Seismic-prone Countries Research Articles

Experimental and Numerical Characterization of the In-Plane Shear Behavior of a Load-Bearing Hollow Clay Brick Masonry System with High Thermal Performance

Modern masonry systems are generally built with hollow clay bricks with high thermal insulating properties, fulfilling the latest sustainability and environmental criteria for constructions. Despite the growing use of sustainable masonries in seismic-prone countries, there is a notable lack of experimental and numerical data on their structural behavior under lateral in-plane loads. The present study investigates the in-plane shear behavior of load-bearing masonry walls with thin bed joints and thermal insulating hollow clay blocks. Shear-compression tests were performed on three specimens to obtain information about their shear strength, displacement capacity and failure modes. The experimental characterization was supplemented by three shear tests on triplets, along with flexural and compression tests on the mortar for the thin joints. Furthermore, two Finite Element (FE) models were built to simulate the shear-compression tests, considering different constitutive laws and brick-to-brick contact types. The numerical simulations were able to describe both the shear failure modes and the shear strength values. The results showed that the experimental shear strength was 53% higher than the one obtained through Eurocode 6. The maximum shear load was found to be up to 75% greater compared to similar masonry specimens from the literature. These findings contribute to a better understanding of the potential structural applications of sustainable hollow clay block masonry in earthquake-prone areas.

Design and modelling tools for timber-based seismic retrofitting: from research to practice

Reversible retrofitting techniques for protecting existing or historical buildings against seismic events have found increasing application in the recent years. In particular, the use of wood-based strengthening solutions for both timber and masonry structures has shown promising results in terms of reversibility, compatibility, lightness, sustainability, and effectiveness. With reference to existing timber floors, an excellent method to enhance their seismic response is the fastening of an overlay of plywood panels to the existing sheathing, an intervention that greatly improves in-plane strength, stiffness, and energy dissipation. In order to promote the use of this retrofitting method in practice, calculation tools supporting the design and modelling of timber diaphragms strengthened with plywood panels, have been developed. As a result of a fruitful synergy between academic research and professional engineering, this work presents relevant recent examples of application of the developed calculation tools in the seismic retrofitting of timber diaphragms in existing buildings. Three significant case-study buildings are examined: two masonry churches with monumental timber roofs, and an ancient sawmill with a mixed timber-masonry structure, all located in the province of Brescia (Italy). The developed tools allowed to conduct parametric analyses to calibrate the best retrofitting strategy, and to analyse the additional benefits of the plywood-based retrofitting interventions, especially in terms of hysteretic energy dissipation, affordability, and cost- and execution-effectiveness. This work can contribute to the promotion of timber-based techniques in the combined structural, seismic, and conservation upgrading of existing buildings belonging to the architectural heritage of seismic-prone countries.

Seismic Upgrade of Steel Frame Buildings by Using Damped Braces

Supplementary energy dissipation has proved to be an effective way of protecting structures from the disastrous effects of earthquakes and has been used in the last decades both in new and in existing constructions. In this regard, various procedures for the design of the damping system for the seismic retrofit of buildings have been formulated over the years, mainly focused on reinforced concrete (RC) constructions, which represent the largest part of the existing stock in many seismic-prone countries. The study deals with the assessment of a displacement-based design procedure for proportioning the damping system recently proposed in the literature for RC framed buildings, with the goal of establishing a good practice for the application of the procedure to steel buildings as well. The method was applied to three case-study frames, regular in plan and in elevation, which were assumed as being representative of old structures designed without consideration of seismic requirements. The retrofit was performed by using chevron braces equipped with dampers with an elastic-perfectly plastic behavior. The method aimed at defining the properties of the dampers to achieve a target performance in terms of the maximum lateral deflection for a specific level of seismic intensity. The effectiveness and reliability of the proposed procedure was eventually assessed by evaluating the seismic performance of the upgraded steel structures in static and dynamic non-linear analyses.

