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CONTENTS
Volume 28, Number 5, November 2021
 

Abstract
This study presents the first analysis system and fast-access cloud database for shrinkage and creep of concrete in the world, named "shrinkage and creep database in Taiwan", SCDT. SCDT not only has the most comprehensive experimental data, including NU, JSCE, Europe, and TW databases, but provides a design tool for researchers and engineers. It can further facilitate the development of prediction models for localized concrete. Users can obtain the shrinkage and creep curves based on their selected prediction models in SCDT. Comparisons of the predicted results of selected models and test results in the chosen database can be generated in seconds. One example of the development of basic creep prediction model in Taiwan based on model B4 by using SCDT to reflect concrete characteristics in Taiwan is also presented in this study. Users anywhere in the world can easily access SCDT to browse and upload data, receive predictive results, or develop predictive models.

Key Words
cloud; code development; creep; database; prediction model; shrinkage

Address
Wen-Cheng Liao, Jenn-Chuan Chern, Ho-Cheng Huang, Ting-Kai Liu and Wei-Yi Chin: Department of Civil Engineering, College of Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan

Abstract
Inorganic basalt fiber (BF) is a novel sort of commercial concrete fiber which is made with basalt rocks. Previous studies have not sufficiently handled the behavior of self-compacted concrete, at elevated temperature, containing basalt fiber. Present endeavor covers experimental work to examine the characteristics of this material at high temperature considering different fiber content and applied temperature. Different tests were carried out to measure the mechanical properties such as compressive strength (fc), modulus of elasticity (E), Poisson's ratio, splitting tensile strength (fsplit), flexural strength (fflex), and slant shear strength (fslant) of HSC and hybrid concrete. Gene expression programming (GEP) was employed to propose new constitutive relationships depending on experimental data. It was noticed from the testing records that there is no remarkable effect of BF on the Poisson's ratio and modulus of elasticity of self-compacted concrete. The flexural strength of basalt fiber self-compacted concrete was not sensitive to temperature in comparison to other mechanical properties of concrete. Fiber volume fraction of 0.25% was found to be the optimum to some extend according to degradation of strength. The proposed GEP models were in good matching with the experimental results.

Key Words
basalt fiber concrete; GEP analysis; mechanical properties; self-compacting concrete; strength at elevated temperature

Address
Samadar S. Majeed: College of Engineering, Nawroz University, Kurdistan Region, Iraq
James H. Haido: Department of Civil Engineering, College of Engineering, Univesrity of Duhok, Kurdistan Region, Iraq
Dawood Sulaiman Atrushi: Department of Civil Engineering, College of Engineering, Univesrity of Duhok, Kurdistan Region, Iraq
Yaman Al-Kamaki: Department of Civil Engineering, College of Engineering, Univesrity of Duhok, Kurdistan Region, Iraq
Youkhanna Zayia Dinkha: Department of Civil Engineering, College of Engineering, Univesrity of Duhok, Kurdistan Region, Iraq
Shireen T. Saadullah: Department of Civil Engineering, College of Engineering, Univesrity of Duhok, Kurdistan Region, Iraq
Bassam A. Tayeh: Civil Engineering Department, Faculty of Engineering, The Islamic University of Gaza, P.O. Box 108, Gaza Strip, Palestine


Abstract
On the premise of ensuring that the static performance of the concrete spreader is met, the first-order natural frequency of the concrete spreader is increased, and the weight of the main beam is reduced. ANSYS is used as an analysis tool to perform modal analysis on the concrete spreader. The natural frequency, mode shape and modal test verification will be obtained to ensure the accuracy of finite element model analysis. Using the ANSYS designxplorer module, the size of the main beam is set, and the response surface model between the parameter variables and the optimization objective is established according to the experimental design points. Screening algorithm and MOGA algorithm are used to multi-optimize the stress, first-order natural frequency and girder weight, and the optimal solution is obtained by comparison. The results of modal analysis are consistent with those of the experiment, and a set of optimal solutions is obtained through the optimization algorithm. The optimal solution obtained can meet the purpose of increasing the first-order natural frequency of the concrete spreader and reducing the weight of the main beam under the premise of ensuring the overall dynamic and static performance of the concrete spreader.

