Bottlebrush polymers have densely tethered side chains grafted to a linear polymer backbone, resulting in stretching of both the side chains and backbone. Prior studies have reported that the side chains are only weakly stretched while the backbone is highly elongated. Here, scaling laws for the bottlebrush backbone and side chains are determined through small-angle neutron scattering analysis of a systematic series of poly(lactic acid) bottlebrush polymers synthesized via a "grafting-through" ring-opening polymerization. Scattering profiles are modeled with the empirical Guinier-Porod, rigid cylinder, and flexible cylinder models. Side chains are found to be only weakly stretched, with an end-to-end distance proportional to N 0.55 , while the overall bottlebrush increases in size proportional to N 0.77 . These results demonstrate that the bottlebrush backbone is not fully extended and that both side chains and backbone have significant conformational flexibility in solution.
Local scour of bridge piers is one of the main threats responsible for bridge damage. Adopting scour countermeasures to protect bridge foundations from scour has become an important issue for the design and maintenance of bridges located in erodible sediment beds. This paper focuses on the protective effect of one active countermeasure named an “anti-scour collar” on local scour around the commonly used cylindrical bridge pier. A cylindrical pier model was set up in a current flume. River sand with a median particle size of 0.324 mm was selected and used as the sediment in the basin. A live-bed scour experimental program was carried out to study the protective effect of an anti-scour collar by comparing the local scour at a cylindrical bridge pier model with and without collar. The effects of three design parameters including collar installation height, collar external diameter and collar protection range, on the scour depth and scour development were investigated parametrically. According to the experimental results, it can be concluded that: the application of an anti-scour collar alleviates the local scour at the pier effectively; and the protection effect decreases with an increase in the collar installation height, but increases with an increase in the collar external diameter and the protection range. Design suggestions for improving the scour protective effect of the anti-scour collar are summarized and of great practical guiding significance to the development of anti-scour collars for bridge piers.
Local scour around caissons under currents has become one of the main factors affecting the safety of foundation construction and operation in coastal and offshore bridge engineering. Local scour occurs not only in the operation stage, when the caisson has settled into the sediment, but also in the construction stage, when the caisson is suspended in water. In this study, the local scour induced by unidirectional and tidal currents around settled caissons with different cross-sections (circular, square, and diamond) was experimentally investigated. Circular and square caissons were selected to investigate the difference in local scour of suspended caissons under unidirectional and tidal currents. The main findings from the experimental results were: (1) the temporal development of scour under tidal current was slower than that of unidirectional current; (2) the effect of current type can significantly influence the size and location of maximum scour depth around circular and square caissons; (3) the appropriate choice of cross-section could reduce the maximum scour depth around the settled caisson; (4) the maximum scour depth of tidal current was smaller than that of unidirectional current when the caisson was settled into the sediment, while the opposite effect occurred when the caisson was suspended in water.
Roads and Bridges (R-B) infrastructure development in Benin Republic have being topical issues and have beenidentified by many as crucial components for economic development of the country. In light of the above, this study analyzes the R-B infrastructure agreeable priority issues, by diagnosing the current problems of development and the perspectives. Historical as well as descriptive approaches were adopted in data collection and were complemented by surveys. The study revealed, on one hand, the large gap between national R-B provision and the road transportation demand, and in the other hand, an inequality in the provision of road infrastructure and rehabilitation of roads in the area, resulting in disparities in the level of development. Based on this, the paper concludes with a range of best recommendations and proposals formulated in aim to respond efficiently to the R-B problems in Benin Republic and meet today's development goals.
Abstract. In recent years, with the rapid and continuous increase in traffic demand, a new upsurge in the construction of transport system is being made in Porto-novo. Thus, the problem of how to make modal transport system in this area play its full role and make its helpful to the development of integrated multimodal transportation networks needs to be urgently put forward. Recognizing these needs, this paper systematically addresses key issues and challenges toward developing integrated multimodal national transportation networks in the banded development axis of Abomey-Calavi-Pkota, Cotonou and Porto-novo with an emphasis to regional connectivity. Particularly, the paper addresses issues with the planning process, institutions, governance, strengths and weaknesses, funding and integrated multimodal development.
With marine bridges extending to the deep sea, wave current force action and scouring on bridge foundations have become the main factors threatening bridge safety. To ensure the design rationality as well as construction and operation safety of bridges, this paper sorts out the major problems faced by marine bridges in terms of wave force action and foundation scour, and proposes that marine bridges should be developed in high-precision prediction method, environmental prediction and pre-warning systems, research on multi-factor coupling effect of environment, scour numerical simulation technology, and wave current force calculation method. Furthermore, countermeasures are proposed from the aspects of macroscopic management, industrial application, and academic technology.
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