روزی يک مرد روحانی با خداوند مکالمه ای داشت: "خداوندا! دوست دارم بدانم بهشت و جهنم چه شکلی هستند؟ "، خداوند او را به سمت دو در هدايت کرد و يکی از آنها را باز کرد، مرد نگاهی به داخل انداخت، درست در وسط اتاق يک ميز گرد بزرگ وجود داشت که روی آن يک ظرف خورش بود، که آنقدر بوی خوبی داشت که دهانش آب افتاد، افرادی که دور ميز نشسته بودند بسيار لاغر مردنی و مريض حال بودند، به نظر قحطی زده می آمدند، آنها در دست خود قاشق هايی با دسته بسيار بلند داشتند که اين دسته ها به بالای بازوهايشان وصل شده بود و هر کدام از آنها به راحتی می توانستند دست خود را داخل ظرف خورش ببرند تا قاشق خود را پر نمایند، اما از آن جايی که اين دسته ها از بازوهايشان بلند تر بود، نمی توانستند دستشان را برگردانند و قاشق را در دهان خود فرو ببرند
مرد روحانی با ديدن صحنه بدبختی و عذاب آنها غمگين شد، خداوند گفت: "تو جهنم را ديدی، حال نوبت بهشت است"، آنها به سمت اتاق بعدی رفتند و خدا در را باز کرد، آنجا هم دقيقا مثل اتاق قبلی بود، يک ميز گرد با يک ظرف خورش روی آن و افراد دور ميز، آنها مانند اتاق قبل همان قاشق های دسته بلند را داشتند، ولی به اندازه کافی قوی و چاق بوده، می گفتند و می خنديدند، مرد روحانی گفت: "خداوندا نمی فهمم؟!"، خداوند پاسخ داد: "ساده است، فقط احتياج به يک مهارت دارد، می بينی؟ اينها ياد گرفته اند که به یکديگر غذا بدهند، در حالی که آدم های طمع کار اتاق قبل تنها به خودشان فکر می کنند!"
هنگامی که موسی فوت می کرد، به شما می اندیشید، هنگامی که عیسی مصلوب می شد، به شما فکر می کرد، هنگامی که محمد وفات می یافت نیز به شما می اندیشید، گواه این امر کلماتی است که آنها در دم آخر بر زبان آورده اند، این کلمات از اعماق قرون و اعصار به ما یادآوری می کنند که یکدیگر را دوست داشته باشید، که به همنوع خود مهربانی نمایید، که همسایه خود را دوست بدارید، زیرا که هیچ کس به تنهایی وارد بهشت خدا نخواهد شد
تخمين زده شده که 93% از مردم اين متن را برای ديگران ارسال نخواهند کرد، زیرا آنها تنها به خود می اندیشند، ولی اگر شما جزء آن 7% باقی مانده می باشيد، اين پيام را برای دیگران ارسال نمایید، من جزء آن 7% بودم، همچنین به ياد داشته باشيد که من هميشه حاضرم تا قاشق غذای خود را با شما سهیم شوم.
Shear enhancement of reinforced concrete beams strengthened with FRP composite laminates
Ayman S. Mosallam
*, Swagata BanerjeeCivil and Environmental Engineering Department, University of California at Irvine, California 92697, United States
Received 1 April 2006; accepted 1 October 2006
Available online 18 January 2007
Abstract
This paper presents the results of an experimental investigation on shear strength enhancement of reinforced concrete beams externally reinforced with fiber-reinforced polymer (FRP) composites. A total of nine full-scale beam specimens of three different classes, as-built (
unstrengthened), repaired and retrofitted were tested in the experimental evaluation program. Three composite systems namely carbon/epoxy wet layup, E-glass/epoxy wet layup and carbon/epoxy precured strips were used for retrofit and repair evaluation. Experimental results indicated that the composite systems provided substantial increase in ultimate strength of repaired and strengthened beams as compared to the pre-cracked and as-built beam specimens. A comparative study of the experimental results with published analytical models, including the ACI 440 model, was also conducted in order to evaluate the different analytical models and identify the influencing factors on the shear behavior of FRP strengthened reinforced concrete beams. Comparison indicated that the shear span-to-depth ratio (a/d) is an important factor that actively controls the shear failure mode of beam and consequently influences on the shear strength enhancement. 2007 Elsevier Ltd. All rights reserved.Keywords:
A. Polymer-matrix composites (PMCs); B. Debonding; C. Analytical modelling; D. Mechanical testing; Infrastructureجهت مطالعه متن کامل مقاله از لینک زیر استفاده نمایید
Sensitivity analysis of reinforced concrete beams
strengthened with FRP laminates
Carlos A. Coronado
a,1, Maria M. Lopez b,*a
Department of Civil and Environmental Engineering, The Pennsylvania State University, 3127 Research Drive CATO Park,Room 117, State College, PA 16801, USA
b
Department of Civil and Environmental Engineering, The Pennsylvania State University, 212 Sackett Building, University Park,State College, PA 16802-1408, USA
Received 13 July 2004; accepted 19 July 2005
Available online 20 October 2005
Abstract
Numerical procedures are proposed to predict the failure of reinforced concrete (RC) beams strengthened in flexure with fiber-reinforced polymeric (FRP) laminates. The framework of damage mechanics was used during the modeling. Numerical results were validated against experimental data obtained from 19 beams strengthened with different types of FRP. These beams failed by concrete crushing, cover failure and plate debonding. The numerical models were capable of predicting the experimentally observed load–deflection, failure load and failure modes. The sensitivity of the numerical results was studied. In particular, the effect of the concrete constitutive behavior and different modeling considerations was evaluated. It was found that the fracture energy of the concrete–repair interface plays a central part in predicting plate-debonding failures.
