Moment-less Arches for Reduced Stress State

This paper presents a study of two-pin arches of constant cross-section that are moment-less under statistically prevalent (permanent) load. The arches are defined by analytical form-finding previously reported in [1]. The work provides guidance regarding the solution process, and expressions for reactions and axial forces. New analytical results include the derivation of the arch length, and a method for finding co-ordinates of individual arch segments in pre-fabricated construction. The accuracy of the shape prediction for inextensible moment-less arches is good, compared to the results from elastic models. Case studies report on medium and large-span arches, with the latter resembling the iconic Hoover Dam arch. Comparative studies of the moment-less and conventional arch forms (mostly of parabolic configuration), are carried out using permanent and variable loads. Additionally, the Hoover Dam arch is analysed for a discrete load transfer from the deck. Circular arches are analysed for the permanent load only, and are shown to be extremely inefficient in load resistance. Moment-less arches are found to provide a minimal stress response to loading and require least amount of material – a feature observed in natural objects. These characteristics are important from a durability perspective – a key concern for our future infrastructure.

Time and the Hydroelectric Dam

The hydroelectric dam is an interface in which contrasting temporalities converge and undergo transformation. Its massive wall sits at the center of operations where age-old ecosystems clash with rapid modernization, white water turns into a placid lake, and dynamos convert the lake’s gravitational pull into high-voltage electrical current. The hydroelectric dam exploits and exacerbates differences among the temporalities distinguishing these operations to generate power. In doing so, it has rendered the variance of time more perceptible. To support this claim I focus on the iconic Hoover Dam and on the works of Oskar J. W. Hansen, Joan Didion, Allen Tupper True, Francis Ponge and Fabrice Gobert. The main themes I examine in their works pertain to the notion of temporal interface and to the conceptions of deep, nested and haunted time.

Lake Mead and Hoover Dam monitoring in Nevada and Arizona states, USA using InSAR

<p>Man-made reservoirs and lakes are key elements in the terrestrial water system. The increased concern about the impact of anthropogenic interventions on and the dynamics of these water resources has given rise to various approaches for representing human-water interactions in land surface models. Synthetic aperture radar interferometry (InSAR) has become a powerful geodetic tool for this purpose, by evidencing changes of ground and water surfaces across time and space. In this research, the Lake Mead and associated Hoover Dam are studied using Small Baseline Subset (SBAS) technique. Lake Mead is the largest reservoir in the United States, in terms of water capacity, supplies water and hydropower for millions of people in Las Vegas, Los Angeles and southwestern part of the USA. In recent years, rising temperature, increasing evaporation and decreasing precipitation have decreased water levels substantially, and probably modified its surrounding groundwater and surface as well.</p><p>This study aims to identify a hydrology-induced ground deformation around the lake Mead and a probable Hoover dam movement displacement. For the reservoir, we used the SBAS technique using 138 SAR data, including ERS1/2, Envisat, ALOS PALSAR and Sentinel-1, covering a time-spam between 1995 and 2019. For the analysis on the dam, we used the SBAS technique from 2014 to 2019 with descending and ascending modes of Sentinel-1A/B imageries. We found two main deformation patterns around the lake associated with the water level changes. Firstly, ERS and Sentinel-1 data evidenced a ground deformation that manifested itself as as a subsidence pattern in 1995 that has gradually changed into an uplift up to 2019. Secondly, the correlation trend between the deformation and water level changes has changed from negative to positive, with a transition point around March 2008. A possible interpretation for this is that the ground has initially reacted to the water fluctuations in the reservoir before March 2008 but after no longer plays a dominant role in the deformation occurring around the lake. The findings will help us to have a better understanding over the changes happened around the lake due to the water level changes and provide the valuable information for more effective management and maintenance of hydraulic structures and facilities near by the lake and water control in the future.</p>

Special Issue on Expectations for Upgrading Dams Under Operation

IntroductionThere are approximately 2,700 dams in Japan. Their total reservoir capacity is approximately 25 billion m3(BCM), far less than the 34.4 BCM of Hoover Dam in the US or the 39.3 BCM of the Three Gorges Dam in China. Lake Biwa, with a capacity of 27.5 BCM, which has recently been used for multiple purposes by the Lake Biwa Comprehensive Development Project, is equivalent in scale to such artificial lakes. On the other hand, dams in Japan that were constructed on mountain rivers with considerable sediment deposits are decreasing their capacity more rapidly than those constructed on continental rivers, so they require measures against deposition to maintain their long-term reservoir capacity. In addition, extreme weather phenomena (increased rainfall and drought intensity) under climate changes increase high demand for storage capacity of dams. In order to effectively use these dams as limited resources and to hand them over to the next generation in healthy state, continuous investment and development of maintenance technology are required. Recently, to promote this investment and development, “A vision for upgrading dams (effective use of existing dams to mitigate damage from frequent floods and droughts and to generate renewable energy)” was established by the Ministry of Land, Infrastructure, Transport, and Tourism (MLIT) on June 27, 2017 [1]. This special issue is collecting the significance of the dam upgrading projects and important challenges from various aspects to be implemented.