Static Loading System Research Articles

Strengthening of RC Beam with GFRP Composites in Shear N. B. Bhopale

The rehabilitation, repair and strengthening of existing reinforced concrete (RC) structures is essential due to factors such as aging, steel reinforcement corrosion, construction/design defects, increased service loads demand, seismic events, and advancements in design guidelines. Fiber-reinforced polymers (FRP) are now being recognized as a promising material for the rehabilitation of such structures, through strengthening or repairing. In buildings and bridges, RC sections are commonly found in the form of beams and girders. Shear failure of RC beams is particularly due to its sudden occurrence without warning. Therefore, the utilization of externally bonded (EB) FRP composites for shear strengthening of RC beams has gathered popularity as a structural enhancement technique, primarily due to advantages of FRP composites, such as high strength-to- weight ratio and exceptional corrosion resistance. In addition, FRP repair systems give a cost-saving choice to traditional repair methods and materials. A study was performed to analyse the shear characteristics of RC beams enhanced with continuous glass fiber-reinforced polymer (GFRP) sheets. Reinforced concrete beams externally bonded GFRP sheets subjected to failure using a symmetrical two-point concentrated static loading system. The experimental data obtained included load, deflection, and failure modes of each beam, along with the effect of the number of GFRP layers on the beams The failures observed in strengthened beams typically commence with the debonding of the FRP sheets, followed by brittle shear failure. The shear capacities of these beams were higher than that of the control beam.

Experimental Investigation of Mechanical and Fracture Behavior of Parallel Double Flawed Granite Material under Impact with Digital Image Correlation

During the excavation of underground projects, the rock masses left as the bearing support system are also subjected to dynamic loads from the excavation activities ahead. These rock masses have been damaged and fractured during the initial exposure (dynamic loads) and are subjected to static loads in the subsequent process as the support system. In this study, granite rock samples and specimens with different angles were produced, preloaded with different confining pressure, and under a combination of dynamic and static loading tests using a modified dynamic and static loading system: split Hopkinson pressure bar (SHPB). The peak strain and dynamic modulus of elasticity are weakened by the inclination angle in a similar way to the strength, with the specimens showing an evolutionary pattern from tensile strain to shear damage. The change in the inclination angle of flaws would weaken the dynamic and combined strengths, and a larger inclination flaw results in a significant decrease in its strength. Fractal analysis revealed that the fractural dimension was closely related to the fissure angle and showed a good linear correlation with the strain rate. This study will provide an important security assurance for deep mining.

Structural and cracking behaviour of RC T-beams strengthened with BFRP sheets by experimental and analytical investigation

Shear and flexural failure are commonly known as the highest catastrophic failure mode as it never gives any earlier notice before the collapse. The most common shape in the structure of beams and girders is T-section. Therefore it will be more necessary to investigate the condition of these structures. In this research, the flexural behaviour of RC T-beams is investigated experimentally and analytically strengthened with Basalt Fiber Reinforced Polymer (BFRP). A symmetrical one-point static loading system is applied on RC T-beams superficially bonded with 45° degree, and 90° wrapping up to failure. The effects of both wrapping patterns of BFRP on RC T-beams were investigated for ultimate load carrying capacity, deflection, strain, and failure modes. The experimental results demonstrate that superficially bonded BFRP can enhance the flexural capacity and reduce the deflection of the beam significantly. Further, the results show that the most effective wrapping pattern was a 45° degree than 90°wrapping and without wrapping. Then the RC T- beam was modeled by using ABAQUS to validate the present experimental and analytical results. After a series of comparative studies, the analytical results fairly admit with the experimental results. In the end, this study surmised showing different cracking patterns and yield points of the beam with and without strengthening. It is hoped that the results of this study will be of considerable help for the strengthening of T- beams and structures.

