Retrofit System Research Articles

Retrofit of RC buildings using vertical shear links and hybrid connections

This study employs a retrofit system with a vertical shear link inside a steel frame to improve the structural behavior of an existing reinforced concrete (RC) frame. The steel frame is connected to the RC frame through a hybrid connection system. The hybrid connection not only provides a rigid, strong connection between the steel and RC frames but also increases the shear strength of RC columns and beams. It is referred to as a hybrid connection in light of such combined measures. The connection is composed of thin steel plates, bolts, and infilling grout. This study tested four one-bay one-story RC frames. One of the RC frames was the benchmark, while the three remaining RC frames were retrofitted under different schemes. The scale factor of the frames was set to 1/3 ∼ 1/4 to model a low-rise RC building. The experimental results of the retrofitted RC frames by vertical shear links demonstrated that the boundary steel frame played a key role in obtaining a stable hysteretic response. Moreover, the hybrid connection strongly withstood the shear force between the RC frame and the steel frame. A series of calculation approaches were proposed to find the lateral strength of retrofitted frames under different failure mechanisms. The calculated lateral strengths were observed to agree with the experimental results.

A Design Process for Preventing Brittle Failure in Strengthening RC Slabs with Hybrid FRP-HPC Retrofit Systems.

The retrofitting of existing RC slabs with an innovative system comprising FRP and HPC has been demonstrated to be effective in strengthening and overcoming the logistical challenges of installation. Nonetheless, the excessive improvement of flexural strength over shear strength would cause the sudden failure of rehabilitated flexural members. The literature has previously recommended failure limits to determine the additional moment strength compared with the shear strength to prevent brittle shear failure of strengthened, continuous RC slabs. This study suggests a design process for preventing shear failure and inducing the ductile-failure mode to improve the safety and applicability of retrofitted RC slabs based on the proposed failure limits. The effectiveness of the procedure in brittle-failure prevention for the end and interior spans of retrofitted RC slabs is illustrated via a case study. The outcomes showed that the retrofit system with 0.53-mm-thick-CFRP prevented brittle failure and significantly enhanced the design-factored load and ultimate failure load by up to 2.07 times and 2.13 times, respectively.

Marine vessel powertrain design optimization: Multiperiod modeling considering retrofits and alternative fuels

Over the coming decades, maritime transportation will transition from fossil hydrocarbon fuels to hydrogen, ammonia, and synthetic hydrocarbon fuels produced using renewable electricity as the primary energy source. In this context, a shipowner needs to identify a cost-efficient plan for the adoption of alternative fuels and onboard energy conversion system retrofits. This paper presents a multiperiod decision model for the selection of energy system components under increasingly stringent CO2 emissions regulations and cost forecasts over a multidecade planning horizon. The model considers the choice of newbuild architecture, timing of retrofits, component sizes, and allocation of fuels to converters with the objective of minimizing total cost of ownership (TCO). The decision problem is formulated as a discrete time multiperiod mixed-integer linear program. The application of the model is numerically illustrated for a Baltic Sea roll-on/roll-off ferry. The main findings are: (i) modifying the energy system with retrofits obtains 43% lower TCO compared to fuel switching alone; (ii) batteries contribute to 23% lower TCO; (iii) optimal component installation period can be shorter than their maximum lifetime; (iv) running an engine with hydrogen is favored over fuel cells and (v) hybrid propulsion is the key future-proofing design choice for short sea vessels.

Feasibility study on solar coupled gas-fired boiler heating system retrofit in residential buildings in the HSCW zone of China

Residential buildings in the hot summer and cold winter (HSCW) zone rely on gas-fired boiler for heating have a certain application basis, but high operating costs and limited gas consumption seriously limit the promotion of gas-fired boiler. To reduce domestic gas consumption in Wuhan, two solar auxiliary gas-fired boiler heating systems formed in parallel and series are proposed and explore the feasibility of coupled heating system retrofit. The simulation models of two solar coupled gas-fired boiler heating systems are established by TRNSYS, and the results indicate that the indoor thermal environment of the two systems is good and the temperature of the tank is stable. The solar fraction of the parallel system reaches 24.40%, which has better energy saving. The optimization analyses display that the system has the best economy when the collector area ratio is 10.0%, and the collector area and tank volume ratio is 8/0.7. The solar-assisted parallel heating system retrofit can save 2.02 × 104 MJ over the entire life cycle, and the increased initial investment can be recovered within 4.75 years. The research results can provide a basis and new ideas for the heating retrofit of the gas-fired boiler in residential buildings in the HSCW zone.

