Debonding-Related Strain Limits for Externally Bonded FRP Sheets in Flexurally Strengthened Reinforced Concrete Beams

Debonding problems of externally bonded fiber reinforced polymer (FRP) sheets in flexurally FRP-strengthened reinforced concrete (RC) beams have been a concern and a research challenge since their application of this strengthening technique. Intermediate crack induced debonding is the most common failure mode which is that the debonding initiates at the critical flexural-shear or flexural cracks and propagates towards the direction of moment decrease. To mitigate debonding failure, most Codes and proposed models take the method by limiting the allowable tensile strain in FRP laminates. This paper presents experimental tests of concrete beams flexurally strengthened with externally bonded CFRP sheets to investigate debonding initiation and tensile strain of FRP laminates. The allowable tensile strain of FRP sheets in flexurally FRP-strengthened RC beams proposed by prevalent Code provisions and models was assessed based on the data obtained from experimental programs. It has beenshown that the allowable tensile strains provided by these provisions and models have a great difference with that of experimental results and exhibit a high level of dispersion. Furthermore, the FRP laminates of most tested RC beams were debonded before reaching the proposed allowable tensile strain. The Code provisions and models are inadequate to effectively prevent intermediate crack induced debonding failure in flexurally FRP-strengthened RC members. This is known to be a critical issue in engineering design and application of RC beams flexurally strengthened by FRP sheets.

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Reliability-Based Balanced Condition for Strengthened RC Beams

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.756-759.25 ◽

2013 ◽

Vol 756-759 ◽

pp. 25-28 ◽

Cited By ~ 2

Author(s):

Chun Xia Li ◽

Zhi Sheng Ding ◽

Shi Lin Yan ◽

Jun Ming Chen

Keyword(s):

Reinforced Concrete ◽

Carbon Fiber ◽

Stress Distribution ◽

Tensile Strain ◽

Concrete Beams ◽

Reinforced Concrete Beams ◽

Experimental Result ◽

Rc Beams ◽

Yield Strain ◽

Reliability Indicator

Based on the experimental result of the flexure capability of reinforced concrete beams strengthened by carbon fiber sheets, the stress distribution changes only after steel yielding and carbon fiber sheets function better. However serious the extent of the damage is before strengthened, the tensile strain of main steel reaches about 1.6 times of the yield strain for the secondary grade of steel as failure happens. To satisfy the object reliability indicator, reliability is analyzed using the ratio of the steel strain at the balanced failure to the yield strain as variable to obtain its optimum value, which is coincide with the experimental result, and makes better consistency between calculated reliability indicator and object reliability indicator.

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Test Analysis for RC Beams Strengthened with Externally Bonded Prestressed CFRP Laminates

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.385-387.41 ◽

2008 ◽

Vol 385-387 ◽

pp. 41-44 ◽

Cited By ~ 1

Author(s):

Shi Qi Cui ◽

Jin Shan Wang ◽

Zhao Zhen Pei ◽

Zhi Liu

Keyword(s):

Reinforced Concrete ◽

Bearing Capacity ◽

Concrete Beams ◽

Reinforced Concrete Beams ◽

Rc Beams ◽

Test Results ◽

Test Analysis ◽

Cfrp Laminates ◽

Cfrp Sheet ◽

Externally Bonded

Reinforced concrete beams strengthened with externally bonded CFRP sheet and prestressed CFRP are analyzed in this paper. Crack developments and displacements with curvatures for different beams are analyzed. Test results show that prestressed CFRP are able to control the development of macro cracks in concrete and prestressed CFRP is an effective method to improve the toughness of concrete, reduce strengthening cost and meanwhile enhance bearing capacity of concrete beams.

