analytical models

To solve the traffic load imbalance issue in cellular networks, which is often in the form of hot-spots caused by the different user mobility levels, one of the good solutions at present is to construct heterogeneous integrated wireless networks that combine cellular networks and wireless local area networks （WLANs） together. In general, the traffic volume is significantly heavier in the hot-spots of cellular networks and a higher data transferring rate can be provided by introducing a WLAN so as to raise the utilization of the channel and achieve a good balance between user satisfaction and the efficiency of the network. In this paper, we provide a comprehensive performance comparison of the systems both before and after the integration, based on an existing mathematical model, focusing on both the qualitative and the quantitative analysis of changes in the performance of the system to validate the efficiency and superiority of the cellular/WLAN integrated systems over cellular-only systems.