Retrofit Solutions Research Articles

Online characterization of solid biofuels via pocket sized and low-cost near-infrared devices during small-scale boiler operation: Model development, evaluation and application tests

Optimal boiler settings are required to ensure high efficiencies during biomass combustion and to enable compliance with emission thresholds despite lower and fluctuating fuel qualities. Thus, an affordable and simple near-infrared retrofit solution for online fuel characterization was developed and tested to allow for automatic adjustments of the boiler control with respect to actual characteristics of the used fuel assortments. To this end, a low-cost online near-infrared spectroscopy device (SCiO™, Consumer Physics), with investment costs less than 1000 € was employed. Partial least squares regression models based on 13 different spectral preprocessing methods for the prediction of moisture, ash, nitrogen and potassium content, as well as the net calorific value were developed and validated in the lab. The resulting model predictions of biomass properties agree in terms of root mean square error and R2 with the reference values obtained from laboratory analysis. Furthermore, a near-infrared retrofit solution was successfully coupled to the fuel feeding system of a commercially available small-scale biomass boiler for automatic and continuous operation. The automatically predicted values obtained by the near-infrared retrofit solution during continuous boiler operation are stable while the predicted values for moisture and net calorific value are in the range of the reference values obtained from the laboratory analysis but with a small offset. Non-reliable results were obtained for ash and nitrogen content.

Risk-based retrofitting analysis employing the carbon intensity indicator

The study employs a risk-based approach for ship propulsion system retrofitting analysis to reduce CO2 emissions and enhancing cost efficiency. The analysis is based on historical data from the EU-MRV database collected for ships operating in the Black Sea using the Carbon Intensity Indicator (CII). Based on the Attained CII/Required CII rate, four levels are identified as critical thresholds and analysed by the Weibull probabilistic model. Additionally, a cost-benefit analysis is performed, accounting for discounted costs related to the initially installed propulsion system supplied by Very Low Sulphur Fuel Oil (VLSFO) and the retrofitted system on Liquefied Natural Gas (LNG), including the cost of the fuel and taxes related to CO2, insurance, maintenance, interest rate, depreciation, resale, and loss of opportunity, conditional on the retrofitting consequences. The cost-benefit and associated risk-based retrofitting analyses are employed to identify the most appropriate retrofitting solution. The Weibull probabilistic model accounts for the enormous uncertainty and variation of the input parameters. The study demonstrates how the data can address critical issues such as condition-based time and the best ship age for retrofitting, accounting for the associated risk. An effort is made to define when to perform retrofitting, reaching a specific ship age accounting for the time needed for retrofitting.

Does window/door opening behaviour during summer affect the bedroom environment and sleep quality in a high-density sub-tropical city

To investigate the effects of window and/or door opening on sleep quality, a two-week field intervention study was performed in 50 bedrooms in the summer in a high-density city (Shanghai). Each participant slept as they did normally in their own bedroom during the first week and changed the state of windows or doors from open to closed or vice versa in the second week. Their bedroom environment and sleep quality were objectively measured. Available data from 256 person-nights in which the intervention was effective were used for analysis of window or door manipulation. The indoor carbon dioxide (CO2) concentrations were lower and the air temperatures and PM2.5 concentrations were higher when windows were open. The perceived air freshness and noise intensity were both higher and the duration of REM-sleep (Rapid Eye Movement sleep) was lower in this condition. No significant differences were found in other sleep quality indexes. These results suggest that in a high-density city, the increased indoor temperature, PM2.5 concentration as well as noise caused by opening windows may disturb sleep and offset the positive effects of improving the ventilation. Thus, window opening should not be recommended as a universal way of achieving bedroom ventilation to promote sleep. Affordable retrofit solutions for bedroom ventilation should take these aspects into account.