Cyclic shear-compression tests on two stone masonry piers strengthened with CRM and FRCM

This paper discusses the results of an experimental campaign on Composite-Reinforced Mortar (CRM) and Fabric-Reinforced Cementitious Matrix (FRCM) jacketing for the retrofit of stone masonry structures. Two double-leaf natural stone masonry piers were built with the same materials and geometry, including portions of adjoining spandrels above and below. Then CRM was applied to both faces of one of the specimens, using a natural hydraulic-lime mortar, glass-fiber-reinforced polymer meshes, and helicoidal steel connectors. The other pier, instead, was retrofitted with FRCM on both sides, combining a glass-fiber-reinforced cementitious mortar, bidirectional PBO textiles, and PBO connectors. Both specimens were subjected to the same vertical overburden load and to a quasi-static cyclic shear-compression test in double-curvature conditions, up to failure conditions. Different collapse mechanisms were triggered by the two retrofit systems, with flexure dominating the CRM specimen and shear controlling the FRCM one. The displacement capacity was enhanced by factors of about 2.5 in flexure and 3.0 in shear, compared to typical values for unstrengthened piers.

An Innovative Active Control System for The Seismic Retrofit of a Precast R.C. Wall-Bearing Building

Seismic improvement and retrofitting of existing Italian buildings cannot always be an easy problem to solve. In fact, several traditional intervention techniques exist but each one of them is related to practical difficulties in its implementation, since they often involve invasive building activities and inconvenience to the occupants.With the aim of proposing an innovative solution to the problem, ISAAC has developed, patented and tested an active control technology, already introduced by the ISO 3010:2017 standard as Active Mass Damper (AMD). It consists in the use of inertial forces, generated by the active movement of mobile masses installed on the roof of the building, to counteract its oscillations during the seismic event and to limit the expected damage to structural and non-structural elements. This type of intervention gives the possibility of increasing the seismic and dynamic performance of the building acting only externally, quickly and without causing disturbance to residents.The system was tested with experimental tests on a shaking table at the EUCENTRE laboratories in Pavia, which allowed the validation of the technology and the development of software and best practices for FEM modelling techniques of the structural behavior considering the AMD system.The paper presents the case of application of the active control system on a 14-storey residential building with precast reinforced concrete load-bearing wall structure. After a brief description of the construction system of the building, the material investigation campaign and the dynamic identification tests carried out are illustrated. Afterwards, the design and analysis method for the retrofit intervention with AMD technology is described, highlighting the achievable seismic performance improvement.

Demonstration of Center Pivot Uniformity Evaluation and Retrofit to Improve Water Use Efficiency

