Retrofit Method Research Articles

Flexural retrofit of existing reinforced concrete structural walls with various boundary element details under cyclic loading

A recent regulation in Korea allows the rehabilitation of aging apartment buildings, with vertical extensions up to three floors. To satisfy the increased flexural strength requirement, a method that places vertical reinforcements and re-casts concrete after crushing the boundary elements is proposed. In this study evaluates the flexural performance of shear walls to which the boundary element retrofit method was applied. Six real-scale specimens were fabricated and reversed cyclic loading tests were performed. The experiments showed that the flexural strength increased as the vertical rebar ratio of the boundary element increased. As the development length of the post-installed rebar was reduced, the anchorage of the rebar was effective. When using shear studs to connect the existing and the retrofitted wall, the flexural strength was similar; however, the deformation due to shear was controlled. It was confirmed that a discontinuous strain distribution occurred. Based on the experimental results, a flexural design model under limited conditions was proposed, which accurately predicted the flexural strength. However, because there is a tendency to overestimate the tensile rebar strain, future studies should develop a flexural design model that can make a more accurate prediction by further analyzing the variables affecting the boundary element retrofit method.

Structural analysis and optimal retrofitting solutions for historical monument with masonry walls

Abstract ”Braila Emergency County Hospital (ECH)” historical monument represents one of the main objectives of structural rehabilitation in both Braila county and Braila city. Thus, a structural strength verification for Pavilion B, Section 2, using ETABS software was performed, in order to find optimal retrofitting (rehabilitation) solutions. This analytical procedure proved to be beneficial and absolutely necessary, due to observations regarding the spatial contribution of masonry shear walls and finally the proper establishment of capable/design efforts. Following the structural calculation, it was concluded that the best solution would be to use composite materials for retrofitting a certain number of masonry shear walls, as classical retrofitting methods proved to be more expensive and structurally inefficient. Furthermore, in the context of the COVID-19 pandemic, the solution to use composite materials is beneficial, as it would entail no personnel or patients to be evacuated during the rehabilitation works, i.e. the hospital being able to continue to operate.

Parametric Study on Fatigue Behaviour of Beam - Column Joint Retrofitted with Various Patterns of Fibre Reinforced Polymer Sheets

Shear failure of B-C joints is recognized as the primary cause of collapse of various moment-resisting frame buildings during recent earthquakes. When B-C joint subjected to huge forces during severe ground shaking and its behaviour has a very much influencing on the structure, sometimes it may Leeds to collapse of entire structure. To study the energy dissipation of B-C joint with different types and combinations of FRP sheets used to retrofit the BC joint in this study. Fiber reinforced polymer is composite material made up of polymer matrix reinforced with fibres. It is alternative method for retrofitting of structures. In this project work, a RC beam- column joint model was developed and externally wrapped with FRP sheets using ABAQUS-CAE. Then parametric study was carried out for beam-column joint retrofitted with various pattern of FRP sheets like different orientation, layers and material of fibres. Various materials of the fibres used carbon, glass and basalt. Orientation of fibres were used like 00,- 450,450,900 and combinations of CFRP&GFRP, CFRP&BFRP and GFRP&BFRP were used in this parametric study. Finally FEA analysis was compared and discussed with respect to layers and materials of fibres. Specimens with B-C joint are retrofitted with FRP and their performances are compared with corresponding un-retrofitted specimens under cyclic loading. It has been found that after retrofitted with CFRP, GFRP and BFRP the energy dissipation capacity had increases to 44.56, 46.3 and 60.58% and stiffness, ductility also increased. Key Words: Finite Element Method (FEM); Beam- column joints; Carbon fibre reinforced polymer (CFRP); Glass fibre reinforced polymer (GFRP); Basalt fibre reinforced polymer (BFRP); Strengthening.

