Seismic-prone Regions Research Articles

Modification of the data-driven period/height relationship for buildings located in seismic-prone regions such as Quito (Ecuador)

The fundamental period of structures is a parameter used in structure under design and for evaluating existing structures. Data-driven methods using ambient vibrations have become popular, particularly for the adjustment of empirical relationships applied to building classes. This study presents the results of a survey of ambient vibrations performed in 146 reinforced concrete buildings in the center of Quito (Ecuador). Classical functional forms giving period (T) for height (H) or number of floors (N) are derived and compared with the relationships available in the Ecuadorian seismic design provisions. We highlight variations in the empirical relationships according to soil conditions, but above all according to the date of construction and the historic seismic sequence to which the buildings have been exposed. The cumulative damage effect is finally confirmed by repeating ambient vibration measurements after the 2016 Mw 7.8 Pedernales earthquake located in the subduction zone, about 175 km from Quito. Even with such a long epicentral distance, leading to low macroseismic intensity (IEMS98 = IV), the seismic ground motion of between 0.017 and 0.081 g recorded in Quito reduced the resonant frequency of the buildings tested by between 2 and 13%. This confirms the effect of cumulative damage in reinforced concrete buildings located in seismic zones, even for weak ground motions, and the variability of empirical T/H relationships associated with damage.

Recent Findings and Open Issues concerning the Seismic Behaviour of Masonry Infill Walls in RC Buildings

The extension of the damages observed after the last major earthquakes shows that the seismic risk mitigation of infilled reinforced concrete structures is a paramount topic in seismic prone regions. In the assessment of existing structures and the design of new ones, the infill walls are considered as nonstructural elements by most of the seismic codes and, generally, comprehensive provisions for practitioners are missing. However, nowadays, it is well recognized by the community the importance of the infills in the seismic behaviour of the reinforced concrete structures. Accurate modelling strategies and appropriate seismic assessment methodologies are crucial to understand the behaviour of existing buildings and to develop efficient and appropriate mitigation measures to prevent high level of damages, casualties, and economic losses. The development of effective strengthening solutions to improve the infill seismic behaviour and proper analytical formulations that could help design engineers are still open issues, among others, on this topic. The main aim of this paper is to provide a state‐of‐the‐art review concerning the typologies of damages observed in the last earthquakes where the causes and possible solutions are discussed. After that, a review of in‐plane and out‐of‐plane testing campaigns from the literature on infilled reinforced concrete frames are presented as well as their relevant findings. The most common strengthening solutions to improve the seismic behaviour are presented, and some examples are discussed. Finally, a brief summary of the modelling strategies available in the literature is presented.

A parametric study: High performance double skin tubular column using rubberised concrete

Rubberised concrete is the new age construction material which can be effectively used in seismic prone regions due to its high ductility. Based on the experimental results of the co-authors on rubberised concrete filled double skin tubular (RuCFDST) columns with both outer and inner circular hollow steel (CHS) tubes, finite element (FE) models were developed in this study. The proposed methodology is validated by generating axial load-shortening curves and ultimate strength values, and a good agreement is shown with the experimental results. A detail parametric study was carried out on thirty nine finite element models to examine the effects of outer tube diameter to thickness ratio, outer tube yield strength, hollow section ratio, length to diameter ratio and outer tube to inner tube thickness ratio of columns with 0%, 15% and 30% rubber contents. The rubberised concrete specimens showed an improvement in the axial displacement at peak load and they were more ductile in the post-peak region compared to those with normal concrete. After a comprehensive parametric investigation, this study summarized that RuCFDST columns can be considered as high performance structural columns for critical infrastructure applications in seismic prone areas and they can be specifically optimised for their ductile characteristics.

Splice Connection Details for Eccentrically Braced Frame Replaceable Links

ABSTRACTEccentrically braced frames (EBFs) can be used as a lateral load resisting system in seismic prone regions. A typical EBF consists of links, beams, columns and braces. Links are the fuse members providing energy dissipation during an earthquake. After a seismic event, damaged links need to be replaced with the new ones to recover initial stiffness and ductility of the structure. A comprehensive experimental research program has been undertaken to develop new replaceable link details. One of the proposed details is based on splicing the beam outside of the link and braces. In this type of a replaceable link, both the bearing type and slip critical type connections can be employed with different levels of bolt pretension. Four nearly full scale EBFs with replaceable links were tested to study the effect of the type of connection and gap size adopted in splice connections. The results indicate that both the bearing and slip critical type of connections can be employed for the splice connections if the bolts are fully pre‐tensioned and frictional faying surfaces are provided.

