Abstract: The feasibility of built-up steel section as barriers of seismic metamaterials is proposed in this study. We consider two types of built-up steel sections (as resonators) and the surface waves propagation in a single layer homogenous medium and a six-layered soil medium (substrate) is investigated by analytical and computational techniques. The presence of resonator on the surface of a semi-infinite substrate results in the generation of local resonance that induces low frequency wide bandgaps. The generation of local resonance bandgaps are mainly governed by the impedance mismatch between resonator and substrate and the coupling of surface waves propagating on the surface of a semi-infinite substrate with a longitudinal mode of resonator. We further consider the surface waves propagation in both types of media and compared the bandgap frequencies. For layered soil media, a bandgap with relative bandwidth greater than 1.5 is reported that indicates the surface wave bandgap is relatively wide and it is located at a low frequency. The result also shows the effect of impedance mismatch on the bandgap width. Furthermore, with a change in geometric parameter of the resonator and material properties of substrate, the position and width of bandgap do vary. The infinite unit cell model study is further validated by a finite unit cell based frequency response and time transient analyses. An excellent agreement is observed. The time transient analysis results indicate more than 50% reduction in vibration amplitude of the surface waves. The study provides an insight for having steel piles to protect critical infrastructures from earthquake hazards.
A. Prof. Fadzli Mohamed Nazri
Universiti Sains Malaysia
Title : The efficiency of an improved seismic vulnerability index under strong ground motions
Abstract: This paper examines the seismic performance of a Hospital Building damaged during the Ranau earthquake in Malaysia of intensity level (VIII), through an improved empirical seismic vulnerability index (SVI). The research aims at reducing the limitations and the uncertainties associated with the GNDT and the EMS approaches related to RC buildings, which can possibly be resolved by implementing the analytical techniques via applying nonlinear parametric analysis. Nonlinear time-history analyses were performed by incorporating an array of strong ground motions divided between far-field and near-field sets to assess the influence of each category on the SVI values and then comparing with SVI values obtained from the nonlinear static analysis (NSA). For a better comparison, the results are depicted in terms of collapse fragility curves for the modelled parameters. The proposed approach has been verified through observational fragility curves after Ranau earthquake. Whereas, the obtained SVI values were similar for the near-field and far-field, but with different collapse intensities and mean damage grades.
A. Prof. Gang Li
Shaanxi Key Laboratory of Safety and Durability of Concrete Structures, China
Title: Creep behaviors of interactive marine-terrestrial deposit soils
Abstract: The interactive marine-terrestrial (IMT) deposit soils were formed in the complex depositional environment, their mechanical properties are different from the other deposits. The creep behaviors of Dalian clayey soils were studied according to one dimensional creep tests and drained triaxial creep tests. Based on the creep test results, the empirical model was established to describe the one dimensional creep behavior and triaxial creep behavior, respectively. The results showed that Dalian deposits have typical nonlinear creep behavior. With the increasing of consolidation pressure, the strain is increased, stability time is extended, and the demarcation point between primary and secondary consolidation is more obvious. The deposits belong to medium to high secondary compressibility soil, and the secondary consolidation coefficient is decreased with the increasing of consolidation time, and increased with consolidation pressure increasing. The ratio between secondary consolidation coefficient and compression index in different depth change from 0.033 to 0.058, which conform to Mesri conclusion. Under low deviator stress, the creep processes showed the characteristic of attenuation creep and shear contraction. However, it showed the characteristic of acceleration creep, shear contraction and shear dilatancy under damage deviator stress. The axial strain rate decreased with the increasing of creep time, and increased with the deviator stress increasing, while the deviator stress has little effect on the m values. The tests results agree well with the calculation results, which showed that the creep equation is suitable for describing the creep behaviors of Dalian interactive marine-terrestrial deposits.