Study On Seismic Performance Of Concrete Box Structures

In the dissertation, the seismic performance of six reinforced concrete (RC) boxtype piers and three high performance concrete (RPC) box type piers were researchedwith the experimental methodology. The seismic performance of the box piers underthe loads with different directions and the influence of the stirrup ratio on its seismicperformance were analyzed mainly. Through experimental and theoretical method, theseismic performances of the box type piers including the anti-earthquake ductility,hysteresis curve, skeleton curve, and energy dissipation capacity were studiedrespectively. Based on the pre-stressed concrete continuous rigid frame bridge withmain span of200m, a pre-stressed RPC continuous rigid frame bridge with the samemain span was designed, the designed RPC and the RC bridge with the same spanwere used to discuss the seismic performance of high-pier bridge and to study thefeasibility of RPC applied in the big span beam typed bridge. The experimental andtheoretical analysis results are shown that:(1) In the situation of the same cross-section and reinforcement, the influenceof the direction of the horizontal loads on the seismic performance of box type pier issignificantly. The failure mode of the RPC box type pier is the bending-failure underthe axial force and laterally reversed low-cyclic loads, and its shape of hysteresiscurve is full and spindle-shaped and is showed as a good capacity of energydissipation. The skeleton curve of the R-BP-34(loading along the specimen directionof rectangular diagonal section) is showed a quick downward trend under it arrivedthe ultimate bearing capacity, while the skeleton curve of R-BP-0(loading along thestrong axis) and R-BP-90(loading along the weak axis) shows a slow decline trendwhen the skeleton curve arrived the ultimate bearing capacity. The curve shows thatthe piers have a down strength platform and a good ductility. Before the loaddegradation occurred in the specimen, the carrying capacity of the specimen had nosignificant change as the increscent of the loading displacement and the increas es ofthe number of loading cycles at the same level load. After the load degradationoccurred in the specimen, the carrying capacity of the specimen increased as theincreases of the loading displacement while a significant attenuation occurred withthe increases of the number of loading cycles at the same level load. The R-BP-34hadthe most obvious phenomenon, and the R-BP-0take the second place; All the specimens showed they had a good ductility (R-BP-90’s ductility is best, and R-BP-0is the second one) and the ductility coefficients were all larger than4. For RC boxtype pier: loading the low cyclic loading imposed on the specimen from the0degreedirection (the strong axis), it had a maximum carrying capacity, when loading the lowcyclic loading imposed on the specimen from the90degree direction (the weak axi s),it had a minimum carrying capacity, but it had a good capacity of ductility, however,when we loaded an oblique loading on the specimen, it got a middle bearing capacity,while it’s ductility was the worst.(2) At the same circumstances of horizontal loading direction and the axialcompression ratio, different stirrup ratio had great impact on the seismic properties ofthe specimen such as RC box-type pier; the specimens with different stirrup ratio hadthe different hysteresis curves. For the specimens with stirrup ratio of1%, thehysteresis curves are spindle and relatively plump, which can show that this specimenhad a good capacity of energy dissipation, but as for the specimens with the stirrupratio of0.5%, the hysteresis curves showed some pinch phenomenon, in contrast,when the in the lateral horizontal load reached maximum, hysteresis curve didn’tappear enough stable platform. The specimens with stirrup ratio of1%had almost thesame peak load（relative ratio in the range of0or5%） as the ones with stirrup ratioof0.5%; but the peak value of displacement of the pier on the top of the specimenswith stirrup ratio of1%was2.5times or more bigger than the one of the specimenswith stirrup ratio of0.5%. The ductility of the specimen with a higher stirrup ratiowas better than the lower ones. The deformability of the specimen was better. Such asthe limit displacement of specimens BP-1-0and BP-1-34were45.62mm and38.94mm respectively; while the limit displacement of specimens BP-0.5-0and BP-0.5-34were27.13mm and22.85mm respectively.(3) Based on the character of the hysteresis curves, the restoring force model ofbox type pier was established with considering the dual axle horizontal force couplingeffect. The nonlinear properties of the bridge pier under one-way and two-way loadswere analyzed, they are concluded that the hysteresis curve, moment-curvature theoryrelationship of the test pier cross-section and the relationship of load-displacement onthe top of the pier. Theoretical results are in good agreement with experimental results,and indicate that the analysis model is valid.(4) Both RPC and RC box test pier measured the shape of the skeleton curvewas similar to the theory of monotonic loading load-displacement curve in general,but the former’s ultimate load was slightly lower. Load-displacement curve had a long decline platform under the condition of low axial compression ratio. With theincreases of the axial compressive ratio, the decline platform gradually disappeared,and load declined faster when the peak load appeared. Horizontal load loadingdirection angle had geart influence on the seismic behavior of both RPC and RC boxbridge pier. The displacement ductility ratio did not decrease monotonically as theangle of the load direction increased. When the loading direction angle is less than avalue, the displacement ductility ratio drab reduced, but when the loading directionangle was greater than a certain angle, the displacement ductility ratio increased onthe contrary.For this test specimen, the critical angle was60or so. The ductility of theweak axis force specimen was better than the strong ones at the same axialcompression ratio, which showed the horizontal load loading direction angle had greatinfluence on the ductility of the specimens at the same section and reinforcement. Theductility of the weak axis force specimen was better than the strong ones at the sameaxial compression ratio, which showed the horizontal load loading direction angle hadgreat influence on the ductility of the specimens at the same section andreinforcement.(5) The ductility of the box-type pier would be decreases with the increases oflongitudinal reinforcement ratio, when the axial compression ratio is very small,especially for the situation of the ratio no more than0.3, the trend of ductility of thebox-type pier would be decreases rapidly with the increases of longitudinalreinforcement ratio. This phenomenon would be explain that the ultimate state can becontrolled by the longitudinal reinforcement, which will limit the change of ultimatedisplacement and moment, and thus ductility of the box-type pier would be decreases.When the axial compression ratio more than0.3, the broken failure of the sampleswill be the over-compression failure or the equilibrium failure.(6) When the longitudinal reinforcement ratio was certain, axial compressionratio affected the pier top limit bearing capacity and the displacement ductility ratioand it had almost the same influence law for the box bridge pier of RPC&RC. As forthe RPC box pier specimens, when the longitudinal reinforcement ratio ranged from1.9%to3.7%, the pier top limit bearing capacity did not increase monotonically withthe increases of axial compression ratio, as the axial compression ratio was around0.4,the horizontal limit bearing capacity reaches a maximum value. As for the RC boxpier specimen，when the longitudinal reinforcement ratio ranged from1.13%to2.54%,as the axial compression ratio is less than0.4, specimen horizontal ultimate bearingcapacity increases with the increscent of the axial compression ratio, while the axial compression ratio exceeds0.4,the horizontal ultimate load decreases with theincreasment of axial compression ratio.(7)Taking an ordinary concrete continuous rigid frame for engineeringbackground, based on the main girder stress and structure stiffness for control goal,we drew up a pre-stressed RPC continuous rigid frame bridge with equal span.Comparing the mechanical performance and economical efficiency of the two bridgescomprehensively. There was a substantially amount decrease of concrete andpre-stressed reinforcement as well as the common reinforcement;at the same timeRPC will have more economic competitiveness in improving the using life ofstructure and reducing the maintenance costs because of its excellent seismicperformance.