Non-Linear Analysis and Retrofitting by Steelwork of a Precast RC Warehouse

Seismic upgrading and retrofitting of existing constructions is a pressing need for designers and researchers. The necessity of efficient seismic upgrading/retrofitting techniques is, therefore, required in seismic-prone countries, such as Italy. In this framework, steelwork has clearly shown many advantageous applications in the last century. Nonetheless, if compared to other different technologies, steelwork is still limited for consolidation purposes. Moreover, the wide damage provoked by earthquakes to industrial buildings have induced scientific research to investigate the seismic vulnerability of such constructions much more. In the current study, the attention has been, therefore, focused on the use of steelwork systems as anti-seismic intervention techniques from a precast RC industrial warehouse hit by the 2012 Northern Italy earthquakes. Besides the usefulness of steelwork in implementing reliable techniques against earthquakes, the paper has the aim of discussing the different seismic behaviour of the building deriving from dissimilar beam-to-column joint types obtained using steelwork interventions. Other than the widely diffused static scheme with hinges, other types of joints (semi-rigid and rigid), along with the presence of a rigid roof, have been investigated, and the different seismic risk indicators derived from these static schemes have been achieved, highlighting the case of the best seismic behaviour of the warehouse. Finally, the effectiveness of local steel interventions in improving the efficient global response of the building has also been highlighted.

Predicting the Inelastic Response of Base Isolated Structures Utilizing Regression Analysis and Artificial Neural Network

Indeed, utilizing a base isolation system in RC structures can remarkably minimize the possibility of failure, particularly in seismic-prone countries. Despite that, the design of these structures is a long procedure that consists of choosing the appropriate isolator to optimize the nonlinear behavior of the superstructure. Moreover, the numerical simulations require huge computational effort when high accuracy is required. In recent decades, scientists and engineers have applied numerous estimation approaches such as multiple linear regression and artificial neural networks to decrease the required cost and time for daily design problems. Thus, this study's main objective is to solve the difficulty of rapid response prediction by using soft-computing techniques. Additionally, it aims to study the capability of multiple linear regression and artificial neural networks in estimating the seismic performance of base-isolated RC structures under earthquakes. A nonlinear response history analysis of four different lead rubber-bearing isolated RC structures will be performed in order to determine the responses of these structures. Subsequently, the prediction models will be developed using the responses of the structures as inputs for multiple linear regression and artificial neural networks. Lastly, the reliability of both estimation approaches in terms of the response of base-isolated structures will be investigated by comparing the prediction models' capability. In general, the results of the study show that artificial neural networks provide considerably better accuracy in estimating base-isolated structures compared to multiple linear regression, and their performance results in reliable prediction. Doi: 10.28991/CEJ-2022-08-06-07 Full Text: PDF

Tensile Capacity of Adhesive Anchors in Damaged Masonry

In Europe, the qualification of injection anchors in masonry under static and quasi-static actions is based on an assessment of tests performed in undamaged masonry. Nevertheless, in seismic prone countries like Italy the influences deriving from earthquake actions cannot be disregarded. Masonry elements are very sensitive to cyclic/seismic action and research on the behavior of anchors in damaged masonry is rather limited. The paper presents the results of an experimental campaign aimed at evaluating the residual tensile strength of adhesive anchors installed into undamaged walls that were subsequently subjected to cyclic in-plane loading to simulate seismic actions before. Consequently, the anchors experienced different stresses depending on their location within the walls. Overall, 29 tests were performed with anchors placed both, in undamaged and damaged areas. The results showed that there is a correlation between residual tensile strength and masonry initial conditions, and therefore the installation of anchors in masonry elements should be carefully planned avoiding areas that could be heavily damaged during seismic events or considering redundant connections in critical areas. In particular, it seems that the width of the crack (created by cyclic actions) that passes nearby/into the anchor borehole is the main parameter that affects the ultimate resistance of the anchors.

Evaluation of Seismic Vulnerability of Hospitals in the Tehran Metropolitan Area

The Tehran metropolitan area is extremely vulnerable to earthquakes due to the location of its active faults and its dense population. Assessing the probable damage of a high magnitude earthquake on buildings and facilities relies on a precise structural survey, which has an empirical basis depending on historic ground motions. The probability of damage and failure in discrete limits based on different ground motions is estimated by fragility curves. Using the most matching fragility curves for buildings in Tehran, the vulnerability of the hospitals in the capital, as one of the most critical structures in crisis management of disasters, was investigated in this study. Subsequently, the existing fragility curves, developed for Tehran and the other seismic prone countries such as Japan and the United States, were compared considering the typology of Tehran’s hospitals. Finally, the possible damages for each hospital were calculated based on the most conservative fragility curve and the most pessimistic scenario, which were used to evaluate the seismic vulnerability of hospitals and health care systems for different damage states. After zoning the damage of therapeutic areas of Tehran, it was observed that at least 2% to 10% damage occurred in all hospitals of Tehran, and none of the healthcare centers would remain structurally undamaged after a strong earthquake with the moment magnitude of 7 or more. In addition, the healthcare buildings could be prone to significant structural damage, especially in southern parts, which necessitates proactive management plans for Tehran metropolitan area.

