Earthquake Protection of Existing Structures with Limited Seismic Joint: Base Isolation with Supplemental Damping versus Rotational Inertia

Existing civil engineering structures having strategic importance, such as hospitals, fire stations, and power plants, often do not comply with seismic standards in force today, as they were designed and built based on past structural guidelines. On the other hand, due to their special importance, structural integrity of such buildings is of vital importance during and after earthquakes, which puts demands on strategies for their seismic protection. In this regard, seismic base isolation has been widely employed; however, the existing limited seismic joint between adjacent buildings may hamper this application because of the large displacements concentrated at the isolation floor. In this paper, we compare two possible remedies: the former is to provide supplemental damping in conventional base isolation systems and the latter consists in a combination of base isolation with supplemental rotational inertia. For the second strategy, a mechanical device, called inerter, is arranged in series with spring and dashpot elements to form the so-called tuned-mass-damper-inerter (TMDI) directly connected to an isolation floor. Several advantages of this second system as compared to the first one are outlined, especially with regard to the limitation of floor accelerations and interstory drifts, which may be an issue for nonstructural elements and equipment, in addition to disturbing occupants. Once the optimal design of the TMDI is established, possible implementation of this system into existing structures is discussed

Improving the dynamic performance of base-isolated structures via tuned mass damper and inerter devices: A comparative study

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Automatic modal identification of bridges based on free vibrations and advanced signal decomposition techniques

Free vibration tests are attractive because they can be performed by means of a network consisting of few sensors temporarily installed on the structure in such a way to limit duration and cost of the experimental campaign. Additionally, free vibration tests are usually performed by introducing an initial perturbation that can induce a structural response significantly higher than the ambient excitation. This, in turn, allows to reduce the noise-to-signal ratio in the final measurements and/or to consider less stringent requirements about the technical specifications of the sensors. Since free vibration tests can provide accurate estimates of the modal parameters while being rather cheap and easy to implement, they have been performed in many applications, such as the experimental dynamic characterization of base-isolated buildings, masonry towers, ancient tie-rods, and bridges. An efficient and automatic computational framework is thus presented for the modal identification of bridges based on their free vibrations. The novel procedure proposed in the current work combines advanced signal decomposition techniques and a robust approach for damping identification. Two advanced signal decomposition techniques are considered, namely the Variational Mode Decomposition and the Empirical Fourier Decomposition. Experimental applications are then illustrated for roadway and railway bridges

Acoustical comfort in university lecture halls: simulating the dynamic role of occupancy

The acoustic comfort in teaching environments is generally determined through requirements concerning reverberation time, speech intelligibility and HVAC noise. The presence of students reduces the reverberation time but concurrently increases the background noise, that undermines the focus of students and the vocal effort of teachers. A double set of measures were acquired in two university lecture halls in unoccupied and occupied state to investigate the consequences of occupancy variations. Acoustic simulations allowed to assess the dynamic effects of the occupancy detecting the differences of speech intelligibility. Predicting the student activity may return reliable outcomes improving the quality of lessons

A family of 0-simple semihypergroups related to sequence A000070

For any integer n 65 2, let R_0(n + 1) be the class of 0-semihypergroups H of size n + 1 such that {y} 86 xy 86 {0, y} for all x, y 08 H - {0}, all subsemihypergroups K 86 H are 0-simple and, when |K| 65 3, the fundamental relation \u3b2_K is not transitive. We determine a transversal of isomorphism classes of semihypergroups in R0(n + 1) and we prove that its cardinality is the (n + 1)-th term of sequence A000070 in [21], namely, 11 _{k=0}^n p(k), where p(k) denotes the number of non-increasing partitions of integer k

Multi-Valley Superconductivity In Ion-Gated MoS2 Layers

Layers of transition metal dichalcogenides (TMDs) combine the enhanced effects of correlations associated with the two-dimensional limit with electrostatic control over their phase transitions by means of an electric field. Several semiconducting TMDs, such as MoS$_2$, develop superconductivity (SC) at their surface when doped with an electrostatic field, but the mechanism is still debated. It is often assumed that Cooper pairs reside only in the two electron pockets at the K/K' points of the Brillouin Zone. However, experimental and theoretical results suggest that a multi-valley Fermi surface (FS) is associated with the SC state, involving 6 electron pockets at the Q/Q' points. Here, we perform low-temperature transport measurements in ion-gated MoS$_2$ flakes. We show that a fully multi-valley FS is associated with the SC onset. The Q/Q' valleys fill for doping$\gtrsim2\cdot10^{13}$cm$^{-2}$, and the SC transition does not appear until the Fermi level crosses both spin-orbit split sub-bands Q$_1$ and Q$_2$. The SC state is associated with the FS connectivity and promoted by a Lifshitz transition due to the simultaneous population of multiple electron pockets. This FS topology will serve as a guideline in the quest for new superconductors.Comment: 12 pages, 7 figure

