Retrofit Alternatives Research Articles

Experimentally Verified Retrofit Combining Hybrid Solutions for Enhancing the Seismic Response of Multistory RC Structures

ABSTRACTThis experimental and numerical study proposes hybrid retrofit alternatives involving multiple contemporary techniques to upgrade the fundamental seismic response characteristics of multistory reinforced concrete frame (MSRCF) structures. The impact of thin high‐performance reinforced concrete (HPRC) jackets on the concrete framing system's seismic response is first investigated through shake table testing (STT). The performance of the HPRC‐retrofitted frame is then compared with another STT campaign conducted for fabric‐reinforced cementitious matrix (FRCM)–retrofitted frame. The STT results indicated that at the same input ground motion intensity that caused failure for the FRCM‐retrofitted frame, the curvature ductility and interstory drift ratio of the HPRC‐retrofitted specimen were reduced by 79% and 87%, respectively. Upon verifying the fiber‐based modeling technique of HPRC and FRCM alternatives through STT, the study probabilistically assesses the seismic performance of a benchmark MSRCF building considering different hybrid retrofit alternatives by combining each technique with a self‐centering energy dissipation (SCED) bracing system. Following a systematic seismic assessment framework, it is concluded that the performance‐cost index of the less disruptive HPRC‐SCED option exceeded that of the FRCM‐SCED by 36%, confirming its preference among the considered alternatives for upgrading the seismic response of MSRCF deficient in stiffness, strength, and ductility.

Robustness assessment of RC structures designed for progressive collapse under multiple hazards

The goal of robustness assessment is to enable stakeholders to obtain efficient information, for reducing potential adverse effects of hazards before a natural disaster occurs, to obtain more realistic evaluation results and retrofit alternatives. A series of tests were carried out to investigate the effect of secondary beam on resisting progressive collapse. To further estimate the structural performance, a risk-based fuzzy conditional robustness assessment approach is established. The developed framework is applied to three various design RC structures subjected to multiple hazards, which is simulated by OpenSEEsPy. In this framework, the effect of the dependence configuration and the epistemic uncertainty on the vulnerability curves, loss-PGA curves, and the robustness index are studied by introducing the Vine-Copula and fuzzy theories. Results show that the effect of epistemic uncertainty on the hazard consequence becomes more pronounced with the increasing of PGA, and the lack of such consideration causes incurring additional retrofit costs for the stakeholders. Moreover, the fuzzy conditional robustness index of the models indicated that the installation of secondary beam showed a superior performance, compared with another reinforcement strategy of additional steel ratio. Finally, a method of survival probability-based robustness assessment is built on the developed assessment procedure and verified.

Non-linear 3D seismic analysis of a RC bridge and retrofit alternatives with passive protective systems

Non-linear 3D seismic analysis of a RC bridge and retrofit alternatives with passive protective systems

Life cycle evaluation of seismic retrofit alternatives for reinforced concrete columns.

The critical earthquakes of the last few years highlight the urgent seismic retrofitting of existing buildings due to their aging or inadequate design. This paper aims to evaluate reinforced concrete column retrofit alternatives in a region of high seismic risk. Significant economic, environmental, and functional factors must be considered when deciding between various building retrofit options. The study uses a cradle-to-grave analysis to examine the economic and environmental impacts through life cycle assessments. Specifically, the life-cycle performance of three classic alternatives for rehabilitating columns lacking adequate confinement is compared: concrete jacketing, steel jacketing, and carbon fiber incorporation. The research adopts a holistic approach using multi-criteria decision-making methods, integrating economic, environmental, and functional criteria. A set of criteria and indicators is presented in a structured hierarchy that facilitates the orderly evaluation of alternatives. The results suggest that steel jacketing is preferred, as it presents a balanced performance in most criteria. The incorporation of carbon fiber is viable due to its low environmental and functional impact, although the high production costs of the raw materials limit it. In contrast, concrete jacketing has the highest environmental and functional impacts, making it the least favorable option. The results of this study will provide relevant information for engineers and decision-makers to select the most suitable options for building retrofit when considering several simultaneous perspectives.