Keywords:
Composite materials; Fracture energy; Finite element modeling; Damage mechanics; Debonding; Numerical modeling; FRP laminate; Reinforced concrete beam.جهت مطالعه متن کامل مقاله از لینک زیر استفاده نمایید
Performance of reinforced concrete beams strengthened by hybrid FRP laminates
Abdelhady Hosny
a, Hamdy Shaheen b, Amr Abdelrahman a,*, Tamer Elafandy ba
Structural Engineering Department, Ain Shams University, Cairo, Egyptb
RC Department, Housing and Building Research Center, Giza, EgyptAbstract
In the last two decades, the use of advanced composite materials such as Fiber Reinforced Polymers (FRP) in strengthening reinforced concrete (RC) structural elements has been increasing. Research and design guidelines concluded that externally bonded FRP could increase the capacity of RC elements efficiently. However, the linear stress–strain characteristics of FRP up to failure and lack of yield plateau have a negative impact on the overall ductility of the strengthened RC elements. Use of hybrid FRP laminates, which consist of a combination of either carbon and glass fibers, or glass and aramid fibers, changes the behaviour of the material to a non-linear behaviour.
This paper aims to study the performance of reinforced concrete beams strengthened by hybrid FRP laminates. This paper presents an experimental program conducted to study the behaviour of RC beams strengthened with hybrid fiber reinforced polymer (HFRP) laminates. The program consists of a total of twelve T-beams with overall dimensions equal to 460
· 300 · 3250 mm. The beams were tested under cyclic loading up to failure to examine its flexural behaviour. Different reinforcement ratios, fiber directions, locations and combinations of carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) laminates were attached to the beams to determine the best strengthening scheme. Different percentages of steel reinforcement were also used. An analytical model based on the stress–strain characteristics of concrete, steel and FRP was adopted. Recommendations and design guidelines of RC beams strengthened by FRP and HFRP laminates are introduced.مقاله کامل توسط لینک زیر قابل دسترسی است
On the parameters influencing the performance of reinforced concrete beams strengthened with FRP pla
On the parameters influencing the performance of reinforced concrete beams strengthened with FRP plates
F. Taheri
*, K. Shahin, I. WidiarsaDepartment of Civil Engineering, Dalhousie University, 1360 Barrington Street, Halifax, NS, Canada B3J 1Z1
Abstract
This paper presents a summary of our investigations that were aimed to assess the influence of various physical and mechanical parameters on the performance of reinforced concrete (RC) beams strengthened with fiber reinforced plastic (FRP) plates. The work was divided into two phases. The first phase investigated the influence of FRP plate length, fiber orientation, and surface preparation on the performance of FRP-reinforced RC beams. The FRP in this phase of the work was E-glass/epoxy. The second phase of the study was designed to confirm the validity of our hypothesis, which postulated that the delamination of the FRP plate would be a function of the Poisson ratio mismatch between concrete and FRP plate. Results from the second phase also suggested that less expensive glass FRP plates could adequately replace the more expensive carbon FRP plates by offering the beam more ductility, without sacrificing its expected performance. Moreover, results from both phases showed that the lateral stiffness of the FRP plate contributed to the overall flexural stiffness of the strengthened beam.
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Flexural strengthening of reinforced lightweight polystyrene aggregate concrete beams with near-surf
Flexural strengthening of reinforced lightweight polystyrene aggregate concrete beams with near-surface mounted GFRP bars
W.C. Tang, R.V. Balendran
, A. Nadeem, H.Y. LeungDepartment of Building and Construction, City University of Hong Kong, China
Received 26 November 2004; received in revised form 4 January 2005; accepted 19 May 2005
Abstract
Application of near-surface mounted (NSM) fibre reinforced polymer (FRP) bars is emerging as a promising technology for increasing flexural and shear strength of deficient reinforced concrete (RC) members. In order for this technique to perform effectively, the structural behaviour of RC elements strengthened with NSM FRP bars needs to be fully characterized. This paper focuses on the characterization of flexural behaviour of RC members strengthened with NSM glass-FRP bars. Totally, 10 beams were tested using symmetrical two-point loads test. The parameters examined under the beam tests were type of concretes (lightweight polystyrene aggregate concrete and normal concrete), type of reinforcing bars (GFRP and steel), and type of adhesives.
Flexural performance of the tested beams including modes of failure, moment–deflection response and ultimate moment capacity are presented and discussed in this paper. Results of this investigation showed that beams with NSM GFRP bars showed a reduction in ultimate deflection and an improvement in flexural stiffness and bending capacity, depending on the PA content of the beams. In general, beams strengthened with NSM GFRP bars overall showed a significant increase in ultimate moment ranging from 23% to 53% over the corresponding beams without NSM GFRP bars. The influence of epoxy type was found conspicuously dominated the moment–deflection response up to the peak moment. Besides, the ultimate moment of concrete beams reinforced with GFRP bars could be predicted satisfactorily using the equation provided in ACI 318-95 Building Code.
لینک فایل کامل مقاله
Design against cracking at openings in reinforced concrete beams strengthened with composite sheets
H.A. Abdalla
a,*, A.M. Torkey a, H.A. Haggag b, A.F. Abu-Amira aa
Structural Engineering Department, Faculty of Engineering, Cairo University, Cairo 12613, Egyptb
Structural Engineering Department, Faculty of Engineering, Helwan University, Cairo 11321, EgyptAbstract
Web openings in beams and girders occur quite often in practice to provide a convenient passage for utility ducts. Accommodating the environmental services in such a manner eliminates a significant amount of dead space and results in a more compact and, often, more economical design. However, introducing an opening into the web of a reinforced concrete beam causes local cracking around the opening leading to reduction in stiffness and capacity of the beam. In this paper the use of fibre reinforced polymer (FRP) sheets to strengthen the opening region is presented. Several design parameters are varied including opening width and depth, and amount and configuration of the FRP sheets in the vicinity of the opening. The experimental program included testing of 10 reinforced concrete beams, five of which were strengthened with FRP sheets around the opening, four were tested without strengthening, and the remaining beam was solid without opening considered as a control beam. The effect of this strengthening technique on deflection, strain, cracking, and ultimate load is investigated.
