The Research On Design Method For Steel Deck Asphalt Pavement On Large-span Steel Box Beam Bridges

The steel deck asphalt pavement on large-span steel box beam bridges is adifficult engineering problem and research focus at home and abroad. The importantreasons for short service life of asphalt pavement on steel deck in China are thedefects of systematic design method, reasonable selection of materials, standardizeconstruction and scientific management. The design model and calculation methodare base for solving this problem. In this thesis, the calculation methods of loadaffects in asphalt pavement on long span steel suspension bridge have beenresearched as the objective. The researches include the calculation methods of loadaffects in asphalt pavement system using full-bridge model, section model and localmodel, which is called three hierarchies’ structure model and thermal stress model.The researches also include the fatigue type of asphalt pavement on steel deck, andits design indexes system, design calculation method and fatigue reliability analysis.The research works and new developments are as follows:(1) The three hierarchies’ structure models for live load effects have beenmodeled and solved.Based on elastic laminated continuous beam as the basic model, the formulas ofsupport stiffness of suspender in suspension bridge acting on steel box beam andU-stiffener acting on steel deck have been derived. The formulas of cross-sectionwarping stiffness of steel box beam have been derived too. Based on the theory ofinfluence-line loading, bending theory of beam and plane section assumption, theanalytic calculation methods for live loads stress in asphalt pavement have been got.The calculation results based on analytical formulas in this paper agree with theresults using finite element method, and the tedious modeling process can besimplified in calculation for design index of asphalt pavement. The calculationresults show that the most dangerous sagging moment of steel box girder inlong-span suspension bridges do not occur in midspan. Its position depends on thestiffness distribution of elastic support. The distortion angle being caused bysegment distortion of steel box girders show obvious local characteristic. Theinfluence scope is about five to six times distance between diaphragms. Theinfluence scope of local loads moment is about six times distance betweenU-stiffeners. So the interact of two wheel load on one axle can be ignored.(2) The laminated beam models for thermal stress have been modeled and solved.The stress functions of interface between steel deck and asphalt pavement havebeen expanded by Fourier series. The analytical formulas of thermal stress of asphaltpavement have been derived. The maxwell model has been used in calculation forrelaxation modulus, and the calculation method of pavement thermal stressconsidering viscoelasticity of material has been got. The calculation results showthat the max thermal tensile stress occurs in the end of beam. The calculation ofthermal stress must take the relaxation of asphalt material into consideration. Theconditions of most dangerous thermal stress are extreme low temperature and rangeof temperature change.(3) The asphalt pavement fatigue types and design indexes system have beendetermined.The two fatigue types of asphalt pavement have been got based on lots ofdamage investigation and full-scale fatigue experiment in straight track test. One isbending fatigue in asphalt pavement surface. Another one is shear fatigue ininterface between steel deck and asphalt pavement. The analysis showed that themechanism of longitudinal fatigue crack in pavement, which half bridge crosssection has less traffic volume, is the transverse flexural stress in asphalt pavementsurface caused by segment distortion of steel box girders. The pavement longitudinalfatigue cracks appeared on the region of sagging moment between U-stiffeners iscaused by interface bond destroys. The shear failure will cause the bending tensionstress in bottom of asphalt pavement and the flexure fatigue cracking can expandupward. Load combinations of live load stress and thermal stress cause thetransverse cracking. The flexural stress in pavement and shear stress in interface canbe used as design indexes and the most unfavorable stress combination should beconsidered.(4) The design method of steel deck asphalt pavementThe design method of asphalt pavement, which being called checking mode, hasbeen proposed based on dynamic design indexes system. The axle-load-conversionformulas for typical pavement materials have been derived considering fatigueproperty of pavement material, bearing capacities of steel deck and trafficcharacteristic. Using method of load combination, which including live load stress inthree hierarchies’ models and thermal stress, the results show that the transversestress is controlled by live load effect and the longitudinal stress is controlled bytemperature effect. The fatigue design for pavement should use live load effect as the design index and thermal stress as the checking index. The performances ofasphalt pavement, which including high temperature stability, low temperature crackresistance, water stability and so on, have been analyzed.(5) The computer method for reliability of steel deck asphalt pavementThe reliability of asphalt pavement has been analyzed based on formulas in thisthesis and random sampling principle of Monte Carlo method. The result show that thereliability of fatigue design can satisfy the code requirement using the mostdangerous combination of live load effect and the material strength of asphaltpavement should consider temperature correction when checking the most dangerouscombination of thermal stress.