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CONTENTS
Volume 8, Number 4, December 2019
 

Abstract
Several reinforced concrete structures that get deteriorated by rebar corrosion are retrofitted using Carbon Fiber Reinforced Polymer (CFRP). When rebar comes in direct contact with CFRP, rebar may corrode, as iron is more active than carbon. Progression of corrosion of rebar in strengthened RC structures has been carried out when rebar comes in direct contact with CFRP. The experimentation is carried out in two phases. In phase I, corrosion of bare steel bar is monitored by making its contact with CFRP. In phase II, concrete specimens with surface bonded CFRP were casted and subjected to the realistic exposure conditions keeping direct contact between rebar and CFRP. Progression of corrosion has been monitored by various parameters: Half-cell potential, Tafel extrapolation and Linear Polarisation Resistance. On termination of exposure, to find residual bond stress between rebar and concrete, pull-out test was performed. Rebar in contact with CFRP has shown substantially higher corrosion. The level of corrosion will be more with more area of contact.

Key Words
reinforced concrete; rebar corrosion; Carbon Fiber Reinforced Polymer (CFRP); half-cell potential; corrosion rate (Icorr) Tafel Plots; linear polarisation resistance (LPR); bond stress; mass loss

Address
Prasad V. Bahekar and Sangeeta S. Gadve: Department of Applied Mechanics, Visvesvaraya National Institute of Technology, Nagpur-440010, India

Abstract
This paper presents the results of cyclic loading tests on new high-strength concrete (HC) short columns. The seismic performance and deformation capacity of three reinforced high-strength concrete filled Polyvinyl Chloride tube (RHCPVCT) short columns and one reinforced high-strength concrete (RHC), under pseudo-static tests (PSTs) with vertical axial force was evaluated. The main design parameters of the columns in the tests were the axial compression ratio, confinement type, concrete strength, height-diameter ratio of PVCT. The failure modes, hysteretic curves, skeleton curves of short columns were presented and analyzed. Placing PVCT in the RHC column could be remarkably improved the ultimate strength and energy dissipation of columns. However, no fiber element models have been formulated for computing the seismic responses of RHCPVCT columns with PVT tubes filled with high-strength concrete. Nonlinear finite element method (FEM) was conducted to predict seismic behaviors. Finite element models were verified through a comparison of FEM results with experimental results. A parametric study was then performed using validated FEM models to investigate the effect of several parameters on the mechanical properties of RHC-PVCT short columns. The parameters study indicated that the concrete strength and the ratio of diameter to height affected the seismic performance of RHC-PVCT short column significantly.

Key Words
high-strength concrete; pseudo-static tests; high-strength concrete filled PVCT; seismic performance; finite element method

Address
Jianyang Xue: School of Civil Engineering, Xi\'an University of Architecture and Technology, Xi\'an 710055, China
Xiangbi Zhao: School of Civil Engineering, Xi\'an University of Architecture and Technology, Xi\'an 710055, China
Xiaojun Ke: College of Civil Engineering and Architecture, Guangxi University, Nanning 530004, China
Fengliang Zhang: Shaanxi Institute of Architecture Science, Xi\'an 710082, China
Linlin Ma: School of Civil Engineering, Xi\'an University of Architecture and Technology, Xi\'an 710055, China

Abstract
The cracking and spalling caused by fracture of concrete lining have adverse impacts on serviceability and durability of the tunnel, and the subsequent maintenance work for damaged structure needs to be specific to the damaging causes. In this paper, a particular case study of an operational tunnel structure is presented for the serious cracking and spalling behaviours of concrete lining, focusing on the multi-factors inducing lining failure. An integrated field investigation is implemented to characterize the spatial distribution of damages and detailed site situations. According to results of nondestructive inspection, insufficient lining thickness and cavity behind lining are the coupled-inducement of lining failure bahaviors. To further understanding of the lining structure performance influenced by these multiple construction deficiencies, a reliable numerical simulation based on extended finite element method (XFEM) is performed by using the finite element software. The numerical model with 112 m longitudinal calculation, 100 m vertical calculation and 43 m vertical depth, and the concrete lining with 1450 solid elements are set enrichment shape function for the aim of simulating cracking behavior. The numerical simulation responses are essentially in accordance with the actual lining damaging forms, especially including a complete evolutionary process of lining spalling. This work demonstrates that the serious lining damaging behaviors are directly caused by a combination of insufficient thickness lining and cavity around the surrounding rocks. Ultimately, specific maintenance work is design based on the construction deficiencies, and that is confirmed as an efficient, time-saving and safe maintenance method in the operational railway tunnel.

