The Diffraction of Rayleigh Waves by Twin Circular Cavities in a Poroelastic Half-Space

The diffraction of Rayleigh waves by twin circular cavities in a poroelastic half-space is investigated using the indirect boundary integral equation method (IBIEM). To satisfy the boundary conditions on the free surface, Green’s functions of compressional and shear wave sources in a poroelastic half-space are derived based on Biot’s theory. It is verified that the IBIEM has great accuracy and numerical stability. Then, the influences of the drainage boundary condition, incident wave frequency, porosity, and cavity spacing on the dynamic responses are investigated by numerical examples. The results show that the amplification effect of the twin cavities is greater in the case of undrained boundary conditions, lower frequencies, and smaller cavity spacings. The porosity of the saturated medium also influences the dynamic responses because the velocity of the Rayleigh wave will change with the porosity of the saturated medium.     

Modeling and Control of the CSCEC Multi-Function Testing System

In order to promote the research and development on evaluating the seismic performance of structures, China State Construction Engineering Corporation (CSCEC) planned to construct a large-scale loading testing facility, the Multi-Function Testing System (MFTS). This facility can perform full-scale, real-time, 6-degree-of-freedom static and dynamic testing of rubber bearings and many types of structural components including long columns, shear walls and cross shape joints. The basic performances of the MFTS are a clearance of 9.1 m × 6.6 m × 10 m for specimen installation, maximum x-directional displacement 1500 mm, maximum y-directional velocity 1570 mm/s and maximum z-directional compressive load 108 MN. The system configuration and performance specifications of the MFTS are presented in this paper. The inverse kinematics model and the nonlinear model of the hydraulic servosystem of the MFTS are built. A modified feedback forward kinematics algorithm is developed for real-time control of the MFTS. Internal force characteristics of the loading system are analyzed. The internal force control method based on real-time solution of basis of internal force space is proposed for the system with large motion ranges. The motion controller combining position control loop and internal force control loop is developed. To meet the requirement of simultaneously imposing vertical compressive load and horizontal displacement, a mixed load and displacement controller is designed, where a direct force control loop is used to improve the response speed of the force control and reduce spatial dynamic coupling effects. Finally, a dynamic bearing testing is performed. The test results demonstrate that the system using the proposed controller has good abilities on position tracking, force balance, and load following.     

A Single-Run Dynamic-Based Approach for Pushover Analysis of Structures Subjected to Near-Fault Pulse-Like Ground Motions

In this paper, a fairly effective procedure called dynamic load pattern (DLP), is proposed to account for the effects of near-fault ground motions in estimating the seismic demands of structures from pushover analyses. The seismic demands are obtained by enveloping the results of single-run conventional first-mode and single-run DLP pushover analyses. Improving the estimation of target displacement is another objective, implemented by performing response-spectrum analysis. Three special steel moment-resisting frames are considered and the seismic demands resulting from DLP are compared to those from the nonlinear time-history analysis as a benchmark solution, as well as to those predicted from modal pushover analysis.     

行为区位论的初步研究

本文论述了行为区位论的产生和发展历程,分析了区位决策行为、空间位移行为和消费行为空间等模式,并对行为区位论在区位理论中的地位和作用进行了评价。     

Mixed Force and Displacement Control for Testing Base-Isolated Bearings in Real-Time Hybrid Simulation

This paper presents a robust mixed force and displacement control strategy for testing of base isolation bearings in real-time hybrid simulation. The mixed-mode control is a critical experimental technique to impose accurate loading conditions on the base isolation bearings. The proposed mixed-mode control strategy consists of loop-shaping and proportional-integral-differential controllers. Following experimental validation, the mixed-mode control was demonstrated through a series of real-time hybrid simulation. The experimental results showed that the developed mixed-mode control enables accurate control of dynamic vertical force on the base isolation bearings during real-time hybrid simulation.     

Unsettling feminist geopolitics: forging feminist political geographies of violence and displacement

