An Investigation of the Ground Motion Scaling Procedures for the Nonlinear Seismic Analyses of Concrete Gravity Dams

Seismic assessment of gravity dams is generally carried out using time history analyses. Scaling of the motions is commonly used; however, in contrast to buildings, the performance of scaling procedures at predicting the mean and reducing the dispersion in engineering demand parameters (EDPs) is not known. The main goal of this study is to assess the performance of different scaling procedures in predicting seismic demands on dams. The performance regarding the prediction of the damage and the required number of motions for effective analysis was investigated. The results show that techniques commonly used for moment frames should not readily be applied to these structures.     

The Gravity of Archaeology

One of the defining features of the material culture of space exploration is the fact that much of it is “out there”: in orbit around celestial bodies and on planetary surfaces. In outer space, we have to rethink the meaning of place. Cartesian coordinates must be replaced with equations of motion to describe the ceaseless movement of heavenly objects in relation to centres of gravity. Archaeological sites in space are not solid condensations of artefacts, hundreds or thousands of years compressed into layers perhaps only centimetres deep. The materials of an archaeological deposit become rather a cloud or swarm. But for both Earth and space, gravity is the structuring force. In this paper I want to reconceptualise archaeological sites according to their position in the gravity well, using dynamical systems and Riemann surfaces. I then consider the Mir space station as an example of a site existing simultaneously on Earth and in orbit, as a preliminary excursion towards a frame of reference that can be used to effectively conduct an archaeology in outer space.     

Seismic Rotational Displacements of Gravity Quay Walls Considering Excess Pore Pressure in Backfill Soils

The effect of excess pore pressure developed in backfill soil during earthquake is an important consideration in rotational displacement prediction of gravity quay walls. Based on Newmark’s sliding block concept and stress-based excess pore pressure model, a new method is proposed to predict the critical rotational acceleration and angular acceleration time histories considering the development process of excess pore pressure in earthquake events. Then, the rotational displacement of gravity quay walls is predicted according to the calculated angular acceleration time histories. By using the proposed method, the effects of various parameters involved in the calculation have been studied by carrying out a parameter study. Analysis results reveal that the influence of excess pore pressure on the rotational displacement of gravity quay walls with saturated backfill soil is significant, so, can not be ignored; and rotational displacement is sensitive to the magnitude of earthquake, horizontal and vertical seismic accelerations of ground motion, wall and soil friction angle, and soil relative density. When the rotation and sliding of wall occur simultaneously, rotation and sliding will be inhibited by each other.     

Understanding Prehistoric Lithic Raw Material Selection: Application of a Gravity Model

Provenance studies can tell us which sources of lithic raw material were used in the past, but can they tell us why? After all, many factors can have entered into a person’s choice to use one source rather than another. Those factors can be grouped into two categories, the geologic/geographic characteristics of the source itself (quality, abundance, size of pieces, etc.), and the human factors (direction of travel, time available, social restrictions, etc.). This paper demonstrates how the geologic/geographic characteristics can be quantified and calculated together to give one value, the attractiveness of the source, which can then be used in a gravity model approach to predict which sources ‘should’ have been used more than others. Deviations from the predicted pattern point to situations where the human factors were of greater or lesser importance. The values are also used to delineate geographical areas within which particular sources would be likely to be used (‘areas of influence’), which gives us a useful new way of understanding the landscape within which the prehistoric group lived.     

The contentious politics of hydropower dam impact assessments in the Mekong River basin

Since the 1990s, many large hydropower dams have been built in the Mekong River Basin. There has been considerable concern about resettlement and compensation linked to reservoir flooding, as well as the impacts of dams on wild-capture fisheries, riparian livelihoods, and aquatic biodiversity and ecosystems. Anti-dam activists in the Mekong Basin have contested these impacts by claiming that dam impact assessments limit the spatial scale of recognized impact areas in order to reduce both the political backlash against projects and the costs of dam development. In this article, we consider the contentious politics of hydropower dam impact assessments in order to understand how the spatial strategies of anti-dam activists influence the recognized scale of dam impacts. We analyze three of the most contested hydropower projects in the Mekong River Basin: the operational Pak Mun dam in northeastern Thailand, the recently completed Lower Sesan 2 dam in northeastern Cambodia, and the planned Sambor dam on the mainstream Mekong River in Cambodia. We argue that the recognized scale of impacts is in part an outcome of anti-dam activists’ different spatial imaginaries and associated scale frames—along with those of state actors, business interests, and project consultants—that inform activist strategies for mobilizing geographically dispersed people to make claims about dam impacts. Although activists have sometimes challenged the spatial extent of project impact assessments, they have also sometimes inadvertently adopted strategies to contest dams that have reproduced project scale frames favorable to dam proponents.     

