Regions Of Seismic Risk Research Articles

Mechanical Response Study of a Cross-Fault Water Conveyance Tunnel under the Combined Action of Faulting Dislocation and Seismic Loading

This paper investigated the response of a cross-fault water conveyance tunnel under the combined action of faulting dislocation and seismic loading. The current work studied the mechanical properties of the wall rock–lining contact surface. Finite difference method (FDM) code was used for the numerical simulation test to reproduce the shear test and calibrate the parameters. In the analysis of the combined faulting dislocation and strong earthquake impact on the cross-fault tunnel, the FDM was used with special consideration of the wall rock–lining interaction. The result showed that the Coulomb contact model in the FDM code could satisfactorily simulate the shear behavior of wall rock–lining contact surface. In the mechanical response calculation of the cross-fault tunnel under the faulting dislocation–seismic loading action, the magnitude of the initial faulting distance had a significant effect on the seismic relative deformation of the tunnel. The permanent deformation caused by the seismic loading increased with the initial faulting dislocation. The position of the maximum shear stress on the contact interface was related to the faulting dislocation mode, and it was distributed on the side of the tunnel squeezed by the active plate. In the high seismic risk regions with extensive development of active faults, it was necessary to consider the initial crack caused by the faulting dislocation in the stability evaluation of the cross-fault tunnel. Then, the seismic resistance study of the tunnel was followed.

Seismic design parameters of double-layer diamatic domes

The effect of past earthquakes (e.g., the 1995 Kobe and 2016 Kumamoto earthquakes) on the space structures revealed the fact that the assumption of the invulnerability of these structures is incorrect despite their light self-weight and high degree of redundancy, and space structures may suffer severe damage during strong ground motions. Therefore, special attention should be paid to the design of this type of structure in high seismic-risk regions. Nevertheless, the existing seismic design codes have not provided the seismic design parameters (i.e., the seismic response modification factors), including the behavior factor, R, and the displacement amplification factor, Cd for space structures. This research aims to extract the seismic design parameters of double-layer diamatic domes (DLDDs) to answer the challenges that structural engineers face in the design of this type of structure. For this purpose, 16 DLDD models with different rise-to-span ratios (RSRs) and span lengths were considered. After designing the models and performing the nonlinear time history analysis using the simultaneous effect of the three transitional components of ground motions, the target displacement at the control node was determined. Then, the pushover analysis was carried out to derive the capacity curve of the structures and calculate the seismic response modification factors in both horizontal and vertical directions. The results indicate that the domes with RSRs of 1/7 and 1/5 should be designed such that they remain in the elastic state in the horizontal direction. Then, with the growth of RSR, the value of R increases and reaches 1.792. Finally, equations were presented in this study for the period, behavior factor, and displacement amplification factor of DLDD structures in both horizontal and vertical directions using the nonlinear regression analysis.

Life cycle evaluation of seismic retrofit alternatives for reinforced concrete columns.

The critical earthquakes of the last few years highlight the urgent seismic retrofitting of existing buildings due to their aging or inadequate design. This paper aims to evaluate reinforced concrete column retrofit alternatives in a region of high seismic risk. Significant economic, environmental, and functional factors must be considered when deciding between various building retrofit options. The study uses a cradle-to-grave analysis to examine the economic and environmental impacts through life cycle assessments. Specifically, the life-cycle performance of three classic alternatives for rehabilitating columns lacking adequate confinement is compared: concrete jacketing, steel jacketing, and carbon fiber incorporation. The research adopts a holistic approach using multi-criteria decision-making methods, integrating economic, environmental, and functional criteria. A set of criteria and indicators is presented in a structured hierarchy that facilitates the orderly evaluation of alternatives. The results suggest that steel jacketing is preferred, as it presents a balanced performance in most criteria. The incorporation of carbon fiber is viable due to its low environmental and functional impact, although the high production costs of the raw materials limit it. In contrast, concrete jacketing has the highest environmental and functional impacts, making it the least favorable option. The results of this study will provide relevant information for engineers and decision-makers to select the most suitable options for building retrofit when considering several simultaneous perspectives.

