Search

Many developing countries are located in earthquake-prone areas where buildings are often of poor design and not sufficiently protected against earthquakes. This causes damage or total collapse of buildings and heavy casualties whenever an earthquake occurs. Elastomeric isolators are special devices for the seismic isolation of structures. Typically, they consist of alternate layers of steel or fiber-reinforced laminas and rubber. They are positioned between the ground and the foundation to increase the structure's natural period and reduce the inertia forces applied in case of an earthquake. This study proposes a detailed 3D Finite Element (FE) modelling of elastomeric isolators for low-rise masonry buildings in developing countries, developed with the FE software code Abaqus. The isolator consists of an energy dissipation core made of relatively High Damping Rubber and an external Ethylene Propylene Diene Monomer (EPDM) ring. In addition, it presents unbonded boundary conditions to reduce production costs and allow its applicability in developing countries. The upper and lower edges do not exhibit any bond with the supports. The main feature of such a device is the large deformability thanks to the roll-over deformation and the favourably lower lateral stiffness compared to the bonded isolator.

Elastomeric seismic isolation is a technique diffused in civil engineering to protect existing and new structures against earthquakes. It consists in introducing between the superstructure and the foundation several devices (called seismic isolators) having the property to carry vertical loads maintaining at the same time the shear modulus small, increasing considerably the natural period of the structure, where the spectral acceleration drops down (Habieb et al., 2020 and 2019a, 2019b, 2019c, 2019d, 2018). This study investigates the possibility of using recycled rubber in the form of reactivated EPDM (made by 2/3 of regenerated rubber and 1/3 of virgin rubber) for the production of low cost rubber isolators (Habieb et al., 2020). A Fiber Reinforced Elastomeric Isolator FREI prototype constituted by five EPDM pads and four GFRP laminas interposed between contiguous pads is cured in the lab at 130°C and the level of vulcanization is experimentally provided measuring Shore A hardness on several points. A 3D numerical model based on both finite differences and FEM is proposed to predict the degree of vulcanization of the FREI numerically. It is found that the crosslinking density obtained is suboptimal (but still acceptable for an engineering point of view) and that it is required to increase the vulcanization temperature to obtain a full and homogeneous curing.

Nel caso di strutture sismicamente isolate è in genere richiesta la presenza di importanti capacità dissipative nei dispositivi di isolamento, al fine di controllarne la risposta in termini di spostamento. Tuttavia, secondo alcuni Autori, l’impiego di valori elevati del rapporto di smorzamento dei dispositivi può amplificare significativamente gli effetti sulla sovrastruttura. Il presente lavoro affronta lo studio della risposta di strutture isolate alla base mediante dispositivi elastomerici LRB-HD con valori del rapporto di smorzamento ξ compresi nell’intervallo 0.2-0.3. Con riferimento a sistemi MDOF corrispondenti ad organismi resistenti in cemento armato a 2,4,6,8 piani modellati con una matrice di smorzamento “completa” ed isolati alla base con dispositivi LRB-HD, sono state valutate in primo luogo le risposte strutturali mediante analisi time-history con integrazione frontale delle equazioni del moto, considerando per i dispositivi un legame di tipo bilineare. Sono stati a tal fine impiegati segnali accelerometrici artificiali e registrazioni di terremoti storici significativi. I risultati ottenuti dalle analisi time-history in campo non lineare mostrano, in molti casi, un incremento significativo dei parametri di risposta della sovrastruttura per valori di ξ superiori al 20%. Sono state infine condotte analisi di confronto tra le risposte di cui innanzi e quelle ottenute attraverso l’analisi modale con spettro assegnato. Tali analisi evidenziano come quest’ultima procedura conduce in generale a stime non accurate di tutti i parametri di risposta ed in particolare a stime non conservative dei parametri di risposta della sovrastruttura.

The authors have assessed the concentration of 7 antibiotics in the bile of patients undergoing biliary surgery or carriers of a T tube in the common bile duct. 1 hour preoperatively, 122 patients were administered with the following chemotherapeutic agents: Cefoxitin 2 g i.v.; Cefamandole 2 g i.v.; Ceftriaxone 1 g i.v.; Clindamycin 600 mg i.v.; Amikacin 500 mg i.v.; Gentamycin 160 mg i.v.; Norfloxacin 400 mg by mouth; 30 patients showed obstructive jaundice or obstructed cystic duct. Samples of bile were withdrawn from gallbladder and common bile duct. The same antibiotics were administered to 81 patients carrying a T tube. Samples of bile and serum were collected at baseline and every 30 minutes for 4 hours and subsequently at 12 and 24 hours following administration. 18 patients showed altered liver function tests. The chemotherapeutic agents were tested by the microbiological assay as well as by HPLC. Mean concentration in the gallbladder bile was: Cefoxitin 209 +/- 86 micrograms/ml; Cefamandole 436 +/- 108 micrograms/ml; Ceftriaxone 482.7 +/- 214.84 micrograms/ml; Clindamycin 64 +/- 22 micrograms/ml; Amikacin 5 +/- 1.4 micrograms/ml; Gentamycin 4 +/- 2 micrograms/ml; Norfloxacin 22 +/- 14 micrograms/ml. In the bile of jaundiced patients or with non-visualized gallbladder no antibiotics were detected.(ABSTRACT TRUNCATED AT 250 WORDS)