Retrofit Techniques Research Articles

Seismic evaluation and cost of retrofitting of load bearing structures – a case study-based approach India perspective

The load bearing masonry structures in India are reported to be non-engineered buildings and are found to be among the most vulnerable structures for damage against seismic loads. This paper gives an overall view of the procedure to be followed for the condition assessment of a load bearing structure standard codes based on the research works as addressed by various researchers in the industry. This study follows a comprehensive evaluation of a case study building based on the Indian Standards: IS:1905 (1987) and IS:1893 (PART-1: 2016) for the detailed reasons for the identification of structural distress in load bearing masonry structure based on the damageability grade as per IS:13935 (2009). Furthermore, the paper also insinuates the support of the decision of structural retrofitting based on-demand capacity ratio (DCR) calculated for the permissible stress values calculated for the load-bearing walls in the case study as per IS:15988 (2013). The paper demonstrates a viable retrofitting technique of Ferro cement mesh overlay that has been used to enhance the strength of the existing structure as applied on the case study along with its cost analysis.

Effect of the backfill material in the seismic response of multi-span masonry arch bridges under seismic loading

The present study deals with numerical modelling of multi-span masonry arch bridges under seismic loading. Based on the evidence coming from an experimental program reported in the literature, a reference 3D nonlinear Finite Element model is calibrated. The numerical model is realized in Abaqus software by adopting a macro-modelling strategy for simulating the masonry behavior. To this purpose the Concrete Damage Plasticity material model is used. The backfill material follows a Drucker-Prager behavior, while the interaction between the two materials is simulated by means of an appropriate contact constitutive law. After calibration, the response of the bridge under longitudinal seismic loads is thus investigated. In particular, a mass proportional load distribution is adopted. Then, the effects of the mechanical parameters of the backfill material on the global response of the bridge are investigated by means of a parametric analysis, which is carried out by varying: i. elastic modulus, ii. cohesion, iii. backfill-masonry contact law, and iv. backfill friction angle. The obtained results provide preliminary indications about reliable retrofitting techniques for cases similar to the one under consideration.

Experimental investigation on tensile and shear bond behaviour of Basalt-FRCM composites for strengthening calcarenite masonry elements

The use of Fabric Reinforced Cementitious Matrix (FRCM) composites for structural retrofit has seen an increased interest among the scientific community, during the last decade. Various studies have revealed their effectiveness as external retrofitting technique of masonry elements, offering numerous advantages respect to the well know Fibre Reinforced Polymer (FRP) in terms of compatibility with masonry support, reversibility of intervention and sustainability. Despite the growing use, the characterization of FRCM mechanical behaviour is still an open issue, due to numerous uncertainties involved in test set-up adopted and fibre-mortar combination. The proposed experimental study aims to investigate the tensile and shear bond behaviour of Basalt-FRCM for strengthening calcarenite masonry elements. Calcarenite is a natural stone with sedimentary origin and it is widely present in existing buildings of the Mediterranean areas. Direct tensile tests are performed on two types of Basalt-FRCM coupons, with cement-based and lime-based mortar, adopting two different test-set-up based on clamping and clevis grip methods. Moreover, double shear bond tests are carried out to evaluate the adhesion properties of the two types of Basalt-FRCM with calcarenite support. Experimental outcomes are compared in terms of stress-strain curves, evaluating the influence of mortar grade and test set-up on the mechanical performances of Basalt-FRCM composites. The comparisons provide information about the mechanical stress transfer phenomena that occur at the fibre-to-matrix and FRCM-to-substrate interface level and the failure modes.

Seismic performance of lap-spliced pre-damaged and intact concrete columns strengthened or retrofitted with UHPC and NSM

Reinforced concrete (RC) columns with deficient lap splice details such as short lap splice length and widely spaced stirrups were vulnerable to earthquakes. In the present study, to evaluate the effectiveness of an innovative retrofitting technique using the combination of ultra-high performance concrete (UHPC) and near surface mounted (NSM) technique on the seismic performance of RC columns with deficient lap splices details, cyclic loading tests were performed on four large-sized RC column specimens. Two RC columns were strengthened with UHPC or the combination of UHPC and NSM, and the other two were retrofitted with the combination of UHPC and NSM after the lateral strength decreased to 85% peak strength during the pre-damage cyclic tests. The load–displacement relationship, stiffness degradation, energy dissipation, and residual displacement of RC columns are evaluated. The test results showed that the peak strength and ductility of RC columns with deficient lap splice are significantly improved after strengthening or retrofitting with the combination of UHPC and NSM. The seismic performance of severely damaged RC columns due to deficient lap splice details can still be effectively restored after retrofitting with the combination of UHPC and NSM. Considering the adverse effect of pre-damage, a design method is proposed to predict the flexural capacity of RC columns retrofitting with UHPC or the combination of UHPC and NSM. The proposed method is also applied to predict the flexural capacity of RC beams strengthened with UHPC. The proposed method predicted well the test results of this study and existing tests.

