Performance of damaged RC continuous beams strengthened by prestressed laminates plate: Impact of mechanical and thermal properties on interfacial stresses

Tahar, Hassaine Daouadji,Abderezak, Rabahi,Rabia, Benferhat,Tounsi, Abdelouahed Techno-Press 2021 Coupled systems mechanics Vol.10 No.2

Strengthening of reinforced concrete beams with externally bonded fiber reinforced polymer plates/sheets technique has become widespread in the last two decades. Although a great deal of research has been conducted on simply supported RC beams, a few studies have been carried out on continuous beams strengthened with FRP composites. This paper presents a simple uniaxial nonlinear analytical model that is able to accurately estimate the load carrying capacity and the behaviour of damaged RC continuous beams flexural strengthened with externally bonded prestressed composite plates on both of the upper and lower fibers, taking into account the thermal load. The model is based on equilibrium and deformations compatibility requirements in and all parts of the strengthened beam, i.e., the damaged concrete beam, the FRP plate and the adhesive layer. The flexural analysis results and analytical predictions for the prestressed composite strengthened damaged RC continuous beams were compared and showed very good agreement in terms of the debonding load, yield load, and ultimate load. The use of composite materials increased the ultimate load capacity compared with the non strengthened beams. The major objective of the current model is to help engineers' model FRP strengthened RC continuous beams in a simple manner. Finally, this research is helpful for the understanding on mechanical behaviour of the interface and design of the FRP-damaged RC hybrid structures.

Fire Damage Identification in RC Beams based on Support Vector Machines considering Vibration Test

Chaofeng Liu,Caiwei Liu,Chengxin Liu,Xuhong Huang,Jijun Miao,Wenlong Xu 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.10

In order to obtain the degree of damage in reinforced concrete (RC) beams exposed to fire, using the equivalent fire exposure time as the damage index, a new method of damage identification based on the support vector machine technology was proposed. Firstly, the feasibility analysis was conducted based on finite element models of simply supported beams. Thereafter, four RC simply supported beams were designed for fire test and vibration test, which were used to amend the finite element model and the SVM-based identification method. Fire tests were carried out on 4 beams for 60, 90, 120, and 150 min, respectively. During and after the fire tests, structural modal information were recorded. The first two order modal information, as SVM input paraments, was used to predict the equivalent fire exposure time based on SVM. The predicted results were very close to the actual fire exposure time. The residual bearing capacities of the beams after fire were calculated according to the predicted fire exposure time, which were close to experimental results. It indicated that the equivalent fire exposure time as the output parameter for damage identification was reliable. Finally, on the basis of damage identification method for simply supported beams, a new three-step positioning method was established for identifing the degree of damage in continuous beams. The method was applied to a thress-span continuous beam. The numercial situlation results revealed that the three-step positioning method was accurate.

Effect of geometrical configuration on seismic behavior of GFRP-RC beam-column joints

Ghomia, Shervin K.,El-Salakawy, Ehab Techno-Press 2020 Advances in concrete construction Vol.9 No.3

Glass fiber-reinforced polymer (GFRP) bars have been introduced as an effective alternative for the conventional steel reinforcement in concrete structures to mitigate the costly consequences of steel corrosion. However, despite the superior performance of these composite materials in terms of corrosion, the effect of replacing steel reinforcement with GFRP on the seismic performance of concrete structures is not fully covered yet. To address some of the key parameters in the seismic behavior of GFRP-reinforced concrete (RC) structures, two full-scale beam-column joints reinforced with GFRP bars and stirrups were constructed and tested under two phases of loading, each simulating a severe ground motion. The objective was to investigate the effect of damage due to earthquakes on the service and ultimate behavior of GFRP-RC moment-resisting frames. The main parameters under investigation were geometrical configuration (interior or exterior beam-column joint) and joint shear stress. The performance of the specimens was measured in terms of lateral load-drift response, energy dissipation, mode of failure and stress distribution. Moreover, the effect of concrete damage due to earthquake loading on the performance of beam-column joints under service loading was investigated and a modified damage index was proposed to quantify the magnitude of damage in GFRP-RC beam-column joints under dynamic loading. Test results indicated that the geometrical configuration significantly affects the level of concrete damage and energy dissipation. Moreover, the level of residual damage in GFRP-RC beam-column joints after undergoing lateral displacements was related to reinforcement ratio of the main beams.

