Techno Press
Tp_Editing System.E (TES.E)
Login Search


eas
 
CONTENTS
Volume 12, Number 6, June 2017
 

Abstract
To prevent or limit the damage caused by earthquakes on existing buildings, several retrofitting techniques are possible. In this work, an ultra high performance concrete based on sand dune has been formulated for use in the reinforcement of a multifunctional tower in the city of Skikda in Algeria. Tests on the formulated ultra high performance concrete are performed to determine its characteristics. A nonlinear dynamic analysis, based on the

Key Words
UHPC; dune sand; seismic; retrofitting; shear wall; pushover

Address
Abderraouf Trabelsi: Université de Tunis El Manar, Ecole Nationale d

Abstract
This paper presents investigation into the behavior of beam-column joints, with the joint region concrete being replaced by steel fiber reinforced concrete (SFRC) and by ultra-high performance concrete (UHPC). A total of ten beam-column joint specimens (BCJ) were tested experimentally to failure under monotonic and cyclic loading, with the beam section being subjected to flexural loading and the column to combined flexural and axial loading. The joint region essentially transferred shear and axial stresses as received from the column. Steel fiber reinforced concrete (SFRC) and ultra-high performance concrete (UHPC) were used as an innovative construction and/or strengthening scheme for some of the BCJ specimens. The reinforced concrete specimens were reinforced with longitudinal steel rebar, 18 mm, and some specimens were reinforced with an additional two ties in the joint region. The results showed that using SFRC and UHPC as a replacement concrete for the BCJ improved the joint shear strength and the load carrying capacity of the hybrid specimens. The mode of failure was also converted from a non-desirable joint shear failure to a preferred beam flexural failure. The effect of the ties in the SFRC and UHPC joint regions could not be observed due to the beam flexural failure. Several models were used in estimating the joint shear strength for different BCJ specimens. The results showed that the existing models yielded wide-ranging values. A new concept to take into account the influence of column axial load on the shear strength of beam-column joints is also presented, which demonstrates that the recommended values for concrete tensile strength for determination of joint shear strength need to be amended for joints subject to moderate to high axial loads. Furthermore, finite element model (FEM) simulation to predict the behaviour of the hybrid BCJ specimens was also carried out in an ABAQUS environment. The result of the FEM modelling showed good agreement with experimental results.

Key Words
beam-column joint; hybrid joint; steel fiber reinforced concrete; ultra high performance concrete; joint shear strength; finite element model

Address
M.A. Al-Osta, A.M. Al-Khatib, M.H. Baluch, A.K. Azad: Department of Civil Engineering, King Fahd University of Petroleum & Minerals (KFUPM), Dhahran 31261, Saudi Arabia
M.K. Rahman: Center for Engineering Research, Research Institute, King Fahd University of Petroleum & Minerals (KFUPM), Dhahran 31261, Saudi Arabia


Abstract
The intent of this paper is to investigate the propagation of Love waves in a dry sandy medium sandwiched between fiber-reinforced layer and prestressed porous half-space. Separate displacement components have been deduced in order to characterize the dynamics of individual materials. Using suitable boundary conditions, the frequency equation has been derived by means of separation of variables which reveals the significant role of reinforcement parameters, sandiness, thickness of layers, porosity and prestress on the wave propagation. The phase velocity of the Love wave has been discussed in accordance with its typical cases. In both cases when fiber-reinforced and dry sandy media are absent, the derived equation of Love type wave coincides with the classical Love wave equation. Numerical computations have been performed in order to graphically illustrate the dependencies of different parameters on phase velocity of Love waves. It is observed that the phase velocity decreases with the increase of parameters pertaining to reinforcement and prestress. The results have certain potential applications in earthquake seismology and civil engineering.

Key Words
Love wave; fiber-reinforced medium; dry sandy medium; prestress; phase velocity; dispersion equation

Address
Shishir Gupta and Mostaid Ahmed: Department of Applied Mathematics, Indian Institute of Technology (Indian School of Mines), Dhanbad -826004, India

Abstract
Foundation plays a significant role in safe and efficient turbo machinery operation. Turbo machineries generate harmonic load on the foundation due to their high speed rotating motion which causes vibration in the machinery, foundation and soil beneath the foundation. The problems caused by vibration get multiplied if the soil is poor. An improperly designed machine foundation increases the vibration and reduces machinery health leading to frequent maintenance. Hence it is very important to study the soil structure interaction and effect of machine vibration on the foundation during turbo machinery operation in the design stage itself. The present work studies the effect of harmonic load due to machine operation along with earthquake loading on the frame foundation for poor soil conditions. Various alternative foundations like rafts, barrette, batter pile and combinations of barrettes with batter pile are analyzed to study the improvements in the vibration patterns. Detailed computational analysis was carried out in SAP 2000 software; the numerical model was analyzed and compared with the shaking table experiment results. The numerical results are found to be closely matching with the experimental data which confirms the accuracy of the numerical model predictions. Both shake table and SAP 2000 results reveal that combination of barrette and batter piles with raft are best suitable for poor soil conditions because it reduces the displacement at top deck, bending moment and horizontal displacement of pile and thereby making the foundation more stable under seismic loading.