Experimental investigation of a compound force tracking control strategy for electro-hydraulic hybrid testing system with suppression of vibration disturbances

Electro-hydraulic hybrid testing, which imposes the desired acceleration and force on the specimen in parallel, is a novel structural testing method for structures or facilities and is extensively applied in civil and seismic engineering. To efficiently suppress the surplus force resulted from the acceleration motion of the specimen during the force control process, a compound force tracking control strategy comprised of a force and voltage feedforward controller (FVFC) and feedforward inverse with disturbance observer (FIDOB) controller is presented in this research. The FVFC controller as an inner loop feedforward component is first constituted by the generated force feedback signal and the real-time control voltage signal of the acceleration actuator so as to compensate for the acceleration motion of the specimen for a better disturbance rejection performance, and the FVFC controller requires little information of the system dynamic structure or parameters. The FIDOB controller composed by a feedforward inverse controller and an inverse model-based disturbance observer is then combined with the FVFC controller as an outer loop to further deal with the remaining disturbances for the FVFC-controlled electro-hydraulic hybrid testing system. The inverse model applied in the FIDOB controller is obtained with the frequency domain complex curve fitting and zero magnitude error tracking technology with respect to the proportional–integral controlled static loading system. Hence, the proposed controller integrates the advantages of the FVFC controller and FIDOB controller in terms of easy implementation and high tracking performance. Finally, comparative experiments are carried out on an uniaxial electro-hydraulic hybrid testing test rig with the xPC rapid prototyping technology and experimental results demonstrate the effectiveness of the proposed control strategy.

Strengthening of a RC Beam using Synthetic FRP Laminates

Objectives: The present research paper summarizes the study of use of synthetic polyester fiber for the strengthening of the reinforced concrete beams. Methods: In this experimental study, ten reinforced concrete beams were casted. They were externally strengthened with the help of synthetic polyester fiber using epoxy resin and hardener. The application of Polyester Fibre Reinforced Polymer sheets for strengthening of RC beams was done in u-wrap and bottom wrap. The effect of this on ultimate load carrying capacity and flexural strength was examined. Findings: The reinforced concrete beams were tested to failure using symmetrical two point concentrated static loading system. The results were found experimentally on load, deflection and failure types of each of the beams. The effect of various positions of wrapping of Polyester Fiber Reinforced Polymer on ultimate load carrying capacity was investigated. The results obtained showed increase in the ultimate load carrying capacity and flexural strength of the beams as compared with the control beam. The ultimate load obtained with polyester fibre reinforced beam was, however less compared to Carbon/Glass/Aramid as recorded in the literature. But the results obtained were encouraging and useful. Applications: Defects occur in reinforced concrete due to many factors like-age, corrosion of steel reinforcement, defective structural design etc. Fibre reinforced polymers can be successfully utilized for rehabilitation of these RC structures.

노출강연선으로 보강된 하이브리드 건축용 OCB보의 실물모형 재하실험연구

최근 국내의 건축구조는 공간활용을 극대화할 수 있도록 계획되고 있다. 공간활용의 장점을 실현하기 위하여 하이브리드 OCB (Optimized Composite Beam)를 개발하였다. 건축용 OCB는 부모멘트 구간에서는 노출강연선으로 보강된 H형강으로 구성되고 정모멘트 영역에서는 PSC 구조로 구성된다. 본 연구에서는 건축용 OCB의 휨성능을 조사하였다. 15 m 길이의 시험체를 제작하여 3점 휨실험을 실시하였다. 실험을 통해서 다음과 같은 결과를 얻었다. 1) 시험체의 재하실험에서 초기 균열은 설계사용 하중의 171%에서 발생되었다. 2)사용하중에서 처짐은 건축구조설계기준에 제시된 허용처짐량 이내로 만족하였다. 3)균열의 양상, 파괴모드 그리고 극한하중 등의 실험결과는 3D 수치해석결과와 비교검토되었다. 본 실험연구 결과로부터 건축용 OCB보의 구조적인 신뢰성이 입증되었다.