Retrofitting Alternatives for an Existing Maillart-Arch-Type Bridge: A Case Study

This article examines different retrofit approaches for a still-in-use deck-stiffened arch bridge, the Viadotto Olivieri in Salerno (A3 Highway—South Italy). In its current state, the viaduct is characterized by a central Maillart-arch system, separated by 6 cm-deep joints from two lateral girder portions: the whole system works as an isostatic scheme on a global scale. Dating back to the 1960s, it derives from an early design approach, not including the effects of seismic actions. Considering the demands of current codes, also in light of recent bridge collapses and the resulting plan for assessing the structural safety and vulnerability of existing bridges, studies on seismic capacity become necessary to highlight the potentials and deficits of such complex structures. Analysing a still-in-use example of a Maillart-arch-type bridge, the article examines two different retrofit approaches. The first retrofit alternative includes the strengthening and partial modification of the original deck bridge: it exploits the beneficial effects of making the slender vault collaborate with a more rigid single deck, resulting from joint closure. Moving in the opposite direction, the second alternative considers the application of seismic isolation to the original scheme. An intermediate Isolation System (IS) has been postulated, inserting rubber devices—High Damping Rubber Bearings (HDRBs)—below the deck, at the top of the cross-walls. The advantages of an IS are clear, observing a great reduction of base reactions; moreover, the introduction of the IS completely modifies the original static scheme and exacerbates bridge deformability, at the expense of slender cross-walls, suffering for buckling. A comparison between these retrofit alternatives is argued in the article, evaluating the impact of different types of solution on the valuable original structural scheme.

Retrofits in Twin Tub Girder Bridges for System-Level Redundancy

Because of the perceived risk of fracture critical members (FCMs) in steel bridges, hands-on inspection cycles are mandated, resulting in high maintenance costs. This paper describes the redundancy evaluation of three twin tub girder bridges with FCM designations. Several failure scenarios of primary members are considered using refined finite element analysis of each structure to determine whether fractures result in collapse or loss of serviceability of the bridge. The analysis follows the American Association of State Highway and Transportation Officials Guide Specifications for Analysis and Identification of Fracture Critical Members and System Redundant Members. Based on the outcomes of these analyses, the feasibility of retrofit alternatives is assessed with the purpose of reclassifying FCMs as system redundant members and precluding hands-on inspection requirements.

Reliability-Based Selection of Retrofit Works for Schools under Seismic Hazard

A reliability-based procedure is proposed to assess and compare the economic effectiveness of three retrofit alternatives for actual schools located in three zones with different seismic hazards. The procedure calculates the school failure probability under the damaged conditions, by considering the damages produced by the 2017 earthquake in Mexico, and the failure probability under each retrofit alternative, from the seismic spectra corresponding to the seismic hazard of each site. The best retrofit alternative is the one with the minimum expected life-cycle cost for each school. The global failure probability is calculated according to the Ditlevsen’s bounds, and the limit states consist of the event in which the maximum moment exceeds the bending capacity for beams, and the combined axial and bending forces exceed the capacity of the columns; the maximum responses are obtained through nonlinear analyses. The proposed retrofit alternatives are column and beam jacketing with steel angles and plates, increment of the concrete cross sections of columns and beams, and the addition of bracing. The effectiveness of each alternative, in terms of failure probability reduction and expected life-cycle cost, was assessed for each school. The procedure may be used to update the current retrofit specifications for schools.

Energy retrofit alternatives for three apartment buildings in Kosovo

AbstractThe need to decrease energy use represents a challenge particularly in developing countries, including Kosovo, considering the unsustainable, insufficient, and inconsistent energy supply. This contribution presents a simplified yet comprehensive approach to evaluate the energy performance improvement potential of three selected multi-family residential buildings using building energy models generated from calibrated and simplified input parameters. To this end, alternative retrofit measures were tested via a simulation-based parametric study. The energy benefit of each retrofit alternative was estimated and analyzed. Results are expected to provide valuable information towards outlining design guidelines for energy-efficient residential buildings in Kosovo.

Comparative Performance Evaluation of Retrofit Alternatives for Upgrading Simply Supported Bridges Using 3D Fiber-Based Analysis

This study aims to select an effective mitigation approach from different alternatives to upgrade substandard RC bridges to meet the seismic performance objectives of current design standards. The performance assessment results for an existing benchmark bridge confirmed that the bent curvature ductility and bearing displacement control the seismic response. Thus, five contemporary retrofit solutions were investigated, including adding different supplementary lateral force-resisting systems (SLFRSs), replacing old bearings with those equipped with shape memory alloy (SMA), and combinations of these retrofit options. Fourteen earthquake records representing long- and short-period seismic events and the seismo-tectonic characteristics of a moderate seismic region were progressively scaled and applied separately in the two orthogonal directions of detailed simulation models representing the retrofitted benchmark bridge. This study provided insights into the impact of combining contemporary seismic risk mitigation techniques on improving the seismic performance of substandard bridges and presented a range of fragility functions for delaying structural damage and minimizing disruption of existing bridges to avoid traffic interruption. The dynamic response simulation results in the longitudinal direction (LD) confirmed that utilizing SMA bearings reduces curvature ductility and bearing displacement demands. Although the probabilistic assessment study in the transverse direction (TD) indicated that SMA bearings adequately reduce displacement demands, the bridge should be equipped with SLFRSs to overcome the bents’ high curvature ductility demands. Therefore, the most effective retrofit technique in TD is achieved using both SMA bearings and steel bracings.

