Seismic Upgrading Research Articles

Behavior of circular reinforced concrete columns strengthened with corrugated steel sheets and high-performance concrete

Reinforced concrete (RC) columns are frequently strengthened due to the damage caused by environmental exposure, changes in loading conditions, or seismic upgrading. This paper presents experimental and numerical investigations into the behavior of circular RC columns strengthened using galvanized corrugated steel sheets (GCSS) filled with concrete under eccentric and concentric loads. The effects of the loading condition, the types of concrete used to fill the void, and the existence of additional longitudinal steel bars on structural behavior are examined. The types of concrete include normal concrete, engineered cementitious composite (ECC), ultra-high-performance ECC (UHPECC), and high-strength grout (GR). Test results show that the proposed strengthening technique significantly improves the performance of RC columns. The elastic stiffness and energy absorption of the strengthened columns increase by about 98 %, and 123 %, respectively when compared to those of the control column under concentric loading. Under eccentric loading, the ductility of columns with high-performance concrete (HPC) is better than that of other columns. Moreover, the type of concrete has a remarkable effect on structural behavior. The grout-filled GCSS columns have a higher axial load, ductility, energy absorption, and elastic stiffness than columns constructed with other types of concrete. The finite element (FE) model developed by using ABAQUS is shown to simulate well the experimentally measured responses of concrete-filled composite columns.

Seismic Upgrading of the Heritage-Protected Reinforced Concrete Warehouse in Rijeka, Croatia

Despite Croatia experiencing two strong earthquakes in 2020, Rijeka was not directly affected, underscoring the importance of proactive seismic assessment and strengthening in all seismic regions. This paper presents a comprehensive case study on the seismic strengthening of a 20th-century concrete building located in Rijeka, Croatia, originally designed according to Austro-Hungarian construction norms and practices. As a heritage-protected structure, the building’s architectural features and construction practices were examined and contextualized within its historical background. The assessment and renovation phases of this project are discussed in detail, demonstrating the practical application of modern seismic strengthening techniques while preserving the building’s historical integrity. This case study aims to highlight the need for such measures to protect heritage structures and to show the implementation of rapid and new (ad hoc) norms for earthquake-damaged buildings in Croatia. This study serves as a reference for engineers, architects, and conservationists involved in the preservation of heritage buildings, demonstrating that it is possible to enhance their structural safety without compromising their architectural authenticity.

Adaptive Seismic Upgrading of Isolated Bridges with C-Gapped Devices: Model Testing

The seismic safety margins of seismically isolated bridges have not been thoroughly studied or comprehended due to a lack of actual on-site data observations. This study introduces a newly validated method for the efficient seismic protection of bridges that may be exposed to extremely strong, multidirectional near-source and critical far-source earthquakes. The isolated system was improved by incorporating innovative adaptive horizontal C-multigapped (HC-MG) energy dissipation devices to overcome the safety limitations associated with solely using isolated bridges under seismic loads. The newly developed adaptive C-gapped (ACG) bridge system was systematically validated through extensive experimental seismic tests on bridge models and additional analytical studies. The new ACG bridge system represents an advanced technical solution that integrates the benefits of seismic isolation and energy dissipation. The seismic isolation system for the large-scale ACG bridge prototype was designed using double spherical rolling seismic bearings (DSRSB). The seismic performance of the system was enhanced with adaptive HC-MG energy dissipation devices. The improved seismic performance of the system was demonstrated through extensive seismic shaking-table tests on the ACG bridge prototype, simulating selected seismic inputs characteristic of typical near- and far-source earthquakes. Doi: 10.28991/CEJ-2024-010-09-01 Full Text: PDF

Methodology and Monitoring of the Strengthening and Upgrading of a Four-Story Building with an Open Ground Floor in a Seismic Region

