فهرست مطالب

Asian journal of civil engineering - Volume:18 Issue:6, 2017
  • Volume:18 Issue:6, 2017
  • تاریخ انتشار: 1396/03/17
  • تعداد عناوین: 10
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  • T. Manju *, H. Silpha Pages 853-861
    LiteSteel Beam (LSB) was introduced in order to meet the growing demand of light structural elements that are easier to carry and install. They are in a way different from normal CFS sections in terms of their hollow flange which increases its load carrying capacity, the absence of free edges in LSB which minimizes local buckling failure, higher bending moment carrying capacity as the materials are distributed away from the neutral axis and greater bending stiffness. The LSB sections considered, consisted of two rectangular hollow flanges and a thin web in between, joined by welding. The basis of this study involved fabricating three sections 1.2 mm thick and depth varied as 300 mm, 250 mm, 200 mm as a representative of using it as purlin and in few cases as a secondary beam in small steel-framed houses. The Web crippling behaviour of these sections was studied by finding the sectional properties of the specimens using Cornell university finite strip method (CUFSM), followed by an experimental study which consisted of i)material characterization through tensile coupon tests ii)test on specimens to obtain maximum load carrying capacities and desired buckling modes. Further, using Finite element analysis software (ABAQUS) a model was generated to reproduce the results.
    Keywords: LiteSteel beam, finite strip method, web crippling, finite element analysis
  • T.M. Jeyashree, C. Arunkumar *, S. Ashok Kumar Pages 863-878
    Shell foundations are economical alternatives to the conventional flat shallow foundation, regarding material-saving technique. Shell foundation comes under the category of the shallow foundation. Concrete funicular shells of square plan, double curvature with various thicknesses are analyzed for the concentrated load. Specimens of size 680 × 680 mm are prepared using cement M30 concrete grade for which the mix design is carried by IS method. Formwork is prepared by concrete above which test specimen is prepared. The specimens are prepared with various thicknesses of 40 mm, 50 mm, 60 mm. The specimens are moist cured for 28 days before testing. The concentrated load over the column is applied, and the corresponding deflections and settlement characteristics are measured within elastic range. Beyond elastic range specimens are subjected to fail, and the ultimate loads are determined. The experimental result shows that load carrying capacity for 60 mm thick specimen (8 mm ɸ bar) is more compared to 40 mm and 50 mm thick specimen. Also by increasing the area of steel of edge beam reinforcement by 40% causes the increase in ultimate load carrying capacity by 15% and it also reduces the maximum settlement by 26%. A comparative study of the flat foundation and shell foundation shows that ultimate load carrying capacity for shell foundation increases by 50%. Finite element analysis was done using SAP 2000. Using the finite element model, a parametric study was conducted to determine the changes in stress level in the funicular shell. The magnitude of concentrated load used for the FEM analysis is same as the ultimate load of experimental work.
    Keywords: Funicular shell, double curvature, deflections, ultimate load, shell foundation
  • S. Pradeep * Pages 879-891
    In this paper an attempt was made in reinforced concrete structures where windows or door openings have been left in the infill walls due to architectural necessities. The columns with partial infill has been damaged seriously during the past earthquakes due to short column effect and this type of column leads to major failure of structure during earthquake. The behaviour of such columns is not known fully. This paper investigates analytically the behaviour of short column under cyclic lateral loading. The aspect ratio of infill wall (Lw/Hw, where Lw = infill length, Hw = infill height) and its placement configurations were the parameters of the analytical study. The behaviour of the three short columns in the frame with different aspect ratios were studied for load displacement hysterisis curve, stiffness degradation, ductility ratio, Von Mises Stress and crack pattern. Test results indicates that when the aspect ratio of the infill was increased, the lateral strength and rigidity increased and at the same time displacement and ductility of structure were decreased. In addition to this, crack pattern results indicates that in the bare frame without infill, initial cracks are developed at the beam column joint and at the ultimate load level, a series of wide cracks are developed at the support which makes the structure instable and leads to failure. In the partial infill frame, cracks are developed at the junctions of beam column and masonry infill. Nominal cracks are developed at the support since the portion below is completely restrained by the tight fitted masonry infill. So this tends to the formation of short column effect in the frame member with partial infill, which leads to major collapse.
