Exert Lateral External Prestressing Reinforcement Fabricated Hollow Slab

For such advantages as low construction height,being easily prefabricated and economical material using,assembly pre-stressed concrete hollow board bridge is applied widely in bridge engineering. Bridges of the type built in 1970s and 1980s have faults as low load bearing capacity and small tongue-and-groove joint between boards. With modern economy developing highly,heavy vehicles and overload vehicles appear frequently,and cause that longitudinal cracks and pitfalls along tongue-and-groove between boards emerge in bridges of the type recently. Concrete near tongue-and-groove tattered or fallen off,and leakage over large areas lead to fail transverse contact and single plate bearing. As an ultimate result,driving safety and traffic capacity of the whole highway are imperiled. Therefore,reinforcement research on these sick bridges of the type is of great practical engineering value.In connection with diseases as mentioned above existing in assembly pre-stressed concrete hollow board bridges,a strengthening method has been put forward lately,that's strengthening the bridge by imposing external transverse pre-stressing force on it. The reinforcement mechanism is that,exerting pre-stress on assembly concrete hollow board bridges makes concrete at bottom in compressive station and cancel out transverse moment, enables boards to deliver vertical shear and moment simultaneously,changes contact style form hinge joint to rigid connection,and improves load transverse contribution. It is also beneficial to boards' teamwork of sharing vehicle loads. Ultimately the load bearing capacity of the whole bridge is increased. The reinforcement mechanism of the method is simple and clear. Now the method has been put into practical project,however,the actual figures of reinforcement effect hasn't been given out,so we can't evaluate reinforcement effect of the method quantitatively at the moment.In the text,MIDAS/Civil FEM software is used to build three dimensional FEM computation model of a whole assembly pre-stressed concrete hollow board bridge,using solid element of the FEM program. When building the model,conversion elastic modulus of concrete and steel is adopted in reinforced concrete area at the top of section,in consideration of influence of steel. As to pre-stressed concrete area at the bottom of section,rigidity equivalent pre-stressed plate-belt is adopted to simulate. The bridge deck,tongue-and-groove, concrete pavement and balustrade are all simulated by solid element. Transverse pre-stressed bar is imitated by truss element which can only withstand tension but not compression. In the text,we not only dicuss whether the reinforcement method is useful to hollow board bridge, but also evaluate the influence of factors on reinforcement effect,such as value of transverse pre-stress imposed,variation of location in the direction of longitudinal span,ratio of width to span of the bridge. As for orthogonal slab bridges,we set three cases,that is to say,pre-stress of seven transverse pre-stressed bars are fixed 100kN/stalk,150kN/stalk and 200kN/stalk separately to analyse the influence of the transverse pre-stress value on reinforcement result. To obtain transverse load distribution influence line of the bridge,we exert unit load on No1 to N08 board's width centre at the mid-span respectively. Each unit load possesses four load cases: 1,unit load only; 2,unit load + transverse pre-stress of 100kN/stalk; 3,unit load + transverse pre-stress of 150kN/stalk; 4,unit load + transverse pre-stress of 200kN/stalk. The whole bridge has 32 load cases in total. The same FEM is applied to study assembly skew slab bridges. Then the text researches whether it's also effective to skew slab bridges by imposing external transverse pre-stressing force. In the last,the influence of skew angle's value on reinforcement effect is analysed.The results manifest that: when this method is used to strengthen hollow board bridges, it's easy in construction and evident in reinforcement effect; It's more efficient to assembly orthogonal slab bridges than to assembly skew slab bridges; Value of transverse pre-stress has little influence on reinforcement effect; Efficiency is higher at longitudinal mid of span than two ends of the span; Smaller the ratio of width to span is,higher the efficiency of the reinforcement becomes; Larger the skew angle is,lower the efficiency of the reinforcement is. The analytical results may serve as reference to strengthening the other bridges of the type.Since the type of assembly pre-stressed concrete hollow board bridge is used widely at present and a mount of bridges of the type have the faults of tongue-and-groove cracking longitudinally between boards now,it will produce enormous social significance and practical value to popularize this reinforcement technology vigorously to strengthen sick assembly pre-stressed concrete hollow board bridges.