ចំរៀង ABC song
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Thursday, November 29, 2018
Wednesday, November 14, 2018
Moving Load
Highway Bridge Loads. The primary live loads on bridge spans are
those due to traffic, and the heaviest vehicle loading encountered is that
caused by a series of trucks. Specifications for truck loadings on highway
bridges are reported in the LRFD Bridge Design Specifications of the
American Association of State and Highway Transportation Officials
(AASHTO). For two-axle trucks, these loads are designated with an H,
followed by the weight of the truck in tons and another number which
gives the year of the specifications in which the load was reported.
H-series truck weights vary from 10 to 20 tons. However, bridges located
on major highways, which carry a great deal of traffic, are often designed
for two-axle trucks plus a one-axle semitrailer as in Fig. 1–10. These are
designated as HS loadings. In general, a truck loading selected for design
depends upon the type of bridge, its location, and the type of traffic
anticipated.
The size of the “standard truck” and the distribution of its weight is
also reported in the specifications. Although trucks are assumed to be on
the road, all lanes on the bridge need not be fully loaded with a row of
trucks to obtain the critical load, since such a loading would be highly
improbable.The details are discussed in Chapter 6.
Railroad Bridge Loads. The loadings on railroad bridges, as in
Fig. 1–11, are specified in the Specifications for Steel Railway Bridges
published by the American Railroad Engineers Association (AREA).
Normally, E loads, as originally devised by Theodore Cooper in 1894,
were used for design. B. Steinmann has since updated Cooper’s load
distribution and has devised a series of M loadings, which are currently
acceptable for design. Since train loadings involve a complicated series
of concentrated forces, to simplify hand calculations, tables and graphs
are sometimes used in conjunction with influence lines to obtain the
critical load. Also, computer programs are used for this purpose.
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Tuesday, November 13, 2018
Monday, November 12, 2018
ល្បែងផ្នាល់
លោកសមរង្សីជាមនុស្សឆ្លាតដោយយកសេរីភាពរបស់ លោក គឹម សុខា មកផ្នាល់ជាមួយសម្តេច។
កាផ្នាល់បង្កើតរឿងនេះ អ្នកឈ្នះគឺលោកសមរង្សី ព្រោះបើសម្តេចព្រមផ្នាល់ គឺចាញ់ ដោយលោសមរង្សីនិងលើកថា តុលាកាពិតជា មិនឯករាជ្យដោយស្ថិតនៅក្រោម អំណាចរបស់ លោក ហ៊ុនសែន បើទោះបីមានកាបកស្រាយបែបណាក៏នៅមិនអាចលាងភាព ស្អាតស្អំរបស់តុលាកាបានឡើយ ។ តែបើមិន ភ្នាល់ នោះ លោកសមរង្សីនិង ឈ្នះ ដោយលើកថា រដ្ឋាភិបាលកំពង់រងសម្ពាធ អន្តរជាតិពិតប្រាកដមែន ។ ចឹង រឿងនេះមិនខុសអី ពី ចាក់ទឹកចូលរុន្ធកណ្តុរ ចឹង ចេញក៏ងាប់មិនចេញក៏ងាប់ ។ អ
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