Many buildings around the world fail to meet current earthquake resistance requirements and have significant potential to be a risk to human life and property. Therefore, a seismic upgrade of such buildings is quite necessary. Over the past decades, hundreds of buildings have been strengthened and upgraded to improve their seismic resistance, and thousands more are planned for years to come. In Israel, this was followed by National Outline Plan No. 38, which provides a basis for retrofitting and adding new areas to existing buildings. It should be noted that adding new floors to existing buildings increases seismic forces. Moreover, structure material properties change over a building’s lifetime, which should be also considered for strengthening. The proposed research investigates and validates the existing practice for strengthening and upgrading buildings in seismic regions and suggests ways of improving their efficiency. Experiments and numerical analysis were performed on a real existing residential building that requires strengthening and upgrading. A corresponding methodology was proposed for monitoring the strengthening and upgrading processes, including selecting measurement devices and their real use. Using sensors with the highest sensitivity enabled measurements of micro-vibrations and investigations of the recorded signal to obtain the building’s natural vibration frequencies. Experimental measurements allowed us to distinguish different frequencies of the building at all strengthening and upgrading stages. The measured dynamic parameters of the building allowed a more accurate calculation of seismic forces for all of these stages and consequently made the design more effective. Therefore, we recommended monitoring buildings in each stage of seismic strengthening and upgrading.

The evolution of sustainable renovation of existing buildings: from integrated seismic and environmental retrofitting strategies to a life cycle thinking approach

The sustainable renovation of existing buildings is currently at the top of the agenda of the European Union. Sustainability is typically defined as the result of the interaction of environmental, economic, and social aspects, and it is now considered a major target objective in all sectors of our economy, including the construction one. The concept of sustainable renovation has changed significantly over time, leading to the current interpretation that considers the need to simultaneously improve safety and resilience against natural hazards and minimise energy and resource consumption, as well as to reduce impacts along the life cycle of the building. This manuscript presents insights into combined/integrated environmental and seismic retrofitting techniques and assessment methods for the sustainable renovation of the existing building stock, specifically focussing on those conceived according to a Life Cycle Thinking (LCT) approach. This manuscript goes beyond the current available state of the art by highlighting the evolution of the concept of building sustainability throughout time, as well as defining a comprehensive taxonomy of available retrofitting strategies, while also identifying common clusters among available research papers. This research effort is part of the mission of the European Association of Earthquake Engineering (EAEE) Working Group 15 (WG15), which focusses on ‘combined seismic and environmental upgrading of existing buildings”.

A Practice-Oriented Approach for Seismic and Energy Performance Upgrading of Existing Buildings

ABSTRACT Recent studies have focused on identifying the optimal seismic and energy upgrading interventions, among different alternatives, for poorly performing existing buildings. Most of such studies use detailed methodologies to assess the seismic and energy performance of buildings, which are time and computationally demanding, making it nearly unfeasible for practitioners and decision-makers to use them, rendering practice-oriented approaches extremely needed. To overcome the current limitations of more research-oriented methods, this study employs different available simplified approaches, namely SPO2FRAG, cloud-based capacity spectrum method and the Italian seismic risk classification guidelines (Sismabonus), to estimate some of the variables considered when using a multi-criteria decision-making (MCDM) framework to select the optimal combined retrofitting strategy, among a set of different options. To this end, a case-study school building was selected and four seismic retrofitting solutions, combined with three energy-based interventions, were identified. The performance of the building, in its as-built and retrofitted conditions, was analysed considering both simplified and detailed approaches for the estimation of two of the seismic-related variables, namely annual probability of failure and expected annual losses. Such simplified and refined estimates were used as MCDM input, comparing the ranking of retrofitting combined alternatives obtained in both cases, demonstrating the suitability of the proposed simplified methodology for engineering practice.

Seismic upgrade of a non-code compliant multi-storey steel building: A case study

This study aims to develop a step-by-step design procedure for the seismic upgrade of existing steel buildings based on local strengthening interventions of the connections and the use of conventional X-concentrically bracings (X-CBFs), which are designed to account for both architectural and time/cost-saving constraints. The proposed procedure is applied to an existing non-code-compliant six-storey steel building, which is located in Naples (Italy). Both local and global numerical analyses are performed to investigate the effectiveness of the proposed procedure. The obtained results show that it is possible to decrease by up to 25 % the resistance and stiffness of new X-CBFs if the beam-to-column connections are strengthened to resist the flexural capacity of the connected beams. The pushover-based seismic fragility of as-built and upgraded structures is compared, and the seismic risk reduction is further quantified according to the Italian guidelines for the risk classification of constructions. The variation of seismic risk class induced by designed interventions is evaluated, thus confirming substantial risk mitigation of the upgraded building.

