The 1974 edition of IS 4995 Part 2 establishes detailed guidelines for designing reinforced concrete bins intended to store granular and powdery substances. It addresses various bin shapes such as circular and polygonal configurations, specifying structural design principles including allowable stresses, load computations, wall and base design, reinforcement detailing, and stability verification. This standard is crucial for engineers engaged in the structural design of bulk storage bins for materials like cement, fertilizers, and food grains.
Overview
The 1974 edition of IS 4995 Part 2 establishes detailed guidelines for designing reinforced concrete bins intended to store granular and powdery substances. It addresses various bin shapes such as circular and polygonal configurations, specifying structural design principles including allowable stresses, load computations, wall and base design, reinforcement detailing, and stability verification. This standard is crucial for engineers engaged in the structural design of bulk storage bins for materials like cement, fertilizers, and food grains.
Audience
Contents
Structure
This section outlines the scope of design parameters and notation conventions for reinforced concrete bins used to store bulk granular and powdery materials such as cement. It covers circular, polygonal, and interstice bins, defining symbols and units used throughout the standard.
Key definitions and notations relevant to bin design are provided. This includes parameters like cross-sectional area of stored material, reinforcement areas, bin dimensions, modulus of elasticity for materials, and permissible crack widths. The section also presents tables for crack width control and permissible bar diameters.
General requirements for applying the working stress approach are discussed, including consideration of all stress states, monolithic construction effects, and permissible stress limits for various types of steel reinforcement. Tables specify allowable stresses for mild steel, medium tensile steel, high yield steel, and welded wire fabric.
Details on materials used in reinforced concrete bin construction are given, including types of steel bars conforming to IS codes, properties of concrete, and key notations. Construction practices addressing reinforcement placement and tolerances are also summarized.
Comprehensive design criteria are elaborated, covering load considerations such as dead, live, wind, and seismic loads, foundation design as per relevant IS codes, and safety factors. Design formulas for modular ratios, pressure calculations, reinforcement percentages, and thermal moments are included. Stability checks under various load cases are described.
This subsection presents important design parameters such as bin dimensions, reinforcement areas, and load notations. It includes formulas for modular ratio, reinforcement percentage, thermal stresses, and crack width limitations. Design checks for bending moments and safety factors are also discussed.
Permissible stresses for concrete grades and steel reinforcement are tabulated. The section distinguishes between tension, compression, shear, and bond stresses for concrete, and tension and compression limits for different steel types and bar diameters.
Guidelines for designing walls of polygonal and circular bins are provided. Polygonal bin walls are treated as slabs or beams depending on load direction, while circular bin walls are designed primarily for hoop stress. Stability checks for full and empty bin states are also included.
Design procedures for ring girders supporting bins, particularly under conical hoppers, are outlined. Formulas for calculating bending moments and torsional forces based on the number of supports and load distribution are provided along with coefficient tables.
This section describes the approach to designing flat and hopper bottoms of bins, accounting for vertical loads including machinery and impact loads. Use of ring girders and mechanics principles for non-standard hopper shapes is discussed.
The impact of temperature variations on bin structures is analyzed. Key formulas for calculating bending moments due to thermal gradients are provided. Assumptions regarding neglected tensile concrete strength and radial temperature distribution are explained.
Shrinkage in concrete is treated as an equivalent temperature drop, particularly significant near restrained edges. The need for additional reinforcement near such areas to counter shrinkage stresses is emphasized, along with simplified crack width checks.
This segment details criteria for controlling crack widths in reinforced concrete bins, including simplified checks based on reinforcement percentages and bar diameters. Tables with permissible bar sizes and coefficients for crack control formulas are provided.
Load cases for stability checks—covering full and empty bin conditions—are specified. The section includes calculation methods for overturning and sliding resistances, safety factor requirements, and relevant load combinations for lateral and vertical forces.
A summary of minimum mandatory design parameters is presented, including key notations, crack width control thresholds, modular ratio, and reinforcement percentages. Tables assist in determining when detailed crack width assessments are necessary.
Frequently Asked
IS 4995 Part 2 (1974) specifies permissible stresses for concrete and steel used in reinforced concrete bins. Concrete stresses vary by grade, with compression limits ranging from 50 to 130 kg/cm² and shear stresses from 5.0 to 11.0 kg/cm². Tensile bending stresses for concrete are equal to permissible inclined shear stresses. For steel reinforcement, permissible tensile stresses depend on steel type and bar diameter; for example, mild steel bars up to 40 mm diameter have an allowable tensile stress of 1400 kg/cm², while larger diameters have 1300 kg/cm². Medium tensile and high-yield steels have different permissible values as detailed in the standard's tables.
The ring girder design at the junction of conical hoppers must accommodate axial forces, bending moments, torsional moments, and shear forces. Axial forces arise from the horizontal component of the hopper's inclined pull minus lateral thrust from stored material. Bending moments and torsion are calculated considering load distribution, number of supports, and girder geometry using coefficients provided in IS 4995 Part 2. The girder cross-section and reinforcement are then designed to resist these combined stresses, ensuring adequate anchorage of meridional reinforcement into adjoining vertical walls for effective load transfer.
Stability assessments must consider two primary load cases. When the bin is full, all vertical loads—including self-weight, stored material, and frictional wall loads—are considered along with the maximum lateral forces from wind or seismic activity, whichever is more critical. When the bin is empty, vertical loads exclude the stored material and frictional loads but still include dead and live loads, combined with maximum lateral loads. These comprehensive load combinations ensure safety against overturning, sliding, and structural failure.
The standard mandates that interconnected polygonal bins without interstices be designed considering the worst-case load combinations where adjoining bins are alternately full or empty, focusing on the junction walls. For bins with one interstice, two critical scenarios must be evaluated: one where the interstice bin is empty and adjacent bins are full, and another where the interstice bin is full while the adjoining bins are empty. This approach ensures structural integrity under varying load distributions in connected bin assemblies.
Although IS 4995 Part 2 does not explicitly provide detailed rules for openings, it requires that openings must not undermine the bin wall's capacity to withstand combined vertical (including frictional) and lateral loads under full and empty conditions. Walls with openings should be reinforced adequately around the perimeter to compensate for reduced cross-sectional area, typically with vertical reinforcement not less than 0.2% of the cross-sectional area for single or exterior walls. The design should treat these walls as deep beams or two-way slabs, ensuring stress concentrations are managed to maintain overall stability.
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