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a b s t r a c tIn case of non-diagonal modal damping, normal modes of vibration do not decouple modal equations. The usual way to handle such a non-diagonal modal damping matrix is to neglect its off-diagonal elements. In this paper, we propose an approximate method based on an asymptotic expansion of the transfer function. It is intermediate between the classical decoupling approximation and the formal solution requiring a full matrix inversion. Indeed, on the one hand, it allows to partially account for modal coupling and, on the other hand, still allows the modal equations to be solved independently from each other. We first provide the mathematical background necessary to canvass the proposed method, then consider a benchmark against which the benefits of the method are measured.

Massive volcano-related materials (VRMs) erupted from volcanoes bring the impacts to natural environment and humanity health worldwide, which include generally volcanic ash (VA), volcanic pumice (VP), volcanic tuff (VT), etc. Considering the pozzolanic activities and mechanical characters of these materials, civil engineers propose to use them in low carbon/cement and environment-friendly concrete industries as supplementary cementitious materials (SCMs) or artificial/natural aggregates. The utilization of VRMs in concretes has attracted increasing and pressing attentions from research community. Through a literature review, this paper presents comprehensively the properties of VRMs and VRM concretes (VRMCs), including the physical and chemical properties of raw VRMs and VRMCs, and the fresh, microstructural and mechanical properties of VRMCs. Besides, considering environmental impacts and the development of long-term properties, the durability and stability properties of VRMCs also are summarized in this paper. The former focuses on the resistance properties of VRMCs when subjected to aggressive environmental impacts such as chloride, sulfate, seawater, and freezing-thawing. The latter mainly includes the fatigue, creep, heat-insulating, and expansion properties of VRMCs. This study will be helpful to promote the sustainability in concrete industries, protect natural environment, and reduce the impacts of volcano disaster. Based on this review, some main conclusions are discussed and important recommendations regarding future research on the application of VRMs in concrete industries are provided.

Open-to-Circular Hollow Section (CHS) connections are highly encouraged nowadays in modern multistoried structures due to the extensive resistance provided by the CHS columns against high compression, tension as well as flexure in all directions, combined with their exceptional aesthetics. However, using more and more gusset plates or stiffeners to strengthen a conventional open-to-CHS connection causes economic disadvantage due to excessive welding quantities and substantial CHS chord yielding further limits any opportunity to exploit the full advantages offered by the open sections therefore minimizing its frequent application. However, if designed efficiently, the CHS connection can offer an extensive range of solutions which makes it an impeccable choice for the modern multi-storey structures. To that purpose, a "LASTEICON" solution is proposed in this paper investigating a "passing-through" concept, which is obtained by using laser cutting technology (LCT). Initially, a suitable moment resisting Plate-to-CHS-column connection is characterized through a detailed understanding of the relevant parameters, where the primary beams are connected at either side of the CHS column by two transverse and one longitudinal plate passing through the CHS column via laser cut slots. A detailed parametric study is conducted based on multiple Finite Element (FE) models primarily calibrated from an experimental campaign to understand the effect of each parameter and further verify and therefore establish the analytical assumptions to calculate the ultimate resistance of such connections. Finally a comprehensive design procedure is proposed to design such "passing-through" Plateto-CHS column connections. A short comparison study is also made with the conventional (direct weld) joints to highlight the advantages offered by this LASTEICON solution.

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This paper investigates through nonlinear static and dynamic analyses the behaviour of a newly introduced steel and concrete hybrid coupled wall (HCW) system made by a single reinforced concrete (RC) wall coupled to steel columns by means of steel links, a structural solution of potential interest for seismic-resistant multi-storey buildings. The considered HCW is conceived as seismic resistant system where the RC wall and the steel columns remain undamaged while the seismic energy is dissipated by yielding concentrated in the steel links only. In order to achieve such a desired seismic behaviour, a proper design procedure must be adopted and validated. Accordingly, this study reviews a recently proposed design approach and presents some modifications to further improve the seismic behaviour of the considered HCW system. Case studies are designed using the proposed modified design method as well as its former version. Afterwards, the seismic behaviour of the considered case studies is analysed to identify the optimal degree of coupling between the RC wall and steel columns, also evaluating the influence of the building height and uniform or nonuniform distribution of shear links. The obtained results confirm the improvements of the modified design method proposed in this study and provide support for the selection of the design parameter that influences the most in the seismic behaviour of the innovative HCW system, i.e. the degree of coupling between RC wall and steel columns, controlled by the adopted steel links.