متن کامل مقاله توسط لینک زیر قابل دسترسی می باشد
Composite Structures 60 (2003) 197–204
Creep behaviour of CFRP-strengthened reinforced concrete beams
G. Al Chami, M. The´riault, K.W. Neale
*Department of Civil Engineering, University of Sherbrooke, Sherbrooke, Quebec, Canada J1K 2R1
Abstract
The strengthening of reinforced concrete structures with externally bonded fibre reinforced polymer (FRP) laminates has shown excellent performance and, as a result, this technology is rapidly replacing steel plate bonding techniques. The numerous studies that have been carried out to date on FRP-strengthened concrete elements have mainly focussed on the static and short-term responses; very little work has been done regarding the long-term performance. This paper addresses this issue, and presents results from a series of experiments on the time-dependent behaviour of carbon FRP-strengthened concrete beams. Twenty-six reinforced concrete beams with dimensions 100
· 150 · 1800 mm, with and without bonded CFRP laminates, were investigated for their creep behaviour. Different reinforcement ratios were used to evaluate the contribution of the external reinforcement on the creep resistance of the beams. High levels of sustained load were used in order to determine the maximum sustained load that can be applied without any risk of creep failure. The applied sustained loads varied from 59% to 78% of the ultimate static capacities of the un-strengthened beams. For most of the long-term tests, the applied sustained loads were higher than the service loads. This was done to account for the fact that strengthening is typically required when a structure is expected to carry increased service loads. The main parameters of this study were (i) the level of sustained load and (ii) the strengthening scheme. The results confirm that FRP strengthening is effective for increasing the ultimate capacities of the beams; however, there is virtually no improvement in performance with regard to the long-term deflections. 2007 Elsevier Ltd. All rights reserved.Keywords:
Carbon fibre reinforced polymers (CFRPs); Reinforced concrete beams; Flexural strengthening; Creep; Sustained loads; Long-term deflectionsجهت مطالعه متن کامل مقاله از لینک زیر استفاده نمایید
fly ash for concrete block manufacturing
The manufacturing of concrete masonry units uses a dry, harsh concrete mixture compacted into molds with great mechanical energy. When demolded, these units maintain their shape during handling and transportation into a curing environment. Curing methods consist of the high pressure, high temperature autoclave, or the atmospheric pressure, high temperature kiln. The use of high quality fly ash has become accepted practice in the industry.
F
ly ash improves block manufacturing in two basic ways. It gives producers the strength required and, at the same time, the added plasticity that fly ash contributes (reported by Belot, 1976) to the relatively harsh block mixes assures improved finish and texture; better mold life, and better, sharper corners. Additional benefits of fly ash in block include reduced permeability and shrinkage, increased durability and virtual elimination of efflorescence.Fly Ash Chemical Activity.
Fly ash is produced by burning powdered coal to generate electricity. Fly ash is a chemically active, finely divided mineral product high in silica, alumina and iron. Fly ash that has been burned in the process of manufacturing (in the same sense that portland cement clinker is “burned”) seeks lime. One hundred pounds of portland cement usually liberates from 12 to 20 pounds or more of free lime (calcium hydroxide) during hydration. Fly ash then chemically reacts with this free lime to form additional stable cementitious compounds. The formation of insoluble cementing compounds is accelerated and can be secured in a matter of hours in the steam curing cycle of the concrete products plant (autoclave or atmospheric).Steam Curing.
Autoclave curing, though not as common as in the past, is still used to manufacture high quality masonry units. Concrete masonry units cured in high-pressure autoclaves show early strength equivalent to that of 28-day moist-cured strength and reduction in volume change in drying (Hope 1981). The process uses temperatures of 275° to 375°F (135° to 275°C) and pressures of 75 to 170 psi (0.52 to 1.17MPa). These conditions allow for the use of fly ash as a cement replacement up to 35 percent for Class C and 30 percent for Class F fly ashes. Particular care should be taken to insure that the fly ash meets the soundness requirement of ASTM C618, indicated in Note C, Table 2 especially where the fly ash will constitute more than 20 percent of the total cementitious material.Low-pressure steam curing is usually performed in insulated kilns at elevated temperatures, the exact emperature used being a function of the materials and operation of the specific plant. This process allows for the use of fly ash as a cement replacement up to 35 percent for Class C and 25 percent for Class F fly ash. Tests with 25 percent Class F fly ash were successful with a curing temperature above 160°F (71°C) and indicate that drying shrinkage of low pressure steam-cured concrete units can be reduced by the addition of fly ash. Accelerated curing techniques allow for a period of preset before the concrete products are subjected to elevated temperatures. The preset period may lengthen slightly where cement is replaced with fly ash and if so, it must be allowed for.
Tests for resistance to freezing and thawing of concrete masonry units containing fly ash indicate that such units, in general, could be expected to perform well in vertical wall construction. For the more severe condition of horizontal exposure, a minimum compressive strength of 3,000 psi (21MPa) based upon the net area of the unit is recommended when normal weight aggregates are used. This is true whether fly ash is used or not. Air-entrainment is not practical at the extremely low or zero slumps used for concrete block. It could be applicable to slump block or quarry tile. To provide adequate freezing and thawing durability for units made with slump concrete, air-entrainment is needed (Redmond 1969). Acceptance by the engineering profession and most code bodies to use concrete masonry units for high-strength, high-rise, load-bearing construction is increasing. To meet this demand, block producers find it necessary to produce both light and normal weight units testing 3,500 psi net area (1,860 gross area assuming 53 percent solid units) and 5,000 psi net area (2,650 gross area), respectively. The 1,860 psi gross area strength units are known as high strength block and those of 2,650 psi gross area strength are known as extra high strength block.