Instance segmentation of soft‐story buildings from street‐view images with semiautomatic annotation

AbstractIn high seismic risk regions, it is important for city managers and decision makers to create programs to mitigate the risk for buildings. For large cities and regions, a mitigation program relies on accurate information of building stocks, that is, a database of all buildings in the area and their potential structural defects, making them vulnerable to strong ground shaking. Structural defects and vulnerabilities could manifest via the building's appearance. One such example is the soft‐story building—its vertical irregularity is often observable from the facade. This structural type can lead to severe damage or even collapse during moderate or severe earthquakes. Therefore, it is critical to screen large building stock to find these buildings and retrofit them. However, it is usually time‐consuming to screen soft‐story structures by conventional methods. To tackle this issue, we used full image classification to screen them out from street view images in our previous study. However, full image classification has difficulties locating buildings in an image, which leads to unreliable predictions. In this paper, we developed an automated pipeline in which we segment street view images to identify soft‐story buildings. However, annotated data for this purpose is scarce. To tackle this issue, we compiled a dataset of street view images and present a strategy for annotating these images in a semi‐automatic way. The annotated dataset is then used to train an instance segmentation model that can be used to detect all soft‐story buildings from unseen images.

Configuration Features and Calculation Mechanisms of the Composite RC Column-Steel Beam (RCS) Joints: State of the Art

Reinforced concrete and steel (RCS) composite moment frame structures consist of reinforced concrete (RC) columns and steel (S) beams. Such systems combined with several advantages of the two structural members have larger structural stiffness, lower cost, and faster construction speed than the traditional concrete or steel frame system to be a particularly well viable alternative for use in seismic risk regions. The calculation of joint shear capacity is an essential step in seismic design. This study introduces the typical configuration characteristics of the RCS connection and reviews the state of the art of the shear bearing capacity in terms of failure models, shear distribution mechanisms, calculation mechanisms, and requirements given in the experimental and theoretical study to provide reference and foundation for the subsequent study. Finally, the development of recommendations and further research studies on seismic performance of RCS composite frames are provided.

Performance of CFRP strengthened full-scale SHS connections subjected to cyclic loading

Square hollow section (SHS) beam–column connections are prevalent in steel structures and extensively used in high seismic risk regions due to their significant architectural and structural benefits. Rehabilitation and strengthening of SHS connections are important considerations due to the vulnerable effects of cyclic loading. Studies on the structural performance of CFRP strengthened SHS connections under large displacement cyclic loading are, however, very limited and the finite element (FE) modelling numerical approach not yet been developed. The objective of the current research is to develop a FE modelling numerical approach to simulate the cyclic response of CFRP strengthened SHS beam–column connections. The modelling techniques are validated by comparing the FE model simulated results with the authors’ experimental results. A detailed parametric study is then conducted to study the effects of the thickness of the beam and column section, moment arm, and the strengthening scheme on the cyclic performance of CFRP strengthened SHS beam–column connections. CFRP strengthened SHS beam–column connections have shown improvements in structural performance with respect to moment hysteresis response, stiffness and energy dissipation capacity. Moreover, CFRP strengthened connections showed less tendency for buckling compared to their bare counterparts. Research findings of the present study will be beneficial to restore the structural integrity of SHS beam–column connections through CFRP strengthening.

Seismic isolation of railway bridges using a self-centering pier

Earthquakes cause severe damages to bridge structures, and rocking isolation of piers has become a superior option for the seismic protection of bridges during earthquakes. A seismic isolation method with free rocking mode is proposed for railway bridge piers with medium height. Experimental and numerical analysis are conducted to evaluate the seismic performance of the rocking-isolated bridge pier. Shaking table test is carried out with a scaled model by using three strong input earthquake records. The measured data includes displacement, acceleration and time history response of the pier-top and the bending moment of the pier-bottom. Test results show that the expected uplift and rocking of the isolated pier occur under strong earthquakes and the rocking-isolated pier has self-centering capacity. Slight damage appears at the collision surface between pier and base due to pier uplift, while there is no damage in the pier body. The bending moment of pier-bottom is less affected by the spectrum of input ground motions. The two-spring model is provided to simulate the isolated pier with free rocking mode under earthquakes. A seismic response analysis model for the rocking-ioslated pier is established with the assistance of OpenSees platform. The simulated results agree well with the measured results by shaking table test. Therefore, the seismic isolation method with a self-centering pier is worthy of promotion for railway bridges in high seismic risk regions.