A Systematic Analysis of Phase Change Material and Optically Advanced Roof Coatings Integration for Athenian Climatic Conditions

Energy retrofit solutions that concern a building’s roof structure play a significant role in the enhancement of a building’s thermal behaviour. This study investigates the integration of phase change materials (PCMs) with cool coatings (CCs) or thermochromic coatings (TCCs), namely, a PCM roof, a PCM-CC roof, and a PCM-TCC roof, as alternative and novel tactics for the simultaneous control of solar heat transfer and solar heat reflection. An energy simulation analysis with the DesignBuilder tool is conducted for a one-story residence and the climatic conditions of Athens. The simulation results indicate that, compared to the existing concrete roof construction, the PCM roof, PCM-CC, and PCM-TCC roof systems demonstrate energy savings that reach up to 13.55%, 16.04%, and 21.70%, respectively. The systematic analysis reveals that the increase in PCM’s thickness leads to an increase in the total electricity savings of the buildings, but in the case of PCM-CC and PCM-TCC roof systems, they merely effect the cooling thermal loads. The mean phase transition temperature that favours the cumulative electricity savings is 28 °C in the case of PCM and PCM-TCC roof systems and 35 °C in the case of PCM-CC roof systems. The methodology of this study allows the design of efficient, integrated roof systems with advanced thermal and optical properties as energy retrofit solutions for Mediterranean climatic conditions.

Analysis of the seismic vulnerability and innovative retrofit solutions of cavity brickwork walls

This paper offers the results of an experimental investigation aimed at assessing the seismic vulnerability of a type of cavity wall, with a brief discussion of the advantages of this form of construction. Cavity walls were mainly designed to carry vertical loads and to improve the thermal behaviour of the building envelope: these are made of two single-wythe walls (typically using low-perforated bricks) with a cavity filled with a polystyrene panel. Cavity walls often exhibit poor seismic performance. A total of 12 full-size cavity-wall panels were tested in this experimental programme at the laboratory, by conducting shear and bending tests aimed at studying the in-plane and out-of-plane structural responses under simulated seismic actions. In addition, different retrofit solutions were studied and used to reinforce the cavity-wall panels: this included the traditional method to tie the wall leaves with steel connectors, an innovative method made of GFRP (Glass Fiber Reinforced Polymers) rods, and a mortar coating reinforced with a composite grid, known as FRCM (Fiber Reinforced Cementitious Matrix). It was found that the lateral bending-capacity of the panels reinforced with the GFRP rods and a FRCM coating greatly increased over that of the control unreinforced specimens. The proposed reinforced method was able to provide some seismic resisting capacity to the cavity walls, especially against bending and out-of-plane loading, in a more effective way than the traditional method of steel ties.

Structural performance study and improvement of Artemio Franchi Stadium in Florence

Artemio Franchi Stadium in Florence is the first world-famous work by Pier Luigi Nervi, and is celebrated as a masterpiece of the Rationalist movement. In view of this, it has been declared a work of cultural and historical interest by the Italian Ministry for Cultural Heritage and Activities, with several specific preservation restrictions on its most distinguishing structural and architectural elements. With a view to the recently planned restyling and modernization works, a diagnostic field survey and testing campaign, and a static and seismic performance assessment study of the Stadium were commissioned by the Municipality of Florence. Furthermore, a retrofit design respectful of the architectural preservation requirements was requested for its reinforced concrete structure. The contents of the diagnostic and assessment study, as well as of the retrofit design, are presented in this paper. The results of the structural analyses, carried out by means of a detailed finite element model calibrated on the field survey and testing data, show slightly unsafe static conditions in less than 10% of the beams and columns constituting the bleacher sloped frames, and diffused unsafe conditions under seismic action scaled at the Basic Design Earthquake level. The proposed retrofit solution consists in incorporating dissipative braces equipped with fluid viscous spring-dampers in several spans oriented in orthogonal direction to the bleacher frames, and installing fluid viscous pure dampers across the majority of the technical separation gaps between adjacent bleacher blocks, so as to prevent their mutual pounding. The results of the analyses in retrofitted conditions highlight a transition to safe conditions for more than half of the unsafe members, and a remarkable reduction of the demand/capacity ratios in the remaining members. Safe stress states can be reached in the latter by means of simple additional local strengthening interventions. This substantial improvement of seismic performance is achieved with a minimal visual and functional impact on the existing structures, as prescribed by the imposed preservation restrictions.