New retrofit method to cooling capacity improvement of mechanical draft wet cooling tower group

The airflow distribution of the mechanical draft wet cooling tower group will become very uneven under crosswind conditions, and the cooling capacity of leeward towers can be seriously reduced. To strengthen the heat and mass transfer of the leeward tower and improve the cooling capacity of the tower group, a new retrofit method is proposed that removes the tower wall between the rain zone of the tower group. The airflow can enter the leeward tower from the windward tower, even flow out from the air inlet of the leeward tower under crosswind conditions, and the airflow distribution becomes more uniform in the tower group. A 3D numerical model of the mechanical cooling tower group is established and validated. The cooling capacity of the tower group is studied under variation crosswind velocities (0 m/s–12 m/s) and crosswind angles (0°–90°) by numerical calculation. The results show that the distribution of outlet water temperature in the retrofit tower group is more uniform. The retrofit tower group can increase the circulating water temperature drop of the leeward tower under the crosswind angle of 0° and 45°. Under the crosswind angle of 0°, the temperature drop of the circulating water increases 0.52 ℃ maximum and 0.31 ℃ on average. Under the crosswind angle of 45°, it increases 0.92 ℃ maximum and 0.59 ℃ on average. Under the crosswind angle of 90°, it increases 0.19 ℃ maximum and 0.09 ℃ on average.

LCA of Mortar with Calcined Clay and Limestone Filler in RC Column Retrofit

Cement manufacture contributes about 5–7% of the global carbon dioxide emission. The fastest short-term remedy is to replace parts of ordinary Portland cement (OPC) in concrete with supplementary cementitious materials (SCMs) to reduce CO2 emissions. Calcined clay and limestone filler have proven to be potential substitutes to good quality SCMs such as fly ash and slag because of their abundance, low cost, and potential reactivity to calcium hydroxide to form calcium silicate hydrates (C-S-H) which are responsible for the strength and other mechanical properties of concrete. A life cycle assessment (LCA) to evaluate the environmental impact of mortar with calcined clay and limestone filler in reinforced concrete (RC) column retrofitting is carried out using data from a multi-purpose complex project in Rizal province in the Philippines. A total of four retrofitting methods are evaluated based on two retrofitting techniques (RC column jacketing and steel jacketing) with two material alternatives (pure OPC-based mortar and mortar with partial replacements). Results show that RC column jacketing using patched mortar with partial replacement of calcined clay and limestone fillers is the least environmentally damaging retrofit option. The use of these SCMs resulted in a 4–7% decrease in global warming potential and a 2–4% decrease in fine particulate matter formation. Meanwhile, RC column jacketing decreased the effect on human carcinogenic toxicity by 75% compared to steel jacketing.

Seismic Performance Evaluation of RC Columns Retrofitted by 3D Textile Reinforced Mortars.

The paper investigates the seismic performance of rectangular RC columns retrofitted by a newly developed 3D Textile Reinforced Mortar (TRM) panel. The 3D-TRM used in this study consists of two components: self-leveling mortar and 3D textiles. Firstly, the flexural capacity of the 3D-TRM panel was investigated through the four-point flexural test. Secondly, a total of five specimens were constructed and experimentally investigated through static cyclic loading tests with constant axial load. One specimen was a non-seismically designed column without any retrofit, while the others were strengthened with either the 3D-TRM panel or conventional Fiber Reinforced Polymer (FRP) sheets. Experimental results in terms of hysteretic behavior, ductility ratio, and energy dissipation are investigated and compared with the cases of specimens with conventional retrofitting methods and without any retrofit. The maximum lateral force, ductility, stiffness degradation, and energy dissipation of RC columns with 3D-TRM panels were significantly improved compared with the conventional RC column. Therefore, it is concluded that the proposed retrofitting method can improve the seismic performance of non-conforming RC columns.