Tribological investigation on metal mating surfaces to explore real use conditions of a novel friction damper for seismic applications

The seismic rehabilitation of existing buildings is a strategic goal for many countries located in high seismic risk areas of the globe. Retrofit techniques based on energy dissipation by implementing additional mechanical dampers into the structure have proved to be very efficient. Among the others, friction-based dampers have revealed to be particularly simple and cheap; nonetheless, for this kind of device, the selection of mating surfaces set a crucial point. This paper shows the experimental investigation performed for the development of a novel Friction Damper (FD) using Pin-on-Disk (PoD) tests and highlights the main tribological aspects useful for the full-scale tests. PoD tests have been set to simulate the real use condition of the device in development under the action of subsequent earthquakes. Sliding surface’s material and machining processes have been selected taking into account the S355JR steel main body of the device in development, and the need of reducing the friction’s abrasive component and the particle formation during sliding. The experimental campaign has been addressed to highlight the influence of surface roughness, machining processes, additional treatment, and different coupling materials on Coefficient of Friction (COF) mean value and its statistical dispersion.

Seismic retrofitting of a deteriorated RC building

Numerous existing reinforced concrete (RC) buildings don’t fulfill current seismic code provisions as they haven’t been designed to satisfy these provisions. Also, due to many environmental factors, structural members such as columns, beams, and slabs are exposed to severe deterioration leading to high-risk levels. In this research, the performance of an existing seven-floor reinforced concrete building in Zagazig city, Egypt, constructed about 50 years ago, without considering the seismic requirements prescribed in the current Egyptian code (ECP-2012) is studied. The studied building suffers severe deterioration in its main structural elements, especially the basement floor slab. SAP2000 software is utilized to evaluate the structural behavior of the building under vertical loads (dead and live loads). The model failed to fulfill the ECP-2012 requirements under the applied loads. After building investigation, a retrofitting technique was proposed through providing the building with new grid beams at the basement floor level as well as replacing the existing basement floor slab with a new one. Moreover, RC jackets were provided to all basement floor columns. Through response spectrum analysis (RSA), the performance of the building with the newly proposed technique was assessed considering a peak ground acceleration equals 0.15 g (seismic zone 3). The model showed a significant enhancement in its response that fulfilled the ECP requirements concerning both strength and serviceability. Utilizing SeismoStruct software, the horizontal capacity of the model was inspected through the pushover analysis to check the efficiency of the proposed retrofitting technique. The model showed acceptable capacity in its two main directions.

Seismic Vulnerability and Consolidation by FRP/FRCM Systems of a Masonry School Building in the District of Naples

The paper discusses the seismic vulnerability of structures susceptible to overcrowding due to their intended use. Specifically, it addresses the analysis towards earthquake actions of a masonry school located in the Municipality of San Giorgio a Cremano, within the neighbourhood of Naples, providing different reinforcement interventions to ensure its seismic consolidation. After a brief introduction, the description of the analysis representative of the current condition of the structure is performed considering both static and seismic actions. The analysis results determine the seismic risk class of the building, allowing to identify its deficiencies, so to design structural consolidation interventions following the standard code indications. In particular, two retrofit techniques, namely, FRP and FRCM systems, are proposed with the purpose to evaluate their benefits to the school building from a seismic viewpoint. Finally, a comparison between the proposed intervention techniques is made to establish which one guarantees the best upgrading of the seismic condition of the examined building.

