مقاوم سازی سازه های بتنی

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پل ورسک

cfrp — Sat, 10 Mar 2012 04:45:18 GMT

بهشت و جهنم

cfrp — Mon, 27 Jul 2009 20:48:46 GMT

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

cfrp — Sat, 14 Jun 2008 13:07:16 GMT

Shear enhancement of reinforced concrete beams strengthened with FRP composite laminates

Ayman S. Mosallam *, Swagata Banerjee

Civil 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; Infrastructure

جهت مطالعه متن کامل مقاله از لینک زیر استفاده نمایید

Composites: Part B 38 (2007) 781–793

Sensitivity analysis of reinforced concrete beams strengthened with FRP laminates

cfrp — Sat, 14 Jun 2008 13:04:24 GMT

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

Cement & Concrete Composites 28 (2006) 102–114

Performance of reinforced concrete beams strengthened by hybrid FRP laminates

cfrp — Sat, 14 Jun 2008 13:00:34 GMT

Performance of reinforced concrete beams strengthened by hybrid FRP laminates

Abdelhady Hosny a, Hamdy Shaheen b, Amr Abdelrahman a,*, Tamer Elafandy b

a Structural Engineering Department, Ain Shams University, Cairo, Egypt

b RC Department, Housing and Building Research Center, Giza, Egypt

Abstract

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

Cement & Concrete Composites 28 (2006) 906–913

On the parameters influencing the performance of reinforced concrete beams strengthened with FRP pla

cfrp — Sat, 14 Jun 2008 12:57:06 GMT

On the parameters influencing the performance of reinforced concrete beams strengthened with FRP plates

F. Taheri *, K. Shahin, I. Widiarsa

Department 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.

جهت مطالعه اصل مقاله از لینک زیر استفاده نمایید

Composite Structures 58 (2002) 217–226

Flexural strengthening of reinforced lightweight polystyrene aggregate concrete beams with near-surf

cfrp — Sat, 14 Jun 2008 12:54:29 GMT

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. Leung

Department 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

Building and Environment 41 (2006) 1381–1393

Design against cracking at openings in reinforced concrete

cfrp — Sat, 14 Jun 2008 12:49:59 GMT

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 a

a Structural Engineering Department, Faculty of Engineering, Cairo University, Cairo 12613, Egypt

b Structural Engineering Department, Faculty of Engineering, Helwan University, Cairo 11321, Egypt

Abstract

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

cfrp — Sat, 14 Jun 2008 12:44:54 GMT

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.

Keywords: Carbon fibre reinforced polymers (CFRPs); Reinforced concrete beams; Flexural strengthening; Creep; Sustained loads; Long-term deflections

جهت مطالعه متن کامل مقاله از لینک زیر استفاده نمایید

Construction and Building Materials xxx (2007) xxx–xxx