Strengthening Schemes Research Articles

Efficacy of FRCM systems in flexural strengthening of RC T-beams

This paper presents an experimental study on the flexural behaviour of RC beams strengthened with fabric reinforced cementitious matrix (FRCM) system. Eight T-shaped RC beams with two different flexural reinforcement ratios (ρs = 0.40% and ρs = 1.02%) were constructed and tested as simply supported under monotonic three-point loading. Two beams were kept unstrengthen to act as references while the remaining six beams were strengthened with different types and geometric schemes of FRCM system. Three different test parameters have been considered: (a) FRCM type (carbon and glass), (b) FRCM strengthening scheme (side bonded versus U-shaped scheme), and (c) internal flexural reinforcement ratio. The strengthening system increased the ultimate load carrying capacity by 16.52 – 46.73% in carbon FRCM strengthened beams and 4.84 – 29.41% for glass fRcM strengthened beams relative to the reference beams. The strengthening performance of FRCM system decreased with an increase in the amount of internal flexural reinforcement. Moreover, U-shaped strengthening scheme performed better than the sided bonded counterparts in terms of the gain in the ultimate load and failure modes.

Integrated seismic risk and resilience assessment of roadway networks in earthquake prone areas

Intercity networks constitute a highly important civil infrastructure in developed countries, as they contribute to the prosperity and development of the connected communities. This was evident after recent strong earthquakes that caused extensive structural damage to key transportation components, such as bridges, overpasses, tunnels and geotechnical works, that in turn led to a significant additional loss associated with the prolonged traffic disruption. In cases of seismic events in developed societies with complex and coupled intercity transportation systems, the interdependency between citizens’ life and road functionality has further amplified the seismically-induced loss. Quantifying therefore, the resilience of road networks, defined as their ability to withstand, adapt to, and rapidly recover after a disruptive event, is a challenging issue of paramount importance towards holistic disaster risk mitigation and management. This study takes into account the above aspects of network resilience to earthquake loading and establishes a comprehensive, multi-criterion framework for mitigating the overall loss expected to be experienced by the community due to future earthquake events. The latter is decoupled into the direct structural damage-related loss and the indirect loss associated with the travel delays of the network users, as well as the wider socio-economic consequences in the affected area. In order to reflect the multi-dimensional nature of loss, a set of novel, time-variant indicators is herein introduced, while cumulative indicators are proposed for assessing the total loss incurred throughout the entire recovery period. This probabilistic risk management framework is implemented into a software to facilitate informed decisions of the stakeholders, both before and after a major earthquake event, thus prioritizing the pre-disruption strengthening schemes and accelerating the inspection and recovery measures, respectively.

CASE STUDY OF SEISMIC EVALUATION AND STRENGTHENING OF EXISTING LOW-RISE REINFORCED CONCRETE BUILDING

All new buildings nowadays have to be designed and executed to overcome any imposed type of loading (lateral/vertical). On a universal scale, the stock of buildings built before 1980’s is believed to be many times more than the number of newer buildings in most urban cities. In Beirut, as an example, a large proportion of Reinforced Concrete (RC) structures were constructed in the absence of mandatory earthquake design requirements, and unquestionably recognized as the type of construction most vulnerable to earthquakes. The performed research focused on how to evaluate the status of old building and how to design and execute the convenient seismic strengthening schemes. A case study has been selected to implement the evaluation process and design proposals. Conventional seismic upgrading technique has been assessed like the addition of shear walls in addition to more innovative approach which is the installation of steel bracing system. The strengthening schemes proposed aimed to create an ideal harmonization of the technical, economic and social aspects of the issue in hand. Analysis of the three structural systems (existing, modified with shear walls and with bracing systems) has been performed using the ETABS software including static equivalent, dynamic and pushover analyses. The research sorted out with a comparison between the systems based on different structural criteria followed by general recommendations and suggestions.