Trial Mixes. Proportioning mixtures for the manufacture of concrete masonry units is not an exact science. Conditions may vary widely from plant to plant. When proportioning mixtures, concrete producers should check the grading and types of aggregates, cements, equipment, and kiln temperatures, and then adjust trial batches with various amounts of fly ash to achieve specific technical or economic objectives (Valore 1970). For assistance in this regard, the reader is referred to Siliceous Fines in the Cementing Medium of Steam Cured Concrete Masonry Units”, a 1967 publication by the National Concrete Masonry Association.
Debonding of FRP in bending: Simplified model and
experimental validation
Joan R. Casas
*, Jordi PascualSchool of Civil Engineering, Technical University of Catalonia (UPC), Bridge Engineering, Jordi Girona 1-3, Modulo C1, Campus Norte, 08034 Barcelona, Spain
Received 2 August 2005; received in revised form 15 January 2006; accepted 31 May 2006
Available online 2 October 2006
Abstract
Reinforced concrete members strengthened in bending by bonding of surface-mounted fiber-reinforced polymer (FRP) may present several failure modes: failure of material (reinforcing steel, concrete and composite material) or failure of the interface between concreteadhesive or adhesive-FRP. Nevertheless, experience gained from testing confirms that in most cases delamination prevails over the other possible rupture modes. Delamination in FRP strengthened sections is difficult to model because it involves multiple parameters such as FRP stiffness, adhesive material properties, presence of cracks in concrete, among others. A simplified model to predict strain of FRP at failure is presented in this paper. The experimental validation is presented as well. With this purpose carbon FRP and aramid strengthened specimens and large scale bridge models are considered. The types of bridge models tested include externally-prestressed segmental box-girder and monolithic RC continuous girders. Based on the results of the proposed model, an equation for the prediction of the ultimate force per unit width in the FRP to prevent FRP debonding is proposed. The equation has been experimentally checked with beams of small and large size, representative of real structures. In comparison to other available models, the equation is very simple to apply.
2006 Elsevier Ltd. All rights reserved.Keywords:
Fiber-reinforced polymer; Debonding; Bending; Strengthening; Concrete; Test; Delaminationبرای دریافت اصل مقاله از لینک زیر استفاده نمایید
Construction and Building Materials 21 (2007) 1940–1949
Design recommendations for the strengthening of reinforced concrete beams with externally bonded com
Design recommendations for the strengthening of reinforced concrete beams with externally bonded composite plates
Yung-Chih Wang
*, Kai HsuDepartment of Civil Engineering, National Central University, Jhongli, Taoyuan 32001, Taiwan
Abstract
A design approach for strengthening reinforced concrete beams with externally bonded fibre reinforced polymer (FRP) laminates is proposed. The use of staggered FRP laminate bonding to the tension face of the beam is suggested as an economical design. The FRP development length suggested in the guidelines is adopted. It is recommended that the FRP U-shaped strips be mechanically anchored so as to increase the longitudinal FRP bond strength and enhance the beam’s shear strength. With this design method failure due to debonding of the FRP laminate to the beam soffit can be avoided by the incorporation of FRP U-side strips. Recommendations based on the idea of modified shear friction are also given.
2007 Elsevier Ltd. All rights reserved.Keywords:
Design; Reinforced concrete beams; Retrofitting; Fibre reinforced polymer (FRP); Bending; Shearبرای جهت مطالعه اصل این مقاله از لینک زیر استفاده نمایید
Composite Structures xxx (2008) xxx–xxx
Aspects of behaviour of CFRP reinforced concrete beams in bending
Muhammad Masood Rafi
*, Ali Nadjai, Faris Ali, Didier TalamonaFire Safety Engineering Research & Technology Centre (FireSERT), University of Ulster at Jordanstown, Shore Road, Newtownabbey BT37 0QB, UK
Received 13 February 2006; received in revised form 24 July 2006; accepted 30 August 2006
Available online 18 October 2006
Abstract
The corrosion of steel poses a serious problem to the durability of reinforced concrete structures and fibre reinforced polymer (FRP) has emerged as a potential alternative material to the traditional steel. The results of a test series consisting of carbon FRP (CFRP) and steel bars reinforced concrete beams are reported in this paper. The results indicated that the behaviour of CFRP and steel reinforced beams was similar in many aspects. Both type of beams failed in their predicted modes of failure. The strength design method underestimated nominal moment capacity of CFRP reinforced beams. The deflection of CFRP reinforced beams was satisfactory at service load level, corresponding to theoretical load capacity. The deformability factor of CFRP reinforced beams was more than 6 indicating their ductile nature of failure.
2006 Elsevier Ltd. All rights reserved.Keywords:
Fibre reinforced polymer; Carbon FRP; Mode of failure; Concrete beams; Reinforcement; Moment; Deflection; Deformabilityبرای دریافت اصل مقاله از لینک زیر استفاده کنید
FRP-strengthened RC beams. I: review of debonding strength models
S.T. Smith, J.G. Teng *Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hong Kong, People’s Republic of China
Received 11 April 2001; received in revised form 5 September 2001; accepted 12 September 2001
Abstract
Bonding of a fibre-reinforced polymer (FRP) plate to the tension face of a beam has become a popular flexural strengthening method in recent years. As a result, a large number of studies have been carried out in the last decade on the behaviour of these FRP-strengthened beams. Many of these studies reported premature failures by debonding of the FRP plate with or without the concrete cover attached. The most commonly reported debonding failure occurs at or near the plate end, by either separation of the concrete cover or interfacial debonding of the FRP plate from the RC beam. This and the companion paper are concerned with strength models for such plate end debonding failures. In this paper, a comprehensive review of existing plate debonding strength models is presented. Each model is summarised and classified into one of the three categories based on the approach taken, and its theoretical basis clarified. The review not only brings together for the first time all existing plate end debonding strength models into a unified framework for future reference, but also provides the necessary background information for them to be assessed in the companion paper using a large test database assembled by the authors from the published literature.