A modified rock mass classification considering seismic effects in the basic quality (BQ) system

Safe construction and operation of tunnels in high seismic risk regions require special aseismic design. A possible solution to this issue is to consider the earthquake damage that a tunnel may suffer beforehand in the process of engineering rock mass classification during the geotechnical investigation phase. Then, the tunnel support system is designed with this modified classification result. To verify this hypothesis, this work investigates the Chinese engineering rock mass classification system, the basic quality (BQ) rating system, considering seismic effects. The main contribution of the current work is to quantitatively modify the rock mass intactness index Kv in the BQ system considering the potential earthquake damage under various levels of design peak ground acceleration. The procedure to obtain the rock mass basic quality index considering the design peak ground acceleration is proposed and verified with real field data from the 2008 Wenchuan earthquake. This approach is a promising enhancement of the empirical methods for considering the seismic effects for tunnels that require special design against possible earthquake impacts.

Earthquake-Related Signals in Central Italy Detected by Hydrogeochemical and Satellite Techniques

Central Apennines are one of the regions of highest seismic risk of Italy. A number of energetic events (M_W > 5) hit the region during the period 2004-2017, killing several hundreds of people (e.g., 294 casualties associated with the August 24th, 2016, M_W 6.0 event of Amatrice). These earthquakes impacted piezometric levels, springs discharge, and groundwater chemistry on a large area, even at distances of several tens of kilometers from the epicenters. Here we present a multidisciplinary dataset based on hydrogeochemical and satellite observations associated with the seismic events occurred in Central Italy during the period 2004-2017, that combines information derived from the application of groundwater monitoring and satellite techniques. Groundwater monitoring techniques allowed to detect hydrogeochemical anomalies in spring and well waters (20 sampling points over the observation period), whereas satellite techniques were applied to detect time-space variations in ground thermal emissions. We detected two significant, almost synchronous, anomalies in 2009 and 2016-2017 with both techniques, and we tentatively correlated them to crustal deformation processes. Part of the observed signals was detected before mainshocks, and they appear to be related to aseismic slip or to seismic slip eventually induced by minor fluctuations in seismicity. We argued that the combination of two factors, i.e., the shallow depth of local earthquakes and the concurrent deepening of groundwater circulation paths to several km depth, allowed for the recording of variations in the stress field by geofluids released at the surface.

Seismic strengthening of rigid steel frame with CFRP

Steel frames are a very popular choice in building construction and are used extensively in high seismic risk regions across the world. These existing and future constructed steel frames may need to undergo seismic strengthening to mitigate the high collapse risk during possible earthquakes in the future. In this study a finite element (FE) model was developed, analysed and the results compared with the present self-performed experimental study using shake table tests of steel frames strengthened with externally bonded carbon fibre reinforced polymers (CFRP) composites to validate the modelling techniques. The validated modelling technique are then used for a comprehensive parametric study on the effects of frequency of excitation, maximum acceleration, modulus of CFRP, thickness of CFRP, number of CFRP layers and adhesive type on the seismic response of the frame structure. The results indicate that externally bonded CFRP strengthening is very effective for seismic strengthening of steel frames. The CFRP strengthening technique reduced the lateral deflection by improving the stiffness and energy absorption capacity of the steel frames.