A modelling framework for modern heritage buildings energy simulation

The latest European polices highlight the urgent need to rehabilitate the existing building stock, responsible for 40 % of the EU's total energy consumption. In this process, a key role is played by thermal simulations, assessing the effective energy performances. However, significant discrepancies between real and simulated consumptions are frequently outlined. Inaccurate results are particularly dangerous for modern buildings, which, rarely protected, are often altered by invasive retrofitting solutions, with little regard for their heritage and cultural value. This paper introduces a comprehensive framework for the building energy simulation, ensuring the necessary model credibility. It consists of dynamic modelling, calibration and validation, enhancing the usefulness of the final results. A validated model is in fact the premise to propose a well-balanced retrofitting scenario, improving the current energy performances, reducing the operational costs, and preserving the historical values of existing buildings. As operative case-study, Chauderon administrative building in Lausanne (1969–1974), designed by the Atelier AAA in collaboration with Jean Prouvé, has been selected. Today, the complex is well-preserved in its original materiality and represents an iconic example of the modern aesthetics, with an expressed need for retrofitting. Following the proposed framework, a reliable model in WUFIplus has been created and validated according to ASHRAE 14, allowing to reliably test the efficacy of future retrofitting scenarios. The final aim of this process is to minimize the risk of inappropriate interventions. For high-quality or recognized post-World War II building stock, the use of a calibrated and validated model is justified and recommended over the static or simplified modelling approaches still commonly employed today.

Enabling residential heating decarbonization through hydronic low-temperature thermal distribution using forced-air assistive devices

Space heating represents approximately one-tenth of the United States’ energy use and has a breadth of potential for emission reduction. An element of space heating, hydronic heat distribution methods, use water supply temperatures up to 82.2 °C (180 °F). However, this operating temperature can be incompatible with high-efficiency heat generation systems, which typically provide heating temperatures of up to 60 °C (140 °F). In this work, a low-cost retrofit solution is developed using experimentally validated computational tools by incorporating an airflow distributor that preferentially directs the airflow from a fan to enhance heat transfer over the finned-tube heat exchanger found in conventional baseboards. The same heat output of traditional baseboard heat distribution systems operating at higher water supply temperatures (71.1 – 82.2 °C) can also be achieved at lower temperatures (≤ 60 °C). Specifically, results indicate that the technology can produce more than a 46.7% improvement in the heat transfer output at temperatures as low as 60 °C (140 °F), effectively matching the same output range achieved by 71.1 – 82.2 °C (160–180 °F) water supply temperatures. An important benefit of this solution is that it utilizes the existing infrastructure as opposed to requiring the replacement of the entire distribution system. Additionally, this technology enables existing building infrastructure to be coupled with newer, high-efficiency heating systems such as condensing boilers, solar-thermal systems, and geothermal/air-to-water heat pumps that may produce lower water supply temperatures (60 °C). A geospatially resolved techno-economic and environmental analysis is completed and presented to further understand the equivalent carbon footprint of enabling higher efficiency heat generation systems with the improved efficiency heat distribution system disclosed. Using 2021 grid-average emission factors, an emission reduction of up to a 67.5% decrease (2658 kgCO2/yr) for a single-family home, depending on state and climate region, could be realized by replacing a traditional natural gas-fired boiler with an air-to-water heat pump coupled to the same high-temperature heat distribution system along with the low-cost retrofit solution. A complete CO2 emission reduction of 6688 kgCO2/yr, depending on state and climate region, could be realized if all electricity is further renewably sourced. Thus, this study provides a possible pathway towards enabling the reduction of operational emissions in space heating.