Key Words
turbo machinery; raft; barrette; batter pile; dynamic loading; computational analysis

Address
Sungyani Tripathy and Dr. Atul K Desai: Applied Mechanics Department, Sardar Vallabhbhai National Institute of Technology, Surat, Gujarat-395007, India

Abstract
One of the methods to strengthen the structures against the seismic lateral loading is the employment of the composite columns. A concrete-filled tube (CFT) has the cumulative advantages of steel and concrete. Concrete-filled steel tube columns have been widely used in the moment-resisting frame (MRF) structures, located in both non-seismic zones and high-risk seismic zones. In this paper, the results of studies on two important seismic parameters of ductility and the response modification factor (RMF) of the MRFs with CFT columns are submitted. While the studies are carried out, the effects of span length-story height ratio, the strength of materials and seismic behavior of MRFs are considered. In this regard, the ductility, RMF and the strength of 36 models of the steel MRFs with CFTs are analyzed. The fiber plastic hinges numerical simulation and pushover analysis method are used in the calculations. Based on the obtained results, the RMFs suitable for the 5-, 10- and 15- story frames are proposed.

Key Words
response modification factor; ductility, CFT column, pushover analysis, fiber plastic hinge

Address
Seyed Sh. Hashemi, Mohammad Vaghefi: Department of Civil Engineering, Persian Gulf University, Shahid Mahini Street, P.O. Box: 75169-13817, Bushehr, Iran
Kabir Sadeghi: Department of Civil Engineering, Near East University, ZIP Code: 99138, Nicosia, North Cyprus, Mersin 10, Turkey
Kaveh Shayan: Department of Civil Engineering, Islamic Azad University of Bushehr, Varzesh Street, P.O. Box: 75196-1955, Bushehr, Iran

Abstract
A seismic margin assessment evaluates how much margin exists for the system under beyond design basis earthquake events. Specifically, the seismic margin for the entire system is evaluated by utilizing a systems analysis based on the sub-system and component seismic fragility data. Each seismic fragility curve is obtained by using empirical, experimental, and/or numerical simulation data. The systems analysis is generally performed by employing a fault tree analysis. However, the current practice has clear limitations in that it cannot deal with the uncertainties of basic components and accommodate the newly observed data. Therefore, in this paper, we present a Bayesian-based seismic margin assessment that is conducted using seismic fragility data and fault tree analysis including Bayesian inference. This proposed approach is first applied to the pool-type nuclear research reactor system for the quantitative evaluation of the seismic margin. The results show that the applied approach can allow updating by considering the newly available data/information at any level of the fault tree, and can identify critical scenarios modified due to new information. Also, given the seismic hazard information, this approach is further extended to the real-time risk evaluation. Thus, the proposed approach can finally be expected to solve the fundamental restrictions of the current method.

Key Words
seismic margin assessment; seismic probabilistic risk assessment; fault tree analysis; Bayesian inference; research reactor; fragility analysis; hazard curve

Address
Shinyoung Kwag, Jinho Oh, Jong-Min Lee and Jeong-Soo Ryu:Research Reactor Mechanical Structure Division, Korea Atomic Energy Research Institute, 111 Daedeok-daero, Yuseong-gu, Daejeon 34057, Republic of Korea

Abstract
Cold-formed steel is widely used in steel structures, especially in transmission towers, because of advantages such as low weight, high strength, excellent mechanical properties, etc. However, there is not a special design code for cold-formed steel use in transmission towers in China. For this study, a total of 105 compression members were tested statically to investigate the bearing capacity of cold-formed steel members under different boundary conditions in transmission towers. The test results were compared to the results predicted by the current design codes. For deeper insight, additional coupled members were simulated using finite element analysis. An improved design method was developed based on the experimental and analytical results.

Key Words
bearing capacity; instability; cold-formed steel; transmission tower; boundary condition

Address
Junke Han: Beijing Key Lab of Earthquake Engineering and Structural Retrofit, Beijing University of Technology, Beijing, 100124, China; China Electric Power Research Institute, Beijing 100055, China
Xu Zhao, Zhenyun Tang, Hua Ma and Zhenbao Li: Beijing Key Lab of Earthquake Engineering and Structural Retrofit, Beijing University of Technology, Beijing, 100124, China

Abstract
A three-dimensional structural health monitoring (SHM) system based on multiscale entropy (MSE) and multiscale cross-sample entropy (MSCE) is proposed in this paper. The damage condition of a structure is rapidly screened through MSE analysis by measuring the ambient vibration signal on the roof of the structure. Subsequently, the vertical damage location is evaluated by analyzing individual signals on different floors through vertical MSCE analysis. The results are quantified using the vertical damage index (DI). Planar MSCE analysis is applied to detect the damage orientation of damaged floors by analyzing the biaxial signals in four directions on each damaged floor. The results are physically quantified using the planar DI. With progressive vertical and planar analysis methods, the damaged floors and damage locations can be accurately and efficiently diagnosed. To demonstrate the performance of the proposed system, performance evaluation was conducted on a three-dimensional seven-story steel structure. According to the results, the damage condition and elevation were reliably detected. Moreover, the damage location was efficiently quantified by the DI. Average accuracy rates of 93% (vertical) and 91% (planar) were achieved through the proposed DI method. A reference measurement of the current stage can initially launch the SHM system; therefore, structural damage can be reliably detected after major earthquakes.

