02-05-2013, 02:29 PM
STEEL STRUCTURES AND ITS APPLICATIONS IN INDUSTRIAL BUILDINGS
STEEL STRUCTURES.pptx (Size: 618.67 KB / Downloads: 127)
Objective:
Industrial steel building is a special type of framed structure with one storey height.These are used for automobile industries, metal industries, thermal power stations,textile mills, storage, manufacturing units, small scale industries etc.
INTRODUCTION:
Industrial buildings are low rise steel structures that do not normally have interior floors, walls and partitions. Industrial steel buildings are used for steel plants, metalindustries, thermal power stations, small scale industries etc. The roofing system of such buildings is a truss with roof covering. The walls are non load bearing but must be adequately strong to resist lateral forces due to wind or earthquakes. The roof truss together with the supporting column is called a bent. The length of an industrial building is divided into bays. A bay is a space between two adjacent bents. Thestructural engineer has to consider the following points for the design of the steel buildings
:1.Structural framing scheme
2.Roof and side cladding material
3.Purlins and sag rod
s4.Roof trusses
5.Cranes, columns and base footings&Bracing system
STRUCTURAL FRAMING SCHEME:
A structural framework consists of steel trusses supported over columns making atransverse bent, and the horizontal bent is formed by joining the transverse bents
Depending on the need of the industry, the size of various members is adjusted sothat the following requirements are fulfilled:
(a)Adequate horizontal and vertical clearances: Generally, column spacing (baylength) is kept between 3m to 12m, truss span varies between 6 to 42m, theheight up to crane rail level varies from 4 to 15m.
(b)Sufficient light and greater flexibility for present and future needs: Therequirements of good lighting are its intensity and uniformity. Frequently daylight have to be supplemented by electric lamps to suffice for themanufacturing process. Whatever source is used the light should be of uniform intensity without shadows or glare. North light is therefore superior because it does not admit direct sun and only diffused light enters the building. Also, for lighting and ventilation of a space where people work, awindow area at least one eighth of the floor area must be provided in the wallsor the roof.
©minimum consumption of steel
(d)structurally efficient system
Structural frame of an industrial building:
The framing scheme is developed after making a schematic layout of an industrial building. The steps of structural framing system are:
(i)The column rows are first located according to clearance requirements.Generally, the column rows at wide distances and with large trusses areeconomical than closely spaced columns and short span trusses
CRANE GIRDERS, GANTRY GIRDERS AND CRANE COLUMNS:
Gantry girders are laterally unsupported beams that are provided in industrial buildings to carry cranes. The cranes are provided to lift and transport heavy jobs,machines etc. from one place to another. A typical arrangement of a crane system isshown in Fig. 1.8. The crane consists of a bridge made up of two truss girders. This bridge is called the crane girder or crab girder. It spans the bay of the shop andmoves in the longitudinal direction. To facilitate movement, wheels are attached atthe ends of Crane Bridge. These wheels move over rails placed centrally over thegirders called the gantry girders. Fig.shows the typical sketches of the cranegirder, gantry girder and the column. Some types of sections of the gantry girder areshown in Fig. Since the gantry girder is the major part of industrial buildings,its design is dealt in detail.
BRACING SYSTEM:
The bracings are provided to increase lateral rigidity of the structure and to transfer the lateral forces due to wind, earthquake etc. efficiently to the foundation of the building. Various types of bracings are discussed in the following sections:
Transverse bracings: The transverse bracing is provided in order to reduce the endmoments in the columns. This is achieved either by providing knee braceor by rigid frame portals. The rigid frame portals is a welded structure Transverse bracing
Longitudinal bracing: Wind acting in the longitudinal direction of the building,that is, normal to the plane of trusses, will require a horizontal truss to transmit the load to the columns and then across frame or bracing in thelongitudinal vertical planeof the columns to transmit the load to thefoundations.Fig. shows the bracing system in the plane of the top chord of the roof truss and in the vertical plane of the longitudinal bent. In this way, every fourth or fifth bay may be braced but no industrial building should have less than two braced bays.The stresses in the members of the bracing system are small in magnitude and anominal section is sufficient to resist the stresses.