Maurice Anthony Biot was not only the scientific founder of earthquake engineering. His pioneering contributions extended well beyond, to many other fields, including mechanics of porous media, wave propagation, aerodynamics and aeronautic fluid mechanics, non-linear elasticity, theory of folding and thermodynamics. Combin- ing simplicity and breadth, his work achieved the aesthetic qualities displayed by foremost nineteenth century and turn of the century practitioners of mathematical physics like Maxwell, Rayleigh and Sommerfeld. In the following we review only Biot’s contributions to earthquake engineering, the first steps, the background, the time in which he grew and several other factors, which may have influenced him and contributed to his formulation of the response spectrum method. Today, Biot’s response spectrum method continues to be the basis for all modern seismic design work, a condicio sine qua non in all of earthquake engineering.
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Current U.S. practice of seismic qualification of suspended ceilings by means of shake table tests
Suspended ceilings are among the most widely used nonstructural components. Past earthquakes have demonstrated the susceptibility of suspended ceilings to failure during seismic events. To address this vulner- ability, design codes have incorporated specific design and installation criteria for suspended ceilings. However, ceiling and grid manufacturers continue to innovate and introduce new products that are requested by engineers and architects but are not addressed in the code. Therefore, it is necessary to have the means to evaluate such prod- ucts. Because these units are difficult to analyze numerically, earthquake simulation testing can be used to assess the seismic performance of suspended ceilings. Such technique was used by one of the major manufacturers in the United States to characterize the performance of a standard code-prescribed ceiling and to use that performance as a benchmark for assessing the response of this manufacturer’s alternate installation. Testing and evaluation of data showed that the code-prescribed installation had an acceptable performance. It was also noted that the ceil- ing constructed with the proposed alternate installation performed as well as or better than the specimen installed using the code procedure. Finally, the test data revealed some of the shortcomings of the current experimental and evaluation methodology that require revisions.
Analysis of the seismic vulnerability of the “Quinto Orazio Flacco” school in Bari (Italy)
Due to the high level of uncertainty characterizing existing buildings, the evaluation of the seismic behaviour of these structures must be preceded by an accurate reconstruction of their history. At this aim the present paper focuses firstly on the historical analysis and successively on the investigation of the seismic vulnerability of the “Quinto Orazio Flacco” school, built in Bari in 1933. The three-storey main masonry building has a M-shaped plan with maximum dimensions equal to 57.8 m and 82.4 m respectively in the transversal and longitudinal directions. In 1963 a new reinforced concrete building separated from the preexistent masonry one was realized along its free perimeter. By the analysis of the capacity curves obtained by suitable pushover procedures performed separately for each building, it emerges that masonry and reinforced-concrete buildings are vulnerable to earthquake-induced structural pounding in the longitudinal direction. In order to investigate this structural aspect, in this paper time history analyses are carried out, using detailed finite element three-dimensional models of the two buildings and a numerical procedure suitable elaborated by Matlab software.
For this paper is available an extended abstract after the text in Italian
Damage analysis of the town of Onna (L’Aquila) after the April, 6, 2009 earthquake
The paper addresses the analysis of the seismic damage of Onna, a village near L’Aquila almost completely destructed during the 6 April event. A purposely developed data form has been used to collect the ob- servations of several surveyors. The analysis of the construction typologies, of the seismic vulnerability and of the damage lead to the conclusion that the poor characteristics of the masonry played a dramatic role in the seismic damage suffered by the buildings, despite that some typical historical seismic provisions were present (limited height of the buildings, wood ties). The low level of damage of some unreinforced masonry buildings in Onna, built following a good construction practice, indirectly confirms the heavy role played by the seismic vulnerability in the damage observed.
For this paper is available an extended abstract after the text in Italian.
Linear methods for the seismic vulnerability analysis of R.C. buildings
Checking the seismic safety of existing structures is a complex task, mainly due to uncertainities connected with material properties, loads and structural geometry. Before O.P.C.M. 3274, with the exception of applications to masonry buildings (and after important seismic events), no italian code has defined methods specifically devoted to existing, structures considering also r.c. buildings. included. The real novelty of new code applications consists in the development of reliable and applicable produres for the analysis of existing structures, especially of the reinforced concrete ones. The more credited methods (also for practical purposes) may be divided into two classes: linear and non linear ones (among them pushover analysis). These methods may be applied either to static analysis and to dynamic analysis. Static analysis is carried out by assigning a standard distribution of lateral forces along the heigth of the considered building following the assumed shape of “first vibration mode” of regular structures. Dynamic analysis enables to analyze also geometrically articulated structures by considering modal shapes derived from eigenvectors and eigenvalues of a generalized system. The methods are shortly, with particular emphasis on the linear one, in order to estimate the ultimate PGA for the considered structure. This method represents an appropriate compromise between reliability and rapidity of calculations. By using design spectrum with behaviour factor q, it is possible to consider, for existing buildings, a minimum value of ductility.
