IS 13920:1993 outlines detailed practices for ductile reinforcement detailing in reinforced concrete structures to withstand seismic forces effectively. This standard serves as a critical resource for engineers and designers focused on earthquake-resilient monolithic concrete constructions, emphasizing enhanced ductility and toughness through proper detailing.
Overview
IS 13920:1993 outlines detailed practices for ductile reinforcement detailing in reinforced concrete structures to withstand seismic forces effectively. This standard serves as a critical resource for engineers and designers focused on earthquake-resilient monolithic concrete constructions, emphasizing enhanced ductility and toughness through proper detailing.
Audience
Contents
Structure
IS 13920 prescribes ductile detailing requirements for reinforced concrete structures subjected to seismic loading. It defines essential symbols and parameters such as factored shear forces, effective depths, reinforcement inclination angles, and material strengths, including concrete compressive strength and steel yield stress. The standard mandates factoring dead and live loads by 1.2 for shear design and stipulates minimum and maximum reinforcement ratios to ensure ductility and structural resilience.
This section consolidates critical equations and material properties relevant to seismic detailing, including calculations for factored shear forces at beam ends, shear resistance at joints, and reinforcement needs. It also covers the geometric properties of the neutral axis, diagonal reinforcement angles in coupling beams, and the elastic modulus of steel. The section includes key figures illustrating design shear forces, joint detailing, and special confining reinforcement.
Clarification of important definitions and symbols used throughout the standard, such as shear forces, neutral axis depth, and reinforcement areas. Tables provide the meaning, units, and typical values for parameters like diagonal reinforcement inclination, effective depths of members and walls, and nominal shear stress.
Outlines the overall requirements for shear force calculations at beam ends, detailing of reinforcement to resist factored shear forces, and the specification of material strengths. It emphasizes the calculation of neutral axis depth for flexure-shear interaction and the necessity of ductile detailing conforming to IS 13920 and related standards.
Details the material characteristics vital for seismic-resistant design, including concrete compressive strength, steel yield stress, and elastic modulus. It specifies the use of Fe 415 and Fe 500 grade steel as per IS 1786 and provides formulas for calculating vertical reinforcement ratios and neutral axis depths.
Describes procedures for calculating shear forces on beams, including factored shear at beam ends and joints, and the corresponding reinforcement requirements. It covers diagonal reinforcement inclination, nominal shear stress calculations, and specifications for minimum and maximum reinforcement, anchorage, and development lengths to ensure ductile performance under seismic forces.
Focuses on calculating design shear forces on columns considering axial loads and seismic effects. It prescribes special confining reinforcement detailing in plastic hinge zones with maximum hoop spacing of 300 mm or less, transverse reinforcement requirements, minimum longitudinal bar provisions, and development length criteria to secure ductility and confinement.
Provides guidelines for the design of coupling beams in coupled shear wall systems, including shear stress limits triggering the use of diagonal reinforcement. It specifies formulas for calculating diagonal reinforcement area and anchorage lengths, with emphasis on anchoring bars into adjacent walls to ensure energy dissipation and structural integrity during seismic events.
Details minimum longitudinal and transverse reinforcement ratios for shear walls, uniformly distributed across the cross-section. It addresses shear and flexural strength calculations incorporating concrete and reinforcement contributions, boundary element detailing, reinforcement around openings and joints, and development length requirements for anchorage.
Specifies requirements for development length in tension, lap splice lengths, and hoop/tie spacing over splices. It restricts lap splice locations away from joint faces and flexural yielding zones and limits the percentage of bars spliced at any section to a maximum of 50%, ensuring proper load transfer and ductility.
Covers detailing requirements for construction joints including minimum vertical reinforcement ratios to resist factored shear stresses. For openings in walls, reinforcement along the edges must match interrupted bar areas, with vertical bars extending full storey height and horizontal bars having adequate development lengths beyond openings to maintain continuity.
Prescribes length and placement of special confining reinforcement extending from joint faces into adjacent member spans, not less than the largest lateral dimension, one-sixth clear span, or 450 mm. It mandates hoops with crossties for confinement, especially in columns with large cross sections, and advises checking shear demands to use the higher transverse reinforcement requirement.
Defines discontinuous walls as those not spanning full column height and requires special confining reinforcement around supporting columns extending at least 300 mm beyond the discontinuity. The detailing includes closely spaced ties or hoops with hooks to ensure ductility and confinement, preventing brittle failure near wall terminations.
Details calculation methods for factored shear forces, shear resistances, and the shear force carried by reinforcement. It also provides formulas for nominal shear stress and flexural moment capacity, considering effective depth, steel yield strength, concrete compressive strength, and neutral axis depth to ensure structural adequacy under seismic loads.
Includes annexes such as formulas for moment of resistance of rectangular shear walls with vertical reinforcement and lists the members of the Earthquake Engineering Sectional Committee (CED 39) responsible for the code development. The annex details parameters used in design like wall thickness, reinforcement areas, and axial loads.
Frequently Asked
Per IS 13920 Clause 9.1.4, the minimum reinforcement ratio for shear walls subjected to seismic forces is 0.25% (0.0025) of the gross cross-sectional area in both longitudinal and transverse directions. This reinforcement must be uniformly distributed throughout the wall section. Additionally, if the factored shear stress exceeds 0.25 times the square root of the concrete compressive strength or if wall thickness exceeds 200 mm, reinforcement must be provided in two layers in both directions to ensure ductility.
IS 13920 requires special confining reinforcement at column ends extending through the joint, with hoop spacing not exceeding 150 mm in joints. If beams frame into all four faces of a column and have widths at least three-quarters of the column width, half the special confining reinforcement may be provided through the joint. For beams framing into columns, minimum two bars are required on top and bottom faces where columns project beyond the confined core by more than 100 mm. Elsewhere, hoop spacing should not exceed d/4 or 8 times the longitudinal bar diameter. These detailing rules ensure adequate confinement and ductility in seismic zones.
Lap splices must be located within the central half of a member's length and should not be placed within joints, within a distance of twice the effective depth (2d) from the joint face, or within one-quarter length of flexural yielding zones. The lap length must be at least equal to the development length in tension (Ld). Hoops or ties must be provided over the entire lap splice length with maximum spacing of 150 mm. For bars larger than 16 mm diameter, tie diameter should be at least one-quarter of the bar diameter or 6 mm minimum. Additionally, no more than 50% of bars should be spliced at a single section to maintain structural integrity.
The code specifies that coupling beams must be designed for ductility to dissipate seismic energy effectively. If the shear stress induced by earthquake forces exceeds 0.25 times the square root of the concrete compressive strength, diagonal reinforcement must be provided to resist both shear and flexure. The area of diagonal reinforcement is calculated based on the shear force, steel yield strength, and reinforcement inclination angle. Anchorage lengths for diagonal and horizontal bars must be at least 1.5 times the development length in tension, ensuring proper load transfer into adjacent walls.
IS 13920 permits the use of Fe 415 grade steel as standard reinforcement per IS 1786:1985. Additionally, high-strength deformed bars such as Fe 500 and Fe 550 grades with elongation exceeding 14.5% are allowed, provided they comply with the same specification. Concrete and steel materials must conform to IS 456:1978 and IS 1786:1985, respectively, ensuring sufficient ductility and strength for seismic resistance. The minimum tension steel ratio is defined as 0.24 times the characteristic compressive strength of concrete divided by the steel yield strength.
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