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CONTENTS
Volume 84, Number 5, December10 2022
 


Abstract
In this paper, bond-slip behavior of high strength concrete filled circular steel tube (HSCFCST) after elevated temperatures treatment was studied. 17 specimens were designed for push-out test. The influence was discussed as following parameters: (a) concrete strength, (b) constant temperature, and (c) bond length. The results showed that (1) after elevated temperatures treatment, the bond strength of the HSCFCST specimens increased first and then decreased with temperature rising; (2) the bond strength increased with the increase of concrete strength at room temperature, while the influence subsided after elevated temperatures treatment; (3) the strain of the circular steel tube was distributed exponentially along its length, the stress changed from exponential distribution to uniform distribution with the increase of load; (4) the bond damage process was postponed with the increase of constant temperature; and (5) the energy consumption capacity of the bonding interface increased with the rise of concrete strength and constant temperature. Moreover, computational formulas of ultimate and residual bond strength were obtained by regression, and the bond-slip constitutive models of HSCFCSTs after elevated temperatures was established.

Key Words
bond behavior; constitutive models; elevated temperatures test; high-strength concrete; steel tube

Address
Ji Zhou, Maogen Ban, Yunsheng Pang: College of Civil Engineering and Architecture, Guangxi University, Nanning, 530004, China
Zongping Chen: College of Civil Engineering and Architecture, Guangxi University, Nanning, 530004, China; College of Architecture and Civil Engineering, Nanning University, Nanning 530200, China; Key Laboratory of Disaster Prevention and Structure Safety of Chinese Ministry of Education, Guangxi University, Nanning,530004, China

Abstract
A gravity wall combined with an anchoring lattice frame (a combined retaining structure) is adopted at a typical engineering site at Dali-Ruili Railway Line China. Where, the combined retaining structure supports a soil deposit covering on different inclined rock slopes. With an aim to investigate and compare the effects of inclined rock slopes on the response of combined retaining structure under seismic excitation, three groups of shaking table tests are conducted. The rock slopes are shaped as planar surfaces inclined at angles of 20o, 30o, and 40o with the horizontal, respectively. The shaking table tests are supplemented by dynamic numerical simulations. The results regarding the horizontal acceleration response, vertical acceleration response, permanent displacement mode, and axial anchor force are comparatively examined. The acceleration response is more susceptible to outer structural profile of combined retaining structure than to inclined angle of rock slope. The permanent displacement decreases when the inclined angle of the rock slope increases within a range of 20o-40o. A critical inclined angle of rock slope exists within a range of 20o-40o, and induces the largest axial anchor force in the combined retaining structure.

Key Words
gravity wall; inclined rock slope; lattice frame; model test; numerical analysis

Address
Yu-liang Lin: School of Civil Engineering, Central South University, Changsha 410075, China; Key Laboratory for Disaster Prevention and Mitigation of Rail Transit Engineering Structures of Hunan Province, Central South University, Changsha 410075, China
Jie Jin: School of Civil Engineering, Central South University, Changsha 410075, China
Zhi-hao Jiang: China Construction Third Engineering Bureau Co. Ltd., Wuhan 430000, China
Wei Liu: China Construction Third Engineering Bureau Co. Ltd., Wuhan 430000, China
Hai-dong Liu: China Construction Third Engineering Bureau Co. Ltd., Wuhan 430000, China
Rou-feng Li: China Construction Third Engineering Bureau Co. Ltd., Wuhan 430000, China
Xiang Liu: Joint International Research Laboratory of Key Technology for Rail Traffic Safety, Central South University, Changsha 410075, China; Key Laboratory of Traffic Safety on Track, Ministry of Education, School of Traffic & Transportation Engineering, Central South University, Changsha 410075, China

