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Month: July 2011
Effect of infills on the seismic response of high-rise RC buildings designed as bare according to Eurocode 8
The aim of the work is to evaluate the influence of masonry infills on the seismic behaviour of reinforced concrete frames designed according to Eurocode 8 provisions as bare frames. To this purpose, non linear dynamic analyses of a twelve storey–three bay plane frame are performed considering four different infills configurations, named bare, fully infilled, open ground storey and open seventh storey frames. Artificially generated and recorded near fault ground motions are used in the numerical analyses. The accelerograms are scaled to attain the same intensity of the design one. The analyses are performed by means of a finite element code with fiber elements for the modelling of columns and beams. The infill walls are modelled through equivalent diagonal no tension struts, of which the constitutive law and the hysteretic behaviour are described in detail in the article. The structural response is evaluated through several parameters, such as top horizontal displacement, maximum interstorey drift and dissipated energy. The main inference is that the effect of uniformly distributed infills on the seismic performance is beneficial due to the additional strength, stiffness and energy dissipation capacity provided. The presence of an open storey may change this general conclusion, especially in the open seventh story model. Anyway the building retains strength and ductility resources when subjected to earthquakes of the same intensity of the design one.
The Haiti Earthquake Mw = 7.0 of January 12th 2010: structural and geotechnical engineering field observations, near-field ground motion estimation and interpretation of the damage to buildings and infrastructure in the Port-au-Prince area
The Mw 7.0 destructive earthquake that struck the Republic of Haiti on January 12, 2010 was one of the deadliest of the last century in the region. What has been concluded after a field study during the period from 16th to 22nd of January 2010 is that this event is mostly a man-made natural disaster. This is due to the very adverse social, political and economic conditions that existed before the earthquake that greatly contributed to the lack of any building-construction code and control of land use and the lack of any governmental – public services during the post-earthquake emergency. The primary effects of the earthquake were worsened due to the inability or absence of any preparedness for search and rescue and help the victims. The frozen response of the structures to the seismic event, observed during the field trip, gave valuable information about the ground motion, since instrumental records were unavailable. The response of a fence functioning as a primitive seismoscope was analyzed, resulting to an effective ground horizontal acceleration of about 0.6 to 0.7 g. Similarities between Haitian structures and their response with instrumented cases in other regions, resulted in the acceptance of a 1.0 g vertical acceleration for the site. Finally, the detailed investigation of the whole liquefaction phenomenon at the site, documented that this is starting with ejection of sand and water, before the large ground displacements take place and continues after the strong phase of the ground motion.
Evaluation of the equivalent viscous damping (EVD) coefficient for steel concentrically brace frame structures with hollow rectangular section (HRS): direct displacement based design (DDBD)
The work presented here concerns the assessment of the corrected equivalent viscous damping coefficient for concentric braced steel frames, referring to the direct displacement based design method (DDBD) described at Section 3. First, concentric braced steel frames and displacement based design are described, with particular attention given to the evaluation of the damping coefficient. The models realized to perform non-linear analysis and the procedure used to determine the corrected equivalent viscous damping coefficient are then described (Sections 4 and 5). Finally, the results obtained through non-linear dynamic analysis are presented and used to propose a relation between the damping coefficient, the slenderness of braces and the ductility level.
The influence of infill panels on the seismic behaviour of reinforced concrete buildings
As it is well known in literature, infills modify the behaviour of framed structures under lateral loads. Nevertheless, infills are generally neglected in structural analysis, and this, in many cases, may lead to unreliable evaluations of structural response. Although several theoretical and experimental researches express the necessity to take into account the infills, today reliable models of infilled structures do not exist, due to the difficult interpretation of experimental results. The aim of the proposed approach is to evaluate the effect of infills in the global and local response of a building under earthquake loads, identifying the most significant parameters that influence its behaviour. In this paper a convenient tool for the evaluation of the effects of the infills is suggested, in order to reach acceptable results in global and local analyses. The attention is focused on the most used typology in Italy: reinforced concrete structures infilled with masonry panels, realized in contact with the frame after its hardening and without connectors nor joints.