Assessment of damages on a RC building after a big fire

Ada, Mehmet,Sevim, Baris,Yuzer, Nabi,Ayvaz, Yusuf Techno-Press 2018 Advances in concrete construction Vol.6 No.2

This paper presents a case study about the damages on the structural elements of a cast in place reinforced concrete (RC) building after a big fire which was able to be controlled after six hours. The fire broke off at the $2^{nd}$ basement floor of the building, which has five basements, one ground, and two normal floors. As a result of intensely stocked ignitable materials, it spread out to the all of the upstairs. In visual inspection, most of the typical fire damages were observed (such as spalling, net-like cracks, crumbled plasters, bared or visible reinforcement). Also, failures of the $2^{nd}$ basement columns were encountered. It has been concluded that the severity failures of the columns at the $2^{nd}$ basement caused utterly deformation of the building, which is responsible for the massive damages on the beam-column connections. All of the observed damages were categorized related to the types and presented separated regarding the floors. Besides to the visual inspection, the numerical analysis was run to verify the observed damaged on the building for columns, beams, and the connection regions. It is concluded from the study that several parameters such as duration of the fire, level of the temperature influence on the damages to the RC building. Also, it is highlighted by the study that if the damaged building is considered on the overall structural system, it is not able to satisfy the minimum service requirements neither gravity loads nor earthquake conditions.

Prediction of flexural behaviour of RC beams strengthened with ultra high performance fiber reinforced concrete

Murthy A, Ramachandra,Aravindan, M.,Ganesh, P. Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.65 No.3

This paper predicts the flexural behaviour of reinforced concrete (RC) beams strengthened with a precast strip of ultra-high performance fiber-reinforced concrete (UHPFRC). In the first phase, ultimate load capacity of preloaded and strengthened RC beams by UHPFRC was predicted by using various analytical models available in the literature. RC beams were preloaded under static loading approximately to 70%, 80% and 90% of ultimate load of control beams. The models such as modified Kaar and sectional analysis predicted the ultimate load in close agreement to the corresponding experimental observations. In the second phase, the famous fatigue life models such as Papakonstantinou model and Ferrier model were employed to predict the number of cycles to failure and the corresponding deflection. The models were used to predict the life of the (i) strengthened RC beams after subjecting them to different pre-loadings (70%, 80% and 90% of ultimate load) under static loading and (ii) strengthened RC beams after subjecting them to different preloading cycles under fatigue loading. In both the cases precast UHPFRC strip of 10 mm thickness is attached on the tension face. It is found that both the models predicted the number of cycles to failure and the corresponding deflection very close to the experimental values. It can be concluded that the models are found to be robust and reliable for cement based strengthening systems also. Further, the Wang model which is based on Palmgren-Miner's rule is employed to predict the no. of cycles to failure and it is found that the predicted values are in very good agreement with the corresponding experimental observations.

Prediction of flexural behaviour of RC beams strengthened with ultra high performance fiber reinforced concrete

Ramachandra Murthy A,M. Aravindan,P. Ganesh 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.65 No.3

This paper predicts the flexural behaviour of reinforced concrete (RC) beams strengthened with a precast strip of ultra-high performance fiber-reinforced concrete (UHPFRC). In the first phase, ultimate load capacity of preloaded and strengthened RC beams by UHPFRC was predicted by using various analytical models available in the literature. RC beams were preloaded under static loading approximately to 70%, 80% and 90% of ultimate load of control beams. The models such as modified Kaar and sectional analysis predicted the ultimate load in close agreement to the corresponding experimental observations. In the second phase, the famous fatigue life models such as Papakonstantinou model and Ferrier model were employed to predict the number of cycles to failure and the corresponding deflection. The models were used to predict the life of the (i) strengthened RC beams after subjecting them to different pre-loadings (70%, 80% and 90% of ultimate load) under static loading and (ii) strengthened RC beams after subjecting them to different preloading cycles under fatigue loading. In both the cases precast UHPFRC strip of 10 mm thickness is attached on the tension face. It is found that both the models predicted the number of cycles to failure and the corresponding deflection very close to the experimental values. It can be concluded that the models are found to be robust and reliable for cement based strengthening systems also. Further, the Wang model which is based on Palmgren-Miner’s rule is employed to predict the no. of cycles to failure and it is found that the predicted values are in very good agreement with the corresponding experimental observations.