3D seismogenic model of the 2015 Gorkha earthquake and subsequent seismic risk

On April 25th, 2015, the moment magnitude (M-w) 7. 8 Gorkha earthquake, Nepal occurred in Himalaya orogenic belt, which seems insufficient to release the accumulated energy as suggested previously. The following seismic risk assessments are mostly based on the two dimensional or pseudo-three dimensional inversions of tectonic deformation. Here we analyze the relationship between the main shock and biggest aftershock of the 2015 Gorkha earthquake sequence, and its unevenness in time and space. Combining focal mechanism solutions, crustal velocity structure, relocated aftershocks, and inversion results from InSAR, we construct a three dimensional model which changes along both the strike and dip directions of the Main Himalayan Thrust. The finite element method with nonlinear friction is used to calculate the fault behavior and block deformation in one earthquake recurrence period. Comparison between the forward calculation results and the co-seismic deformation observed from InSAR, and co-seismic slip inverted from deformation observations, and time-space evolution of historical earthquakes revealed that the three dimension model is close to the reality. The results suggest two potential seismic risk regions in the future: a big earthquake might be located in the east of the 1934 Bihar-Nepal M-w similar to 8. 1 earthquake, and a moderate to major event might take place to the southeast of the aftershock M(w)7. 3 earthquake.

The suitability of the Pieve Fosciana hydrothermal system (Italy) as a detection site for geochemical seismic precursors

The Serchio valley is one of the regions of highest seismic risk in Tuscany, Italy. As a part of a seismic prevention/prediction pilot project funded by Regional Government of Tuscany, the geochemical and hydrologic processes that control the composition of the thermal waters emerging near the Pieve Fosciana village (Prà di Lama site), have been investigated to assess the suitability of the site for the monitoring of geochemical precursors of earthquakes. The investigation protocol considered the coupled use of chemical analyses on water aliquots sampled during discrete surveys, and of continuous signals for selected physical-chemical parameters acquired via an automatic station equipped with a suite of parameter-specific sensors. Concentrations of major inorganic dissolved aqueous components have been processed with geochemical modeling techniques to obtain a quantitative description of water–rock interactions occurring at depth in local Mesozoic aquifers. The geochemical background of the system was defined by combining these data, and an integrated hydrogeological and geochemical model of the hydrothermal aquifer feeding the springs was elaborated. Based on the very low variability of physical and geochemical parameters over a long observation time, the relatively long and deep underground circulation paths of discharged waters under confined conditions, the site-specific sensitivity of monitored parameters to local crustal strain, and the proximity to seismically active neotectonic structures, the Pieve Fosciana system ranks as a favorable site for recognizing fluids possibly connected to energy release and/or permeability variations induced by seismogenic processes at depth. The integrated geological, hydrogeological, geochemical and modeling approach presented here could be profitably applied for the design of similar projects elsewhere.

Physically based ground motion prediction and validation: a case study medium-size magnitude Marmara Sea earthquakes

The evaluation of realistic time histories for various locations around Marmara Region is aimed to provide reliable input for performance-based seismic design, hazard or risk management studies and developing new seismic standards. The applicability of empirical Green’s functions methodology and physics-based solution of earthquake rupture have been assessed in terms of modeling complex geologic structures. This paper has two main objectives. The first one is to simulate five medium-size magnitude earthquakes (M w ≈ 5.0) recorded in the Marmara Region. A series of synthetic ground motion waveforms for three components are evaluated with a ‘physics-based’ solution of earthquake rupture. The simulation methodology is based on the studies of Hutchings and Wu (J Geophys Res 95:1187–1214, 1990), Hutchings (Seismol Soc Am 81:88–121, 1991; Seismol Soc Am 84:1028–1050, 1994), Hutchings et al. (Geophys J Int 168:569–680, 2007), and Scognamiglio and Hutchings (Tectonophysics 476:145–158, 2009). For each earthquake, we calculate synthetic seismograms by using 500 different rupture scenarios that are generated by Monte Carlo method for a selection of parameters within a range based on prior knowledge of where the earthquakes will occur. The second objective is to validate synthetic seismograms with real seismograms. To improve the credibility of synthetic seismograms from an engineering point of view, the methodology presented by Anderson (in 13th world conference on earthquake engineering, Vancouver, 2003) is followed. This methodology proposes a similarity score based on averages of the quality of fit measuring ground motion characteristics and uses a suite of measurements. In order to compute goodness of fit, ten different ground motion parameters were compared on a scale from 0 to 100, where 100 means perfect agreement. Because the methodology produces source- and site-specific synthetic ground motion time histories, and the goodness-of-fit scores of obtained synthetics are between ‘good’ and ‘excellent’ range (61.128–82.164) based on the Anderson’s score, we conclude that it can be used to produce reliable ground motion time histories for seismic risk regions to develop or improve seismic codes and standards.

