Regions Of High Seismic Risk Research Articles

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.

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.

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.

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.

Sustainable Selective Mitigation Interventions towards Effective Earthquake Risk Reduction at the Community Scale

Risk reduction policies are crucial in regions of high seismic risk, having significant exposure and building vulnerability. In Italy, the Sismabonus incentive mechanism was recently approved, which regulates the possibility of benefiting tax deductions after seismic strengthening interventions on buildings. This paper presents a simplified approach for evaluating the effects of implementation of the Sismabonus policy at the territorial scale. Considering only reinforced concrete RC building typologies, a speed method for calculating the probability of being in relevant risk classes is introduced and it is applied to a town in southern Italy. The evaluation is based on simplified modeling of lateral seismic behavior and on the estimate of the peak ground acceleration corresponding to the attainment of building capacity. The effect of possible retrofit interventions is also considered. This performance-based procedure allows for taking into account the cost for selective retrofit interventions and contemporarily to estimate the variation of mean expected annual loss that is obtained with building upgrading.

Steel plate shear walls with outriggers. Part I: Plastic analysis and behavior

Steel plate shear walls (SPSWs) are ductile and economical energy dissipating systems for buildings located in regions of high seismic risk. In spite of many advantages of SPSWs; however, their overturning stiffness is relatively low, especially when their width is narrow compared to the building height. Therefore, additional flexural stiffness must be provided to the system when designing narrow SPSWs. A logical solution that can be effectively used in SPSW systems is to rigidly connect the beams of adjacent bays to the columns of SPSWs (on both sides) forming an interacting system of SPSW and moment frame in which the adjacent beams act as outriggers resulting in an overall reduction of overturning in the SPSW. However, insufficient information exists on the behavior and efficiency of such structural systems, herein referred to as SPSW with outriggers (SPSW-O). This paper discusses four different potential SPSW-O options that can be used in mid- to high-rise buildings to enhance the flexural stiffness of the system. Plastic mechanisms, ultimate lateral load resistance and overturning stiffness of such systems are investigated, and key design parameters are identified through a combined analytical and numerical investigation. A parameter called the outrigger efficiency factor (OEF) is defined to quantify the contribution of the outrigger system to the overall overturning stiffness of a SPSW-O. Analytical expressions are derived for the lateral load resistance and OEF of the four SPSW-O options, and are then compared with numerical analysis results with reasonable agreement. Furthermore, parametric studies are performed to investigate the influence of a number of parameters on the overall behavior and characteristics of the SPSW-O systems. Parameters subject to investigation include height of the wall, outrigger beam and connection properties.

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.

Effect of out-of-plane behavior on seismic fragility of masonry buildings in Turkey

This study focuses on the evaluation of seismic safety of unreinforced masonry buildings in Turkey by using fragility curves generated for two behavior modes of load bearing walls: in-plane and out-of-plane. During generation of fragility curves, a force-based approach has been used. There exist two limit states in terms of base shear strength for in-plane behavior mode and flexural strength for out-of-plane behavior mode. To assess the seismic vulnerability of unreinforced masonry buildings in Turkey, fragility curves generated for in-plane behavior were verified by the observed damage during the 1995 Dinar (Turkey) earthquake and fragility curves generated for out-of-plane behavior were verified by the observed damage during the 2010 Elazig (Turkey) earthquake. The verification results reveal that the proposed fragility-based procedure can provide an alternative for the seismic safety evaluation of unreinforced masonry buildings in Turkey. Using this procedure, it becomes possible to investigate a large population of masonry buildings located in regions of high seismic risk in a short period of time. The obtained results are valuable in the sense that they can be used as a database during the development of strategies for pre-earthquake planning and risk mitigation for earthquake prone regions of Turkey.

Design of environmentally responsible structures in regions of high seismic risk

Historically, the effects of buildings on the changing environment were evaluated based on the daily operations and energy use of their mechanical, electrical and plumbing building systems. Structures themselves were typically given little or no consideration. Structures contribute to carbon emissions during the building process and over their service life, especially if they are located in regions of high seismic risk. The carbon footprint associated with the damage, repair, partial or full demolition and reconstruction of structures has a considerable effect on the environment. The efficiency of structures must not only be evaluated based on initial cost, constructability and material availability but also be evaluated based on the long-term environmental effects. The superior performance of enhanced structural systems may have a positive effect on limiting carbon emissions depending on the regional seismicity. A carbon footprint calculator including life cycle, damage and cost–benefit models has been developed to consider a building's overall impact on the environment from initial construction through the full service life of the structure.