Experimental study on compressive behavior of intermediate slender timber columns with local damage and the retrofitting techniques for the damaged columns

The existing historic timber constructions are often affected by local damage such as decay, and their mechanical properties are significantly reduced. In order to explore the influence of local decay on the compression behavior of timber columns, this work conducted experimental investigations of 10 intermediate slender columns with different damaged conditions under axial compression. Damaged areas, damaged positions and damaged forms of the columns were considered. Based on the failure mechanism of damaged timber columns, the retrofitting technique for locally damaged columns using the combination of wood block, profile and carbon fiber reinforced polymer (CFRP) wrap was proposed, compared with the traditional methods of using wood block only, and both wood block and CFRP wrap. Experimental investigations of 10 retrofitted columns with 4 retrofitting techniques were also conducted. The compressive performances and effect among these retrofitting techniques had been compared based on the failure modes and ultimate load-carrying capacity stiffness and ductility. The results indicated that the compressive performance of the damaged columns was significantly reduced which magnified with the increase of damaged area, and the loss of the load-carrying capacity was much larger than the loss of the cross-section area. The load-carrying capacity and stiffness of the damaged columns were appreciably restored by these retrofitting techniques. The load-carrying capacity of the bilaterally damaged column retrofitted by the combination of wood block, GFRP profile and CFRP wrap was the highest, reaching 98.30% of the intact column.

Retrofit of exterior reinforced concrete beam-column joint using pre-tensioned stiffened steel angles

This paper presents an innovative retrofit technique to strengthen the non-seismically designed reinforced concrete beam-column joint. For this purpose, five half-scale exterior beam-column joints were prepared and tested. Four of the joints were strengthened with stiffened steel angles under various pre-tensioning levels and stiffened steel angle sizes. The columns were loaded under constant axial compression, and the beams were loaded under quasi-static cyclic load. The experiment test results showed that this retrofit technique can relocate the plastic hinge from the critical joints toward beams. This improved the sudden joint shear failure mode to a ductile beam failure mode. Besides, this retrofit technique improved the seismic behaviours, including load-carrying capacity, ductility, energy dissipation, and stiffness of the beam-column joints. This paper showed that the pre-tensioning level affects the bond behaviour between the reinforcement steel and the concrete, whereas stiffened steel angle size affects the failure mode and seismic behaviours.

Experimental Evaluation of Steel Bracings and Metallic Yield Damper as Retrofit Techniques for Severely Damaged RC Building Frames

ABSTRACT The concentrically placed hollow circular steel bracings and hybrid metallic yield dampers as structural retrofitting techniques for severely damaged reinforced concrete (RC) portal frames are evaluated under reverse-cyclic load conditions. In addition, the efficiency of a specially designed coupler-box assembly to retrofit severely damaged columns of the model frame by reconnecting the buckled or ruptured longitudinal reinforcing bars at the plastic hinge locations is evaluated under similar load conditions. Competency of the proposed techniques is assessed by comparing the hysteresis behavior, performance index parameters, and failure mechanism of the retrofitted frames with the native-tested conventional bare frame. The lateral load and deformation capacities are significantly enhanced in the retrofitted frames with a comprehensive increase of 2.0 times in the braced frame and 2.5 times in the damper-equipped frame compared to the conventional bare frame. A stable and symmetric post-yield behavior is noticed in the retrofitted frames until a lateral drift of 3.5% and 6% in braced and damper-fit frames, respectively, which is even higher than the collapse prevention drift level specified in FEMA codal guidelines.

Retrofitting of a Precast Reinforced Concrete Industrial Building Using Friction Dampers Without Stopping Functionality

This paper presents a seismic retrofit of an industrial-type precast reinforced concrete building structure using friction dampers. This project consisted of retrofitting two precast reinforced concrete buildings, of which one of them will be presented here. Precast concrete is one of the most preferred methods of construction for industrial structures due to its low cost, fast construction and availability in rural areas. Unfortunately, most structures constructed before “Specification for Buildings to be Built in Seismic Zones(TBDY 2018)” are not sufficiently engineered and are expected to have poor performance when exposed to a major seismic event. Because stopping the production cost can be tolerated by the owners, a retrofitting technique that can be assembled during normal function of the industrial structures is required. As a result of this requirement, friction dampers are selected as the supplemental energy dissipation device. ASCE 41-17 [10] is employed for the damper design and performance evaluation of the building. Before the damper study, some instability and weak connection problems are solved by some traditional measures of strengthening. The most effective damper configuration and capacities are selected after an iterative trial-and-error linear study using the simplified methods developed by PROMER. Nonlinear push-over analysis are conducted after linear prestudies. Finally, a nonlinear time-history analyses is performed for confirmation of the results. , It is shown that the proposed retrofit scheme satisfies the desired performance goals for both DBE and MCE events. Overall, it is considered that proposed retrofit scheme with dampers provides the optimal solution for the stakeholders of the project from a performance, design, constructability, and economical point of view. Some application photos will be presented and methods are explained in detail in the paper. The friction damper behavior is based on the rotational friction hinge concept