SHEAR STRENGTHENING OF R/C BEAMS USING AFRP STIRRUPS WITH ANCHORED ENDS

Many studies have been conducted on the behaviour of reinforced concrete (R/C) beams shear-strengthened with fiber reinforced polymer (FRP) sheets. The studies show that FRP materials can produce good performance when used to carry some portions of shear force in the shear-strengthened beam. However, the performance of the FRP sheets used for shear strengthening is found limited by bond capacity between the FRP sheets and concrete surface. To improve the bond performance, an anchorage system can be introduced to the FRP strengthening scheme. This paper presents experimental and analytical studies conducted to evaluate the contribution and behaviour of aramid fiber reinforced polymer (AFRP) sheets with anchored ends in carrying the shear force in reinforced concrete beams. In the study, nine reinforced concrete beam specimens were fabricated and tested. Test parameters of the study include thickness of AFRP sheet used, type of wraps applied, type of anchors and diameter of anchor head used. Two types of anchorage system were proposed in the study, i.e. insert anchor system and C-embedded anchor system. The results from this study showed that the proposed anchorage system can improve the contribution of the FRP sheets in carrying the shear force in beams. In addition, the C-embedded anchor system exhibits better performance than the insert anchor system. Lastly, the behaviour of beams strengthened using FRP stirrups with anchored ends can be closely predicted by the ACI 440 design equations applicable for full-wrap scheme.

A novel differentiation sectionalized strengthen planning method for transmission line based on support vector regression

According to the ideas of risk assessment, the theory of support vector regression is introduced to forecast the ice thickness distribution and achieve the ice extreme value of the wire. Combined with the exponential function of failure rate when the line is under stress, the failure rate model of the line is established in the particular icing condition. The ice strengthening standard is developed by the icing thickness of transmission line, which is used to strengthen lines differentially. Especially, the lines that cross different meteorological conditions are strengthened by the method of segmentation. Finally, the method of economic assessment based on the total life cycle cost is improved, and the comprehensive failure rate is used to calculate differentiated “impairment” benefits. Different lines are made differentiated planning through the simulation example. Various economic indicators are comprehensively compared, in that case, economic assessment results of lines under different strengthening schemes are obtained, which proves the effectiveness of the proposed method.

Problems of financial and investment support modeling of the regional social and economic development

Ponte Academic JournalJul 2018, Volume 74, Issue 7 Problems of financial and investment support modeling of the regional social and economic developmentAuthor(s): Guliyeva Aygun Eldar giziJ. Ponte - Jul 2018 - Volume 74 - Issue 7 doi: 10.21506/j.ponte.2018.7.1 Abstract:The main aim of the research is to investigate the problems of financial and investment support modeling of the regional social and economic development, to analyse the conceptual practical approach to these problems and definition of the adequate mechanisms. Proceeding from the objective situation of the regional social and economic development in Azerbaijan there was justified a complex functional structure of the regions.The factors which enables the sustainable development of the regions, the principles and measures of the financial and investment support were determined.The significance of conceptual practical approach to financial and investment support of the regional social and economic development was revealed. The significance of financial and investment support in the modeling of social economic development on the regional level, the maximum rational use of the local natural and economic supplies in formation of the financial resources, and enterprises modeling issues were analysed. There was prepared a structure of regional investment policy formation and implementation system.The formation factors and implementation ways of preparation mechanisms of the regional investment policy were determined.The directions of strengthening of the finance and credit support of the social and economic development prorams were justified. There was also given a scheme of strengthening of the financial and credit support rationality of the regional social economic development program. The fraction of regions in the total amount of the economic agents in Azerbaijan was analysed. There was prepared a scheme of importnt directions of the multiplicative effect in the social economic development of the regions.The efficiency issues of the regional social economic development program in Azerbaijan were analysed. There were presented the dynamics of funds oriented to the nominal capital on regions in Azerbaijan and dynamics of funds oriented to the nominal capital per capita on regions. The current situation of the regional social economic development in Azerbaijan and production of outputs on the economic regions were analysed. The dynamics of outputs production per capita in the main fields of economics region-wise and the dynamics of industrial production volume region-wise were also presented. There were generalized the factors determining the strengthening of financial and investment support of the regional social economic development. There were shown the ways of strategic approach to the financial and investment support of the social economic development in the regions in the short and long terms in Azerbaijan. There were prepared suggestions and given advice on the issues reviewed in the article. Download full text:Check if you have access through your login credentials or your institution Username Password

