Reinforced Concrete School Buildings Research Articles

Machine Learning-Based Retrofit Scheme Development for Seismically Vulnerable Reinforced Concrete School Buildings

Machine Learning-Based Retrofit Scheme Development for Seismically Vulnerable Reinforced Concrete School Buildings

Understanding the Impact of Seismic Hazard and Climate Conditions on Multi Criteria–Based Retrofitting of Existing Buildings

A large share of the reinforced concrete (RC) building stock in Mediterranean countries faces a dual challenge of seismic vulnerability and energy inefficiency, calling for urgent renovation efforts. While energy upgrades have been the focus of previous renovation policies, recent research highlights the critical need for integrated retrofitting solutions that address both structural integrity and energy performance. Multi-criteria decision-making (MCDM) approaches are a promising tool for optimizing the combined choice of these integrated interventions, considering various decision variables (DVs) of economic, social, environmental, and technical nature. To understand the impact of climate and seismic hazard conditions on multi-criteria-based retrofitting assessment, a case-study RC school building is selected and assumed to be located in three distinct climate conditions, cold, mild, and warm, and three seismic hazard levels, low, medium and high. Moreover, given the complexity and challenges of quantifying seismic performance metrics for practitioners, an available simplified (practice-oriented) approach is compared herein with a more thorough research-based one for quantifying the seismic performance of RC buildings within the MCDM framework. Both approaches are applied to the case-study building, considering twelve possible combinations of energy and seismic interventions. The accuracy of the practice-oriented approach and its impact on the retrofitting rankings is evaluated, emphasizing the importance of accessible and efficient evaluation methods in facilitating informed decision-making for building renovation.

Seismic Damage Probability Assessment of Existing Reinforced Concrete School Buildings in Afghanistan

Existing Reinforced Concrete School buildings with low earthquake resistance may suffer structural failure or severe damage in a catastrophic seismic event. Ascertaining earthquake resistance in existing school buildings is vital to confirming the safety of students, teachers, and all school members. Reinforced concrete (RC) has been used significantly for numerous years as the primary material due to its easy access and low cost-effectiveness in construction. The current research focused on analyzing the existing RC school buildings designed and constructed in various regions of Afghanistan over the last three decades. Seismic fragility curves, which are generated from incremental dynamic analysis (IDA), have been used to evaluate the damage probability of RC school buildings against earthquake ground motions. In this investigation, 34 RC school buildings were selected from an extensive database and subsequently classified as either A-type or B-type based on specific criteria, including design details and construction year. Following this classification, an assessment of the seismic damage probability for these buildings was conducted using probabilistic models based on IDA curves. The results indicate that A-type school buildings with newer construction are less prone to damage compared to B-type school buildings, showing improved resilience. Especially the B-type buildings in seismic Zone-I are found to be highly vulnerable under the maximum considered earthquake scenarios.

Sustainable Renovation of Public Buildings through Seismic–Energy Upgrading: Methodology and Application to an RC School Building

There are many existing buildings for which seismic rehabilitation interventions are required, especially in earthquake-prone areas like Italy. At the same time, the deep energy crisis that Europe is facing highlights the need for sustainable techniques that are able to increase the energy efficiency of buildings. In order to mitigate the social and cultural obstacles for deep renovations of buildings, effective techniques and methods are required to avoid relocating users, which often discourages such interventions. To this purpose and as the main novelty, this research is aimed at presenting a new strengthening technique for reinforced concrete buildings that is able to integrate structural seismic strengthening and energy efficiency improvements. It is made up of new framed structures connected from the outside to the existing building, thus reducing the intrusiveness and relocation needs of users. At the same time, the seismic strengthening technique is conceived for an optimal coupling with energy saving interventions like high-performance external insulation finishing systems. In this study, these techniques are described and applied to a reinforced concrete (RC) school building designed only for gravity loads, according to outdated standards. The results show that the considered strengthening technique increases the seismic performance of the building with respect to both life safety and damage limitation requirements, avoiding any further local interventions to the building’s interior. On the other hand, the energy renovation allows for significant savings, since the resulting reduction in the total non-renewable energy consumption is larger than 80%.