Uncertainty-based optimal energy retrofit methodology for building heat electrification with enhanced energy flexibility and climate adaptability

To reach net zero emissions by 2050, the UK government relies heavily on heat degasification in buildings by using heat pump technology. However, existing buildings may have terminal radiators that require a higher operating temperature than what heat pumps typically provide. Increasing the size of radiators and thermally insulating building envelopes could be a potential solution, but the feasibility of these practices is uncertain due to space constraints and high retrofit costs. This study investigates the feasibility and potential benefits of incorporating air-source heat pumps into existing gas boiler heating systems to meet heating demands. The proposed probabilistic optimal air-source heat pump design method enhances energy flexibility and climate adaptability, taking into account a wide range of uncertainty sources and multiple flexibility services (e.g., energy and ancillary services). Heating systems of three educational buildings at the University of Cambridge are used as a testbed to assess and validate the effectiveness of the proposed method, under future climate scenarios and projected decreases in heating demand due to climate change. Results indicate that the best retrofit alternative of the hybrid heating system reduces carbon emissions by 88%, total costs by 54% over its lifespan, and has an average payback period of around 3 years. Air-source heat pumps can meet the majority of the heating demand (around 80%) with gas boilers used for “top-up” heating during high demand. Furthermore, air-source heat pumps' design capacity can fulfil future cooling demand even if retrofit optimization is initially focused on meeting heating needs.

A Performance-Based Decision Support Workflow for Retrofitting Residential Buildings

The trend towards high-performance residential buildings with new building regulations necessitates fundamental changes in the residential market, which is currently driven by low initial investment costs and dominated by weak innovative cycles. This change involves a difficult decision-making process that must consider the multiple and generally conflicting objectives regarding optimal retrofitting for residential buildings. This study aimed to develop an approach that would provide feedback about a building’s energy and economic performance in relation to the decision-making process to ensure that the complex residence retrofitting process is more efficient. For this purpose, a performance-oriented decision support workflow is recommended for a typical multifamily apartment block within a hypothetical settlement context in Istanbul Province, which includes (i) an automated parametric energy simulation through the coupling of EnergyPlus and MATLAB® to determine differences between retrofit alternatives in relation to the building envelope, energy systems and renewable energy systems, and (ii) a multiple-criteria decision analysis to determine the retrofit alternatives by which the optimal performance can be achieved, taking into account the conflicting nature of key performance indicators (primary energy saving and life-cycle cost saving). Architects and residence owners—who are the main decision makers—can use this proposed workflow to explore effective retrofit alternatives and to make informed decisions about performance-based retrofitting by comparing the energy and economic performance of these alternatives.

Revamping of crude distillation unit for enhancement of processing capacity and LPG extraction through steady state simulation modeling

The scope of this work covers the debottlenecking of operational constraints for increasing the processing capacity of crude distillation unit and LPG extraction from crude oil. Simulation modeling on Aspen HYSY V7.1 is used for thoroughly investigating and evaluation of retrofit alternatives. Design and operations data of a crude distillation unit at Attock Refinery Limited is used as a case study. Capacity expansion through the addition or rearranging of circulating reflux/Pump-around is selected among the various available revamp alternates like addition of Pre-flash columns, tray geometry and hydraulics etc. Then crude distillation unit is revamped for maximum possible expansion in processing capacity by re-arranging of Pump-around circuits. Pump-around balances re-arranged based on specific crude oil operating blend. Some modifications are also proposed in stabilizer section of the crude distillation unit to enhance LPG extraction from crude oil and finally crude distillation unit simulated for revamped processing capacity with re-arranged pump-around circuits and suggested modifications in stabilizer section. The results of Simulation Modeling validate propose modifications for revamping of processing capacity and LPG extraction.