Agricultural irrigation is a primary user for freshwater withdrawal. Irrigation plays an important role in crop production, as it provides the benefit of reducing the effects of prolonged dryness and erratic precipitation. Center pivot irrigation system is the most common irrigation system in agriculture. As the center pivot irrigation system ages, the system could develop a leaking joint, clogged sprinklers, and physical damage. This can cause areas of non-uniformity that can lead to under- or over-irrigated in some areas of the land, resulting in excess energy use and cost, wasting resources, and environmental impacts. Thus, it is important to evaluate the performance of a center pivot irrigation system regularly to maximize return on investments and minimize wasting resources. This study focuses on evaluating the impacts and benefits of improved center pivot irrigation distribution uniformity by performing distribution uniformity evaluations pre- and post-retrofit. This study also focused on demonstrating an unmanned aerial vehicle (UAV) to assess the performance of the center pivot irrigation system in two irrigated farmlands. The Coefficient of Uniformity (CU), Distribution Uniformity (DU), and Scheduling Coefficient (SC) were calculated based on the catch can test data. The values were utilized to evaluate water and energy savings from the improved coefficients. The team has found that replacing sprinkler packages increased the CU from 78 to 89 and the DU from 77 to 82, and reduced the SC from 1.3 to 1.2 in Field A. In Field B, replacing sprinkler packages increased the CU from 73 to 91 and the DU from 62 to 84 and reduced the SC from 1.6 to 1.2. The estimated water savings in Field A due to the reduced scheduling coefficient was approximately 151,000 liters/hectare/year, with consideration of the corn and soybean rotation field in Michigan. The estimated water savings in Field B was 608,000 liters/hectare/year. The data from this demonstration study showed the value of distribution uniformity evaluation and retrofit of irrigation systems. This information will encourage farmers and agricultural industries to consider performing more distribution uniformity evaluations, ultimately improving irrigation water use efficiency and supporting sustainable water management in agriculture.

3D numerical characterization of a dissipative connection system for retrofit of prefabricated existing RC sheds

Prefabricated industrial sheds featured a high seismic vulnerability during the 2012 Emilia earthquake (Italy). The buildings typically exhibited a rigid collapse mechanism that was a consequence of the loss of support between columns, beams and roof elements.The study presents a numerical characterization of a novel dissipative connection system (DCS) designed to improve the seismic performance of industrial sheds. The device, which is placed on the top of the columns, exploits the movement of a rigid body on a sloped surface to provide horizontal stiffness and control the lateral displacement of the beam.A 3D finite element model of the prototype is formulated in Abaqus and used to switch the backbone curve from the scaled model to the full-scale device. A parametric study is conducted to evaluate the influence of the slope of the contact surface and the coefficient of friction on the output force of the system.In the second part of the study, non-linear dynamic analyses are performed on a finite element model of a portal frame implementing, at beam-column joints, either the DCS or a pure friction connection. The results highlight the effectiveness of the DCS in controlling beam-to-column displacements, reducing shear forces on the top of columns, and limiting residual displacements that can accrue during ground motion sequences.

An enhanced system for the combined seismic and energy retrofit of masonry buildings

The Italian existing building stock is characterized by low-performance levels in terms of energy efficiency and seismic safety. The development of retrofit solutions fulfilling both targets is therefore of strong interest, as proven by a series of fiscal incentives recently approved, in Italy, to encourage the implementation of both energy and seismic intervention. Nevertheless, energy and seismic retrofitting techniques often present specific features that make it difficult to pursue both objectives. In this framework, an innovative solution is proposed, focused on the enhancement of unreinforced masonry buildings using expanded-clay blocks infill walls. Expanded-clay block walls technique has proven to provide excellent energy performance and ensure high seismic safety in new buildings. This technique's feasibility and efficiency as a retrofit solution were analysed when applied to a representative case-study building, analysed in the current condition and after the application of the retrofit system. Dynamic thermal simulations were carried out to evaluate the hygrothermal performance, showing a general decrease in the overall thermal transmittance and an improvement in the indoor thermal comfort for the retrofitted configuration. The seismic behaviour was assessed according to actual standards, showing an increased capacity of the building towards horizontal actions post-retrofit application.

Importance of HVAC System Selection in Reducing the Energy Consumption of Building Retrofits–Case Study: Office Building in London

The analysis of the holistic life cycle and energy has become more important due to the escalating energy demands in existing office stock. HVAC system retrofits to save energy are an outstanding way when compared to envelope improvements. The study proposes a parametric workflow to analyze and reduce energy, carbon and cost in HVAC retrofits. Based on the workflow, the energy demands of an existing office building were gathered using energy modelling software. The results then were calibrated with the building's energy data. Using the equation-based modelling workflow, HVAC plant side systems were simulated parametrically to calculate energy, carbon and cost. In total, 5184 iterations of 10 interventions were tested. It was found that heating plant type and heat recovery were the prominent savings inputs in the case study. The study presented a comprehensive approach to the HVAC system retrofit of existing buildings, which uses real energy data calibration, verifiable, and parametric methods.