FEM Analysis of Steel Eccentric Braces for Seismic Retrofitting

The paper discusses issues about the finite element modelling of steel eccentric braces with vertical shear links used as hysteretic dampers to improve the seismic performance of existing reinforced concrete (RC) buildings. To this end, eccentric bracing systems have been designed for seismic upgrading of a case-study existing RC school building in Italy. Multiple finite element modelling approaches are described, using both frame and shell finite elements, various steel stress strain relationships, as well as including both geometrical imperfections and residual stresses. Numerical models were built using two commercial structural analysis programs, SAP2000 and Ansys, and one open-source software, Code_Aster. The numerical study allowed to (i) quantify values of the plastic overstrength factor of the considered shear links; (ii) evaluate the overall system stability and general inelastic response; (iii) compare various modelling approaches.

Seismic fragility of lightly reinforced concrete school building typologies with different masonry infill configurations

This paper presents the outcome of a research study conducted to establish seismic fragilities of school building typologies in Sri Lanka. The school buildings in Sri Lanka can be characterised as lightly reinforced concrete (RC) buildings, infilled with masonry walls (IMW). However, they are categorised into two typologies based on the structural layouts used (1) Type 1 (T01) and (2) Type 2 (T02). Although, the school buildings can be grouped into two typologies, variabilities in terms IMW configurations and their arrangements are observed among those school buildings. These variabilities in terms of building typologies as well as IMW arrangements were taken to establish seismic fragility curves. The seismic performances of the school buildings were numerically assessed, where in total 640 building cases were analysed by varying typologies, IMW configurations, and stochastic material properties. Since, the RC school buildings are lightly reinforced, a simplified, yet a novel approach was followed to account the shear failure of RC columns under seismic actions. Then, four damage thresholds were established (slight, moderate, severe and collapse) and the corresponding fragility curves are presented in terms of school building typologies considered. Finally, based on the fragility curves, damage probability matrices of the building typologies were established.

Infill Variability and Modelling Uncertainty Implications on the Seismic Loss Assessment of an Existing RC Italian School Building

Past earthquake evidence has shown the high vulnerability of Italian school buildings, given by the extensive damage observed to structural and non-structural elements. Such vulnerability demonstrates the need to undertake a seismic risk assessment and reduction strategies for critical facilities and allocation of national funds for retrofit interventions to those regions where seismic risk is higher. To do so, Expected Annual Losses (EAL) are evermore considered one of the main seismic risk metrics, which can, however, be largely affected by the epistemic uncertainty that typically characterizes the material and geometrical properties of existing buildings, particularly masonry-infilled reinforced concrete (RC) ones. This paper investigates the implications of accounting for a thorough identification of sources and characterization of uncertainty in seismic loss estimates on the risk assessment of a typical Italian masonry-infilled RC school building. The variability in masonry infill properties and modeling assumptions, as well as the subsequent epistemic uncertainty, are explicitly considered in the loss estimation of the RC school building. Specifically, the impact on the expected annual loss ratio is quantified in terms of both structural and non-structural components, depending on the engineering demand parameter to which they are sensitive. The results show that, when considering the uncertainty related to the variability in masonry infills, higher loss ratios of up to 30% are obtained with respect to the available literature estimates.