Analytical and numerical studies on hollow core slabs strengthened with hybrid FRP and overlay techniques

The objective of this study is to understand the behaviour of hollow core slabs strengthened with FRP and hybrid techniques through numerical and analytical studies. Different strengthening techniques considered in this study are (i) External Bonding (EB) of Carbon Fiber Reinforced Polymer (CFRP) laminates, (ii) Near Surface Mounting (NSM) of CFRP laminates, (iii) Bonded Overlay (BO) using concrete layer, and (iv) hybrid strengthening which is a combination of bonded overlay and NSM or EB. In the numerical studies, three-dimensional Finite Element (FE) models of hollow core slabs were developed considering material and geometrical nonlinearities, and a phased nonlinear analysis was carried out. The analytical calculations were carried out using Response-2000 program which is based on Modified Compression Field Theory (MCFT). Both the numerical and analytical models predicted the behaviour in agreement with experimental results. Parametric studies indicated that increase in the bonded overlay thickness increases the peak load capacity without reducing the displacement ductility. The increase in FRP strengthening ratio increased the capacity but reduced the displacement ductility. The hybrid strengthening technique was found to increase the capacity of the hollow core slabs by more than 100% without compromise in ductility when compared to their individual strengthening schemes.

Research of Laser Screens of Electronic Optical Targets

Приведены результаты исследований по разработке лазерных экранов электронных оптических мишеней для стрелкового оружия на кафедре «Вычислительная техника» ИжГТУ имени М. Т. Калашникова и в Институте механики УрО РАН. Электронные оптические мишени, отличающиеся высокими точностными и помехоустойчивыми свойствами, но вместе с тем громоздкостью конструкции, высоким энергопотреблением и трудоемкостью настройки, широко используются для испытания и диагностики стрелкового и артиллерийского оружия на производствах и военных приемках, улучшение их эксплуатационных свойств является актуальной задачей. Исследованы варианты конструкции лазерных экранов с использованием зеркальных решеток и лазерных плоскостей. Сначала проведен выбор фотодиодов для оптических датчиков и режимы их работы исходя из соотношения сигнал/шум и длительности фронта сигнала. Далее исследованы параметры лазерной зеркальной решетки, выявлены такие недостатки, как существенное ослабление лазерного луча при многократном отражении, трудоемкость механической настройки решетки и наличие «мертвых зон» в призеркальных областях. Но ограничение размеров зоны регистрации позволяет все же использовать лазерные зеркальные решетки для частных случаев испытаний. Также исследована лазерная плоскость на базе лазерного уровня. Исходя из малого уровня полезного сигнала необходимо использовать щелевые диафрагмы, оптическую систему и электронную схему усиления. Усложнение конструкции лазерной плоскости позволило получить лучшее соотношение сигнал/шум, но оптическая система и параметры лазерного уровня также ограничивают размеры зоны регистрации меньшими значениями, чем у лазерной зеркальной решетки. Приведены результаты экспериментальных испытаний лазерных экранов. Сделан вывод о перспективности дальнейших исследований и усовершенствований оптических мишеней с целью расширения их сфер использования и снижения себестоимости.

Finite Element Analysis of Increasing Column Section and CFRP Reinforcement Method under Different Axial Compression Ratio

Eight less stirrups in the core area frame joints are simulated by ABAQUS finite element numerical software. The composite reinforcement method is strengthened with carbon fiber and increasing column section, the axial compression ratio of reinforced specimens is 0.3, 0.45 and 0.6 respectively. The results of the load-displacement curve, ductility and stiffness are analyzed, and it is found that the different axial compression ratio has great influence on the bearing capacity of increasing column section strengthening method, and has little influence on carbon fiber reinforcement method. The different strengthening schemes improve the ultimate bearing capacity and ductility of frame joints in a certain extent, composite reinforcement joints strengthening method to improve the most significant, followed by increasing column section, reinforcement method of carbon fiber reinforced joints to increase the minimum.