Comparative evaluation of seismic performance and environmental impact of traditional and dissipation-based retrofitting solutions for precast structures

Seismic rehabilitation is crucial to extend the nominal service life and help reduce the seismic losses of reinforced concrete precast industrial buildings. Along with traditional retrofitting techniques, the latest decades are witnessing a growing use of innovative solutions, the latter including devices that can dissipate the ingoing seismic energy and are characterised by the replaceability after a seismic event. The goal of this work is to compare two retrofitting solutions, respectively of traditional and innovative type, in terms of structural performance enhancement and their own life cycle environmental impact. A case study single-storey precast industrial building was retrofitted firstly adopting a traditional solution with concrete jacketing of columns, and then using two innovative energy dissipation devices, namely a friction rotation damper for beam-to-column connections and a bracing system with dissipative sacrificial elements. A comparative analysis of the seismic response of the structure in its as-built and post-retrofit configurations was undertaken, subjecting three 3D numerical models created in OpenSees to nonlinear static and dynamic analyses in both the main directions. Subsequently, two environmental impact metrics were adopted to compare the life cycle environmental impact of both the traditional and innovative retrofitting solutions, confirming that the one encompassing the dissipation-based devices is expected to be more environment-friendly, under a life cycle perspective, than the traditional concrete jacketing.

MEVO: A Metamodel-Based Evolutionary Optimizer for Building Energy Optimization

A deep energy retrofit of building envelopes is a vital strategy to reduce final energy use in existing buildings towards their net-zero emissions performance. Building energy modeling is a reliable technique that provides a pathway to analyze and optimize various energy-efficient building envelope measures. However, conventional optimization analyses are time-consuming and computationally expensive, especially for complex buildings and many optimization parameters. Therefore, this paper proposed a novel optimization algorithm, MEVO (metamodel-based evolutionary optimizer), developed to efficiently identify optimal retrofit solutions for building envelopes while minimizing the need for extensive simulations. The key innovation of MEVO lies in its integration of evolutionary techniques with design-of-computer experiments, machine learning, and metaheuristic optimization. This approach continuously refined a machine learning model through metaheuristic optimization, crossover, and mutation operations. Comparative assessments were conducted against four alternative metaheuristic algorithms and Bayesian optimization, demonstrating MEVO’s effectiveness in reliably finding the best solution within a reduced computation time. A hypothesis test revealed that the proposed algorithm is significantly better than Bayesian optimization in finding the best cost values. Regarding computation time, the proposed algorithm is 4–7 times faster than the particle swarm optimization algorithm and has a similar computational speed as Bayesian Optimization.

Repair, flexural upgrading and seismic retrofit of RC columns with reinforced FRCC light jacket

An innovative repair, flexural upgrading and seismic retrofit solution consisting of a reinforced light jacket (i.e., 3–4 cm) made of Fibre Reinforced Cement Composites, FRCC coupled with a High-Performance steel reinforcement is proposed for existing reinforced concrete (RC) columns. The proposed solution consists in a FRCC light jacketing coupled with a High-Performance steel reinforcement that works both as anchorage system for the jacket and as additional transverse reinforcement (Reinforced FRCC light jacketing or RFRCC). The goal of the solution is to improve the columns resistance against the migration of aggressive agents and at the same time to increase its flexural capacity. The potential of the proposed solution is demonstrated on 6 full-scale RC columns experimentally tested under quasi-static cyclic loading. The RC columns under investigation are subjected to a seismic pre-damage before the application of the RFRCC jacket. Square and rectangular columns with smooth and deformed rebars are tested to assess the feasibility of the technique for the repair and flexural strengthening of existing deficient RC columns. The experimental results attest the high potential of the proposed technique in recovering and enhancing the flexural capacity, ductility and energy dissipation of seismically pre-damaged RC columns.