Evaluation of mixing capability improvement of a circular water storage tank by nozzle system retrofit using computational fluid dynamics

ABSTRACT Studies on the mixing of water storage tanks typically consider vertically oriented nozzles, however, not much consideration was given for horizontally oriented nozzles. This paper aims to employ computational fluid dynamics (CFD) to study the influence of horizontal nozzle configurations on the mixing within a typical circular water storage tank. The impact of the outlet locations and water depths on mixing time was also investigated. The results from the numerical simulations show that nozzle configuration with horizontal distance between the sets of nozzles of 0.71 tank diameters apart performed the best. An outlet located in the center of the circular storage tank encourages near-floor lateral movement of fluid and improved the velocity uniformity across the water column. The water depth was found to have a non-monotonic relationship with the mixing time and the depth to diameter ratio of 0.4 provides the best mixing in the studied tank with nozzles.

Asset management-based resilience index formulation for pavements via principal components analysis

PurposeThis paper extends the authors’ previous research work investigating resilience for municipal infrastructure from an asset management perspective. Therefore, this paper aims to formulate a pavement resilience index while incorporating asset management and the associated resilience indicators from the authors’ previous research work.Design/methodology/approachThis paper introduces a set of holistic-based key indicators that reflect municipal infrastructure resiliency. Thenceforth, the indicators were integrated using the weighted sum mean method to form the proposed resilience index. Resilience indicators weights were determined using principal components analysis (PCA) via IBM SPSS®. The developed framework for the PCA was built based on an optimization model output to generate the required weights for the desired resilience index. The output optimization data were adjusted using the standardization method before performing PCA.FindingsThis paper offers a mathematical approach to generating a resilience index for municipal infrastructure. The statistical tests conducted throughout the study showed a high significance level. Therefore, using PCA was proper for the resilience indicators data. The proposed framework is beneficial for asset management experts, where introducing the proposed index will provide ease of use to decision-makers regarding pavement network maintenance planning.Research limitations/implicationsThe resilience indicators used need to be updated beyond what is mentioned in this paper to include asset redundancy and structural asset capacity. Using clustering as a validation tool is an excellent opportunity for other researchers to examine the resilience index for each pavement corridor individually pertaining to the resulting clusters.Originality/valueThis paper provides a unique example of integrating resilience and asset management concepts and serves as a vital step toward a comprehensive integration approach between the two concepts. The used PCA framework offers dynamic resilience indicators weights and, therefore, a dynamic resilience index. Resiliency is a dynamic feature for infrastructure systems. It differs during their life cycle with the change in maintenance and rehabilitation plans, systems retrofit and the occurring disruptive events throughout their life cycle. Therefore, the PCA technique was the preferred method used where it is data-based oriented and eliminates the subjectivity while driving indicators weights.

A Retrofit Strategy for Real-Time Monitoring of Building Electrical Circuits Based on the SmartLVGrid Metamodel

The Internet of things (IoT) paradigm promotes the emergence of solutions to enable energy-management strategies. However, these solutions may favor the disposal or replacement of outdated but still necessary systems. Thus, a proposal that advocates the retrofit of pre-existing systems would be an alternative to implement energy monitoring. In this sense, this work presents a strategy for monitoring electrical parameters in real time by using IoT solutions, cloud-resident applications, and retrofitting of legacy building electrical systems. In this implementation, we adapted the SmartLVGrid metamodel to systematize the insertion of remote monitoring resources in low-voltage circuits. For this, we developed embedded platforms for monitoring the circuits of a building electrical panel and application for visualization and data storage in the cloud. With this, remote monitoring of the consumer unit was carried out in relation to energy demand, power factor, and events of variations of electrical parameters in the circuits of the legacy distribution board. We also carried out a case study with the proposed system, identifying events of excess demand in the consumer unit, mitigating the individual contribution of the installation circuits in this process. Therefore, our proposal presents an alternative to enable energy management and maximum use of existing resources.