Emergency repair of severely damaged reinforced concrete column elements under axial compression: An experimental study

Reinforced concrete (RC) columns in a framed construction can be severely damaged under earthquake, blast, fatigue and other loads. It is essential to quickly restore the strength and stiffness of columns after its damage for maintaining the serviceability of the building. The objective of this study is to assess the efficiency of different strengthening techniques on emergency repair of the severely damaged RC columns under axial compression. Six short RC columns elements were cast and tested under axial compression until 20% drop in the peak strength. Thereafter, these severely damaged columns were repaired using strengthening schemes, namely (i) repairing the damaged portions using quick setting cement mortar, (ii) Near Surface Mounting (NSM) of CFRP (Carbon Fiber Reinforced Polymer) laminates and (iii) Hybrid strengthening technique. The hybrid strengthening technique uses the combination of CFRP NSM laminates as additional longitudinal reinforcement and external bonding with CFRP fabric for confinement. The hybrid strengthening scheme was found to be the most efficient in restoring the lost strength and initial stiffness when compared to the only NSM strengthening or repair with quick setting cement mortar.

Investigating the seismic behavior of RC shear walls with openings strengthened with FRP sheets using different schemes

This paper investigates the seismic behavior of RC shear walls strengthened by Fiber Reinforced Polymer (FRP) composites. In this research, the e ects of strengthening shear walls with di fferent strengthening schemes and also strengthening walls with openings in di fferent dimensions and locations are studied. The development of nonlinear nite element methods has improved the accuracy of seismic analysis of complex structures. In this study, the ABAQUS software is used to investigate the nal resisting parameters,ductility, and behavior factor in these walls using nonlinear static analysis. The ndings prove that the applied strengthening schemes increase the nal strength of the wall. Also, the increasing ductility, behavior factor, and increased overstrength factor in some of these walls compared with original walls are observed. The ndings also prove that special openings with limited dimensions to improve seismic behavior of the wall are e ective, and the only limitation of using these openings is decreasing the nal strength which can be made up by using a proper strengthening scheme of FRP.

Axial compression performance of steel box columns with different strengthening schemes

Welding the reinforced component on the surface of a steel structure is a common method to reinforce steel structures in practical engineering. Work efficiency is low in actual construction because of continuous welding. Intermittent welding was adopted in this study to address this issue. The axial compression performance of reinforced steel columns in an actual project was studied through experiments and with the numerical method. The influence of different intermittent welding reinforcement schemes on the reinforcement of steel box columns was analyzed. Steel box columns with different weld intervals were placed relatively close because of their failure mechanism. The discontinuous welding reinforcement scheme reduced cost and improved efficiency. A simplified numerical model was established to conduct a parametrical analysis. An improved reinforcement scheme was proposed based on the analyzed results. The improved reinforcement scheme enhanced the load conditions and strength of steel angles.

FRP strengthening of 60 year old pre-stressed concrete bridge deck units

Over the past few decades fibre reinforced polymers (FRPs) have gradually gained recognition as an effective material for the strengthening of reinforced concrete (RC) structures. FRP strengthening techniques provide an attractive alternative to the existing cumbersome traditional bridge strengthening methods due to FRPs superior properties, such as lightweight, easy to install, and highly resistant to corrosion. FRP strengthening has been sought as an option for strengthening pre-stressed concrete deck unit bridges in Queensland, Australia. This paper presents an investigation in to the effectiveness of two different FRP strengthening techniques on increasing flexural capacity and flexural stiffness of pre-stressed RC deck units. Two different FRP strengthening schemes, one with adhesively bonded carbon FRP (CFRP) pultruded plates and another with adhesively bonded and mechanically fastened glass FRP (GFRP) I beam and adhesively bonded CFRP pultruded plates were investigated. Three 60years old pre-stressed RC deck units taken from a bridge in Queensland, Australia were tested. One beam was tested as the control specimen, while the other two were strengthened with the two different FRP strengthening techniques. FRP strengthening using the two proposed systems found to increase the loads at serviceability limit by 10% and 31%, while ultimate strength was increased by 54% and 105%. A section analysis based on perfect composite section assumption was found to predict the moment curvature behaviour of the FRP strengthened specimens quite accurately. Existing design code methods were found to provide conservative design strength of the FRP strengthened pre-stressed RC deck units.