Study of different retrofitting techniques on skyscraper building

A skyscraper is a multi-storey framed structure. Initially, the term was utilized to depict a building of at any rate 35–50 stories, for the most part for office, mechanical and private purposes. A skyscraper is otherwise called a tall structure, albeit the word skyscraper alludes to structures that are in excess of 50 m tall (164 ft). A steel structure that supports shade dividers is an average attribute of skyscrapers. Rather than load-bearing dividers, these shade dividers either bear on the design underneath or are suspended from the structure above. The heaviness of the development material itself is essentially liable for the heap that a skyscraper bears. The heaviness of the casing is generally a lot more prominent than the heaviness of the material it can take care of over its fair share in most development designs. The dead burden, or design load, is more prominent than the live burden in specialized terms. For short, medium, and elevated structures, the essential principles of engineering for vertical and horizontal loads (wind and seismic) continue as before. At the point when a construction arrives at a specific tallness, nonetheless, both vertical and parallel loads become restricting powers. The upward loads are relative to the floor territory and the quantity of floors. The effect of sidelong loads on a design, then again, isn't straight and increments quickly as the building's stature rises. Redirection and minutes on steel parts would be high because of these horizontal loads. These sorts of shortcomings can be tried not to by retrofit the design. The current examination will zero in on a 40-storey skyscraper. At zone V, it will be tried utilizing different retrofitting methods, for example, shear dividers, bracings, and fixed dampers. The construction will be assessed in each of the four zones and will be based on medium soil. The entirety of the cases can measure up as far as minutes, float, twist, and storey shear. ETABS, a business bundle, can be utilized to break down skyscrapers up to 120 m tall and in different regions. To track down the most streamlined arrangement, the outcomes will be thought about utilizing tables and diagrams.

A new non-invasive method for the seismic retrofit of rubble masonry using composite connectors

A new non-invasive method for the seismic retrofit of rubble masonry using composite connectors

Behaviour of retrofitting in reinforced concrete structures

Quality is the most important factor for the success of any construction project. Some of the major factors that affects the quality of the constructions are delign, labour, materials, machineries, environmental conditions, hydrology, topography, method of construction and management system. It will affects resident’s aspect of life and give a bad image of the building’s parties. Detailed investigation report has made for possibilities for failure of structure in the construction and some feasible retrofitting methods which are adopted for structural elements. Constructional strengthening is aprocess, to boost performance or build up structural system of an existing building, under existing loads or increasing the strength of structural elements to switch to auxiliary loads. It is the system of repairing or modifying something, after it is built in construction industry. This study includes different types of retrofitting for the structure and the suitable methods of retrofitting for the structure along with that cost effective for the structure. And the process of inserting of new features to the building. This also explains about two major methods of columns retrofitting methodologies in constructions, i.e. concrete jacketing and plate bonding along with its cost analysis.

Case study on structural health assessment for existing reinforced concrete building

Retrofitting is a method of renovating/repairing and strengthening the weak structure that was affected due to the excessive load on structure during any uncertainty load like earthquake or due to end of service life of the infrastructure. The objectives of this paper are to design reinforced concrete and fiberreinforced polymer jacketing of failed columns of an existing building, after addition of two more storey in previous design and to compare suitability of before mentioned methods of retrofitting. The presented work also describes design procedure of reinforced concrete, carbon fiber reinforced polymer jacketing for strengthening existing columns. This study is fruitful to gauge suitability of the two retrofitting methods for weakened structural members. The existing buildings in Nepal designed as using Mandatory Rules of Thumb are most vulnerable types of building; to mitigate further crack in structural members with appropriate type of retrofit will be considered with proper management of construction related to post-earthquake activity. After analysis and design of existing building its extremely necessary to plan construction management for economic and safety concern. Most cases of such projects will lead improper work without proper construction management leading uneconomic and prolonging of completion of project.

A framework for the lifecycle cost assessment of structures considering multiple mainshock-aftershock sequences

Structures in an earthquake-prone region have the potential to experience multiple mainshock-aftershock (MSAS) sequences during their lifetime. The multiple aftershocks of a given mainshock would further aggravate the damage extent of the mainshock-damaged structure, and meanwhile extend its recovery time. This manuscript proposes a probabilistic framework for lifecycle cost assessment of the structure under multiple MSAS sequences. This framework comprehensively considers the effects of repair status (i.e, finished repair or not) and uncertainties related to multiple MSAS sequences and damage state of the structure. Then this framework is applied to six 4-story reinforced concrete moment frames (i.e., one original structure and five retrofitted scenarios). The results indicate that ignoring repair status would underestimate the lifecycle cost by maximum level of 20%. Multiple aftershocks would increase the lifecycle cost of structures, and such an increment varies from 6% to 137% for different retrofitted scenarios. FRP wrapping is the best retrofit method while Shear wall is the worst one from the perspective of lifecycle cost.

