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CONTENTS
Volume 20, Number 4, October 2017
 

Abstract
The effects of the vertical component of a ground motion on the earthquake performances of semi-ductile high-rise R/C structures were investigated in the present study. Linear and non-linear time-history analyses were conducted on an existing in-service R/C building for the loading scenarios including and excluding the vertical component of the ground motion. The ratio of the vertical peak acceleration to the horizontal peak acceleration (V/H) of the ground motion was adopted as the main parameter of the study. Three different near-source earthquake records with varying V/H ratio were used in the analyses. The linear time-history analyses indicated that the incorporation of the vertical component of a ground motion into analyses greatly influences the vertical deflections of a structure and the overturning moments at its base. The lateral deflections, the angles of rotation and the base shear forces were influenced to a lesser extent. Considering the key indicators of vertical deflection and overturning moments determined from the linear time-history analysis, the non-linear analyses revealed that the changes in the forces and deformations of the structure with the inclusion of the vertical ground motion are resisted by the shear-walls. The performances and damage states of the beams were not affected by the vertical ground motion. The vertical ground motion component of earthquakes is markedly concluded to be considered for design and damage estimation of the vertical load-bearing elements of the shear-walls and columns.

Key Words
vertical ground motion; seismic performance; performance level; earthquake behavior

Address
Selcuk Bas: Department of Civil Engineering, Faculty of Engineering, Bartin University, 74100 Bartin, Turkey
Jong-Han Lee: Department of Civil Engineering, College of Engineering, Daegu University, 38453 Gyeongsan, Korea
Mukadder Sevinc and Ilker Kalkan: Graduate School of Natural and Applied Sciences, Department of Civil Engineering, Kirikkale University, 71450 Kirikkale, Turkey

Abstract
The various types of structural materials that are available in the construction industry nowadays make it necessary to predict their stress-strain behavior. Geopolymer are alternatives for ordinary Portland cement concrete that are made from pozzolans activation. Due to relatively new material, many mechanical specifications of geopolymer are still not yet discovered. In this study, stress-strain behavior has been provided from experiments for unconfined geopolymers. Modulus of Elasticity and stress-strain behavior are critical requirements at analysis process and knowing complete stress-strain curve facilitates structural behavior assessment at nonlinear analysis for structures that have built with geopolymers. This study intends to investigate stress–strain behavior and modulus of elasticity from experimental data that belongs for geopolymers varying in fineness and mix design and curing method. For the sake of behavior determination, 54 types of geopolymer are used. Similar mix proportions are used for samples productions that have different fineness and curing approach. The results indicated that the compressive strength ranges between 7.7 MPa and 43.9 MPa at the age of 28 days curing.

Key Words
geopolymer; stress-strain behavior; modulus of elasticity; uniaxial compression

Address
Mehrzad Mohabbi Yadollahi and Ahmet Benli: Department of Civil Engineering, Bingol University, Bingol, 12100, Turkey

Abstract
Fiber reinforced polymer (FRP) bars have been recently used to reinforce concrete members in flexure due to their high tensile strength and especially in corrosive environments to improve the durability of concrete structures. However, FRPs have a low modulus of elasticity and a linear elastic behavior up to rupture, thus reinforced concrete (RC) components with such materials would exhibit a less ductility in comparison with steel reinforcement at the similar members. There were several studies showed the behavior of concrete beams with the hybrid combination of steel and FRP longitudinal reinforcement by adopting the experimental and numerical programs. The current study presents a numerical and analytical investigation based on the data of previous researches. Three-dimensional (3D) finite element (FE) models of beams by using ANSYS are built and investigated. In addition, this study also discusses on the design methods for hybrid FRP-steel beams in terms of ultimate moment capacity, load-deflection response, crack width, and ductility. The effects of the reinforcement ratio, concrete compressive strength, arrangement of reinforcement, and the length of FRP bars on the mechanical performance of hybrid beams are considered as a parametric study by means of FE method. The results obtained from this study are compared and verified with the experimental and numerical data of the literature. This study provides insight into the mechanical performances of hybrid FRP-steel RC beams, builds the reliable FE models which can be used to predict the structural behavior of hybrid RC beams, offers a rational design method together with an useful database to evaluate the ductility for concrete beams with the combination of FRP and steel reinforcement, and motivates the further development in the future research by applying parametric study.