Seismic performance upgrade of highway bridges using a novel hybrid placement of bonded and unbonded laminated rubber bearings

To enhance the seismic performance of highway bridges supported by laminated rubber bearings, this study proposes a novel hybrid placement of bonded and unbonded bearings. The typical analytical models of the hybrid bearing system are obtained and its critical design parameters are identified through theoretical analysis. A design procedure is then established to rapidly determine the design parameters for the hybrid bearing system according to specified design objectives. Nonlinear time history analyses are conducted to demonstrate the impact of the hybrid bearing system on the seismic responses of bridges. The analytical results indicate that the hybrid bearing system, when designed using the proposed procedure, can achieve the desired hysteretic behavior. The hybrid system combines the benefits of both bonded and unbonded bearings, effectively controlling maximum and residual bearing displacements without significantly increasing the seismic demand on bridge piers. The design parameters for the hybrid bearing system should be determined by carefully balancing the responses between the bearings and the piers.

Multicriteria decision tools for selection of sustainable integrated retrofits: application to the seismic and energy upgrade of a masonry building

The design of sustainable integrated retrofits is a new frontier in civil engineering that aims to minimize economic and environmental impacts of interventions on existing buildings. The enhanced methodology presented in this paper combines seismic and energy performance metrics with economic and environmental indicators associated with each integrated retrofit. The purpose is to identify the optimal retrofit through histograms, radar charts, proficiency ratios and iso-class plots, as the one corresponding to the higher seismic and energy performances and the minimum economic and environmental impacts. Such a methodology can be applied to either the installation phase of the retrofit or its entire life cycle, making it possible to compare these two scenarios in a long-term perspective. The methodology, generally valid for any building materials or structural typologies, is here applied to a two-story natural-stone masonry building, damaged by the 2016 Central Italy earthquake sequence.

Integrated Approach of Retrofitting an Existing Residential Building to a Nearly Zero Energy Building with Simultaneous Seismic Upgrading

Introduction The current study's goal is to apply an integrated approach of retrofitting a typical building in Cyprus that was designed and constructed for the refugee settlements in the period 1975-1985. The existing building is retrofitted to a nearly zero-energy building. Methods This typical type of building examined represents approximately 15,347 houses and stands for 3.57% of households in Cyprus. This percentage is considered significant with regards to energy consumption, as this type of structure has an estimated energy consumption of 1000 kWh/m2/y and CO2 emissions of 293.74kg CO2/m2/y. This corresponds to 0.293 Mt CO2/y, which stands for 4.18% of total CO2 emissions in Cyprus for 2011, based on the latest IEA (International Energy Agency) data. An integrated approach is followed for the retrofitting of the existing building, which involves both energy and structural upgrades, taking into account the earthquake resistance upgrade. Since Cyprus is in a highly seismic region, an important factor in this approach is the ability of the structure to survive a strong earthquake during its remaining lifetime, according to the design criteria. The study presents and discusses three possible coalitions with multiple scenarios of approaching the upgrade of the existing building. In each coalition, various criteria and implementation actions are considered based on the energy consumption, the CO2 footprint, and the seismic resistance. Results The study also investigates whether the extension of life expectancy of the existing structure through earthquake resistance upgrade will have a positive or negative effect on the CO2 life cycle footprint and cost of the building. Results show that for the examined typical building, simultaneous energy and earthquake resistance upgrade is more efficient in terms of cost and environmental impact. The building with the smallest construction age had the smallest Decision-Making Index (DMI) from the A, B and C coalitions. Conclusion It is important that for an existing building, the option to remain in its original state (coalition A) without any upgrading intervention is not the most favorable option. Therefore, the need to evaluate the existing building stock and plan the upgrade of the buildings in question is of utmost importance.

Investigation on Seismic Performance of Reinforced Concrete Frame Retrofitted by Carbon Fiber-Reinforced Polymer

In order to improve the seismic performance of reinforced concrete (RC) frames, carbon fiber-reinforced polymer (CFRP) was used to retrofit reinforced concrete frame structures. The comparison pseudo-static test results show that the peak load, initial stiffness and ductility of the CFRP retrofitted model were increased by 43.89%, 39.27% and 30.1%, respectively. Based on the parametric study of the finite element model, the contribution of CFRP to the seismic upgrading effect of RC columns was quantitatively revealed, and an optimized design of retrofitted CFRP was proposed. The results show that the peak load, ductility and energy dissipation capacity of the whole structure are improved by using CFRP full-wrap reinforcement and strip reinforcement models with different coverage areas. The damage degree of the column decreases, the damage degree of the beam increases, and the failure mode changes from “column hinge” to “beam hinge”. Simultaneously, different CFRP reinforcement areas and the distance between strip CFRP have different reinforcement effects on concrete structures. Based on the investigation results, the recommended ratio of CFRP strip to spacing is 1 to 1.25.