Key Words
ANSYS; concrete spreader; dynamic and static performance; modal analysis; response surface optimization

Address
Shiying Zhang: School of Mechanical Engineering, Shenyang Jianzhu University, Shenyang, China; Northern Heavy Industries Group Co., Ltd., China
Bo Song: Ccteg Shenyang Engineering Company, China
Ke Zhang: School of Mechanical Engineering, Shenyang Jianzhu University, Shenyang, China
Hongliang Chen: Ccteg Shenyang Engineering Company, China
Defang Zou: School of Mechanical Engineering, Shenyang Jianzhu University, Shenyang, China
Chang Liu: Ccteg Shenyang Engineering Company, China
Chunxia Zhu: School of Mechanical Engineering, Shenyang Jianzhu University, Shenyang, China
Dong Li: Northern Heavy Industries Group Co., Ltd., China
Wenda Yu: School of Mechanical Engineering, Shenyang Jianzhu University, Shenyang, China



Abstract
Reinforced concrete (RC) slabs are exposed to several static and dynamic effects during their period of service. Accordingly, there are many studies focused on the behavior of RC slabs under these effects in the literature. However, impact loading which can be more effective than other loads is not considered in the design phase of RC slabs. This study aims to investigate the dynamic behavior of two-way RC slabs under sudden impact loading. For this purpose, 3 different simply supported slab specimens are manufactured. These specimens are tested under impact loading by using the drop test setup and necessary measurement devices such as accelerometers, dynamic load cell, LVDT and data-logger. Mass and drop height of the hammer are taken constant during experimental study. It is seen that rigidity of the specimens effect experimental results. While acceleration values increase, displacement values decrease as the sizes of the specimens have bigger values. In the numerical part of the study, artificial neural networks (ANN) analysis is utilized. ANN analysis is used to model different physical dynamic processes depending upon the experimental variables. Maximum acceleration and displacement values are predicted by ANN analysis. Experimental and numerical values are compared and it is found out that proposed ANN model has yielded consistent results in the estimation of experimental values of the test specimens.

Key Words
artificial neural networks; dynamic effects; RC slabs; test setup

Address
R. Tuğrul Erdem: Department of Civil Engineering, Manisa Celal Bayar University, Manisa, Turkey

Abstract
The use of prestressed concrete box girder bridges built by segmentally balanced cantilevers has bloomed in the last decades due to its significant structural and construction advantages in complex topographies. In Colombia, this typology is the most common solution for structures with spans ranging of 80-200 m. Despite its popularity, excessive deflections in bridges worldwide evidenced that time-dependent effects were underestimated. This problem has led to the constant updating of the creep and shrinkage models in international code standards. Differences observed between design processes of box girder bridges of the Colombian code and Eurocode, led to the need for a validation of in-service status of these structures. This study analyzes the long-term behavior of the Tablazo bridge with data scarcity. The measured leveling of this structure is compared with a finite-element model that consider the most widely used creep and shrinkage models in the literature. Finally, an adjusted model evidence excessive deflection on the bridge after six years. Monitoring of this bridge typology in Colombia and updating of the current design code is recommended.

Key Words
box girder bridges; concrete; creep; long-term deflections; segmentally balanced cast-in-place cantilevers; shrinkage; time-dependent phenomena

Address
Luis F. Rincon: School of Civil Engineering, Universidad Industrial de Santander, 680002 Bucaramanga, Colombia
Alvaro Viviescas: School of Civil Engineering, Universidad Industrial de Santander, 680002 Bucaramanga, Colombia
Edison Osorio: Faculty of Civil Engineering, Universidad Antonio Nariño, 111511 Bogotá, Colombia
Carlos A. Riveros-Jerez: School of Engineering, Universidad de Antioquia, 050010 Medellín, Colombia
José Antonio Lozano-Galant: Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain

Abstract
Steel-concrete composite structures and precast concrete elements have a common prefabrication process and allow fast construction. The use of hollow-core slabs associated with composite floors can be advantageous. However, there are few studies on the subject, impeding the application of such systems. In this paper, a numerical model representing the considered system using the FE (finite element)-based software DIANA is developed. The results of an experimental test were also presented in Souza (2016) and were used to validate the model. Comparisons between the numerical and test results were performed in terms of the load versus displacement, load versus slip, and load versus strain curves, showing satisfactory agreement. In addition, a wide parametric study was performed, evaluating the influence of several parameters on the behaviour of the composite system: The strength of the steel beam, thickness of the web, thickness and width of the bottom flange of the steel beam and concrete cover thickness on top of the beam. The results indicated a great influence of the steel strength and the thickness of the bottom flange of the steel beam on the capacity of the composite floor. The remaining parameters had limited influences on the results.