BIM-based retrofit method (RBIM) for building envelope thermal performance optimization

Retrofitting building envelope thermal performance is crucial to ensure adequate interior thermal comfort of the building, minimize cooling load rate and, therefore, reduce overall building energy consumption. The retrofit process of an existing building envelope involves the design team selecting the best performing building materials and components based on various design variables and predefined design objectives. Worldwide, an overall thermal transfer value (OTTV) metric has been developed and used for assessing heat transfer through the building envelope. However, the application of OTTV implicates dealing with many design variables and much information, which makes the design decision-making process time-consuming and complicated. Furthermore, selecting the most appropriate design alternative in terms of OTTV performance while considering the most cost-effective design option could be a very challenging task. Therefore, this research proposes a method for retrofitting building information modelling (RBIM) to achieve a tradeoff design set between two conflicting objectives, namely minimizing OTTV and minimizing the retrofit cost. The prototype system derived from this method integrates BIM authoring tools (e.g., Autodesk Revit®), visual scripting (e.g., Dynamo), and a non-dominated sorting genetic algorithm (NSGA-II) customized in MATLAB®. The applicability of the proposed system is validated with a case study of an office building. The results show that the developed system provides a valuable design decision support system for retrofitting building envelope thermal performance while considering the retrofit cost. Additionally, the system shows an improved level of automation in terms of data management compared to the conventional methods.

Seismic retrofit of large-scale interior RC beam-column-slab joints after standard fire using steel haunch system

Steel haunch system was proposed to retrofit fire-damaged reinforced concrete (RC) beam-column-slab joints and ensure their seismic safety. Five RC beam-column-slab joints were designed, including one control specimen without fire damage, one control fire-damaged specimen, three fire-damaged specimens retrofitted with different types of steel haunch system, i.e., separate steel haunches, a combination of steel haunches and carbon fiber-reinforced polymer (CFRP) sheets, and a combination of steel haunches and bolted side plates (BSP). The fire-damaged RC joints were subjected to ISO 834 standard fire. After fire tests, low-cycle reversed loading tests were conducted on all the control and retrofitted specimens. The influence of fire damage and retrofit methods on the hysteretic behavior, load capacity, stiffness, ductility factor, and energy dissipation capacity of the joints was analyzed. Experimental results showed that fire exposure significantly reduced the seismic performance of RC beam-column-slab joints. The plastic hinges of spatial joints were transferred from the beam-column interface to the zone outside steel haunches after retrofitting. Compared with the control fire-damaged specimen, the hysteretic curves of the retrofitted specimens were more stable and plumper. All the three strengthening methods effectively enhanced the ultimate load capacity (increased by 24–70%), stiffness, ductility and cumulative hysteresis energy (increased by 107–362%) of the post-fire joints. CFRP sheets and bolted side plates show excellent compatibility with the steel haunches. The preload degradation of bolts used to fix the steel haunches reduced the retrofit efficiency of the steel haunch system. The numerical results of the sequentially coupled thermal-stress analysis model for retrofitted post-fire RC joints based on ABAQUS were consistent with the experimental results.

Integrating Digital Twin Technology Into Large Panel System Estates Retrofit Projects

As sustainability is now a standard for the proposed developments, the focus ought to be shifted towards the existing buildings and, among them, the worldwide stock of large panel system (LPS) buildings. Major upgrades and retrofits were done to some of the LPS estates in Germany and France, but a leading sustainable way must still be developed for LPS buildings in Eastern European countries, where apartments in those half-a-century-old estates are privately owned. Both sustainability and ownership issues make the demolition option redundant, and therefore the method for deep thermal retrofit and urban intervention is being developed with the use of BIM simulation tools. Digital twin (DT) technology allows for calibration to intertwine with the Internet of Things applications that reward the inhabitants for sustainable behaviour while feeding the relevant data back to the DT. Thanks to this, smart technology can be used to raise the level of social participation in the projects and thus help educate the end-users, which is paramount in establishing and maintaining good ecological habits, and as such, also for the efficacy and viability of the final endeavour. This article proposes a procedure of creating a 3D model typology repository for facilitating DT technology to provide a good analytical tool for community consultation and enable virtual testing of technical and urban solutions before implementation. It aims to determine the method for virtual technology to give deteriorating estates a new lease of life and improve their perception in the wider community while being a conduit for the adaptation of CEE to the digital revolution.