Development of seismic resilience index methodology for RC structures via functionality curve

Seismic resilience index (SRI) approach describes the post-seismic recovery phase of a single building by incorporating the time dimension. In recent decades, numerous quantitative frameworks have been developed to quantify earthquake resilience. The seismic resilience of existing reinforced concrete (RC) structures in Malaysia under far-field (FF) and near-field (NF) earthquake scenarios is examined in this research methodology using a seismic resilience index (SRI) and functionality curve. SRI is implemented to a four-story RC school building and a five-story RC hospital structure damaged by the 2015 Ranau earthquake. In addition, a total of 25 existing RC structures have been selected as target case studies for evaluating the SRI and presenting the results graphically using the Geographical Information System (GIS) platform. These buildings are primarily divided into three clusters: low, mid, and high rise. Non-linear dynamic analysis (NL-DA) is utilized in this approach to analyze the case studies and the selected buildings using the Finite Element platform (FE). Moreover, a group of seismic records encompassing of far-field and near-field are selected for simulation process using non-linear time history analysis (NL-THA). Eventually, Incremental Dynamic Analysis, fragility and vulnerability assessment, functionality assessment, time of recovery (TREC), loss of resilience (LOR), robustness (R) and SRI indicator are all part of this approach.•SRI helps decision-makers create or suggest repair or retrofitting solutions with acceptable recovery time and cost.•The consequences of failures for people's lives, properties, as well as the economy, will be mitigated.•Improve the sustainability and serviceability of structures to ensure seismic safety and meet Sustainable Development Goal 11.

Post-earthquake preliminary seismic assessment method for low-rise RC buildings in Taiwan

After the 1999 Chi-Chi Earthquake in Taiwan, to improve the safety of a huge number of low-rise reinforced concrete (RC) buildings, including typical RC school buildings and street houses, preliminary seismic assessments were conducted to pre-screen for seismic capacity. The main purpose of this work is to modify the existing preliminary seismic assessment method to make it applicable to earthquake-damaged low-rise RC building structures. In this work, reduction factors of strength, stiffness and energy dissipation, which are based on experimental data in past research, are used to modify the nonlinear plastic hinges of damaged RC column members with various damage levels. Additionally, the behavior of modified nonlinear plastic hinges is verified using experimental data. To develop a method of preliminary seismic assessment for a damaged low-rise RC building structure, the reduction factors of shear strength per unit area are suggested using the modified nonlinear plastic hinges of the damaged RC column members. Furthermore, the effect of the stiffness reduction on the development curve of strength of an RC column member is also considered in determining the reduction factors of shear strength per unit area for the preliminary seismic assessment. Finally, in a case study of ten real damaged low-rise RC building structures, in addition to the strength reduction factors, a post-earthquake preliminary seismic assessment method is thus proposed and verified using the detailed seismic assessment method.

Seismic Upgrading of Reinforced Concrete School Buildings

This paper evaluates the seismic behavior of four methods for retrofitting typical reinforced concrete school building. The original school (SO) suffers from limited ductility and lateral resistance. The four seismic upgrading methods are using carbon fiber reinforced polymers (SUFRP), steel jacket (SUSJ), bracing (SUBR), or concrete jacket (SUCJ). Nonlinear pushover and time history analyses are made for the five schools. Three code-scaled natural earthquakes are utilized for the inelastic response history analysis. The pushover analysis revealed that providing the school with bracing (SUBR) results in reducing the lateral displacements. However, the three other types of seismic retrofit (SUFRP, SUSJ, and SUCJ) develop larger lateral displacements when compared to the original school (SO). The translation ductility and energy dissipation for school SUBR is poor while they are good for schools SUFRP, SUSJ, and SUCJ. The base shear is increased for the four upgrading methods (SUFRP, SUSJ, SUBR, and SUCJ) compared to school SO. From the nonlinear time-history analysis, the maximum interstorey drift was approximately similar for schools SO, SUFRP, and SUCJ. Lesser values for the maximum interstorey drift are obtained for schools SUSJ and SUBR. The nonlinear time-history analysis also gives similar base shear for all the upgrading methods compared to school SO with the exception of school SUCJ which showed increase in the base shear.

