Graphical dynamic trends for earthquake incidence response of plan-asymmetric systems

A Graphical Dynamic model is derived to describe the directional earthquake response of two-ways plan-asymmetric systems, which retains the insightful educational evidence of traditional graphical static methods and the accuracy of computational methods of analysis. The dynamic directional response is expressed in terms of modal rotational kinematics about modal centers of rotation, referred to as modal torsional pivots. Seismic forces and response decomposition are handled through geometric modal torsional trends and the earthquake incidence response envelopes are described through directional modal participation radii and graphic spectrum-based "8-shaped" directional influence circles. The graphic approach provides good predictions of the maximum response and of the critical angle computed through CQC3 and other directional analysis methods

Performance based earthquake assessment of an industrial silos structure and retrofit with sliding isolators

Recent seismic events pointed out the high vulnerability of existing industrial facilities, stressing on safety and high losses inherent to interruption of economic activities and release of environmentally hazardous materials. These structures often have irregular geometry and structural configuration, are subject to aging and corrosion, and are designed without specific performance-based or seismic design criteria. Due to these inherent complexities, retrofit using friction isolators can be a viable and practical solution for performance improvements. This work presents a case study of irregular industrial storage plant structure consisting of a group of six elevated silos resting on a steel frame on one side and connected to a vaulted RC structure on the other. A computational model is built incorporating nonlinearities from the components (braces, beams, columns, etc.) and from the mitigation devices. Retrofit using friction isolators is analyzed and evaluated through linear and nonlinear dynamic analyses under a set of natural ground motions. Results show the effectiveness of the mitigation strategy in terms of performance improvement

Thermo oxidative aging of polymers and polymer‐matrix composites studied with cyclic indentation

The growing use of polymer-matrix composites in aircraft structures leads to the necessity of understanding the degradation phenomena due to their exposure to high temperatures. For T The aging of three epoxy resins (PR520, Tactix and RTM6) in pure state and reinforced with carbon fibers has been characterized by Ultra-Micro Indentation on force-controlled Fischerscope H100C equipment. These materials were aged at 150°C, in air at atmospheric pressure up to 1000 hours and under pure oxygen environment at a pressure of 2 bar, to accelerate the oxidative aging. Please click Additional Files below to see the full abstract

Mohr circle-based graphical vibration analysis and earthquake response of asymmetric systems

The maximum seismic response of torsionally coupled plan asymmetric structures can be rationally visualized and computed through a Mohr Circle Response Spectrum Analysis (MCRSA). This is done combining the graphic modal properties of the torsional dynamic equations of motion with the structural earthquake demand in terms of a displacement spectrum as a function of the modal eigenvalues SD(ω2). A compact representation of the modal properties and of the response envelope is built and visualized in the Mohr plane. The maximum modal responses are then combined using a graphic adaptation of the SRSS and CCQ combination rules based on the elastic response spectrum. This Graphic Dynamic rule proves to be an effective response prediction tool, and is particularly suited to estimate the response of seismic base isolation systems

Cyclic indentation test to characterize viscoelastic behavior of polymers

The Oliver & Pharr analysis of indentation data is generally acknowledged and used by research labs and industries to characterize the mechanical behaviour of metals at small scales. It is based on the Sneddon’s contact model of a rigid indenter penetrating an elasto-plastic matter and is perfectly suitable for these materials. However, when the nanoindentation technique is used to study polymer behaviour, there is no general agreement on the procedure and analysis method to use. It is clear that getting the elastic and plastic parameters from the fitting of a single unloading is insufficient to fully characterize the time-dependent behaviour of these materials. The indentation methods applied on polymers are usually inspired by the well-known macroscopic mechanical tests and implemented with the nanoindentation equipment. For instance, a creep test is reproduced through nanoindentation at constant force, revealing a logarithmic behaviour similar to macroscopic one. When small oscillations are superposed on the static nanoindentation loading, a dynamical loss and storage moduli can be calculated by an analogy to the macroscopic DMA technique. The direct analogy between macroscopic static and dynamic behaviour, and microscale contact behaviour might be questionable due to many factors. Nevertheless, these methods are the only procedures available today to access the local mechanical properties of polymers with nanoindentation. In this work, we suggest a new cyclic indentation method and material behaviour analysis inspired by a macroscopic tension fatigue test. Our test consists of up to1200 loading-unloading cycles after an initial holding period at low load to correct for a thermal drift. Each hysteresis loop is analyzed to obtain its area, the secant rigidity and mean (ratcheting) displacement similarly to the area, secant modulus and ratcheting strain characterizing the macroscopic test (see Figure 1). The frequency and load ratio effects on these three parameters are also studied. The cyclic indentation test is performed at two glasses, a titanium alloy and several polymers to make sure that the observed time-dependency is due to the material behaviour and not to the indentation technique itself. The results obtained on a high density polyethylene are discussed and compared with the macroscopic tension fatigue behaviour demonstrated by this material previously [1]. Please click Additional Files below to see the full abstract

