Rehabilitation Of Structures Research Articles

Fracture Failure Modes in Fiber-Reinforced Polymer Systems Used for Strengthening Existing Structures

The development of promising new high-performance materials, such as composite materials made of fibers in a polymeric resin (fiber-reinforced polymer, or FRP), has transformed the structural rehabilitation and upgrade industry for buildings and infrastructure. Conventional materials and construction techniques (e.g., strengthening with externally bonded steel plates, known as beton plaqués, or steel/concrete jackets) have been supplanted by innovative ones. The most important emerging techniques involve the use of externally bonded composites as a quick and effective option for repairing and upgrading existing structures. Several issues regarding FRP–substrate interaction, mainly related to brittle failure mechanisms due to fracture phenomena, remain the focus of a great deal of research. This paper presents an overview of debonding behavior and its predictive modelling in externally bonded FRP systems.

Torsion behavior of strengthened RC beams by ferrocement

Now a days, construction industry is one of the most over loaded industry and is responsible for carbon emission, the process of enhancing the life of existing structures reduces the impact on the environment. In this regards, external strengthening of concrete structures is necessary under repair and rehabilitation of structures. This will increase the load carrying capacity and life span of concrete structures. In past decade fiber reinforced polymer (FRP) has been widely used as externally strengthening material due to its high strength and light weight. However, ferrocement is one of the suitable alternatives over costly FRP strengthening technique. Ferrocement is thin composite material having better crack resistance ability, ductility, good impact resistance and can be easily wrapped over beam surfaces. Very less research work is available on torsional behavior of concrete beam strengthened by ferrocement due to its complex loading. As practically beam and slab are cast monolithically, strengthening of beam in U- shape is more practical than strengthening all sides. This paper represents an experimental study conducted on reinforced concrete beam strengthened externally by U- shaped ferrocement with different strengths of mortar. This paper also addresses the torsional capacity and angle of twist of reinforced concrete beams. The experimental study was conducted on total 10 number of reinforced concrete (RC) beams of 150 mm × 200 mm × 1500 mm in size. The main purpose of study was to check the effect of different strength of mortar on ferrocement strengthening system under torsion keeping layer of wire mesh and thickness constant. Different strength of mortar mix, fabricated by varying water/cement ratio of 0.400–0.475 at stepped increment of 0.025. Result shows very less improvement in ultimate torsional strength and average 10.33% increment in angle of twist over normal beams.

Review on structural damage rehabilitation and performance assessment of asphalt pavements

Abstract Asphalt pavements have been extensively used in highway system. However, a great number of asphalt pavements suffer from early distresses after servicing for about 2–3 years, which leads to frequent rehabilitation and increased maintenance cost. To understand the damage propagation principle and the correlated rehabilitation measure, the progress of pavement distress rehabilitation, structural performance, and damage assessment of asphalt pavements has been explored in the perspectives of materials and structures. The current advance on the parameters for describing the cracking and rutting of asphalt pavements has been introduced. The development tendency for the damage self-healing and rehabilitation, and structural assessment has also been discussed. The study can provide a scientific guidance for understanding the generally used structural damage rehabilitation measure and performance assessment methods of asphalt pavements.

Accelerated Laboratory Testing for Reflective Cracking

Abstract One of the most used methods of rehabilitation of road structures is the laying of a protective asphalt layer over a degraded concrete. The main problem of this solution is the reflective cracking, more precisely the transmission of the existing cracks in the lower layer in the asphalt pavement. The method presented in this article involves an accelerated laboratory test on specimens composed of a pre-cracked concrete slab over which an asphalt slab is glued, subjected to equivalent traffic loads. This test allows the observation of the crack propagation from the lower layer to the upper layer, until it yields, through parameters such as deformed specimen, opening and length of the crack in asphalt, but also the opening of the existing crack in concrete, relative to the number of cycles. By relating these parameters, important conclusions can be drawn about the behavior of the composite structure at reflective cracking, being able to choose the optimal recipe of the protective asphalt layer.