Building energy retrofit simulation for exploring decarbonization pathways in a community-scale food-energy-water-waste nexus

• A food-energy-water-waste nexus analysis can aid in low carbon city design • System dynamic modeling analysis synthesizes low carbon city initiative. • Scenario planning helps identify decarbonization pathways for prioritization. The retrofit of existing buildings at a community scale can provide a huge opportunity to reduce the community's energy consumption and subsequent greenhouse gas (GHG) emissions in support of the United Nations agenda for net-zero emissions and decarbonization. This study demonstrates a community-scale food-energy-water-waste nexus through 6 scenarios (A1–A6) by highlighting decarbonization pathways with system dynamics modeling. Several potential retrofit alternatives are proposed for analyzing building energy consumption, energy requirements for rooftop or greenhouse crop production, and potential energy and water savings from renewable energy harvesting. Such a nexus analysis is designed to integrate (1) building energy consumption, (2) waste management and water consumption, and (3) GHG emissions based on life-cycle assessment to prioritize scenarios. The incorporation of solar photovoltaic (PV) systems (i.e., rooftop, parking lot, parking garage, and floating solar PV) sustains approximately 72% of net energy demand (scenario A3), while the integration of all solar, wind, and anaerobic digestion alternatives provides around 41% of net energy demand (scenario A6). It is vital to emphasize decarbonization pathways through the use of renewable energy by 2030 in scenario A5 (i.e., solar and wind energy) and A6, both of which avoid energy consumption from the utility grid and result in 250% total carbon emissions offset.

Cost estimation models for seismic retrofit of masonry school buildings

Seismic retrofits can significantly reduce the vulnerability of masonry buildings. Multiple seismic retrofit alternatives are often available for a given building. Estimating the cost of each candidate action is essential to selecting and implementing the appropriate seismic retrofit initiatives. This research harnesses the capabilities of various regression models for cost estimation. A dataset from 167 retrofit projects for masonry school buildings was used to develop models. Three main retrofit actions were taken into consideration: shotcrete, steel belt and fiber-reinforced polymer. Various regression methods, including multiple linear regression, ridge regression, lasso regression, and elastic net regression, were applied to develop models that estimate the cost of each of the three retrofit actions based on a set of explanatory variables. Next, the models underwent a reduction process to simplify and increase their prediction precision. In most models, the reduction process eliminated multiple terms and enhanced the model prediction performance. This article identifies the height of the building as the most influential parameter governing retrofit costs. It examines the effect of proxy variables (e.g. lateral area of walls and added lateral strength) on the final retrofit cost by adding them as explanatory variables.

Optimal energy performance of dynamic sliding and insulated shades for residential buildings

The paper evaluates the potential energy efficiency benefits for dynamic sliding exterior shades suitable for windows of both new and existing buildings. In particular, the analysis outlined in the paper summarizes the energy performance of dynamic sliding shades when applied to windows for apartment units located in various US climates. A series of sensitivity analyses is performed using a detailed whole-building simulation coupled with modeling techniques of dynamic envelope systems to determine the optimal positions for the dynamic sliding shades to minimize the annual demand for US housing units. Several operation strategies are evaluated using continuous and stepped settings of the positions for the dynamic sliding shades using monthly, daily, and hourly adjustment frequencies. The results of the analyses indicate that the dynamic shades have significant energy efficiency potential for all US climates and design conditions with annual savings in HVAC energy end-use of over 50% especially in hot and mild climates. The performance of the dynamic shades is even higher for large and single-pane windows indicating that these systems can serve as retrofit alternatives to window replacements.

노후 건축물 그린리모델링안 작성에서 전문가와 건물 사용자 관점의 차이에 따른 에너지 절감효과의 분석

The purpose of this study was to analyze the energy saving effects according to differences in interests between energy experts and building users, when establishing a green remodeling plan for old buildings. The survey was conducted to investigate building users’ opinions on building retrofitting. The results show that retrofit alternatives between experts and building users were different. The experts focus on energy saving in making alternatives, whereas building users mainly want to improve building appearance. Approximately 31.8% of building energy was saved with the experts’ retrofit alternatives. On the other hand, only 12.6% of building energy was saved through applying the retrofit alternatives of building users.

Applying the response surface methodology to predict the energy retrofit performance of the TABULA residential building stock

Recent advances in computing software have enabled the development of calibrated building energy simulations tools that allow retrofit-related analysis including optimization and energy-efficient building design. However, to create a national energy and climate plan, using these tools may imply a great deal of effort (time, cost, and human resources) to carry out simulations for the full set of different building types, construction, geometries, design parameters, and retrofit scenarios. Because of this, simplified approaches that can reliably estimate the impact of energy-efficiency retrofit alternatives based on averaged building stock characteristics could offer a significant advantage, especially in middle-income countries such as Bosnia and Herzegovina. This study aims to explore the energy reduction potential of a representative building from the national residential building stock by utilizing the response surface methodology (RSM). In this study, RSM is combined with the energy simulation tools EnergyPlus and DesignBuilder to model the energy savings associated with energy-efficient retrofit measures for a residential building from the national TABULA registry in Bosnia and Herzegovina. This study introduces a novel energy consumption model that can be applied to optimize energy-efficient retrofit design solutions for reducing the energy consumption for heating and cooling in the residential building sector. Moreover, the model developed was validated by using the results of a national survey on energy consumption in Bosnia and Herzegovina. Therefore, the use of the model developed is versatile and suitable for rapid prediction of energy-efficient retrofit-related energy consumption and energy savings of the residential building stock.

