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CONTENTS
Volume 19, Number 1, January 2017
 

Abstract
Prestressed concrete I-girders are subject to different load types at their construction stages. At the time of strand release, i.e., detensioning, prestressed concrete girders are under the effect of dead and prestressing loads. At this stage, the camber, total net upward deflection, of prestressed girder is summation of the upward deflection due to the prestressing force and the downward deflection due to dead loads. For the calculation of the upward deflection, it is generally considered that prestressed concrete I-girder behaves linear-elastic. However, the field measurements on total net upward deflection of prestressed I-girder after detensioning show contradictory results. In this paper, camber calculations with the linear-elastic beam and elastic-stability theories are presented. One of a typical precast I-girder with 120 cm height and 31.5 m effective span length is selected as a case study. 3D finite element model (FEM) of the girder is developed by SAP2000 software, and the deflections of girder are obtained from linear and nonlinear-static analyses. Only geometric nonlinearity is taken into account. The material test and field measurement of this study are performed at prestressing girder plant. The results of the linear-elastic beam and elastic-stability theories are compared with FEM results and field measurements. It is seen that the camber predicted by elastic-stability theory gives acceptable results than the linear-elastic beam theory while strand releasing.

Key Words
camber; deflection; detensioning; finite element model; linear and non-linear static analyses; prestressed concrete

Address
Barbaros Atmaca and Şevket Ateş: Department of Civil Engineering, Karadeniz Technical University, 61080, Turkey

Abstract
In Chinese Design Codes, for super high-rise buildings with complex structural distribution, which are regarded as code-exceeding buildings, elasto-plastic time history analysis is needed to validate the requirement of \"no collapse under rare earthquake\". In this paper, a 117-story super high-rise building is discussed. It has a height of 597 m and a height-width ratio of 9.5, which have both exceeded the limitations stipulated by the Chinese Design Codes. Mega columns adopted in this structure have cross section area of about 45 m2 at the bottom, which is infrequent in practical projects. NosaCAD and Perform-3D, both widely used in nonlinear analyses, were chosen in this study, with which two model were established and analyzed, respectively. Elasto-plastic time history analysis was conducted to look into its seismic behavior, emphasizing on the stress state and deformation abilities under intensive seismic excitation. From the comparisons on the results under rare earthquake obtained from NosaCAD and Perform-3D, the overall responses such as roof displacement, inter story drift, base shear and damage pattern of the whole structure from each software show agreement to an extent. Besides, the deformation of the structure is below the limitation of the Chinese Codes, the time sequence and distribution of damages on core tubes are reasonable, and can dissipate certain inputted energy, which indicates that the structure can meet the requirement of \"no collapse under rare earthquake\".

Key Words
super high-rise building; elasto-plastic time history analysis; seismic behavior; rare earthquake

Address
Xiaohan Wu, Yimiao Li and Yunlei Zhang: Research Institute of Structure Engineering and Disaster Reduction, College of Civil Engineering, Tongji University, Shanghai, 200092, China


Abstract
This paper uses modelling and experiment to perform a quantitative analysis for the gypsum and ettringite formations in cement pastes subjected to sulfate attack. Firstly, based on Fick\'s law and chemical reaction kinetics, a diffusion model of sulfate ions in cement pastes is proposed, and then the model of the gypsum and ettringite formations is established to analyze its contents in cement pastes with corrosion time. Secondly, the corrosion experiment of the specimens with cement pastes immersed into 2.5%, 5.0% and 10.0% Na2SO4 solutions are carried out, and by using XRD-Rietveld method, the phases of powder samples from the specimens are quantitatively analyzed to obtain the contents of gypsum and ettringite in different surface depth, solution concentration and corrosion time. Finally, the contents of gypsum and ettringite calculated by the models are compared with the results from the XRD experiments, and then the effects of surface depth, corrosion time and solution concentration on the gypsum and ettringite formations in cement pastes are discussed.

