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CONTENTS
Volume 24, Number 2, August 2019
 

Abstract
Current article proposes a cheap prototype of an embedded wireless sensor to monitor concrete structures. The prototype can measure temperature and relative humidity concurrently at a controlled through smartphone time interval. It implements a maturity method to estimate in-place concrete strength, which is considered as an alternative for traditional shock impulse method and compression tests used in Kazakhstan. The prototype was tested and adequately performed in the laboratory and field conditions. Tests aimed to study the effect of internal and ambient temperature and relative humidity on the concrete strength gain. According to test results revealed that all parameters influence the strength gain to some extent. For a better understanding of how strongly parameters influence the strength as well as each other, proposed a multicolored cross-correlation matrix technique. The technique is based on the determination coefficients. It is able to show the value of significance of correlation, its positivity or negativity, as well as the degree of inter-influence of parameters. The prototype testing also recognized the inconvenience of Bluetooth control due to weakness of signal and inability to access several prototypes simultaneously. Therefore, further improvement of the prototype presume to include the replacement of Bluetooth by Narrow Band IoT standard.

Key Words
strength; temperature and relative humidity; Arduino; wireless embedded sensor; prototype

Address
Yelbek Utepov: Alizhan Kazkeev: Department of Civil Engineering, L.N. Gumilyov Eurasian National University, 2 Satpayev, Nur-Sultan 010000, Republic of Kazakhstan;
CSI Research & Lab (LLP), 2 Kunayev, Nur-Sultan 010000, Republic of Kazakhstan
Olzhas Khudaibergenov, Yerzhan Kabdush: Department of Civil Engineering, L.N. Gumilyov Eurasian National University, 2 Satpayev, Nur-Sultan 010000, Republic of Kazakhstan

Abstract
In this study, the strength and stiffness (EI) of wood-concrete composite beams for bridges with T-shaped cross section were evaluated. Two types of connectors were used: connectors bonded with epoxy adhesive and connectors attached to the wood just by pre-drilling (without adhesive). The connectors consisted of common steel bars with a diameter of 12.5 mm. Initially, the strength and stiffness (EI) of the beams were analyzed by bending tests with the load applied at the third point of the beam. Subsequently, the composite beams were evaluated by numerical simulation using ANSYS software with focus on the connection system. To make the composite beams, Eucalyptus citriodora wood and medium strength concrete were used. The slip modulus K and the ultimate strength values of each type of connector were obtained by direct shear tests performed on composite specimens. The results showed that the connector glued with epoxy adhesive resulted in better strength and stiffness (EI) for the composite beams when compared to the connector fixed by pre-drilling. The differences observed were up to 10%. The strength and stiffness (EI) values obtained analytically by Möhler\' model were lower than the values obtained experimentally from the bending tests, and the differences were up to 25%. The numerical simulations allowed, with reasonable approximation, the evaluation of stress distributions in the composite beams tested experimentally.

Key Words
timber-concrete; composite beams; stiffness EI; strength; numerical simulation; steel bar connector; analytical Möhler model

Address
Julio C. Molina, Nadia B. Gomes: Mechanical Engineering Department, University of São Paulo State - UNESP, 333 Ariberto Pereira da Cunha, Pedregulho, Guaratinguetá-SP, 12516-410, Brazil
Carlito Calil Junior: Department of Structural Engineering, São Carlos School of Engineering of the University of São Paulo, 400 Trabalhador São-carlense Street, Downtown, São Carlos - SP, 13566-590, Brazil
Diego R. de Oliveira: Wood Science and Engineering Department, Oregon State University, 119 Richardson Hall 97331 - Corvallis, USA

Abstract
Optimization is an important subject which is widely used in engineering problems. In this paper, an analytical method is developed for optimum design of reinforced concrete beams considering both flexural and shear effects. A closedform formulation is derived for optimal height and rebar of beams. The total material cost of steel and concrete is considered as the objective function which is minimized during the optimization process. The ultimate flexural and shear capacities of the beam are considered as the main constraints. The ultimate limit state is considered for deriving the relations for flexural capacity of the beam. The design requirements are considered according to the item 9 of the Iranian National Building. Analytical formulas and some curves are proposed to be used for optimum design of RC beams. The proposed method can be used to perform the optimization of RC beams without the need of any prior knowledge in optimization. Also, the results of the studied numerical example show that the proposed method results in a better design comparing with the other methods.

