A finite element model was developed to study the effect of mortar bed thickness in the compressive behavior of masonry prisms. For this, microplane models, calibrated using 10 mm mortar bed prisms, ...were used to predict the behavior of prisms with 30 mm and 60 mm mortar beds. The results showed the model could replicate the behavior of the experimental data generally. The models whose components differed significantly in compressive strength were affected by a variation of mortar thickness. In them, a reduction of the confinement effect of brick units over mortar beds was observed when mortar bed thickness increased.
A strength–ductility type seismic retrofit technique for soft first-story reinforced concrete (RC) buildings via adding wing-walls to the existing RC columns is called thick hybrid wall (THW) ...technique. In this technique, the additional wing-wall does not require longitudinal, transverse and anchor reinforcements; therefore, its construction is easy and cost-effective. In this study, THW technique was applied to an existing pilotis RC building in Okinawa. The objectives of this study were (1) to compare the advantages of THW and conventional retrofit techniques applied to this pilotis building, and (2) to assess the future retrofitting activities through this study.
In order to investigate the effect of middle tie beams on confined masonry walls, we conducted experiments of test specimens in which the variables were brick strength and the presence or absence of ...middle tie beam. In this paper, we report the effects of each parameter from the results obtained in the experiment. First, the test specimen composition and the experimental plan will be explained. The experimental results are shown below. Finally, from these results, a comparative examination is carried out.
In order to investigate the effect of middle tie beams on confined masonry walls, we conducted experiments of test specimens in which the variables were brick strength and the presence or absence of ...middle tie beam. In this paper, we report the effects of each parameter from the results obtained in the experiment. First, the test specimen composition and the experimental plan will be explained. The experimental results are shown below. Finally, from these results, a comparative examination is carried out.
This study explores a seismic retrofit method for existing RC columns using a cast-in-site partial thick hybrid wing-wall (THW) technique. The THW technique plays two important roles: (1) to enable ...easy and cost-effective construction and (2) to considerably increase lateral strength and ductility. The aim of this study is to experimentally determine the shear resistance (truss and arch mechanism) and shear strength of the columns retrofitted using the THW technique. Based on the analytical assessment of the THW technique, design equations of ultimate shear strength and steel plate thickness are proposed.
This study proposes a rehabilitation method (emergency retrofitting) to restore the axial compression capacity and shear resistance mechanism of shear-damaged reinforced concrete (RC) columns. For ...the emergency retrofitting of shear-damaged RC columns, coupler and aramid fiber belts are used. The key concept of this approach is to provide active confinement to firmly confine damaged RC columns externally. The active confinement is used to close cracks in damaged RC columns and to recover their vertical and lateral load-carrying capacities and ductility. To investigate the rehabilitation capacity using fiber-belt prestressing, axial compression and cyclic loading tests were conducted in this study.
This study proposes a rehabilitation method (emergency retrofitting) to restore the axial compression capacity and shear resistance mechanism of shear-damaged reinforced concrete (RC) columns. For ...the emergency retrofitting of shear-damaged RC columns, coupler and aramid fiber belts are used. The key concept of this approach is to provide active confinement to firmly confine damaged RC columns externally. The active confinement is used to close cracks in damaged RC columns and to recover their vertical and lateral load-carrying capacities and ductility. To investigate the rehabilitation capacity using fiber-belt prestressing, axial compression and cyclic loading tests were conducted in this study.