Discontinuous CFRP-Jacketing of Masonry Columns

Existing masonry columns are often susceptible to cracking due to overloading. Moreover, their fragility under earthquakes’ forces is of particular concern in seismic-prone regions. In order to mitigate these structural deficiencies, Fiber Reinforced Polymers (FRPs) are commonly used for external confinement. Full-jacketing, by means of FRP-wrapping is recognized to be very effective in improving the load bearing capacity and the ductility of masonry columns. Unfortunately, long-term effects seem to be detrimental for the masonry core, since its breathability is obstructed by the polymeric resin. Thus, a discontinuous application of the FRP-confinement appears to be more indicated in stone-masonry columns, allowing the humidity cycles to recur. On the other hand, the discontinuous wrapping negatively affects the confinement effectiveness, since both confined and unconfined masonry regions participate in the bearing capacity. In this sense, the present research is aimed to study the discontinuous confinement of half-scale masonry columns by means of Carbon-FRP strips. Unconfined and confined specimens were tested under uniaxial compression. The CFRP-confinement was studied by investigating the lateral strain in the confined and unconfined portions of the specimens. The results are reported and discussed in the paper in terms of failure modes, axial stress-strain and axial stress versus lateral strain relationships. The outcomes are reasonably convenient for a proper analytical interpretation of the phenomenon.

Sustainable housing using confined masonry buildings

Much of India is prone to substantial earthquakes, and vulnerability associated with both unreinforced masonry (URM) and improperly built reinforced concrete (RC) frame constructions has been unmasked by past earthquakes. URM structures present a severe hazard in earthquake-prone regions. And non-engineered RC structures can lead to devastating consequences. Housing for families in the economically weaker sector and the lower-income group is undoubtedly challenging to such events. Regardless of residing in a city or village, everyone desires a house with masonry walls and RC roof, just like the buildings in larger urban areas. Confined masonry (CM) construction, which is a popular building system in many countries, can fulfil this need of society. Though CM building started informally, the seismic performance is found to be really well in several destructive earthquakes. This type of construction combines the advantages of URM and RC structures and does not need sophistication required in RC construction. In this paper, the seismic response of URM, infilled RC frame and CM buildings is compared using past seismic performance and literature. It is concluded that confined masonry is a better alternative for sustainable housing in seismic-prone regions of India.

Uncertainty Quantification in Seismic Collapse Assessment of Iranian Code-Conforming RC Buildings

Structural collapse is the main concern in the existing structures which are built in the seismic-prone regions. Therefore, the primary goal of the seismic provisions in building codes is to prevent the global collapse. Iran is located in the Alpine-Himalayan belt, and has experienced some of the most destructive earthquakes in the past century. To evaluate the extent to which the Iranian building code provisions meet this objective, the authors have conducted a detailed assessment of collapse risk on a set of moderate moment resisting reinforced concrete (RC) buildings. This study considers P-Delta effects, deterioration in strength and stiffness, and cyclic deterioration in structural components.Structural assessment is performed using OpenSees platform and the multiple-record incremental dynamic analysis (IDA). Results are presented in terms of the IDA capacity curves and the collapse fragility functions at different seismic hazard levels. Results show that probability of instability increases with height of the buildings. Moreover, the collapse confidence level was evaluated considering the available uncertainties. Assuming a minimum confidence level of 90% for the buildings, the collapse prevention limit state under the 2%/50 hazard level is not satisfied for the 9 and 12 story frames, and they need to re-designed.

Predictive model for seismic sliding displacement of slopes based on a coupled stick-slip-rotation approach

This paper represents a predictive model for the earthquake-induced displacement of slopes using a coupled stick-slip-rotation approach recently proposed by the authors in a preceding paper. A collection of 1363 strong motion records associated with 25 worldwide earthquakes was used to generate the model on the basis of results of sliding block analyses. The proposed model predicts sliding displacement in terms of yield acceleration coefficient ratio (ky/kmax), period ratio (Ts/Tm), and slip length (L). The regression analysis indicates that dividing the results into the smaller intervals of period ratio can provide a noticeable higher degree of accuracy. Probable bias of the residuals versus the input variables is examined in detail. Predictions of the developed equation are compared with some available sliding block equations which similarly assumed a flexible sliding mass. The proposed model can be simply used to estimate landslide hazard in seismic prone regions.