Key Words
composite slim floor; composite structures; headed stud; hollow-core slab; numerical simulation; steel beam

Address
Patricia T.S. Spavier, Marcela N. Kataoka and Ana Lucia H.C. El Debs: Department of Structural Engineering, The São Carlos School of Engineering, University of São Paulo,
Av. Trabalhador Saocarlense n

Abstract
In this study, a new procedure was proposed in order to predict the crack pattern and failure mode of steel fiber reinforced concrete (SFRC) corbels. Moreover, an experimental study was carried out in order to investigate the effect of several parameters, such as compressive strength, tensile strength, steel fiber ratio, shear span on the mechanical behavior of SFRC corbels in detail. Totally, 24 RC and SFRC corbels were prepared for the experimental study. Experimental results indicate that each investigated parameter has noticeable effect on the load capacity and failure mode of SFRC corbels. Moreover, finite element (FE) model of the tested corbels were prepared and efficiency of FE model was investigated for further studies. Comparison of FE and experimental results show that there is an acceptable fit between them regarding load capacity and crack patterns. Thereafter, parametric study was carried out via FE analyses in order to obtain a methodology for crack pattern and failure mode prediction of SFRC corbels. As a result of parametric studies, a new procedure was proposed as flowcharts in order to predict the failure mode of SFRC corbels for normal and high strength concrete class separately.

Key Words
corbels; crack pattern; failure mode; FE modeling; steel fiber reinforced concrete

Address
Mehmet Eren Gulsan: Department of Civil Engineering, Gaziantep University, University Avenue, 27310, Gaziantep, Turkey
Abdulkadir Cevik: Department of Civil Engineering, Gaziantep University, University Avenue, 27310, Gaziantep, Turkey
Sarwar Hasan Mohmmad: Department of Civil Engineering, Gaziantep University, University Avenue, 27310, Gaziantep, Turkey; Department of Civil Engineering, Sulaimani Polytechnic University, Sulaimani, Iraq

Abstract
Present paper focuses on the modeling of size effect on the compressive strength of normal concrete with the application of Discrete Element Method (DEM). Test specimens with different size and shape were cast and uniaxial compressive strength test was performed on each sample. Five different concrete mixes were used, all belonging to a different normal strength concrete class (C20/25, C30/37, C35/45, C45/55, and C50/60). The numerical simulations were carried out by using the PFC 5 software, which applies rigid spheres and contacts between them to model the material. DEM modeling of size effect could be advantageous because the development of micro-cracks in the material can be observed and the failure mode can be visualized. The series of experiments were repeated with the model after calibration. The relationship of the parallel bond strength of the contacts and the laboratory compressive strength test was analyzed by aiming to determine a relation between the compressive strength and the bond strength of different sized models. An equation was derived based on Bazant's size effect law to estimate the parallel bond strength of differently sized specimens. The parameters of the equation were optimized based on measurement data using nonlinear least-squares method with SSE (sum of squared errors) objective function. The laboratory test results showed a good agreement with the literature data (compressive strength is decreasing with the increase of the size of the specimen regardless of the shape). The derived estimation models showed strong correlation with the measurement data. The results indicated that the size effect is stronger on concretes with lower strength class due to the higher level of inhomogeneity of the material. It was observed that size effect is more significant on cube specimens than on cylinder samples, which can be caused by the side ratios of the specimens and the size of the purely compressed zone. A limit value for the minimum size of DE model for cubes and cylinder was determined, above which the size effect on compressive strength can be neglected within the investigated size range. The relationship of model size (particle number) and computational time was analyzed and a method to decrease the computational time (number of iterations) of material genesis is proposed.

Key Words
compressive strength; Discrete Element Method; normal strength concrete; PFC; size effect

Address
Zoltán Gyurkó and Rita Nemes: Department of Construction Materials and Technologies, Budapest University of Technology and Economics, 1111 Budapest, Műegyetem rkp. 3, Hungary

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