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CONTENTS
Volume 7, Number 3, May 2019
 

Abstract
Irregular distribution of mass in elevation is regarded as a structural irregularity by which the modes with high energy levels are excited and in addition, it can lead the structure to withstanding concentration of nonlinear deformations and consequently, suffer from unpredictable local or global damages. Accordingly, with respect to the lack of knowledge and insight towards the performance of concrete buildings making use of tunnel-form structural system in seismic events, it is of utmost significance to assess seismic vulnerability of such structures involved in vertical mass irregularity. To resolve such a crucial drawback, this papers aims to seismically assess vulnerability of RC tunnel-form buildings considering effects of irregular mass distribution. The results indicate that modal responses are not affected by building

Key Words
tunnel-form structural system; performance level; irregular mass distribution; vertical irregularity; seismic reliability

Address
Vahid Mohsenian and Ali Nikkhoo: Civil Engineering Department, University of Science and Culture, Tehran, Iran

Abstract
This study presents the fracture properties of nano modified medium strength concrete (MSC). The nano particle used in this study is nano silica which replaces cement about 1 and 2% by weight, and the micro steel fibers are added about 0.4% volume of concrete. In addition to fracture properties, mechanical properties, namely, compressive strength, split tensile strength, and flexural strength of nano modified MSC are studied. To ensure the durability of the MSC, durability studies such as rapid chloride penetration test, sorptivity test, and water absorption test have been carried out for the nano modified MSC. From the study, it is observed that significant performance improvement in nano modified MSC in terms of strength and durability which could be attributed due to the addition pozzolanic reaction and the filler effect of nano silica. The incorporation of nano silica increases the fracture energy about 30% for mix without nano silica. Also, size independent fracture energy is arrived using two popular methods, namely, RILEM work of fracture method with P–u tail correction and boundary effect method. Both the methods resulted in nearly the same size-independent GF irrespective of the notch to depth ratio of the same specimen. This shows evidence that either of the two procedures could be used in practice for analysis of cracked concrete structures.

Key Words
steel fibre; nano silica; mechanical properties; fracture properties; durability

Address
A. Ramachandra Murthy and P. Ganesh: CSIR-Structural Engineering Research Centre, Chennai, 600113, India

Abstract
This paper introduces a new efficient analytical method, based on shear deformations obtained with 2D elasticity theory approach, to perform an explicit closed-form solution for calculation the interfacial shear and normal stresses in plated RC beam. The materials of plate, necessary for the reinforcement of the beam, are in general made with fiber reinforced polymers (Carbon or Glass) or steel. The experimental tests showed that at the ends of the plate, high shear and normal stresses are developed, consequently a debonding phenomenon at this position produce a sudden failure of the soffit plate. The interfacial stresses play a significant role in understanding this premature debonding failure of such repaired structures. In order to efficiently model the calculation of the interfacial stresses we have integrated the effect of shear deformations using the equilibrium equations of the elasticity. The approach of this method includes stress-strain and strain-displacement relationships for the adhesive and adherends. The use of the stresses continuity conditions at interfaces between the adhesive and adherents, results pair of second-order and fourth-order coupled ordinary differential equations. The analytical solution for this coupled differential equations give new explicit closed-form solution including shear deformations effects. This new solution is indented for applications of all plated beam. Finally, numerical results obtained with this method are in agreement of the existing solutions and the experimental results.

Key Words
two-dimensional elasticity; RC beam; interfacial shear stress; interfacial normal stress; debonding; coupled differential equations; soffit plate; shear deformations

Address
B. Guenaneche: Civil Engineering Department, Faculty of Technology, Material and Hydrology Laboratory, University of Sidi Bel Abbes, Algeria
S. Benyoucef: Civil Engineering Department, Faculty of Technology, Material and Hydrology Laboratory, University of Sidi Bel Abbes, Algeria
A. Tounsi: Civil Engineering Department, Faculty of Technology, Material and Hydrology Laboratory, University of Sidi Bel Abbes, Algeria; Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia
E.A. Adda Bedia: Centre of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah, 21589, Saudi Arabia

Abstract
Metakaolin (MK), which is increasingly being used to produce high performance concrete, is produced by calcining purified kaolinite between 650 and 700oC in a rotary kiln. The carbonation resistance of metakaolin blended concrete is lower than that of control concrete. Hence, it is critical to consider carbonation durability for rationally using metakaolin in the concrete industry. This study presents microstructure modeling during the carbonation of metakaolin blended concrete. First, based on a blended hydration mo del, the amount of carbonatable substances and porosity are determined. Second, based on the chemical reactions between carbon dioxide and carbonatable substances, the reduction of concrete porosity due to carbonation is calculated. Furthermore, CO2 diffusivity is evaluated considering the concrete composition and exposed environment. The carbonation depth of concrete is analyzed using a diffusion-based model. The proposed microstructure model takes into account the influences of concrete composition, concrete curing, and exposure condition on carbonation. The proposed model is useful as a predetermination tool for the evaluation of the carbonation service life of metakaolin blended concrete.