Inelastic design of high-axially loaded concrete columns in moderate seismicity regions

In regions of high seismic risk, high-strength concrete (HSC) columns of tall buildings are designed to be fully ductile during earthquake attack by providing substantial amount of confining steel within the critical region. However. in areas of low to moderate seismic risk, the same provision of confining steel is too conservative because of the reduced seismic demand. More critically, it causes problematic steel congestion in the beam-column joints and column critical region. This will eventually affect the quality of concrete placing owing to blockage. To relieve the problem, the confining steel in the critical region of HSC columns located in low to moderate seismicity regions can be suitably reduced, while maintaining a limited ductility level. Despite the advantage, there are still no guidelines developed for designing limited ductility HSC columns. In this paper, a formula for designing limited ductility HSC columns is presented. The validity of the formula was verified by testing half-scale HSC columns subjected to combined high-axial load and flexure, in which the confining steel was provided as per the proposed formula. From the test results, it is evident that the curvature ductility factors obtained for all these columns were about 10, which is the generally accepted level of limited ductility.

Effect of Beam's Subassemblies Geometry on Behavior of Steel Moment Connection

Steel moment resisting frames are widely employed in regions of high seismic risk to resist seismic forces. Comparisons among different analytical investigations show that geometric characteristics of connection parts have great influences on connection's behavior. In order to evaluate this issue, a special connection is detailed that consists of a top and a bottom flange plate which is fillet welded to beam flange and groove welded to column flange. This connection is considered as an exterior connection. Beam is the most important part of connection, so we focused on varying the depth of the beam. Considering that, this parameter isn’t independent in rolled shape profiles, i.e. when beam depth increases, the thickness of flange and web will increase at the same time, we cannot examine the effect of beam depth alone. Therefore, we have used the plate girder instead to consider beam depth separately. All of models are designed according to AISC 360-05 provisions. Three-dimensional nonlinear finite element analyses of the connections were carried out. The results show, when beam depth increases, strength increases too, but stiffness and ductility decrease significantly. On the other hand, fracture potential of connection changes significantly.

Seismic performance of composite reinforced concrete and steel moment frame structures – state-of-the-art

Composite reinforced concrete and steel moment frame structures are comprised of reinforced concrete (RC) columns and steel (S) beams – the so-called composite RCS frames. Extensive research over the past several decades suggests that such systems are particularly well proper and economic for use in mid- to high-rise buildings in low to moderate seismic risk regions and low to mid-rise buildings in moderate to high seismic risk regions. This paper reviews the state-of-the-art in testing, finite-element analysis and design of composite RCS systems. Development of guidelines and recommendations of RCS beam–column connections and RCS moment frames are presented and a future research on composite RCS systems is provided.

Post earthquake performance monitoring of a typical highway overpass bridge

Bridges form crucial links in the transportation network especially in high seismic risk regions. This research aims to provide a quantitative methodology for post-earthquake performance evaluation of the bridges. The experimental portion of the research involved shake table tests of a 4-span bridge which was subjected to progressively increasing amplitudes of seismic motions recorded from the Northridge earthquake. As part of this project, a high resolution long gauge fiber optic displacement sensor was developed for post-seismic evaluation of damage in the columns of the bridge. The nonlinear finite element model was developed using Opensees program to simulate the response of the bridge and the abutments to the seismic loads. The model was modified to predict the bent displacements of the bridge commensurate with the measured bent displacements obtained from experimental analysis results. Following seismic events, the tangential stiffness matrix of the whole structure is reduced due to reduction in structural strength. The nonlinear static push over analysis using current damaged stiffness matrix provides the longitudinal and transverse ultimate capacities of the bridge. Capacity loss in the transverse and longitudinal directions following the seismic events was correlated to the maximum displacements of the deck recorded during the events.