Key Words
RC beam; optimization; lagrange multipliers method; LMM; INBR9

Address
Ahmad Zivari, Alireza Habibi: Department of Civil Engineering, Shahed University, Tehran, Iran
Nima Khaledy: Department of Civil Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran

Abstract
Concrete pipelines are the most efficient and safe means for gas and oil transportation over a long distance. The use ofnano materials and nono-engineering can be considered for enhancing concrete pipelines properties. the tests show that SiO2 nanoparticles can improve the mechanical behavior of concrete.Moreover, severe hazard for pipelines is seismic ground motion. Over the years, scientists have attempted to understand pipe behavior against earthquake most frequently via numerical modeling and simulation. Therefore, in this paper, the dynamic response of underwater nanocomposite submerged pipeline conveying fluid is studied. The structure is subjected to the dynamic loads caused by earthquake and the governing equations of the system are derived using mathematical model via Classic shell theory and Hamilton\'s principle. Navier-Stokes equation is employed to calculate the force due to the fluid in the pipe. As well, the effect of external fluid is modeled with an external force. Mori-Tanaka approach is used to estimate the equivalent material properties of the nanocomposite. 1978 Tabas earthquake in Iran is considered for modelling seismic load.The dynamic displacement of the structure is extracted using differential quadrature method (DQM) and Newmark method.The effects of different parameters such asSiO2 nanoparticles volume percent, boundary conditions, thickness to radius ratios, length to radius ratios, internal and external fluidpressure and earthquake intensity are discussed on the seismic response of the structure.From results obtained in this paper, it can be found that the dynamic response of the pipe is increased in the presence of internal and external fluid. Furthermore, the use of SiO2 nanoparticles in concrete pipeline reduces the displacement of the structure during an earthquake.

Key Words
dynamic response; concrete pipeline; Tabas earthquake; internal and external fluid; Differential Quadrature Method

Address
Mostafa Maleki, Mahmood Rabani Bidgoli and Reza Kolahchi: Department of Civil Engineering, Jasb Branch, Islamic Azad University, Jasb, Iran

Abstract
In this paper, surrogate models such as multivariate adaptive regression splines (MARS) and M5P model tree (M5P MT) methods have been investigated in order to propose a new formulation for the 28-days compressive strength of selfcompacting concrete (SCC) incorporating metakaolin as a supplementary cementitious materials. A database comprising experimental data has been assembled from several published papers in the literature and the data have been used for training and testing. In particular, the data are arranged in a format of seven input parameters covering contents of cement, coarse aggregate to fine aggregate ratio, water, metakaolin, super plasticizer, largest maximum size and binder as well as one output parameter, which is the 28-days compressive strength. The efficiency of the proposed techniques has been demonstrated by means of certain statistical criteria. The findings have been compared to experimental results and their comparisons shows that the MARS and M5P MT approaches predict the compressive strength of SCC incorporating metakaolin with great precision. The performed sensitivity analysis to assign effective parameters on 28-days compressive strength indicates that cementitious binder content is the most effective variable in the mixture.

Key Words
artificial intelligence models; compressive strength; multivariate adaptive regression splines (MARS); M5P model tree; self-compacting concrete; surrogate models

Address
Panagiotis G. Asteris: Computational Mechanics Laboratory, School of Pedagogical and Technological Education, Heraklion, GR 14121, Athens, Greece
Ali Ashrafian: Department of Civil Engineering, Tabari University of Babol, P.O. Box 47139-75689, Babol, Iran
Mohammad Rezaie-Balf: Department of Civil Engineering, Graduate University of Advanced Technology-Kerman, P.O. Box 76315-116, Kerman, Iran

Abstract
The sustainable development principle of replacing natural resources with renewable material is an important research topic. In this study, waste LCD (liquid crystal display) glass powder was used to replace cement (0%, 10%, 20% and 30%) through a volumetric method using three water-binder ratios (0.47, 0.59, and 0.71) to make cement mortar. The compressive strength was tested at the ages of 7, 28, 56 and 91 days. The test results show that the compressive strength increases with age but decreases as the water-binder ratio increases. The compressive strength slightly decreases with an increase in the replacement of LCD glass powder at a curing age of 7 days. However, at a curing age of 91 days, the compressive strength is slightly greater than that for the control group (glass powder is 0%). When the water-binder ratios are 0.47, 0.59 and 0.71, the compressive strength of the various replacements increases by 1.38-1.61 times, 1.56-1.80 times and 1.45-2.20 times, respectively, during the aging process from day 7 to day 91. Furthermore, a prediction model of the compressive strength of a cement mortar with waste LCD glass powder was deduced in this study. According to the comparison between the prediction analysis values and test results, the MAPE (mean absolute percentage error) values of the compressive strength are between 2.79% and 5.29%, and less than 10%. Thus, the analytical model established in this study has a good forecasting accuracy. Therefore, the proposed model can be used as a reliable tool for assessing the design strength of cement mortar from early age test results.

