Effects of cyclic loading on the long-term deflection of prestressed concrete beams

Lihai Zhang,Priyan Mendis,Wong Chon Hon,Sam Fragomeni,Nelson Lam,Yilun Song 사단법인 한국계산역학회 2013 Computers and Concrete, An International Journal Vol.12 No.6

Creep and shrinkage have pronounced effects on the long-term deflection of prestressed concrete members. Under repeated loading, the rate of creep in prestressed concrete members is often accelerated. In this paper, an iterative computational procedure based on the well known Model B3 for creep and shrinkage was developed to predict the time-dependent deflection of partially prestressed concrete members. The developed model was validated using the experimental observed deflection behavior of a simply supported partially prestressed concrete beam under repeated loading. The validated model was then employed to make predictions of the long-term deflection of the prestressed beams under a variety of conditions (e.g., water cement ratio, relatively humidity and time at drying). The simulation results demonstrate that ignoring creep and shrinkage could lead to significant underestimation of the long-term deflection of a prestressed concrete member. The model will prove useful in reducing the long-term deflection of the prestressed concrete members via the optimal selection of a concrete mix and prestressing forces.

Modelling the dynamic response and failure modes of reinforced concrete structures subjected to blast and impact loading

Ngo, Tuan,Mendis, Priyan Techno-Press 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.32 No.2

Responding to the threat of terrorist attacks around the world, numerous studies have been conducted to search for new methods of vulnerability assessment and protective technologies for critical infrastructure under extreme bomb blasts or high velocity impacts. In this paper, a two-dimensional behavioral rate dependent lattice model (RDLM) capable of analyzing reinforced concrete members subjected to blast and impact loading is presented. The model inherently takes into account several major influencing factors: the progressive cracking of concrete in tension, the inelastic response in compression, the yielding of reinforcing steel, and strain rate sensitivity of both concrete and steel. A computer code using the explicit algorithm was developed based on the proposed lattice model. The explicit code along with the proposed numerical model was validated using experimental test results from the Woomera blast trial.

Modelling the dynamic response and failure modes of reinforced concrete structures subjected to blast and impact loading

Tuan Ngo,Priyan Mendis 국제구조공학회 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.32 No.2

Responding to the threat of terrorist attacks around the world, numerous studies have been conducted to search for new methods of vulnerability assessment and protective technologies for critical infrastructure under extreme bomb blasts or high velocity impacts. In this paper, a two-dimensional behavioral rate dependent lattice model (RDLM) capable of analyzing reinforced concrete members subjected to blast and impact loading is presented. The model inherently takes into account several major influencing factors: the progressive cracking of concrete in tension, the inelastic response in compression, the yielding of reinforcing steel, and strain rate sensitivity of both concrete and steel. A computer code using the explicit algorithm was developed based on the proposed lattice model. The explicit code along with the proposed numerical model was validated using experimental test results from the Woomera blast trial.

Ductility Design of Reinforced Very-High Strength Concrete Columns (100–150 MPa) Using Curvature and Energy-Based Ductility Indices

Shanaka Kristombu Baduge,Priyan Mendis,Tuan Duc Ngo,Massoud Sofi 한국콘크리트학회 2019 International Journal of Concrete Structures and M Vol.13 No.5

The paper aims to develop theoretical expressions for the ductility design of very-high strength concrete (VHSC)(> 100 MPa) columns using curvature and a new flexural energy-based ductility approach. Eventually, the study aims to evaluates the feasibility of VHSC columns for different ductility classes, considering the limitation of providing a higher volume of transverse reinforcement due to possible steel congestion in the construction phase. An analytical program based on the experimental stress–strain relationship of confined VHSC, which is validated using experimen-tal programs on VHSC columns, is used to evaluate the ductility of VHSC columns for different parameters such as axial load ratio, confinement pressure, longitudinal steel ratio, yield strength of transverse steel, cover area and compressive strength of concrete. The theoretical curvature ductility and flexural rotation-based energy ductility of 3200 rectan-gular columns were evaluated using the analytical program. Using curvature ductility and the new flexural rotation-based energy ductility for different parameters, a regression analysis is carried out to develop expressions for the ductility design of VHSC columns up to 150 MPa. Using the new definition of energy-based ductility, a new expression is developed for limited ductility design of VHSC; and it is concluded that the new approach reduces the required amount of steel confinement due to an increase in the energy ductility of VHSC at higher axial load ratios and higher strengths. The studies show that reinforced VHSC can be used for structures with nominal ductility demands.

