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CONTENTS
Volume 29, Number 1, January 2022
 


Abstract
Several aspects influence corrosive processes in reinforced concrete (RC) structures such as environmental conditions, structural geometry and mechanical properties. Since these aspects present large randomnesses, probabilistic models allow a more accurate description of the corrosive phenomena. Besides, the definition of limit states in the reliability assessment requires a proper mechanical model. In this context, this study proposes a straightforward methodology for the mechanical-probabilistic modelling of RC structures subjected to reinforcements' corrosion. An improved damage approach is proposed to define the limit states for the probabilistic modelling, considering three main degradation phenomena: concrete cracking, rebar yielding and rebar corrosion caused either by chloride or carbonation mechanisms. The stochastic analysis is evaluated by the Monte Carlo simulation method due to the computational efficiency of the Lumped Damage Model for Corrosion (LDMC). The proposed mechanical-probabilistic methodology is implemented in a computational framework and applied to the analysis of a simply supported RC beam and a 2D RC frame. Curves illustrate the probability of failure evolution over a service life of 50 years. Moreover, the proposed model allows drawing the probability of failure map and then identifying the critical failure path for progressive collapse analysis. Collapse path changes caused by the corrosion phenomena are observed.

Key Words
carbonation; chloride corrosion; Lumped Damage model; stochastic analysis; reinforcements

Address
Karolinne O. Coelho: School of Civil Engineering, Architecture and Urban Design, University of Campinas, Rua Saturnino de Brito, 224, Campinas, SP, 13083889, Brazil
Edson D. Leonel: Department of Structural Engineering, São Carlos School of Engineering, University of São Paulo, Av. Trabalhador São Carlense, 400, São Carlos, 13566590, Brazil
Julio Flórez-López: School of Civil Engineering, Chongqing University, ShapingbaDistrict, 400045 Chongqing, China

Abstract
Concrete-filled steel tubes (CFSTs) are increasingly used as composite sections in structures owing to their excellent load bearing capacity. Therefore, predicting the mechanical behavior of CFST sections under axial compression loading is vital for design purposes. This paper presents the first study on the nonlinear analysis of heated CFSTs with high-strength concrete core containing steel fiber and waste tire rubber under axial compression loading. CFSTs had steel fibers with 0, 1, and 1.5% volume fractions and 0, 5, and 10% rubber particles as sand alternative material. They were subjected to 20, 250, 500, and 750oC temperatures. Using flow rule and analytical analysis, a model is developed to predict the load bearing capacity of steel tube, and hoop strain-axial strain relationship, and axial stress-volumetric strain relationship of CFSTs. An elastic-plastic analysis method is applied to determine the axial and hoop stresses of the steel tube, considering elastic, yield, and strain hardening stages of steel in its stress-strain curve. The axial stress in the concrete core is determined as the difference between the total experimental axial stress and the axial stress of steel tube obtained from modeling. The results show that steel tube in CFSTs under 750oC exhibits a higher load bearing contribution compared to those under 20, 250, and 500oC. It is also found that the ratio of load bearing capacity of steel tube at peak point to the load bearing capacity of CFST at peak load is noticeable such that this ratio is in the ranges of 0.21-0.33 and 0.31-0.38 for the CFST specimens with a steel tube thickness of 2 and 3.5 mm, respectively. In addition, after the steel tube yielding, the load bearing capacity of the tube decreases due to the reduction of its axial stiffness and the increase of hoop strain rate, which is in the range of about 20 to 40%.

Key Words
axial compression; concrete-filled steel tube (CFST); elevated temperature; hoop strain; steel fiber; waste tire rubber

Address
Hassan Sabetifar: Department of Civil Engineering, Faculty of Engineering and Technology, University of Mazandaran, Babolsar, Iran
Mahdi Nematzadeh: Department of Civil Engineering, Faculty of Engineering and Technology, University of Mazandaran, Babolsar, Iran
Aliakbar Gholampour: College of Science and Engineering, Flinders University, SA, Australia

