Long-term Responses Of Steelnormal/Recycled Concrete Composite Slabs Accounting For The Non-uniform Shrinkage Effects

Composite steel-concrete slabs show their advantages due to the fast construction speed and high degree industrialization.The use of recycled aggregate concrete(RAC)into composite steel-concrete slabs provides a possibility to extend the structural applications of RAC.A non-uniform shrinkage gradient develops through the thickness of the composite slab due to the impermeable steel deck at the slab soffit and causes great shrinkage deflection.The use of RAC aggravates the non-uniform shrinkage gradient and thus the shrinkage deflection.However,the effect of non-uniform shrinkage on the longterm deflection of composite slab is not considered in Chinese code and current design approaches provided by researchers are complex to use.Besides,little research has been undertaken on the in-service behaviour of steel decks and negative steel reinforcements considering non-uniform shrinkage.In this context,theoretical study was conducted in this thesis aiming to investigate the long-term behaviour of simply-supported and continuous composite steel-natural/recycled aggregate concrete slabs considering nonuniform shrinkage.The main work is presented as follows:(1)Based on MATLAB software,a finite element model was established using Newton-Rapson method to account for the long-term behaviour of simply-supported and continuous composite steel-natural/recycled aggregate concrete slabs by including the combined effects of concrete cracking,creep and non-uniform shrinkage.The experimental data was collected and used to validate the finite element model.(2)A parametric study was carried out to evaluate the effects of various parameters on the long-term behaviour of simply-supported and continuous composite steel-natural aggregate concrete slabs.The effect of non-uniform shrinkage on the long-term deflection of composite slabs and the in-service stress of steel decks and negative steel reinforcements was studied.The results indicate that the long-term deflection of composite slabs is 37%~488% greater due to the effect of non-uniform shrinkage and the span-to-depth ratio is the key parameter.Design procedures which were easy to use were then proposed to calculate the long-term deflection of simply-supported and continuous composite steel-natural aggregate concrete slabs and the in-service stress of steel decks.The results obtained by proposed design procedures are in good agreements with finite element results.(3)A parametric study was carried out to evaluate the effects of various parameters on the long-term behaviour of composite simply-supported and continuous steel-recycled aggregate concrete slabs.The effect of recycled aggregate ratio on the long-term deflection of composite slabs and the in-service stress of steel decks and negative steel reinforcements was studied.The results indicate that the long-term deflection of composite slabs is 28%~45% greater due to the effect of recycled aggregates.Design procedures were then proposed to calculate the long-term deflection of simply-supported and continuous composite steel-recycled aggregate concrete slabs and the in-service stress of steel decks and negative steel reinforcements.The results obtained by proposed design procedures are in good agreements with finite element results.