Key Words
FRP; hybrid combination; finite element modeling; reinforced concrete

Address
Linh V. H. Bui and Boonchai Stitmannaithum: Department of Civil Engineering, Chulalongkorn University, 254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand
Tamon Ueda: Laboratory of Engineering for Maintenance System, Hokkaido University, Sapporo, Hokkaido Prefecture 060-0808, Japan

Abstract
Turkey owns a very important cultural and historical heritage that bears the traces of thousands of years of culture and civilization. It is an inevitable duty to carry these treasuries to the future generations. In this paper, structural safety assessment and strengthening stages of one of these important historical heritages namely Amasya Taşhan was investigated in details as a case study. For this purpose, the detailed architectural projects of the structure with the information of all load carrying and structural elements were prepared. Then, the structural dynamic analyses were performed by using SAP2000. The internal forces obtained from the dynamic analyses determined the weak regions. By obtaining the information from dynamic analyses, the method of state of the art technique of application of the structure that needs structural strengthening was selected. The last step is the application of these precautions to the whole structure. At the end of this study, this study not also contains several strengthening techniques that is used in one masonry structure together but also provides a useful reference to the practicing engineers.

Key Words
Amasya Taşhan; strengthening; structural safety assessment; masonry

Address
Zeki Karaca: Department of Civil Engineering, Faculty of Engineering, Ondokuz May

Abstract
A methodology, based on fragility functions, is proposed to evaluate the seismic performance of seismic isolated 45o skewed concrete bridge: 1) twelve types of seismic isolation devices are considered based on two different design parameters 2) fragility functions of a three-span bridge with and without seismic isolation devices are analytically evaluated based on 3D nonlinear incremental dynamic analyses which seismic input consists of 20 selected ground motions. The optimum combinations of isolation device design parameters are identified comparing, for different limit states, the performance of 1) the Seismic Isolated Bridges (SIB) and 2) Not Seismic Isolated Bridge (NSIB) designed according to the AASHTO standards.

Key Words
skewed bridge; seismic isolation device; fragility function methodology; incremental dynamic analysis (IDA); isolation device design parameters

Address
M. Bayat: Young Researchers and Elite Club, Roudehen Branch, Islamic Azad University, Roudehen, Iran
F. Daneshjoo: Department of Civil and Environmental Engineering, Tarbiat Modares University, Tehran, Iran
N. Nisticò: Department of Structural and Geotechnical Engineering, Università degli Studi di Roma

Abstract
In this study, the effect of the tensile strength and ratio of disc spacing to penetration depth on the efficiency of tunnel boring machine (TBM) is investigated using Particle flow code (PFC) in two dimensions. Models with dimensions of 150x70 mm made of rocks with four different tensile strength values of 5 MPa, 10 MPa, 15 MPa and 20 MPa were separately analyzed and two \"U\" shape cutters with width of 10 mm were penetrated into the rock model by velocity rate of 0.1 mm/s. The spacing between cutters was also varied in this study. Failure patterns for 5 different penetration depths of 3 mm, 4 mm, 5 mm, 6 mm, and 7 mm were registered. Totally 100 indentation test were performed to study the optimal tool-rock interaction. An equation relating mechanical rock properties with geometric characteristics for the optimal TBM performance is proposed. The results of numerical simulations show that the effective rock-cutting condition corresponding to the minimum specific energy can be estimated by an optimized disc spacing to penetration depth, which, in fact, is found to be proportional to the rock\'s tensile strength.

Key Words
TBM; PFC2D; disc spacing to penetration depth; rock tensile strength

Address
Vahab Sarfarazi: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
Hadi Haeri: Young Researchers and Elite Club, Bafgh Branch, Islamic Azad University, Bafgh, Iran
Alireza Bagher Shemirani: Department of Civil Engineering, Sadra Institute of Higher Education, Tehran, Iran
Ahmadreza Hedayat: Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, Colorado 80401, USA
Seyed Shahin Hosseini: Department of Civil Engineering, Aria University of Sciences and Sustainability, Tehran, Iran

Abstract
Reinforced concrete (RC) infrastructures often require strengthening due to error in design, degradation of materials properties after prolong utilization and increases load carrying capacity persuaded by new use of the structures. For this purpose, a newly proposed Side Near Surface Mounted (SNSM) composite technique was used for flexural strengthening of RC beam specimens. Analytical and non-linear finite element modeling (FEM) using ABAQUS were performed to predict the flexural performance of RC specimens strengthened with S-NSM using steel bars as a strengthening reinforcement. RC beams with various SNSM reinforcement ratios were tested for flexural performance using four-point bending under monotonic loading condition. Results showed significantly increase the yield and ultimate strengths up to 140% and 144% respectively and improved failure modes. The flexural response, such as failure load, mode of failure, yield load, ultimate load, deflection, strain, cracks characteristic and ductility of the beams were compared with those predicted results. The strengthened RC beam specimens showed good agreement of predicted flexural behavior with the experimental outcomes.