Kywords: Debonding; FRP; RC beams; Retrofitting; Strengthening; Strength models
برای مطالعه اصل این مقاله از لینک زیر استفاده نمایید
Engineering Structures 24 (2002) 385–395
Finite Element and Experimental Serviceability
Analysis of HSC Beams Strengthened with FRP Sheets
1Seyed Hamid Hashemi, 2Reza Rahgozar, 3Ali Akbar Maghsoudi
1PhD. Candidate and 2, 3 Assist. Professor, Department of Civil
Engineering,
Abstract:
The use of externally bonded composite sheets or laminates is by now a diffuse technique to strengthen existing RC structures. However, some aspects of flexural condition still need experimental and numerical analysis; furthermore, especially for serviceability checks, there is a lack of code provisions. In this paper six reinforced high strength concrete (HSC) beams strengthened with FRP sheets were fabricated and tested, the finite element (FE) models adopted by ANSYS was performed to examine the structural behavior of tested beams was performed. A comparison between the finite element analysis results and the experimental data available on the specimens is made and by using trial and error method, the finite element model was calibrated. Six under-reinforced concrete beams were fabricated and tested to failure. With the exception of the control beam, one or four layers of CFRP were applied to the specimens. The structural response throughout the loading regime was primarily captured in terms of the load deflection behavior. The load deflection plots obtained from numerical study show good agreement with the experimental results. The serviceability characteristics of the test beams were evaluated in terms of the crack width, deflection and stress in steel and concrete. The crack patterns in the beams are also presented.
Keywords: Finite Element Model, FRP, HSC, Serviceability
American Journal of Applied Sciences 4(9):725-735, 2007
ISSN 1546-9239
Science Publications 2007
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Full text is availlable from the below link
B
EHAVIORAL TRENDS OF RC BEAMS STRENGTHENED WITHE
XTERNALLY BONDED FRPBy J. F. Bonacci,
1 Member, ASCE, and M. Maalej21
Assoc. Prof., Dept. of Civ. Engrg., Univ. of Toronto, Toronto, Canada M5S 1A4.2
Asst. Prof., Dept. of Civ. Engrg., Nat. Univ. of Singapore, Singapore 119260.A
BSTRACT: The performance of conventionally reinforced concrete (RC) beams strengthened in flexure with externally bonded fiber-reinforced polymers (EB-FRP) was studied by compiling and analyzing an experimental database. A total of 127 specimens from 23 separate studies were included in the database. A profile of specimens in the database is given, followed by an analysis of trends in failure mode, strength gain, and deformability. Failure by debonding of FRP was prevalent among specimens in the database. One-third of the specimens with external reinforcement added showed strength increases of 50% or more in combination with considerable deflection capacity. It was clear from the experimental studies that the procedures followed were most representative of member strengthening rather than repair. Most of the specimens in the database were not subjected to sustained loading or damage causing loss of original capacity before external reinforcement was added. To assess the real potential of using FRP for expedient and economical field repair and strengthening of RC members, it was concluded that future research on the application of FRP to RC members should focus on conditions that are similar to what is observed in the field, including the effects of sustained load during repair/ strengthening as well as corrosion- and load-induced damage.جهت مطالعه متن کامل مقاله فوق از طریق لینک زیر اقدام نمایید
Journal of Composites for Construction, Vol. 5, No.2, may 2001
M
ECHANICAL INTERACTION BETWEEN CONCRETE AND FRP SHEETBy Hwai-Chung Wu
11
Asst. Prof., Adv. Infrastr. Mat. Lab., Dept. of Civ. and Envir. Engrg.,Wayne State Univ., Detroit, MI 48202. E-mail: hcwu@ce.eng.wayne.eduA
BSTRACT: In this technical note, fiber-reinforced plastics (FRP) strengthening efficiency for reinforced-concrete columns will be examined from a micromechanical point of view by accounting for direct mechanical interaction between FRP sheet and concrete. Concrete compressive failure is initiated by wing-crack propagation. The mechanical interaction dictates the compressive behavior of FRP-wrapped concrete from the first bent-over point to the peak load in the load/displacement curve. A possible detailed interaction under compression is described.برای مشاهده متن کامل مقاله از لینک زیر استفاده نمایید
JOURNAL OF COMPOSITES FOR CONSTRUCTION / MAY 2000
Structural assessment of externally flexural strengthened reinforced concrete beam after repaired wi
Structural assessment of externally flexural
strengthened reinforced concrete beam after
repaired with polymer mixture
JONGSUNG SIM
1 and HONGSEOB OH21
Department of Civil and Environmental Engineering, Hanyang University, 1271, Sa1-dong,Ansan, 425-791, Korea
2
Department of Civil Engineering, Jinju National University, 150 Chilam-dong, Jinju,Kyeongnam, 660-758, South Korea
Abstract:
