Lateral clearance on the inside of horizontal curves is required by all geometric design guidelines in order to provide at least stopping sight distance. There already exist graphical models, analytical models, and de...Lateral clearance on the inside of horizontal curves is required by all geometric design guidelines in order to provide at least stopping sight distance. There already exist graphical models, analytical models, and design charts for determining minimum clearance offsets to meet the requirement. Some of these models determine the offsets based on constant design sight distance values on the assumption that drivers negotiate horizontal curves at constant speed. Therefore, those models are suitable for sites where there is no difference in speeds between tangent and curved sections. Past studies have reported that there are sites where drivers decelerate on entering horizontal curves and accelerate on departing from the curves. At those sites stopping sight distance for a given driver varies with driver location due to variable speed. This paper presents an analytical model and a chart for determining minimum offsets needed to provide desired sight distances at horizontal curves with variable operating speeds. At those sites the offsets yield roadside clearance boundaries that have transition arcs with performances that are similar to those of elliptical arcs. Therefore, practitioners may choose to use elliptical equations or equations and the chart developed herein. Results of this study will be of value to practitioners in the area of roadside design.展开更多
AASHTO’s guideline for geometric design of highways and similar guidelines require that roadside areas on the inside of horizontal curves be cleared of high objects to provide stopping sight distance. The guidelines ...AASHTO’s guideline for geometric design of highways and similar guidelines require that roadside areas on the inside of horizontal curves be cleared of high objects to provide stopping sight distance. The guidelines have analytical models for determining the extent of clearance, known as the horizontal sightline offset or clearance offset, for simple curves. Researchers in the past have developed analytical models for clearance offsets for spiraled and reverse curves. Very few researchers developed analytical models for available sight distances for compound curves. Still missing are models for horizontal sightline offsets and locations of the offsets for compound curves. The objective of this paper is to present development of analytical models and charts for determining horizontal sightline offsets and their locations for compound curves. The paper considers curves whose component arcs are individually shorter than stopping sight distance. The resulting models and the charts have been verified with accurate values determined using graphical methods. The models and the charts will find application in geometric design of highway compound curves.展开更多
According to revised Cailikefu’s rolling shear force formula,motion path equation of spatial seven-bar path is built,and mechanical model,with such new structural features as negative offset,is thus successfully esta...According to revised Cailikefu’s rolling shear force formula,motion path equation of spatial seven-bar path is built,and mechanical model,with such new structural features as negative offset,is thus successfully established for 2800 mm heavy shear of some Iron&Steel Company.Shear force and bar force of steel plate,before and after adoption of negative offset structure,are analyzed,as well as horizontal force component of mechanism that influences pure rolling shear and back-wall push force that keeps blade clearance.The discovery is that back-wall push force could be kept large enough at rolling start-up(i.e.the time that the maximum rolling shear produces),meanwhile,back-wall push force is the most approximate to side forces with adoption of 60 mm-100 mm offset.Theoretical results and on-site shear quality both indicate that new structural features such as negative offset plays an important role in ensuring pure rolling shear and keeping blade clearance constant,which provide an effective means to improve quality of steel plate.展开更多
文摘Lateral clearance on the inside of horizontal curves is required by all geometric design guidelines in order to provide at least stopping sight distance. There already exist graphical models, analytical models, and design charts for determining minimum clearance offsets to meet the requirement. Some of these models determine the offsets based on constant design sight distance values on the assumption that drivers negotiate horizontal curves at constant speed. Therefore, those models are suitable for sites where there is no difference in speeds between tangent and curved sections. Past studies have reported that there are sites where drivers decelerate on entering horizontal curves and accelerate on departing from the curves. At those sites stopping sight distance for a given driver varies with driver location due to variable speed. This paper presents an analytical model and a chart for determining minimum offsets needed to provide desired sight distances at horizontal curves with variable operating speeds. At those sites the offsets yield roadside clearance boundaries that have transition arcs with performances that are similar to those of elliptical arcs. Therefore, practitioners may choose to use elliptical equations or equations and the chart developed herein. Results of this study will be of value to practitioners in the area of roadside design.
文摘AASHTO’s guideline for geometric design of highways and similar guidelines require that roadside areas on the inside of horizontal curves be cleared of high objects to provide stopping sight distance. The guidelines have analytical models for determining the extent of clearance, known as the horizontal sightline offset or clearance offset, for simple curves. Researchers in the past have developed analytical models for clearance offsets for spiraled and reverse curves. Very few researchers developed analytical models for available sight distances for compound curves. Still missing are models for horizontal sightline offsets and locations of the offsets for compound curves. The objective of this paper is to present development of analytical models and charts for determining horizontal sightline offsets and their locations for compound curves. The paper considers curves whose component arcs are individually shorter than stopping sight distance. The resulting models and the charts have been verified with accurate values determined using graphical methods. The models and the charts will find application in geometric design of highway compound curves.
基金Supported by the National tenth-five Key Technologies R&D Programme(ZZ01-13A-03-03-04).
文摘According to revised Cailikefu’s rolling shear force formula,motion path equation of spatial seven-bar path is built,and mechanical model,with such new structural features as negative offset,is thus successfully established for 2800 mm heavy shear of some Iron&Steel Company.Shear force and bar force of steel plate,before and after adoption of negative offset structure,are analyzed,as well as horizontal force component of mechanism that influences pure rolling shear and back-wall push force that keeps blade clearance.The discovery is that back-wall push force could be kept large enough at rolling start-up(i.e.the time that the maximum rolling shear produces),meanwhile,back-wall push force is the most approximate to side forces with adoption of 60 mm-100 mm offset.Theoretical results and on-site shear quality both indicate that new structural features such as negative offset plays an important role in ensuring pure rolling shear and keeping blade clearance constant,which provide an effective means to improve quality of steel plate.
