The standard outlines detailed procedures and specifications for designing and building jack-arch style built-up floors and roofs, which integrate brick arches with lime concrete layers supported on steel or concrete joists. It serves as a crucial reference for engineers, architects, and construction experts to ensure structural soundness, durability, and correct use of materials in such composite flooring and roofing systems.
Overview
The standard outlines detailed procedures and specifications for designing and building jack-arch style built-up floors and roofs, which integrate brick arches with lime concrete layers supported on steel or concrete joists. It serves as a crucial reference for engineers, architects, and construction experts to ensure structural soundness, durability, and correct use of materials in such composite flooring and roofing systems.
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Contents
Structure
Frequently Asked
The code specifies that bricks should comply with IS 1077-1976, commonly sized at 190 mm × 90 mm × 40 mm, suitable for jack-arch applications. These bricks are laid on edge in a single course using lime or cement mortar with an appropriate mix ratio. Lime concrete topping, made with broken brick aggregates, is applied over the arch for finishing. Aggregate grading and mix design should facilitate adequate compaction and strength, generally following IS 383 and IS 456 guidelines.
Steel joists should be designed following IS 800-1962. Tie rods, made from mild steel conforming to IS 432 (Part I)-1966 and IS 226-1975, must have a minimum diameter of 12 mm. They are positioned approximately 75 mm above the joist bottom flange, with spacing not exceeding 20 times the flange width. Anchorage uses robust mild steel washers or angle irons, and for thin end walls, a separate encased beam is recommended to secure tie rod ends, ensuring structural stability and proper load transfer.
Recommended mixes involve combining lime mortar or lime-pozzolana mortar with broken brick coarse aggregates complying with IS 3068-1975. Preparation entails evenly spreading lime over the aggregates, mixing thoroughly by turning the blend at least four times, then adding sufficient water to uniformly coat the aggregates without excess. Mortar mixing follows IS 2250-1980 and IS 2541-1974 standards, ensuring a consistent and durable lime concrete suitable for jack-arch applications.
Curing periods stipulated include a minimum of six days of water sprinkling for concrete before applying floor or roof finishes. Terrace and ceiling surfaces require extended curing of at least three weeks. Supporting structural components like walls, columns, and beams must be completed and properly cured, typically seven to fourteen days or as per design, before the jack-arch flooring or roofing work begins. These durations ensure adequate strength and durability before further construction.
The standard mandates that joists at junctions rest on walls or parapets over cement concrete or stone bed blocks, or steel bearing plates, to evenly distribute loads and avoid local crushing of masonry. Jack-arches are constructed with bricks laid on edge in mortar and topped with a leveling lime concrete course at least 60 mm thick, providing a smooth transition. The floor or roof finishes are applied atop this leveling course, and ceiling finishes continue up to the wall junction, ensuring stable load transfer and structural integrity at these critical connections.
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