Key Words
three-dimensional; structural health monitoring; vertical; planar; cross-sample entropy; multiscale

Address
Tzu Kang Lin, Tzu Chi Tseng and Ana G. Laínez: Department of Civil Engineering, National Chiao Tung University, 1001 University Road, Hsinchu, Taiwan 300, ROC


Abstract
Nowadays, there are a great number of various structures that have been retrofitted by using different FRP Composites. Due to this, more researches need to be conducted to know more the characteristics of these structures, not only that but also a comparison among them before and after the retrofitting is needed. In this research, a model steel structure is tested using a bench-scale earthquake simulator on the shake table, using recorded micro tremor data, in order to get the dynamic behaviors. Beams of the model steel structure are then retrofitted by using CFRP composite, and then tested on the Quanser shake table by using the recorded micro tremor data. At this stage, it is needed to evaluate the dynamic behaviors of the retrofitted model steel structure. Various types of methods of OMA, such as EFDD, SSI, etc. are used to take action in the ambient responses. Having a purpose to learn more about the effects of FRP composite, experimental model analysis of both types (retrofitted and no-retrofitted models) is conducted to evaluate their dynamic behaviors. There is a provision of ambient excitation to the shake table by using recorded micro tremor ambient vibration data on ground level. Furthermore, the Enhanced Frequency Domain decomposition is used through output-only modal identification. At the end of this study, moderate correlation is obtained between mode shapes, periods and damping ratios. The aim of this research is to show and determine the effects of CFRP Composite implementation on structural responses of the model steel structure, in terms of changing its dynamical behaviors. The frequencies for model steel structure and the retrofitted model steel structure are shown to be 34.43% in average difference. Finally, it is shown that, in order to evaluate the period and rigidity of retrofitted structures, OMA might be used.

Key Words
experimental modal analysis; CFRP; modal parameter; EFDD; shake table

Address
Azer A. Kas

Abstract
This study evaluates the effectiveness of a newly developed retrofitting scheme for masonry-infilled non-ductile RC frames experimentally and by numerical simulation. The technique focuses on modifying the load path and yield mechanism of the infilled frame to enhance the ductility. A vertical gap between the column and the infill panel was strategically introduced so that no shear force is directly transferred to the column. Steel brackets and small vertical steel members were then provided to transfer the interactive forces between the RC frame and the masonry panel. Wire meshes and high-strength mortar were provided in areas with high stress concentration and in the panel to further reduce damage. Cyclic load tests on a large-scale specimen of a single-bay, single-story, masonry-infilled RC frame were carried out. Based on those tests, the retrofitting scheme provided significant improvement, especially in terms of ductility enhancement. All retrofitted specimens clearly exhibited much better performances than those stipulated in building standards for masonry-infilled structures. A macro-scale computer model based on a diagonal-strut concept was also developed for predicting the global behavior of the retrofitted masonry-infilled frames. This proposed model was effectively used to evaluate the global responses of the test specimens with acceptable accuracy, especially in terms of strength, stiffness and damage condition.

Key Words
non-ductile frame; masonry infill; seismic retrofitting; cyclic test; macro model

Address
Jarun Srechai, Arnon Wongkaew: Department of Civil Engineering, Burapha University, 169 Saen-Sook, Chonburi, 20131, Thailand
Sutat Leelataviwat: Department of Civil Engineering, King Mongkut\'s University of Technology Thonburi,126 Thung Khru, Bangkok, 10140, Thailand
Panitan Lukkunaprasit: Department of Civil Engineering, Chulalongkorn University, 254 Phatumwan, Bangkok, 10330, Thailand

Abstract
Steel plate shear walls (SPSWs) are effective lateral systems which have high initial stiffness, appropriate ductility and energy dissipation capability. Recently, steel plate shear walls with low yield point strength (LYP), were introduced and they attracted the attention of designers. Structures with this new system, besides using less steel, are more stable. In the present study, the effects of plates with low yield strength on the seismic design parameters of steel frames with steel plate shear walls are investigated. For this purpose, a variety of this kind of structures with different heights including the 2, 5, 10, 14 and 18-story buildings are designed based on the AISC seismic provisions. The structures are modeled using ANSYS finite element software and subjected to monotonic lateral loading. Parameters such as ductility (µ), ductility reduction (Rµ), over-strength (

Key Words
steel plate shear wall; low yield strength; ductility factor; over-strength factor; response modification factor; displacement amplification factor

Address
Negin Soltani, Karim Abedi, Mehdi Poursha: Faculty of Civil Engineering, Sahand University of Technology, Tabriz, Iran
Hassan Golabi: Department of Structural Engineering, Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran


Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2018 Techno-Press
P.O. Box 33, Yuseong, Daejeon 34186 Korea, Tel: +82-42-828-7996, Fax : +82-42-828-7997, Email: subs@techno-press.com