This study investigated the flexural strengthening effect of the Thick Hybrid Wall (THW) technique as a seismic retrofit approach for Unreinforced Masonry Wall (URM)-infilled Reinforced Concrete (RC) ...frames. THW is a strength–ductility-type seismic retrofit technique, which was developed for pilotis-type RC buildings. In this study, the flexural strength and failure mechanisms of URM-infilled RC frames retrofitted using the THW technique were investigated. Consequently, a comprehensive theoretical model was developed to measure the flexural strength, and a previously proposed equation was modified. Additionally, an equation was developed to determine the minimum additional-wall length, and another equation was developed to determine the demand length of the additional wall to obtain the demand flexural strength. These equations enhance the cost-efficiency and reduce the irregularities risks. The interaction between the URM infill and surrounding RC columns was modeled, and a cyclic loading test was performed under the influence of a constant axial force on the four specimens. The results indicate that THW technique changes the failure mechanism of URM-infilled RC frames from shear to flexure and that the retrofitted URM acts as part of the lateral resisting system owing to the active lateral confinement pressure. The accuracy of the analytical models was confirmed via experimental results, and the developed models facilitate the practical implementation of the THW technique on intended frames.
•Flexural strength and failure mode of retrofitted URM-infilled RC frames were investigated.•A comprehensive flexural-strength calculation model was developed.•Equations for minimum and demand additional wall lengths were developed.•The interaction between the URM infill and the surrounding RC columns was defined.•The accuracy of the proposed analytical model was examined using the test results.
A ductility-type seismic retrofitting technique is proposed for reinforced concrete (RC) columns. This involves arranging high-strength steel prestressing bars (PC bars) on the four faces of an RC ...column as external hoops. Hence, active confinement due to the tensile forces in the PC bars as well as passive confinement and transverse reinforcement can be expected. With regard to the active and passive confinements, previous authors have shown that the compressive strength and ductility of confined concrete are greatly improved and have proposed a stress–strain relation for confined concrete. The aim of the present study is to experimentally investigate the shear strength and shear resistance mechanism of RC columns retrofitted by this technique. The retrofitting details of the test specimens are shown in Table 1. The elevation and cross-section are shown in Fig. 1. To investigate the shear resistance mechanism (truss or arch mechanism), two types of specimen are considered in this study. One is a retrofitted RC column with no bond force between the concrete and the embedded longitudinal reinforcement, thereby generating the arch mechanism. The other is a retrofitted RC column with bonded rebars to evaluate the truss mechanism, which relies heavily on the bond resistance between the rebars and concrete. The column specimens used in this test had a square cross-sectional dimension of 250×250 mm2, a height of either 500 mm or 750 mm, and a shear span-to-depth ratio (M/VD) of either 1.0 or 1.5. The longitudinal reinforcement ratio (pg) of the retrofitted specimens with bonded rebars was either 3.67% (8-D19) or 5.51% (12-D19) and that of the specimens with unbonded rebars was 1.36% (12-D10). The shear reinforcement ratio (pw) of the column specimens was 0.08%. The test parameters of the column specimens are the initial tension strain of the PC bars, their spacing, the axial force ratio, shear span-to-depth ratio, and the bonded/unbonded nature of the rebars. In Chapter 3, the following main points are discussed. (1) The initial tension force of the PC bars enhances the shear strength of the truss mechanism. (2) Applying a lateral confinement pressure to an unbounded RC column, the shear strength of the arch mechanism can be increased. (3) For the bonded specimens, the measured gradient of the compressive diagonal force of the truss mechanism, which is one of the internal forces of an analogous truss comprising PC bars that act as tension members, the bond force of rebars, and the diagonal concrete force was nearly 45°. (4) The shear strength of the arch mechanism increases with increasing axial force. (5) In the unbonded specimens, the slope of the line of thrust and the depth of the compression zone of the arch mechanism correlate with the lateral confinement pressure and the vertical axial load. (6) In the bonded specimens, the depth of the compression zone of the arch mechanism had no correlation with the lateral confinement pressure and the vertical axial load. Chapter 4 describes the comparison between the experimental shear strength and calculated results based on the modified Arakawa mean and Minami equations shown in Figs. 17 and 18. These figures show that the test results are in agreement with the modified Arakawa mean equation, and that the modified Minami equation can reasonably be applied to assess the shear strength considering the truss and arch mechanisms.
PDF