Integrated seismic-energy retrofit systems for preventing failure of a historical RC school building: Comparison among metal lightweight exoskeleton solutions

Italian built heritage is highly vulnerable due to old public and private buildings designed without recent seismic and energy regulations. In particular, school buildings represent a critical typology that should be retrofitted to guarantee safety and comfort to the users. In this framework, interventions from building outside able to avoid interruption of school activities should be required. A solution to solve this issue can be found in the retrofit solution with exoskeletons. In this scenario, the paper presents the comparison among three similar solutions of metal lightweight exoskeletons for the integrated seismic-energy retrofit of a RC school building assumed as a case study. The RC structure of the school is firstly modelled with a finite element software and then subjected to pushover analysis before and after retrofit interventions to assess the benefit of each exoskeleton solution. The comparisons among intervention techniques are made in terms of the seismic safety index (ζE) provided by the Italian technical standard. The results show the more or less efficacy of the different inspected systems, even if integrative local interventions are needed to reach the minimum safety index (0.60) required for school buildings. As a conclusion, these novel light metal exoskeletons have proven to be efficient retrofitting systems for residential buildings or even for school buildings with regular façades and plan layouts.

A Novel FRP Retrofit Solution for Improved Local and Global Seismic Performance of RC Buildings: Development of Fragility Curves and Comparative Cost-Benefit Analyses

ABSTRACT This paper evaluates the effectiveness of a novel capacity-design based retrofit for improving both the local and global behaviour of existing reinforced concrete buildings using fibre-reinforced polymers. The approach was previously tested on beam-column joints and is here extended to the building level. A new fibre-element model for the global retrofit is proposed and validated against full-scale experiments. Non-linear push-over analyses confirm the adequacy of the retrofit and fragility analyses are used to compare it to a simpler local retrofit. Finally, cost-benefit analyses for three levels of seismicity highlight the cost-effectiveness of the global retrofit for moderate to high seismicity.

Optimum fenestration characteristics in mediterranean Tunisian context: An energetic, economic and environmental (EEE) study

This paper aims to investigate the energy performance of several techniques integrated into the fenestration system of an office building. The first step was to compare the simulated and real energy consumption of a case study of an office building located in Tunis City. In a second step, the study explores the impact of a glazing retrofit solutions on annual energy saving. To determine the possible energy savings for the existing office building in various climatic zones, we performed several simulations, using the Design Builder software.For these zones, the optimum window-to-wall-ratio (WWR), ensuring a compromise between daylighting and energy consumption, is found to be 40%. Then, for the chosen WWR, we evaluated a retrofit process involving existing commercial technologies such as double-glazed insulated windows, as well as innovative technologies consisting of intelligent coating, in addition to passive techniques including several shading concepts.It is found that, the double-glazed window with outside reveal depth of 20 cm equipped with both low-emissivity (LoE) and electrochromic (EC) coatings ensures the lowest annual energy consumption. Besides, energy savings depends on the climate zone; it reaches 23% in hot climates (ZT3) and almost 20% in cold (ZT1) and temperate climates (ZT2). The possibility of using electrochromic coating was excluded following the economic study because of its exorbitant cost. In fact, this type of renovation can lead to payback periods of up to 74 years for the cases treated.The optimized window designs consist in using a double-glazing window with a LoE coating, an outside reveal depth of 20 cm, and as a shading system (Overhang). These designs save 8 to 20% of energy and reduce CO2 emissions by 6 to 10 kg CO2/m2 per year, with a payback period of less than 6 years depending on the climatic zone.

