Seismic Soil Characterization to Estimate Site Effects Induced by Near-Fault Earthquakes: The Case Study of Pizzoli (Central Italy) during the Mw 6.7 2 February 1703, Earthquake

Many of the urban settlements in Central Italy are placed nearby active faults and, consequently, the ground motion evaluation and seismic site effects under near-fault earthquakes are noteworthy issues to be investigated. This paper presents the results of site investigations, the seismic site characterization, and the local seismic response for assessing the effects induced by the Mw 6.7 2 February 1703, near-fault earthquake at the Madonna delle Fornaci site (Pizzoli, Central Italy) in which notable ground failure phenomena were observed, as witnessed by several coeval sources. Even though recent papers described these phenomena, the geological characteristics of the site and the failure mechanism have never been assessed through in-situ investigations and numerical modeling. Within a project concerning the assessment of soil liquefaction potential and co-seismic ground failure, deep and shallow continuous core drilling, geophysical investigations and in-hole tests have been carried out. Subsequently, the geotechnical model has been defined and the numerical quantification of the different hypotheses of failure mechanisms has been evaluated. Analyses showed that liquefaction did not occur, and the excess pore water pressure induced by the shaking was not the source of the ground failure. Therefore, it was hypothesized that the sinkhole was likely caused by earthquake-induced gas eruption.

Numerical investigation of ground tanks for storage subjected near-fault earthquakes

Finite element method is known as the most common methods in a numerical analysis of reservoirs subjected to the influence of an earthquake. Investigating the effects of interaction between structures and fluid during the earthquake is among the major objectives of the present research. In this article, by selecting a variety of conventional modes of fluid storage, the dynamic effects of the reservoir and their mutual effects based on changes in physical parameters are analyzed. Unexpectedly, based on the results of this study, it was observed that the crisis situation always does not occur in the full state of the tank. Moreover, the filled and semi-filled reservoirs require seismic retrofitting for mode 10% below the tank height.

Investigation on Seismic Behavior of Historical Tokatlı Bridge under Near-Fault Earthquakes

The main purpose of this study is to compare the static and dynamic behavior of a historical single-span masonry arch bridge under different near-fault earthquakes. The historical Tokatlı Bridge, built in Karabük, is chosen for this study. To investigate the behavior of near-fault earthquakes on the historical masonry bridge, first, a finite element model is built and analyzed under various near-fault earthquakes by using ANSYS and SAP2000. To build a finite element model, 162920 nodes and 47818 elements are used in ANSYS. First, finite element analysis results are compared to each other under Earth gravity. Then, ground motions near the fault are chosen to be used in this study. These earthquakes can be listed as follows: Cape Mend (1992), Kobe (1995), Superstition Hills (1987), Northridge (1994), Imperial Valley (1979), and Chi-Chi (1999). The behavior of the single-span historical bridge is obtained under these ground motions, and the results are compared with each other using contour diagrams using ANSYS. Furthermore, at the end of these analyses, it is observed that the tensile stresses have reached the permissible masonry tensile strength, especially on the upper side of the large belt, on the upper side of the belt, and on the side of the belt, and pose a risk for damage.

Performance Evaluation of bi-directional Roller Bearings for Seismic Isolation of Buildings Under Near-fault Earthquakes

An advantage bidirectional sloped rolling type isolation device composed of multiple rollers in both orthogonal-in-plane directions is studied in this research. The analytical model of a single direction of roller bearing (RB) system is extended to a two-direction RB system. Also, a 3D linear-elastic frame element to build the finite element model is used to incorporate the response of the building model. Several experimental tests of a physical building model with and without an RB system are used to validate the numerical model. The model is used to assess the nonlinear response history analysis of a four-story multi-column building system with two different physical properties that represent buildings with low and high lateral stiffness when subjected to pairs of scaled near-fault earthquake records. The effect of the angle of inclination of bearing plates in the range of 1.0o to 4.0o and sliding friction force is also investigated in a parametric analysis to evaluate the performance of RB with supplementary damping mechanisms ranging from 0.0 to 0.5N/kg, i.e., friction force normalized with the structure mass. Results show that the proposed bi-directional RB system is suitable for reducing the seismic response of rigid and flexible multi-column structures. In particular, the RB system reduces structure acceleration responses by 5–85% in the flexible structure and 86–96% in the rigid structure. Furthermore, an angle of inclination of bearing plates greater than or equal to 3.0o is an advantage to ensure the self-centering capacity.