Experimental investigation on axially loaded adobe masonry columns confined by polymeric straps

Due to widespread applications of adobe masonry construction in rural areas of many seismic-prone countries, there is a high demand for conducting research on retrofitting of adobe buildings; however, such research is scarce. Among various structural aspects, confinement of an assemblage of adobe (i.e., unbaked clay brick) units and mud mortar is of primary concern in the current paper. To this aim, scaled adobe columns were wrapped by polypropylene (PP) straps, which are low-strength and low-cost polymeric materials, and were tested under uniaxial compression. The PP straps are placed at a certain interval while the two ends of a strap are joined together by a steel wire. No bonding agent is used between the straps and adobe surface. Three series of adobe columns with different aspect ratios of the cross section and different arrangements of adobe units in the cross section plan are examined and the experimental results in terms of axial stress versus axial strain, crack patterns, lateral strain variations, and tensile strain in the confining straps are reported. The comparison between the non-retrofitted adobe specimens and their confined counterparts revealed that the proposed retrofit technique by use of PP straps is highly efficient in improving the compressive strength and, more importantly, the ultimate axial strain of adobe columns. Besides, the retrofitted adobe specimens could maintain a considerable amount of post-peak residual strength up to large axial displacements. Finally, the experimental outcomes on the compressive strength are compared with predictions of an equation available in the literature.

In-plane static tests on a structural timber frame system proposal (TRAROM) inspired from traditional architecture and using local materials

A lightweight structural timber system is proposed, inspired from traditional Romanian architecture, and adapted to the current needs (wider spaces and increased comfort) and to the local construction market (low skill workforce, poorly controlled material quality, diversity of materials). A good seismic behavior was, also, a target, because Romania is one of the most seismic prone countries in Europe. In order to satisfy these requirements, a team of researchers, an architect, and design and construction site engineers gathered and tested walls with a new structural system inspired from a certain traditional house type. The tests were conducted in-plane in static cyclic loading.Several parameters were tested on 8 distinct specimens: the layout of the timber elements and that of the screw nails. As a waypoint in the project, a layout that was deemed the most satisfying (by considering strength capacity and manufacture parameters), so three additional specimens were tested to check variation of the results on this layout. The paper presents the details of the proposed system and also the main seismic characterization parameters. The resulting best layout is to be proposed for a house, as an example project, in order to be used by the government for reconstruction in case of disaster recovery (earthquake, floods), but also for other interested parties.

Macroseismic Intensity Estimation from Instrumental Ground Motion Recordings in the Case of Small and Moderate Vrancea Subcrustal Earthquakes

Romania is one of the most seismic-prone countries in Europe due to the periodically occurrence of strong intermediate-depth earthquakes in Vrancea seismogenic zone. The Vrancea area is located beneath the South-Eastern Carpathian Arc bend, at the contact between the East - European plate and the Intra-Alpine and Moesian sub-plates. An intense seismic activity is recorded in the mantle, within a narrow, almost vertical descending volume between 60 and 180 km depth. Earthquakes with magnitudes larger than 5.0 (Mw) and macroseismic effects exceeding V MSK degrees on extended populated area occur in Vrancea seismic zone, with a return period of around 2 years. Besides the extended scientific studies, the near real time estimation of the macroseismic intensity recently became mandatory for the insurance companies to cover some of the losses and damages that earthquakes might cause to houses, belongings, and other buildings. The first approach to obtain intensity values was to develop an online environment for collecting people feedback regarding the effects of earthquakes and for the automatic approximation of the intensity. The automatic intensity estimation code from the online feedback proposed by [1], [2] and adopted by [3] for the Romanian earthquakes was improved and used for this study. Additionally, there were used prediction equations to obtain intensity values from the epicentral intensity, and epicentral and hypocentral distances. Besides the estimation of macroseismic intensities from online people feedback and from attenuation relations, equations for conversion of peak ground acceleration in macroseismic intensity were also required for a rapid evaluation of ground motion effects. In order to avoid the increase of the prediction uncertainties, the data must be selected in such a way that they represent the parameters’ rank for which the prediction will be accomplished and the selected data must be representative for the investigated regions and seismic source. In this paper were developed conversion methods from PGA to macroseismic intensity for moderate intermediate depths earthquakes with 4.5<Mw<6.0. All the studies were realised in the case of Vrancea recent (2014-2019) moderate intermediate depth earthquakes, felt on the extra-Carpathian region.

