Urban Expansion and Driving Force Analysis of Ulaanbaatar in Mongolia in Recent Thirty Years

Since the reform of the regime in the 1990s，Mongolian urban experienced a rapid development.Understanding the characteristics of urbanization and development in Mongolia is much of significance to China’s implementation of the “Belt and Road” strategy and “China-Mongolia-Russia Economic Corridor”.This study was based on theLandsat TM/OLI remote sensing image，using object-oriented classification method，and obtained 1990，2001，2010，2017 land cover data set，the overall classification accuracy were 86%，89%，91.6%，94.80% respectively，Kappa coefficient were 0.83，0.869，0，898，0，935.based on the transfer matrix，the information of land cover change from 1990 to 2017 in Ulaanbaatar was mined，the results showed that：① the areas of built area，barren，and water showed an increasing trend，and the built area was increased most.On the contrary，the area of forest，cropland，and grassland showed a tendency to decrease，and the forest area decreased most.② the transfer between grassland and forest，grassland and built area，forest and grassland played a major role in land cover change of Ulaanbaatar.The change area from 1990 to 2001，2001 to 2010 and 2010 to 2017 accounted for nearly 71%，74%，and 79% of the total change area.③ the expansion trend of built area was significant，the area has increased from 99.87 km2to 216.16 km2，the growth rate has reached 216%，the expansion rate was 8.01 km2/a，which belonged to the rapid expansion mode.The middle-north with the type of summer house，northeast with the types of traditional houses based on the structure of home-household-yard，mixture of Mongolian yurts and low buildings，west with the types of industrial land and residential land.The urbanization in Ulaanbaatar caused by the interaction of external social economic development and national policies，among of which，land privatization and market economic were the main policy driving forces of urbanization     

Experimental evaluation of joints consisting of parallel perfobond ribs in steel-PSC hybrid beams

The objective of this paper is to estimate the structural capacity and application feasibility of joints with parallel perfobond ribs in steel-PSC (prestressed concrete) hybrid beams. In order to investigate the joints, two steel-PSC hybrid beams of 8 m length are fabricated, and experimental tests are performed. The hybrid beams consist of a steel beam in the center, PSC beams at both ends, and joints connecting the steel beam and the PSC beams. In the joints, perfobond ribs are used as shear connectors in place of studs which are generally used. The parallel perfobond ribs are attached to the steel plates horizontally and vertically to assess joint performance under both flexural moments and shear forces. The test results reveal that the failure of hybrid beams occurs at the PSC region near the interface between the PSC component and the joint. No joint failure is observed in the test beams up to the fracture load stage. In addition, the test beams show sufficient ductility by virtue of the arrangement of adequate reinforcements, even though perfobond ribs are considered to be stiff shear connectors. Therefore, it is concluded that the joint with parallel perfobond ribs is an applicable system to utilize in steel-PSC hybrid beams. In addition, the perfobond ribs can be an alternative to stud shear connectors in joints of hybrid beams.