Investigation of an innovative PC box girder with basalt FRP webs

PC box girder is widely applied for simply supported girder bridges or rigid frame bridges within a span of 300 m owing to its high performance-cost ratio. However, diagonal cracks in the webs of PC box girder induced by loss of vertical prestressing or creep of concrete greatly affect the serviceability and durability of the bridge. To overcome this deficiency and achieve integrated high performance, an innovative PC box girder with basalt FRP webs is proposed in this paper, which consists of PC flanges and bidirectional basalt fiber reinforced polymer (BFRP) webs. The cross- sectional composition and the texture of fibers in BFRP webs were first discussed. An analysis by finite element method was conducted to evaluate the static behaviour of a PC box girder bridge subjected to the live loads, and the deflection of middle span and stress distribution of the flanges and webs of BFRP and PC materials were compared and discussed. The major results show that 1) various FRP cross-sections can be referred according to previous applications, the optimal design of web should be determined by local buckling analysis; 2) substantially low longitudinal stiffness of BFRP webs due to vertical arrangement of basalt fibres can greatly decrease the loss of prestressing in top and bottom flanges; 3) the bridge with BFRP webs increase the mid-span deflection under the live loads but it still satisfies serviceability limitation. BFRP webs in PC box girder can decrease the tensile stress in the bottom flange and lighten 27% of self-weight of the whole girder, which benefits crack control and extension of the main span; 4) the connections of BFRP webs and PC flanges should be designed in practical application.