| In the prestressed steel wire rope strengthening technology,composite mortar are generally used as bonding material to protect steel wire rope.However,composite mortar is easy to crack,and it will lead to corrosion of steel wire rope.Polyurethane cement composite has the characteristics of high strength and toughness.The problem of cracking can be solved by replacing composite mortar with polyurethane cement composite.The strengthening technology of prestressed steel wire rope embedded in polyurethane cement composite(PSWR-PUC)can combine active strengthening method of prestressed steel wire rope with passive strengthening method of polyurethane cement increasing section effectively.The advantages of the two strengthening methods are brought into play in the new strengthening technology.This paper is based on the key scientific and technological project of Jilin Province"Research on strengthening technology of bridge with prestressed steel wire rope embedded in polyurethane cement "(Project No.20150107).Firstly,the mechanical properties of polyurethane cement composite are studied.Then,experimental study,finite element analysis and theoretical research are carried out for reinforced concrete beams with shear strengthened by prestressed steel wire rope embedded in polyurethane cement.Finally,the new shear strengthening technology is applied for the actual bridges.The main contents of this paper are as follows.(1)Polyurethane and cement are the major processed materials of polyurethane cement composite.The reaction speed and setting time of polyurethane and cement are adjusted by catalyst.Polyurethane cement composite is dense and homogeneous with high strength and toughness.Bubbles should be prevented in preparation process of polyurethane cement,and water is the most important reason for bubbles appearing.Drying and dehydration of cement is the key step in preparation process.The optimal mix proportion of polyurethane cement can be obtained based on compressive and flexural tests.The ratio of polyurethane to cement(P:C)has little effect on strength,but it has a great effect on modulus of elasticity.Polyurethane cement mainly shows toughness with high ratio of polyurethane to cement,conversely it shows brittleness.(2)Bending and fatigue properties of polyurethane cement composite are greatly affected by ambient temperature.In terms of bending properties of polyurethane cement,flexural tensile strength and failure load decrease firstly,then increase and decrease lastly,failure strain and displacement increase,and stiffness modulus decreases with temperature increasing.Polyurethane cement shows brittle failure at low temperature,but it turns to elastic-plastic failure with temperature increasing,then it shows flexible failure at high temperature.In terms of fatigue properties of polyurethane cement,bending tensile modulus and residual stiffness modulus decrease slowly at low temperature,then they decrease rapidly at high temperature.With temperature increasing,modulus of initial bending stiffness and dissipation energy of each loading decrease,but hysteresis angle and fatigue life increase.Based on classical fatigue theory,fatigue life prediction model of polyurethane cement is proposed under coupling action of temperature and external force.The proposed model is in good agreement with experimental data.The proposed model can predict fatigue life and fatigue limit of polyurethane cement.(3)Reinforced concrete test beams are shear strengthened by prestressed steel wire rope only,polyurethane cement only and prestressed steel wire rope embedded in polyurethane cement.The effects of different strengthening methods and steel wire rope ratio on shear performance are studied.Failure process,load-displacement curves,characteristic load and displacement,load-strain curves of test beams are analyzed.The results show that the strengthening effect of prestressed steel wire rope embedded in polyurethane cement is the best,and shear capacity and ductility can be greatly improved.In the strengthening technology of prestressed steel wire rope embedded in polyurethane cement composite,on the one hand,steel wire rope can provide pressure to concrete to improve its core strength,limit the development of concrete crack,and play a role of stirrup to directly participate in shear resistance,on the other hand,polyurethane cement strengthening layer can increase shear area and shear rigidity in shear-span,so it can play a similar role in concrete shear resistance with high-strength feature and play a similar role in steel shear resistance with high-toughness feature.The shear resistance of strengthened beams can be significantly improved by combination of steel wire rope and polyurethane cement.(4)Finite element model is established by using ABAQUS of reinforced concrete beam with shear strengthening by prestressed steel wire rope embedded in polyurethane cement.It is found that they are in good agreement of finite element results and test results,which shows that ABAQUS finite element model can calculate shear capacity of strengthened beams effectively and reasonably.Based on finite element model,shear performance of strengthened beams is analyzed which are affected by external parameters,original beam parameters and strengthening parameters.It shows a linear decreasing trend between temperature and ultimate bearing capacity,but the decreasing range is very small.Shear span ratio has a great influence on ultimate bearing capacity,but shear capacity of strengthened beams will not be improved when shear span ratio is greater than 3.The relationship shows approximately linear increasing trend between ultimate bearing capacity and concrete strength,stirrup ratio and reinforcement ratio.Ultimate bearing capacity of strengthened beams decreases with original beam damage degree increasing.Strengthening effect is unchanged when damage degree is more than 70%.The relationship shows approximately linear trend between ultimate bearing capacity and steel wire rope ratio.Bearing capacity of strengthened beam increases greatly when prestress level is less than 0.35,but bearing capacity increases very little when it is greater than 0.35.It has the best strengthening effect of U-shaped adhesive of polyurethane cement paste method.It shows a linear growth trend between ultimate bearing capacity and paste thickness when polyurethane cement paste thickness is small.But bearing capacity will not increase when paste thickness is larger than a certain value.(5)Based on the concept of zone B and D,shear span can be divided into D-D beam,D-B-D short beam and D-B-D long beam of strengthened beams by using prestressed steel wire rope embedded in polyurethane cement.Strut-tie model is established of strengthened beams.Stiffness calculation formulas are summarized of member in strut-tie model.Shear mechanism is analyzed of beams strengthened with different shear span ratio.Shear transfer of D-D beam is divided into direct transfer and indirect transfer,and they distribute in proportion.Shear force of D-B-D beam is all transferred indirectly.The length of zone B is small of D-B-D short beam,so force flow only takes place once indirectly.However,the length of zone B is larger of D-B-D long beam,so the force flow can be transferred indirectly for several times.Compared with test and simulation results,it is found that calculation results of strut-tie model are in good agreement with above.Effectiveness can be verified that strut-tie model is applied to calculate ultimate shear capacity of strengthened beam.The influence of shear deformation on deflection is considered.Calculation method of diagonal struts angle in zone D and B is studied.Deflection calculation formula is put forward considering shear deformation.The proposed formulas can better predict deformation of strengthened beam during the normal usage stage.(6)Two reinforced concrete T-beam bridges were shear strengthened by prestressed steel wire rope embedded in polyurethane cement and steel plate.Load tests were conducted before and after strengthening.After T-beam strengthening,shear stiffness of web is enhanced,so deflection and principal strain are reduced.However,deflection and principal strain reduce more of T-beam with shear strengthened by prestressed steel wire rope embedded in polyurethane cement,and the strengthening effect is better.Two load tests were carried out on T-beam bridge strengthened by prestressed steel wire rope embedded in polyurethane cement at different temperatures.It is found that influence of temperature on deflection and principal strain is less than 5%,so the influence degree of temperature is little. |
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