Numerical Analysis Of Thermal Buckling And Postbuckling Of Continuous And Joint Functionally Graded Concrete Slab

Concrete slab may buckle and postbuckle due to the thermal stress when it is chronically exposed to heatwaves.Solar radiation directly affecting the top layer of slab can lead to a nonuniform temperature field through the thickness direction.Traditional concrete slabs usually use Portland cement(PPC)which contributes less blow-up resistance but considerable airborne environmental pollutants.This paper proposes a novel functionally graded(FG)concrete slab to enhance thermal buckling and postbuckling resistance but decline the harmful gases.The FG concrete consists of fiber reinforced concrete(FRC)and geoploymer concrete(GPC)because of their outstanding mechanical property and environment-friendly characteristic while PPC is still an irreplaceable part due to its lower manufacturing cost.Being different with beam and plane,concrete slab possesses high density and rough surface of bottom layer,so neglect of self-weight and friction will result in a significantly under-estimated thermal critical buckling temperature and thermal postbuckling behaviour.The thermal buckling and postbuckling theoretical solution of FG concrete sab are complexed and have not been studied in open literatures,while the experimental method to extreme long slab may cost heavy expenditure.Based on those impacts,the finite element(FE)method(commercial software ABAQUS)is employed to implement parametric study of functionally graded material property and geometry and to discuss the effect of nonuniform temperature field.The main research work are listed below:1.According to different lengths of slab,two types of slab model(continuous and joint)are built in ABAQUS.Two most common geometric imperfections considered in the continuous slab are seen to come from the nonuniform cross-section of the slab(Imperfection I)and the initial curvature due to the curved foundation(Imperfection II),respectively.The boundary condition of joint slab is assumed to be one long slab weaken by a joint(Joint I)and the other continuous slab adjoining a rigid structure like abutment et al.(Joint II).The FE models are built based on mentioned situations.2.Validation of FE model and convergence study is first carried out before proceeding to the parametric study.To compare the FE results of PPC slab with the experiment-based theoretical results reported in the open literature can ensure the accuracy of the FE modeling process about slab thermal buckling and postbuckling.Meanwhile,comparing the FE results of PPC beam with theoretical results by using differential quadrature method can ensure the accuracy of the FE modeling process about FG concrete slab.The FE results with varying total number of elements along the thickness direction are compared to make FE model have an excellent agreement and enhance computation speed.3.The thermal buckling and postbuckling results of slab model with or without gravity and friction are compared.The effect of slenderness ratio and imperfection amplitude of slab to the safe temperature and postbuckling results are further discussed.In addition,The relevant material property parameters are obtained from calculating various FG layer thickness and volume fraction index and are added into FE model.According to the thermal critical buckling temperature and postbuckling results,the effects of those parameters can be predicted.4.The user subroutine UTEMP is adopted to define the nonuniform temperature field in ABAQUS.The thermal critical buckling temperature and postbuckling results of slab under the temperature filed,which is gradient across the thickness direction of slab are built by linear interpolating function in ABAQUS,can prove the importance of considering nonuniform temperature field in this issue.We built the reasonable FE model of functionally graded concrete slabs to calculate the thermal buckling and postbuckling,which can help to design the FG material distributions and control FG layer property,including FG layer thickness and volume fraction index,then realize to enhance thermal buckling and postbuckling resistance,reduce carbon dioxide gases emission and save cost.Furthermore,the influence of gravity,friction,imperfection amplitude,slenderness ratio and nonuniform temperature field are also discussed here.