Some Issues in Seismic Analysis and Design of Blockwork Wharves

During past decades, a number of ports worldwide have suffered extensive earthquake-related damage. As seaports play a key role in the world's economy, their seismic performance should be enhanced, clearly stated and reliably pursued by designers. This work focuses on seismic vulnerability of wharves in Italy. According to a recently carried out statistical study, most of the existing wharves are gravity-type, made of superimposed, dry-connected blocks, particularly in older facilities. Such technology is widely in use worldwide but it has not attracted much research interest so far. In the present study, the validity of current, simplified design approaches has been investigated by comparison with the results of inelastic dynamic time-history analyses. Permanent displacements of the wall blocks have been calculated. Available performance criteria have been reviewed. A real wharf structure in the Port of Ancona (Italy) has been studied in depth, as a methodological example. For such structure, a parametric study has been conducted with the aim of investigating the role played by different design parameters and to assess the validity of the widely in use pseudo-static method.     

Seismic Resistant Effects of Composite Reinforcement on Rockfill Dams Based on Shaking Table Tests

In this article, the seismic resistant effect of a new reinforcement measure on rockfill dams, the Composite Reinforcement, is investigated based on 1-g large-scale shaking table tests. A 1 m high rockfill dam, which is scaled from the Yele rockfill dam in China, is tested by inputting a series of motions designed from a realistic Wenchuan earthquake record. The model dam is divided into two sections, with one section representing a normal rockfill dam (RD) while the other section employing the Composite Reinforcement (composite reinforced rockfill dam (CRRD)). The seismic-resistant effect of the Composite Reinforcement is investigated by comparing the recorded dynamic response of the two dams, in terms of the peak acceleration amplification factor distribution along the dam core, the crest settlement, and the visualized failure pattern. Results show that the application of the Composite Reinforcement can effectively mitigate the seismically induced deformation of the rockfill dam by reducing the peak crest acceleration and residual crest settlement by 18% and 55%, respectively, when subjected to a 0.5 g input motion. The investigation of the captured failure pattern on the two dams further indicates the effective reinforcing effect of the Composite Reinforcement on preventing the sliding failures of rockfill materials in the top 20% height of the dam body.     

基于力矩平衡原理的秦兵马俑重心测量及临界地震加速度计算

随着近年来地震灾害的频发,分析浮放于俑坑中的秦兵马俑在地震波影响下的运动方式是秦俑地震灾害防御研究中的首要环节。本研究利用力矩平衡的原理测量秦兵马俑的重心位置,进而初步计算得到陶俑的临界地震加速度,依据陶俑的形体特征计算出每类陶俑的抗倾倒极限地震加速度,验证了测量结果的可靠性,为制定秦俑的地震设防等级和防震保护工作提供了基础数据。     

Seismic Analysis of Masonry Gravity Dams Using the Discrete Element Method: Implementation and Application

Much research in recent years has focused on the seismic analysis of concrete and earthfill dams, and few works have addressed the case of masonry dams. The structural behavior of masonry dams is controlled essentially by its discontinuous nature, which may induce significant nonlinear response during an intense earthquake. In this article, a numerical tool based on the Discrete Element Method is presented, aimed at the static, dynamic, and hydromechanical analysis of masonry gravity dams. The use of discontinuous models is mandatory for the study of failure mechanisms involving the masonry discontinuities, the dam-rock interface or the rock mass joints. The Discrete Element Method is able to assemble continuous and discontinuous meshes simultaneously in the same model, providing a versatile tool to consider various assumptions and levels of analysis, ranging from simplified to detailed structural representations. A comprehensive study of the seismic behavior of Lagoa Comprida Dam, located in Portugal, is presented. Both continuous and discontinuous models were developed to assess the main failure mechanisms, including overstress, partial and global sliding, and overturning.