Key Words
fracture; field investigation; numerical simulation; maintenance; XFEM

Address
Yiding Zhao: School of Civil Engineering, Central South University, Changsha 410075, China; College of Civil Engineering, Yancheng Institute of Technology, Yancheng 224051, China
Yongxing Zhang: School of Civil Engineering, Nanjing Forestry University, Nanjing 210037, China; Changsha University of Science & Technology, Changsha 410114, China
Junsheng Yang: School of Civil Engineering, Central South University, Changsha 410075, China

Abstract
In evaluating explosion-protection capacity, safety distance is broadly accepted as the distance at which detonation of a given explosive causes acceptable structural damage. Safety distance can be calculated based on structural response under blast loading and damage criteria. For the applicability of the safety distance, the minimum required stand-off distance should be given when the explosive size is assumed. However, because of the nature of structures, structural details and material characteristics differ, which requires sensitivity analysis of the safety distance. This study examines the safety-distance sensitivity from structural and material property variations. For the safety-distance calculation, a blast analysis module based on the Kingery and Bulmash formula, a structural response module based on a Single Degree of Freedom model, and damage criteria based on a support rotation angle were prepared. Sensitivity analysis was conducted for the Reinforced Concrete oneway slab with different thicknesses, reinforcement ratios, reinforcement yield strengths, and concrete compressive strengths. It was shown that slab thickness has the most significant influence on both inertial force and flexure resistance, but the compressive strength of the concrete is not relevant.

Key Words
explosion; SDOF; safety distance; RC slab; sensitivity analysis; slab thickness

Address
Jung Hun Kee, Jong Yil Park: Department of Safety Engineering, Seoul National University of Science and Technology, Seoul 01811, Republic of Korea
Joo Hyun Seong: Korea Infrastructure Safety and Technology Corporation, 24, Ena-ro 128beon-gil, Jinju-si, Gyeongsangnam-do, 52856, Republic of Korea

Abstract
In the present paper, the fiber theory has been employed to model the reinforced concrete (RC) deep beams (DBs) considering the reinforcing steel bar-concrete interaction. To simulate numerically the behavior of materials, the uniaxial materials\' constitutive laws have been employed for reinforcements and concrete and the bond stress-slip between the reinforcing steel bars and surrounding concrete are taken into account. Because of the high sensitivity of DBs to shear deformations, the Timoshenko beam theory has been applied. The shear stress-strain (S-SS) relationship has been defined by the modified compression field theory (MCFT) model. By modeling about 300 RC panels and employing a produced numerical database, a study has been carried out to show the sensitivity of the MCFT model. This is performed based on the multiple linear regression (MLR) models. The results of this research also illustrate how different parameters such as characteristic compressive strength of concrete, yield strength of reinforcements and the percentages of reinforcements in different directions get involved in the shear behavior of RC panels without applying complex theories. Based on the results obtained from the analysis of the MCFT S-SS model, a relatively simplified numerical S-SS model has been proposed. Application of the proposed S-SS model in modeling and analyzing the considered samples indicates that there is a good agreement between the simulated and the experimental test results. The comparison between the proposed S-SS model and the MCFT model indicates that in addition to the advantage of better accuracy, the main advantage of the proposed method is simplicity in application.