Carbon Footprint Reduction through Residential Building Stock Retrofit: A Metro Melbourne Suburb Case Study

Since existing residential buildings are a significant global contributor to energy consumption and greenhouse gas (GHG) emissions, any serious effort to reduce the actual energy and carbon emissions of the building sector should explicitly address the carbon mitigation challenges and opportunities in the building stock. This research investigates environmentally and economically sustainable retrofit methods to reduce the carbon footprint of existing residential buildings in the City of Greater Dandenong as a case study in Metropolitan Melbourne, Australia. By categorizing energy use into various building age brackets and dwelling types that align with changes in energy regulations, we identified various retrofit prototypes to achieve a targeted 6.5-star and 8-star energy efficiency rating (out of a maximum 10-star rating system). The corresponding operational energy savings through different retrofit options are examined while also considering the quantity of materials required for each option, along with their embodied energy and GHG emissions, thus allowing a more comprehensive lifecycle carbon analysis and exploration of their financial and environmental payback times. Results show that when buildings are upgraded with a combination of insulation and double-glazed windows, the environmental benefits rise faster than the financial benefits over a dwelling’s lifecycle. The size or percentage of a particular dwelling type within the building stock and the remaining lifecycle period are found to be the most important factors influencing the payback periods. Retrofitting the older single detached dwellings shows the greatest potential for lifecycle energy and carbon savings in the case suburb. These findings provide households, industry and governments some guidance on how to contribute most effectively to reduce the carbon footprint of the residential building sector.

Experimental and numerical investigation on seismic performance of retrofitted RC columns with web direct/indirect bonding external H-section

This paper presents experimental and numerical investigations of existing reinforced concrete (RC) columns enhanced by two seismic retrofit methods, web indirect bonding and web direct bonding combined with a steel endplate. The former retrofit system is an H-shaped steel member connected to an existing RC column with anchor bolts and an infilled-concrete layer. The latter is quite similar to the web indirect bonding method but incorporates a steel endplate and a stud bolt layer additionally. Three RC columns with/without the retrofitted methods, designated BC, SC-T2, and SC-T4, were built and tested under cyclic loading. The experimental findings showed that the retrofitted RC columns were superior to the non-retrofitted specimen in terms of initial stiffness, peak strength, and energy dissipation capacity. Based on the experimental responses, finite element (FE) models were developed and verified with the experimental results. The results obtained from the simulations were consistent with those from the experiments, indicating the finite element (FE) models can reproduce the seismic responses of bare and retrofitted RC columns with slight simulation variation. Finally, a parametric analysis was carried out to investigate the effect of the material strength and length of the added components on the seismic behavior of the SC-T2 specimen.

Seismic performance of RC beam-column-slab joints strengthened with steel haunch system

Function alteration and revision of seismic design codes require the improvement of seismic performance of existing spatial RC joints. An innovative and practical seismic retrofitting method using steel haunch system is recommended for existing spatial RC joints with the floor slab and the transverse beam. Four spatial RC joints were designed including one control specimen without strengthening, three retrofitted specimens strengthened with only steel haunches, combined steel haunches and carbon fibre-reinforced polymer (CFRP) sheets, and combined steel haunches and bolted side plates (BSP) on beam's sides. All specimens were subjected to low-cycle reversed loading. The effects of different retrofit methods on failure modes, crack patterns, hysteretic behavior, ultimate load capacity, stiffness degradation, ductility factor, and energy dissipation capacity were analyzed. Results showed that hysteretic curves of retrofitted specimens were more stable and plump. The plastic hinge of spatial joints was transferred from the beam end to the zone outside steel haunch after retrofit. The ultimate load capacity, stiffness, ductility and cumulative hysteresis energy were significantly enhanced with a maximum proportion of 63.8%, 315%, 30% and 165%, respectively. Steel haunch can be effectively combined with bolted side plates and CFRP in the strengthening of RC beam-column-slab joints to make full use of material properties. The preload degradation of the bolts used to install the steel haunch reduced the retrofit efficiency. Combined steel haunches and BSP exhibited the best cooperative performance with the spatial joint. The strains demonstrated that the steel haunches were still in the elastic stage and subjected to eccentric loading during the entire loading stage. Finite element models of retrofitted joints were established based on ABAQUS. The load-displacement curves calculated by ABAQUS agreed well with test results. Numerical analysis shows the stress and strain contribution of each component which is helpful to further optimize this retrofit system.