Isomorphism classes of the hypergroups of type U on the right of size five

AbstractBy means of a blend of theoretical arguments and computer algebra techniques, we prove that the number of isomorphism classes of hypergroups of type U on the right of order five, having a scalar (bilateral) identity, is 14751. In this way, we complete the classification of hypergroups of type U on the right of order five, started in our preceding papers [M. De Salvo, D. Freni, G. Lo Faro, A new family of hypergroups and hypergroups of type U on the right of size five, Far East J. Math. Sci. 26(2) (2007) 393–418; M. De Salvo, D. Freni, G. Lo Faro, A new family of hypergroups and hypergroups of type U on the right of size five Part two, Mathematicki Vesnik 60 (2008) 23–45; M. De Salvo, D. Freni, G. Lo Faro, On the hypergroups of type U on the right of size five, with scalar identity (submitted for publication)]. In particular, we obtain that the number of isomorphism classes of such hypergroups is 14865

Semihypergroups obtained by merging of 0-semigroups with groups

We consider the class of 0-semigroups (H;star) that are obtained by adding a zero element to a group (G; cdot) so that for all x,yin G it holds x star y not=0 Rightarrow x star y = xy. These semigroups are called 0-extensions of (G; cdot). We introduce a merging operation that constructs a 0-semihypergroup from a 0-extension of (G; cdot) by a suitable superposition of the product tables. We characterize a class of 0-simple semihypergroups that are merging of a 0-extension of an elementary Abelian 2-group. Moreover, we prove that in the finite case all such 0-semihypergroups can be obtained from a special construction where (H;star) is nilpotent

Comparison of Dynamic Responses of Parallel-Placed Adjacent High-Rise Buildings under Wind and Earthquake Excitations

Two parallel-placed adjacent high-rise buildings are often linked to each other through passive control devices for vibration mitigation purposes. The mitigation efficiency of these control devices mainly depends on the characteristics of relative dynamic responses, namely, opposite-sign and same-sign responses of the two buildings. The present research first identifies an opposite-sign response factor to estimate the time ratio of opposite-sign responses. Subsequently, a structure comprising two adjacent high-rise buildings (with different natural frequency ratios) subjected to both wind and earthquake excitations is analyzed. Wind-induced responses are evaluated based on wind loads obtained from wind tunnel tests, while earthquake responses are determined through a suite of 44 natural ground-motion records. The results indicate that opposite-sign factors of the displacement, velocity, and acceleration responses under wind loads, especially at across-wind direction, are larger than those under earthquake excitations, and opposite-sign response factors under wind loads are insensitive to variation of the natural frequency ratio of the two adjacent buildings compared with those under earthquake excitations. The conclusions of this research may be helpful for wind-resistant and antiseismic design of parallel-placed adjacent high-rise buildings

Capturing wave dispersion in heterogeneous and microstructured materials through a three-length-scale gradient elasticity formulation

Abstract Long-range interactions occurring in heterogeneous materials are responsible for the dispersive character of wave propagation. To capture these experimental phenomena without resorting to molecular and/or atomistic models, generalized continuum theories can be conveniently used. In this framework, this paper presents a three-length-scale gradient elasticity formulation whereby the standard equations of elasticity are enhanced with one additional strain gradient and two additional inertia gradients to describe wave dispersion in microstructured materials. It is well known that continualization of lattice systems with distributed microstructure leads to gradient models. Building on these insights, the proposed gradient formulation is derived by continualization of the response of a non-local lattice model with two-neighbor interactions. A similar model was previously proposed in the literature for a two-length-scale gradient formulation, but it did not include all the terms of the expansions that contributed to the response at the same order. By correcting these inconsistencies, the three-length-scale parameters can be linked to geometrical and mechanical properties of the material microstructure. Finally, the ability of the gradient formulation to simulate wave dispersion in a broad range of materials (aluminum, bismuth, nickel, concrete, mortar) is scrutinized against experimental observations