Full-scale testing of masonry-infilled RC frames retrofitted with cross-laminated timber panels

This paper presents the results from an experimental study on an innovative timber-based seismic retrofit solution for existing reinforced concrete (RC) buildings. The intervention aims at enhancing the overall seismic resistance of RC framed structures with a light, cost-effective, sustainable, and reversible approach, allowing possible integration with energy efficiency upgrades. The retrofit technique relies on cross-laminated timber (CLT) panels mechanically connected through steel fasteners to the RC frame. This strengthening technique is investigated experimentally for the first time in this paper. The study examines two intervention configurations with different degrees of invasiveness: the first (RC-TP) involves replacing the existing masonry infill wall with a CLT panel, whereas the latter (RC-TPext) consists in applying the panel to the outer face of the frame. Both retrofit configurations were assessed experimentally through cyclic quasi-static in-plane tests on full-scale single-storey, single-bay RC frames. The frames were identical in geometry and characterised by poor mechanical material properties and steel reinforcement details, promoting the development of a strong-beam-weak-column mechanism. The experiments comprised tests on four specimens: a non-retrofitted masonry-infilled frame employed as a reference specimen and three frames strengthened with CLT panels as infills or externally connected retrofitting elements. The paper presents construction details of the strengthening interventions, demonstrates a step-by-step application procedure, and summarises the main observations from the tests, illustrating the evolution of structural damage, the ultimate failure mode, and the cyclic hysteretic response of the specimens. The experiments showed promising results, proving that both retrofit configurations improved the seismic behaviour of the RC frames considerably. Specifically, the RC-TP and RC-TPext retrofit interventions increased the lateral strength of the reference frame by approximately 169% and 104%, respectively. At the same time, both configurations prevented the shear collapse of the columns.

Detailed 3D FE modeling approach for 2D and 3D beam-column joints retrofitted with fully fastened haunch retrofit solution including anchor behavior

Fully fastened haunch retrofit solution (FFHRS) is a low-invasive method for seismic retrofitting of substandard beam-column joints. The method is quite effective provided a good performance of the anchors used for connecting the haunch elements and structural members is ensured. Therefore, to assess the performance of the joints retrofitted with FFHRS, realistic modeling of anchors connecting haunch elements to the joint members is essential. The paper presents a new numerical modeling approach for detailed 3D finite element analysis of substandard beam-column joints retrofitted with FFHRS, where bonded anchors are used to connect the haunch elements to structural members. The model includes detailed and realistic modeling of concrete, reinforcement, bond, haunch elements and anchors. A special focus is laid on the detailed modeling of anchor behavior. The model is validated against two experiments reported in the literature, by comparing the complete performance obtained in the tests and analysis in terms of load–displacement response, failure modes and forces in the haunch elements. The validated model is used to carry out parametric studies to investigate the performance of the single haunch retrofit solution and the performance of FFHRS as well as the efficacy of FFHRS in a 3D beam-column joint with transverse beams and slab.

Decision-making approaches for optimal seismic/energy integrated retrofitting of existing buildings

Given the ambitious targets of carbon emission reduction set for the very near future, it is now expected that retrofitting operations on existing buildings aim both at reducing their operational energy consumption and at improving their seismic performance. Indeed, it is now well acknowledged that, if a sole energy efficiency upgrade is provided to a given building, in case of an earthquake occurrence, double economic and environmental losses will be experienced due to both the lost investment for energy retrofitting and the repair and retrofitting activities for post-earthquake damage. Moreover, social losses may also be experienced in terms of casualties, injured or homeless due to the seismic and structural deficiencies of the existing structure. To aid thus the process of a coupled seismic/energy renovation of the existing building stock, several multi-criteria decision-making (MCDM) approaches have been developed for the identification of optimal retrofitting solutions for buildings. Such procedures typically consider a range of economic, social, technical, and, more recently, environmental aspects that are assumed to be of interest to decision makers (e.g., installation cost, duration of works, architectural impact, need for specialised workers, etc.). The present study demonstrates the application to a case-study school building of two different MCDM approaches, which account for seismic vulnerability and energy efficiency, as well as related environmental impacts of buildings. The main differences between the two procedures are explored in terms of considered decision-making parameters and corresponding weights, rankings of retrofitting options and identification of the optimal retrofitting strategies.

