Design And Experimental Test For Innovative Jointless Bridges System

This dissertation proposed an innovative structural design for jointless bridge-approach system, which eliminates the expansion joint between the bridge deck and approach pavement by combing the design method for jointless bridge with that for jointless approach pavement. The systematic theoretical analysis, experimental test, and in-situ bridge monitoring were implemented. The major achievements are summarized as following:1. Structural design for jointless approach pavement(1) Two forms of cross section for jointless approach pavement were proposed: one is in the terms of semi-rigid pavement structure which consists of asphalt concrete cover and cement stabilized base course; another is the composite rigid pavement comprised the asphalt concrete carpet and continuous reinforced concrete subjacent bed.(2) According to the different forms of jointless approach pavement, the dissertation proposed several structural styles available for jointless connections of approach pavement and bridge deck, which include that of semi-rigid approach pavement via sloping approach slab and geogrid and that of composite rigid pavement via flat approach slab and continuous reinforcing rebar.(3) Based on the mature bonding-sliding theories for reinforced, concrete, the dissertation derived formulas for reinforcing calculation, width and space of cracking, and reinforcing length of jointless composite rigid approach pavement, and developed the relevant program QDLJG for practical application.(4) Formulas were derived for indicating the effect of the influence length of jointless approach pavement and the additional force for jointless bridge in the case of temperature ascending.(5) The global load carrying capacity of the jointless approach pavement was investigated to verify its potential under vehicle load.(6) For the jointless rigid approach pavement, the dissertation investigated the effects of the slab/base friction coefficientμ_l, bridge deformation△l, reinforcing ratioρ, thickness of RC base course h, concrete strength f_t, and temperature variation△t on the jointless approach pavement and jointless bridge.2. Structural deformation characteristics of the innovative jointless bridge (1) Compared to the conventional jointless bridge with pavement expansion joints between the bridge and the approach pavement, the thermal deformation of the innovative jointless bridge is restricted by the approach pavement. Note that the magnitude of the restriction force is relevant to the slab/base friction coefficientμ_l, which will result in the decreasing of the free thermal deformation of the deck, particularly in the case of temperature ascending. The investigations indicate that the former conclusions are in accordance with the conclusions such as "the practical thermal deformation is smaller than that of calculation value", "the calculated deformation is in agreement with that of general bridge with expansion joints in the case of temperature descending", and "only 2/3 bridge length should be considered for deformation calculation in the case of temperature ascending ", which are derived from the international references on conventional jointless bridge.(2) The thermal deformation of the innovative jointless bridge is restricted by the jointless approach pavement, which makes the bridge deck bear the additional axial forces and bending moment. Note that in the case of temperature descending the additional axial tensile forces and negative bending moment will result in the strengthening of the overall structural cross section, while in the case of temperature ascending the additional axial pressure and positive bending moment will advantage the structural performance in some degree. The temperature fluctuation has an apparent impact on the side span of the bridge, which requires special reinforcing design.3. Experimental test on the jointless approachesAccording to the special mechanical characteristics of the jointless approach pavement, a series of experimental tests such as the cleavage comparative test for the geogrid-reinforcing cement stabilized material, the eccentric tension test for geo-material reinforcing specimen, the horizontal tension test for foundation beam, and the full-scale model test for the approaches behind the abutment and the approach pavement were implemented to systematically investigate the critical jointless structural design for semi-rigid and rigid approach pavement. The reinforcing effects of the materials such as uniaxial geogrids, biaxial geogrids, glass geogrids and steel rebar were demonstrated to validate the accuracy of the former theoretical analysis.4. Case studyThere are several fully jointless bridges constructed with jointless approach pavement and bridge deck. An integral bridge with jointless semi-rigid approach pavement and a semi-integral bridge with jointless composite rigid approach pavement are mentioned in the paper. They are all open to traffic for more than 1 year, and performing very well. The successful application of innovative jointless bridge-approach system has indicated the effectiveness of the theoretical analysis and its future prospect for medial and short bridge.