The use of externally bonded Fiber Reinforced Polymer (FRP) composites as a means of upgrading the flexural capacity of Reinforced Concrete (RC) one-way slabs is experimentally and numerically investigated in this study. A total of four groups of eight slabs were tested under four-point bending. The two slabs of the first group were left unstrengthened to be used as control specimens. The two slabs of the second group were externally strengthened with adhesively bonded pultruded, pre-cured CFRP plates. The four slabs of the last two groups were externally upgraded with unidirectional carbon (or E-glass) fiber fabric impregnated with an epoxy resin. In addition to the experimental program, a numerical investigation utilizing nonlinear Finite Element (FE) analysis was conducted using LS-DYNA software. Besides the eight slabs tested in this study, another eleven slabs were collected from the literature for the purpose of finite element validation. A comparison was made between the experimental and numerical results and good agreement was achieved. Based on FE validation, the numerical analysis was extended to include additional cases to study the effect of axial FRP stiffness and FRP-to-concrete width ratio on the flexural performance of upgraded slabs. As a result of the numerical study, new stiffness and reinforcement parameters were introduced in this research. These parameters were employed in the development of two new formulas for predicting the FRP debonding strain and percent gain in flexural capacity of FRPstrengthened slabs.

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.

High-strength concrete (HSC) has several well-known technical, aesthetic, and economic advantages over normal-strength concrete (NSC), which explains the increasing popularity of the former material in the construction domain. As in the case of NSC, however, high temperature adversely affects HSC mechanical properties even more than in NSC, as indicated by the many studies performed so far on HSC at high temperature (hot properties) or past a thermal cycle at high temperature (residual properties). Since many code provisions concerning concrete properties versus high temperature were developed for ordinary concrete and the available models (in terms of stress-strain relationship) come mostly from the tests on NSC—as the tests on HSC are less numerous—developing predictive relationships for HSC exposed to high temperature is still an open issue, especially with reference to many parameters affecting concrete compressive strength, like temperature as such, heating rate, water-to-binder ratio, and strength in compression, to cite the most relevant parameters. To this purpose, a large database (more than 600 tests) is examined in this paper, which is focused on HSC residual properties and on the variables affecting its residual strength. Available design models from various guidelines, standards, codes, and technical reports are tested against the database, and new regression-based models and design formulae are proposed for HSC strength in compression, after the exposure to high temperature.

The use of externally bonded fiber-reinforced polymer (FRP) composites for upgrading the out-of-plane flexural resistance of unreinforced masonry (URM) walls is experimentally and analytically investigated in this study. A total of six hollow concrete block walls were tested to failure using an airbag and a reaction frame to obtain a uniform load on the wall. The masonry walls were placed horizontally and tested as one-way slabs with span direction perpendicular to the bed joints. The first wall was left unstrengthened to be used as control specimen; the other five walls were strengthened using different schemes of externally attached glass-fiber-reinforced polymer (GFRP) sheets. The main parameters studied experimentally were FRP reinforcement ratio and stiffness. In addition to the experimental program, an analytical model was developed to predict the ultimate moment capacity of the URM walls. The procedure outlined in standard guidelines was also utilized to compute the flexural capacity of wal...

The multi-story buildings are susceptible to progressive collapse in the event of the removal of one or more columns due to the exposure to blast loads. The lack of structural continuity in precast concrete buildings makes these buildings more vulnerable to progressive collapse as compared to the regular cast-in-situ concrete buildings. This study presents experiments involving two types of detailing of precast beam-column joints using half-scale test specimens when the middle column is suddenly removed. The test specimens represent the most prevalent precast beam-column joints. One conventional cast-in-situ test specimen, having continuous top and bottom beam rebars, was used for comparison. The progressive collapse scenario was simulated by removing the central column support and applying a sudden vertical load on this column at a rate of 100 mm/s until failure. Test results helped in developing better understanding about the progressive collapse potential in the existing precast buildings. This study highlights the need for the rehabilitation of beam-column connections in existing precast buildings and necessitates the need for innovative beamcolumn connections for improving the progressive collapse resistance.