Combining retrofitting techniques, renewable energy resources and regulations for residential buildings to achieve energy efficiency in gated communities

This paper presents a multi-objective method of analysing the energy efficiency associated with upper class houses in Gated Communities in Arid Zones. The application of building energy regulations has an impact on improving energy efficiency. Energy codes identify the effective techniques that could help in achieving energy efficiency on the building scale, but there is a gap in applying these techniques on the existing urban community scale. This paper proposes a method of integrating energy retrofitting techniques with renewable energy systems to achieve energy efficiency in residential gated communities. The study applies simulation analysis to determine the energy performance when applying these strategies using different building materials in light of the requirements stipulated in the Egyptian Energy Code for Residential Buildings (EECRB). The results show that the entire gated community’s energy usage is reduced by 88.68 percent and suggest a framework for achieving energy efficiency in existing buildings and communities.

Providing a feasible energy retrofitting technique based on polyurethane foam injection to improve windows performance in the building stock

Energy renovation of existing buildings represents an outstanding potential field for providing efficient, viable and easy-to-produce retrofitting techniques that allow addressing energy targets under a global warming scenario. Aiming to fulfil a current research gap on promoting feasible passive techniques to improve thermal performance in the building stock, this research contributes with the design, procedure and in situ application of a novel energy retrofitting solution based on the injection of polyurethane foam insulation in carpentry profiles of existing aluminium windows, which implies relevant insights towards energy efficiency and ensures more comfortable indoor environments through a quick, non-destructive and affordable solution. This innovative plan has been experimentally tested in social housing, with a monitoring campaign during summer conditions, allowing to obtain thermal results before and after the insulation injection treatment. The key outcomes highlight a favourable indoor thermal balance after the foam injection, increasing the thermal jump up to 25 % or more than 4 °C net, as the daily maximum temperature difference recorded between outdoor and indoor simultaneously. Conclusions incorporate key implications to technicians, manufacturers and construction firms, on introducing new possibilities for improving energy efficiency in existing aluminium windows with low investment, linked towards an efficient management of the built environment.

In-Plane Loading Tests and a Retrofitting Technique for Masonry Infill Panels in RC Frames with Eccentric Openings

In-Plane Loading Tests and a Retrofitting Technique for Masonry Infill Panels in RC Frames with Eccentric Openings

Technological analysis of a prefabricated timber-based system for the integrated renovation of RC framed buildings

Most of the building stock in European seismic countries is highly energy-intensive and earthquake-prone since it was built before the enforcement of effective energy and seismic codes. Renovation actions that synergically integrate both energy-efficient and anti-seismic interventions are strongly needed in these countries. However, the implementation of such interventions is currently limited by barriers that are mostly related to the high cost and invasiveness of traditional seismic retrofit techniques. A new holistic design approach to the building renovation is required to overcome these barriers. This should result in innovative and integrated retrofit interventions able to specifically meet the needs of cost-effectiveness, quick installation, reduced users’ disruption, and low environmental impact. In this framework, the use of cross-laminated timber (CLT) has been recently investigated for retrofit purposes in light of its good mechanical and physical performance. In this research context, this paper illustrates a novel timber-based retrofit technology for RC framed buildings developed within the e-SAFE H2020 project. This technology consists of cladding the external building envelope with a new prefabricated timber-based shell that acts as seismic-resistant and energy-efficient skin, also contributing to renovating the architectural image of the building. The new skin combines structural CLT-based panels – equipped with novel devices for seismic energy dissipation – with non-structural wooden-framed panels. Specifically, this paper presents a construction analysis of the proposed retrofit technology, investigating its technical feasibility, versatility, and potentialities, as well as possible application limits.