Key Words
nonlinear analysis; RC deep beam; shear stress-strain; shear deformation; MCFT

Address
Seyed Shaker Hashemi, Saeid Javidi, Mahmoud Malakooti: Department of Civil Engineering, Persian Gulf University, Shahid Mahini Street, Bushehr, Iran
Kabir Sadeghi: Department of Civil Engineering, Near East University, ZIP Code: 99138, Lefkosa, TRNC, Mersin 10, Turkey

Abstract
The lateral displacement or drift may be the cause of the damage in the reinforced concrete (RC) columns under the seismic load. In many regulations, lateral displacement was limited according to the properties of columns. The design displacement limits may be represented indirectly through the material strain limits and the mechanical properties of columns. EUROCODE-8 and FEMA356 calculate displacement limits by taking into account the mechanical properties of columns. However, Turkey Building Earthquake Code (TBEC) determine displacement limits by taking into account the material strain limits. The aim of this study is to assess the seismic design codes for RC columns through an experimental study. The estimates of seismic design codes have been compared with the experimental results. It is observed that the lateral displacement capacities of columns estimated according to some seismic codes are not in agreement with the experimental results. Also, it is observed that TBEC is conservative in the context of the performance indicator of RC columns, compared to EUROCODE-8 and FEMA356. Moreover, in this study, plastic hinge length and effective stiffness of test elements were investigated.

Key Words
drift capacity; reinforced concrete; columns; plastic hinge length; effective stiffness

Address
Sinan Cansiz: Department of Construction Technology, Istanbul Aydin University, Istanbul, Turkey
Cem Aydemir: Department of Civil Engineering, Istanbul Aydin University, Istanbul, Turkey
Güray Arslan: Department of Civil Engineering, Yildiz Technical University, Istanbul, Turkey

Abstract
Pervious concrete pavements are the need of the day to avoid urban flooding and to facilitate ground water recharge. However, the strength of pervious or porous concrete is considerably less compared to conventional concrete. In this experimental investigation, an effort is made to improve the strength of pervious concrete by adopting fibres and a small amount of fine aggregate. A porous concrete with cement to aggregate ratio of 1:5 and a water-powder ratio of 0.4 is adopted. 30% of the cement is replaced by cementitious material ground granulated blast furnace slag (GGBS) for better strength and workability. Recron fibres at a dosage of 0.5, 1.0 and 1.5% by weight of cement were included to improve the impact strength. Since concrete pavements are subjected to impact loads, the impact strength was also calculated by \"Drop ball method\" in addition to compressive strength. The effect of fine aggregate and recron fibres on workability, porosity, compressive and impact strength was studied. The investigations have shown that 20% inclusion of fine aggregate and 1.5% recron fibres by weight of cement give better strength with an acceptable range of porosity.

Key Words
porosity; pervious concrete; drop ball method; impact strength; compressive strength; fibrecrete

Address
Savithri S. Karanth, U. Lohith Kumar and Naveen Danigond: Department of Civil Engineering, Global Academy of Technology, Bangalore, India

Abstract
In this study, the effect of cellulose nanocrystals (CNCs) on the fire resistance properties of fiber-reinforced cement composites was investigated. The main variables were CNCs content (0.4, 0.8 and 1.2vol.% compared with cement), steel fiber ratio, and exposure temperature (100, 200, 400, 600 and 800oC). The fire resistance properties, i.e., residual compressive strength, flexural strength, and porosity, were evaluated in relation with the exposure temperature of the specimens. The CNCs suspensions were prepared to composited dispersion method of magnetic stirring and ultra-sonication. CNCs are effective for increasing the compressive strength at high temperatures but CNCs do not seem to have a significant effect on flexural reinforcement. Porosity test result showed CNCs reduce the non-hydration area inside the cement and promote hydration.