A Quasi-Experiment on the Effectiveness of Cardiac Rehabilitation in Quality of Life of Cardiac Patients with the Caregivers’ Involvement

Introduction: Coronary Heart Disease can result in impaired quality of life which can inhibit an early recovery with successful outcomes for cardiac patients. Objective: To investigate the effect of a structured cardiac education and early intervention cardiac rehabilitation program on quality of life in cardiac patients involving caregivers. Method: A quasi experimental study with a purposive sampling was carried out where 132 acute coronary syndrome patients hospitalized for treatment were recruited and allocated to the experiment and control group with and without caregivers. A structured educational intervention and cardiac rehabilitation was initiated for the experimental group with and without caregivers. The outcome was measured using the World Health Organization Quality Of Life-BREF (WHOQOL-BREF) instrument.Results: Data was measured with repeated measures ANOVA between baseline, discharge and follow-up between the intervention and control group with p<0.05 There was a statistically significant difference in QOL in both the groups with and without caregivers in the following domains: psychological health (F=3.784, p=0.002); social relationship (F=4.267, p=0.000) and environment (F=3.578, p=0.004). There was not a statistically significant difference between both the groups in the physical health domain (F=1.316, p=0.266).Conclusion: The results indicated that a structured cardiac educational intervention and cardiac rehabilitation with the involvement of the caregivers have significant effects on the quality of life of cardiac patients. The findings provide useful evidence to improve health outcomes of acute coronary syndrome patients involving the caregivers.

A Review of the Performance of Infilled RC Structures in Recent Earthquakes

The primary objective is to present the most representative types of damage observed in reinforced concrete (RC) structures due to earthquakes. Those damages are divided according to the ten most representative types. Examples and the main reasons that could trigger each failure mechanism are presented. The definition of these damage types is supported by post-earthquake damage reconnaissance missions in Sichuan (China) in 2008, L’Aquila (Italy) in 2009, Lorca (Spain) in 2011, Emilia-Romagna (Italy) in 2012, Gorkha (Nepal) in 2015, Muisne (Ecuador) in 2016 and Chiapas (Mexico) in 2017. An extensive discussion is presented concerning the infill walls’ seismic behaviour and their interaction with the RC structural elements. The presentation of the significant learnings and findings concerning the typical damage herein presented and discussed are compared with the common Southern European construction practice. The impact of the infill walls on the rehabilitation costs of damaged RC buildings is also studied. These costs are compared to those related to the structural damage and rehabilitation of the entire building structure to understand the impact of the infill walls. Finally, a case study is presented to study the effect of implementing simplified retrofitting strategies to prevent the soft-storey mechanism, one of the most common problems observed in past earthquake events.

Seismic response comparison of an existing hospital structure rehabilitated with BRBs or conventional braces

Conventional braces (CBs) are commonly used for seismic rehabilitation of structures. However, even when these are designed to comply code standards, they can exhibit an unexpectedly poor structural performance during an earthquake event. In this paper, one of these cases is presented and the possible consequences are discussed. A case study hospital is analyzed. It is an actual reinforced concrete structure located in the city of Puebla, Mexico; near the epicenter of the September 19, 2017 earthquake. The structure is a traditional moment-resistant frame building with reduced lateral stiffness and soft storey problems. Three rehabilitation proposals are analyzed and discussed. For Cases 1 and 2, the building was equipped with buckling-restrained braces (BRBs) using different configurations. For Case 3, a conventional bracing system was considered. The seismic response of the existing building before rehabilitation was also studied as a benchmark (Case 0). Results showed that Cases 1 and 2 outperformed Case 3, with Case 2 being superior to the others. On one hand, it was observed that the configuration of BRBs plays a significant role in the structure’s energy dissipating capacity. On the other hand, the use of conventional braces led to a surprisingly poor performance during the earthquake simulations, generating soft storey problems due to premature buckling of the braces.

Rehabilitation of Load Bearing Structures without Dismantle

Rehabilitation of Load Bearing Structures without Dismantle

Rehabilitation of concrete one-way slabs using precast prestressed concrete prisms

The rehabilitation of structures is a complex process that involves many considerations. This paper presents results of a feasibility study on the use of precast prestressed concrete prisms (PCPs) as a near-surface mounted reinforcement for rehabilitation of cracked one-way slabs. The PCPs were cast with high-strength concrete and were concentrically prestressed by one 9 mm diameter stress-relieved seven-wire steel strand. Six identical one-way slabs with a length of 3000 mm, a width of 600 mm, and a depth of 200 mm were tested. They were first loaded until cracking, then were fully unloaded and subsequently rehabilitated with four PCPs before loading them to failure. Deflected profiles and crack widths of the slabs before and after rehabilitation were compared in this research. This rehabilitation method reduced the magnitude of deflection and crack width of the samples. The cracks induced in the first phase of loading before PCP rehabilitation appeared fully closed after the PCP rehabilitation until load equal to five times the original cracking loads of the slabs was reached.