Efficiency and Cost-Benefit Analysis of Seismic Strengthening Techniques for Old Residential Buildings in Lisbon

ABSTRACTThis paper presents a study on the techno-economic efficiency of seismic strengthening techniques for old residential buildings, with application to construction typologies in Lisbon (stone masonry and “Placa” buildings). A comprehensive review on strengthening techniques and implications for the seismic behavior is made. Different strengthening schemes are implicitly simulated within equivalent frame models of the representative buildings. Then, pushover analysis is applied in order to compare the seismic performance of the buildings, before and after strengthening. A cost-benefit analysis of the strengthening solutions is finally performed, comparing the economic benefit gained by reducing the seismic damage, against the intervention cost.

Investigation of the Influences of Asymmetric Damages on Seismic Assessments for Existing Masonry Structures

Masonry structures have been widely used in residences and in commercial and public buildings around the world. Most existing masonry structures have asymmetric damages that significantly influence their safety in earthquakes. Their seismic assessment would not be reliable without considering the influences of these asymmetric damages. To address the issue, the authors conduct a pseudo-static test on a masonry model with asymmetric damages. Before the test, the authors apply asymmetric damages by weakening one of the load-bearing walls of the model. In the test, the authors apply synchronized horizontal displacements on top of the load-bearing walls in a cyclical manner, and record the deformation, crack distributions, and reaction forces. Based on the records, the authors analyze the deformation patterns, failure procedure, cracking pattern, hysteretic behaviors, and stiffness degradation of the model. The test results indicate that asymmetric damages cause nontrivial structural rotation under horizontal loading, and then make the walls fail in different patterns. The structural rotation significantly influences the distribution of the seismic internal forces. Excluding the rotation in the calculation, one can underestimate the seismic internal forces for walls without damages and overestimate the forces for walls with damages. The structural rotation also influences the seismic strengthening scheme. One should apply strengthening measures both in the member scale and in the structural scale. The findings can be referred to in seismic assessment for most existing masonry structures.

Property and Digitization: With Special Reference to NLRMP Scheme in India

The term ‘property’, is extraordinarily difficult to define. One of America’s foremost property law scholars even asserts that “[t]he question is unanswerable.” The problem arises because the legal meaning of “property” is quite different from the common meaning of the term. Land is a subject falling within the powers of the State Governments under the Constitution of India and hence, property laws in India may differ from State to State. Besides the local laws, several laws enacted by the Central Government also govern acquisition and ownership of property (including an interest in property) through purchase/sale, transfer, mortgage, inheritance or gift. Transfer of property other than agricultural land, registration of deeds and document fall in the Concurrent List. The scheme of Strengthening of Revenue Administration & Updating of Land Records (SRA& ULR) was launched in 1987-88 to help states and union territories in updating and maintaining land records, setting up survey and settlement organisations and strengthening the revenue machinery.The NLRMP is expected to provide a comprehensive database for development planning as well as regulatory and disaster management activities by providing location-specific information while providing citizen services based on land records. The data and the conclusive titles would also be linked to the development process such as credit institutions, land acquisition, rehabilitation & resettlement, land use planning, cropping pattern and food security, and other secondary data such as issue of various certificates.

Behavior of Tapered Self-Compacting Reinforced Concrete Beams Strengthened by CFRP

This study presents an experimental investigation on the behavior of fourteen reinforced self-compacting concrete tapered beams with or without strengthening. The strengthening was applied by using carbon fiber reinforced polymer (CFRP) to beams with simply supported span and subjected to two points loading. Those beams have an overall length of 2000 mm, a width of 150 mm and a height of 250 mm at supports (hs) and a mid-span depth (hm) varies between 150 mm and 200 mm and with different strengthening scheme, they are investigated to evaluate the behavior at experimental test and to study the effect of the parameters which include haunch angle α, shear-span to effective depth ratio a/d and strengthening strips number and locations on beams behavior. The experimental results show that decreasing the value of haunch angle α increased the load capacity by about 56% and decreased the corresponding deflection while when tapered beams are strengthened by CFRP the ultimate load is increased up to 39% with decrease of deflection. On the other hand, increasing a/d ratio leads to a decrement in load capacity and increment in deflection.