An Efficient Method for Optimizing HPC-FRP Retrofit Systems of Flexural Strengthened One-Way Continuous Slabs Based on ACI 440.2R.

An innovative retrofit system consisting of fiber-reinforced polymers (FRP) and high-performance concrete (HPC) considering the difficulty of the accessibility and installation of FRP on the underside of reinforced concrete (RC) slabs was found to be efficient in the flexural strengthening of existing RC slabs. It is important to note that continuous slabs using the FRP-HPC retrofit systems are less effective in exploiting FRP tensile strength and can cause sudden failure once excessively enhanced flexural strength exceeds shear strength. A design method to ensure ductile failure mode was also proposed for strengthened continuous RC slabs in the previous literature. Thus, it is necessary to optimize retrofit systems in terms of mechanical performance aspects to improve the efficiency of retrofitted slabs in serviceability. This study proposes a design method for optimizing the strength of materials and inducing ductile failure of continuous slab retrofitting FRP-HPC systems. The proposed approach demonstrated its effectiveness for strengthening a continuous RC slab with various FRP-HPC retrofit systems through a case study. The results show that the design factored load in the serviceability limit state does not change appreciably from a decrease in carbon fiber-reinforced polymers (CFRP) of 38%; the design factored load decreased only by 9% and the ultimate failure load by 13% while reducing CFRP by 20% and HPC by 25%.

Reinforced concrete beams externally strengthened by CFRP rods with steel plate, anchorage bolts, and concrete jacketing

This study proposed a new scheme for the retrofitting of Reinforced Concrete (RC) beams using Carbon Fiber Reinforced (CFRP) rods restrained using steel plates and anchorage bolts called the mechanical anchorage system (MAS). This system also employed an external concrete jacket to cover the MAS and CFRP rods. The performance of the proposed technique was experimentally assessed using the four-point flexural testing of retrofitted beams under incremental cyclic load using a dynamic actuator. A total of eight beams were cast and tested in different configurations to determine the effectiveness of the design parameters including the number of CFRP rods, the contribution of MAS, and concrete jacketing (CJ) in terms of load capacity, cracking, failure mode, and ductility. The results revealed that the efficiency of the proposed retrofitting system was achieved by increasing the load capacity of retrofitted beams and preventing the premature debonding failure of CFRP rods. Although de-bonding can occur on the surface between the old and new concrete, the utilization of a perfect adhesive epoxy on the concrete contact surface led to sufficient bonding between the two surfaces. Therefore, overall, the proposed strengthening technique can be considered a reliable method to enhance the performance of RC beams without the risk of de-bonding.

BIM-aided large-scale group decision support: Optimization of the retrofit strategy for existing buildings

With the rapid development of the construction industry, buildings have become the single largest consumer of energy in the world. The retrofitting of existing buildings offers an excellent opportunity to reduce global energy consumption and promote sustainable development. As the retrofit strategy determines the success of the retrofitting process, this paper proposes a decision support framework for retrofitting that integrates the building information modeling (BIM) with large-scale group decision-making, which is a new application of digital technology to the retrofitting of existing buildings. Within this framework, BIM provides massive geometric and non-geometric data for the multi-criteria large-scale group decision-making process. Taking into account the needs of various stakeholder groups and sustainable principle, we establish a comprehensive and innovative evaluation index system for community retrofitting, and use the group best-worst method to determine the criteria weights. The stakeholers evaluate alternative retrofit strategies through distribution linguistic preferences, with a consistency-driven optimization model used to personalize the stakeholers’ numerical evaluation scales. Through k-means clustering and the consensus-reaching process, combined with objective data from BIM, we obtain the ranking of the alternative strategies. Finally, we apply the abovementioned decision support framework to the retrofitting of the Suifeng Garden community in China to demonstrate the rationality and superiority of the proposed approach.