Rapid Prestressed Concrete Retrofit with Prestressed Mechanically-Fastened Fiber-Reinforced Polymer: Field Performance and Observation for a Deteriorated Prestressed Concrete Bridge

This paper presents repairs to rural bridges in North Carolina that deteriorated as a result variously of aging, overweight traffic, and exposure to salts and sulfates. The prestressed concrete C-channel superstructures exhibited prestressing strand loss and displayed significant concrete spalling, with one structure having to be closed to traffic after a routine inspection. Analysis conducted using the American Association of State Highway and Transportations Officials (AASHTO) bridge load rating criteria concluded that repair techniques which strengthen deteriorated flexural elements without also restoring lost prestressing forces are insufficient to maintain load ratings in C-channel structures with heavily damaged prestressing tendons. A prestressed mechanically-fastened fiber-reinforced polymer (MF-FRP) retrofit solution was developed and successfully installed on three structures by the authors and North Carolina Department of Transportation maintenance crews. The most extensive of these three repairs is presented here in detail. The field applications and associated analysis show the temporary MF-FRP repair system is capable of restoring lost prestressing forces, allowing original inventory and operating ratings to remain in place until a permanent superstructure replacement can be scheduled. The most heavily repaired bridge remains in service after 23 months, its performance demonstrated by long-term monitoring data. As currently implemented, the MF-FRP repair is a viable temporary solution for maintaining traffic on a degraded structure while a replacement structure is designed, programmed, and implemented. Efforts to expand the MF-FRP repair into a longer-term solution are underway.

Topology optimization of thermally activated building system in high-rise building

The building sector accounts for nearly 1/3 of global energy end-use and associated carbon emissions. Fulfilling buildings' thermal demand in an efficient way is critical for decarbonizing the building sector. Therefore, this paper introduces the thermally activated building system (TABS) as an energy retrofit solution. A TABS floor-by-floor return water temperature control approach is proposed to reduce buildings' energy use and carbon emissions. The approach includes the topology optimization of TABS and flow control. The bypass pipe connections of the TABS to each floor, namely, the floor-by-floor pipe network topology, have been optimized by using genetic algorithms to achieve the lowest total cost. A case study of a high-rise building located in Beijing demonstrates that the proposed approach can improve the system's energy efficiency compared to the conventional TABS without optimization. The reduction of energy cost can be up to 11.21% with a 13.53% annual emission reduction. In general, the proposed TABS floor-by-floor return water temperature control approach can significantly improve the building efficiency comprehensively, therefore can be considered as a promising energy retrofit solution for the decarbonization of high-rise buildings.

A RETROFIT SOLUTION FOR UNCODED STEEL RAFTER TO CONCRETE RING BEAM CONNECTIONS

Some building contractors in the Caribbean have been constructing non-coded steel rafter to concrete ring beam connections on low budget residential buildings. These connections may resist failure under normal loading conditions, but critical connections fail under moderate to high loads resulting in partial or full dislodgement of the roof. In this study, the performance of non-coded steel rafter to concrete ring beam designs were analyzed in a finite element program and a retrofit solution for the failed uncoded connections were designed and modeled. Nine versions of the connection were identified and consisted of several variations including mechanically anchoring the rebar to the rafter without welds, using one and two rebars, varying the rebar embedment depth and using 90 degree hooks and straight rebars. A standard, code-compliant, bolted-endplate connection was used as the control for the investigation. The connections were analyzed in “ABAQUS” with a bond slip and damage plasticity model. The maximum load resistances were compared with category 1 hurricane loads for the region. The load capacities of all the connections were found to be lower than the control connection but were still adequate for hurricane category 1 loads, with the exception of the connection in which the rebars were mechanically anchored to the rafter without welds. Connections with welds to the top flange of the rafter were less stiff, experienced larger rafter displacements, inflicted less damage on the concrete ring beam, and required less rebar embedment to prevent pull out failure than the connections to the bottom flange.