This code outlines detailed procedures for designing and building reinforced concrete foundations tailored for self-supporting radar antennas, microwave, and TV towers. It emphasizes considerations like uplift forces, soil bearing capabilities, settlement control, and structural integrity under environmental loads such as wind and seismic actions. The standard serves as a vital reference for engineers focusing on foundation stability and safety in telecommunications infrastructure.
Overview
This code outlines detailed procedures for designing and building reinforced concrete foundations tailored for self-supporting radar antennas, microwave, and TV towers. It emphasizes considerations like uplift forces, soil bearing capabilities, settlement control, and structural integrity under environmental loads such as wind and seismic actions. The standard serves as a vital reference for engineers focusing on foundation stability and safety in telecommunications infrastructure.
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Structure
Frequently Asked
The code recommends several foundation types for radar antenna and TV towers including isolated footings beneath each tower leg, combined raft foundations with or without beams, annular or ring foundations particularly for circular RCC towers, pile foundations, rock anchors for towers on rocky terrain, and combinations such as isolated footings paired with piles or rock anchors. Special attention is given to uplift loads, especially for tall self-supporting towers, with strict limits on allowable total and differential settlements to ensure structural integrity.
Uplift forces are addressed through various means depending on foundation type. For shallow foundations, uplift resistance is provided by the combined weight of the footing and an inverted frustum of soil with side slopes up to 30° from vertical. In pile foundations, uplift is resisted via friction along the pile shaft and bearing on annular projections, with safety factors applied. Enlarged footings require that the resultant vertical and lateral forces remain within one-sixth of the footing width from the toe for stability. Rock anchors are designed as per referenced standards to counter uplift forces effectively.
Before foundation design, comprehensive soil investigations must be conducted including detailed subsoil profiling to at least 10 meters depth or twice the foundation width, assessment of physical and strength properties of soil layers, groundwater level monitoring with seasonal variations, and evaluation of soil aggressiveness. Tests such as bore logs, Standard Penetration Tests (SPT), dynamic core penetration tests, consolidation tests for compressible soils, and determination of compression coefficients are essential to provide a thorough geotechnical report supporting safe, efficient foundation design.
Pile foundations should be designed ensuring the load per pile does not exceed safe vertical and horizontal capacities, considering group effects for multiple piles. Uplift resistance is calculated based on shaft friction and bearing on annular under-reamed projections, applying a factor of safety of 3. Multiple under-reamed piles or rock anchors are recommended for loads involving significant uplift or moments. The design also incorporates the weight of pile caps and the overlying soil cone to counteract uplift forces, following safety factors specified in the code.
The code specifies safety factors typically ranging between 2.5 and 3.0 for soil bearing capacity to ensure stability against failure. Permissible stresses for concrete and reinforcement align with IS 456 and IS 800 standards respectively, following working stress design principles. Soil bearing pressures should not exceed the safe bearing capacity after factoring in these safety margins. For uplift and lateral loads, structural stresses must remain within permissible limits to prevent failure. Additionally, the code allows for increases in permissible bearing pressure due to moments, usually up to 25-30%, based on load distribution.
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