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.
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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.
Sergio Musmeci. Discordant structures
For this paper is available an extended abstract after the text in Italian
A sustainable seismic input reduction system for monuments, for existing and new structures by creating large, stiff and strong foundations – practical applications
A system is described, aiming at reducing the seismic excitation of structures, based on pure struc- tural solutions. The basic idea is to exploit the phase lag of the incident seismic waves along the foundation and, accordingly, to design it in order to possess the adequate stiffness and strength. The longer the foundation is, the larger the phase lag becomes. It is, therefore, well understandable that under this requirement, foundations of the maximum possible length must be designed. The presented methodology might be proved quite valuable for exist- ing structures and especially for monuments, where, in most cases, it is not possible to proceed to the necessary strengthening interventions in the structure above its foundation. As a technical support of the present investigation, the size of the foundation as a two dimensional elastic beam and the velocity of the propagation of the ground motion are examined as basic parameters. Two strong ground motions have been used, each one with quite differ- ent characteristics compared to the other one: an artificial time history of rather high frequency, fitting to EC8, Type 1, ground class A and a natural ground motion of the Edessa, Greece 1990, M = 5.9, earthquake. The Edessa earthquake is characterized by much longer predominant periods of vibration compared to the artificial one. Vari- ous lengths of the foundation beam have been examined in combination with the velocity of the propagation of the ground motion along the longitudinal direction of the beam. The achieved motions at the center of gravity of the beam as well as the pertinent response spectra are calculated. These spectra are compared to the free field ones. At the beginning of the paper, it is tried to explain the inconsistency between macroseismic observations and earth- quake code requirements concerning the effects of the size of the building foundation. At the end of the paper, the results of the described methodology are demonstrated in several practical case studies.
Local seismic response in presence of subsurface cavities
In this paper the effect of underground cavities on the seismic response under incident plane waves of volume and surface has been studied.The numerical solution is obtained using the boundary element method in the BESOIL /14/ computer code that allows a 2D analysis of propagation both of volume and Rayleigh waves, and any geometry of the cavity and the ground surface.The main parameters that govern the phenomenon of amplification are considered and the criteria for determining their importance are provided. Finally a realistic cavity of irregular shape has been examined for different values of its depth and dimension.
A numerical study on the b shape factor of the shear strength criterion of unreinforced masonry panels
After summarising the failure criteria for unreinforced masonry panels provided by the new Italian technical law (NTC 2008), the paper presents a numerical study aimed to investigate the b shape factor. This shape factor is a coefficient used to evaluate the ultimate shear strength of masonry panels for the failure mechanism with diagonal cracking. The numerical results show that the computed values of the coefficient b are higher than those proposed by the rules. Consequently, the shear strength obtained applying the equation given by the NTC 2008 does not appear conservative.
Structural Engineering Codes and Standards in the United States. An Overview
Structural codes and Standards in the US