| As a passive rockfall protection structure,Shed-tunnel has been widely used in engineering.But its dynamic response for rockfall impact and structure optimization analysis need for further study.With the support of the National Natural Science Foundation of China(ID:51108488)and method of numerical simulation,this thesis analyzed the dynamic response for rockfall impact of shed-tunnel with different structures,and got the better structure of shed-tunnel that is the inclined column and semi-arch shed-tunnel structure;This type of shed-tunnel structure was further optimized;Made a comparative analysis of the impact force of the rockfall under different forms of shed-tunnel structure.The main research results are as follows:(1)When the roof of inclined column and semi-arch shed-tunnel structure,inclined column and gantry shed-tunnel structure,straight column and semi-arch shed-tunnel structure,straight column and gantry shed-tunnel structure were vertical impacted by rock,the maximum equivalent stress are at the column structure.At the same conditions,the maximum equivalent stress and amount of the settlement of roof of inclined column and semi-arch shed-tunnel structure is the minimum.That inclined column and semi-arch shed-tunnel structure are the best form of shed-tunnel structure.For the inclined column ones,the maximum equivalent stress distribution of the structure is descending: inside of column crown > inside of column bottom > inside of towing beam > below the rockfall impact position.With the shed-tunnel structure in the form of different,The maximum impact force of falling rocks descending: straight column and gantry shed-tunnel structure > inclined column and gantry shed-tunnel structure > inclined column and semi-arch shed-tunnel structure > straight column and semi-arch shed-tunnel structure.Rockfall impact force affected not only by the size of the rockfall,cushion,energy dissipation materials of shed tunnel,but by the differences of shed tunnel structure,it is recommended to consider this structure in the calculation of the impact of falling rocks an important factor.(2)When rockfall impact at different positions,the maximum equivalent stress of inclined column and semi-arch shed-tunnel structure quite different.Rockfall impact position closer to the oblique lateral column,the greater the effect of the force structure,and is much larger than other locations.Therefore,the structure of the most unfavorable impact oblique position near the top of the column,it is recommended shed tunnel structure is designed in consideration of rockfall impact position caused by different structural dynamic response differences.(3)Under different rockfall impact angles,the maximum equivalent stress of inclined column and semi-arch shed-tunnel structure quite different.With the change in the angle of impact the maximum equivalent stress descending: 45°>15°>30°>60°>0°,That is under rockfall impact angle of 45,the shed-tunnel structure generated the greatest maximum equivalent stress.Meanwhile,with the rockfall impact angle increases,the normal rockfall impact force decreases,the tangential rockfall impact force present the trend of first increase and after decreas.At an angle of 45 tangential impact force reaches a maximum value.So we recommend that 45 angle of impact as the control standards of structural safety in the structural design of shed-tunnel.(4)For inclined column and semi-arch shed-tunnel structure,when the colu mn slope is 1:0,the structure maximum equivalent stress is the maximum,when the column slope is 1:0.2,the structure maximum equivalent stress is small,when the column slope is 1:0.25,the structure maximum equivalent stress is minimum.When the column slope is 1:0,the vertical displacement of the roof is maxi mum,when the column slope is 1:0.25,the vertical displacement of the roof is small,when the column slope is 1:0.3,the vertical displacement of the roof is minimum.So we recommend that the optimum column slope of inclined column and semi-arch shed-tunnel structure ranges from 1:0.2 to 1:0.3.(5)Under different column spacing,the oscillation frequency of equivalent stress of inclined column and semi-arch shed-tunnel structure is consistent,but the time that equivalent stress peak appears inconsistent and no law.The overall performance is that the larger the column spacing is,the greater the maximum equivalent stress is.From the point of view of safety,economy and so on,the distance of 5m inclined column can be regarded as a reasonable value.(6)In the optimization in inclined column section of inclined column and semi-arch shed-tunnel structure,the effect of horizontal strengthening measures taken on the column structure is obvious,the larger equivalent stress produced in the column are uniformly distributed.For the longitudinal strengthening measures,although the equivalent stress is reduced in the strengthening place,but there is still a large stress appears on the inner side of the bottom of the inclined column,failuring to improve the stress concentration of the structure.Therefore,it is suggested that in the design of shed tunnel structure,the transverse transition of the column structure can be considered,no transition zone can be set up in the longitudinal direction.(7)With the different roof angles of inclined column and semi-arch shed-tunnel structure,the equivalent stress of the structure is greatly different after impact.For structure with negative value of roof inclination,the equivalent stress at the outside of the column is larger than that of the roof with an inclination angle of 0,for structure with positive roof inclination,the equivalent stress at the outside of the top of the column is larger than that of the roof with an inclination angle of 0.It is shown that the equivalent stress of the structure is the smallest when the roof is 0 degrees,the optimal angle of the roof is 0 degrees.(8)A roof structure with curved roof is explored,the results of the study show that: the maximum equivalent stress of curved roof structure under different rockfall impact position is small than flat roof structure,and can be reduced to an average of 3%~12%.At the same time,rockfall impact force changes of shed tunnel structure local impact is relatively large. |
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