    Keywords: Short column effect, cyclic loading, aspect ratio, partially infilled frame, stiffness, ductility
  • N. Djedoui *, A. Ounis, Jp. Pinelli, M. Abdeddaim Pages 893-909
    This paper deals with the efficiency of a hybrid vibration control for rigid buildings structures under earthquakes. The hybrid control consists of a base isolator and tuned mass damper (TMD) or active tuned mass damper (ATMD). The active control force is calculated within a feedback loop by the mean of the linear quadratic controller (LQR) designed to penalize the displacement and the velocity of the floor on which the ATMD is installed. A total of four cases are studied based on the placement and the type of the control system either passive TMD or active TMD. The lower and top floor alternatively carries the TMD control system. The case of a rigid six-degree of freedom base isolated frame structure illustrates the effectiveness of the hybrid control through simulations. Simulation results, obtained from real time-history data of three earthquakes (El Centro, Northridge and Loma Prieta) show that the proposed control is effective. The hybrid control system is able to reduce the vibration amplitudes especially the base isolator displacement and acceleration without affecting the super-structure response regardless of the placement of the TMD control system. Such a hybrid control system can protect high importance buildings containing sensitive equipment.
    Keywords: Hybrid control, active tuned mass damper, linear quadratic regulator, base isolated structure, vibration control
  • M. Pavan Kumar, P. Markandeya Raju *, M. Navya, G.T. Naidu Pages 911-927
    Monopole and Self-Supporting Towers are the most common types of Telecommunication Towers adopted in construction industry. This paper presents a comparison between Monopole and Self-Support type Towers with different heights of 30m, 40m and 50m for basic wind speeds of 33m/sec, 47m/sec and 55m/sec. Dead loads and Wind loads are considered for analysis of the tower using STAAD(X) Tower software which is tailor made for analyzing Telecommunication Towers. It is concluded from this study that Self-Support Towers have lower lateral displacements compared to the Monopole Towers of same height for same amount of loading. This is because they have higher stiffness. But, the steel quantity required for Self-Support Towers is about 2 times more than the Monopole Towers for a given tower height, wind speed and loading. However, due to their rigidity, SelfSupport Towers have more load carrying capacity than Monopoles. For towers of height below or equal to 40m, Monopoles might be preferred. But, with the increase in height beyond 50m, Self-Support Towers are recommended. This is because, in case of any unexpected and abnormally high wind speeds during cyclones, the structural rigidity will be intact and the damage and repair for the structure may not be so high unlike Monopole.
    Keywords: STAAD(X) tower, monopole tower, self, supporting tower, lateral displacements
  • E. Shahsavari *, A. Taheri Pages 929-943
    Offshore platforms are in a rough environmental condition and therefore structural damages are undeniable for the aging platforms. These structural damages, which are the results of fatigue, corrosion and other unavoidable events, reduce the stiffness of the structure. When the stiffness of the structure decrease, the dynamic response of the structure is becoming important and must be investigated. In this research, dynamic behavior of an existing jacket platform in the Persian Gulf under extreme environmental condition is investigated by using random time domain simulation method to reach a reliable value for DAF in the extreme condition. Fifteen, 1-hour storm, simulations for the water surface elevation is produced to capture the statistical properties of extreme sea condition. Time series of base shear and overturning moment are derived from both dynamic and static responses. By calculating the maximum DAF from each simulations and fitting the collected data to Weibull distribution, the Most Probable Maximum Extreme (MPME) value for the DAF is achieved. Results show that DAF for this type platform is a noticeable value and should be included in any analyses.