Seismic Collapse Risk Assessment of Braced Frames under Near-Fault Earthquakes

Special concentrically braced frames (SCBFs) located in regions close to earthquake faults may be subjected to near-fault ground motions, often characterized by pulses with long periods. These near-fault pulses could impose additional seismic demands on structures and increase the risk for structural collapse. Currently, there is limited research on the seismic collapse risk of SCBFs under near-fault earthquakes. This paper uses a general simulation-based framework to assess the seismic collapse risk of SCBFs under near-fault earthquakes. To quantify the large variability and uncertainty associated with the seismic hazard, a stochastic ground motion (SGM) model is used where the near-fault pulse characteristics are explicitly incorporated. The uncertainties in the SGM model parameters (including the near-fault pulse characteristics) are addressed through appropriate selection of probability distribution functions. To accurately predict the occurrence of collapse, numerical models capable of capturing the nonlinear and collapse behavior are established and used. Efficient stochastic simulation approaches are proposed to estimate the seismic collapse risk with or without considering the near-fault pulse. As an illustration, the seismic collapse risks of two SCBFs are investigated and compared. Probabilistic sensitivity analysis is also carried out to investigate the importance of uncertain model parameters within the SGM towards the seismic collapse risk.

Seismic Fragility Analysis of Base Isolated Structure Subjected to Near-fault Ground Motions

In order to better evaluate the performance of the base isolated structure under the near-fault earthquakes, this paper takes into consideration an existing engineering case study in China as the prototype, and uses OpenSEES platform to establish the nonlinear finite element model of the base isolated structure. The nonlinear response of the isolated structure under the near-fault earthquake is analyzed. The incremental dynamic analysis (IDA) method is used to calculate the damage probability of the structure under the near-fault earthquake, and the fragility curve of the base isolated structure is established. The fragility equation is obtained by nonlinear regression, and the error of fragility equation is analyzed. The results show that the maximum value of the inter-story drift of the upper structure under the action of near-fault earthquake is significantly greater than that under the action of far-fault earthquake. With the increase of seismic intensity, the damage probability of base isolated structure increases nonlinearly, and the maximum response value of horizontal displacement of bearing and inter-story drift of superstructure increases generally. In addition, the exceeding probability of the fragility curve based on PSDA is greater than that based on EDP criterion. When the sample points of the two methods are the same, the exceeding probability points calculated based on PSDA can be regarded as accurate values. The fragility curve based on PSDA may overestimate the exceeding probability to some extent, and the overestimation may be enlarged with the increase of failure stage.

Seismic characterization of Pizzoli (Central Italy) to estimate site effects induced by near-fault earthquakes

<p>Most of the towns, villages and infrastructures settled in Central Italy are placed nearby active faults and, consequently, the ground motion evaluation and the ground failures characterization under near-fault earthquakes are noteworthy issues to be investigated. The Madonna delle Fornaci - MDF – site, close to Pizzoli village (L’Aquila in Central Italy), has been selected as an emblematic site for assessing the effects induced by near-fault earthquakes, because it is located very close to the Pizzoli-Barete active Fault accountable for the February 2, 1703 Mw 6.67 earthquake. After this historical earthquake, remarkable surface manifestations, attributed to soil liquefaction and coseismic ground sinkholes, were observed at the MDF site, occurred in the Holocene alluvial deposit of the Aterno River, as witnessed by several written sources (among which Uria De Llanos, 1703). As concerns the geological setting, the MDF site is placed in the Plio-Quaternary NW-SE elongated L’Aquila intramontane basins which is bounded by a framework of active NW-SE trending and SW-dipping extensional faults which includes also the above mentioned Pizzoli-Barete active Fault. A comprehensive geophysical, geological, and geotechnical campaign has been carried out at the MDF site with the goal to obtain the seismic site characterization and the shallow and deep subsoil model preparatory to the quantitative estimation of the near-fault ground motion and the evaluation of the soil liquefaction potential induced by the 1703 seismic event.</p><p>The field survey consisted of three shallow continuous core drilling 15-20 m-deep boreholes; in one of the them, a down hole test and SPT measurements were conducted every 1 m depth; an open tube piezometer at the 11-12 m depth was installed in one of the boreholes; a couple of undisturbed samples were sampled for geotechnical laboratory tests; a MASW, Seismic refraction and ERT investigations were performed along two perpendicular 70-m long alignments; several single station microtremor measurements performed also in the neighbouring area. These data permitted preliminary to elaborate a quite confident 1-2D litho- and seismo-stratigraphic model for the MDF test site.</p><p>The MDF site is characterized by mainly calcareous grain-supported Holocene alluvial deposit: sandy gravel and gravelly sand with a silty component, sometimes predominant, in the matrix with water table level about 8-12 m b.g.l. Moreover, the following horizons are noteworthy to mention: an orange sand level at 11-12 m b.g.l. which could be considered preliminary as a liquefaction-prone level and an organic reddish-brown silty clay at 14-15 m b.g.l., which could be used for C14 dating.</p><p>Further, a 200 m-deep continuous core drilling borehole, executed nearby the MDF site by ISPRA for the mapping of the Italian geological sheet 348 “Antrodoco”, was also taken into consideration to obtain the complete 1D subsoil model for the near-fault ground motion amplification modelling.</p><p>The near-fault ground motion evaluation of the MDF site, considered as paradigmatic of the Central Italy seismicity, will go on through the geotechnical characterization of the alluvial deposits, the shear wave velocity versus depth profile and the seismic input evaluation to use for the numerical modelling.</p>