This study investigated the effectiveness of external strengthening technique. The experimental variables were the strengthening material and overlay materials using polymer mixtures. Beams considered in this study are the ones strengthened either with external steel plate or carbon fiber sheet (CFS) bonded to the overlay soffit or with reinforcing rebars in the overlay. An analytical method based on the nonlinear layered finite element method is used to simulate the load–deflection behavior of strengthened beam. The theoretically obtained load–deflection relationships and strains of the strengthened beams are compared to the corresponding experimental values. Efficiencies of the repairing techniques are evaluated by comparing the approximate measures on the cumulative slips. Parametric studies are then obtained using the developed model to investigate the effects of design variables on the overall flexural behavior of the strengthened beam. Simply supported beams under monotonically increasing symmetrical loads are considered exclusively.Keywords
: Carbon fiber sheet; nonlinear layered finite element method; polymer mixture structural strengthening.جهت دریافت اصل مقاله از لینک زیر استفاده کنید
Composite Interfaces, Vol. 13, No. 1, pp. 47–66 (2006)
Also available online - www.vsppub.com
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مقالات برتر حوزه مهندسی عمران اعلام شد تاریخ : شنبه، 9 تير، 1386 سایت سیویلیکا، به عنوان بزرگترین بانک مقالات تخصصی در حوزه مهندسی، با بیش از 20،000 مقاله تخصصی تمام متن، مقالات برتر در این حوزه را اعلام نمود. این مقالات هر ساله بر اساس تعداد دریافت مقالات توسط هزاران کاربر متخصص عضو این سایت در سراسر کشور انتخاب می شوند. مشخصات سه مقاله برتر طی سال گذشته عبارتند از:
مسلح شده ( FRP)، نوشته آقای سید حمید هاشمی، دانشجوی دکترای سازه دانشگاه شهید باهنر کرمان که در کنفرانس بین المللی زلزله (یادواره فاجعه بم) منتشر شده است. 2. انواع خسارتهای ناشی از روانگرایی و ارزیابی روشهای مختلف بهسازی خاکهای روانگرا، به قلم آقای مهدی درخشندی، دانشجوی دکترای مهندسی عمران، گرایش مکانیک خاک و پی دانشگاه صنعتی امیرکبیر، که در نخستین کنفرانس بهسازی زمین منتشر شده است. 3. معرفی بتن سبک اسفنجی از نوع کفی یا فوم بتن به عنوان مصالحی با قابلیتهای بالا، نوشته آقای محمد صیامی، از مرکز تحقیقات مهندسی جهاد آذربایجان شرقی که در اولین همایش بین المللی زلزله و سبک سازی ساختمان انتشار یافته است. عناوین مقالات نشان می دهد، مباحث نوین در ساختمان سازی، و استفاده از تکنولوژیهای نوین ساخت و ساز از نظر متخصصان عمران کشور در اولویت اول قرار دارد. مبحث رده بندی مقالات بر اساس میزان استفاده متخصصان، جایگاه بسیار ویژه ای در جهان علم دارد و میزان تمایل و نیاز متخصصان و دانشمندان در هر رشته را نشان می دهد که هر ساله توسط سازمانها و ارگانهای جهانی اعلام می شوند. بر اساس اعلام آمار کنفرانسهای تخصصی توسط سیویلیکا، هر ساله تعداد بسیار زیادی مقاله در حوزه های مهندسی عمران، محیط زیست و معدن منتشر می شود که در سال گذشته، 5645 مقاله با حجمی حدود پنجاه هزار صفحه در کنفرانسهای تخصصی در سطح کشور انتشار یافته است. آدرس این مطلب http://www.civilica.com/modules.php?name=News&file=print&sid=485 |
SERVICEABILITY AND DUCTILITY OF HSRC BEAMS
STRENGTHENED WITH CFRP PLATES
Seyed Hamid Hashemi, Ali Akbar Maghsoudi, Reza Rahgozar
Deptartment of Civil Engineering, University of Kerman, Iran
ABSTRACT
The use of fiber reinforced plastics (FRP) in repairing and strengthening RC beams has been researched in recent years. In particular, attaching unidirectional FRP to the tension face of RC beams has provided an increase in stiffness and load capacity of the structure. However, due to the brittle nature of unidirectional FRP, the ductility of the beam decreases. Consequently, the safety of the structure is compromised due to the reduction in ductility. The purpose of this research is to investigate the behavior of high strength reinforced concrete beams strengthened with FRP sheets. The major test variables were included the different layouts of CFRP sheets and tensile reinforcement ratio. More particularly, the change in strength and ductility of the beams as the number of FRP layers and tensile reinforcement bar ratio are altered is investigated. Six under-reinforced concrete beams were fabricated and tested to failure. With the exception of the control beam, one or four layers of CFRP were applied to the specimens.
جهت دسترسی به اصل مقاله از طریق لینک زیر اقدام نمایید
عملكرد بهره برداري تيرهاي بتن مسلح مقاومت بالاي تقويت شده با ورقهاي FRP از نظر قابليت سرويس
سيدحميد هاشمي
دانشجوي دكتري سازه دانشگاه كرمان و عضو هيئت علمي دانشگاه اراك
خلاصه مقاله:
امروزه نگهداري و مرمت سازه ها به دليلي هزينه هاي بالاي ساخت آنها اهميت بسيار زيادي پيدا نموده است، به همين دليل و به علت نياز روز افزون مهندسين و متخصصين صنعت ساختمان به تقويت، ترميم و بهسازي سازه هاي بتني روشهاي مختلف و متعددي براي اين موضوع مطرح گشته است. سادگي اجراي FRP ها در عين سرعت عمل بالا، وزن كم، مقاومت كششي بالاي ورق ها، مقاومت در برابر خوردگي، جذب ارتعاشات و افزايش مقاومت و استحكام سازه خصوصا د مقابل بارهاي ديناميكي از جمله مزيت هاي اين مواد است. در اين تحقيق اثر ورقهاي FRP در مقاوم سازي خمشي تيرهاي بتن مسلح حاوي بتن با مقاومت بالا مورد بررسي قرار گرفته است. ميزان آرماتور كششي و تعداد لايه FRP در ساخت نمونه ها و تقويت آنها به عنوان متغير در نظر گرفته شده است. تعداد شش تير بتني داراي سطح مفطع ، طول و ميزان ميلگرد فشاري و برشي يكسان حاوي بتن با مقاومت بالا، داراي آرماتور كششي برابر با [فرمول در متن مقاله] ياخته شده و تحت آزمايش خمش چهار نقطه اي قرار گرفته و شرايط بهره برداري آنها مورد بررسي قرار گرفته است. از شش نمونه بدون FRP به عنوان شاهد و چهار نمونه ديگر با يك چهار لايه FRP مقاوم سازي شده اند.جهت بررسي دقيق رفتار اين تيرها تعداد قابل توجهي كرنش سنج روي ميلگردهاي كششي، فشاري و همچنين سطح بتن و FRP نصب شده كه نتايج حاصله در اين تحقيق دال ب عملكرد مطلوب ورقهاي تقويت كننده در شرايط بهره برداري مي باشد.