Key Words
model; XRD-Rietveld analysis; gypsum; ettringite; cement pastes; sulfate attack

Address
Xiao-Bao Zuo, Jia-Lin Wang, Guang-Ji Yin: Department of Civil Engineering, Nanjing University of Science & Technology, Nanjing 210094, China
Wei Sun, Hua Li: Jiangsu Key Laboratory of Construction Materials, Southeast University, Nanjing 211189, China

Abstract
In this study, two types of aggregate were used for making self-compacting concrete. Standard cubic specimens were exposed to different temperatures. Seventy-two standard cylindrical specimens (150x300 mm) and Seventy-two cubic specimens (150 mm) were tested. Compressive strengths of the manufactured specimens at 23oC were about 33 MPa to 40 MPa. The variable parameters among the self-compacting concrete specimens were of sand stone type. The specimens were exposed to 23, 100, 200, 400, 600, and 800oC and their mechanical specifications were controlled. The heated specimens were subjected to the unconfined compression test with a quasi-static loading rate. The corresponding stress-strain curves and modulus of elasticity were compared. The results showed that, at higher temperatures, Scoria aggregate showed less sensitivity than ordinary aggregate. The concrete made with Scoria aggregate exhibited less strain. The heated self-compacting concrete had similar slopes before and after the peak. In fact, increasing heat produced gradual symmetrical stress-strain diagram span.

Key Words
thermal effects; self-compacting concrete; elastic module; stress-strain curve; aggregate types

Address
Hamoon Fathi and Tina Lameie: Young Researchers and Elite Club, Sanandaj Branch, Islamic Azad University, Sanandaj, Iran

Abstract
The use of external carbon-fiber-reinforced polymer (CFRP) wraps is one of the most effective techniques existing for the confinement of the circular concrete columns. Currently, several researches have been made to develop models for predicting the behavior of this type of confinement. The disadvantage of the most models, is to not take into account the contribution of the transverse steel reinforcements (TSR) effect, However, very limited models have been recently developed that considers this combined effect and gives less accurate results. This paper presents the development of a new model for the axial behavior of circular concrete columns confined by combining external CFRP warps-and-internal TSR (hoops or spirals) based on the existing experimental data. The comparison between the proposed model and the experimental results showed good agreement comparing to the several existing models. Moreover, the expressions of estimating the ultimate strength and the corresponding strain are simple and precise, which make it easy to use in the design applications.

Key Words
reinforced concrete columns; CFRP; stress-strain model; confinement; TSR

Address
Mohammed Berradia and Amar Kassoul: Department of Civil Engineering, Laboratory of Structures, Geotechnics and Risks (LSGR), Hassiba Benbouali University of Chlef, BP 151, Hay Essalam, UHB Chlef, Chlef (02000), Algeria


Abstract
The paper presents the experimental investigations for studying the effect of ground granulated blast furnace slag (GGBFS) on the time-dependent deflection of reinforced concrete (RC) beams due to creep and shrinkage. The RC beams were reinforced with 2-10 mm bars at tension side and subjected to constant sustained two-point loading for the period of 150 days. The amount of cement replacement by GGBFS was varied from 0 to 60% with an increment of 20%. The total deflection was measured at different ages of up to 150 days under sustained loads. The experiments revealed that the time-dependent deflection of the reinforced concrete RC beams containing GGBFS was higher than that of plain concrete RC beams. At 150 days, the average creep and shrinkage deflection of RC beams containing 20%, 40% and 60% GGBFS was 1.25, 1.45 and 1.75 times higher than the plain concrete beams. A new model, which is an extension of authors\' earlier model, is proposed to incorporate the effect of GGBFS content in predicting the long-term deflection of RC beams. Besides validating the new model with the current data with higher percentage of tension reinforcement, it was also used to predict the authors\' earlier data containing lesser percentage of tension reinforcement with reasonable accuracy.

Key Words
beams; creep: deflection; GGBFS; RC; shrinkage

Address
M. Shariq: Department of Civil Engineering, Aligarh Muslim University, Aligarh, India
H. Abbas: Research and Studies in Strengthening and Rehabilitation of Structures, Department of Civil Engineering, King Saud University, Riyadh 11421, Saudi Arabia
J. Prasad: Department of Civil Engineering, Indian Institute of Technology Roorkee, India


