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Showing 2 results for Downgrade

S. F. Eftekharzadeh, A. Khodabakhshi,
Volume 12, Issue 3 (9-2014)
Abstract

The previous studies show that a high percentage of traffic accidents take place in two-lane rural highways and most of which happen at horizontal curves. Meanwhile the horizontal alignment is often subject to hard topographic conditions where because of economic aspects designers are forced to design horizontal curves at grades. Vertical angle of longitudinal slope reduces the normal force of vehicle on road and friction force in tire-pavement surface will decrease. This leads to a lack of sufficient driver control over the vehicle especially if the curve with small radius is located at downgrade. In this paper, the suitability of operating speed and lateral friction coefficient as geometric design criteria for horizontal curves in downgrades are studied with regard to traffic safety and vehicle stability. The investigation of speed reduction of the vehicles running on a horizontal curve at downgrade as a response of driver behavior and the use of friction ellipse theory give the available friction coefficient. Whereas the dynamic analysis of forces applied on the vehicle in curve which is located at downgrade if combined with operating speed results in the required coefficient of lateral friction. Finally, a comparison of these two parameters based on safety evaluation criteria gives an estimation of actual safety level in designing horizontal curve at downgrades with regard to AASHTO’s data in horizontal curve design.

Volume 15, Issue 4 (6-2017)
Abstract

THIS IS THE REVISED VERSION OF THE PAPER A-10-581-3, CONSIDERED AS "MAJOR REVISION": One of the best methods to improve structural seismic behavior is to strengthen the infills by shotcreting. Most rehabilitation codes have a special part for masonry buildings and masonry infill panels. However they are completely silent for infills improved by concrete covers, probably for the lack of sufficient experimental test data. This paper focuses on the ultimate strength and modification factor of this type of infill panels, based on some experimental studies. The proposed formula of the existing codes for the equivalent width of the masonry infill panels is improved for the ultimate strength of shotcreted infill panels. It is also shown that the modification factors of the masonry and clay tile infill panels are downgraded and upgraded, respectively, if they are rehabilitated by concrete covers. The envelopes of the load-displacement behavior of the specimens are applied to calculate the modification factor, rather than the standard back bone curves. It is shown that they give more conservative values for the m-factor. Subsequently, some suggestions are proposed to estimate m-factor of shotcreted infill panels.



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