Feminist geopolitics has analyzed violence across scales and critiqued the dominant epistemology of political geography for almost two decades. What theoretical and political purchase does it have today, given the potpourri of perspectives and reimaginings of the idea? Current research on violence, human displacement and the security of people out of place is used to explore answers to this question, finding that feminist political geography – a bigger tent than just feminist geopolitics – is indispensable to geographical thinking. Recent non-human feminist geopolitics of ‘earthliness’ offer an original theoretical departure from what has come before, though truncate political possibilities by refusing to engage the individuated subjects of ‘conventional’ feminist geopolitics. Feminist geopolitics and its consonant concepts remain relevant to addressing the fast violence of war, displacement, detention and the attendant waiting, or slow violence, that these power relations imply. Feminist geopolitics can and has been enriched by critical work on subaltern geopolitics and post-secular geographies and is shown to be vital to understanding human displacement for those living in the postcolonies of the global South. A case study of private refugee sponsorship to Canada is critically analyzed as one pathway out of protracted displacement. While resettlement is valorized by states and their civil societies as a laudable ‘solution’ offering permanent protection, a feminist geopolitical analysis exposes the Canadian Government’s racialized preferences and prejudice against Sub-Saharan African asylum seekers, masked as geography. The research presented exposes some of the Orientalist assumptions that frame and figure private refugee sponsorship. Taking this Orientalist critique and these additional literatures into the fold of feminist geopolitics, ‘feminist political geography’ offers a larger umbrella under which to collaborate, innovate, and intervene in political struggles that interrupt salient geopolitics and state discourse across world regions and inhibit violence wherever possible.     

Inelastic Displacement Demand of Strength-Degraded Structures

This article presents findings from parametric studies involving nonlinear time-history analyses of inelastic systems with and without strength degradation. Results showed that estimates based on the equal-displacement and equal-energy propositions can be exceeded significantly by the inelastic displacement demands in the acceleration and velocity-sensitive regions of the response spectrum. The displacement demand behaviour is sensitive to the strength degradation and the frequency properties of the ground shaking. With a modest strength reduction factor of 2, the inelastic displacement demand would typically be constrained by the Peak Displacement Demand as indicated on the elastic displacement response spectrum for 5% damping.     

Experimental Investigation of Circular Reinforced Concrete Columns under Different Loading Histories

Three reinforced concrete (RC) circular column specimens without an effective concrete cover were tested under constant axial compressive as well as cyclic lateral loading. The seismic behavior of the specimens under different loading paths was examined with the objective of understanding the influence of displacement history sequence on the seismic behavior of the columns in near-fault earthquakes. The influence of displacement history sequence upon the hysteretic characteristics, stiffness degradation, lateral capacity, as well as energy dissipation analysis was conducted. The hoop strains of lateral reinforcement at varied column heights under cyclic loading were attained by means of 8–16 strain gauges attached along the hoops. Additionally, the characteristics of strain distribution were investigated in the transverse reinforcement. The results of strain distribution were evaluated with Mander’s confinement stress model and the distribution around the cross section. The length of the plastic hinge at the end of the specimen was evaluated by measurement as well as the inverse analysis. Finally, the deformation of the specimen, which includes the components of shear deformation, bending deformation and bonding-slip deformation, was evaluated and successfully separated.     

Equivalent Damping Ratio Equations in Support of Displacement-Based Seismic Design for Pile-Supported Wharves

This study primarily proposes new equivalent damping ratio equations based on Jacobsen’s approach for displacement-based seismic design of pile-supported wharves to account for wharf configurations and soil-pile interaction. It is found that Pivot hysteresis model and Masing rule can accurately capture nonlinear behavior of concrete and steel wharves, respectively. To verify applicability of proposed equations, analyses were conducted to three typical wharves to make a comparison of maximum displacements obtained from nonlinear time-history analyses and substitute structure method with various damping equations. The verification reveals proposed equations are better than those in practice for their higher precision in determining displacements.     

Lapp Cairns as a Source on Metal Period Settlement in the Inland Regions of Finland 1

This article presents an overview of the history of research of the so-called Lapp cairns. On the basis of the limited find material from these cairns, they are assumed to be from the archaeologically poor Iron Age period of the Finnish inland regions. The situation is similar throughout large wilderness areas in northern Europe, and in Norway it has sometimes been called the "findless period" ( den funntomme perioden ). Six so-called Lapp cairns excavated in central Finland in the 1980s and 1990s are discussed in detail. Three of the cairns contained sufficient amounts of burnt bone for testing the new AMS dating method of burnt bone based on crystalline carbonate on Finnish material. As far as is known, these are the first datings of burnt bone in the Finnish material. The oldest Lapp cairn, cairn no. 1 at Pyykkisaari in Viitasaari, is from the end of the Stone Age, and the other two are from the Early Metal Period. This article briefly discusses problems related to defining Lapp cairns, their age and function. The early dating of the Lapp cairns gives new topicality to the prevailing conception that the Lapp cairns resulted from the influence of the cairns of the coastal Bronze Age. The burnt bone from the oldest cairn included the remains of seal. It is possible that these fragments of bone represent relict ringed seal that lived in Lake Keitele in the past.