Study On Nonlinear Mechanical Behavior Of Prestressed Concrete Beamwith Cracking

With the continuous development of highway bridge construction, the constantdevelopment of the highway bridges’ construction, the prestressed concrete structureis becoming more widely used. However, the damage, such as cracking anddeflection of structure, generally exists in prestressed concrete structure owing to theincreasing volume of traffic, serious overloading, the injuries just after completionand the lack of maintenance. As a result, it leads to the differences of prestressedconcrete structure in designing and actual operating, and it seriously affects andthreatens the use and operation of the bridges in service. At present, theexperimental studies and theoretical analyses on mechanical properties of crackedprestressed concrete structures are relatively backward at home and abroad.Therefore, it is very important to reveal the mechanical properties and degradationmechanism of cracked prestressed concrete structure, and evaluate the technicalcondition of the bridges in service correctly. In this paper, the study refers toResearch on Concrete Structure Performance Based on Cracking Test, which is ascience and technology project of the Hall of Jiangxi province traffic in2010. Thisexperimental research is based on6narrowed prestressed concrete beams, which areconverted into the scale of1:5according to the similarity relation. And the prototype,30meters of prestressed concrete T beam, is widely used in construction of highwaybridges in China. In order to study the nonlinear mechanical behavior of prestressedconcrete beams after their cracking, this research adopts model tests and the3Delastoplastic entity finite element numerical simulation, and gets the developmentpatterns of the response of structures in the deformation, strain, crack etc.ofprestressed concrete beams, which are tested under three point loading in the wholeprocess. And the main conclusions are as follows:(1)This paper describes the mechanical properties of bonded prestressedconcrete T beam by using nonlinear finite element theory. The calculation resultsand the experimental results are identical, which means that it reveals the changesbetween concrete and the prestressed tendons when taking the beams’ material andgeometric nonlinearity into consideration. Thus, the rationality and feasibility ofelement type, material constitutive equation and failure criterion are verified by theexperimental models. It also further reveals the prestressed concrete T beams after cracked on mechanical properties and working mechanism, which providesreference basis for theoretical analysis.(2)Based on the load deflection data of6test beams, the equivalent flexuralrigidity of the cross section can be figured out, and the regular patterns of bondedand unbonded test beams’ stiffness degradation can be concluded when in differentdegrees of cracking.(3)According to strain data of the concrete test beams, it’s apparent that thestrain of the top concrete is maximum when it is approaching to the failure load. Andit’s obvious that the sooner of the section is cracked, the higher of the growth rate ontop of the concrete beams.The relationship of the top concrete between strain rateand loading can be also concluded in different loading stages.(4)It can be summarized that the sooner of the section is cracked, the higher ofthe stress growth rate of the prestressed steel bars which are arranged in the crosssection when according to the data of test beams and prestressed tendon stress’increment. When it comes to other countries for calculating the ultimate stress ofunbonded prestressed beam, JGJ92-2004measured some safety in the calculatedvalues of ultimate stress increment compared to the measured values, which meanssafer and more rational for designing.(5)The stress redistribution of the reinforced after the beams are cracked can beconcluded according to the data of the loading on the test beams and the strainincrement of the reinforcing bars. The earlier the cracking of test beams, the higherthe strain ratio of the common steel bars which are arranged in the section.(6)Deducing the calculation formula of residual load bearing capacity ofbonded and unbonded prestressed beams based on the data of test beams’ load todeflection, load and the average cracking width. And deducing the carrying capacityof the original beam basing on similarity relation and similarity theory. Thisprovides reference for the operation and design of the prestressed concrete structurein service, which is of important engineering significance.