Key Words
cement mortar; LCD glass powder; prediction model

Address
Chien-Chih Wang: Department of Civil Engineering and Geomatics, Cheng Shiu University, Kaohsiung City 83347, Taiwan
Chun-Ling Ho: College of Civil Engineering, Huaqiao University, Intelligence and Automation in Construction Fujian Province Higher-educational Engineering Research Centre, Xiamen, 361021, China
Her-Yung Wang: Department of Civil Engineering, National Kaohsiung University of Science and Technology, Kaohsiung City 80778, Taiwan
Chi Tang: Department of Soil and Water Conservation, National Pingtung University of Science and Technology, Pingtung County 91201, Taiwan

Abstract
This paper presents an investigation into the flexural behavior of reinforced concrete (RC) beams retrofitted by ultra-high performance fiber-reinforced concrete (UHPFRC) layers. The experimental study has been conducted in two parts. In the first part, four methods of retrofitting with UHPFRC layers in both the up and down sides of the beams have been proposed and their efficiency in the bonding of the normal concrete and ultra-high performance fiber-reinforced concrete has been discussed. The results showed that using the grooving method and the pre-casted UHPFRC layers in comparison with the sandblasting method and the cast-in-place UHPFRC layers leads to increase the load carrying capacity and the energy absorption capacity and causes high bond strength between two concretes. In the second part of the experimental study, the tests have been conducted on the beams with single UHPFRC layer in the down side and in the up side, using the effective retrofitting method chosen from the first part. The results are compared with those of non-retrofitted beam and the results of the first part of experimental study. The results showed that the retrofitted beam with two UHPFRC layers in the up and down sides has the highest energy absorption and load carrying capacity. Afinite element analysis was applied to prediction the flexural behavior of the composite beams. Agood agreement was achieved between the finite element and experimental results. Finally, a parametric study was carried out on full-scale retrofitted beams. The results indicated that in all retrofitted beams with UHPFRC in single and two sides, increasing of the UHPFRC layer thickness causes the load carrying capacity to be increased. Also, increases of the normal concrete compressive strength improved the cracking load of the beams.

Key Words
ultra-high performance fiber-reinforced concrete; retrofitted beams; bonding surface; load carrying capacity; energy absorption capacity; numerical analysis

Address
Leila Meraji, Hasan Afshin and KarimAbedi: Department of Civil Engineering, Sahand University of Technology, P.O. Box 51335-1996, Tabriz, Iran

Abstract
This study presents experimental and numerical results of prestressed concrete composite beams with different casting and stressing sequence. The beams were tested under three-point bending and it was found that prestressed concrete composite beams could not achieve monolith behavior due to interface slippage between two layers. The initial stress distribution due to different construction sequence has little effect on the maximum load of composite beams. The multi-step FE analyses could simulate different casting and stressing sequence thus correctly capturing the initial stress distribution induced by staged construction. Three contact algorithms were considered for interaction between concrete layers in the FE models namely tie constraint, cohesive contact and surface-to-surface contact. It was found that both cohesive contact and surface-to-surface contact could simulate the interface slip even though each algorithm considers different shear transfer mechanism. The use of surface-to-surface contact for beams with more than 2 layers of concrete is not recommended as it underestimates the maximum load in this study.

Key Words
prestressed concrete beam; finite element (FE) analysis; interface shear; post-tensioning; interface slip; staged construction

Address
Hin Foo Low, Sih Ying Kong, Daniel Kong: School of Engineering, Monash University Malaysia, Bandar Sunway, 47500, Malaysia
Suvash Chandra Paul: School of Engineering, Monash University Malaysia, Bandar Sunway, 47500, Malaysia; Department of Civil Engineering, International University of Business Agriculture and Technology, Dhaka 1230, Bangladesh


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