Scientia Iranica
Volume:27 Issue: 5, Sep Oct 2020

In this paper, instability of single layer reticulated domes is discussed. This purpose is elaborated by a case study on Talakan oil tank dome which is analyzed in this work with research package. This paper provides technical information related to the design, fabrication and collapse of Talakan dome. The secondary paths, especially in unstable buckling, can play an important role in the loss of stability and led to failure of the structure. The authors show that the stiffness of the dome is not adequate to prevent buckling under the prescribed snow loads. It is also shown that the capacity of the dome to resist eccentric snow load is about half of its capacity to resist symmetric snow loads. Although six combinations of load and support fixity are included in design assumptions, considerable attention has been focused on the bifurcation behavior in Talakan dome. The stiffness of the aluminum sheets of the roof cover have not been taken into account in the stability analysis.

The behavior factor is used to reduce the elastic spectrum ordinate or the forces obtained from a linear analysis in order to take into account the non-linear structural properties. The more accurate this parameter is estimated, the more exact responses of the structures will be obtained. Recently, coupled walls with steel coupling beams are extensively utilized as an efficient system against lateral forces in high-rise buildings. But, there is not enough information about the behavior of these walls during earthquake, and design codes have not suggested any behavior factor for this structural system. Consequently, this paper is devoted to find the behavior factor of this structural system. To achieve this goal, six-, twelve- and twenty-story buildings are assessed. Except for the number of stories, all characteristicsof these buildings are completely similar. Buidlings’ height, the length of the coupling beams and the coupling ratio are key parameters which influence the behavior factor of the aforesaid structural system. In this work, the effect of these parameters on this factor are studied.

Liquefaction during earthquakes can result in severe damage to structures, primarily from excess pore water pressure generation and subsoil softening. Deep Soil Mixing (DSM) is a common method of soil improvement and is also used to decrease shear stress in liquefiable soils to control liquefaction. The current study evaluated the effect of Deep Soil Mixing (DSM) columns and implementation of different column patterns on controlling liquefaction and decreasing settlement of shallow foundations. A series of shaking table physical modelling tests were conducted for three different distribution patterns of Deep Soil Mixing (DSM) columns (i.e.: square, triangular and single) with a treatment area ratio of 30%. The treatment was applied to a liquefiable soil under a shallow model foundation. The results showed that the excess pore water pressure decreased 20% to 50% in comparison with the unimproved soil, depending on the Deep Soil Mixing (DSM) column pattern used. For improved soil, the shallow foundation settlement was about 10% that of the unimproved soil in the best case. The increase in soil shear stiffness after use of the Deep Soil Mixing (DSM) columns was compared with the results of existing practical relations to increase soil shear strength.

In this study, a new class of shape functions, namely spherical Hankel shape functions, are derived and applied to reformulate the deflection, free vibration, and buckling of Mindlin plates based on finite element method (FEM). In this way, adding polynomial terms to the functional expansion, in which just spherical Hankel radial basis functions (RBFs) are used, leads to obtaining spherical Hankel shape functions. Accordingly, the employment of polynomial and spherical Bessel function fields together results in achieving more robustness and effectiveness. Spherical Hankel shape functions benefit from some useful properties, including infinite piecewise continuity, partition of unity, and Kronecker delta property. In the end, the accuracy of the proposed formulation is investigated through several numerical examples for which the same degrees of freedom are selected in both the presented formulation and the classical finite element method. Finally, it can be concluded that a higher accuracy is reachable by utilizing spherical Hankel shape functions in comparison with the Lagrangian FEM.

Structures located beside each other interact under dynamic loads both through the underlying soil and possibly by impact. In this paper, this dynamic cross-interaction phenomenon is studied parametrically. While simultaneous modeling of different adjacent buildings would be possible from the beginning, by resorting to simple physical models the cases susceptible to impact under harmonic loads are identified first with much less effort. Then comprehensive models containing two nonlinear multistory shear buildings connected at the base with suitable springs & dampers and impacting at story levels are developed. The system is analyzed under selected ground motions. It is shown that impact and cross-interaction have an increasing effect on lateral displacements for stiff and heavy structures and a decreasing effect for other cases. Also, the shear forces of stories increase and decrease in upper and lower stories, respectively, as a result of the mentioned mutual effect. Finally, the study shows that under a sample ground motion, simultaneous impact and cross-interaction increase the ductility demands of stories for taller structures while it decreases the ductility demand of shorter buildings.

Effects of polyphosphoric acid (PPA) on the ultraviolet (UV) aging properties of asphalt and asphalt mixture were studied. The morphologies of these binders were characterized by FTIR spectra and TG analysis, then the influence of PPA on asphalt and its mixture before and after UV aging were investigated by the physical properties and pavement performances. Results show that the mechanisms of PPA modified asphalt are physical and chemical reactions; both UV aging and PPA additive could prompted the polycondensation of light components in asphalt. Compared with control samples, the introduction of PPA enhances the asphalt properties and intensifies the asphalt mixture performances. Furthermore, the asphalt performance aging variations (penetration aging index, softening point increment, ductility aging index, G*/sinδ aging index) decrease significantly due to the introduction of PPA. This manifests that the effects of UV aging on the behaviors of asphalt and asphalt mixture are restricted by the addition of PPA through inhibiting the increase of carbonyl in the oxidation process.