Remarks on damage and response of school buildings after the Central Italy earthquake sequence

The seismic assessment of the vulnerability of existing public structures, especially school buildings, is a crucial issue in seismic prone countries. Recently, several national and regional programs and activities have focussed on the mitigation of Italian public buildings. They promote the scheduling of public buildings’ structural safety assessment and, when needed, the design and execution of strengthening interventions. Nevertheless, the three strong earthquakes that occurred in the last decade in Italy, Abruzzo (2009), Emilia (2012), and Central Italy (2016), confirmed the vulnerability of school buildings and the social importance of their quick re-opening after a damaging earthquake. In the present paper, the activities carried out on 1514 school building structures in the aftermath of the 2016 Central Italy earthquake sequence are reported and analysed. According to survey data collected by post-earthquake usability inspections, the paper analyses the school buildings characteristics, damage level and extent to structural and non-structural components as well as the correlation between seismic intensity and observed damage.

Safety Assessment of Gravity Load–Designed Reinforced Concrete–Framed Buildings

AbstractA large number of gravity load–designed (GLD) reinforced concrete (RC) buildings are found in many seismic-prone countries including India. Many of them were built before the advent of seis...

Upgrade Decision-Making for Earthquake-Vulnerable Wooden Houses Using Probabilistic Damage Index Functions

AbstractThere is widespread awareness in seismic-prone countries of the necessity to improve the seismic performance of old buildings and houses for disaster mitigation. To support the decision mak...

Seismic Vulnerability Assessment of an Infilled Reinforced Concrete Frame Structure Designed for Gravity Loads

In the last decades, particular attention has been paid to the seismic vulnerability of existing reinforced concrete buildings designed for gravity loads only. Such buildings, designed before the introduction of capacity design in modern seismic codes, are very common, particularly in seismic prone countries of the Mediterranean area. Due to poor detailing and lacking of capacity design principles, high vulnerability has been highlighted in several past studies. In this article, inadequate seismic response and peculiar damage pattern are investigated by means of shake table tests performed on a 1:2 scaled 3-story infilled prototype. Particular attention is given to the role of beam-column joints and frame-panel interaction. The effectiveness of the EC8-based assessment approach is then evaluated; both linear and nonlinear numerical models, with different levels of sophistication, have been implemented in order to explore their behavioral aspects.

SOME PARAMETERS AFFECTING THE BEHAVIOUR OF R.C. FRAMES DESIGNED FOR GRAVITY LOADS ONLY AND SUBJECTED TO EARTHQUAKES

Time history analysis was performed to study the effect of selected parameters in the behaviour of reinforced concrete frames under earthquake loads. The RC frames were designed for gravity-loads only as typically found in most seismic prone countries before the introduction of adequate seismic design code provisions. The parameters considered in this study were the number and span of bays, the number of stories, and the presence of infill wall (full infilled frame and infilled frame with open ground stories). It was observed that the presence of infill wall may affect the seismic behaviour of frame structure to large extent, and the infill wall increases the strength and stiffness of the structure. Also it was observed that infilled frames are preferred in seismic regions than the open ground story ones, because the story drift of first story in open ground story frames is very large than the upper stories, this may probably cause the collapse of structure.

Construction and Strengthening of Non-Engineered Buildings in Developing Seismic-Prone Countries

Non-engineered buildings in seismic-prone developing countries account for at least 50% and in some cases more than 90% of the dwelling stock. Approximately 75% of fatalities due to earthquakes during the past century were caused by the collapse of non-engineered weak masonry buildings, thus stressing the need for their improvement to resist earthquakes. Although one solution would be to limit their construction in highly seismic regions, this is not viable due to a number of socio-economic reasons. Therefore, damage-prevention strategies for the new construction of non-engineered structures are proposed. Good practices for seismic-resistant construction and strengthening are presented. Finally, the experience from the 2010 Haiti earthquake serves to highlight points raised in this paper.