Barriers to completion of a novel pediatric cardiac rehabilitation program

IntroductionPediatric cardiac rehabilitation addresses physical and emotional challenges related to underlying heart disease. While the benefits of cardiac rehabilitation have largely been established, the challenges that patients and their families experience when participating in these programs have yet to be examined in detail. In this study, we evaluated the barriers that families face when asked to complete a structured cardiac rehabilitation program. ObjectivesThe objectives of this study were to measure the success of a novel pediatric cardiac rehabilitation program and to evaluate the barriers that families face when asked to complete a structured cardiac rehabilitation program. MethodsParents of patients referred for cardiac rehabilitation and who attended at least one session were recruited to participate in a phone survey regarding their experience using a published psychometric validation of the cardiac rehabilitation barriers scale. Results9 families participated in the study. 67% of patients were male and 3 patients completed the program in its entirety. Challenges associated with time, travel, and insufficient insurance coverage, were the highest rated barriers to completion of the rehabilitation program. Families universally enjoyed the program. 5 of 9 felt that the biggest positive of the experience was gaining an understanding of what exercise is safe. 3 of 9 stated that cardiac rehabilitation should be a standard component of therapy for all pediatric cardiology patients. ConclusionsPediatric cardiac rehabilitation is effective and liked by families. The barriers to completing a structured in-person program are difficulty getting to appointments due to time and travel and level of insurance coverage for the program. As such, ensuring insurance coverage and perhaps virtual rehab programs would be beneficial.

Performance of Fiber Reinforced Mortar coating for irregular stone masonry: Experimental and analytical investigations

Nowadays, the application of Fiber Reinforced Mortar (FRM) is widely used for the consolidation and rehabilitation of masonry structures because represents an effective solution in terms of reversibility and applicability. The paper illustrates the results of cyclic diagonal compression tests performed in situ on stone masonry specimens isolated from the walls of a historic building of L’Aquila (Italy). The tested stone masonry is representative of existing structures of the territories of the central Apennines in Italy. Only two of four panels were strengthened by FRM to provide also the reference value of the unreinforced masonry. The FRM comprised a glass-fiber grid embedded in a natural hydraulic lime (NHL)-based mortar applied as a coating to the masonry surfaces as well as carbon shear connectors. The tests were analyzed to derive the shear strength and the shear modulus of the masonry, as well as their evolution during the tests. Moreover, these tests were compared and integrated with a consistent number of experimental data collected in the current literature aiming to validate a new analytical equation for the estimation of the shear strength of the reinforced masonry, merely based on the properties of the unreinforced masonry and the FRM mortar.

Experimental and finite element analysis of flexural performance of RC beams retrofitted using near-surface mounted with CFRP composites and cement adhesive

Fiber reinforced polymer (FRP) composite has been used effectively for the rehabilitation of concrete and steel structures in the last decades due to its excellent properties compared with conventional reinforcing materials such as steel. Despite the major role of epoxy resins as a bonding material between fibre and substrate, the rapid deterioration of the mechanical properties at elevated temperature is the critical issue for the epoxy matrix. Therefore, substitution of epoxy adhesive with cementitious bonding agent will be beneficial in order to provide more resistant systems at elevated temperatures. Near-surface mounted (NSM) strengthening technique with cement adhesives has only been investigated for torsion. Flexural performance is a significant factor in the strengthening of different structures. This paper reports the experimental study on the behavior of small scale retrofitted beams using Near-Surface Mounted strengthening system with carbon fiber reinforced polymer (CFRP) textile and laminate and cement-base adhesives for flexure. The beams retrofitted with modified cement-based adhesive achieved 98% to 100% ultimate loads of that beams strengthened with epoxy adhesives. Numerical analyses is utilized to evaluate the experimental results, and comparable results were observed between the experimental results and finite element analysis.

