Experimental Study On Shear Lag Effect In Simply Supported T Beam

The shear lag came into the vision of scholars both at home and abroad gradually since the 1920 s and brilliant achievements have been made during the past decade.Up to the present study,however,the displacement unknown function is mainly assumed to solve the shear lag of thin-walled box girders while the experimental research of T beam with wide flange is less and no widely accepted principle could be given as well.The existing T beam tests are also unable to be used to study the law of shear lag effect along the thickness direction of the wing plate due to the small size of the model.In view of these problems,two large scale wide flange concrete simply supported T beams are made in this paper to do tests to study the cause of the shear lag effect and its influencing factors from the perspective of mechanics.In order to accomplish the above vision,6 different typical cross sections which are pure shear,bending and pure bending sections respectively are selected in the two beams.At the same time,a total of three strain gauges containing surface strain gauges,steel strain gauges,concrete strain gauges are arranged to collect the strain.The influence of shear and bending moment on the strain distribution along the transverse direction of T beam is studied by analyzing the state of strain distribution under different stress characteristics.Then,the shear lag coefficient is used to study the influence of different stress characteristics and the change of load level on the shear lag effect.Finally,the two test beams were compared to study the influence of the change of the ratio of the flange plate width and web plate width on the shear lag effect.It is shown in the experimental results that the positive shear lag effect is produced in the whole beam range when the simply supported T beam is under the vertical load.The shear force is the main factor to produce shear lag effect,and the single moment can also produce weak shear lag effect.For the shear lag effect mainly caused by the shear force,the increase of the ratio of the flange plate width and web plate width will weaken the effect of the shear lag while for the shear lag effectcaused by the bending moment,the change of the ratio of the flange plate width and web plate width has little effect on the shear lag effect.On the strain distribution in a certain range near the point of its action,the concentration force has a decisive effect,which is positively correlated with the distance from the point of its action.With the increase of the load level,the effect of shear lag is getting weaker and weaker,and finally tends to be gentle.The existence of reinforcement can alleviate the effect of shear lag to a certain extent.