Damage Survey and Residual Seismic Capacity Evaluation of Reinforced Concrete School Buildings after the 2018 Hokkaido Eastern Iburi Earthquake

ABSTRACT In this study, a damage survey was conducted on the buildings of two schools located in the town of Abira, where a Japanese seismic intensity of 6 upper was recorded during the 2018 Hokkaido Eastern Iburi Earthquake. The damage classes of the reinforced concrete structural members and residual seismic capacity ratios were examined. Both schools had performed seismic evaluation and retrofitting before the earthquake, and no serious damage occurred, but flexural and shear cracks in columns and walls were observed. Analysis using drone photographs was conducted to perform crack detection and crack width evaluation and create point cloud models.

Experimental dynamic characterization of friction brace dampers and application to the seismic retrofit of RC buildings

Previous earthquakes have caused extensive damage to reinforced concrete (RC) structures with insufficient lateral force resistance or energy dissipation capacity. There is a need to retrofit vulnerable existing RC buildings, particularly those not originally designed for seismic effects or designed to an outdated seismic specification. This study investigates the use of friction dampers as displacement-dependent energy dissipation devices to retrofit RC moment frame structures. First, an experimental program was conducted to characterize the dynamic behavior of friction brace dampers with several different materials, finding that a sintered metal compound provided a stable friction coefficient of 0.4. A strength-based equivalent linearization design procedure was then developed based on the required friction slip force and considering the cracked state of the existing RC structure. A four-story RC school building was then designed using the proposed retrofit design method, validated using nonlinear response history analysis and compared to a previous retrofit scheme that employed buckling-restrained braces (BRBs) and a stiffness-based equivalent linearization design method. The analysis results suggest that the proposed retrofit design method and friction brace dampers are effective in reducing the maximum story drift.

Two frugal options to assess class fragility and seismic safety for low-rise reinforced concrete school buildings in Southern Italy

A study is presented on the seismic fragility of a sample of 15 reinforced-concrete school buildings built between 1960 and 1980s in the province of Foggia, Southern Italy, for which near-perfect information is provided on geometrical and mechanical parameters. In particular, the focus is on the application of two probabilistic methods, employing different compromises in terms of complexity versus accuracy. First, a Eurocode 8 compatible nonlinear static approach is employed, which is augmented via the use of the regression expressions of the SPO2FRAG tool to incorporate record-to-record variability. Second, a nonlinear dynamic approach is used to directly account for record-to-record variability via a constrained multi-stripe analysis. In particular, in view of practitioners’ needs (analysis time, computational efforts, software used), a practical mode for application of the multi-stripe analyses is proposed, based on conducting few stripe analyses, in order to predict the behavior of structures in both the elastic and inelastic ranges of response. Both the static and the dynamic approaches are shown to be viable alternatives, offering fairly matching results at the individual building-level and even closer predictions at the level of ensemble regional fragility curves that incorporate both inter-building and intra-building uncertainties.

Nonlinear Seismic Analysis of Existing RC School Buildings: The “P3” School Typology

The seismic assessment of existing school buildings is an important issue in earthquake prone regions; such is the case of the Algarve, which is the southern region of Portugal mainland. Having this problem in mind, the PERSISTAH project (Projetos de Escolas Resilientes aos SISmos no Território do Algarve e de Huelva, in Portuguese) aimed to develop a computational approach enabling the damage evaluation of a large number of individual school buildings. One of the school typologies assessed was the so-called “P3” schools. This typology is composed of several different modules that are combined in different manners depending on the number of students. Each module was built in accordance with architectural standardised designs. For this reason, there are many replicas of these modules all over the Algarve region. The structural system of each module is composed of a frame of reinforced concrete (RC) elements. Nonlinear static seismic analysis procedures were adopted to evaluate the structural seismic behaviour, namely by using the new concept of performance curve. Based on the obtained results, it was possible to conclude that the seismic safety of this type of school building is mainly ruled by the shear capacity of the columns. This study also shows the difficulties of carrying out accurate seismic assessments of existing buildings using the methods of analysis that are established in the Eurocode 8.

