Special earthquake-resistant concrete
The provisions for reinforced concrete construction given in this standard apply specifically to monolithic reinforced concrete construction. Provisions on minimum and maximum reinforcement have been elaborated which includes the requirements for beams at longitudinal reinforcement in beams at joint face, splices and anchorage requirements. Provisions have been included for calculation of design shear force and for detailing of transverse reinforcement in beams.
Material specifications are indicated for lateral force resisting elements of frames.
Earthquake-Resistant Design of Reinforced Concrete Structures: Shortcomings of Current Methods
The provisions are also given for detailing of reinforcement in the wall web, boundary elements, coupling beams, around openings, at construction joints, and for the development, splicing and anchorage of reinforcement. This standard covers the selection of materials and techniques to be used for repair and seismic strengthening of damaged buildings during earthquakes.
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It also covers the damageability assessment and retrofitting for upgrading of seismic resistance of existing masonry buildings covered under IS and IS These are based on damaging seismic intensities VII and more on M. Intensity scales.
The scheme of strengthening should satisfy the requirements stipulated for the seismic zone of IS Part-1 , building categories of IS and provisions made in this code and in IS for low strength masonry building. No special seismic resistance features are considered necessary for buildings in seismic Zones II, but the important buildings in this Zone may also be considered for upgrading their seismic resistance.
The buildings affected by earthquake may suffer both non-structural and structural damages. Guidelines have been given for selection of materials for repair work such as cement, steel, epoxy resins, epoxy mortar, quick setting cement mortar and special techniques such as shotcrete, mechanical anchorage etc.
Seismic strengthening techniques for the modification of roofs or floors, inserting new walls, strengthening existing walls, masonry arches, random rubble masonry walls, strengthening long walls, strengthening reinforced concrete members and strengthening of foundations have been elaborated in detail. This standard deals with the safety of structures during underground blasting and is applicable to normal structures like buildings, elevated structures, bridges, retaining walls, concrete and masonry dams constructed in materials like brickwork, stone masonry and concrete.
As underground blasting operations have become almost a must for excavation purposes, this standard lays down criteria for safety of such structures from cracking and also specifies the effective accelerations for their design in certain cases. This standard covers the criteria for design of structures for blast effects of explosions above ground excluding blast effects of nuclear explosions.
This standard covers recommendations for instrumentation for investigation of seismicity , study of micro tremors and predominant period of a dam site and permanent installation of instruments in the dam and appurtenant structures and in surrounding areas. These standards endeavour to provide a guideline in designing and repairing of buildings under seismic forces. For the case of cyclic loading, however, the longitudinal extension of criss-crossing inclined cracking within noncritical regions was found to destroy the bond between concrete and steel, thus leading to premature reduction of the strength and energy-absorption capacities of all the structural elements tested.
It appears, therefore, that an efficient earthquake-resistant design method must also safeguard against failure associated with bond destruction. Click here to become an online Journal subscriber. ACI Materials Journal. CI Magazine.
ACI Collection Online. It is based on an experimental investigation of the behavior of simply supported two-span linear elements designed from first principles by using methods based on two contrasting concepts: the truss analogy as applied by the design methods incorporated in current codes of practice and the compressive-force path concept.
These elements were tested under both monotonic and cyclic transverse loading combined with a constant axial-compressive concentric force. The results of the tests indicated that not only does the truss analogy not safeguard against a brittle type of failure in the region of the point of inflection, but it may, in fact, cause such a failure in regions heavily reinforced with stirrups widely referred to as critical lengths.
In contrast with the truss analogy, the compressive-force path method was found to yield design solutions that fulfil the code requirements for strength and ductility for the case of monotonic loading. For the case of cyclic loading, however, the longitudinal extension of criss-crossing inclined cracking within noncritical regions was found to destroy the bond between concrete and steel, thus leading to premature reduction of the strength and energy-absorption capacities of all the structural elements tested.
It appears, therefore, that an efficient earthquake-resistant design method must also safeguard against failure associated with bond destruction.
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