Upgrading of Precast Roof Beam–Column Connections with Seismic Safety Key Devices

To meet the increasing demands for innovations in precast systems with high seismic resistance, in this study, we introduced a novel seismic upgrading technique for roof beam-column (RBC) connections, termed the targeted seismic upgrading (TSU) method, incorporating the innovative seismic safety key (SSK) devices we developed. These devices significantly enhance seismic resilience, offering a substantial improvement over traditional pin-based RBC connections in precast structures, which are known to have limited effectiveness. Our experimental tests on half-scale models of conventional RBC connections, coupled with comprehensive refined finite element method-based nonlinear analytical studies, conclusively demonstrated the enhanced seismic retrofitting capabilities of RBC connections augmented with SSK devices. The paper delineates a technical procedure for applying the SSK, our proprietary innovation, for the targeted seismic upgrading of RBC connections within modern precast systems. Notably, the SSK-upgraded RBC connections exhibited a marked increase in safety, as evidenced by results from experimentally validated nonlinear three-dimensional micro-analytical models. The incorporated flexible design elements in the TSU method ensure its high effectiveness and general applicability for seismic upgrading of both existing and new precast industrial hall structures, offering a significant advancement in this specific seismic engineering topic. Doi: 10.28991/CEJ-2024-010-05-06 Full Text: PDF

Improving the dynamic behaviour of historic buildings using experimental data: application to a Baroque church

Vibration-based Structural Health Monitoring represents an efficient and reliable tool to build models that can predict the dynamic behaviour of heritage structures for, but not limited to, monitoring purposes. Indeed, built heritage consists of unique structures often characterized by high fragility, and the design of interventions implies several challenges, also related to restrictions on the application of modern regulations. In this context, the corroboration of the mechanical model should accompany the entire process, from design to implementation, with test campaigns performed before and after the strengthening operations to assess their effectiveness. Thus, the work presents the experimental process used for the tailoring of the seismic upgrading interventions on the church of Santa Caterina, in Casale Monferrato. More recently, the model has been updated with the results acquired from a permanent monitoring system installed in 2022, following the interventions, hence allowing assessments of their effectiveness.

RiskSchools: a prioritization-based system for the risk assessment of school buildings combining rapid visual screening smartphone app and detailed vulnerability analysis

AbstractA multi-purpose and multi-scale tool for the seismic vulnerability and risk classification of critical buildings, such as schools, is proposed for pre- and post-event decision-making to mitigate the risk and reduce losses. The herein proposed “RiskSchools” system, is capable of performing the seismic risk assessment and grading of school buildings at various scales (district, municipality, region etc.), using (a) a pre-seismic rapid visual screening and grading of the school buildings in different vulnerability-risk classes and (b) a seismic risk assessment of the school buildings population, applying probabilistic or scenario-based methods for the seismic hazard and analytical methods for the vulnerability and risk assessment, also leading to a grading of the buildings’ risk. The results of the two approaches are compared and combined through a flexible and adaptable expert elicitation scheme to provide a final classification of the seismic risk of the school buildings in the scale of interest and a prioritization scheme with respect to the need for seismic upgrade and retrofitting. The RiskSchools system consists of a powerful, state-of-the-art, user-friendly, and easy-to-use smartphone application for the compilation of the inventory and the rapid visual screening, and a project-dedicated multi-purpose webGIS platform for the seismic vulnerability and risk classification of school buildings at any scale. Although it is initially developed and applied to the school building stock of the Region of Central Macedonia in Greece, it has been specifically designed to be easily applied to other regions of Greece and worldwide and adapted to other critical buildings, like health care and hospital buildings. The ultimate scope of the RiskSchools System is to allow for the optimal design of decision-making procedures in support of disaster management to enhance critical buildings resilience.

Nonlinear Viscous Damping-Based Negative Stiffness Isolation System for Over-Track Complex Structures

ABSTRACT The over-track complex structures are driven by transit-oriented urban development, leading to the necessity for advanced seismic performance upgrades. An innovative solution is presented in this study, involving the negative-stiffness amplification system-enabled isolation system (NSAS-IS) with nonlinear viscous damping to establish a flexible isolation layer beneath over-track buildings. The multi-benefit-based design procedure and easy-to-use formula are developed. Its effectiveness and comparative superiority over conventional ones, particularly in mitigating negative effects of over-track buildings on lower podiums, is confirmed by case studies. NSAS-IS with an optimized nonlinear viscous damping exponent exhibits a significant reduction in isolation-layer displacement and robustness against earthquakes.

