Rizwan A. Iqbal

Experimental and Numerical Study for the Shear Strengthening of Reinforced Concrete Beams Using Textile-Reinforced Mortar

In this paper, the effectiveness of textile-reinforced mortars (TRMs), as a means of increasing the shear resistance of reinforced concrete beams, is experimentally and numerically investigated. Textiles comprise of fabric meshes made of long woven, knitted or even unwoven fiber rovings in at least two (typically orthogonal) directions. Mortars—serving as binders—may (or may not) contain polymeric additives usually used to have improved strength properties. These TRMs may be considered as an alternative to fiber-reinforced polymers (FRP), providing solutions to many of the problems associated with application of the latter without compromising much of the performance of strengthened members. In the present study, a new type of textile (basalt-based textile) was used as strengthening material. Two different mortar types’ viz. cementitious and polymer-modified cementitious mortars were used as binding material for the textile sheets. The studied parameters also included the number of textile layers as well as the orientation of the textile material. The experimental program comprises of testing two control beams which were intentionally designed to be deficient in shear, in addition to testing eight beams which were externally upgraded by TRM sheets for enhancing their shear capacity. On the basis of the experimental response of reinforced concrete members strengthened in shear, it is concluded that textile-mortar composite provides substantial gain in shear resistance; this gain is higher as the number of layers increases. With higher number of layers, textile with 45° orientation along with polymer-modified cementitious mortar provides the highest shear strength enhancement. Nonlinear finite-element (FE) analysis was also carried out on the tested beams using LS-DYNA, which is transient nonlinear dynamic analysis software. The numerical analysis carried out involved case studies for TRM modeled, with and without mortar. Good agreement was achieved between the experimental and numerical results especially for the ultimate load carrying capacity for the case of FE models incorporating mortar. The study was extended numerically to include additional cases of TRM-strengthened specimens with more number of TRM layers as well as a case of FRP-strengthened specimen.

Effect of high temperature on structural response of reinforced concrete circular columns strengthened with fiber reinforced polymer composites

This research investigates the effect of elevated temperature on behavior of reinforced concrete (RC) circular columns strengthened with different fiber reinforced polymer (FRP) systems. For this purpose, 32 column specimens were prepared. The test matrix comprised: 14 unstrengthened columns, 14 columns strengthened with a single layer of CFRP sheet, and 4 specimens strengthened with a single layer of GFRP sheet. Out of the 14 CFRP-wrapped specimens, 4 columns were thermally insulated with commercially available fire-protection mortar. In addition to control specimens at room temperature, some other columns were subjected to high temperature regimes of 100℃, 200℃, 300℃, 400℃, 500℃, and 800℃ for a period of 3 h. After cooling down, the columns were tested under axial compression until failure. It was indicated that exposure to elevated temperature adversely affected the residual strength, stiffness, and axial/lateral stress–strain response of unstrengthened columns. FRP composites were found effective in enhancing the axial load capacity of exposed columns provided that the temperature at the FRP level does not exceed the decomposition limit of the epoxy resin. The degradation in strength and stiffness was higher in CFRP-strengthened columns compared with GFRP-strengthened columns when exposed to the same temperature level. The used insulation material was found efficient in preventing heat induced damage to CFRP-strengthened columns up to temperature of 800℃ for 3 h duration. Besides this study, the experimental data of 48 uninsulated FRP-strengthened circular concrete specimens subjected to different heating regimes were collected from the literature. The dataset of 55 uninsulated FRP-strengthened specimens was then employed to evaluate the ACI 440.2R-08 model used for assessing compressive strength of FRP-confined concrete. This model was found non-conservative for 48.6% of the data and thus it was revised by the inclusion of an FRP strength reduction factor due to heating, which can be utilized in the design of FRP-strengthened RC columns exposed to elevated temperature.