Prediction of premature separation of bonded CFRP plates from strengthened steel beams using a fracture criterion

Lenwari, A.,Thepchatri, T.,Watanabe, E. Techno-Press 2002 Structural Engineering and Mechanics, An Int'l Jou Vol.14 No.5

This paper presents a method for predicting premature separation of carbon fiber reinforced plastic (CFRP) plates from strengthened steel beams. The fracture criterion based on material-induced singularity is formulated in terms of a singular intensity factor. Static test on double strap joints was selected to provide the critical stress intensity factor in the criterion because good degree of accuracy and consistency of experimental data can be expected compared with the unsymmetrically loaded single lap joints. The debond/separation loads of steel beams with different CFRP lengths were measured and compared with those predicted from the criterion. Good agreement between the test results and the prediction was found.

Prediction of premature separation of bonded CFRP plates from strengthened steel beams using a fracture criterion

A. Lenwari,T.Thepchatri,E.Watanabe 국제구조공학회 2002 Structural Engineering and Mechanics, An Int'l Jou Vol.14 No.6

Genetic Algorithms-Based Gain Optimization of a Simple Learning Control for Single-Phase Shunt Active Filters

Wanchak Lenwari 제어로봇시스템학회 2010 제어로봇시스템학회 국제학술대회 논문집 Vol.2010 No.10

The repetitive or learning based control has proven to achieve high steady-state performances for control systems. The iterative learning algorithm aims to accomplish zero tracking error without full knowledge of the system model. However, its dynamic behaviors were not satisfied in some conditions particularly under non-periodic disturbances since the control uses the information from the previous iteration to calculate the system input. This paper proposes the investigation of the use of genetic algorithm to optimize the learning gain of a simple proportional-type (P-type) learning control applied to current control for shunt active filters. The merit of the proposed control is its simplicity, potentially suitable for commercial active filters. All design concepts are verified and the results obtained in the simulation confirm the improvement in the dynamic responses during the transient condition while the harmonic control accuracy in steady-state can remain excellent with the proposed control system.

Intermediate crack-induced debonding analysis for RC beams strengthened with FRP plates

Peelak Wantanasiri,Akhrawat Lenwari 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.56 No.3

This paper presents the analysis of intermediate crack-induced (IC) debonding failure loads for reinforced concrete (RC) beams strengthened with adhesively-bonded fiber-reinforced polymer (FRP) plates or sheets. The analysis consists of the energy release and simple ACI methods. In the energy release method, a fracture criterion is employed to predict the debonding loads. The interfacial fracture energy that indicates the resistance to debonding is related to the bond-slip relationships obtained from the shear test of FRP-toconcrete bonded joints. The section analysis that considers the effect of concrete‟s tension stiffening is employed to develop the moment-curvature relationships of the FRP-strengthened sections. In the ACI method, the onset of debonding is assumed when the FRP strain reaches the debonding strain limit. The tension stiffening effect is neglected in developing a moment-curvature relationship. For a comparison purpose, both methods are used to numerically investigate the effects of relevant parameters on the IC debonding failure loads. The results show that the debonding failure load generally increases as the concrete compressive strength, FRP reinforcement ratio, FRP elastic modulus and steel reinforcement ratio increase.

Strength Analysis of Cellular Steel Members under Combined Compression and Major-Axis Bending

Horsangchai Voraphol,Anuntasena Worakarn,Lenwari Akhrawat 한국강구조학회 2024 International Journal of Steel Structures Vol.24 No.3

Cellular steel shapes off er greater section depth and strong-axis fl exural stiff ness than their parent hot-rolled shapes, along with web openings for duct system installation. However, their use as structural members other than beams has been constrained by a lack of design guidelines. This research employs both an analytical approach and nonlinear fi nite element analysis to investigate the strength of cellular steel members under combined compression and major-axis bending. In the analytical approach, the strength interaction equation for cellular steel beam-columns incorporating an initial imperfection is derived using the principle of stationary potential energy. A total of 864 FE models covering practical confi gurations of cellular steel shapes are analysed to assess the analytical solution and the extension of AISC360 and EC3 strength interaction equations. Eff ects of the parent shape, web opening confi guration, member slenderness, and load eccentricity on the member strength are investigated. The results show that the proposed analytical solution accurately predicts the capacity of cellular steel members under combined compression and major-axis bending. Also, the European Code EC3 strength interaction equation that adopts the refi ned elastic buckling equation specifi cally derived for the cellular steel members can accurately predict the strength of practical cellular steel shapes. Finally, a criterion for eff ective utilisation of the cellular steel shapes is proposed to ensure that they exhibit greater strength than their parent shapes.

Axial load-strain relationships of partially encased composite columns with H-shaped steel sections

Papan Bangprasit,Worakarn Anuntasena,Akhrawat Lenwari 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.45 No.1

This paper presents the axial compression behavior of partially encased composite (PEC) columns using H-shaped structural steel. In the experimental program, a total of eight PEC columns with H-shaped steel sections of different flange and web slenderness ratios were tested to investigate the interactive mechanism between steel and concrete. The test results showed that the PEC columns could sustain the load well beyond the peak load provided that the flange slenderness ratio was not greater than five. In addition, the previous analytical model was extended to predict the axial load-strain relationships of the PEC columns with H-shaped steel sections. A good agreement between the predicted load-strain relationships and test data was observed. Using the analytical model, the effects of compressive strength of concrete (21 to 69 MPa), yield strength of steel (245 to 525 MPa), slenderness ratio of flange (4 to 10), and slenderness ratio of web (10 to 25) on the interactive mechanism (Kh = confinement factor for highly confined concrete and Kw = reduction factor for steel web) and ductility index (DI = ratio between strain at peak load and strain at proportional load) were assessed. The numerical results showed that the slenderness of steel flange and yield strength of steel significantly influenced the compression behavior of the PEC columns.

Effect of hybrid polypropylene-steel fibres on strength characteristics of UHPFRC

Nuaklong, Peem,Chittanurak, Jithaporn,Jongvivatsakul, Pitcha,Pansuk, Withit,Lenwari, Akhrawat,Likitlersuang, Suched Techno-Press 2020 Advances in concrete construction Vol.10 No.1

This study intends to produce an ultra-high performance fibre reinforced concrete (UHPFRC) made with hybrid fibres (i.e., steel and polypropylene). Compressive and tensile strength characteristics of the hybrid fibres UHPFRC are considered. A total of 14 fibre-reinforced composites (FRCs) with different fibre contents or types of fibres were prepared and tested in order to determine a suitable hybrid fibre combination. The compressive and tensile strengths of each concrete at 7 days were determined. The results showed that a hybrid mix of micro-polypropylene and steel fibres exhibited good compromising performances and is the ideal reinforcement mixture in a strong, cost-effective UHPFRC. In addition, maximum compressive strength of 167 MPa was achieved for UHPFRC using 1.5% steel fibres blended with 0.5% macro-polypropylene fibres.