Seismic retrofit of an existing reinforced concrete building with buckling-restrained braces

Background: The seismic retrofitting of frame structures using hysteretic dampers is a very effective strategy to mitigate earthquake-induced risks. However, its application in current practice is rather limited since simple and efficient design methods are still lacking, and the more accurate time-history analysis is time-consuming and computationally demanding. Aims: This paper develops and applies a seismic retrofit design method to a complex real case study: An eight-story reinforced concrete residential building equipped with buckling-restrained braces. Methods: The design method permits the peak seismic response to be predicted, as well as the dampers to be added in the structure to obtain a uniform distribution of the ductility demand. For that purpose, a pushover analysis with the first mode load pattern is carried out. The corresponding story pushover curves are first idealized using a degrading trilinear model and then used to define the SDOF (Single Degree-of-Freedom) system equivalent to the RC frame. The SDOF system, equivalent to the damped braces, is designed to meet performance criteria based on a target drift angle. An optimal damper distribution rule is used to distribute the damped braces along the elevation to maximize the use of all dampers and obtain a uniform distribution of the ductility demand. Results: The effectiveness of the seismic retrofit is finally demonstrated by non-linear time-history analysis using a set of earthquake ground motions with various hazard levels. Conclusion: The results proved the design procedure is feasible and effective since it achieves the performance objectives of damage control in structural members and uniform ductility demand in dampers

On some properties of the Laplacian matrix revealed by the RCM algorithm

In this paper we present some theoretical results about the irreducibility of the Laplacian matrix ordered by the Reverse Cuthill-McKee (RCM) algorithm. We consider undirected graphs with no loops consisting of some connected components. RCM is a well-known scheme for numbering the nodes of a network in such a way that the corresponding adjacency matrix has a narrow bandwidth. Inspired by some properties of the eigenvectors of a Laplacian matrix, we derive some properties based on row sums of a Laplacian matrix that was reordered by the RCM algorithm. One of the theoretical results serves as a basis for writing an easy MATLAB code to detect connected components, by using the function “symrcm” of MATLAB. Some examples illustrate the theoretical results.The research has been supported by Spanish DGI grant MTM2010-18674, Consolider Ingenio CSD2007-00022, PROMETEO 2008/051, OVAMAH TIN2009-13839-C03-01, and PAID-06-11-2084.Pedroche Sánchez, F.; Rebollo Pedruelo, M.; Carrascosa Casamayor, C.; Palomares Chust, A. (2016). On some properties of the Laplacian matrix revealed by the RCM algorithm. Czechoslovak Mathematical Journal. 66(3):603-620. doi:10.1007/s10587-016-0281-yS60362066

Seismic performance of a reinforced concrete building retrofitted with self-centering shape memory alloy braces

Self-centering earthquake-resistant structures have received increased attention due to their ability to reduce post-earthquake residual deformations and, thus, repair time and cost. This stimulated the development of recentering shape memory alloy (SMA) dampers that use superelastic nitinol wires to dissipate energy and self-center the structure. However, there are still a few case studies applications on full-scale RC buildings in the literature. Moreover, general guidelines or even simplified approaches for the practical design of SMA damped braces are still lacking. This paper focuses on evaluating the effect of using self-centering shape memory alloy dampers for buckling-restrained braces applied for the seismic retrofit of a complex RC building structure. A design method originally proposed for elastoplastic dampers was implemented to size the SMA dampers to be placed on selected spans and stories of a building. The effectiveness of the design procedure was demonstrated by nonlinear time-history analyses under different sets of earthquake strong ground motions. The analysis results show that the recentering shape memory alloy bracing system is effective in limiting the maximum transient inter-story drifts and reducing the residual inter-story drifts after strong seismic events, due to its excellent recentering behavior together with its not negligible energy dissipation capacity

Design of controlled rupture structure for safe vector ejection

The design of structures, which have a controlled rupture, is a topic of interest of both civil and military industry and the definition of design guidelines and criteria can be helpful for future configurations. Automotive, aerospace and defence study solutions can be useful to meet the high-performance requirements of lightness and safety, and more the latest studies concerning composite materials and the relative fracture micromechanics can help to achieve these targets. The research activity of this work is focused on the numerical analysis with the aim to design a possible part for new Maritime Firing Tubes. In particular the design of new tailgate configuration was studied considering the correct structure fragmentation to ensure a clear ejection, while reducing the weight of the panels by exploiting the characteristics of the composite material. The goal of this research is the development of a scientific and methodological approach to the study of controlled rupture structure for the design and optimization of launcher tailgate. An innovative concept of hatch composed by just one carbon resin composite laminate is studied and by varying the geometric configuration it is possible to optimize the breaking path and the contact force. The complex geometry of the hatch, the high impulsive load, the energy transferred during the impact between a sort of missile and hatch, and the ways of safely breaking large flaps of panels are elements that have characterized the dimensioning of the composite in order to satisfy the stringent requirements about the ejection event in a missile lifecycle during its own firing. The focus is the evaluation of the material fragmentation behavior and element deletion followed by excessive deformation in controlled fragments closely distributed around one or several specific sizes in presence of high-speed environment

