The IS SP Part 43 (1987) serves as a detailed guide for the design and structural detailing of reinforced concrete portal frames excluding crane provisions. It encompasses analytical methods, load considerations including wind and seismic effects, material grades, and detailing practices for various spans, roof inclinations, and support configurations. This handbook is vital for professionals engaged in ensuring the durability and safety of portal frame structures in industrial and commercial constructions.
Overview
The IS SP Part 43 (1987) serves as a detailed guide for the design and structural detailing of reinforced concrete portal frames excluding crane provisions. It encompasses analytical methods, load considerations including wind and seismic effects, material grades, and detailing practices for various spans, roof inclinations, and support configurations. This handbook is vital for professionals engaged in ensuring the durability and safety of portal frame structures in industrial and commercial constructions.
Audience
Contents
Structure
This section defines the parameters covered by the handbook including spans up to 30 meters, frame spacings of 6 and 12 meters, column heights between 5 and 12.5 meters (inclusive of 0.5m embedment), roof slopes of 1:3, 1:4, and 1:5, fixed and hinged supports, and applicability across wind zones I to III and seismic zones I to V. The design approach utilizes the stiffness method via computer analysis, incorporating internal pressure and suction as specified by IS 875-1964. Concrete grades M25 and M40 are applied for portal frames and purlins, with prismatic rafters and columns designed according to support conditions. The section also outlines the inclusion of design examples for purlins, cladding runners, brackets, and foundation forces.
Details on material grades are provided with M25 concrete and Fe 415 steel reinforcement as standard. Design tables offer steel and concrete quantities for various frame types, including hinged gable frames. Purlin spacing varies by roof slope and is tabulated for exterior and interior rafters. Support conditions are elaborated with hinged bases recommended for all wind and seismic zones. Foundation forces and bracing design are supported with tabulated values and diagrams.
Ultimate design forces including bending moments, compressive and shear forces are tabulated for different frame sections. The handbook distinguishes between dead, live, and wind loads and their combined effect on foundation forces at service load stage. Load combinations follow prescribed factors to ensure safety under varying scenarios.
Key design force parameters such as hogging and sagging bending moments, compressive axial forces, and shear forces are summarized across frame sections. The section clarifies the nature of these forces, typical load combinations during service, and presents formulas for calculating ultimate design forces incorporating load factors.
This portion outlines the structural analysis methodology applying the stiffness method for frames with specified spans, column heights, slopes, and support types. It provides design ultimate forces and foundation forces tables for various sections under different load cases. The analysis caters to all wind and seismic zones and incorporates service load considerations.
Design of primary rafters is detailed using cross-sections of 400 mm by 800 mm with M25 concrete and Fe 415 steel. Effective depth calculations, factored hogging moments, and relevant flexural design formulas from IS 456 are provided. Purlin numbers and spacing for various roof slopes and support conditions are tabulated.
Typical column dimensions and heights including embedment depth are specified. Support conditions (fixed and hinged) and their influence on design forces are discussed. Design forces including bending moments, axial loads, and shear forces are tabulated for different sections and load cases. Examples of ultimate moment calculations and design checks per IS 456 are included.
The importance of bracing for longitudinal stability against wind loads is emphasized. Bracing locations at rafter and column levels, types of bracing (compression, tension, vertical), and their design parameters depending on building geometry and wind zones are covered. Typical spacing and frame details are provided, along with force calculation formulas.
Foundation design is guided by axial, bending, and shear forces at service load stages. Tables provide ultimate and service load forces for various sections under dead, live, and wind loads. Notes on the application of these forces for foundation bearing checks and design are included alongside relevant formulae.
Detailing requirements for precast structures with 12m spans include stirrup spacing, development lengths, and mechanical connection provisions for joints. Handling and erection holes, bracing details, and reinforcement layout are specified with reference drawings and tables. Emphasis on ductility and connection safety is highlighted.
Guidelines for precast eaves beams, including stirrup spacing and ductility detailing, are described. Joint and lifting details with reference to drawings for safe handling, mortar bedding for precast columns on foundations, rafter connection welding methods, and bracing construction details are given. General considerations for joint location and erection methods are also discussed.
Standard roof slopes of 1:3, 1:4, and 1:5 are covered along with corresponding frame spacings of 6 and 12 meters. Span and column height variations are tabulated. Purlin numbers and spacing for fixed support frames across slopes and wind/seismic zones are provided with dimensional details.
Support types including fixed and hinged are defined with typical parameters and their influence on design forces. Tables summarizing spans, spacings, column heights, and support conditions are included. Purlin arrangement and spacing under different slopes and supports are detailed with notes on wind and seismic zone considerations.
This section presents example design tables and drawings for portal frames, allowing adaptation for different materials or section dimensions. Usage guidelines for tables and drawings in preliminary and detailed design stages are provided. An adaptation formula for scaling moments, shear, and axial forces with changed section properties is included.
The final section lists key references, including design tables for various frame configurations, roof slopes, support types, and load zones. It summarizes design specifications per IS 456 and IS 875 standards, and provides sample design force data and material estimation guidance.
Frequently Asked
The standard specifies M25 concrete for portal frames and RCC purlins of 6 meters span, while M40 concrete is required for prestressed concrete purlins of 12 meters span. Foundations typically use M15 concrete. Reinforcement steel grades include Fe 415 or Fe 500 for concrete reinforcement, whereas structural steel sections follow IS 800 guidelines, commonly utilizing Fe 250 or Fe 410 grades. These material selections ensure structural integrity and compatibility with design loads.
Wind loads predominantly influence the design of low-rise reinforced concrete portal frames, often producing greater member forces than seismic loads, even in strong earthquake zones. For seismic zones with a seismic coefficient of 0.05 or higher, the standard mandates special ductile detailing of joints per IS 4326:1976 to enhance seismic performance. Analysis uses the elastic stiffness method considering dead, live, and wind loads. Lateral loads transverse to the frame are resisted by frame action, while longitudinal lateral loads are managed through column bracing.
The code considers fixed and hinged support conditions. Fixed supports restrain both translation and rotation, resulting in higher bending moments and design forces. Hinged (pinned) supports allow rotation but restrain translation, leading to lower bending moments but potentially increased shear and axial forces. The selection of support type affects moment distribution and ultimate forces, influencing structural safety and economy.
Bending moments and shear forces are determined by analyzing dead, live, and wind loads separately for frames of various spans (9m, 12m, 18m) and roof slopes (1:3, 1:4, 1:5). Wind loads depend on roof slope and frame geometry, affecting load distribution. The frames are generally assumed fixed at supports for moment calculations. The calculations employ load coefficients and projected areas to compute wind forces, and tabulated results provide section-wise moments and shears.
For seismic zones IV and V, the standard requires ductile detailing of joints with adequate stirrup spacing and development lengths per IS 4326-1976. Precast portal frames must have mechanical connections such as pins, welded rods, and cover plates to assure joint safety. Stirrups are specified at a maximum spacing of 100 mm or H/6 or effective depth, whichever is greater. Bracing details include steel gusset plates and RCC bracing to ensure lateral stability and ductility.
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