Erdem Canbay

Bond Strength of Lap-Spliced Bars

The performance of reinforced concrete structures depends on adequate bond strength between concrete and reinforcing steel. This article reports on a study of the bond strength of lap-spliced bars. The authors note that calculation methods to evaluate the strength of tension lap splices are based primarily on nonlinear regression analysis of test results. However, the results from these analyses may not be generalizable to situations beyond the domain of the data. In this study, the authors developed an expression for the calculation of bond strength based on a physical model of tension cracking of concrete in the lap-spliced region. Two different types of failure modes are considered: horizontal splitting that develops at the level of the bars (side-splitting failure), and vertical splitting that develops along the bar on the face cover (face-splitting failure). The developed expression was verified using results from 203 unconfined and 278 confined beam tests where the splice region was subjected to constant moment. Results showed that the relation between splice strength and splice length is not linear. The use of the fourth root of the concrete strength provides an improved estimate regarding the behavior of lapped splices as compared with the square root. In addition, the effect of the thickness of the concrete cover surrounding the bar is not linear.

Numerical Study on CFRP Strengthening of Reinforced Concrete Frames with Masonry Infill Walls

AbstractIn the last decade, a new strengthening methodology has been developed for reinforced concrete (RC) frames with hollow clay tile (HCT) infill walls by means of diagonally applied carbon fiber–reinforced polymer (CFRP) fabrics. In the experimental part of a study conducted by the authors, this user-friendly methodology was experimentally investigated considering different aspect (height/width) ratios of the infill walls. In this study, first a numerical model of the FRP strengthened infill walls strengthened with the proposed methodology is developed. Afterwards, the numerical simulation results are validated by use of experimental response curves and finally, a parametric study, which further investigates the effect of aspect ratio of HCT infill walls is presented.

Testing and analysis of infilled reinforced concrete frames strengthened with CFRP reinforcement

There is an excessive demand for the rehabilitation of frame-type RC buildings which do not satisfy current seismic code provisions. Therefore, it is imperative to develop user-friendly strengthening methodologies which do not necessitate the evacuation of the building during rehabilitation period. The aim of this study was to strengthen the masonry infill walls by means of diagonal carbon fiber-reinforced polymer fabrics and to integrate them with the existing structural frame in order to form a new lateral load resisting system. This study investigated the possible effects of height-to-width ratio of the infills on the overall behavior attained by the previously developed rehabilitation methodology. In the first part of the study, eight 1/3 scaled, one-bay, two-story RC frames with two different aspect ratios were tested. The experimental results in terms of lateral stiffness, strength, drift, and energy dissipation characteristics of the specimens were discussed. In the second part, a numerical study of the frames was conducted to estimate the non-linear behavior of the specimens.

Design of Lap-Spliced Bars: Is Simplification Possible?

While the estimation accuracy of the strength of lap splices has been improving, the complexity of design for reinforcement development has progressively increased. This research study investigates the development of a simple and reliable design expression. Equations on development and splices of reinforcement in ACI 318-05 along with other design proposals are critically assessed in light of 203 unconfined and 278 confined beam tests where the splice region was subjected to constant moment. A simple design provision is developed that is based on a physical model of tension cracking of concrete in the lap spliced region. This new expression is shown to be consistent with current design practice, applicable to existing test results, and simple in application.

Repair and strengthening of reinforced concrete columns with CFRPs

In this study, seismic retrofitting of undamaged and moderately damaged RC columns with CFRP was investigated. The experimental program was conducted on five RC columns with inadequate tie spacing, 90-degree hooks at tie ends, and plain (undeformed) reinforcing bars. Columns were tested under a constant axial load of 27% of axial capacity and under reversed lateral cyclic loading. The primary objective of this study was to investigate the influence of sustained axial load during repairing, damage, and corner-rounding radius of CFRP wraps on the seismic performance of RC columns. Improved performance in terms of ductility, dissipated energy, and secant-stiffness degradation was observed for the CFRP strengthened columns. Reducing the corner-rounding radius deteriorated the seismic behavior of the columns, while the stiffness degradation response remained unaffected. The sustained axial load during repairing had only minor effect on column behavior. After CFRP repairing, the increase in yield drift ratio and curvature was observed to be in proportion with the corresponding consumed ductility values during damage cycles. A drift-based design equation for FRP repaired columns was proposed that considers the damage amount and axial load level as the major parameters as consistent with the experimental results.