Abstract
Glass fiber reinforced polymer (GFRP) elastic gridshells consist of long continuous GFRP tubes that form elastic deformations. In this paper, a method for the form-finding of gridshell structures is presented based on the interpretable machine learning (ML) approaches. A comparative study is conducted on several ML algorithms, including support vector regression (SVR), K-nearest neighbors (KNN), decision tree (DT), random forest (RF), AdaBoost, XGBoost, category boosting (CatBoost), and light gradient boosting machine (LightGBM). A numerical example is presented using a standard double-hump gridshell considering two characteristics of deformation as objective functions. The combination of the grid search approach and k-fold cross-validation (CV) is implemented for fine-tuning the parameters of ML models. The results of the comparative study indicate that the LightGBM model presents the highest prediction accuracy. Finally, interpretable ML approaches, including Shapely additive explanations (SHAP), partial dependence plot (PDP), and accumulated local effects (ALE), are applied to explain the predictions of the ML model since it is essential to understand the effect of various values of input parameters on objective functions. As a result of interpretability approaches, an optimum gridshell structure is obtained and new opportunities are verified for form-finding investigation of GFRP elastic gridshells during lifting construction.

Key Words
form-finding; gridshell structure; interpretability methods; machine learning; regression

Address
Soheila Kookalani, Sandy Nyunn and Sheng Xiang: Department of Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, China

Abstract
Reinforced concrete (RC) structures may be subjected to sudden dynamic impact loads such as explosions occurring for different reasons, the collision of masses driven by rockfall, flood, landslide, and avalanche effect structural members, the crash of vehicles to the highway and seaway structures. Many analytical, numerical, and experimental studies focused on the behavior of RC structural elements such as columns, beams, and slabs under sudden dynamic impact loads. However, there is no comprehensive study on the behavior of the RC column-beam connections under the effect of sudden dynamic impact loads. For this purpose, an experimental study was performed to investigate the behavior of RC column-beam connections under the effect of low-velocity impact loads. Sixteen RC beam-column connections with a scale of 1/3 were manufactured and tested under impact load using the drop-weight test setup. The concrete compressive strength, shear reinforcement spacing in the beam, and input impact energy applied to test specimens were taken as experimental variables. The time histories of impact load acting on test specimens, accelerations, and displacements measured from the test specimens were recorded in experiments. Besides, shear and bending crack widths were measured. The effect of experimental variables on the impact behavior of RC beam-column connections has been determined and interpreted in detail. Besides, a finite element model has been established for verification and comparison of the experimental results by using ABAQUS software. It has been demonstrated that concrete strength, shear reinforcement ratio, and impact energy significantly affect the impact behavior of RC column-beam connections.

Key Words
FEM; free drop test; impact load; RC beam-column connection; strengthening

Address
Murat Aras: Civil Engineering Department, Bilecik Şeyh Edebali University, Bilecik, Turkey
Tolga Yilmaz: Civil Engineering Department, Konya Technical University, Ankara, Turkey
Özlem Çalişkan: Civil Engineering Department, Bilecik Şeyh Edebali University, Bilecik, Turkey
Özgür Anil: Civil Engineering Department, Gazi University, Ankara, Turkey
R. Tuğrul Erdem: Civil Engineering Department, Manisa Celal Bayar University, Manisa, Turkey
Turgut Kaya: Civil Engineering Department, Batman University, Batman, Turkey

Abstract
In this study, the effect of circle tunnel on the force distribution around underground rectangular gallery was investigated using theoretical approach, experimental test and Particle flow code simulation (PFC). Gypsum model with dimension of 1500x1500 mm was built. Tensile strength of material was 1 MPa. Dimension of central gallery was 100 mmx200 mm and diameter of adjacent tunnel in its right side was 20 mm, 40 mm and 60 mm. Horizontal distance between tunnel wall and gallery edge were 25, 50, 75, 100 and 125 mm. using beam theory, the effect of tunnel diameter and distance between tunnel and gallery on the induced force around gallery was analyzed. In the laboratory test, the rate of loading displacement was set to 0.05 millimeter per minute. Also sensitivity analysis has been done. Using PFC2D, interaction between tunnel and gallery was simulated and its results were compared with experimental and theoretical analysis. The results show that the tensile force concentration has maximum value in center of the rectangular space. The tensile force concentration at the right side of the axisymmetric line of gallery has more than its value in the left side of the galleries axisymmetric line. The tensile force concentration was decreased by increasing the distance between tunnel and rectangular space. In whole of the configurations, the angles of micro cracks fluctuated between 75 and 105 degrees, which mean that the variations of tunnel situation have not any influence on the fracture angle.