Key Words
Cellulose Nanocrystals (CNCs); fire resistance; porosity; residual strength; microstructure

Address
Hyung-Joo Lee, Seung-Ki Kim, Heon-Seok Lee, Woosuk Kim: Department of Architectural Engineering, Kumoh National Institute of Technology, 61 Daehak-ro, Gumi, Gyeongsangbuk-do 39177, Republic of Korea
Yong-Hak Kang: Daegu & Gyeongbuk Branch, Korea Conformity Laboratories, Daegu 42994, Republic of Korea
Thomas H.-K. Kang: Department of Architecture & Architectural Engineering, Seoul National University, Seoul 08826, Republic of Korea

Abstract
The present study targets to access the consequence of utilization of coarse aggregates retrieved from waste concrete as a substitution of coarse fraction of natural aggregates and silica nano-particles as partial substitution of cement using principles of factorial design. Furthermore, procedures of design of experiments are employed to examine the effect of use of recycled aggregates and nano-silica. In this investigation, compressive strength found after at 7, 28, 90 and 365 days, split and flexural tensile strength, ultrasonic pulse velocity and rebound number and are chosen as responses, whereas the percentages of recycled coarse aggregates (RCA%) and nano-silica (NS(%)) are selected as factors. Analysis of Variance has been conducted on the experimental results for the selected responses with consideration the both factors, which indicates that RCA (%) and NS (%) have substantial impact on the various responses. However, the present analysis depicts that interaction between factors has considerable effect on the chosen parameters of concrete. Furthermore, validation experiments are carried to validate these models for compressive and tensile strength for 100% RCA and 1% NS. The results of comparative study indicates that that the error of the estimation determined using the relevant models are found to be small (

Key Words
ANOVA; colloidal nano-silica; recycled aggregate concrete; design of experiments

Address
Bibhuti Bhusan Mukharjee: Department of Civil Engineering, Biju Patnaik University of Technology, Odisha, India
Sudhirkumar V Barai: Department of Civil Engineering, Indian Institute of Technology Kharagpur, Kharagpur, India

Abstract
To investigate the axial compressive performance of the recycled aggregate concrete (RAC) filled glass fiber reinforced polymer (GFRP) tube and profile steel composite columns, static loading tests were carried out on 18 specimens under axial loads in this study, including 7 RAC filled GFRP tube columns and 11 RAC filled GFRP tube-profile steel composite columns. The design parameters include recycled coarse aggregate (RCA) replacement percentage, profile steel ratio, slenderness ratio and RAC strength. The failure process, failure modes, axial stress-strain curves, strain development and axial bearing capacity of all specimens were mainly analyzed in detail. The experimental results show that the GFRP tube had strong restraint ability to RAC material and the profile steel could improve the axial compressive performance of the columns. The failure modes of the columns can be summarized as follow: the profile steel in the composite columns yielded first, then the internal RAC material was crushed, and finally the fiberglass of the external GFRP tube was seriously torn, resulting in the final failure of columns. The axial bearing capacity of the columns decreased with the increase of RCA replacement percentage and the maximum decreasing amplitude was 11.10%. In addition, the slenderness ratio had an adverse effect on the axial bearing capacity of the columns. However, the strength of the RAC material could effectively improve the axial bearing capacity of the columns, but their deformability decreased. In addition, the increasing profile steel ratio contributed to the axial compressive capacity of the composite columns. Based on the above analysis, a formula for calculating the bearing capacity of composite columns under axial compression load is proposed, and the adverse effects of slenderness ratio and RCA replacement percentage are considered.

Key Words
recycled aggregate concrete; GFRP tube; profiles steel; composite column; axial compression behavior

Address
Hui Ma: School of Civil Engineering and Architecture, Xi\'an University of Technology, Xi\'an, 710048, China; State Key Laboratory of Eco-hydraulics in Northwest Arid Region, Xi\'an University of Technology, Xi\'an, 710048, China
Hengyu Bai: School of Civil Engineering and Architecture, Xi\'an University of Technology, Xi\'an, 710048, China
Yanli Zhao: School of Architecture, Chang\'an University, Xi\'an, 710064, China
Yunhe Liu: School of Civil Engineering and Architecture, Xi\'an University of Technology, Xi\'an, 710048, China; State Key Laboratory of Eco-hydraulics in Northwest Arid Region, Xi\'an University of Technology, Xi\'an, 710048, China
Peng Zhang: School of Civil Engineering and Architecture, Xi\'an University of Technology, Xi\'an, 710048, China


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