Key Words
SNSM composite; numerical simulation; analytical model; ductility; strengthening

Address
Md. Akter Hosen:
1) Department of Civil Engineering, Faculty of Engineering, University of Malaya, 50603, Kuala Lumpur, Malaysia
2) Department of Civil Engineering, Dhaka University of Engineering & Technology (DUET), Gazipur-1700, Bangladesh
Mohd Zamin Jumaat and Kim Hung Mo: Department of Civil Engineering, Faculty of Engineering, University of Malaya, 50603, Kuala Lumpur, Malaysia
A. B. M. Saiful Islam: Department of Construction Engineering, College of Engineering, University of Dammam, 31451 Dammam, Saudi Arabia
Md. Abdus Salam: Department of Civil Engineering, Dhaka University of Engineering & Technology (DUET), Gazipur-1700, Bangladesh

Abstract
Fresh and hardened behaviors of a new hybrid fiber (steel fiber, polyvinyl alcohol fiber and calcium carbonate whisker) reinforced cementitious composites (HyFRCC) with admixtures (fly ash, silica fume and water reducer) have been studied. Within the limitations of the equipment and testing program, it is illustrated that the rheological properties of the new HyFRCC conform to the modified Bingham model. The relations between flow spread and yield stress as well as flow rate and plastic viscosity both conform well with negative exponent correlation, justifying that slump flow and flow rate test can be applied to replace the other two as simple rheology measurement and control method in jobsite. In addition, for the new HyFRCC with fly ash and water reducer, the mathematical model between the rheological and mechanical properties conform well with the quadratic function, and these quadratic function curves are always concave upward. Based on mathematical analysis, an optimal range of rheology/ flowability can be identified to achieve ideal mechanical properties. In addition, this optimization method can be extended to PVA fiber reinforced cement-based composites.

Key Words
whisker; hybrid fiber; Rheology; flowability; mechanical properties; mathematical model

Address
Mingli Cao, Li Li and Ling Xu: Department of Civil Engineering, Dalian University of Technology, Dalian, China

Abstract
With the increasing demand in the production of concrete, there is a need for adopting a feasible, economical and sustainable technique to fulfill practical requirements. Self-Compacting Concrete (SCC) is one such technique which addresses the concrete industry in providing eco-friendly and cost effective concrete. The objective of the present study is to develop a mix design for SCC with Crushed Rock Fines (CRF) as fine aggregate based on the plastic viscosity of the mix and validate the same for its fresh and hardened properties. Effect of plastic viscosity on the fresh and hardened properties of SCC is also addressed in the present study. SCC mixes are made with binary and ternary blends of Fly Ash (FA) and Ground Granulated Blast Slag (GGBS) with varying percentages as a partial replacement to Ordinary Portland Cement (OPC). The proposed mix design is validated successfully with the experimental investigations. The results obtained, indicated that the fresh properties are best achieved for SCC mix with ternary blend followed by binary blend with GGBS, Fly Ash and mix with pure OPC. It is also observed that the replacement of sand with 100% CRF resulted in a workable and cohesive mix.

Key Words
crushed rock fines; self-compacting concrete; plastic viscosity; compressive strength; mix design; GGBS; fly ash

Address
Kalyana Rama J S, Vasan A and Sai Kubair: Department of Civil Engineering, BITS Pilani, Hyderabad Campus, Hyderabad, India
Sivakumar M V N: Department of Civil Engineering, National Institute of Technology, Warangal, India
Ramachandra Murthy A: CSIR-Structural Engineering Research Centre, Chennai, India

Abstract
This paper aims to analytically investigate the effect of shear stress at the concrete-steel interface on the mechanical behavior of the circular steel tube-confined concrete (STCC) stub columns with active and passive confinement subjected to axial compression. Nonlinear 3D finite element models divided into the four groups, i.e. circumferential-grooved, talc-coated, lubricated, and normal groups, with active and passive confinement were developed. An innovative method was used to simulate the actively-confined specimens, and then, the results of the finite element models were compared with those of the experiments previously conducted by the authors. It was revealed that both the predicted peak compressive strength and stress-strain curves have good agreement with the corresponding values measured for the confined columns. Then, the mechanical properties of the active and passive specimens such as the concrete-steel interaction, longitudinal and hoop stresses of the steel tube, confining pressure applied to the concrete core, and compressive stress-strain curves were analyzed. Furthermore, a parametric study was performed to explore the effects of the concrete compressive strength, steel tube diameter-to-wall thickness ratio, and prestressing level on the compressive behavior of the STCC columns. The results indicate that reducing or removing the interfacial shear stress in the active and passive specimens leads to an increase in the hoop stress and confining pressure, while the longitudinal stress along the steel tube height experiences a decrease. Moreover, prestressing via the presented method is capable of improving the compressive behavior of STCC columns.