Behaviour of Beam-Column Subjected to Reversed Lateral Loading

This paper presents an experimental investigation on the behaviour of Concrete Filled Double Skin Tubular (CFDST) column connected to Concrete Filled Steel Tubular (CFST) beam under reversed lateral loading. The CFDST column consists of two concentric cold-formed steel tubes with concrete sandwiched between them and the CFST member consist of cold-formed steel hollow section completely filled with concrete. The specimen in this study consists of a hollow square tube as the outer skin for both CFDST and CFST members. The inner skin of the CFDST column is a circular steel tube and M30 grade concrete having 40% cement replaced with fly ash was filled in between the tubes. The connection between the beams and the columns were provided using through bolts and angle plates. A pair of specimens considered as the control specimens having CFST members for both beam and column were also tested for comparison. All the four specimens were subjected to a constant axial load and reversed lateral loading which simulates the earthquake forces. The seismic characteristics like hysteretic behavior, peak load displacement, ductility, stiffness degradation and energy dissipation of CFDST beam-column were compared with that of the CFST beam-column. The beam-column specimens with CFDST columns exhibited favorable seismic behaviour with reduced self-weight and hence a better choice than CFST columns in regions of seismic risk.

Water-rock Interactions in a Site Investigated for Geochemical Precursors of Earthquakes: The Pieve Fosciana Spring (Italy)

The Serchio Valley is one of the regions of highest seismic risk in Tuscany, Italy. As a part of a seismic prevention/prediction pilot project funded by Regional Government of Tuscany, the Pieve Fosciana spring, a perennial thermo-mineral spring emerging in correspondence with some of the most important neo-tectonic structures of the Serchio Valley, was monitored for possible geochemical precursors of earthquakes. The investigation protocol considered the coupled use of chemical analyses on water aliquots sampled during discrete surveys, and of continuous signals for selected physical-chemical parameters acquired via an automatic station equipped with a suite of parameter-specific sensors. By combining these data, the geochemical background of the system was defined, and an integrated hydrogeological and geochemical model of the hydrothermal aquifer feeding the spring was elaborated.

Innovative low-cost recycled rubber–fiber reinforced isolator: Experimental tests and Finite Element Analyses

An experimental study on unbounded square carbon Recycled Rubber–Fiber Reinforced Bearings (RR-FRBs) was conducted to investigate their lateral and vertical behavior, under seismic loading. These low-cost rubber bearings are innovative elastomeric bearings that employ recycled rubber and fiber as reinforcement material. They have significant advantages compared to those bearings made up of natural rubber reinforced by steel layers or fiber sheets: higher dissipation capacity, lower manufacturing cost, light weight. RR-FRBs are intended for seismic isolation of ordinary low-rise buildings located in high seismic risk regions, and are designed to be mounted with no need of bonding to the upper and lower structures. This feature allows them to deform freely, reducing, and possibly eliminating, the tensile stresses generated by shear deformations. In this work, the seismic performance of the proposed bearings is investigated by means of both experimental tests and Finite Element Analyses (FEAs). The study provides useful information on both horizontal and vertical stiffness, and on the damping properties of the isolators. Moreover, a description of the instability of the bearings is discussed. The sensitivity of RR-FRBs to lateral displacement history and vertical pressure applied on the bearings is pointed out. Moreover, the validity of easy to apply design criteria is discussed.

