Analysis and Design of Multi-Storeyed Building in Steel Using IS 800 Draft Code

Abstract

Institute of steel development & Growth and Ministry of Steel, the bureau of Indian Standards, has jointly circulated a new draft IS: 800, based on Limit State Method. In Introduction to Limit State, the design philosophy is based in probabilistic approach. The design is based on characteristic values for material strengths and applied loads, which take into account the probability of variations in the material strengths and in the loads to be supported. In Limit State Method of design partial safety factors for both material and load variability is considered. In Limit State Method of IS: 800 – Draft, there are separate partial factors for material strengths and applied loads & load combinations.

In India, most of multi-storey buildings are made in concrete. With recent development in steel, it can be possible to construct it in steel. An attempt is made to design 10 storey building in steel using IS: 800 – Draft having RC voided slab. RC voided slab is used to minimise the weight of the slab and to economize section of beam & column which ultimately reduces the total weight of the structure.

The shear connector is designed for full shear connection using eurocde 4 as a composite beam element. The flow chart of the design of flexural member including bearing stiffener is prepared and the built up I section is designed as a laterally restrained beam with all necessary checks such as check for section classification, check for section modulus, check for shear, check for bearing stiffener, check for outstand and check for buckling as per IS 800 Draft. A computer application for the flexural member is prepared in c++ for ISMB, ISWB and ISLB sections. It also provides the percentage strength of the Indian rolled steel I sections. The beam flange and web splices having bolted connection are designed with the use of HSFG bolts as per IS 800 Draft considering reduction in strength due to bolt holes.

The box column with perforated plates and 4-ISA at corners is designed as a beam-column for the governing load condition with all necessary checks i.e. check for section strength, check for slenderness ratio, check for overall member strength, check for shear and check for clear distance between perforations. Also design moment capacity about major axis is reduced due to lateral torsional buckling about minor axis as mentioned in the IS 800 Draft code. This phenomenon is similar to beam column designed by IS 800-1984 where permissible stress about major axis is reduced as compared to permissible stress about minor axis i.e. 0.66fy. Also as an economical section, the comparision of the designed column with the section 2ISHB with cover plates is provided.

Moment resisting welded connections are designed for the tensile force (caused by hogging moments) at the top flange of the beam which is transferred to the top flange plate by fillet welds and from the plates to the column by groove welds. Also stiffening seat at the beam bottom is designed for shear considering its safe bearing length.

The column splices (lap joints) are designed for minimum required strength 0.6 times fyAf for each flange splice and 0.6 times fyAw for each web splice with the partial penetration groove welds considering design strength of the joints of at least equal to 200% of the required strength as mentioned in IS 800 Draft code. The moment resisting column bases are designed with the welded stiffening plates which is provided at all four sides of column. Also HSFG bolts are provided to resist the tension in the base.

Also the effect on drift due to change in the orientation of column is studied. In the analysis of 30 storeyed steel building, the tube in tube structural system is used to resist the lateral loads and the behavior of building as vertical cantilever and shear lag effect is studied.