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CONTENTS
Volume 18, Number 6, December 2016
 

Abstract
The main aim of this study is to predict the compressive and flexural strengths of self–compacting mortar (SCM) containing nano–SiO2, nano–Fe2O3 and nano–CuO using wavelet–based weighted least squares–support vector machines (WLS–SVM) approach which is called WWLS–SVM. The WWLS–SVM regression model is a relatively new metamodel has been successfully introduced as an excellent machine learning algorithm to engineering problems and has yielded encouraging results. In order to achieve the aim of this study, first, the WLS–SVM and WWLS–SVM models are developed based on a database. In the database, nine variables which consist of cement, sand, NS, NF, NC, superplasticizer dosage, slump flow diameter and V–funnel flow time are considered as the input parameters of the models. The compressive and flexural strengths of SCM are also chosen as the output parameters of the models. Finally, a statistical analysis is performed to demonstrate the generality performance of the models for predicting the compressive and flexural strengths. The numerical results show that both of these metamodels have good performance in the desirable accuracy and applicability. Furthermore, by adopting these predicting metamodels, the considerable cost and time–consuming laboratory tests can be eliminated.

Key Words
model mortar; compressive strength; flexural strength; nanoparticles; weighted least squares support vector machine; wavelet

Address
Mohsen Khatibinia and Abdosattar Feizbakhsh: Department of Civil Engineering, University of Birjand, Birjand, Iran

Ehsan Mohseni and Malek Mohammad Ranjbar: Department of Civil Engineering, University of Guilan, Rasht, Iran

Abstract
Beam–column joints are recognized as the weak points of reinforcement concrete frames. The ductility of reinforced concrete (RC) frames during severe earthquakes can be measured through the dissipation of large energy in beam–column joint. Retrofitting and rehabilitating structures through proper methods, such as carbon fiber reinforced polymer (CFRP), are required to prevent casualties that result from the collapse of earthquake-damaged structures. The main challenge of this issue is identifying the effect of CFRP on the occurrence of failure in the joint of a cross section with normal ductility. The present study evaluates the retrofitting method for a normal ductile beam–column joint using CFRP under monotonic and cyclic loads. Thus, the finite element model of a cross section with normal ductility and made of RC is developed, and CFRP is used to retrofit the joints. This study considers three beam–column joints: one with partial CFRP wrapping, one with full CFRP wrapping, and one with normal ductility. The two cases with partial and full CFRP wrapping in the beam–column joints are used to determine the effect of retrofitting with CFRP wrapping sheets on the behavior of the beam–column joint confined by such sheets. All the models are subjected to monotonic and cyclic loading. The final capacity and hysteretic results of the dynamic analysis are investigated. A comparison of the dissipation energy graphs of the three connections shows significant enhancement in the models with partial and full CFRP wrapping. An analysis of the load-displacement curves indicates that the stiffness of the specimens is enhanced by CFRP sheets. However, the models with both partial and full CFRP wrapping exhibited no considerable improvement in terms of energy dissipation and stiffness.

Key Words
Beam-column connection; interior RC joint; earthquake; plastic hinge; CFRP sheet; retrofitting

Address
Arash Rahimipour, Farzad Hejazi, Ramin Vaghei and Mohd Saleh Jaafar: Department of Civil Engineering, Faculty of Engineering, University Putra Malaysia, Malaysia

Farzad Hejazi and Mohd Saleh Jaafar: Housing Research Centre, Faculty of Engineering, University Putra Malaysia, Malaysia

Abstract
Fire loading causes a critical collapse of RC (Reinforced Concrete) Structures since the embedded steels inside are relative week against high elevated temperature. Several numerical frameworks for fire resistance have been proposed, however they have limitations such as unstable convergence and long calculation period. In the work, 2-D nonlinear FE technique is proposed using Galerkin method for RC structures under fire loading. Closed-form element stiffness with a triangular element is adopted and verified with fire test on three RC slabs with different fire loading conditions. Several simulations are also performed considering fire loading conditions, water contents, and cover depth. The proposed numerical technique can handle time-dependent fire loading, convection, radiation, and material properties. The proposed technique can be improved through early-aged concrete behavior like moisture transport which varies with external temperature.

Key Words
fire loading; FE techniques; element stiffness; water content; early-aged concrete behavior

Address
Byung-Chan Han: Department of Architectural Engineering, Woosong College, Daejeon 300-715, Korea

Young-Jin Kwon: Department of Emergency Management Engineering, Hoseo University, Chungnam 336-795, Korea

Byung-Jae Lee: R&D Center, JNTINC Co. LTD., Gyeonggi, 18284, Korea

Seung-Jun Kwon: Department of Civil and Environmental Engineering, Hannam University, Daejeon 306-791, Korea

Young-Suk Chae: Department of Architectural Engineering, Woosong University, Daejeon 300-715, Korea

Abstract
A methodology using neural networks has been proposed for rapid prediction of inelastic bending moments in reinforced concrete continuous beams subjected to service load. The closed form expressions obtained from the trained neural networks take into account cracking in concrete at in-span and at near the internal supports and tension stiffening effect. The expressions predict the inelastic moments (considering the concrete cracking) from the elastic moments (neglecting the concrete cracking) at supports. Three separate neural networks are trained since these have been postulated to represent all the beams having any number of spans. The training, validating, and testing data sets for the neural networks are generated using an analytical-numerical procedure of analysis. The proposed expressions are verified for example beams of different number of spans and cross-section properties and the errors are found to be small. The proposed expressions, at minimal input data and computation effort, yield results that are close to FEM results. The expressions can be used in preliminary every day design as they enable a rapid prediction of inelastic moments and require a computational effort that is a fraction of that required for the available methods in literature.