Key Words
gallery; PFC2D; tensile force; tunnel

Address
Vahab Sarfarazi: Mining Engineering Department, Hamedan University of Technology, Hamedan, Iran
Reza Bahrami: Department of Civil Engineering, Beyza Branch, Islamic Azad University, Beyza, Iran
Shadman Mohammadi Bolbanabad: Mining Engineering Department, Hamedan University of Technology, Hamedan, Iran
Fariborz Matinpoor: Mining Engineering Department, Tehran University, Tehran, Iran

Abstract
A precise prediction of the ultimate bond strength between rebar and surrounding concrete plays a major role in structural design, as it effects the load-carrying capacity and serviceability of a member significantly. In the present study, Gaussian models are employed for modelling bond strength of ribbed steel bars embedded in concrete. Gaussian models offer a non-parametric method based on Bayesian framework which is powerful, versatile, robust and accurate. Five different Gaussian models are explored in this paper-Gaussian Process (GP), Variational Heteroscedastic Gaussian Process (VHGP), Warped Gaussian Process (WGP), Sparse Spectrum Gaussian Process (SSGP), and Twin Gaussian Process (TGP). The effectiveness of the models is also evaluated in comparison to the numerous design formulae provided by the codes. The predictions from the Gaussian models are found to be closer to the experiments than those predicted using the design equations provided in various codes. The sensitivity of the models to various parameters, input feature space and sampling is also presented. It is found that GP, VHGP and SSGP are effective in prediction of the bond strength. For large data set, GP, VHGP, WGP and TGP can be computationally expensive. In such cases, SSGP can be utilized.

Key Words
bond strength; concrete; gaussian; modelling; steel bars

Address
Prabhat R. Prem: CSIR-Structural Engineering Research Centre, Chennai 600 113, India
Branko Savija: Micro Lab., Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, The Netherlands

Abstract
Additive manufacturing is an emerging method to manufacture objects with complex shapes and intricate geometry, such as cellular structures. The cellular structures can widely be used in lightweight application as it provides a high strength-toload ratio. Under the various testing condition, each topology shows different mechanical properties. This study investigates the structural response of various types of cellular structures in compression loading, both experimentally and numerically. For that purpose, honeycomb, modified honeycomb, and spiral-type topology were selected to investigate. Besides, structural properties change by changing the cell size for each topology is also investigated. The specimens were subjected to a compression test by a universal testing machine to determine the absorbed energy and other mechanical properties. An implicit numerical study was also conducted to determine cellular structure's mechanical characteristics. The experimental and numerical results show that the honeycomb structure absorbs the maximum energy compared to the other structures. The experimentally and numerically calculated absorbed energy for the 4.8 mm honeycomb structure was 32.2J and 30.63J, respectively. The results also show that the increase of cell size for a particular cellular structure reduces the energy-absorbing ability of that structure.

Key Words
cellular structures; energy absorption; experimental analysis; FEA; honeycomb structure

Address
Faisal Ahmed Shanta: Department of Mechanical Engineering, Khulna University of Engineering & Technology, Khulna-9203, Bangladesh
Md Abdullah Al Bari: Department of Mechanical Engineering, Khulna University of Engineering & Technology, Khulna-9203, Bangladesh; Department of Chemical and Petroleum Engineering, University of Calgary, 2500 University Drive NW, Calgary, AB, T2N 1N4, Canada

Abstract
The conventional single-degree-of-freedom (SDOF) system is appropriate for dynamic response analysis of paneltype structures without an opening. However, the typical building structures usually have four-sided fixed walls having an opening. Therefore, it may induce a considerable error when dynamic responses are estimated based on the conventional SDOF system, since the SDOF system cannot consider the effect of an opening during the SDOF analysis. For this reason, this study proposes a new SDOF system to consider the effect of an opening by adjusting its load-mass factor. The load-mass factor can be modified based on the assumption that the behaviors of the four-sided fixed wall with an opening is very similar to the behaviors of the same size wall without an opening, when the uniformly distributed blast loaded area is identical. In order to confirm a feasibility of the proposed SDOF system, a series of numerical simulations were carried out for the four-sided fixed reinforced concrete (RC) wall under a blast load. The dynamic responses estimated from the proposed SDOF system and the conventional SDOF system were compared with the dynamic responses evaluated from the finite element (FE) analysis. Especially, for the maximum dynamic responses except for 50% opening case, the proposed SDOF system had about 1.1 % to 25.7 % normalized errors while the conventional SDOF system had about 4.1 % to 49.1 % normalized errors.