La modellazione delle strutture isolate in presenza di sistemi di isolamento nonlineare e l’analisi dinamica non lineare semplificata secondo l’OPCM 3274/3431 (punto 10.7.6)

In addition to the conventional time history analysis for base isolated structures, the Italian building code OPC 3274/3431 allows a simplified nonlinear dynamic analysis, described in section 10.7.6. Although the analysis methods and criteria selection sections of the Italian code are generally very similar to EC8 and other international codes, these codes do not allow such a simplified procedure. This method appears theoretically inconsistent due to an unjustified decoupling of the nonlinear equations of motions of the superstructure and of the isolation system, since the nonlinear analysis is carried out treating the structure as a rigid SDOF system. The experimental tests performed on a full-scale building constructed at Rapolla (Potenza, Italy), pointed out some important effects of energy exchange from the first isolated mode towards the higher modes, due to the nonlinearity of the isolation system. This results in an increased contribution of higher modes to the overall structural response, as already evidenced in some of the principal studies in literature and also translated into practice by the international building codes and guidelines. Some nonlinear seismic response analyses have been carried out in order to show the inconsistency of the simplified analysis of the OPC 3274/3431. This procedure considerably underestimates the forces in the structure even for practical cases of optimal design of the isolation systems

SI113, a Specific Inhibitor of the Sgk1 Kinase Activity that Counteracts Cancer Cell Proliferation

Background/Aims: Published observations on serum and glucocorticoid regulated kinase 1 (Sgk1) knockout murine models and Sgk1-specific RNA silencing in the RKO human colon carcinoma cell line point to this kinase as a central player in colon carcinogenesis and in resistance to taxanes. Methods: By in vitro kinase activity inhibition assays, cell cycle and viability analysis in human cancer model systems, we describe the biologic effects of a recently identified kinase inhibitor, SI113, characterized by a substituted pyrazolo[3,4-d]pyrimidine scaffold, that shows specificity for Sgk1. Results: SI113 was able to inhibit in vitro cell growth in cancer cells derived from tumors with different origins. In RKO cells, this kinase inhibitor blocked insulin-dependent phosphorylation of the Sgk1 substrate Mdm2, the main regulator of p53 protein stability, and induced necrosis and apoptosis when used as a single agent. Finally, SI113 potentiated the effects of paclitaxel on cell viability. Conclusion: Since SI113 appears to be effective in inducing cell death in RKO cells, potentiating paclitaxel sensitivity, we believe that this new molecule could be efficiently employed, alone or in combination with paclitaxel, in colon cancer chemotherapy

Multi-instrument multi-scale experimental damage mechanics for fibre reinforced composites

© Published under licence by IOP Publishing Ltd. Reliable investigation of damage in fibre reinforced composites requires concurrent in- and ex-situ application of multiple instruments at different scale: digital image correlation, acoustic emission registration, optical/electron microscopy, C-scan, X-ray imaging and micro-computed tomography. The multi-instrument experimental mechanics allows detailed damage monitoring and inspection

Thermo-oxidation behaviour of organic matrix composite materials at high temperatures

The present paper is a review of the main activities carried out within the context of the COMPTINN‟ program, a joint research project founded by a FUI program (Fonds Unifiés Interministériels) in which four research teams focused on the thermo-oxidation behaviour of HTS-TACTIX carbon-epoxy composite at „high‟ temperatures (120°C-180°C). The scientific aim of the COMPTINN‟ program was to better identify, with a multi-scale approach, the link between the physico-chemical mechanisms involved in thermo-oxidation phenomena, and to provide theoretical and numerical tools for predicting the mechanical behaviour of aged composite materials including damage onset and development