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ANALYSIS OF METHODS FOR CALCULATING THE WIDTH OF NORMAL CRACKS IN REINFORCED CONCRETE STRUCTURES

Engineering Structures and Technologies ◽

10.3846/skt.2009.03 ◽

2009 ◽

Vol 1 (1) ◽

pp. 23-39 ◽

Cited By ~ 4

Author(s):

Vidmantas Jokūbaitis ◽

Linas Juknevičius

Keyword(s):

Reinforced Concrete ◽

Carrying Capacity ◽

Crack Width ◽

Concrete Beams ◽

Experimental Tests ◽

Reinforced Concrete Beams ◽

Design Codes ◽

Rc Beams ◽

Reinforced Concrete Slabs ◽

Crack Widths

The width of normal cracks at the level of tensile reinforcement was calculated according to various methods using the data obtained from experimental tests on reinforced concrete beams (without reinforcement pre-stress), pre-cast reinforced concrete slabs and ribbed roof slabs. Th e numerical results were compared to actual crack widths measured during the experimental tests. Also, the crack widths of pre-stressed reinforced concrete beams were calculated according to various methods and compared with each other. Th e following conclusions were reached based on the analysis of numerical and experimental results: 1) Design stresses in tensile reinforcement calculated according to [STR] and [EC] design codes are very similar, although the calculation of such stresses is more logical and simple according to [EC]. Design stresses calculated according to [RU] are greater due to the estimation of the plastic deformations of concrete in the compressive zone. Th e method proposed by Rozenbliumas (Розенблюмас 1966) estimates tensile concrete above the crack peak, and thus allows a more accurate calculation of stresses in tensile reinforcement (Fig 3). Therefore, the latter stresses in pre-stressed RC beams may be decreased by 10–12 %, when height hct ≠ 0 (Fig 1, c) and ratio M/MRd varies between 0,65 and 0,75; 2) The widths of normal cracks in conventional RC beams (subjected to load that corresponds approx. 70 % of their carrying capacity) calculated according to [STR] and [EC] design codes are almost equal to the experimentally obtained crack widths. When beams and slabs are loaded by approximately 52 % of their carrying capacity, design crack widths wk [EC] are approximately 12 % less than wk [STR], although the design crack width wk [RU] is signifi cantly greater. Here, ratio β in the beams and slabs is equal to 2 and 3.3 respectively. Th erefore, the design code [RU] ensures higher probability that the crack width will not reach the limit value (for environmental class XO and XC1) equal in all design codes mentioned in this article; 3) In case of loaded prestressed reinforced concrete beams, the calculated increases of crack widths wk [EC], wk [RU] and w [5] are greater if compared to wk [STR] (Fig 6). Th e increased reinforcement ratio ρ has more signifi cant infl uence on the increases of crack widths calculated according to other design codes if compared to wk [STR]. Tensile concrete above the crack peak has signifi cant infl uence on the design crack width when pre-stressed RC beams are lightly reinforced (ρ ≤ 0,008); 4) During the evaluation of the state of fl exural RC members, expression (5) could be used for calculating the crack width or a position of the neutral axis when the heights of the crack and the tensile zone above the crack are known (calculated or measured experimentally). Design crack widths w (5) are very similar to the experimentally obtained results.

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Efficiency of Hybrid Algorithms for Estimating the Shear Strength of Deep Reinforced Concrete Beams

Periodica Polytechnica Civil Engineering ◽

10.3311/ppci.19323 ◽

2022 ◽

Author(s):

Mohammad Sadegh Barkhordari ◽

De-Cheng Feng ◽

Mohsen Tehranizadeh

Keyword(s):

Shear Strength ◽

Reinforced Concrete ◽

Concrete Beams ◽

Search Algorithm ◽

Experimental Tests ◽

Reinforced Concrete Beams ◽

Rc Beams ◽

High Rise ◽

Beam Depth ◽

Artificial Neural Network Ann

Earthquakes occurred in recent years have highlighted the need to examine the strength of reinforced concrete (RC) members. RC beams are one of the elements of reinforced concrete structures. Due to the dramatic increase in the population and the number of medium/high-rise buildings, in recent years, the beams of buildings have been mainly designed and executed in the type of deep beams. In this study, the artificial neural network (ANN) with optimization algorithms, including particle swarm optimization (PSO), Archimedes optimization algorithm (AOA), and sparrow search algorithm (SSA), are used to determine the shear strength of reinforced concrete deep (RCD) beams. 271 samples from experimental tests are employed to develop algorithms. The results of this study, design codes equations, and previous research are compared. Comparison between the results shows that the PSO-ANN algorithm is more accurate than previous methods. Finally, SHApley Additive exPlanations (SHAP) method is utilized to explain the predictions. SHAP reveals that the beam span and the ratio of the beam span to beam depth have the highest impact in predicting shear strength.

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