Key Words
damage assessment; dynamic response; load mass factor; RC wall; SDOF

Address
S.H. Sung and H. Ji: Agency for Defense Development, Yuseong, P.O. Box 35, Daejeon, 34186, Korea

Abstract
Nanotechnology has become one of the interesting technique used in material science and engineering. However, it is low used in civil engineering structures. The purpose of the present study is to investigate the static behavior of concrete plates reinforced with silica-nanoparticles. Due to agglomeration effect of silica-nanoparticles in concrete, Voigt's model is used for obtaining the equivalent nano-composite properties. Furthermore, the plate is simulated mathematically with higher order shear deformation theory. For a large use of this study, the concrete plate is assumed resting on a Pasternak elastic foundation, including a shear layer, and Winkler spring interconnected with a Kerr foundation. Using the principle of virtual work, the equilibrium equations are derived and by the mean of Hamilton's principle the energy equations are obtained. Finally, based on Navier's technique, closed-form solutions of simply supported plates have been obtained. Numerical results are presented considering the effect of different parameters such as volume percent of SiO2 nanoparticles, mechanical loads, geometrical parameters, soil medium, on the static behavior of the plate. The most findings of this work indicate that the use of an optimum amount of SiO2 nanoparticles on concretes increases better mechanical behavior. In addition, the elastic foundation has a significant impact on the bending of concrete slabs.

Key Words
bending; elastic foundations; higher order shear deformation theory; plate theory; reinforced-concrete; silica nanoparticles

Address
Mohammed Chatbi, Baghdad Krour, Mohamed A. Benatta: Laboratoire des Structures et Matériaux Avancés dans le Génie Civil et Travaux Publics, University of Djillali Liabes, Sidi Bel Abbes, Algeria
Zouaoui R. Harrat: Laboratoire des Structures et Matériaux Avancés dans le Génie Civil et Travaux Publics, University of Djillali Liabes, Sidi Bel Abbes, Algeria; Clermont Auvergne University, CNRS, Sigma, Institut Pascal, UMR 6602, Clermont-Ferrand, France
Sofiane Amziane: Clermont Auvergne University, CNRS, Sigma, Institut Pascal, UMR 6602, Clermont-Ferrand, France
Mohamed Bachir Bouiadjra: Laboratoire des Structures et Matériaux Avancés dans le Génie Civil et Travaux Publics, University of Djillali Liabes, Sidi Bel Abbes, Algeria; Thematic Agency for Research in Science and Technology (ATRST), Algiers, Algeria

Abstract
Settlement control techniques are critical for the safety of shield tunnel constructions, especially for facing complex situations. In this study, the shield tunnel structure from Huaita east road station to Heping Road station in Xuzhou metro No.3 line (China) is taken as engineering background, which has various complex problems of the upper-soft and lower-hard composite stratum conditions, twin curve shield tunnels, and underpass the foundation of the piled raft. The deformation characteristics of shield tunnelling passing through buildings are explored. Subsequently, comprehensive research methods of numerical simulation and field measurement are adopted to analyzing the effectiveness of settlement control by using the top grouting technique. The results show that the settlement of the buildings has obvious spatial characteristics, and the hysteresis effect can be obviously observed in soil deformation caused by shield construction. Meanwhile, the two shield constructions can cause repeated disturbances, reducing the soil deformation's hysteresis effect. Moreover, the shield tunnel's differential settlement is too large when a single line passes through, and the shield construction of the outer curve can cause more significant disturbance in the tunnel than the inside curve. Notably, the proposed process control parameters and secondary topgrouting method can effectively control the deformation of the shield tunnel, especially for the long-term deformation.

Key Words
complex strata; foundation deformation; secondary grouting; settlement control; shield tunnel

Address
Jianwei Jia, Ruiqi Gao, Jianjun Li, Ziwen Song, Jinghui Tans: China Construction Sixth Engineering Bureau Co. Ltd., Tianjin 300451, China
Defeng Wang: Institute of Mining and Special Civil Engineering, Technical University of Freiberg, Freiberg 09599, Germany


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