A prioritization RVS methodology for the seismic risk assessment of RC school buildings

The seismic vulnerability assessment of critical facilities, such as hospital and school buildings, is of paramount importance to avoid the collapse in ordinary conditions and to guarantee their immediate functionality in the post-earthquake emergency. Due to the high number of school buildings, and to the need to perform the assessment in a short time, a simple methodology for ranking the more vulnerable buildings through a seismic risk index is highly desirable. In this study, a Rapid Visual Screening (RVS) methodology is proposed. The method aims to prioritize the buildings prone to higher seismic risk and to assist decision-makers in the implementation of seismic risk reduction strategies. The methodology allows to assess the seismic risk of reinforced concrete (RC) school buildings through the compilation of a factsheet. The main sources of structural and non-structural vulnerability are considered in the survey form. The influence of the hazard and exposure are also accounted for in the calculation of the safety index through simplified parameters. The proposed RVS method can be quickly applied to a large number of buildings to identify those that require more accurate analyses. The proposed methodology has been applied to a sample of typical school buildings in Apulian Region, Southern Italy. The results obtained using the proposed RVS method were compared with those of more advanced numerical analyses in order to assess its effectiveness.

An innovative continuous Bayesian model updating method for base-isolated RC buildings using vibration monitoring data

Base isolation is the most widespread passive control strategy for seismic protection of low- and medium-rise Reinforced Concrete (RC) buildings. The excellent performance of base-isolated structures just after construction is well recognized but their seismic behavior after a few operation years can be significantly modified, due to isolators’ aging. In this perspective, the availability of long-term vibration data allows to eventually assess the evolution of degradation and plan maintenance or replacement actions. This paper presents an innovative continuous Bayesian model updating method specific for base isolated buildings. In the proposed method, the Bayesian functions of the isolation system are periodically updated to account for daily measured data. The results of a comprehensive study on a base isolated three-stories RC school building, located in Bojano (Italy), are presented. The investigation comprises Ambient Vibration Testing (AVT), modal identification, installation of a continuous monitoring system and calibration of a Finite Element Model (FEM) of the isolated structure. In order to reduce the computational cost of the model updating procedure, a surrogate model is constructed and calibrated using the complete FEM of the structure through the Response Surface Methodology (RSM). The advantage of having long-term monitoring data on the results of the Bayesian model updating for base isolated structures is highlighted.

Increment of Steel Tonnage for Reinforced Concrete School Building Considering Seismic Design

A series of Indonesian earthquakes, especially from Sumatra caused vibration on buildings in Peninsular Malaysia like Kuala Lumpur and Penang Island. In East Malaysia, Sabah state has been classified as a region with active local seismic fault. A moderate earthquake with Mw6.1 was occurred in Ranau on 5th June 2015 and caused damage on buildings either the structural or non-structural members. Hence, the implementation of seismic design on new buildings is important to ensure public safety. However, such action has its own pro and contra especially when dealing with cost. Therefore, current research work presents the influence of seismic design consideration on the increment of cost for steel reinforcement. For that purpose, a four storey reinforced concrete school building was generated and used as basic model for analysis, design, and taking off. Two level of seismicity representing by the reference peak ground acceleration, αgR equal to 0.07g and 0.10g has been taken into account in the structural analysis and seismic design process. Besides, three soil type namely as soil type A, soil type C, and soil type E also has been considered as variable parameter. Based on result, total steel tonnage in beams for models considering seismic design increases around 14% to 119% higher than the model without seismic design. For columns, the increment is around 13% to 155%. Generally, total cost of steel used as for concrete reinforcement of the whole structure increases around 13% to 131% depending on the level of seismicity and soil type.