Shear‐wave velocity based seismic microzonation of Lorca city (SE Spain) from MASW analysis

Many populated areas located in moderate seismic risk regions have been hit by earthquakes of moderate magnitude which, surprisingly, have caused very serious damage to buildings and led to the loss of human life. The city of Lorca (SE Spain) is a clear example. On 11 May 2011, two main shocks occurred in the vicinity of Lorca city with a maximum magnitude of 5.1 Mw causing some casualties and serious widespread damage in the city and its surroundings.Most of the damage was concentrated in certain districts in the city, while other parts remained intact. Actually, in Lorca, investigators detected both a clear example of seismic site effect and a seismic wave amplification occurrence due to the type of geological materials on which the city is located. For this reason, several studies are being carried out in Lorca city to assess the actual contribution of the soil conditions to the seismic amplification phenomena.In these studies, the shear wave velocity plays a key role as a parameter for evaluating the dynamic behaviour of the shallowest geological materials. Consequently, site characterization applied to calculating seismic hazard is usually based on the near surface shear‐wave velocity distribution. This study looked at the average shear‐wave velocity for the uppermost 30 m of ground, which is referred to as Vs30. The Vs30 values obtained from multichannel analysis of surface waves (MASW) were used to create a new soil classification map of Lorca city. Thus, the derived Vs30 map was transformed into the NEHRP and Eurocode 8 (EC8) standards. In Lorca city, the softness and the thickness of shallow geological formations have been observed as two important factors that affected the level of ground shaking and the degree of damage. The results show that there is a significant correlation between the Vs30 values and the damage distribution within the city.

Tourism business preparedness, resilience and disaster planning in a region of high seismic risk: the case of the Southern Alps, New Zealand

This article examines tourism business disaster planning in areas at risk from low-frequency/high-consequence natural disasters. It presents empirical findings from a tourism business survey in the Southern Alps of New Zealand, an area with high seismic risk that supports a tourism industry comprising many micro-sized, owner-operated businesses. The Alpine Fault is a 450 km geological structure running the length of the Southern Alps, and is considered overdue for a M7.8–8.0 earthquake. A survey of tourism business operators revealed generally poor levels of perceived preparedness and actual planning for a future earthquake disaster, particularly amongst micro-sized businesses. The presence or absence of business resilience ‘tools’ was investigated, all of which are more common in businesses with higher incomes. The article draws on tourism disaster planning and business resilience literature to outline an alternative approach to disaster planning for small tourism-reliant communities. It describes community-based efforts to prepare in two remote Southern Alps townships, lending support to the concept of collective, community-led disaster planning.

INELASTIC DYNAMIC ANALYSIS OF AN RC BUILDING IMPACTED BY A TSUNAMI WATER-BORNE SHIPPING CONTAINER

In the aftermath of the Indian Ocean tsunami of December 26, 2004, buildings without in-fill walls in the first story, which allow the unimpeded flow of tsunami waves, have been constructed in the regions of low seismic risk. However, columns in such buildings could be susceptible to impact of tsunami water-borne massive objects. In the present study, the impact of a tsunami water-borne shipping container on a reinforced concrete (RC) building is considered. The impact force-time histories are obtained from a high-fidelity finite element analysis, for a range of container velocities. These force-time histories are used in the impact analysis of the RC building and potential failure modes of the impacted column, changes in column axial forces, and floor displacements are studied. For the range of container velocities considered, it is found that although the axial load carrying capacity of the impacted column has significantly decreased, the building remains stable due to redistribution of internal forces to adjacent members.

A TOOL TO PREPARE A DATABASE FOR REINFORCED CONCRETE BUILDINGS IN SEISMIC RISK REGIONS

In Turkey, most of the building stock is composed of reinforced concrete buildings. As a developing country located in seismic zone, Turkey faces the risk of casualties and property loss depending on poor quality of material, poor labour and lack of building control mechanism in existing buildings. Therefore, especially after August 17, 1999 earthquake, the need for investigation of earthquake resistance of existing reinforced concrete building stock that are vulnerable to earthquake and identification of buildings with high earthquake risk had been emerged. The objective of this paper is to introduce a tool to prepare a database for assessment of seismic vulnerability of existing building stock in seismic risk regions. The tool consists of general building properties, damages resulting from building deficiencies and decision on strengthening studies. The use of building database form provided in this study has been illustrated by five sample buildings in Golcuk/Turkey. This tool can be used to monitor and strengthening studies and to prepare a database earthquake occurs in seismic risk regions. This study provides a practical contribution to the studies in urban scale in order to increase earthquake resistance of reinforced concrete buildings.