Practical countermeasures for the aerodynamic performance of long-span cable-stayed bridges with open decks

Rui Zhou,Yongxin Yang,Yaojun Ge,Priyan Mendis,Damith Mohotti 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.21 No.2

Open decks are a widely used deck configuration in long-span cable-stayed bridges; however, incorporating aerodynamic countermeasures are advisable to achieve better aerodynamic performance than a bluff body deck alone. A sectional model of an open deck cable-stayed bridge with a main span of 400 m was selected to conduct a series of wind tunnel tests. The influences of five practical aerodynamic countermeasures on flutter and vortex-induced vibration (VIV) performance were investigated and are presented in this paper. The results show that an aerodynamic shape selection procedure can be used to evaluate the flutter stability of decks with respect to different terrain types and structural parameters. In addition, the VIV performance of Π-shaped girders for driving comfortableness and safety requirements were evaluated. Among these aerodynamic countermeasures, apron boards and wind fairings can improve the aerodynamic performance to some extent, while horizontal guide plates with 5% of the total deck width show a significant influence on the flutter stability and VIV. A wind fairing with an angle of 55° showed the best overall control effect but led to more lock-in regions of VIV. The combination of vertical stabilisers and airflow-depressing boards was found to be superior to other countermeasures and effectively boosted aerodynamic performance; specifically, vertical stabilisers significantly contribute to improving flutter stability and suppressing vertical VIV, while airflow-depressing boards are helpful in reducing torsional VIV

Nanomechanical properties of thermal arc sprayed coating using continuous stiffness measurement and artificial neural network

Huen, Wai Yeong,Lee, Hyuk,Vimonsatit, Vanissorn,Mendis, Priyan,Lee, Han-Seung Elsevier 2019 Surface & coatings technology Vol.366 No.-

<P><B>Abstract</B></P> <P>Instrumented indentation continuous stiffness measurement (CSM) method is applied to investigate the nanomechanical properties of the aluminum and zinc arc thermal spray aluminum coating. This study shows that individual component within a multi-phase material can be differentiated through the stiffness characteristic transition in a single indentation. Using this approach, the nanomechanical properties of the individual phases can be isolated and quantified using statistical deconvolution method. This paper further demonstrates that through the use of computational simulation and artificial neural network, the nanomechanical properties can be predicted based on experimental nanoindentation loading and unloading, where the load-unload responses of an individual material phase can be replicated once the nanomechanical properties are made known. This study shows that CSM method is able to predict the material's elasticity and plasticity properties, including elastic modulus, hardness, yield strength and work hardening, of individual aluminum and zinc components of the thermal arc spray coating.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nanoindentation measured elastic modulus and hardness are presented </LI> <LI> CSM stiffness-displacement gradient is unique for each phase </LI> <LI> Stiffness-displacement feature can identify phase change with depth </LI> <LI> ANN can accurately predict elastic and plastic parameters </LI> </UL> </P>

Practical countermeasures for the aerodynamic performance of long-span cable-stayed bridges with open decks

Zhou, Rui,Yang, Yongxin,Ge, Yaojun,Mendis, Priyan,Mohotti, Damith Techno-Press 2015 Wind and Structures, An International Journal (WAS Vol.21 No.2

Open decks are a widely used deck configuration in long-span cable-stayed bridges; however, incorporating aerodynamic countermeasures are advisable to achieve better aerodynamic performance than a bluff body deck alone. A sectional model of an open deck cable-stayed bridge with a main span of 400 m was selected to conduct a series of wind tunnel tests. The influences of five practical aerodynamic countermeasures on flutter and vortex-induced vibration (VIV) performance were investigated and are presented in this paper. The results show that an aerodynamic shape selection procedure can be used to evaluate the flutter stability of decks with respect to different terrain types and structural parameters. In addition, the VIV performance of $\prod$-shaped girders for driving comfortableness and safety requirements were evaluated. Among these aerodynamic countermeasures, apron boards and wind fairings can improve the aerodynamic performance to some extent, while horizontal guide plates with 5% of the total deck width show a significant influence on the flutter stability and VIV. A wind fairing with an angle of $55^{\circ}C$ showed the best overall control effect but led to more lock-in regions of VIV. The combination of vertical stabilisers and airflow-depressing boards was found to be superior to other countermeasures and effectively boosted aerodynamic performance; specifically, vertical stabilisers significantly contribute to improving flutter stability and suppressing vertical VIV, while airflow-depressing boards are helpful in reducing torsional VIV.

Flexural Capacity Prediction Model For Steel Fibre‑Reinforced Concrete Beams

Aocheng Zhong,Massoud Sofi,Elisa Lumantarna,Zhiyuan Zhou,Priyan Mendis 한국콘크리트학회 2021 International Journal of Concrete Structures and M Vol.15 No.4

Steel fibre (SF) reinforcement has been shown to improve the ductility of high strength concrete (HSC), which is known to be brittle. Research conducted to date on steel fibre reinforced concrete and its effects have emphasised post-failure performance and cracking mechanism. The difficulty in predicting the behaviour of fibres is due to the randomly distributed nature of the material within the matrix leading to a probability distribution of results. Published literature has shown a benefit of adding steel fibres in terms of the ductility performance of structures. Clearly, there is a potential for such material as replacement of conventional steel reinforcement. This study proposes a theoretical model of evaluating the potential of using steel fibres as a replacement material to conventional steel reinforcement bars based on the case study, laboratory and theoretical methodologies. The compressive strength of the concrete at key dates, the effective fibre cross-sectional were measured, and a prediction model was created based on the measurement parameters. The use of four-point flexural testing, standard compressive testing and software image modelling provided the study with relevant data used to analyse and compare to the prediction. Greater ductility performance and toughness were observed with increased fibre volumes, confirming proposed predictions and conclusion drawn from published literature. No consistent or conclusive correlations between fibre volumes and the compressive strength of concrete were found. A relationship between fibre volumes and predicted moment capacities of steel fibre reinforced concrete beams was found based on the proposed theoretical flexural analysis method.