On Graphs whose Laplacian Matrices have Distinct Integer Eigenvalues

In this paper, we investigate graphs for which the corresponding Laplacian matrix has distinct integer eigenvalues. We define the set Si,n to be the set of all integers from 0 to n, excluding i. If there exists a graph whose Laplacian matrix has this set as its eigenvalues, we say that this set is Laplacian realizable. We investigate the sets Si,n that are Laplacian realizable, and the structures of the graphs whose Laplacian matrix has such a set as its eigenvalues. We characterize those i \u3c n such that Si,n is Laplacian realizable, and show that for certain values of i, the set Si,n is realized by a unique graph. Finally, we conjecture that Sn,n is not Laplacian realizable for n ≥ 2 and show that the conjecture holds for certain values of n

Immunological response in mice after long-term stimulation with cell wall antigens from Brucella melitensis.

The continuous stimulation of the immune system using cell wall antigens from Brucella melitensis was found to cause both quantitative and qualitative changes in circulating lymphocyte populations in mice. Animals were inoculated in the hind legs with antigens on alternate days for varying lengths of time. During a two-month period, we saw a higher number of circulating lymphocytes, with an increase in the number of CD4+ cells (L3T4+) and B lymphocytes (I-Ad). After two months, a drop in the overall number of circulating lymphocytes occurred, with a decrease in CD4+ cells and an increase in CD8+ cells. During the first two months, we observed a size increase in popliteal lymph nodes and an elevated humoral response. The response then waned with the declining CD4+ cells. In the first two months, the treated animals also showed an in vitro response to two mitogens, concanavalin A and lipopolysaccharide and to the cell wall fraction, after which the treated animals showed a decreased response

Pseudodynamic Tests and Numerical Modelling for Damage Analysis of Infilled RC Frames

Full-scale experimental tests are still needed to enhance knowledge on the seismic response of existing reinforced concrete buildings and to calibrate numerical models aimed at predicting damage. This study deals with pseudo-dynamic (PSD) tests and numerical modeling of full-scale multi-story infilled RC frames with different infill-to-frame connections. Nonlinear numerical models are calibrated using the experimental results at frame level and validated against the results of time-histories in terms of displacement demand, hysteretic response, and attained damage. This model is extended at building level and used to predicted damage to infills. The comparison with damage observed during post-earthquake inspections is reported and discussed

Production of tumour necrosis factor-α, interleukin-1, interleukin-6 and soluble intercellular adhesion molecule-1 by human keratinocytes stimulated in vitro with gram-negative and gram-positive components

Cultured human keratinocytes were analyzed for their ability to release tumour necrosis factor (TNF)-α, interleukin (IL)-1α, IL-6 and soluble intercellular adhesion molecule-1 (sICAM-1) after stimulation with Gram-negative [Salmonella typhimurium porins and lipopolysaccharide (LPS)-R] and Gram-positive components [lipoteichoic acid, muramic acid, muramyl-dipeptide (MDP), adjuvant peptide, protein A, α-haemolysin, toxic shock syndrome toxin (TSST)-1]. The surface expression of ICAM-1 was also investigated. In supernatants of untreated cells, no or minimal amounts of these molecules were found. After stimulation with Salmonella typhimurium porins and LPS-R, significant amounts of TNF-α, IL-1α, IL-6 and sICAM-1 were detected. Protein A induces the release of TNF-α, but not IL-1α, IL-6 and sICAM-1. α-Haemolysin induces IL-1α and IL-6 production. MDP, lipoteichoic acid and TSST-1 were able to induce a significant release of IL-6. TSST-1 also increased the level of sICAM-1 together with adjuvant peptide, which stimulated the production of TNF-α and IL-6. Muramic acid showed an increase of IL-6 release by human keratinocytes. Porins, LPS-R, adjuvant peptide and TSST-1 were also able to upregulate the surface expression of ICAM-1 on keratinocytes. The capacity of these cells to synthesize and release these molecules supports the hypothesis that keratinocytes may play an important role in modulating an immune or inflammatory response