Refurbishment of Existing Building toward a Surplus Energy Building in Jordan

Introduction: Energy consumption rates in residential buildings rely heavily on the modularity of construction. Methods: Traditional building models in Jordan are considered the dominant models in which modern technology is not taken into account in building in order to reduce energy consumption. Recently, interest in modern construction schemes has appeared in Jordan with the intention of saving energy because of its high costs. The objective of this research is to help convert a building in Amman into one that generates more energy than it needs in what is known as surplus energy buildings.Several retrofit systems were considered for this purpose, including insulation, water heating, lighting, air recycling, and photovoltaic systems. This work was handled through a detailed calculation based on the basic fundamental of each subsystem used in the refurbishment process. using refurbishing techniques, the estimated payback period was found 5.08 years for all integrated systems. Results: The work started with a closer look at the reality of energy use in the residential sector based on the reports provided by the Ministry of Energy and the National Electricity and Energy Company. Conclusion: Afterward, the study sample was decided to be home in the city of Amman - Jordan, then several suggestions for improving and verifying ways to conserve energy were discussed.

Seismic Energy Upgrading of an Existing Brick Masonry Building by a Cold-Formed Steel Envelope System

In recent years, new solutions have been studied in order to intervene on existing buildings made of load-bearing masonry or reinforced concrete, both from the seismic point of view and the energy one. In recent years, novel modern techniques using lightweight steel profiles made of steel or aluminium alloys, suitably coupled with heat-insulating panels, have been proposed for requalification of existing building stock. In this paper, the Resisto 5.9 system designed by the Progetto Sisma S.r.l. company was studied and applied as a retrofit system of an existing masonry building. First, this new system for seismic energy requalification of the build-up was presented, describing the basic components and the mounting phases. Subsequently, it has applied to a case study building made of full-brick masonry located in the municipality of Casalecchio di Reno, on the outskirts of Bologna in Northern Italy. Finally, the used coating system was designed for the examined building together with other seismic interventions applied to horizontal structures and foundations. The seismic benefits deriving from using the proposed envelope system and other seismic interventions were proved from the seismic viewpoint by linear dynamic and non-linear static analyses using the TreMuri analysis software. From modal analysis it was seen that the dynamic behaviour of the building with Resisto 5.9 is improved, with an increase of the participating mass (68% instead of 49% of the bare building) of the second mode in the longitudinal direction. Moreover, from pushover analysis it was noticed that the seismic safety factor has passed from 0.51 to 1.05 in the X-direction and from 0.78 to 1.27 in the Y-direction. In conclusion, it was demonstrated that Resisto 5.9, together with all the other planned interventions, is able to accomplish the seismic retrofitting of the studied building.

The Effects of Bond-Slip Laws on the Debonding Failure and Behavior of Flexural Strengthened RC Slabs in Hybrid FRP Retrofit Systems.

The hybrid retrofit system using FRP and concrete overlay applied on the top of slabs has proven effective in strengthening and overcoming logistical constraints, compared with conventional strengthening techniques using externally bonded composite materials to the underside of the slabs. Nevertheless, the performance of retrofitted slabs is governed by debonding failure due to the low bond strength between CFRP and concrete overlay. Thus, this study investigates the behavior of flexural strengthened slabs with FRP retrofit systems and the effect of bond-slip laws on debonding failure. Firstly, two full-scale RC slabs with and without a retrofit system were tested in a four-point bending setup as the control specimens. Then, the same retrofitted slab was simulated by utilizing the commercial program ABAQUS. A sensitivity analysis was conducted to consider the influence of bond-slip laws to predict the failure mechanism of the retrofitted slabs based on load-deflection relationships. The results showed that the strengthened slab enhanced the load-carrying capacity by 59%, stiffness by 111%, and toughness by 29%. The initial stiffness of 0.1K0 and maximum shear stress of 0.13τmax, compared with the corresponding values of Neubauer's and Rostasy's bond-slip law, can be used to simulate the global response of the retrofitted slab validated by experiment results.

Experimental analysis on reinforced concrete beams enlarged with ferrocement retrofit system

Experimental analysis on reinforced concrete beams enlarged with ferrocement retrofit system