Scenario-Based Seismic Risk Assessment for Buried Transmission Gas Pipelines at Regional Scale

AbstractBuried gas pipelines in seismic-prone regions may suffer leaks or breaks as a consequence of an earthquake, especially if the pipeline is subjected to large differential displacements due t...

Earthen masonry infill walls: Use of wooden boards as sliding joints for seismic resistance

The paper describes the results of quasi-static tests performed on a real-scale adobe masonry infill wall partitioned into sub-panels by means of the introduction of vertical wooden planks, acting as sliding joints. The specimen was tested both in-plane and out-of-plane, exhibiting good performance in terms of both stability against out-of-plane actions and in-plane deformation capacity and damage control. The results emphasize the applicability of adobe masonry as material for infill walls in seismic prone regions, coupling the good structural response with the inherent positive performance in terms of indoor ambient comfort and production sustainability demonstrated in literature.

Liquefaction potential of Agartala City in Northeast India using a GIS platform

Agartala is one of the fastest developing cities in Northeast Region (NER) of India and is also the capital city of Tripura state. The whole NER is in zone V in the seismic zoning map of India, one of the most seismic-prone regions in the world. The region is buttressed between the Himalayan collision zone to the north and Indo-Burma subduction zone to the east, and has experienced two (1897 and 1950) great earthquakes (Mw > 8.0) and several large earthquakes (Mw ≥ 7.0) since 1897. The Agartala area lies in an intraplate zone and most recently experienced a well-felt shallow (depth 30 km) earthquake of Mw 5.7 on January 3, 2017 that occurred at a distance ~75 km northeast of the city. Some evidence of liquefaction was identified along the Manu River in Kanchanbari village. In that context, this study is attempted to evaluate the liquefaction potential of the Agartala area. Dynamic properties of soil are determined using data of some 97 standard penetration test (SPT) boreholes. The cyclic shear stress of the soil layers is estimated considering a peak surface ground acceleration of 0.36 g. It is observed that according to the liquefaction potential index (LPI) scale, the central part of the city shows high to moderate, the northern part moderate to non-liquefiable and the southern part low to non-liquefiable potential. The results are presented in maps on a geographical information system (GIS) platform using the QGIS software. The liquefaction potential maps are very useful for professional engineers, government agencies and disaster management authorities for future development and planning of the city against liquefaction failure.

Strain-dependent dynamic properties of Bushehr siliceous-carbonate sand: Experimental and comparative study

Mixtures of calcareous and siliceous sediments are found in extensive areas of the earth including the seismic-prone regions. However, a few experimental studies on dynamic properties of such soils have been conducted, compared with the siliceous soils. The investigations presented in this paper include: (1) experimental study on shear modulus (G) and damping ratio (D) of Bushehr siliceous-carbonate sand under various stress-density states, (2) comparison of the results with the available models of siliceous sands, and (3) development of a modified-hyperbolic model for the studied siliceous-carbonate sand. Cyclic triaxial and resonant column tests were conducted on reconstituted samples of the Bushehr sands, retrieved from the northern coast of the Persian Gulf. The results indicate that dynamic properties of the sand are less affected by the initial stress anisotropy compared with the initial mean confining pressure (σ'm) and relative density (Dr). The effect of Dr and stress anisotropy on the shear modulus is more pronounced in higher values of σ'm. Noticeable discrepancy has been observed between the experimental results of the Bushehr siliceous-carbonate sand and the previous models basically developed for the siliceous sands. Modified hyperbolic models are presented as the shear modulus and damping curves (i.e., G/Gmax-γ and D-γ) of the tested sand. The hyperbolic models presented in this study can be used for site response analysis of the regions with similar siliceous-carbonate deposits.