This paper is available in Italian only
Seismic risk analysis of harp type cable stayed bridges
A seismic risk analysis of harp type cable stayed bridges is presented using the concept of damage probability matrix. The cable stayed bridge is modeled as a two dimensional system with the deck idealized as a continuous beam subjected to bending action and axial compression. The response of the bridge is obtained by the frequency domain spectral analysis. A double filtered power spectral density function with seismic intensity parameter taken as the magnitude of earthquake and a correlation function between the support excitations are considered as a seismic inputs. For a given magnitude of earthquake, the damage probability matrix is determined by defining three damage states namely, major, moderate and minor. The seismic risk index is determined by combining the dam- age probability matrix with the probability of occurrence of different magnitudes of earthquake. As an illustrative example, a three span cable stayed bridge is analyzed for an extensive parametric study. The parameters include degree of correlation, angle of incidence of earthquake, ratio of the components of ground motion and soil condition. Some of the important conclusions of the study indicate that i) Longitudinal component of ground motion has considerable effect on the probability of failure of the bridge deck; ii) Probability of failure is significantly more for the soft soil condition; iii) Fully correlated ground motion between support excitation provides less value of the probability of failure as compared to the uncorrelated ground motion; and iv) Probability of failure is not very sensitive to the variation of angle of incidence of earthquake.
Flexural behaviour of external fibrous reinforced concrete beam-to-column joints
A softened strut-and-tie macro model able to reproduce the flexural behavior of external beam-to- column joints with the presence of horizontal and vertical steel bars, including softening of compressed struts and yielding of main and secondary steel bars, is presented, to be used for the pushover analysis. The model proposed is able to calculate also the flexural response of fibrous reinforced concrete (FRC) beam-to-column sub-assemblages in term of a multilinear load-deflection curves. The model is able to take into account of the tensile behavior of main bars embedded in the surrounding concrete and of the softening of the compressed strut, the arrangement and percentage of the steel bars, the percentage and the geometry of steel fibers. First cracking, yielding of main steel and crushing of concrete were identified to determine the corresponding loads and displacement and to plot the simplified monotonic load-deflection curves of the sub-assemblages subjected in the column to constant vertical load and at the tip of the beam to monotonically increasing lateral force. Through these load-deflection curves the component (beam, joint and column) that first collapse can be recognized and the capacity design can be verified. The experimental results available in the literature are compared with the results obtained through the proposed model. Further, a validation of the proposed model is numerically made by using a non linear finite element program (ATENA-2D) able to analyze the flexural behavior of sub-assemblages.
For this paper is available an extended abstract after the text in Italian
Rocking motion of a masonry rigid block under seismic actions: a new strategy based on the progressive correction of the resonance response
A new strategy of analysis is presented here for the rocking motion dynamics of a rigid and thin block with damping represented by the coefficient of restitution. This is based on the construction of the “limit” artificial accelerogram which involves an upper bound of the block response and on its subsequent correction to consider more realistic situations. The “limit” artificial accelerogram is characterized by a particular sequence of instantaneous pulses and a simplified equation of motion is adopted for the analysis. It is firstly underlined that the amplitude resonance for the block is much more intense and frequent than that for the linear elastic oscillator. A “reduced” accelerogram is then defined by means of two criteria: 1) increasing the frequency of the pulses and 2) considering the limited duration of the stronger phase of an earthquake. The results are discussed with reference to the influencing parameters such as the coefficient of restitution and the size and slenderness of the block. A numerical example shows the comparison between the results from this procedure with those obtained by the Italian seismic codes NTC08 for the limit analysis of masonry blocks.
For this paper is available an extended abstract after the text in Italian
Structural behaviour of masonry spandrels of URM buildings subjected to horizontal loading: experimental analysis
The mechanical behaviour of spandrels has a very significant influence on the seismic capacity of URM multi-storey buildings, which are very common in the historical Italian towns. In this paper the seismic behaviour of masonry spandrels is investigated, in case of a horizontal tensile-resistant element exists at floor level. At this aim experimental tests have been performed on reduced scale (1:10) models of spandrels, made of both tuff masonry and homogeneous material. The specimens have been built using different arrangements of masonry, corresponding to different construction techniques adopted during the time (from XVII up to XX century). The experimental equipment has been purposely designed in order to appropriately reproduce the structural behaviour of spandrels when masonry wall is subjected to horizontal forces acting in their own plane. The observed failure mechanisms and the corresponding M-c curves are reported for all the adopted slenderness ratio and masonry arrangements. Furthermore, in order to evaluate the cyclical performance of this kind of masonry panels, the results of cyclic tests have been analyzed in detail in terms of maximum strength, stiffness at reloading and energy dissipation.
For this paper is available an extended abstract after the text in Italian