Friction-based beam-to-column connection for low-damage RC frames with hybrid trussed beams

Piero Colajanni,Salvatore Pagnotta 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.45 No.2

Hybrid Steel-Trussed Concrete Beam (HSTCB) is structural typology suitable for light industrialization. HSTCBs usually cover long span with small depths, which lead to significant amount of longitudinal rebars. The latter make beamcolumn joints more prone to damage due to earthquake-induced cyclic actions. This phenomenon can be avoided using frictionbased BCCs. Friction devices at Beam-to-Column Connections (BCCs) have become promising solutions to reduce the damage experienced by structural members during severe earthquakes. Few solutions have been developed for cast-in-place Reinforced Concrete (RC) and steel-concrete composite Moment Resisting Frames (MRFs), because of the difficulty of designing costeffective damage-proof connections. This paper proposes a friction-based BCC for RC MRFs made with HSTCBs. Firstly, the proposed connection is described, and its innovative characteristics are emphasized. Secondly, the design method of the connection is outlined. A detailed 3D FE model representative of a beam-column joint fitted with the proposed connection is developed. Several monotonic and cyclic analyses are performed, investigating different design moment values. Lastly, the numerical results are discussed, which demonstrate the efficiency of the proposed solution in preventing damage to RC members, and in ensuring satisfactory dissipative capacity.

New solution for damaged porous RC cantilever beams strengthening by composite plate

Abderezak, Rabahi,Daouadji, Tahar Hassaine,Rabia, Benferhat Techno-Press 2021 Advances in materials research Vol.10 No.3

This research presents a careful theoretical investigation on interfacial stresses in damaged porous RC cantilever beams strengthened with externally bonded composite plate (several types of composites have been used). The model is based on equilibrium and deformations compatibility requirements in and all parts of the strengthened cantilever beam, i.e., the damaged porous concrete cantilever beam, the perfect and/or imperfect composite plate and the adhesive layer. The analytical predictions are compared with other existing solutions and which shows a very good agreement of the results. It is shown that both the normal and shear stresses at the interface are influenced by the material and geometry parameters of the composite beam. In the end, I think this research is very useful for understanding the mechanical behavior of the interface and the design of the hybrid structures.

Repair of Heat-Damaged RC Beams Using Micro-concrete Modified with Carbon Nanotubes

Wasim S. Barham,Mohammad R. Irshidat,Abdelrahman Awawdeh 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.7

This paper investigates the use of micro-concrete modified with carbon nanotubes (CNTs) for the repair of heat-damaged reinforced concrete (RC) beams. Ten RC beams were cast and then subjected to elevated temperature of 550oC for two hours. The damaged beams were then repaired using micro-concrete integrating CNTs and tested under four-point bending. Different factors were taken into consideration in this research: CNTs modification, depth of repair, aggregate size of the repair material, and curing period. The repair material was applied on the tension side of the beam. Test results showed that micro-concrete with a larger aggregate size was more effective as a repair material than smaller sized aggregate micro-concrete. CNTs modification had little impact on the flexural strength of the repaired beams, but clearly enhanced the stiffness. The increase in the repair depth improved the strength recovery of the repaired beams but did not influence the failure mode. Curing period of the repaired beams significantly affected their stiffness but not their ultimate load and toughness. To investigate the mineral composition of repair material, scanning electron microscopy (SEM) was conducted for the micro-concrete with and without CNTs modified cementitious. The SEM image showed the CNTs are uniformly dispersed in the cement matrix. The CNTs and the products of the hydration process formed a meshwork structure. The CNTs acted as fillers to the voids, leading to an increase in the compressive strength.

Modeling and analysis of the imperfect FGM-damaged RC hybrid beams

Abderezak, Rabahi,Daouadji, Tahar Hassaine,Rabia, Benferhat Techno-Press 2021 Advances in computational design Vol.6 No.2

The use of externally bonded composite materials for strengthening reinforced concrete structures has received considerable attention in recent years. Since, concrete is a relatively fragile material and will fail when subject to the influence of many factors whose origins can be mechanical, physicochemical and accidental or related to the design and miscalculations. The bonding of FRP plate to reinforced concrete structure, appeared in the middle of the fourtwenties years, proves to be a promising and fully justified technique. In this paper, an analysis and modeling of the concentrations of interfacial stresses in a damaged reinforced concrete beam strengthening in bending by an imperfect FGM plate, was presented, based on a development of a mathematical formulation taking into account the theory of beams. The theoretical predictions are compared with other existing solutions. This research is helpful for the understanding on mechanical behaviour of the interface and design of the imperfect FGM - damaged RChybrid structures.