NONLINEAR TIME DEPENDENT FINITE ELEMENT MODELING OF TWO-WAY REINFORCED CONCRETE SLABS STRENGTHENED BY FIBER REINFORCED POLYMER CONFIGURATIONS

Abstract

In fact, slabs are a critical structural component of a building that is subject to the different types of structural degradation and structure performance on a long-term basis. External strengthening of reinforced concrete (RC) two-way slabs with fiber-reinforced polymer (FRP) is the most common used strengthening method in recent years. It provides an attractive way to enhance the shear and flexural capacities of RC slabs. A 3D nonlinear finite element (FE) using ANSYS/APDL Version 19.2 package was used to analyze the time-dependent reactions of strengthening two-way slabs under sustained load. Where the effects of accounted creep are to enhance the effectiveness of such a strengthening technique in terms of load-bearing capacity, possible deflection values, and crack patterns. The parameters in the short-term analysis include slab thicknesses, the ratio of externally bonded FRP area, and the ratio of bottom flexural reinforcement, while in the long-term analysis, they include length-thickness ratio, sustained load magnitude, compressive strength, and type of FRP over the strength of the slabs. The result of these simulations proves that the using ANSYS models' capabilities are a good match with the results of the related experimental investigations. In addition to the numerical investigation, this study has an analytical model for the short-term to analyze the two-way slabs strengthening by FRP. The FE analysis provides the best accurate prediction of an analytical method investigated with an average error of 1.37% of the punching shear capacity, while an average error of 14.35% in an analytical analysis for nine slabs (five un-strengthened slabs and four strengthened slabs). According to the parametric studies, the slab thickness was an important factor in the short term that can affect the ultimate load of the strengthened RC slab (using CFRP strip) and mid-span deflection. Increasing the thicknesses by 25% and 50% for (1250mm) length side of the slab lead to increase in the ultimate load by 32.69% and 60% respectively. However, increasing the thicknesses by 40% and 80% for the (1000mm) length side of the slab lead to increase the ultimate load by 43.69% and 74% respectively. An efficient method to reduced deflection is by increasing the slab thickness. Which is the most effective technique to reduce cracking. For long term, when remaining thickness is constant with varying the side length of the slab, in other word increasing the length to thickness ratio (L/h) by (150%) leads to an increase in mid slab deflection about (5.615) times at 1100 days. In the external strengthen two-way slabs by FRP, the effect of steel reinforcement ratio is a little at high area ratios of FRP. The FRP with a high modulus of elasticity can decrease the deflection for 1100 days by 14.23%. Because of the creep within the deflection, where the creep have Inverse relationship with the modulus of elasticity II Finally, the parametric studies in this research is adopted with compressive strengths of concrete (30, 45 and 60) MPa, increasing concrete compressive strength for strengthening slab by FRP leads to a decrease in mid-span slab deflection for long term during 1100 days. When increasing of the compressive strength of concrete by (50 and 100%) lead to decrease the deflection by (12.56 and 17.9%), respectively.