Study On Damage And Protective Measures Of Bridge Piers Under Rockfall Impact

With the construction of infrastructures in the western mountain area,the bridges have become indispensable structures in the construction of mountain area.As the west of our country is the headstream of many major rivers,and there is abundant precipitation in this region,and the mountains are very high along the river banks,and the cliffs are very steep,the geological disasters are prone to happen,such as the landslides,mudslides and rockfall.For the western mountain highway bridges,the accidents of rockfall impact always happen on the bridge piers,and it seriously affects the normal working performance of piers.So the impact of rockfall disaster on the bridge has gradually become great.This has become a key part in the design of bridges in western mountain area.Currently,there are still few literatures of rockfall impact on bridge piers.Especially,the researches on the damage of bridge piers caused by the variation of rockfall impact and the evaluation of bridge operation state after the damage of impact have not been studied.Considering the above,the bridge,which was built in post disaster reconstruction of G213 Chuanzhusi to Wenchuan Road,was taken as the research object.The dynamic response,damage law,residual bearing capacity,evaluation of bridge traffic capacity by the rockfall impact were analyzed by the explicit dynamic analysis method.The main contents are as follows.1.Based on the review of rockfall disasters which occur mostly in the west or mountain area after the earthquake in our country,the background and research significance of this dissertation were given.The literatures about rockfall impact in domestic and international engineering field were introduced,including the research of rockfall disaster risk,rockfall movement characteristic,rockfall impact,protective measure and structural bearing capacity.In the second chapter,the impact concept and basic equations were introduced and deduced.2.Four movement characteristic equations of rockfall were studied,which were free falling,sliding,rolling and impact rebound of rockfall.As the normal coefficient of restitution and tangential coefficient of restitution methods were used in most studies,solving speeds of two directions was very complicated.So the equation of coefficient of restitution of rockfall impact rebound was deduced by integrating the coefficients of restitution of the two directions.It was called "Integrated coefficient of restitution",which could reflect the change of rockfall speed more intuitively.Taken a dangerous slope in Chuanwen Highwan as the prototype,1000 numerical simulations of rockfall characteristic were analyzed by using rockfall trajectory simulation software ROCFALL.And the parameters of rockfall characteristic were calculated,which could provide data basis for the following rockfall impact on piers damage.3.The damage piers under different rockfall impact energy were studied by full-scale and scale tests of rockfall impact.And compared with numerical simulation,the reliability of the numerical simulation was verified,which provided the basis for the subsequent parameters analysis of the impact damage factors.4.Based on the research of rockfall movement characteristic,the relavent parameters of bridge piers,rockfall and steels were determined.The impact numerical calculation method was introduced.The geometric model was established by the professional 3D modeling software Rhinoceros.And it was imported in the high-performance finite element pre-processing software HyperMesh.The finite element model of rockfall impact on piers was established,and the damage constitutive model,boundary conditions and estimation of stability were particularly introduced.5.The rockfall impact on single-column pier and double-column pier that were widely built were analyzed by using the non-linear explicit dynamic software LS-DYNA.The influence of rockfall and piers parameters on damage was studied by comparing damage volume,penetration depth,damage area and top of pier displacement.6.The collapse process of single-column pier and double-column pier under rockfall impact was simulated,and the collapse energy of piers was obtained.But the rockfall energy which made piers damage might not larger than the collapse energy,so the residual bearing capacity was calculated.The residual bearing capacity equations were obtained by data fitting,and damge degree of rockfall impact on piers was defined by reffering the contents an equations of seismic vulnerability.It could evaluate the degree of damage of piers under rockfall impact.Then the damage state of piers was divided into five grades.Through calculating the traffic capacity of the damage piers,the dangerous rockfall impact energy was determined.And on this basis,five protective measures were researched.The theories and results obtained above could provide reference for the design of rockfall impact.