Yunbiao Luo

Earthquake engineering research needs in light of lessons learned from the 2011 Tohoku earthquake

Earthquake engineering research and development have received much attention since the first half of the twentieth century. This valuable research presented a huge step forward in understanding earthquake hazard mitigation, which resulted in appreciable reduction of the effects of past earthquakes. Nevertheless, the 2011 Tohoku earthquake and the subsequent tsunami resulted in major damage. This paper presents the timeline of earthquake mitigation and recovery, as seen by the authors. Possible research directions where the authors think that many open questions still remain are identified. These are primarily based on the important lessons learned from the 2011 Tohoku earthquake.

Behavior and Strength of Headed Stud–SFRCC Shear Connection. II: Strength Evaluation

AbstractThis paper is the second part of a two-part report describing the behavior of headed stud–SFRCC (steel-fiber-reinforced cementitious composite) shear connection. The first paper presented an experimental study of headed stud–SFRCC shear connections, whereas this paper focuses on the strength evaluation of those shear connections. This paper first presents a finite-element model of the connections, which was validated using the experimental results. An updated empirical equation considering the contribution made by the weld collar is proposed to estimate the shear strength of a single headed stud. Finite-element models were developed to evaluate the shear strength of each stud in a densely arranged group of headed studs. The results reveal that the interaction between headed studs mitigated the confining effect on studs, and the studs thus sustained less shear strength than those with larger stud spacing. Studs placed in different positions sustain different shear forces, and this difference is gre...

Behavior and Strength of Headed Stud–SFRCC Shear Connection. I: Experimental Study

AbstractThe performance of a single-headed stud and group of studs embedded in steel-fiber-reinforced cementitious composites (SFRCC) were investigated by conducting push-out tests. A total of 16 specimens were tested with various parameters including diameter of studs, numbers of studs, gauge lengths, pitch lengths, and fiber volume fractions of SFRCC. The test results showed that the headed studs embedded in SFRCC ensured the failure mode of stud fracture even without using steel rebar in the slab. The studs densely arranged with the smallest pitch length permitted for installation provided more than 90% of the full shear strength of a single stud. Using nine studs densely arranged in an area allowing for only four studs in the current design code, the overall shear resistance was twice that of the conventional design. When the fiber volume fraction of SFRCC directly affects the ductility of the stud, it was found using a fiber volume fraction of 6% is most suitable.

Development and Testing of Naturally Buckling Steel Braces

Steel concentrically braced frames inherently provide great strength and stiffness, and are widely used for seismic resisting systems in buildings. These include conventional buckling braced frames and buckling restrained braced frames. Although the latter can prevent brace buckling and provide ductile behavior, both types of braces provide no hysteretic damping at small drift levels and offer very limited post-yielding stiffness. This study proposes a new type of steel brace with a novel mechanism—the naturally buckling brace (NBB). The design combines high-strength and low-yield steels arranged in parallel with a specified initial eccentricity along the brace length, providing ductile seismic behavior. Six tests of various NBB models subjected to cyclic loading were conducted to examine the seismic performance of the proposed NBB. Two specimens out of the six achieved the characteristics intended for NBB. The test results showed that the NBB specimens with appropriate design parameters could achieve early yielding, or hysteretic damping, from around 0.11% story drift and prevent local buckling as well as deformation concentration up to a very large story drift (greater than 3%). A single NBB would provide an asymmetric hysteretic behavior, a large post-yielding stiffness in tension, and a ductile performance with stable energy dissipation. Further systematic studies of NBBs are needed to comprehensively evaluate the capacities and limitations of the NBBs, including the reliability of performance with repeated tests.