| Bus rollover accident is a common phenomenon in road vehicle traffic, whichwill cause large amount of losses in property and human lives. The W-beam guardrailin road-side of highway is of importance in defense of bus rollover accidents. Thestudy of W-beam guardrail at home and aboard has been carried out for many years,and some results have been achieved, but the study of anti rollover on the W-beamguardrail is still a vital subject in the field of highway safety. Based on previousstudies, this paper focuses the research of bus rollover, and the structure parameters ofW-beam guardrail were analyzed and optimized for improvement of guardrailprotective performance. Finally a W-beam guardrail was designed with a improvedtype post which can effectively prevent the bus rollover. The main contents of thearticle are summarized as follows:Firstly, the mathematical model of rollover is presented to put forward thecritical rollover force model of bus to guardrail collision, based on previous criticalrollover force model of the vehicle to ground collision. The critical rollover forcemodel forms the background knowledge for calculation of rollover response curvesand evaluation index by using MATLAB and analysis of the influencing factors to busrollover. The rollover prevention performance of guardrail is then evaluated by usingthe calculated indexes.Secondly, a bus and a guardrail FE model were developed for a simulation of busrollover collision. The bus finite element model was constructed based on a12metersbus UG model. The simulation of bus rollover is made for analysis of the reliability ofbus FE model in terms of the energy and acceleration calculated from bus collision.Then based on the structure requirement of “Specification for Design and Constructionof Expressway Safety Appurtenances”(JTJ074-1994), the W-beam guardrail FEmodels are build by Hypermesh software according to the geometric models. And thesimulation of guardrail impact experiment was made to verify the reliability of theguardrail, through comparing the energy absorption curve of guardrail betweenexperiment and simulation.Thirdly, based on the previous indexes found on the mathematical model, thesimulation of the bus rollover was made to analyze the effects of the guardrails’factors which affect the bus rollover. The five parameters of the guardrail wereselected for simulation study, including the number of W beam, the height of guardrail, the thickness of W beam, the diameter of post, the thickness of post. The simulationstudies were carried out upon the orthogonal experimental model of L18(2×34).After an analysis of the data and curves from simulations, the significant factors thataffect the bus rollover were found out, and the combined optimum values of guardrailwere obtained.Finally, based on the optimum value guardrail, and combined with the steel platespring principle, the reasonable form of guardrail was put forward, that is, animproved post type guardrail. The improved guardrail was compared with theoptimum value type guardrail, the improved semi-rigid guardrail demonstrated astrong anti bus rollover ability.The results of study show that after collision, the maximum angle of theimproved post type guardrail is22°, the collision force impulse is51.5kΝ s, themaximum dynamic displacement was602mm, the maximum Z direction displacementof the bus center is168mm, which are all less than the optimum combination valuebarrier corresponding to42°,52.4k Ν s,876mm,180.8mm. Therefore, it can beinferred that the improved post type guardrail is the semi-rigid guardrail which hasthe best anti bus rollover performance. |
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