Seismic risk assessment of cold-formed steel shear wall systems

This paper presents the probabilistic seismic performance and risk assessment of cold-formed steel (CFS) sheathed shear wall panel (SWP) structures adopting conventional steel moment-resisting frame (MRF) systems as a benchmark with the aim of exploring the viability of using CFS-SWP as a new structural solution in seismic prone regions. A set of 12 building structures of both systems, with 2-, 4- and 5-storey, have been designed for two seismic intensity levels. To simulate their nonlinear behaviour, the structures were modelled adopting recently developed deteriorating hysteresis models. Based on probabilistic seismic hazard analyses (PSHA), a site-specific selection of ground motion records for Incremental Dynamic Analyses (IDA) has been carried out adopting the Conditional Mean Spectrum (CMS) as a more realistic target response spectrum. Subsequently, the seismic risk was evaluated over the structure lifetime (i.e., 50years) in terms of the annual probability of exceeding the Damage Limitation, No-Local Collapse and Near Collapse limit states. The importance and usefulness of the risk metrics are highlighted and adopted as an indicator to explore the behavioural features of both structural systems. Overall, the assessment procedure showed that both systems present an acceptable seismic performance and therefore the CFS-SWP can be seen as a reliable structural solution to achieve performance-based objectives in seismic regions.

Thin-Walled CFST Columns for Enhancing Seismic Collapse Performance of High-Rise Steel Frames

This paper numerically studied the collapse capacity of high-rise steel moment-resisting frames (SMRFs) using various width-to-thickness members subjected to successive earthquakes. It was found that the long-period component of earthquakes obviously correlates with the first-mode period of high-rises controlled by the total number of stories. A higher building tends to produce more significant component deterioration to enlarge the maximum story drift angle at lower stories. The width-to-thickness ratio of beam and column components overtly affects the collapse capacity when the plastic deformation extensively develops. The ratio of residual to maximum story drift angle is significantly sensitive to the collapse capacity of various building models. A thin-walled concrete filled steel tubular (CFST) column is proposed as one efficient alternative to enhance the overall stiffness and deformation capacity of the high-rise SMRFs with fragile collapse performance. With the equivalent flexural stiffness, CFST-MRF buildings with thin-walled members demonstrate higher capacity to avoid collapse, and the greater collapse margin indicates that CFST-MRFs are a reasonable system for high-rises in seismic prone regions.

Seismic vulnerability assessment using association rule learning: application to the city of Constantine, Algeria

We performed a seismic vulnerability assessment of the city of Constantine (Algeria) using the Risk-UE and datamining-based methods [association rule learning (ARL)]. The ARL method consists in establishing relationships between building attributes (number of stories or building age) and the vulnerability classes of the European Macro-seismic Scale, EMS98. This approach avoids the costly process of drawing up an inventory of building characteristics in the field, which often discourages the assessment of seismic risk initiatives in weak to moderate seismic-prone regions. We showed that the accuracy of the assessment is independent of the subset used for the learning phase leading to development of the Constantine vulnerability proxy. Considering only two attributes, the vulnerability assignment is equal to about 75%, reaching 99% if material is added to the attributes considered. Comparison of Risk-UE and ARL results revealed a reliable assessment of vulnerability, the differences having only a slight impact on the probability of exceeding the damage level computed by EMS98 or Risk-UE in Constantine. The results of this study suggest that the ARL-based vulnerability proxy is efficient and could be applied to the rest of Algeria.

Seismic evaluation of the northbound N1/R300 bridge interchange

The design of the Stellenberg Interchange was finalised in 1982, with construction completed in 1986. The bridge was designed using a code of practice which did not include any requirements for seismic excitation. This code was superseded by the Code of Practice for the Design of Highway Bridges and Culverts, which provides detailed analysis guidelines for bridges located in seismic-prone areas. According to this code, the bridge is located in a seismic-prone area with an anticipated peak ground acceleration of 0.1 g. Current research suggests that this region could be exposed to a peak ground acceleration of approximately 0.2 g. Upon inspection of the bridge, it was noted that the bridge does not conform to modern-day best practice guidelines for bridges located in seismic-prone regions. These factors necessitated an exploratory investigation to determine whether the bridge can sustain earthquake magnitudes between 0.05 g and 0.2 g. The study was conducted by experimentally determining the natural frequencies with its corresponding mode shapes, which were used to calibrate a finite element model. The finite element model was subjected to different magnitude earthquakes to determine its structural integrity. The results show that, for an earthquake of 0.1 g, the bending moment at one of the column bases is exceeded, while two other column base moments are within 15% of its design capacity. For a 0.2 g magnitude earthquake, the design bending moments at five columns are significantly exceeded, while three other columns' design moments are close to being exceeded. The exceedance of the design moments could lead to significant damage, with the possibility of collapse of the bridge.