Influence of FE Modelling Approaches on Vulnerabilities of RC School Buildings and Proposal of a CFRP Retrofitting Intervention

Background: The vulnerability assessment of existing school buildings against earthquakes represents a priority concern for society. In recent years, several countries promote seismic rehabilitation projects of school buildings, including the allocation of funds to regions with high seismic hazard. Objective: This research aims to highlight some key role aspects related to difficulties encountered in the numerical modelling of RC structures hosting school activities. This work evaluates the seismic vulnerability of school buildings located in the municipality of Trecastelli (Marche, Central Italy) to quantify the effective influence of typical and specific seismic vulnerabilities detected on the global seismic behaviour of each building. The effectiveness of a possible Carbon Fibre Reinforced Polymer (CFRP) local strengthening intervention, for the case study, aimed to confine unconfined beam-column joints is also considered. Methods: Three different numerical models of a Reinforced Concrete (RC) school building are implemented with the lumped plasticity, the distributed plasticity (fibre) and the 3D Continuum Finite Element (FE) approaches. Nonlinear static (pushover) analyses are performed to assess the global seismic behaviour of the structure, and the limitations to represent the reality with different approaches. After the seismic vulnerability assessment of the case study, a CFRP retrofitting intervention is proposed to confine external beam-column joints. Results: The comparison of the numerical results of three models shows that the fibre model is the least suitable means to represent shear problems, while the lumped plasticity model is closer to reality than the previous one even if it does not take into account the concomitance of bending, shear and axial force and the interaction between them in the inelastic response. Of course, the 3D Continuum model is the most accurate representation to describe the complex and combined mechanisms developed in the joint panels. Nonlinear static (pushover) analyses carried out on unreinforced and reinforced structures of Continuum model demonstrate that the Fibre Reinforced Polymer (FRP) strengthening improves the displacement capacity of the structure. Conclusion: This study has highlighted the strengths and weaknesses of different modelling types. The meaningful information about mechanisms developed in joints given by the 3D Continuum FE model is useful to identify shortcomings of the design project and to conceive a retrofitting strengthening intervention. CFRP sheets externally bonded on beam-column joints may improve the seismic frame performances without a significant change of the structural stiffness, promoting a ductile failure mode with a higher displacement capacity than the unreinforced case.

Strengthening Methods of the Existing Reinforced Concrete School Buildings in Medina, Saudi Arabia

Nowadays, evaluation of the seismic performance of existing buildings has received great attention. This paper was carried out to study the effect of strengthening the existing reinforced concrete (RC) school buildings in Medina, Saudi Arabia through assessing the seismic performance and retrofitting where seismic analysis and design were done using equivalent static analysis method according to Saudi Building Code (SBC 301) and SAP2000 software.
 A Typical five-story RC school building designed according to the SBC301 has been investigated in a comparative study to determine the suitable strengthening methods such as RC shear walls and steel X-bracing methods. The results revealed that the current design of RC school buildings located in Medina was unsafe, inadequate, and unsatisfied to mitigate seismic loads. Moreover, adding steel X-bracing and RC shear walls represent a suitable strategy to reduce their seismic vulnerability.

Seismic performance of RC school buildings after 2011 Van earthquakes

School buildings have been classified by many of the design codes as important buildings, which have to withstand the earthquake excitations without any or with minor structural damages, and special care has to be given in their design and construction phases. This paper mainly aims to investigate the seismic performance of reinforced-concrete (RC) school buildings after 2011 Van earthquakes. The seismic performances of two damaged RC school buildings located in the earthquake-affected region are studied. First, the capacities of the selected buildings are assessed using nonlinear static procedures, and then, nonlinear dynamic time history analyses are performed to evaluate the seismic performances of the selected RC school buildings. Reasons for the observed damages are discussed. Further, recommendations are provided from the viewpoint of enhancing the structural capacity of the heavily damaged school building. As a result, to get an idea about the ductility demands imposed on the buildings, spectral acceleration values are compared with the seismic coefficients of the code that the buildings were adapted to. It can be concluded that the construction quality and detailing of the reinforcement are the key issues affecting the seismic performance of RC school buildings.