Testing and modeling of square carbon fiber-reinforced elastomeric seismic isolators

Steel-reinforced elastomeric isolators (SREIs), as an effective seismic isolation device, are the most common isolators in use. However, SREIs are typically heavy and expensive and, as a result, application of these devices is often limited to large and expensive structures. A reduction in the cost and weight of elastomeric isolators would permit a significant increase in their application to many ordinary residential and commercial buildings. Fiber-reinforced elastomeric isolators (FREIs) are a new type of elastomeric bearing that employs fiber as the reinforcement material rather than steel. FREIs have several advantages over traditional SREIs including superior damping properties, lower manufacturing cost, light weight, and the possibility of being produced in long rectangular strips with individual isolators cut to the required size. This paper presents a brief literature review on experiments with FREIs, and reports on an experimental study conducted on carbon FREIs from which the mechanical properties of the bearings, including displacement characteristics and damping values are evaluated. A brief description of an analytical approach to model the cyclic response of the bearings is another component of this paper. As a special application, the bearings considered in this study were not bonded to the test platens. For bearings having suitable aspect ratio values, this particular type of application resulted in a stable rollover deformation, which reduced the horizontal stiffness and increased the efficiency of the bearing as a seismic isolator device. Test results suggest that for many high seismic risk regions worldwide, the application considered in this study can be viable for the base isolation of ordinary low-rise buildings. Copyright © 2007 John Wiley & Sons, Ltd.

Spatial correlation of shear-wave velocity in the San Francisco Bay Area sediments

Ground motions recorded within sedimentary basins are variable over short distances. One important cause of the variability is that local soil properties are variable at all scales. Regional hazard maps developed for predicting site effects are generally derived from maps of surficial geology; however, recent studies have shown that mapped geologic units do not correlate well with the average shear-wave velocity of the upper 30 m, V s(30). We model the horizontal variability of near-surface soil shear-wave velocity in the San Francisco Bay Area to estimate values in unsampled locations in order to account for site effects in a continuous manner. Previous geostatistical studies of soil properties have shown horizontal correlations at the scale of meters to tens of meters while the vertical correlations are on the order of centimeters. In this paper we analyze shear-wave velocity data over regional distances and find that surface shear-wave velocity is correlated at horizontal distances up to 4 km based on data from seismic cone penetration tests and the spectral analysis of surface waves. We propose a method to map site effects by using geostatistical methods based on the shear-wave velocity correlation structure within a sedimentary basin. If used in conjunction with densely spaced shear-wave velocity profiles in regions of high seismic risk, geostatistical methods can produce reliable continuous maps of site effects.

Seismic performance of steel frames with reduced beam section connections

Reduced beam section (RBS) moment resisting connections are among the most economical and practical rigid steel connections developed in the aftermath of the 1994 Northridge, California, earthquake. Although extensive experimental testing and some numerical simulations have shed light on the behavior of this type of connection, system level studies of RBS steel frames are still quite limited. As part of this research, nonlinear pushover and transient analyses of 4-, 8-, and 16-story frames with RBS connections are conducted with the objective of developing a better understanding of RBS frame behavior and exercising as well as critiquing the recently published FEMA-350 design specifications. The analyses confirm that in spite of inherently low overstrength, RBS frames are capable of economically providing good seismic performance in regions of high seismic risk. Other structural behavior issues with design implications are also discussed.

Acceptance Criteria for Special Precast Concrete Structural Walls Based on Validation Testing

The 2003 Edition of the NEHRP Provisions permits, with validation testing, the use of structural (shear) walls of jointed construction in regions of high seismic risk. Acceptance criteria for such validation testing, accompanied by background and commentary, are presented in this article. Lastly, the future direction of non-emulative design of precast concrete walls is discussed.

Inelastic Dynamic Behavior of Hybrid Coupled Walls

This paper presents an investigation of the seismic behavior of hybrid coupled wall systems, in which steel beams are used to couple reinforced concrete shear walls. System response is studied using transient finite element analyses that account for the effect of concrete cracking, crushing, and steel yielding. Shear stresses in the concrete constitutive model are handled separately from normal stresses, which allows concrete to undergo high shear deformations without causing premature concrete crushing in the model. The developed finite element models are validated through comparisons with more refined models and test data. Suites of analyses are conducted to investigate pertinent parameters including hazard level, earthquake record scaling, dynamic base shear magnification, interstory drift, shear distortion, coupling beam plastic rotation, and wall rotation. The analyses show that hybrid coupled walls are particularly well suited for use in regions of high seismic risk.