Basic Performance Of A Lightweight Composite Bridge Deck With Open Ribs

While Orthotropic steel decks(OSD) are widely used in medium and large span bridges, many of them surfer from premature fatigue cracks and asphalt pavement damages, and it seriously threatens their usability and durability. In order to solve the two above-mentioned chronic diseases of OSD, Prof. Shao proposed a lightweight composite deck system which is composed of a traditional OSD and a thin reinforced ultrahigh-performance concrete(UHPC) layer using the shear stud connectors. At present, both theory and experiments show that the lightweight composite deck can effectively reduce the stress amplitude of steel deck, and the UHPC layer possess high bending-tensile strength and good fatigue resistance.In this paper, the author proposed a simplified lightweight composite deck which is composed of an open-ribbed OSD and a thin ultrahigh-performance concrete(UHPC) layer. The followings are included:(1) In order to decrease the risk of fatigue cracks in U-diaphragm of the lightweight composite bridge deck with U-ribs, a lightweight composite bridge deck with bulb flat ribs was proposed. Taking the Sencond Dongting Lake Bridge(a suspension bridge with a l ightweight composite bridge deck) as an example, local finite element models of the steel truss girder and sub-models of bulb flat rib-diaphragm connections were established. Then parameter analyses were performed to investigate the the likely influence of shape of cutouts and thickness of diaphragms based on hot spot stress method. The results showed that, fatigue properties of 3 typical details at bulb flat rib-diaphragm connections were affected significantly by the thickness of diaphragms. Compared comprehensively, the fatigue properties of apple-like-shaped cutout were the best. Additionally, a full-scale model fatigue test was performed to verify the fatigue strength of 3 details at bulb flat rib-diaphragm connections in a lightweight composite bridge deck which possessed 16-mm diaphragms and apple-like-shaped cutouts. In the test, the most unfavorable detail of the specimen was the free edge of the cutout, which had a stress range of 90.6 MPa. After experiencing 2.5 million cycles of loading, no fatigue cracks developed. Then, the evaluation on fatigue life for UHPC was carried out based on S~N curve. It implied that, the key details in the lightweight composite bridge deck with bulb flat ribs had reliable fatigue endurance, which can meet the fatigue design requirements of Sencond Dongting Lake Bridge.(2) Based on the Second Dongting Lake Bridge, static and fatigue properties of lightweight composite bridge decks with two types of longitudinal rib were analyzed by finite element method, and economic performance of two kinds of structure systems were also carried out. Result shows that:(1) Compared with a traditional OSD, the lightweight composite bridge deck possesses more advantages in static and fatigue properties and lif-cycle cost;(2) The lightweight composite bridge deck with open ribs bascially avoid the shortcomings of traditional OSD with open ribs which is torsionally soft and not very efficient in distributing transverse loads, one has wide application.(3) Stactic and fatigue tests were conducted on six specimens to investigate the static and fatigue properties of small stud shear connectors embedded in thin UHPC layer for a lightweight composite bridge deck. The dynamic explicit analysis method was employed to conduct numerical analysis of static tests by ABAQUS software. And then parameter analysis and analysis of significant factors influencing eigenvalue of a specimen was carried out based on nine orthogonal tests. Finally, the fatigue strength of small stud shear connectors for a lightweight composite bridge deck were calculated and checked based on a practical project. For small stud shear connectors embedded in thin UHPC layer:(1) The shear capacity is reliable, and we proposed its design shear capacity can be calculated according to Eurocode-4, namely Pd=0.8As fu/γv;(2) The shear capacity is influenced by the diameter and yield strength of stud shear connectors, the eigenvalue of slip is influenced by the height of stud shear connectors and the shear stiffness is influenced by the diameter of stud shear connectors;(3) there are no significant change in slip for a long period of time before failure of the specimen, and obvious plastic deformation occurs in a brief period of time.The calculated value of fatigue life based on fracture mechanics method consistent with the results of fatigue tests; and(4) the bearing capacity and fatigue strength of small stud shear connectors satisfy requirements of the Second Dongting Lake lightweight composite bridge deck.(4) Based on an analysis of the effect of wheel load position on the interbedded shear stress in lightweight composite bridge deck, two simplified model — simply supported laminated beam model and cantilever laminated beam model were proposed. Then analytical formulas for interbedded shear stress in the aforementioned two simplified model was deduced based upon the classical mechanics of materials theory. Based on the Second Dongting Lake Bridge, results show that calculation results by analytical formulas are more 55% larger than the values by finite element analysis, which is conservative.Finally, a simplified model for calculating the shear force of stud connection embedded in lightweight composite bridge deck was put forward, which is recommended to be the guideline of layout design of stud connection.