장경간 건축구조를 위한 하이브리드 OCB보의 개발

최근 국내의 건축구조는 공간활용을 극대화할 수 있도록 계획되고 있다. 공간활용의 장점을 실현하기 위하여 하이브리드 OCB(Optimized Composite Beam)보를 개발하였다. 본 논문에서 개발된 건축용 OCB보는 부모멘트 구간에서는 노출강연선으로 보강된 H형강으로 구성되고 정모멘트 영역에서는 프리텐션 방식의 PSC 구조로 구성된다. 본 연구에선 유한요소법을 이용하여 건축용 OCB보의 휨성능을 조사하였다. 15m, 20m, 30m 길이의 OCB모형을 구성하여 재료 및 기하학적 비선형 정적해석을 수행하였다. 해석결과로부터 다음과 같은 결과를 얻었다. 1)해석모델의 초기균열은 사용하중이상에서 모두 발생되었다. 2)사용하중단계에서 처짐은 건축구조설계기준에 제시된 허용처짐량 이내로 만족하였다. 3)유한요소모델의 파괴 시 극한하중은 모두 단면의 설계공칭강도 이상에서 발생되었다. 해석결과로부터 건축용 OCB보의 구조적인 신뢰성이 입증되었다. The building structure in Korea is planned to maximize the use of space in recent. The hybrid OCB(Optimized Composite Beam) beam is developed to take advantage of using the space. The OCB beam is composed of the steel H-beam section reinforced by open strands in negative moment zone and the pretensioned PSC concrete section in positive zone. Flexural behavior of typical architectural hybrid OCB beam section was investigated by F.E.M. The 15m, 20m, 30m OCB models were tested on nonlinear material and geometry under static loading system. Following results are obtained from the analysis; 1)The OCB beam develop initial flexural cracking over full service loading. 2)Overall deflections of OCB beam under the service loads are less than those of the allowable limits in KCI Code(2012). 3)The ultimate load capacity get over the nominal strength of the OCB main section. The OCB beam is verified of structural reliability from the finite element analysis.

Research on Wind Turbine Blade Static Loading System and its Variable Traction Control Mode

According to MW-class wind turbine blades loading system requirements, the load requirement of traction apparatus under the different operating conditions were discussed. At the same time, the variable traction feature of traction apparatus was analyzed. A multi-node hydraulic loading system based on CAN bus was designed in this paper. In order to improve the precision of traction and the following performance of loading system, opting for the “V-F” control mode, we proposed the variable proportional separate integral control algorithm with amplitude limit to enhance the system's adaptive capacity. Experiments show that this program has a good coordination feature in the variable traction control, and fully meets the requirements of blade loading test.

Application of Direct Actuated Digital Servo Valve in Electrohydraulic Static Loading System

Structure static testing is an important means to study the static characteristic of complex engineering structure. Electrohydraulic stactic loading system is the singnificant equipment of the testing. With its function of transfering low-power electrical singal to large-power hydraulic output quickly and precisely, the servo valve plays a key role in an electrohydraulic servo control system and dominates to a large extent the performance of the whole control system. Conventional electrohydraulic servo or proportional control is subject to the nonlinearites of their electro-mechanical interface, such as hysteresis, saturation and finite resolution. In this paper, a direct actuated digital servo valve was applied in electrohydraulic static loading system. It can be driven directly by computer needn’t D/A and has the advantages of simple structure, high tolerance to contamination and high reliability. Practical load-experiment results show that the static loading system with a direct actuated digital servo valve can work steadily and reliably and possess high accuracy and fast response.

PARAMETERIZATION OF DAMAGE IN REINFORCED CONCRETE STRUCTURES USING MODEL UPDATING

This paper describes the application of finite element model updating to reinforced concrete beams in order to detect and quantify damage. Three simply supported beams are considered in this study: two of them are subjected to a single concentrated load while the third one to two concentrated loads. The static loading system is applied in different steps up to failure so that dynamic measurements can be carried out after each load step. The measured modal parameters are used afterwards to update a finite element model in order to localize and to quantify the damage. The updating algorithm is based on the sensitivity approach in which the discrepancies between the analytical and experimental modal data are minimized in an iterative manner. A new concept for damage parametrization is introduced. A damage function characterized by three parameters is proposed. In such a function, only three parameters are used to describe the damage pattern of the reinforced concrete beams. These parameters are related to the bending stiffness of the beams and updated so that the measured natural frequencies are reproduced. The results demonstrate the efficiency of the proposed technique to quantify the damage pattern.