Abstract
This study focused on modeling the behavior of the compressive stress using the average strain and ultrasonic test results in concrete. Feed-forward backpropagation artificial neural network (ANN) models were used to compare four types of concrete mixtures with varying water cement ratio (WC), ordinary concrete (ORC) and concrete with short steel fiber-reinforcement (FRC). Sixteen (16) 150 mmx150 mmx150 mm concrete cubes were used; each contained eighteen (18) data sets. Ultrasonic test with pitch-catch configuration was conducted at each loading state to record linear and nonlinear test response with multiple step loads. Statistical Spearman\'s rank correlation was used to reduce the input parameters. Different types of concrete produced similar top five input parameters that had high correlation to compressive stress: average strain, fundamental harmonic amplitude (A1), 2nd harmonic amplitude (A2), 3rd harmonic amplitude (A3), and peak to peak amplitude (PPA). Twenty-eight ANN models were trained, validated and tested. A model was chosen for each WC with the highest Pearson correlation coefficient (R) in testing, and the soundness of the behavior for the input parameters in relation to the compressive stress. The ANN model showed increasing WC produced delayed response to stress at initial stages, abruptly responding after 40%. This was due to the presence of more voids for high water cement ratio that activated Contact Acoustic Nonlinearity (CAN) at the latter stage of the loading path. FRC showed slow response to stress than ORC, indicating the resistance of short steel fiber that delayed stress increase against the loading path.

Key Words
artificial neural network; linear ultrasonic test; nonlinear ultrasonic test; concrete; fiber-reinforced concrete

Address
Jason Ongpeng, Marcus Soberano, Andres Oreta: Department of Civil Engineering, De La Salle University, Manila, Philippines
Sohichi Hirose: Department of Civil Engineering, Tokyo Institute of Technology, Tokyo, Japan

Abstract
This study aimed at exploring the effect of presoaking degree of lightweight aggregate (LWA) on the fresh and hardened properties of concrete. Two series (i.e., Series A and Series B) of concrete mixes that were made of LWA with different moisture states were prepared. The presoaking degree of LWA was divided into three types: oven dry state, 1 hour prewetted and 24 hours prewetted. For the Series A, the water content of the lightweight aggregate concrete (LWAC) mixes was adjusted in accordance with the moisture condition of the LWA. Whereas the amount of water added in the Series B mixes was deliberately not adjusted for the moisture condition of the LWA. Slump test, mechanical tests, interfacial transition zone microscopical tests and thermal conductivity test were carried out on the specimens of different concretes and compared with control normal-weight aggregate concretes. The test results showed that the effect of mixing water absorption by LWA with different moisture states was reflected in the fresh concrete as the loss of mixture workability, while in the hardened concrete as the increase of its strength. With the use of oven-dried LWA, the effect of reduction of water-cement ratio was more significant, and thus the microstructure of the ITZ was more compact.

Key Words
lightweight aggregate; workability; interfacial transition zone; mechanical property

Address
Chao-Wei Tang: Department of Civil Engineering & Geomatics, Cheng Shiu University, No. 840, Chengcing Rd., Niaosong District, Kaohsiung City, Taiwan R.O.C.


Abstract
This paper summarizes the experimental study of the shear behaviour of Hybrid Fibre Reinforced Concrete (HFRC) beams retrofitted by using externally bonded Glass Fibre Reinforced Polymer (GFRP) laminates. To attain the set-out objectives of the present investigation, steel fibre of 1% and polypropylene fibre of 0.30% was used for hybrid steel-polypropylene fibre reinforced concrete: whereas for hybrid glass-polypropylene fibre reinforced concrete, glass fibre by 0.03% and polypropylene fibre of 0.03% by volume of concrete was used. In this study, 9 numbers of beams were cast and tested into three groups (Group I, II & III). Each group containing 3 numbers of beams, out of which one serve as a control beam or a hybrid steel-polypropylene fibre reinforced concrete beam or a hybrid glass - polypropylene fibre reinforced concrete beam and the remaining two beams were preloaded until shear cracks appeared up to 75% of ultimate load and then preloaded beams (damaged beams) were retrofitted with GFRP laminates at shear zone in the form of strips, as one beam in vertical position and another beam in inclined position to restrict the shear cracks. Finally, the retrofitted beams were loaded until failure and test results were compared. The experimental tests have been conducted to investigate various parameters of structural performance, such as load carrying capacity, crack pattern and failure modes, load-deflection responses and ductility relations. The test results revealed that beams retrofitted using GFRP laminates considerably increased the load carrying capacity. In addition, it was found that beams retrofitted with inclined strip offers superior performance than vertical one. Comparing the test results, it was observed that hybrid steel-polypropylene fibre reinforced concrete beam retrofitted with GFRP laminates showed enhanced behaviour as compared to other tested beams.

