Tensile strength was investigated for hybrid bar (HYB), in this study. HYB is made of both steel reinforcement and glass fiber. Cross section of HYB has a shape in which steel reinforcement wrapped with glass fiber. For the production of HYB, rebar of SD400 class and glass fiber of E class are used as main materials. Vinyl ester resin is used to harden a glass fiber. In order to evaluate for tensile strength of HYB, the direct tensile test was performed about total ten specimens. The length of total specimens is 2,200 mm including the grip. Diameter of HYB according to core diameter was considered as a test variable. Direct tensile test for HYB was performed using a UTM with a capacity of maximum 1,000 kN. Tensile strength and strain were measured for each specimen during the test. From the test results, tensile strength and elastic modulus were 317 ~ 341 MPa, 103 ~ 107 GPa, respectively. Especially, elastic modulus of HYB was improved in comparison with usual GFRP bars such as the Aslan 100 or the V-rod.

The objective of this study is to evaluate the mechanical behaviors and structural integrity of the weldment of high strength steel by using an acoustic emission (AE) techniques. Monotonic simple tension and AE tests were conducted against the 3 kinds of welded specimen. In order to analysis the effectiveness of weldability, joinability and structural integrity, we used K-means clustering method as a unsupervised learning pattern recognition algorithm for obtained multi-variate AE main data sets, such as AE counts, energy, amplitude, hits, risetime, duration, counts to peak and rms signals. Through the experimental results, the effectiveness of the proposed method is discussed.

In the study, direct tensile test was conducted to perform statistical approaches to the maximum tensile strength of design strengths (120, 150 and 180 MPa), and then the direct tensile database construction was made to examine the reliability of the direct tensile test.