Due to increased use of brick masonry for construction of buildings in Pakistan, huge quantities of Brick Kiln Waste (BKW) are generated which not only create disposal problems but are a hazard to the environment. In order to get rid of such problems, it is necessary to investigate suitability of the BKW as a stabilizer to the clayey soils. For this purpose, an experimental program was carried out to stabilize clayey soil with the BKW ranging from 5 to 40%. Basic geotechnical tests were performed on the clayey soil blended with the BKW. The results showed that the clayey soil became coarser and more suitable as a subgrade material with addition of the BKW. There was negligible reduction in dry density up to 7% when the BKW added was 40%. As expected, the cohesion and friction angle of the blended soils respectively decreased and increased with inclusion of the BKW. As compared to the clayey soil, the ultimate bearing capacity of the blended soil having 40% of the BKW increased by 21%. This study shows that clayey soils stabilized with the BKW could be used as a partial fill material for highway embankments and foundations of buildings.

While the bottom soil of the foundation is supposed to be rigid and the flexibility effect is ignored, the seismic response of the structure is affected by dynamic properties of the structure, and the soil flexibility does not have any effect on the response of the structure. Hence, considering the results obtained by analyses based on the fixed base buildings can lead to the unsafe design of the structure. On the other hand, the proximity of the site to the earthquake production resource causes the most earthquake energy to be reached to the structure as a long-period pulse. Therefore, near-field earthquakes produce many seismic needs so that force the structure to dissipate this input energy with relatively large displacements. Accordingly, the primary objective of the present paper is the determination of the seismic response of the 3, 5 and 8-story steel buildings with special moment frame system and by considering the soil-structure interaction and panel zone modeling as well. The selected records of the near and far-field earthquakes in nonlinear time history analysis have been used, and the response of the structure was compared in both states.

The paper shows the aspects of introducing energy-efficient equipment for engineering systems within the context of productivity enhancement in general. The author as research relevance brings a thesis that each of production members reach after implementing possibility for increasing general effectiveness of business operation. The paper reveals the issues of factor and expert assessments for introducing innovations at the enterprise and economic evaluation of the place of energy-efficient technologies in the general medium of production enterprise modernization. The novelty of the study is an aspect that under conditions of energy products’ cost increase and significant energy intensity of present-day production, the issue of energy conservation and choice of priorities of investment into the project of energy efficiency increase at enterprises is a major concern. Reduction of production cost is one of the most important ways of effective competition and increasing of productiveness of an enterprise in the modern conditions. The authors offer to evaluate the process of energy conservation in a complex way, taking into account all investment consequences: economic, technical, ecological, organizational, commercial, and others. The prospect areas of research: cost-to-use analysis from the introduction of personally developed systems of energy conservation.

Chloride ion ingress into concrete causes steel corrosion over time, thereby ending the service life of structures. Sometimes, it severely reduces the loading capacity of reinforced concrete and may even cause the sudden destruction of concrete structures. Concrete cracking stems from different factors, such as shrinkage and tensile stress due to thermal loading and under loading. Modeling and estimating chloride ion ingress into cracked concrete over different periods can aid the appropriate determination of structural lifetime and maintenance of reinforced concrete structures. Accordingly, this research investigated the effects of the width and depth of concrete cracks on the rate of chloride ion diffusion and rebar corrosion. To this end, different concrete specimens characterized by various cracking conditions were modeled in COMSOL Multiphysics. Analytical results showed that the critical crack that reflected the highest extent of chloride ingress into a specific region at different times was not necessarily the defect with the largest thickness and depth. This finding highlights the importance of investigating crack behavior in the appropriate estimation of structural service life. Nevertheless, over time, considerably wide and deep cracks may ultimately be a reflection of substantial rate of ingress.

Given their unique characteristics, Shape Memory Alloys (SMAs) have significant potential for use in different areas of engineering. The phase shift characteristics of these alloys allow them to memorize a certain shape, and if deformed, revert back to that shape through a thermal process. Given the vast potentials of SMAs, they can be utilized to address the limitation of conventional eccentrically braced frames (EBFs) with vertical links in order to achieve better residual and maximum interstory drifts. This paper presents a vibration control system equipped with SMAs to achieve improved operational domain. The Compared to conventional EBFs, the proposed system named recentering damping device (RDD) is easy to fabricate and implement and allows for the redesign of fuse members. A numerical analysis is performed for a 9-story steel frame building using nonlinear analysis program OpenSees to evaluate the system performance. Results of time history analysis demonstrate better self-centering behavior and lower residual interstory drifts of the proposed system as compared to EBF.

This paper aims to examine flexural vibrations of fully saturated poroelastic structures on an elastic bed subjected to moving point loads via an analytical solution. Using a flexural beam model in conjunction with the Biot’s poro-elasticity theory, the equations of motion of the porous structure are derived. Using assumed mode method and Laplace transform, the explicit expressions of displacement and pore pressure are obtained carefully. For a particular case, the predicted results are also compared with those of another work and a reasonably good agreement is achieved. The influences of the moving load velocity, permeability ratio, transverse stiffness of the foundation, viscosity of the pore fluid, and porosity on the maximum elasto-dynamic fields and pore pressure are conclusively discussed. The velocity pertinent to the maximum possible dynamic response is graphically determined and the roles of influential parameters on this crucial factor are displayed. The present model could be easily extended to multi-layered poroelastic structures under moving loads.