كلمات كليدي:
تير بتن مسلح ، بتن مقاومت بالا ، مقاوم سازي ، FRP ، بهر برداري
علاقمندان می توانند جهت دسترسی به اصل مقاله از طریق لینک زیر اقدام نمایند
استاد دکتر مهدی قالیبافیان درگذشت
یادش گرامی باد
علاقمندان جهت مطالعه بخشی از زندگی پر بار ایشان می توانند از لینک زیر استفاده کنند
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ISI چيست؟ |
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داراي يک بانک اطلاعاتي است که مجلات معتبر علمي جهان را فهرست مي کند. شمار مجلات ISI ثابت نيست.
يک مجله ممکن است در يک زمان٬ از مجلات ISI محسوب شود٬ اما به دليل کاهش بار علمي٬ بعدا از ليست
مجلات ISI کنار گذاشته شود. در حال حاضر بيش از ۱۶۰۰۰ مجله٬ در ليست ISI قرار دارند. هر ساله ۲۰۰۰ مجله
جديد مورد ارزيابي قرار مي گيرد و حدود ده درصد آنها به ليست ISI اضافه مي شوند.
ارجاع به خود يا self citation چيست؟ اگر منابع ذکر شده در مقاله٬ پژوهش نويسندگان خود مقاله باشد٬ اين کار از
ارزش مقاله مي کاهد زيرا جنبه بين المللي بودن آن را ضعيف مي کند. درجه ارجاع به خود مجلات ISI معمولا
کمتر از ۲۰٪ است.
ضريب تاثير يا Impact factor چيست؟ اين عامل همه ساله توسط ISI برمبناي ارجاعات به هر يک از مجلات علمي آن محاسبه مي شود و نتيجه در گزارشات ارجاع مجله يا Journal Citation Reports يا به اختصار JCR ٬ منتشر مي شود. اين ضريب٬ نه براي مقاله يا نويسنده٬ بلکه براي مجله محاسبه مي شود. محاسبه برمبناي يک دوره سه ساله صورت مي گيرد. فرضا اگر در سال ۸۴ جمعا ۴۰ ارجاع به يک مجله صورت گرفته باشد و در آن مجله در سال ۸۲ تعداد ۲۶ مقاله و در سال ۸۳ تعداد ۲۴ مقاله چاپ شده باشد٬ ضريب ارجاع آن مجله٬ از تقسيم ۴۰ بر ۵۰ به دست مي آيد که ۸/۰ است. يعني به طور متوسط٬ هر مقاله آن نشريه ۸/۰ مرتبه مورد استناد مقالات ديگر قرار گرفته است. برای جستجوی تخصصی نشريات علمی ISI اينجا کليک کنيد براي توضيحات بيشتر از شماره ۳۵ فصلنامه رهيافت مي توان استفاده کرد : عوامل کيفي و کمي و شرايط لازم براي فهرست شدن يک مجله علمي در بانک اطلاعات ISI
ليست حدود 5000 مجله ISI در سال 2003 و 2004 به همراه ضريب تاثير آنها |
Reinforced High-Strength Concrete Beams in Flexure
by M. A. Rashid and M. A. MansurM. A. Rashid
is an associate professor in the Department of Civil Engineering and Director of Planning and Development at Dhaka University of Engineering & Technology, Gazipur, Bangladesh.M. A. Mansur
is a visiting scholar in the Department of Civil and Environmental Engineering at the University of Michigan, Ann Arbor, Mich.
ABSTRACT
Flexural test results generated on 16 reinforced concrete beams to evaluate the implications of using high-strength concrete (HSC) are reported. Test parameters considered include concrete compressive strength, ratios of tensile and compressive reinforcements, and spacing of lateral ties. It is found that the current code provisions for serviceability requirements of maximum crack width and ultimate strength are adequate up to a concrete strength of approximately 130 MPa. Concerns, however, are expressed regarding the adequacy of those for cracking moment and service load deflection. It is shown that stresses generated by shrinkage of concrete and the creep associated with it can significantly affect the cracking moment and service load deflection of reinforced HSC beams. Also, some detailing requirements for compression reinforcement need to be reassessed so as to utilize its full strength potential and ensure adequate ductile response of the beam when HSC is nvolved.
Keywords:
beam; crack; deflection; ductility; flexural strength; highstrength concrete; reinforced concrete.جهت دریافت اصل مقاله روی لینک زیر کلیک کنید
ACI Structural Journal, V. 102, No. 3, May-June 2005
Deflection Control of Concrete Members
Based on Utility Theory
by Young Hak Lee, Andrew Scanlon, and Heecheul Kim
Design provisions for deflection control of concrete structures are generally empirical in nature and based on previous experience. Due to the increasing use of high strength materials, longer spans, and as a result more flexible members, a more rational approach is desirable. This paper explores the applicability of the utility theory as a basis for developing deflection control criteria. The approach considers uncertainties in member behavior and loading as well as lack of well-defined discrete serviceability limits. Monte Carlo simulation is used to develop histograms of selected deflection parameters. A serviceability loss function is then specified to define the onset of serviceability failure and an upper limit representing complete serviceability failure with associated costs. Optimum structural parameter (member depth) is obtained by minimizing total cost consisting of initial construction cost and probabilistic cost of failure. Results for one-way slabs are developed and compared with current ACI code provisions for minimum thickness.
Keywords:
deflection; reinforced concrete; serviceabilityجهت دریافت اصل مقاله از لینک زیر استفاده کنید
ACI Structural Journal, V. 104, No. 1, January-February 2007
Behavior of Reinforced Concrete T-Beams Strengthened in Shear with Carbon Fiber-Reinforced Polymer—A
Behavior of Reinforced Concrete T-Beams Strengthened
in Shear with Carbon Fiber-Reinforced Polymer—An
Experimental Study
by Abdelhak Bousselham and Omar Chaallal
This paper presents results of a wide and extensive experimental investigation on reinforced concrete (RC) T-beams retrofitted in shear with externally bonded carbon fiber-reinforced polymer (CFRP). In total, 22 tests were performed on 4520 mm-long T-beams.
