鋼モルタル板を用いた座屈拘束ブレースの疲労性能の研究

A buckling-restrained brace is an excellent structural member. In medium- and low-rise buildings, it is often used primarily as an earthquake-resistant brace, and in super-high-rise and high-rise buildings, as a seismic-response controlled brace1-3). It is particularly important to assess the fatigue performance of a buckling-restrained brace where it is used as a seismic-response controlled brace.This study summarizes the results of two studies performed on a buckling-restrained brace using steel mortar planks10,12). A fatigue test using constant strain-amplitude cyclic loading was also conducted under the following two conditions: 1) Using large plastic strain-amplitudes of axial strain exceeding 3% assumed in massive earthquakes, 2) Decreasing the value of restraining index R that affects energy dissipation performance. By combining the results of the test and past studies, the study constructed a fatigue curve in the plastic region. Based on the fatigue curve, a detailed examination was conducted on the tolerable loading cycles Nt, locations of fracture and local deformation, cumulative plastic strain energy ratio ω, compressive-to-tensile strength ratio α and restraining index R for both basic type and high-performance type specimens.Focusing on the buckling-restrained brace using steel mortar planks, a constant strain-amplitude cyclic loading test was conducted using basic type and high-performance type specimens. The following results were obtained:1) In both types of specimen, strain-amplitude ε and tolerable loading cycles Nt in the plastic region have a linear relationship when plotted on a double logarithmic graph, from which the fatigue performance of the buckling-restrained brace can be estimated.2) In both types of specimen, at high strain-amplitudes of axial strain exceeding 3%, the fatigue performance of the brace is determined by the fatigue performance of its core plate, hence, there is little difference in tolerable loading cycles Nt and cumulative plastic strain energy ratio ω between the two types of specimen.3) In both types of specimen, at small strain-amplitudes of axial strain less than 3%, the fatigue performance of the brace is determined by the shape of the stress concentration location: a weld heat-affected zone in the case of the basic type specimen, and the end part (R part) where the area of the core plate plastic zone is decreased in the case of the high-performance type specimen. The high-performance type specimen is super