An integrated regional prioritisation framework for seismic and energy-efficiency performance upgrading of residential buildings

Given the ambitious carbon emission reduction targets, enormous resources are being invested in Europe to foster environmental, economic and social sustainability. An urgent response, foreseen by the 2030 Agenda for Sustainable Development, is also demanded by the European Commission to all the Member States for the energy requalification of buildings, which are responsible for about 36% of European greenhouse gas emissions. While targeting energy efficiency improvement, many regions are prone to other perils, such as seismic hazard, which might compromise the effective sustainability of the energy requalification. In fact, the innate diversity between regions or countries, which do not share the same seismic risk level and social issues, cannot be overlooked. For this reason, specific indicators should be considered to achieve an appropriate level of resilience (energy, seismic and social) of the overall existing building stock. This paper proposes an integrated framework, specifically calibrated and demonstrated for the Italian residential building stock, applicable to any other region or country, based on primary indicators defined for regional assessment. The framework encompasses single and multi-sectoral indicators, providing different prioritisation patterns and refinement scales, from province to national level. The most updated building fragility models are selected and combined through a logic tree strategy. The space heating energy consumption and CO2 emissions are directly taken from a collection of all the Energy Performance Certificates (APE) of Italian buildings and building units, while national and European indices are used to account for socioeconomic aspects. In addition to the socioeconomic aspects related to the development levels of each region, energy poverty and earthquake risk awareness were also considered as indicators of the socioeconomic vulnerability of regions. The proposed framework and the prioritisation patterns obtained in this work can support relevant stakeholders to foresee economic support and strategic financial planning for seismic strengthening and energy renovation interventions on existing buildings, including socioeconomic features, and favour funding in regions of higher needs.

Seismic Upgrade of an Existing Reinforced Concrete Building Using Steel Plate Shear Walls (SPSW)

Steel Plate Shear Walls (SPSW) provide significant lateral load capacity and can be utilized in the seismic retrofit and upgrade of existing reinforced concrete (r/c) buildings. In this study, the application of SPSW to retrofit a r/c building designed according to older seismic provisions is presented. Three different options to model SPSW are utilized, i.e., by equivalent braces, by finite elements, and by membrane elements, seeking not only to appropriately simulate the actual behavior of the SPSW but also to achieve the desired seismic behavior of the retrofitted building. Specific seismic response indices, including plastic hinge formations, are derived by non-linear time-history analyses in order to assess the seismic behavior of the retrofitted r/c building. Inspection of the results provided by non-linear analyses in conjunction with the different modeling options of the SPSW leads to the conclusion that the model with the membrane elements exhibits the best performance, implying that for the seismic retrofit and upgrade of existing r/c buildings, the use of membrane elements to model the SPSW is recommended.

Perspectives on integrated retrofitting of existing reinforced concrete buildings

Buildings account for 40% of energy consumption and 38% of CO2 emissions in the European Union (EU). This substantial impact is primarily due to the delayed implementation of initial energy codes. Additionally, about 40% of the EU's buildings are situated in seismic-prone areas, many of which were constructed without meeting current safety standards. An estimated 65% of these structures require both energy and seismic upgrades. Given these challenges, there is an urgent socio-economic and environmental need to renovate the existing building stock. It is crucial to adopt an integrated retrofitting strategy, enhancing both efficiency and resilience against extreme events. This study provides a detailed examination of the integrated retrofitting of existing Reinforced Concrete (RC) buildings. Additionally, a review of current international policies (or incentive programs) related to independent (i.e., structural or energy) and integrated retrofitting (i.e., seismic plus structural) is presented and discussed. From the ten incentive programs evaluated, 77% focused on energy retrofitting interventions, while only 33% addressed structural improvement interventions. As anticipated, there is an increasing emphasis on programs that also consider the sustainable impact of these buildings’ interventions but the combination of energy plus structural interventions still has a minor relevance.

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 existing structures and earthquake-resistant foundations using self-drilling micropiles

Seismic upgrade of existing structures and earthquake-resistant foundations using self-drilling micropiles