Design Aids For Is: 800 Draft Code

Abstract

Till the late 1960’s, structural steel design was based on Working Stress Method (WSM) all over the world. The more modern Limit State Method (LSM) design approach which was developed in the early 1970’s has been proved to be technologically sound and resulted in significant economy in the completed structures. So, realizing the advantages of Limit State Method (LSM), the Bureau of Indian Standards, IIT Madras and Institute for Steel Design and Growth (INSDAG) Kolkata, together have introduced a draft of IS:800 (LSM Version).

The use of Limit State Method in design of steel structures is a completely new methodology for steel designers in India presently. The designers are familiar with the philosophy of LSM as it is being used in the design of concrete structures but LSM in the design of steel structures considers completely different design considerations. Parameters like fatigue, ultimate strength, member end connections, restrains and many more have great influence on the design considerations. This makes the design of steel structures using IS: 800 (LSM Version) complicated and time consuming for new users. Hence providing design aids to facilitate steel design using IS: 800 (LSM Version) would prove to be very useful and will lead to quick implementation of the new revised IS: 800 as soon as it is published.

So an attempt has been made here in preparation of design aids for IS: 800 (LSM version) using the draft code.

Design aids for angle sections subjected to tension are prepared and presented in the form of solved examples. Capacities of various angle sections i.e. single as well as double, in tension and compression have been calculated for both welded and bolted end connections. The capacities for above mentioned cases have been calculated using draft copy of IS: 800 (LSM Version) and only few cases are compared with those calculated by working stress method using IS: 800-1984. Design of tension member is also been carried out according to IS: 800 draft code. All strength governing factors like yielding of gross section, rupture of critical section and block shear are considered in calculating tension carrying capacity of sections. In calculation of compression carrying capacity, aspects like slenderness ratio, Euler buckling stress, imperfection factor, stress reduction factor, partial safety factor for material and local buckling are considered.

An interactive set of charts calculating tension design capacity of angle sections are been prepared using MS-Excel. A computer program for tension carrying capacity calculation and design of tension member using IS: 800 draft code for angle section is been prepared using Visual Basics whose sample code is been presented.

Flexure member design for laterally restrained and unrestrained beams is shown using design steps, flowchart and solved example. Flexural capacities of all Indian rolled steel I-sections are calculated and charts for design are drawn in MS-Excel. A comparison of flexural capacities of laterally restrained and unrestrained beams is made which is presented in the form of bar charts. An application for flexural capacity and design of laterally restrained and unrestrained beams is prepared in visual basics.

Design for biaxial bending of compression member i.e. beam-column is shown using design steps, flowchart and solved example. Axial load carrying capacity and moment carrying capacity under axial compressive load and biaxial moment of all Indian rolled steel I-sections are calculated as per IS: 800 draft code. Chart for section strength check of ISMB500 with varying P/Pu ratio are plotted and the same work is generalized for all Indian rolled steel I-sections with P/Pu ratio varying upto 0.4. An application for capacity calculation and design for biaxial bending of compression member is prepared in visual basics.