Analysis Of Shear Lag Effect Of Open Thin-Walled Beam With Wide Flage Based On Additional Deflection

The open thin-walled I-beam,T beam and double T beam are widely used in bridge engineering.With the development and application of prestressed technology and new materials,thin-walled beam is more and more wide and the span is also more and more large.So the shear lag effect in the open thin-walled beam has attracted great attention in the academia and engineering field.The shear lag effect leads to the increase of the bending stress at the intersection of the beam flange and web,increasing the deflection of the thin-walled beam,which affect the beam's ultimate bearing capacity simultaneously.Therefore,if the shear lag effect is neglect in the engineering design,the serious accidents in the local failure or the instability of the beam structures may exist.In this thesis,the shear lag effect of open thin-walled I-beam,T beam and double T beam is analyzed and investigated.The main contents include:(1)Taking the deflection and additional deflection as a generalized displacement,the longitudinal displacement function of I-beam,T beam and double T beam is constructed.The analytic solutions for the shear lag effect of open thin-walled I-beam,T beam and double T beam is derived based on the energy variational method.The results show that the method is feasible and reliable.Solving the problems of ambiguity of physical meaning in traditional shear lag theory and difficulty of solving the fixed-simp ly-supported thin-walled beam.(2)The shear lag coefficient based on the deflection is defined.The influence factors of I-beam,T beam and double T beam are analyzed.The results show that the width-span ratio,width-depth ratio have great influence on the shear lag effect,which provides reasonable advice for decreasing the shear lag effect of open thin-walled beam in engineering.(3)The positive and negative shear lag of the open thin-walled beam with wide flange is identified based on the decision method of the additional deflection,which is called moment method of shear lag.The positive and negative shear lag effect in three kinds of thin-walled beams under different constraints is analyzed.And the influences of the width-span ratio,width-depth ratio and the thickness of the flange and web on the effect interval of the positive and negative shear lag are investigated at the same time.(4)The elastic modulus reduction method is used to analyze the influence of the shear lag effect on the ultimate bearing capacity of the I-beam and the influence factors of the ultimate bearing capacity.The research results show that the width-span ratio and the thickness of the flange and web have a great influence on the factors,however the influence of the depth-span ratio and the thickness of the flange and web on the ultimate bearing capacity of the I-beam is not obvious.