FRP Strengthened Brick-Infilled RC Frames: An Approach for their Proper Consideration in Design

A considerable number of existing buildings in seismic prone countries has been constructed either based on earlier concepts for seismic design or without applying seismic provisions. As a consequence, their seismic upgrade is a matter of concern. In urban environments, these structures usually consist of reinforced concrete (RC) frames with brick infill walls. Their strengthening with traditional methodologies, such as concrete jackets and shear wall construction, often results in operation interruption and high cost. The present research examines the complex response of RC frames and brick infill walls strengthened with Fibre Reinforced Polymers (FRP), a recently proposed retrofit scheme that becomes attractive because of its low cost and ease of implementation. Instead of the commonly used pair of compression struts that models the infill wall, a multiple strut masonry panel element model with advanced constitutive laws is applied for the representation of the nonlinear response of the infill wall, while a tension tie is used to consider the FRP sheets contri- bution on the response. The parameters of the wall and the FRP elements that are used in the numerical model are cali- brated against experimental results available in the literature for two-storey, one-bay reinforced concrete frames subjected to cyclic loading. The effectiveness of this innovative technique is presented considering the response of the masonry in- filled RC frame with and without retrofit. By comparison of the results, conclusions are drawn concerning design proce- dures.

Comparison between seismic and domestic risk in moderate seismic hazard prone region: the Grenoble City (France) test site

Abstract. France has a moderate level of seismic activity, characterized by diffuse seismicity, sometimes experiencing earthquakes of a magnitude of more than 5 in the most active zones. In this seismicity context, Grenoble is a city of major economic and social importance. However, earthquakes being rare, public authorities and the decision makers are only vaguely committed to reducing seismic risk: return periods are long and local policy makers do not have much information available. Over the past 25 yr, a large number of studies have been conducted to improve our knowledge of seismic hazard in this region. One of the decision-making concerns of Grenoble's public authorities, as managers of a large number of public buildings, is to know not only the seismic-prone regions, the variability of seismic hazard due to site effects and the city's overall vulnerability, but also the level of seismic risk and exposure for the entire city, also compared to other natural or/and domestic hazards. Our seismic risk analysis uses a probabilistic approach for regional and local hazards and the vulnerability assessment of buildings. Its applicability to Grenoble offers the advantage of being based on knowledge acquired by previous projects conducted over the years. This paper aims to compare the level of seismic risk with that of other risks and to introduce the notion of risk acceptability in order to offer guidance in the management of seismic risk. This notion of acceptability, which is now part of seismic risk consideration for existing buildings in Switzerland, is relevant in moderately seismic-prone countries like France.

Risk-Based Strategies for Upgrading Existing Nonconforming Wooden Houses and Risk Information for Promoting Upgrading

There is widespread awareness in seismic-prone countries about the necessity to upgrade the seismic performance of old buildings and wooden houses for disaster mitigation; however, upgrading occurs at a very slow pace. At present, Japan has approximately 11 million nonconforming old wooden houses, but most of them remain without upgrade because of the large expenditure that would be incurred by both house owners and the local government. An owner would need to spend approximately US$11,000 on average to upgrade his/her house such that it satisfies the current design requirements. In Aichi prefecture alone, upgrading would cost approximately US$10 billion in total, which is approximately 40% of the annual budget. This study, therefore, investigates alternative strategies for upgrading existing nonconforming wooden houses more efficiently and cost-effectively. The seismic risks of wooden houses as a whole in Aichi prefecture are estimated, and then the effective target level for upgrading is discussed from the viewpoint of both economic loss and the number of fatalities. It is shown here that it is worthwhile from the viewpoint of life safety to consider a target upgrading level that is lower than the current design requirements. Although the analytical models discussed in this paper might be specific to Japan, the framework of the risk assessment is universal and the conclusions drawn from this analysis are applicable to other seismic-prone regions and countries.

Sustainable building design under uncertain structural-parameter environment in seismic-prone countries

Abstract The structural member stiffness and strength of buildings are uncertain due to various factors resulting from randomness, material deterioration, temperature dependence, etc. The concept of sustainable building design under such uncertain structural-parameter environment may be one of the most challenging issues to be tackled recently. By predicting the response variability accurately, the elongation of service life of buildings may be possible. In this paper, it is shown that interval analysis in terms of uncertain structural parameters is an effective tool for evaluating the sustainability of buildings in earthquake-prone countries. All the combinations of uncertain structural parameters become huge numbers and this difficulty can be overcome by introducing the sensitivity or Taylor series expansion analysis. In order to demonstrate the usefulness and reliability of the proposed method, a shear building model is used including passive viscous dampers with supporting members. It is demonstrated that the proposed method is actually useful for the development of the concept of sustainable building design under such uncertain structural-parameter environment.