REHABILITACIÓN DEL FIRME DE CUATRO GLORIETAS MEDIANTE UN REFUERZO DELGADO DE HORMIGÓN (“THIN WHITETOPPING”)

This article describes the design and construction of the structural rehabilitation of the bituminous pavement of four roundabouts by means of the arrangement of a 12 cm layer of vibrated concrete with fibres with very close joints (technique known as "thin whitetopping"). The roundabouts, which belong to the N-II National Road as it passes through La Jonquera (Spain), are subject to high levels of heavy vehicle traffic (IMDp > 4,000 heavy vehicles/day). In the project phase, the causes of deterioration of the original road surface were studied, its remaining bearing capacity was characterised and the thickness of concrete to be used was calculated. In the most damaged areas, the bituminous mixture was completely replaced by a lower quality concrete which was adhered to the concrete of the reinforcement by means of metal connectors. In addition, a detailed design of the transitions between the rehabilitated and the existing pavement and the arrangement of the joints was also carried out. Throughout the document, the different tasks carried out for the design and construction of the adopted solution are described in detail and, finally, design and construction recommendations are provided based on the results obtained. Keywords: Concrete, concrete bonding, Concrete with fibres, Reinforcement of pavements with concrete, Fuel resistance, Whitetopping.

Bond behavior of CFRP-concrete bonding interface considering degradation of epoxy primer under wet-dry cycles

The excellent performance of the CFRP-concrete bonding interface is a key to ensure the reliability and effectiveness of the rehabilitation in concrete structures with external fiber reinforced polymer (FRP). Meanwhile, the epoxy primer, which bonded the FRP plate and the concrete substrate, is significantly affected by the aggressive environment. In this paper, two kinds of experiments which associated with the CFRP-concrete specimens and the epoxy primer after corroding in a wet-dry cycles environment were conducted. It shows that the immersion area of the epoxy primer has a significant influence on the properties of the moisture absorption, and that would lead to a degradation in the mechanical properties of the CFRP-concrete interface. Simultaneously, the failure modes of the CFRP-concrete interface presented a transformation from the epoxy/concrete interaction layer to the epoxy primer layer along with the increase of aging duration. To further depict the degraded bond behavior, a time-dependent bond-slip model considering the degradation of epoxy primer was proposed, and the interface fracture energy was utilized to quantify the degree of the deterioration. By comparing with the value of interface fracture energy, it was figured out that the normal bond-slip model (Popovics model) is not enough for the safety of the concrete structures rehabilitated with external CFRP, and the proposed time-dependent bond-slip model is more accurate in evaluating the time-dependent mechanical properties of concrete structures suffering in an aggressive environment.

Let it flow: Modeling ecological benefits and hydropower production impacts of banning zero-flow events in a large regulated river system

Hydropeaking, defined as rapid and frequent changes in flow to optimize hydropower production, is an increasingly common procedure negatively affecting lotic habitats in riverine ecosystems. An important aspect of hydropeaking is zero-flow events, occurring when hydropower stations are stopped due to low energy demand or low electricity prices. We quantified the ecological benefits and consequences for hydropower production of restricting zero-flow events. The 19 major hydropower stations in the Ume River system in northern Sweden stand still with no discharge 9% to 55% of the time a hydrologically normal year, transforming lotic habitat to stagnant water. The duration of zero-flow events is exacerbated in dry years, with no discharge for 28% of the time in a typical station, to be compared with 7% in a wet year. Zero-flow events affect the behavior of fish, altering the fish community, and potentially result in low oxygen levels and low food supply to filter-feeding macroinvertebrates. We modelled the consequences of restricting zero-flow events by introducing minimum flows equaling mean annual low flow or higher for the entire Ume River catchment. The measure would result in an additional 240 ha of shallow lotic habitat with gravel to boulder streambeds having flow velocity exceeding 0.1 m/s, i.e. suitable for lotic species such as grayling Thymallus thymallus. In addition, the measure would enable creating another 107 ha of similar habitat after structural rehabilitation of river reaches. All measures would result in a mean loss of hydropower production of 0.5% per year for the entire river system, 98% of which would occur between May and October when the demand for electricity is lower. Hydropower production would also be partly moved from daytime to nighttime. As zero-flow events are common in several other river systems, restrictions on their frequency and duration could be implemented in many areas.