Key Words
shear behavior; glass fibre reinforced polymer (GFRP) laminates; steel; glass and polypropylene fibres

Address
M. Vinodkumar: Department of Civil Engineering, PSNA College of Engg. and Tech., Dindigul, Tamil Nadu, India
M. Muthukannan: Department of Civil Engineering, Kalasalingam University, Virudhunagar, Tamil Nadu, India

Abstract
In recent year, the coat layer drops and the rebar rust of bridge parapets, which caused the structural performance degradation. In order to achieve the comprehensive rehabilitation, ultra high performance cementitious composites is proposed to existing RC parapet rehabilitation. The influence factors of UHPCC rehabilitation includes two parts, i.e., internal factors related with material, such as UHPCC layer thickness, corrosion ratio of rebars, fiber volume fraction, and external factors related with the load, such as impact speeds, impact angles, vehicle mass. The influence of the factors was analyzed in this paper based on the nonlinear finite element. The analysis results of the maximum dynamic deformation and the peak impact load of parapets revealed the influence of the internal factors and the external factors on anti-collision performance and degree degradation. This research may provide a reference for the comprehensive multifunctional rehabilitation of existing bridge parapets.

Key Words
parapets; rehabilitation; UHPCC; impact load; deformation

Address
Jinkai Qiu, Xiang-guo Wu and Qiong Hu:
1) Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education,
Harbin Institute of Technology, Harbin, 150090, China
2) School of Civil Engineering, Harbin Institute of Technology, Harbin, 150090, China

Abstract
In this paper, the effect of normal load on the failure mechanism of echelon joint has been studied using PFC2D. In the first step, calibration of PFC was undertaken with respect to the data obtained from experimental laboratory tests. Then, six different models consisting various echelon joint were prepared and tested under two low and high normal loads. Furthermore, validation of the simulated models were cross checked with the results of direct shear tests performed on non-persistent jointed physical models. The simulations demonstrated that failure patterns were mostly influenced by normal loading, while the shear strength was linked to failure mechanism. When ligament angle is less than 90o, the stable crack growth length is increased by increasing the normal loading. In this condition, fish eyes failure pattern occur in rock bridge. With higher ligament angles, the rock bridge was broken under high normal loading. Applying higher normal loading increases the number of fracture sets while dilation angle and mean orientations of fracture sets with respect to ligament direction will be decreased.

Key Words
particle flow code; rock bridge angle; normal load; shear and tensile cracks

Address
Hadi Haeri: Young Researchers and Elite Club, Bafgh Branch, Islamic Azad University, Bafgh, Iran
Vahab Sarfarazi: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
Zheming Zhu: College of Architecture and Environment, Sichuan University, Chengdu 610065, China

Abstract
This study aimed to design the accelerated life testing (ALT) of concrete, which stimulating the special natural environment maximumly. Its evaluation indexes, such as dynamic elastic modulus, mass and ultrasonic velocity were measured, and the variation of relative mass and relative dynamic elastic modulus of concrete were studied. Meanwhile, the microanalysis method was used. Moreover, an exploratory application of the stochastic approach, the Weibull distribution and the lognormal distribution, were made to assess the durability of concrete structures. The results show that the ALT for simulating natural environment is more close to the service process of concrete structure under actual conditions; The relative dynamic elastic modulus can be used as the dominant durability evaluation parameters, because it is more sensitive to the environmental factors compared with the relative quality evaluation parameters; In the course of the concrete deterioration, the destruction of the salt freezing cycle is the dominant factor, supplemented by other factors; Both of those two stochastic approaches can be used to evaluate the reliability of concrete specimens under the condition of ALT; By comparison, The lognormal distribution method is better to describe the reliability process.

Key Words
concrete; accelerated life testing; durability; weibull distribution; lognormal distribution; reliability

Address
Binrong Zhu, Hongxia Qiao, Qiong Feng and Chenggong Lu: Key Laboratory of Disaster Prevention and Mitigation in Civil Engineering of Gansu Province, Lanzhou University of Technology, Lanzhou 730050, China
Hongxia Qiao: Western Engineering Research Center of Disaster Mitigation in Civil Engineering of Ministry of Education, Lanzhou 730050, China


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