    Keywords: Offshore platforms, dynamic amplification factor, time history analysis, Persian Gulf
  • Gh. Abdollahzadeh *, S. Shabani Pages 945-960
    When subjected to an earthquake motion, a structure should absorb and dissipate lots of energy in different ways, allowing the structural members to enter the inelastic range enabling them to absorb the energy by their deformations. As structural members enter the inelastic range, permanent deformations occur, and to continue utilization of structure, those members which are too deformed or cannot be utilized anymore should be strengthened or replaced with new members, an operation which is difficult and costly. Therefore, the dampers installed in the structure, through energy absorption induced by earthquake, prevent other parts of the structure to enter inelastic range; as a result, following an earthquake, different parts of the structure can be either still utilized or fixed and replaced, if necessary, by checking the dampers.
    According to the aforementioned things, this study aims to examine the structures to which damper is added as a retrofitting method. For this purpose, by selecting a number of intermediate steel moment frames, seismic vulnerability of these frames in the near- and farfield earthquakes was examined and such parameters as damage to frames and stories, relative story displacement, base shear and roof displacement were examined. In this study, viscoelastic dampers are used in order to reduce drift and structural damage. The results after dampers installation in the middle span of frames were compared with/without using damper, then it was concluded that viscoelastic dampers play an important role in absorbing energy and reducing damage in buildings. Moreover, drift and base shear as well as roof displacement decrease to a great extent. Comparing near- and far-field earthquakes, it was observed that the intensity of near-field earthquakes was higher causing devastating effects in buildings; installation of dampers, however, highly reduces these damages. Furthermore, the effect of dampers on taller buildings was found to be more, and greater reduction was seen in the examined parameters.
    Keywords: Damage, dynamic analysis, retrofitting, viscoelastic damper
  • S. Nazari, J. Keyvani *, A. Meshkat-Dini, M. Azhdarifar Pages 961-976
    In this paper, the performance of a medium-height bundled-tube structural system of 10 stories is studied under strong near-field records as well as produced equivalent mathematical pulses. Assessing analytical results of this research reveal the fact that floors drift in the studied model under natural records and also equivalent mathematical pulses, bring relatively similar results. Therefore, it is observed that by applying suitable closedform models while acknowledging limitations, it is possible to simulate powerful near-field records through mathematical pulses and use them for the purpose of evaluating the seismic behavior in medium-height structural systems.
    Keywords: Velocity pulse, high amplitude wavelet, earthquake record, closed form model, bundled tube
  • D. Ouzandja *, B. Tiliouine, M. Belharizi, M. Kadri Pages 977-992
    This paper aims to present the three-dimensional nonlinear seismic response of concrete gravity dams considering contact elements at dam-reservoir interaction interface. Damreservoir contact interface is modeled with three-dimensional surface-to-surface contact elements based on the Coulomb’s friction. A numerical investigation of the effect of hydrodynamic interaction and sliding of the water along the dam-reservoir interface is performed. The maximum horizontal displacements and principal stresses in the different sections of the dam are presented as well as seismic behavior of dam is examined in empty and full reservoir cases. Besides, the damage placements in the concrete dam are evaluated.
    Keywords: Concrete gravity dam, dynamic dam, reservoir interaction, Lagrangian approach, contact elements, nonlinear seismic response, finite element method
  • N. Benlakehal *, A. Kassoul, P.A.G. Piloto, A. Bouchair Pages 993-1008
    To protect human lives and prevent against failure of structures, the collapse of industrial buildings under fire should always occur inward with a minimum failure time. The objective of this paper is to investigate the behaviour of industrial steel portal frames with haunches in fire situation. The structure is studied using finite element software ANSYS with an uncoupled thermal and mechanical analysis. The inclination angle of the rafter and the haunch’s length for the portal frame are taken as variables. A comparative study of the numerical simulations and the simplified method (R15) show a close agreement between the two analyses according to the failure time.
    Keywords: Industrial buildings, steel portal frames, fire, time resistance, numerical simulations