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Investigation into the Behavior of Cylindrical Steel Silos Composed of Flat or Corrugated Sheets

Moazezi Mehretehran, Alireza | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 52228 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Maleki, Shervin
  7. Abstract:
  8. Steel cylindrical silos are one of the most practical structures in handling and storage of bulk solids in many industries and agricultural sectors. Steel silos may be composed of flat or corrugated sheets. Due to small wall thickness, shell structures are vulnerable to buckling failure. Unsymmetrical loading conditions rising from frequent filling and discharge cycles during the lifetime of these storages are almost the main reason for local or global instability of silos. However, they may experience additional lateral loads such as, wind load and seismic load that essentially impose unsymmetrical pressure on shell walls and can lead to buckling, as well. Under wind pressure, steel cylinders mainly buckled due to circumferential compression formed in the windward zone. Under seismic action, lateral loadings impose transverse shear load that can make diagonal shear wrinkles. Nevertheless, because it also causes global bending of cylinder, diamond-shaped buckles due to axial compression near the lower end of the silos can also occur. At high internal pressure, this diamond-shape could be replaced by a local elastic-plastic bulge near the base known as the elephant’s foot buckling mode. Steel corrugated silos stiffened with vertical stiffeners are widely used for grain storage in Iran, currently. However, few researches have been carried out to assess the buckling behavior of these structures, especially under wind and seismic actions. In this research, considering the design procedures put forward by Eurocode as the most advanced available code for buckling analysis and design of steel shells, comprehensive studies have been conducted on buckling behavior of silos (both with flat and corrugated sheets) under different lateral loads. In more detail, incremental dynamic analysis (IDA) was selected for buckling assessments under seismic action and global numerical buckling analysis, which is a quasi-static finite element method, was utilized for wind buckling resistance evaluations. Accordingly, four distinct study programs have been covered in this research and in each case, relevant conclusions have been made. These studies were classified as follows: 3D buckling assessment of steel silos with uniform wall thickness under seismic action, 3D wind buckling assessment of steel silos with flat stepped walls, 3D seismic buckling assessment of steel silos with stepped walls under horizontal and vertical base excitations and finally, 3D wind buckling of steel corrugated silos with vertical stiffeners. Regarding to these study programs, the main novelties of this research are as follows: 1) Studying the effect of seismic actions on behavior of steel flat sheets silos using IDA, 2) Quasi-static analyses of flat sheets silos under wind and discharge loads introduced in Eurocodes, 3) Comparing the buckling capacities of the silos obtained under seismic actions with those calculated under wind actions or discharge loads and 4) Analyzing the buckling performance of steel corrugated silos under wind pressures with special emphasis on dimensional characteristics of sinusoidal corrugated sheet profiles and making relevant comparisons with an equivalent flat sheets silo. Considering the performed analyses, the outstanding results and conclusions can be summarized as follows: 1) The ratios of critical intensity measure (IM) of base excitations in terms of peak ground acceleration (PGA) that cause elephant’s foot buckling in slender silo with respect to intermediate slender and squat silos are 0.64 and 0.40, respectively. Therefore, slenderer silos are more vulnerable to this form of buckling failure, 2) Wind buckling capacities of steel silos with closed roof are about 40% more than vented silos with small opening on the roof. Also, silos in a group show 7-20 percents smaller buckling resistances as compared with isolated silos, 3) The Eurocode buckling strength interaction expression for the buckling stress design of stepped cylinders, yields satisfactory predictions, while the procedure for converting wind distribution to an equivalent uniform external pressure, results in a rather rough estimation of critical wind pressure, 4) In the case of steel flat sheets silos with stepped walls, as the silo aspect ratio varies from slender to squat, the first dynamic buckling mode alters from the elephant’s foot buckling to the elastic shear wrinkle mode. Moreover, the effect of vertical component of seismic records on dynamic buckling of steel silos was assessed and concluded to be marginal, 5) According to seismic hazard map and wind zone map of Europe, it was concluded that seismic action in high hazard areas can dominate the buckling design compared to wind action for intermediate slender and squat silos. Also, seismic action for slender silos can govern the elastic-plastic elephant’s foot buckling mode in moderate and high hazard areas as compared with discharge load and thus should be specially considered in buckling design of these structures and 6) The depth of sinusoidal corrugation profile is a significant strength parameters in wind buckling capacities of steel corrugated silos (e.g., a silo with 18 mm depth corrugated sheet profile as compared with a 10 mm one showed about 2 times more buckling resistance under the same wind pressure). Furthermore, corrugated silos are much lighter structures as compared to flat sheets silos (e.g., a sample corrugated silo considered in this study is about 3 times lighter than an equivalent flat sheets one with similar buckling capacity)
  9. Keywords:
  10. Steel Silos ; Lateral Loading ; Buckling ; Numerical Analysis ; Euro Codes

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