Key Words
metakaolin; carbonation; concrete; model; service life

Address
Xiao-Yong Wang: Department of Architectural Engineering, Kangwon National University, Chuncheon, Korea
Han-Seung Lee: Department of Architectural Engineering, Hanyang University, Ansan, Korea

Abstract
Low-calcium fly ash (LCFA) were used to prepare cement/LCFA specimens in this study. The basic physical properties including water demand, fluidity, setting time, soundness and drying shrinkage of cement/LCFA paste were investigated. The effects of curing time, immersion time and wet-dry cycles in 3% Na2SO4 solution on the compressive strength and the microstructures of specimens were also discussed. The results show that LCFA increases the water demand, setting time, soundness of cement paste samples. 50% and 60% LCFA replacement ratio decrease the drying shrinkage of hardened cement paste. The compressive strength of plain cement specimens decreases at the later immersion stage in 3% Na2SO4 solution. The addition of LCFA can decrease this strength reduction of cement specimens. For all specimens with LCFA, the compressive strength increases with increasing immersion time. During the wet-dry cycles, the compressive strength of plain cement specimens decreases with increasing wet-dry cycles. However, the pores in the specimens with 30% and 40% LCFA at early ages could be large enough for the crystal of sodium sulfate, which leads to the compressive strength increase with the increase of wet-dry cycles in 3% Na2SO4 solution. The microstructures of cement/LCFA specimens are in good agreement with the compressive strength.

Key Words
low-calcium fly ash (LCFA); cement paste; sulfate resistance; wet-dry cycles; immersion

Address
Wuman Zhang, Yingchen Zhang and Longxin Gao: Department of Civil Engineering, School of Transportation Science and Engineering, Beihang University, Beijing, 100191, P.R. China

Abstract
In this study, it has been tried to prepare an analytical fragility curves for isolated straight continues highway bridges by considering different spectral intensity measures. A three-span concrete isolated bridge has been selected and the seismic performance of the bridge has been improved by Lead Rubber Bearing (LRB). Incremental Dynamic Analysis (IDA) is applied to the bridge in longitudinal direction. A suite of 14 earthquake ground motions from medium to sever motions are scaled and used for nonlinear time history analysis. Fragility function considers the relationship of earthquake intensity measures (IM) and probability of exceeding certain Damage State (DS). A full three dimensional finite element model of the isolated bridge has been developed and analyzed. A wide range of different intensity measures are selected and the optimal intensity measure which has the less dispersion is proposed.

Key Words
straight highway bridge; fragility curve; Incremental Dynamic Analysis (IDA); finite element modeling

Address
Mahmoud Bayat: Jiangxi Provincial Key Laboratory of Environmental Geotechnical Engineering and Disaster Control,
Jiangxi University of Science and Technology, Ganzhou, Jiangxi, 341000, People\'s Republic of China; Department of Civil and Environmental Engineering, University of Pittsburgh, 3700 O

Abstract
Bamboo concrete bond behaviour is investigated through pullout test in this work. The bamboo strip to be used as reinforcement inside concrete is first treated with chemical adhesive to make the bamboo surface impermeable. Various surface coatings are explored to understand their water repellant properties. The chemical action at the bamboo concrete interface is studied through different chemical coatings, sand blasting, and steel wire wrapping treatment. Whereas mechanical action at the bamboo concrete interface is studied by developing mechanical interlock. The result of pullout tests revealed a unique combination of surface treatment and grooved bamboo profile. This combination of surface treatment and a grooved bamboo profile together enhances the strength of bond. Performance of a newly developed grooved bamboo strip is verified against equivalent plain rectangular bamboo strip. The test results show that the proposed grooved bamboo reinforcement, when treated, shows highest bond strength compared to treated plain, untreated plain and untreated grooved bamboo reinforcement. Also, it is observed that bond strength is majorly influenced by the type of surface treatment, size and spacing of groove. The changes in bamboo-concrete bond behavior are observed during the experimentation.

Key Words
surface treatment; pull-out test; bamboo reinforcement; bond strength; semicircular groove; mechanical interlock

Address
Pankaj R. Mali and Debarati Datta: Department of Applied Mechanics, Visvesvaraya National Institute of Technology, Nagpur-440010, Maharashtra, India

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