The parameters investigated were as follows: 1) the CFRP ratio (that is, the number of CFRP layers); 2) the internal shear steel reinforcement ratio (that is, spacing); and 3) the shear length to the beam’s depth ratio,
a/d (that is, deep beam effect). The main objective of the study was to analyze the behavior of RC T-beams strengthened in shear with externally applied CFRP by varying the aforementioned parameters. The results showed that the contribution of the CFRP to the shear resistance is not in proportion to the CFRP thickness (that is, the stiffness) provided, and depends onwhether the strengthened beam is reinforced in shear with internal transverse steel reinforcement. Results also confirmed the influence of the ratio a/d on the behavior of RC beams retrofitted in shear with external fiber-reinforced polymer (FRP). Finally, comparison of the shear resistance values predicted by ACI 440.2R-02, CSA S806-02, and fib TG9.3 guidelines, with the test results clearly indicated that the guidelines fail to capture important aspects, such as the presence of the transverse steel and the ratio a/d on the one hand, and overestimates the shear resistance for high FRP thickness (and hence high FRP stiffness), on the other.Keywords: polymer; reinforced concrete; shear; strain; strengthening
جهت دریافت اصل مقاله از لینک زیر استفاده نمایید
Evaluation of Ratio between Splitting Tensile Strength and Compressive Strength for Concretes up to 120 MPa and its Application in Strength Criterion
by Nihal Arιoglu, Z. Canan Girgin, and Ergin Arιoglu
A large-scale regression analysis was carried out using experimental data gathered from various sources to evaluate the ratio of splitting tensile strength to cylinder compressive strength as a function of compressive strength of concrete. The reliability of the roposed equation based on experimental data for compressive strength ranging between 4 and 120 MPa (580 to 17,400 psi) was assessed by means of the integral absolute error (IAE). It is also shown that, by only knowing compressive strength and the ratio of tensile to compressive strength, the failure envelope for very highstrength concrete can be established using Johnston’s strength criterion without performing triaxial compression tests. A numerical example demonstrates the application of Johnston’s strength criterion.
Keywords:
compressive strength; confinement; high-strength concrete; splitting tensile strength; stress.جهت دریافت اصل مقاله از طریق لینک زیر اقدام نمایید
ACI Materials Journal, V. 103, No. 1, January-February 2006
بنام خدا
طناب
داستان دربارة يک کوهنورد است که مي خواست از بلندترين کوه ها بالا برود. او پس از سالها
آماده سازي ماجراجويي خود را آغاز کرد ولي از آنجا که افتخار اين کار را فقط براي خود مي
خواست تصميم گرفت تنها از کوه بالا برود.
شب بلندي هاي کوه را تماماً در بر گرفت و مرد هيچ چيز را نمي ديد. همه چيز سياه بود اصلاً ديد
نداشت و ابر روي ماه و ستاره ها را پوشانده بود.
همانطور که از کوه بالا مي رفت چند قدم مانده بود به قلة کوه، پايش ليز خورد و در حالي که به
سرعت سقوط مي کرد از کوه پرت شد.
در حال سقوط فقط لکه هاي سياهي را در مقابل چشمانش مي ديد و احساس وحشتناک مکيده
شدن به وسيله قوة جاذبه او را در خود مي گرفت.
همچنان سقوط مي کرد و در آن لحظات ترس عظيم همة رويدادهاي خوب و بد زندگي به يادش
آمد. اکنون فکر مي کرد مرگ چه قدر به او نزديک است. ناگهان احساس کرد که طناب به دور
کمرش محکم شد. بدنش ميان آسمان و زمين معلق بود و فقط طناب او را نگهداشته بود. و در اين
لحظه سکون برايش چاره اي نماند جز آنکه فرياد بکشد:
" خدايا کمکم کن"
ناگهان صداي پر طنيني که از آسمان شنيده مي شد جواب داد:
- از من چه مي خواهي؟
اي خدا نجاتم بده!
- واقعاً باور داري که من مي توانم تو را نجات دهم؟
البته که باور دارم.
- اگر باور داري طنابي را که به کمرت بسته است پاره کن....
يک لحظه سکوت...
و مرد تصميم گرفت با تمام نيرو به طناب بچسبد.
گروه نجات مي گويند که روز بعد يک کوهنورد يخ زده را مرده پيدا کردند. بدنش از يک طناب
آويزان بود و با دست هايش محکم طناب را گرفته بود...
و او فقط يک متر از زمين فاصله داشت.
و ما؟؟؟ چقدر به طناب مان وابسته ايم؟ آيا حاضريم آن را رها کنيم؟
در مورد خدا هرگز يک چيز را نبايد فراموش کنيم. هرگز نبايد بگوييم که او ما را فراموش کرده يا
تنها گذاشته است. هرگز فکر نکنيم که او مراقب ما نيست.
به ياد داشته باشيم که او همواره ما را با
دست راست خود نگه داشته است.
اینجانب قصد دارم به مرور زمان مقالات جدید، کامل و متنوعی در زمینه بتن و به خصوص مقاوم سازی سازه های بتنی توسط الیاف پلیمری و همینطور بتن با مقاومت بالا را در این وبلاگ در اختیار علاقمندان عزیز قرار دهم. اکثر این مقالات در سالهای اخیر در معتبرترین مجلات ISI به چاپ رسیده و مسلماً از کیفیت بالایی برخوردار است. دوستانی که تمایل دارند مطلبی در زمینه مقاوم سازی و به نام خودشان در این وبلاگ قرار داده شود میتوانند مطالب خود را به آدرس ایمیل بنده ارسال کنند. در ضمن از آنجایی که امکان قرار دادن تمام پستها در صفحه نخست وجود ندارد لذا برای مشاهده همه مقالات به آرشیو مراجعه نمایید.
با تشکر و سپاس فراوان