Abstract
Experimental and numerical simulation were used to investigate the effects of angle and number of T shape non-persistent crack on the shear behaviour of crack's bridge area under uniaxial compressive test. concrete samples with dimension of 150 mmx150 mmx40 mm were prepared. Within the specimen, T shape non-persistent notches were provided. 16 different configuration systems were prepared for T shape non-persistent crack based on two and three cracks. In these configurations, the length of cracks were taken as 4 cm and 2 cm based on the cracks configuration systems. The angle of larger crack related to horizontal axis was 0o, 30o, 60o and 90o. Similar to cracks configuration systems in the experimental tests, 28 models with different T shape non-persistent crack angle were prepared in numerical model. The length of cracks were taken as 4 cm and 2 cm based on the cracks configuration systems. The angle of larger crack related to horizontal axis was 0o, 15o, 30o, 45o, 60o, 75o and 90o. Tensile strength of concrete was 1MPa. The axial load was applied to the model. Displacement loading rate was controlled to 0.005 mm/s. Results indicated that the failure process was significantly controled by the T shape non-persistent crack angle and crack number. The compressive strengths of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. Furthermore, it was shown that the compressive behaviour of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the crack number and crack angle. The strength of samples decreased by increasing the crack number. In addition, the failure pattern and failure strength are similar in both methods i.e. the experimental testing and the numerical simulation methods (PFC2D).

Key Words
crack angle; crack number; PFC2D; T shape non-persistent crack

Address
V. Sarfarazi: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
K. Asgari: Department of Mining Engineering, Shahid Bahonar University of Kerman, Kerman, Iran
S. Maroof: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
Sh Fattahi: Department of Mining and Metallurgical Engineering, Amirkabir University of Technology, Tehran Iran

Abstract
The increase in waste tires has brought serious environmental problems. Using waste tires rubber particles as aggregate in concrete can reduce pollution and decrease the usage of natural aggregate. The paper describes an investigation on flexural bearing capacity of self-compacting concrete (SCC) pavement slabs containing crumb rubber. Cyclic loading tests with different stress ratios and loading frequencies are carried out on compact concrete pavement slabs containing crumb rubber. Based on Paris Law and test data, the fatigue life of SCC pavement slab containing crumb rubber is discussed, and a revised mathematical model is established to predict the fatigue life of SCC pavement slab containing crumb rubber. The model applies to different stress ratios and loading frequencies. The fatigue life of SCC pavement slab containing crumb rubber is affected by the stress ratio and loading frequency. The fatigue life increases with the increase of stress ratio and loading frequency. Real-time acoustic emission (AE) signals in the SCC pavement slab containing crumb rubber under cyclic loading are measured, and the characteristics of crack propagation in the SCC pavement slab containing crumb rubber under different stress ratios and loading frequencies are compared. The AE signals provide abundant information of fracture process zone and crack propagation. The variation of AE ringing count, energy and b-value show that the fracture process of SCC pavement slab containing crumb rubber is divided into three stages.

Key Words
acoustic emission (AE); fatigue life; flexural bearing capacity; fracture process zone; self-compacting concrete (SCC) pavement slabs containing crumb rubber

Address
Jiajia Wang, Xudong Chen, Chaoguo Wu, Zhenxiang Shi and Xiyuan Cheng: College of Civil and Transportation Engineering, Hohai University, Nanjing 210098, China

Abstract
In this paper, a reliability-based approach has been implemented to develop seismic analytical fragility curves of highway bridges. A typical bridge class of the Central and South-eastern United States (CSUS) region was selected. Detailed finite element modelling is presented and Incremental Dynamic Analysis (IDA) is used to capture the behavior of the bridge from linear to nonlinear behavior. Bayesian linear regression method is used to define the demand model. A reliability approach is implemented to generate the analytical fragility curves and the proposed approach is compared with the conventional fragility analysis procedure.

Key Words
aleatory uncertainty; epistemic uncertainty; fragility analysis; probabilistic demand model; reliability methods

Address
M. Kia: Department of Civil Engineering, University of Science and Technology of Mazandaran, Behshahr, Iran
M. Bayat: Department of Civil and Environmental Engineering, Univrsity of South Carolina, Columbia, SC, USA
A. Emadi: Department of Civil Engineering, Pajoohesh Consulting Engineers, Tehran, Iran
S. Soleimani Kutanaei: Department of Civil Engineering, Islamic Azad University, Ayatollah Amoli Branch, Amol, Iran
H.R Ahmadi: Department of Civil Engineering, Faculty of Engineering, University of Maragheh, P.O. Box 55136-553, Maragheh, Iran


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