Retrofitting of Beams using Fibre Reinforced Polymer

Retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion etc. Many of the existing reinforced concrete structures throughout the world are in urgent need of rehabilitation, repair or reconstruction because of deterioration due to various factors like corrosion, lack of detailing, failure of bonding between beam- column joints etc. Fibre Reinforced Polymer (FRP) composite has been accepted in the construction industry as a promising substitute for repairing and in incrementing the strength of RCC structures. It stabilizes the current structure of buildings and making them earthquake resistant. This paper presents a representative overview of the current state of using FRP materials as a retrofitting technique for the structures not designed to resist seismic action. It summarizes the scopes and uses of FRP materials in seismic strengthening of RCC structures and masonry retrofitting.

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

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

Comparison of seismic responses of a jumbo-size container crane retrofitted with braces, dampers, and isolation systems

The effectiveness of six seismic retrofitting intervention schemes on an existing jumbo-size container crane is investigated. They include the use of conventional steel braces and buckling-restrained braces, fluid viscous dampers and friction dampers, lead rubber bearing isolators, and natural rubber bearing isolators with viscous dampers. The six schemes can be grouped under three main strategies, i.e., the use of different types of bracings, dampers, and isolation systems. Nonlinear response history analyses, using eight spectrally matched ground motions, were conducted on 3D models of the crane, with and without any upgrading, using SAP 2000. The results showed that with the exception of the conventionally braced crane, which produced inconclusive responses, the other two retrofitting strategies of using different types of dampers and isolation systems significantly reduced the critical seismic responses of the crane. At a target drift of one-third the original, the damping systems caused on average reduction of approximately 32%, 36%, and 98% in the base shear, stress, and uplift responses, respectively. Moreover, a significant reduction of about 65% in the stress and base shear responses and a condition of no uplift were recorded when the isolation systems were applied. The results of this study show that the isolation systems produce the best performance and therefore can be considered as the most effective seismic retrofitting technique.

A Novel Step-by-Step Automated Heat Exchanger Network Retrofit Methodology Considering Different Heat Transfer Equipment

Improving the energy efficiency in heat exchanger networks (HENs) remains a significant industrial problem, specifically in energy-intensive operations. A particular method for such an objective is the modification of HENs at the equipment-use level, where structural changes take place and units within the network are moved, replaced and/or removed. This practice is usually known as retrofit. The objective of a retrofit is to maximize the heat recovery using the minimum modifications possible and minimum retrofit cost. Traditional retrofit techniques would normally consider one type of heat exchanger (based on the original network) with no additional design features (i.e., heat transfer enhancement technologies). The expansion of such alternatives is limited by practical use and availability of theoretical methods. In this context, the inclusion of high-performance heat exchangers such as plate heat exchangers (PHEs) has not been widely explored, even when their design and operational advantages are known. In this work, a new step-by-step automated HENs retrofit approach based on Pinch Analysis is proposed. The approach is possible to identify the best modification, its location within the network, and its cost simultaneously. Moreover, to increase energy savings, this work presents a strategy that seeks to utilize high efficiency heat exchangers such as plate heat exchangers for retrofit. A distinctive feature of this new method is the ability to handle different minimum approach temperatures, given the different types of exchangers, within the optimization of HENs. Three cases are studied using this methodology to quantify the potential benefits of including PHEs in HEN retrofits, via the analysis of the retrofit cost. Results are compared with a baseline consisting in the same network, where only Shell-and-Tube-Heat-Exchangers (STHXs) are used. In addition, the results demonstrate that this methodology is flexible enough to be applied in a wide range of retrofit problems.

Seismic Retrofit Technique Using Plywood and Common Nails for Connections of Low-Rise Timber Frame Construction

Since the Japanese Building Standards Act was revised in 2000, the installation of steel timber connectors (STCs) to reinforce timber frame (TF) connections has been mandated for new-build TF houses in Japan. However, for the TF houses built before then, more than 40% do not have sufficient STCs and are considered earthquake-prone. This study proposed a simple and easy seismic retrofit technique for such earthquake-prone existing houses. The proposed technique can reinforce TF connections using only plywood and common nails and achieve equivalent performance to the benchmark STCs used in Japanese TF houses, such as the “CP-T type” or the combination of “VP type” and “BP type” STCs. Experiments were performed to compare the proposed technique with the STCs using pullout and full-scale in-plane cyclic tests. The experimental results showed that the proposed technique had a higher seismic performance than the STCs, which was particularly excellent in displacement ductility to prevent a collapse of the TF house without damaging the timbers. The proposed technique will be accepted by many carpenters when retrofitting earthquake-prone existing houses because simple and easy.