Key Words
active confinement; bond shear stress; composite column; finite element modeling; mechanical behavior; numerical analysis; STCC

Address
Mahdi Nematzadeh and Jaber Ghadami: Department of Civil Engineering, University of Mazandaran, Babolsar, Iran

Abstract
This paper studies on the behavior of reinforced concrete (RC) pipes used in basic sanitation in the conduction of storm water and sanitary sewer. Pipes with 800 mm and 1200 mm in diameter were analyzed. The 800 mm pipes were built with simple reinforcement and the 1200 mm pipes with double reinforcement. For the two diameters of pipes the presence or absence of the pocket was evaluated, and the denomination of each one is spigot and pocket pipe (SPP) and ogee joint pipe (OJP), respectively. The 3D numerical models reproduce the three-edge-bearing test that provides information about the strength and stiffness of the reinforced concrete pipes. The validation of the computational models was carried out comparing the vertical and horizontal displacements on the springline and crown/invert and it was also evaluated the reinforcement strains and the crack pattern. As a main conclusion, the numerical models represented satisfactorily the behavior of the pipes and can be used in future studies in parametric analysis.

Key Words
reinforced concrete pipes; spigot and pocket pipe; ogee joint pipe; three-edge-bearing test; numerical analysis

Address
Marcela Novischi Kataoka, Luciane Marcela Filizola de Oliveira and Mounir Khalil El Debs: University of Sao Paulo, Engineering School of Sao Carlos, Department of Structural Engineering, Av. Trabalhador Saocarlense,
no 400, Sao Carlos/SP, 13566-590, Brazil
Jefferson Lins da Silva: University of Sao Paulo, Engineering School of Sao Carlos, Department of Geotechnical Engineering, Av. Trabalhador Saocarlense,
no 400, Sao Carlos/SP, 13566-590, Brazil

Abstract
In this research, the application of ultrasonic pulse velocity (UPV) test as a nondestructive method for estimating some of the mechanical and dynamic properties of reactive powder concrete (RPC) containing steel and polyvinyl alcohol (PVA) fibers, as well as their combination was explored. In doing so, ten different mix designs were prepared in 19 experimental groups of specimens containing three different volume contents of steel fibers (i.e., 1, 2, and 3%) and PVA fibers (i.e., 0.25, 0.5, and 0.75%), as well as hybrid fibers (i.e., 0.25-0.75, 0.5-0.5, and 0.75-0.25%). The specimens in these groups were prepared under the two curing regimes of normal and heat treatment. Moreover, the UPV test results were employed to estimate the compressive strength, dynamic modulus, shear modulus, and Poisson\'s ratio of the RPC concrete and to investigate the quality level of the used concrete. At the end, the effect of the specimen shape and in fact the measuring distance length on the UPV results was explored. The results of this research suggest that the steel fiber-containing RPC specimens demonstrate the highest level of ultrasonic pulse velocity as well as the highest values of the mechanical and dynamic properties. Moreover, heat treatment has a positive effect on the density, UPV, dynamic modulus, Poisson\'s ratio, and compressive strength of the RPC specimens, whereas it leads to a negligible increase or decrease in the shear modulus and static modulus of elasticity. Furthermore, the specimen shape affects the UPV of fiber-lacking specimens while negligibly affecting that of fiber-reinforced specimens.

Key Words
reactive powder concrete; nondestructive test; ultrasonic pulse velocity; compressive strength; dynamic modulus; hybrid fibers; heat treatment

Address
Mahdi Nematzadeh and Reza Poorhosein: Department of Civil Engineering, University of Mazandaran, 47416-13534, Babolsar, Iran

Abstract
In this study, fire-damaged concrete was investigated by a nonlinear resonance vibration (NRV) technique, in order to evaluate its residual material properties. For the experiments, five cubic concrete specimens were prepared and four of them were damaged at different temperatures using a furnace. With a thermal insulator wrapped at the sides of specimen, thermal gradation was applied to the samples. According to the peak temperatures and depths of the samples, nonlinearity parameters were calculated with the NRV technique before the tendency of the parameters was evaluated. In addition, compressive strength and dynamic elastic modulus were measured for each sample and a comparison with the nonlinearity parameter was carried out. Through the experimental results, the possibility of the NRV technique as a method for evaluating residual material properties was evaluated.

Key Words
fire-damaged concrete; nonlinear resonance vibration (NRV); thermal gradation; residual material property; compressive strength; dynamic elastic modulus

Address
Gyu-Jin Kim and Hyo-Gyoung Kwak: Department of Civil and Environmental Engineering, Korean Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea


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