A study of variation in soil gas concentration associated with earthquakes near Indo-Burma Subduction zone

In the recent past, several efforts have been made by a number of researchers to measure anomalous emanations of geo-gases in seismic prone regions of the world and radon has been the most preferred geo-gas as possible earthquake precursor since it is easily detectable. In the present investigation, continuous measurements of radon concentration at 80 cm inside the soil has been carried out at Chite Fault (23.73°N, 92.73°E), Aizawl, Mizoram situated in the seismic zone V in North Eastern part of India near Indo-Burma subduction zone, using LR-115 Type-II nuclear track detectors manufactured by Kodak Pathe, France. During the investigation period, the radon concentration varied from 163.27 Bq/m3 to 2557.82 Bq/m3 with an average and standard deviation of 1116.15 Bq/m3 and 591.76 Bq/m3 respectively. Certain anomalies observed in radon concentration have been correlated to the earthquakes within the range of magnitudes 4.7 ≤ M ≤ 5.5, while some other anomalies are due to the influence of meteorological parameters.

Seismic performance evaluation of slender masonry towers: a case study

Summary Historical structures and preserving their cultural values are crucial issues for humanity, not only because of their link to important certain periods in the past, but also their unique architectural features. Although many historical structures continue to offer services while keeping their historical values, some of them are at high risk in seismic prone regions. Therefore, the understanding of their structural performance under strong ground motions has been of significant importance to the civil societies as well as engineering community. The structural systems of historical buildings, generally, consist of masonry walls or piers. The behavior of such walls is controlled by either deformation or force. Seismic performance evaluation of historical structures can be carried out within the framework of performance-based evaluation principles. This paper mainly discusses the basic principles to be considered in performance-based seismic evaluation of historical structures. Proposed seismic hazard levels, evaluation of existing seismic hazard, selection of earthquake ground motions as well as site geology, geological and tectonic settings of the area, seismic activity of the region and local soil conditions are needed for a thorough performance evaluation. Seismic performance evaluation of a clock tower located in eastern Turkey was accomplished based on the proposed principles. Copyright © 2015 John Wiley & Sons, Ltd.

Structural monitoring for the cyclic behaviour of concrete tunnel lining sections using FBG sensors

Summary To demonstrate the viability of using fibre Bragg grating (FBG) sensors capable of detecting the inelastic cyclic response of reinforced concrete sections that are part of tunnel linings, an experimental research programme carried out on different packaging configurations of FBG sensors is presented in this paper. The programme illustrated here was part of a wider research project funded by the European Commission whose objective was the development of a decision support system for monitoring tunnel linings in seismic-prone regions. In particular, a typical metro tunnel located in Rome area, Italy, was considered as a case study. In order to provide useful information for designing an effective sensor packaging to be applied to a final full-scale test representing a whole lining circular section of a tunnel, pure bending tests were designed and performed on five substructure specimens endowed with different sets of fibre packaging. The outcomes of the substructure tests showed that the optimal FBG packaging solutions were unbonded sensors either embedded in concrete or mounted externally. Moreover, the designed fibre sensor system reliably performed at large deformations. In fact, the external FBG fibres applied to the full-scale tunnel test approached maximum values of about 0.63%, whilst the internal fibres reached about 1.2%. The results obtained by FBG sensors were in good agreement with those of traditional transducers. Copyright © 2015 John Wiley & Sons, Ltd.

Attenuation relation predicted observed ground motion of Gorkha Nepal earthquake of April 25, 2015

This paper discusses comparison of recent observed ground motion parameters of Gorkha Nepal earthquake of April 25, 2015 (Mw 7.8) with the predicted ground motion parameters using existing attenuation relation of the Himalayan region. The earthquake took about 8000 lives and destroyed thousands of buildings of poor quality, and the earthquake was felt by millions of people living in Nepal, China, India, Bangladesh, and Bhutan. The knowledge of ground parameters is very important in developing seismic code of seismic-prone regions like Himalaya for better design of buildings. The ground parameters recorded in recent earthquake event and aftershocks are compared with attenuation relations for the Himalayan region, and the predicted ground motion parameters show good correlation with the observed ground parameters. The results discussed in this paper will be of great use to civil engineers in updating existing building codes in the Himalayan and surrounding regions and also for the evaluation of seismic hazards. The results clearly show that the attenuation relation developed for the Himalayan region should only be used, and other attenuation relations based on other regions fail to provide good estimate of observed ground motion parameters.