Key Words
bending moment; closed form expression; cracking; neural network; reinforced concrete; service load

Address
K.A.Patel and A.K.Nagpal: Civil Engineering Department,Indian Institute of Technology Delhi,NewDelhi 110016,India

Sandeep Chaudhary: Civil Engineering Department, Malaviya National Institute of Technology Jaipur, Jaipur 302017, India

Abstract
For investigating the effect of the pre-existing joints on the initiation pattern of hydraulic fractures, the numerical simulation of circular holes under internal hydraulic pressure with a different pattern of the joint distributions are conducted by using a finite element code, FRANC2D. The pattern of hydraulic fracturing initiation are scrutinized with changing the values of the joint length, joint offset angle. The hydraulic pressures with 70% of the peak value of borehole wall breakout pressure are applied at the similar models. The simulation results suggest that the opening-mode fracture initiated from the joint tip and propagated toward the borehole for critical values of ligament angle and joint offset angle. At these critical values, the crack grow length is influenced by joint ligament length. When the ligament length is less than 3 times the borehole diameter the crack growth length increases monotonically with increasing joint length. The opening-mode fracture disappears at the joint tip as the ligament length increases.

Key Words
ligament angle; pre-existing joints; opening-mode fracture; hydraulic fractures; joint offset angle

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

Ahmadreza Hedayat: Department of Civil and Environmental Engineering, Colorado School of Mines,
Golden, Colorado 80401, USA

Zheming Zhu: College of Architecture and Environment, Sichuan University, Chengdu 610065, China

Abstract
According to deformation data measured in some high concrete dams, for dam body deformation, there is a complex relationship with dam height and water head for different projects, instead of a simple monotonic relationship consistently. Meanwhile, settlement data of some large reservoirs exhibit a significant deformation of reservoir basin. As water conservancy project with high concrete dam and large storage capacity increase rapidly these decades, reservoir basin deformation problem has gradually gained engineers

Key Words
reservoir basin deformation; project with high dam and large storage capacity; high concrete dam; forward and inverse analysis; an improved analytical method

Address
Dongjian Zheng, Yanxin Xu, Meng Yang, Hao Gu, Huaizhi Su,
and Erfeng Zhao: State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing, China

Dongjian Zheng and Huaizhi Su: College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing, China

Yanxin Xu, Hao Gu and Erfeng Zhao: National Engineering Research Center of Water Resources Efficient Utilization and Engineering Safety, Hohai University, Nanjing, China

Xinbo Cui: Information Center of land and resources in binzhou city, Binzhou, China

Abstract
Nonlinear models, capable of taking into account all the phenomena involved in the cracking and in the failure of lightly reinforced concrete beams, are nowadays available for a rigorous calculation of the minimum reinforcement. To simplify the current approaches, a new procedure is proposed in this paper. Specifically, the ductility index, which is lower than zero for under-reinforced concrete beams in bending, is introduced. The results of a general model, as well as the data measured in several tests, reveal the existence of two linear relationships between ductility index, crack width, and the amount of steel reinforcement. The above relationships can be applied to a wide range of lightly reinforced concrete beams, regardless of the geometrical dimensions and of the mechanical properties of materials. Accordingly, if only a few tests are combined with this linear relationships, a new design-by-testing procedure can be used to calculate the minimum reinforcement, which guarantees both the control of cracking in service and the ductility at failure.

Key Words
lightly reinforced concrete beams; bending moment; minimum reinforcement; ultimate limit state; serviceability limit state; ductility index

Address
Alessandro P. Fantilli, Bernardino Chiaia and Andrea Gorino: Department of Structural, Building and Geotechnical Engineering, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy


Abstract
In this study, seismic behaviour of reinforced concrete buildings using the pushover and incremental dynamic analysis method was investigated. A numerical study was performed for a reinforced concrete frame building. Pushover analysis according to uniform and triangular load shapes and incremental dynamic analyses were performed for selected building. For the nonlinear analysis, three ground motion records were selected to ensure compatibility with the design spectrum defined in the Turkish Seismic Code. The maximum response, dynamic pushover curve, capacity curves, interstorey drifts and moment rotation curves for various element ends of the selected building were obtained. Results were compared each other and good correlation was obtained between the dynamic analyses envelope with static pushover curves for the building.

Key Words
incremental dynamic analysis; pushover analysis; distributed plastic hinge

Address
Mehmet Emin Öncü and Merve Şahin Yön: Dicle University Civil Engineering Department, Diyarbak

Abstract
This paper describes a deformation-based strut-and-tie model for the flexural members at post-yield state. Boundary deformation conditions by flexural post-yield response are chosen in terms of the flexural bar strains as the main factor influenced on the shear strength. The main purpose of the proposed model is to predict the shear capacities of the flexural members associated with the given flexural deformation conditions. To verify the proposed strut-and-tie model, the estimated shear strengths depending on the flexural deformation are compared with the experimental results. The experimental data are in good agreement with the values obtained by the proposed model.

Key Words
beam; deformation; strut-and-time model; transverse loading; ultimate strength

Address
Sung-Gul Hong, Seongwon Hong and Thomas H.-K. Kang: Department of Architecture and Architectural Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea

Soo-Gon Lee: Samsung C&T, 14 Seocho-daero 74-gil, Seocho-gu, Seoul 06620, Republic of Korea


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