Efficient near surface mounting CFRP strengthening of pretensioned hollowcore slabs with opening – An experimental study

Carbon fiber reinforced polymers (CFRP) are commonly used in strengthening of civil infrastructure due to their superior mechanical properties. Near surface mounting (NSM) of CFRP laminates is an efficient strengthening scheme to restore the capacity of concrete elements. Hollowcore slabs are pretensioned precast concrete elements reinforced only with prestressing strands. Due to various service requirements, openings/cut-outs are provided in the slabs. Reinstating the capacity of hollowcore slabs lost due to the presence of openings is very important as openings can severely reduce the capacity of these slabs and alter the load distribution in the floor system. This paper investigates the efficiency of NSM technique using CFRP laminates in restoring the capacity of hollowcore slabs with openings. Ten full scale hollowcore slabs were tested at two shear span to depth (a/d) ratios and with two different locations of opening. Presence of opening reduced the ultimate capacity of slab by 44% and NSM CFRP strengthening fully restored the lost capacity based on a/d ratio. The adopted strengthening was more effective in shear dominated than in flexure dominated specimens. However, in both a/d ratios, good improvement in initial stiffness was observed due to NSM CFRP strengthening.

The enhanced performance of CFST beams using different strengthening schemes involving unidirectional CFRP sheets: An experimental study

Concrete-filled steel tube (CFST) beam, like any conventional structural member, for several reasons need strengthening, such as by making upgrades to carry extra loads or to make repairs owing to degradation attributed to aging, fire, and fatigue. This study experimentally investigates the strengthening behaviour of the circular and rectangular simply supported CFST beams using unidirectional carbon fibre reinforced polymer (CFRP) sheets, in which partial-unilateral (partial), full-unilateral (full), and full-bilateral (combined) strengthening schemes with varied layers and lengths are used. The results show that the moment capacity, energy absorption capacity, and flexural stiffness of the strengthened beam significantly improved with the increase of CFRP layers. For example, the moment capacity of the rectangular beams increased by about 26% and 38% when they were partially strengthened with two and three CFRP layers, respectively. Also, the beams were partially strengthened with two CFRP layers laid along 75% and 100% of their lengths, and that fully strengthened along 100% of its length, all achieved almost the same load improvements (+26% to +28%) in comparison with their control beam, which means that about 50% of the amount of CFRP sheets or even more can be saved and the same improvement can be achieved. The energy absorption capacity of the circular beams improved by about 21.8% when they were partially strengthened with two CFRP sheets, for example. Moreover, the flexural stiffness values of the strengthened beams fairly agreed with those predicted from the existing standards (AISC, EC4, BS5400, and AIJ) after including the effects of CFRP.

A combination of GFRP sheets and steel cage for seismic strengthening of shear-deficient corner RC beam-column joints

This paper is focused on the performance of a proposed scheme for seismic strengthening of shear deficient joints of 3D reinforced concrete (RC) corner beam-column connections. This technique is composed of a combination of GFRP sheets and a steel cage, and does not require perforating the existing concrete elements to anchor the FRP sheets. Two similar full-scale beam-column connections were made without any transverse reinforcement in their joint region. One of which was tested in its as-built condition, taken as the control specimen, while the other one was tested after strengthening. Seismic behaviour of these specimens was studied under a cyclic loading pattern imposed simultaneously with a constant column’s axial load. Comparison of the test results of these specimens revealed a noticeable improvement in the seismic response of the strengthened specimen. This achievement along with the application feasibility of this technique indicates the suitability of the proposed strengthening scheme for practical applications. Finally, the experimentally obtained joint shear strength of the control and retrofitted specimens are compared to the one estimated by the relationships of the softened strut-and-tie model and ACI-318, respectively. This comparison revealed a satisfactory prediction of joint shear strength for both specimens, the as-built and the strengthened one.