Seismic retrofit of deficient exterior RC beam-column joints using steel plates and angles

This paper proposes a simple and practical method for retrofitting deficient (non-seismic detailed) exterior beam-column joints based on fixing steel plates and angles around the joint with different configurations. Six half-scale exterior RC beam-column joints were tested under quasi-static cyclic loading with a constant axial load on the column. The experimental program included two control specimens representing code-detailed and deficient joints in addition to four retrofitted specimens. The proposed retrofit methods were designed to compensate the lack of joint transverse reinforcement using different steel arrangements (X-shape, horizontal plates) and the short development length of beam bars using angles tied by external or internal anchors. One of the retrofit methods is applicable in the presence of a transverse beam. The test results showed that the deficient joint exhibited brittle joint shear failure, unlike the code-detailed joint which failed by flexure in the beam. The proposed retrofitting methods effectively prevented the brittle joint shear failure and increased the joint strength, ductility, stiffness, and energy dissipation. A softened strut and tie model was applied and modified to predict the joint shear strength of control and retrofitted joints and it showed a good agreement when compared with the experimental results.

A Retrofit Method to Mitigate Progressive Collapse in Steel Structures

AbstractAccidental events, such as impact loading or explosions, are rare events characterized by a very low probability of occurrence. However, their effects often lead to very high human losses and economic consequences as are likely to trigger the progressive collapse of the buildings. The progressive collapse of structures attracted the attention of many researchers and the topic has been widely investigated in recent years. In addition, increasing interest has been shown also on the definition of retrofit strategies able to increase the robustness of existing structures. The present work investigates the performance and the design of a retrofit solution to increase the robustness of steel moment resisting frames. A case study structure is selected and modelled in OpenSees, including both mechanical and geometrical non‐linearities. Non‐linear static analyses have been carried out on the frame, simulating a column loss scenario to investigate the subsequent load redistribution. The simulations showed that the case study was unable to redistribute the load and hence retrofitting was required. Among others, a truss system was added at the rooftop level of the building allowing the definition of an alternative load path. The analyses outcomes showed how the proposed retrofit method allows to increase the robustness of the case study structure and allowed for critical remarks on the checks required when this retrofit system is employed.

Self-Compacting-Geopolymer-Concrete (SCGC) Retrofitted Haunch

Retrofitting methods are widely used to reinforce existing concrete structures and frames. Strengthening becomes necessary when building codes mandate a higher load carrying capacity originated from, for example, changes in earthquake zone mapping. A haunch conclusively relocates the formation of plastic hinges away from the beam-column-joint. Geopolymer concrete is an environmentally friendly material, based on fly ash. Utilizing a haunch with this material is effectual and sustainable. The low workability of geopolymer concrete was in this study improved by adding a superplasticizer, which effectiveness was trigger by the presence of low volume Portland cement and water creating a Self-Compacting-Geopolymer-Concrete (SCGC). This SCGC ensured easy fabrication in the field, and improved the compaction and homogeneousness of the haunch. A full-scale experiment based on water-loading was conducted on an existing building to analyze the behavior of a SCGC haunch. The research concluded that the SCGC resulted in a high-performance haunch with good compatibility to the structure, the integrity of the haunch and the structure was maintained up to working-loading conditions. The load carrying capacity and the serviceability greatly improved. Analytical comparison to the prismatic section showed that the SCGC haunch reduced the deflection at mid-span to 77%.