Application of Mesh Reinforced Mortar for Performance Enhancement of Hollow Clay Tile Infill Walls

The use of mesh reinforcement with mortar on existing brick infill walls of reinforced concrete (RC) frames is a recommended seismic strengthening procedure in the Turkish Seismic Code (2007). The premise of the method lies in its ease of application and success in eliminating the out-of-plane failure of existing infill walls. The performance of the mesh reinforced mortar (MRM) application was investigated by pseudo-dynamic (PsD) and cyclic testing. A three-story-three-bay 1:2 scale RC frame with hollow clay tile (HCT) infills in the middle bay was first tested using a continuous pseudo-dynamic test method for three synthetic ground motions compatible with the Duzce city center response spectrum. The test specimen was code complaint. No significant structural damage besides some cracking in the boundary columns was observed but the infill walls almost collapsed. After removing the infill walls of the central bay, a new HCT wall strengthened with MRM was built and the rehabilitated frame was retested under a second series of PsD and reversed cyclic loading schemes. This Chapter reports the findings of the experimental study by placing special emphasis on the seismic response of the code compliant test frame.

Bond Strength of Spliced Fiber-Reinforced Polymer Reinforcement

To provide increased insight regarding the bond behavior of fiber-reinforced polymer (FRP) bars, 41 glass FRP, carbon FRP, and steel reinforced concrete beams with unconfined tension lap splices were tested. The test results are analyzed to evaluate the influence of splice length, surface deformation, modulus of elasticity, axial rigidity, and bar casting position on bond strength. Furthermore, the test results are compared with the current design expression recommended by ACI Committee 440 to evaluate its applicability. This comparison clearly indicates that the current design expression is inadequate, and that a new design equation is needed. More importantly, however, this research sheds light on the importance of the axial rigidity of the reinforcement on bond strength. Test results demonstrate that bond strength is linearly related to the axial rigidity of the reinforcement. This finding has future implications regarding the development of improved design expressions and allowing for an improved understanding of bond strength.

Performance Examination of Two Seismic Strengthening Procedures by Pseudodynamic Testing

Pseudodynamic testing was employed to observe the seismic performance of two retrofit methods on two-story, three-bay frame structures. The test frames had hollow clay tile (HCT) infill in the central bay and incorporated the seismic deficiencies of Turkish con- struction practice, such as use of plain reinforcing bars, low-strength concrete, and insufficient confining steel. Two noninvasive and occupant-friendly retrofit schemes suggested in the Turkish Earthquake Code, namely, use of fiber-reinforced polymers (FRPs) and precast concrete panels integrated on the HCT infill, were employed. The specimens were subjected to three different scale levels of ground motion from the 1999 Duzce earthquake. The control specimen experienced severe damage at the 100% scale level and reached the collapse stage due to the loss of integrity of the infill wall and significant damage on the boundary columns. The retrofitted test structures were able to survive the highest level 140% Duzce ground motion. Test results confirmed the success of the two previously developed retrofit methods for simulated earthquake loads. DOI: 10.1061/(ASCE)ST.1943-541X.0000434.

Performance Comparisons of Seismic Assessment Methods with PSD Test Results of a Deficient RC Frame

The accuracy of estimating the performance levels of a deficient RC frame using linear elastic and nonlinear dynamic analysis is evaluated in this study. This was achieved by comparing the response of a structure tested with pseudo-dynamic testing and estimated by the linear elastic assessment procedures along with nonlinear dynamic analysis. The test structure (three bay-two storey planar frame) is a ½ scale reinforced concrete frame having masonry infill walls in the central span. The test frame contains a number of structural deficiencies such as low concrete compressive strength (7MPa), lack of transverse reinforcement detailing at potential plastic hinge regions and beam-column joints. Tests were conducted for the NS component of 7.14 magnitudes 1999 Duzce Earthquake for three different scale levels. Test results indicated that drift deformation demands estimated using nonlinear dynamic analysis were within 15% of those observed in the tests. On the other hand, damage estimations of TEC and FEMA 356 were found to be conservative resulting in retrofit decisions. It was also observed that although nonlinear dynamic analysis provided reasonable estimations for inter-storey displacements, local demand parameters such as column curvature demands were estimated with less accuracy.

Seismic Performance Assessment of Masonry Buildings Using In Situ Material Properties

AbstractSeismic performance assessment of existing buildings requires the existing material’s properties to be determined as this has a significant influence on the seismic risk. As one of the most...