Research On Flexural Capacity Of Steel-concrete MVFT Composite Girder

MVFT(Modified-Verbund-Fertigteil-Trager)girder is a novel steel-concrete composite structure,which used composite dowel as shear connector.The steel girder and the concrete slab of MVFT girder are both prefabricated in the mill.MVFT composite girder has the merits of convenient fabrication,light weight,fast construction.In this paper,the flexural capacities of a novel steel-concrete MVFT composite girder and conventional steel-concrete composite girder were studied theoretically,and the bearing capacity calculation formulas based on two strain strengthening models for steel were proposed.The main research contents are as follows:(1)A series of numerical models of MVFT composite girders were established by using the finite element software ABAQUS,and their correctness was validated by comparing the background test results.On this basis,three-point bending tests were carried out on the numerical models.According to the numerical simulation results,the failure mode of MVFT composite girder is concrete slab crushing failure under the assumption of plastic theory.(2)Based on two strain strengthening models for steel,trilinear steel strengthening model and bilinear steel strengthening model,the theoretical formulas for calculating ultimate flexural capacity of MVFT composite girder were derived respectively.The prediction results of the two formulas with two constitutive models for steel(trilinear-formula,bilinear-formula for short,respectively)of MVFT girders were in good agreement with the FE results,and the mean errors were 1.70% and 1.59%,respectively,which verified the correctness of the theoretical formulas proposed in this paper.On this basis,the same calculation method is employed to predict the ultimate flexural capacity of steel-concrete composite girders with full shear connection,and the calculation results of the generalized formulas were compared with the test results of many representative steel-concrete composite girders.The results show that both the generalized trilinear-formula and the generalized bilinear-formula have high accuracy for predicting the ultimate flexural capacity of the conventional steel-concrete composite girders,and the mean errors of the two formulas were 2.07% and 1.75%,respectively.Furthermore,both the bilinear-formula and the generalized bilinear-formula have smaller mean error and more concise formula form,compared with the corresponding trilinear-formula.Therefore,the prediction formula for calculating flexural capacity of composite girders using bilinear strengthening stress-strain model of steel is more applicable.(3)The theoretical formula of the ultimate flexural capacity of MVFT composite girders proposed in this paper was compared with the existing code formula.The results show that the calculation results of the code formula are slightly conservative,about 10%lower than the true values,while the mean error between the predicted value of bilinear-formula and the real values is only 1.59%.(4)Two machine learning models,Back-Propagation(BP)neural network and least squares support vector machine(LSSVM),have been implemented to predict the flexural capacity of MVFT composite girders.The results show that the two machine learning models have high prediction accuracy: Both the maximum relative errors of the two machine learning models are less than 3%,and the mean values of MAPE and RMSE are close to 0.(5)The concept of equivalent yield strength was put forward aiming to tackle the issues caused by the difference of the yield strength of each part of the steel girder,and the correctness of the concept was validated by comparing the calculation results adopting actual yield strength.(6)For the ultimate flexural capacity of conventional steel-concrete composite girders with partial shear connection,a modified formula was proposed based on the calculation formula of the European code.The correction coefficient was determined by selecting many experimental results of steel-concrete composite girders with partial shear connection,and the empirical formula of conventional composite girders with partial shear connection was obtained.