Advances in Dental Materials “at a Glance.”

Dental materials play a fundamental role in the rehabilitation of tooth structures and regeneration of oral tissues [...]

Concrete girders retrofitted with basalt fibre fabric – A feasibility study using lab tests and field application

Basalt fibre fabric is made of igneous rock called basalt and hence, it is a sustainable material which can be used for strengthening and rehabilitation of structural components. As a part of a long-term research program on applications of basalt fibre and fabric for rehabilitation and strengthening of various structures, in 2016, damaged concrete girders of a road bridge were successfully retrofitted using basalt fibre fabric. There was no lost service time for this structure during and now post repair. The continued performance observed from quarterly bridge inspections clearly demonstrates that this rehabilitation technique is a viable and durable method to retrofit and repair of infrastructure since no signs of distress, damage, or delamination have been noticed. Lab testing on thirteen reinforced concrete beams was also undertaken to determine this retrofitting technique, specifically by testing the performance of concrete beams loaded well beyond the service load. The lab test data confirms the validity of the rehabilitation methodology with outcomes beyond the service and yield loads. The lab test data showed that the yield and ultimate moment capacities of the beams were increased significantly. The retrofitted beams also exhibited a better ductility and performance when compared to the control beam.

Rehabilitation of substandard beam-column joint using geopolymer

Geopolymer has been a subject of interest for researchers in recent years. Few studies were conducted to examine feasibility of geopolymer mortar as an alternative repair material. All such studies were limited to structures under monotonic loading. Till date, no study was carried out to investigate suitability of geopolymer based material on rehabilitation of structures subjected to cyclic loading. Therefore, in the present study an attempt has been made to rehabilitate substandard beam-column joint following removal and replacement technique using geopolymer. Two types of repair materials viz. geopolymer mortar (GM) and steel fiber reinforced geopolymer mortar (SFRGM) were used. Test results indicated that both repair materials were successful in restoring the cyclic performance of damaged beam-column joint in terms of maximum load, stiffness degradation, ductility and energy dissipation up to the level of control specimens. However, specimens rehabilitated by GM exhibited undesirable brittle joint failure, similar to that of substandard control specimens. On the other hand, SFRGM was able to alter the failure mode of damaged beam-column joint to ductile beam failure.

Accounting for Uncertainties in the Safety Assessment of Concrete Gravity Dams: A Probabilistic Approach with Sample Optimization

Important advances have been made in the methodologies for assessing the safety of dams, resulting in the review and modification of design guidelines. Many existing dams fail to meet these revised criteria, and structural rehabilitation to achieve the updated standards may be costly and difficult. To this end, probabilistic methods have emerged as a promising alternative and constitute the basis of more adequate procedures of design and assessment. However, such methods, in addition to being computationally expensive, can produce very different solutions, depending on the input parameters, which can greatly influence the final results. Addressing the existing challenges of these procedures to analyze the stability of concrete dams, this study proposes a probabilistic-based methodology for assessing the safety of dams under usual, unusual, and extreme loading conditions. The proposed procedure allows the analysis to be updated while avoiding unnecessary simulation runs by classifying the load cases according to the annual probability of exceedance and by using an efficient progressive sampling strategy. In addition, a variance-based global sensitivity analysis is performed to identify the parameters most affecting the dam stability, and the parameter ranges that meet the safety guidelines are formulated. It is observed that the proposed methodology is more robust, more computationally efficient, and more easily interpretable than conventional methods.

Rehabilitation of heavily damaged beam-column connections with CFRP wrapping and SFRM casing

Results of an experimental testing program on two beam-column connections at full scale are presented. Specimens were first tested without initial damage. After that, rehabilitation was conducted using two different techniques, namely: externally bonded carbon fiber reinforced polymer and ultra-high performance mortar reinforced with steel fibers. Specimens were then re-tested. Different loading protocols were used on each specimen to assess their impact on the load-deformation capacity. Such protocols were displacement-controlled and applied quasi-statically. Performance of the specimens, before and after rehabilitation, is presented and discussed in terms of strength and drift capacity, energy dissipation, equivalent viscous damping, effective stiffness, cracking, and visual damage. Interesting findings, useful for the rehabilitation of concrete structures after strong earthquake ground motions, are presented.