In this study, a post-tensioning method using externally unbonded steel rods was applied to pre-damaged reinforced concrete beams for flexural strengthening. Nine simply-supported beams, three reference beams and six post-tensioned beams, were subjected to three-point bending. The design parameters observed in this study were the amount of tension reinforcements (3-D19, 4-D19, and 2-D22 + 2-D25; “D” indicates the nominal diameter of the rebar) and the diameters of the external rod (φ22 mm and φ28 mm). A V-shaped profile with a deviator at the bottom of the mid-span was applied to the pre-damaged beams, and a post-tensioning force was added to overcome the low load resistance and deflection already incurred in the pre-loading state. The post-tensioning force caused by tightening the nuts at the anchorage corresponded to a strain of 2000 με in the external rods; this value was approximately equal to the strain caused by torque that two adults can apply conveniently. The post-tensioning system increased the load-carrying capacity and flexural stiffness by approximately 40–112% and 28–73%, respectively, when compared with the control beams. However, the external rods did not yield in the post-tensioned beam with larger steel reinforcements and external steel rods. The external rod with the larger diameter increased the flexural strength more effectively.

This study aims to investigate the joint strength of longitudinal plate-to-high-strength steel circular hollow-section X-type joints under plate axial load. The material properties of high-strength steel with nominal yield strengths of 460, 650, 900, and 1100 MPa were used for parametric analysis. The variables for analysis were ratios of chord diameter to thickness, plate width to chord diameter, and utilization. To determine the capacity of connections, the joint strengths using a deformation limit and a strength limit were considered and compared with American Institute of Steel Construction (AISC), Eurocode 3, and ISO 14346. The joint strength determined by the ultimate deformation limit is approximately equal to the joint strength determined by the strength limit state at the yield strength of 460 MPa. The difference between both the joint strengths, however, becomes higher with increasing yield strength. The design equations estimate the joint strength based on the ultimate deformation limit approximately until the limitation of the nominal yield strength in each design code. As the nominal yield strength increases, the joint strengths are overestimated. In using high-strength steel in circular hollow-section X-type joints, the reduction factors of 0.75 and 0.62 for AISC and ISO 14346 are suggested for the nominal yield strengths of 900 and 1100 MPa, respectively. In Eurocode 3, the reduction factor of 0.67 is also suggested for a yield strength of 1100 MPa.

The objective of this study is to develop a computational equation or a method that can predict the shear strength strengthening effect of RC beams with high tension steel rods. The shear capacity of these beams is defined as the summation of shear force of concrete, stirrup and high tension steel rods. Zsutty equation is used to estimate the shear force of concrete. The Zsutty shear equation produces satisfactory predictions in comparison with ACI code equation. The strengthening effect on shear capacity is achieved through the geometrical method in this study. The basic concept of this method is that externally unbonded high tension steel rods are converted to a vertical component, which affects the shear capacity. This geometrical equation contains three parameters such as area under influence, inclined angle and specified yield strength of high tension steel rod. Particularly, the high tension steel rods of specimens of this study did not reach the yield point. Therefore, it is necessary to estimate the stress of high tension steel rod at nominal flexural strength in order to produce more accurate prediction results. There are a way to estimate this stress using the relationship equation between load and deflection. The related equation between load and deflection manifested that the theoretical result agreed with the experimental result between 96∼101%. From the comparison of experimental and predicted shear capacity, an exact agreement is achieved by the proposed method in this study.

A number of apple trees have collapsed in South Korea due to strong winds caused by typhoons. In fact, apple trees are protected by various types of support systems. However, despite this, they have still been damaged. The reason why the trees collapsed is that the installation of a support system is based not on scientific facts but on empirical facts. The purpose of this study was to evaluate the structural safety of the anti-disaster support system of apple trees. Equivalent static tests of the support systems, i.e., fences and matrix supports, were carried out. The result of the equivalent static tests indicated that the bearing capacity of the foundation is considered an important factor for the performance of the fence support, and the elements played a major role in the case of the matrix support due to the connection of the strut wire and the mat wire. Based on this test result, design criteria and standard specifications of the apple tree support system in response to local wind speed are proposed.

A turn-buckle is a device capable of adjusting the tensile force between tension members. However, the measurement of the designed tensile force is practically impossible. A measurement device has been developed to deal with this disadvantage of conventional turn-buckle. The straight elements of conventional turn-buckle are slightly pre-bent to cause the lateral displacement. The lateral displacement due to applied load of curved element is almost linear. The change in gap between curved elements due to applied load is measured with a micrometer or vernier-calipers. Then the measured gap size can be converted to a loading value of the tension member. A theoretical analysis is performed to show the applicability of the developed measurement device. The results of loading and unloading test show acceptable linearity and precision of the measurement device for the field application. Additionally, two measurement devices with different capacity were installed to measure for long-term of six months. The results of this test show that the recovery is acceptable for long-term usage.