Seismic performance upgrade of substandard RC buildings with different structural systems using advanced retrofit techniques

There has been ongoing deliberation to arrive at promising retrofit strategies for pre-seismic code reinforced concrete (RC) structures. Against this backdrop, the research reported in this study puts forth solutions by focusing on advanced retrofit approaches for improving the seismic performance of substandard RC buildings with structural systems common to medium seismicity regions. High-performance reinforced concrete (HPRC) jacket application and self-centering energy dissipative (SCED) braces are the contemporary retrofit alternatives prioritized in this study to upgrade RC structural systems deficient in stiffness, strength and/or ductility. While these retrofit techniques were previously investigated at the member level, this study focuses on implementing thin-HPRC jacket applications, innovative outrigger-belt truss SCED bracing systems, and hybrid approaches on three-dimensional (3D) fiber-based numerical models representing substandard RC structures with different heights. Inelastic pushover analyses and multi-record dynamic response simulations are conducted to assess the retrofit alternatives by monitoring several local damage indices (LDIs) and the related global damage measure (GDM). The study confirms the effectiveness of retrofit measures for a moment-resisting frame building (MRF) deficient in lateral capacity and a high-rise shear wall (SW) building with insufficient global ductility. The presented systematic methodology accounts for the redistribution of seismic demands after retrofitting critical elements and enables selecting effective seismic retrofit solutions, namely SCED bracing system for MRF structure and hybrid retrofit for the high-rise SW building, using probabilistic seismic performance assessment along with cost and practical considerations.

The LCT Challenge: Defining New Design Objectives to Increase the Sustainability of Building Retrofit Interventions

The decarbonization of the construction sector, which is one of the most impactful sectors worldwide, requires a significant paradigm shift from a linear economy to a circular, future-proofed and sustainable economy. In this transition, the role of designers and structural engineers becomes pivotal, and new design objectives and principles inspired by Life Cycle Thinking (LCT) should be defined and included from the early stages of the design process to allow for a truly sustainable renovation of the built environment. In this paper, an overview of LCT-based objectives and principles is provided, critically analyzing the current state of the art of sustainability and circularity in the construction sector. The effectiveness of applying such design principles from the early stages of the design of retrofit interventions is then demonstrated with reference to a case study building. Four seismic retrofit alternatives made of timber, steel and concrete, conceived according to either LCT principles or traditional, were designed and compared to a demolition and reconstruction scenario on the basis of five common environmental impact indicators. The indicators were calculated adopting simplified LCA analyses based on Environmental Product Declarations (EPDs), considering the product and End of Life stages of the building. The results of the comparative analyses confirm that LCT-based retrofit solutions are less impactful than both the traditional seismic retrofit interventions and the demolition and reconstruction scenario.

Influence of Parameter Uncertainty in Multi-Criteria Decision-Making When Identifying Optimal Retrofitting Strategies for RC Buildings

ABSTRACT The evaluation of retrofitting alternatives through multi-criteria decision making (MCDM) approaches allows an optimal selection based on a ranking system. This rank depends on evaluation parameters that assess particular aspects of the retrofitting options and influence the selection of the most advantageous alternative. Moreover, when integrating uncertainty of the input parameters into the procedure, the outcome may be altered and the rank order notably different with respect to a deterministic MCDM implementation. This paper examines an MCDM approach applied to four retrofit alternatives proposed for a case-study building, starting from a deterministic perspective. Subsequently, the MCDM method is extended to consider random variables, in order to compare and understand the influence of uncertainty of the input parameters in the selection of retrofit alternatives for the same building. To ensure that accurate and representative data was used in the stochastic implementation, an ad-hoc survey was developed to collect the views from relevant parties involved in the field of seismic retrofitting interventions, particularly those with an academic/research or practice/industry background. The outcomes of the study are believed to serve as useful guidelines and as a future reference for practitioners in the field of structural retrofitting, on how to select the most convenient retrofit alternative for an existing building.