1. STEEL STRUCTURES AND ITS
APPLICATIONS IN
INDUSTRIAL BUILDINGS
Under the guidance of
Mrs.Kiranmaye By
y.kondala rao

2. INDUSTRIAL BUILDINGS
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.

3. 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

4. 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
  Structural frame of an industrial building
  Structural frame of an industrial building

5. 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.
(c)minimum consumption of steel
(d)structurally efficient system

6. 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
 (ii)The columns in each row are fixed so that they do not interfere with themechanical layout.
(iii)After fixing the column spacing, the pitch of truss is selected and thetype of truss to be provided is decided.
(iv)Provision of sky light, or north light has also to be considered alongwith. The resistance of the frames to horizontal loads due to wind andearthquake is an important point to be decided with regard to the cross sectionof the building.
(v)The sketch of the members, openings, lintels, doors, windows, girts and anend wall column is made. Along with this, the plan that shows lateral bracingsystem is prepared.
(vi)The material to be used for floor, roof walls, partition walls etc. are decided

7. . ROOF AND SIDE CLADDING MATERIAL:
For covering roofs and sides of industrial buildings, corrugated iron sheets which aregalvanized for protection against corrosion (popularly called G. I. sheets) are usuallyadopted.
Alternative to the corrugated steel sheets, Asbestos Cement (A. C.) sheets may beused to cover the roof. These are better insulator of sun's heat which can further beimproved by painting them white on the top surface
ROOF TRUSSES:
The truss is a framework designed to support roofing and ceiling material over alarge area without intermediate columns. The trusses support the purlins on their  principal rafters and the purlins support the roof covering either directly or throughcommon rafters and battens. The joints of the truss are assumed to be hinged. Themember forces are determined by simple statics. The point of intersection of twomembers is known as nodes or joints and the distance between the nodes is known as panel length

8. The various parts of a roof truss are shown in Fig
 The various parts of a roof truss are shown in Fig. and the common types whichare used in building construction are shown inFig. Suitable spans for thevarious trusses are indicated below each type. The truss spacing is usually kept at1/4thof the span of the truss for shorter spans (up to 15m), and 1/5th
of the span for 15 to 30 m spans. The depth of the truss determines its stiffness in relation to spanand also its economy. A height of 1/6 to 1/5 of span for triangular trusses as statedearlier, provides sufficient stiffness against lightloads.
The lower chord of trusses may be left straight or may be cambered.Cambering is done for a better appearance.Fig. 1.5 Camber of lower chord member
A sag tie is used to reduce the moment due to self weight in the long middle tiemember and hence, helps in reducing tension in that member.
Pitch of Trusses:
The pitch of trusses is defined as the ratio of height of the truss to its span. This isessential to drain off rain water on the sheeted slopes. The minimum recommendedrise of trusses with galvanized iron (G.I.) roof covering is 1/6 and that with asbestos-cement (A.C.) sheet is 1/12 of span. Where snow fall does not occur, as in most parts of India, lower pitches upto 1/6 are suitable. Low pitches are advantageous because the wind pressure on the roof is reduced

9. Various types of roof trusses

10. . w= .02 + .0066 L for live loads of 2.0 kN/m2
Loads on roof truss:
The roof trusses are subjected to dead load, live load, snow load and wind load.
 Dead Loads:
The dead loads of the truss include the dead load of roofing material, purlins,trusses and bracing system. Since the self weights of members to be designed arenot known, they are assumed. Weight of roofing, corrugated sheet or A. C.sheeting-are almost standard and are prescribed in IS Purlins are in fact beams and their weight may be assumed easily and rechecked if necessary. Thedead weight of the truss may be assumed to be equal to 10% of the loads on thetruss. There are number of formulas for weight estimation of roof trusses:1
. w= L for live loads of 2.0 kN/m2
(i)Where w= weight of truss in KN/m2
 L = span in m..If live loads other than 2.0 kN/m2,multiply w by the ratio Live Load per sq. m 2.0The weight of the bracing may be assumed to be 12 to 15N/m2of the plan area
 2. Dead weight of the roof truss in N/m2 is (span/3+5)10.
 Live loads:
The live load on roofs shall be taken as per IS : 875 (Second Revision) Part and is given in below.

11. 1.For ≤10 degrees slope live load taken as 1.5kN/m².
2.For >10 degress slope 0.75kN/m² less 0.01kN/m² for every degree increase in slope upto and including 20º and 0.02kN/m² for each degree increase above 20º.
The minimum should not be <0.40kN/m²
Snow Load :
Except for some hilly regions, snow load is not the problem in India. For complete information on snow loads in India reference may be mode to IS: 875 (secondRevision) Part Actual load due to snow will depend upon the pitch of theroof, shape of the roof and the roofing material. The weight of the snow collected onflat ground may be taken as 2.5 KN/m3
. For roofs having slopes greater than 60°,snow load may be disregarded. For flatter slopes possibility of partial coverage of roof with snow should also be considered, that is half the roof may be assumed tohave full snow load and the other half only about 2/3 of this load
Wind Load :
The most critical load on an industrial building is the wind load. For the calculationopf wind load on structures, I.S realtes the intensity of wind pressure tothe basic maximum wind speed.

12. Load Combinations for Design:
The roof trusses should be designed to carry the following combinations of loadsallowing for appropriate permissible stresses:
Dead load + live load or snow load whichever more -use Normal permissiblestresses.
(b) Dead load + wind load, wind direction being normal to ridge or parallel to ridgewhichever is more severe. Use Permissible stresses increased by 331/3% to 50%.
PURLINS:
purlins are the beams that are provided over roof trusses to support the roof covering. The span of the purlin is equal to the spacing of the trusses. Purlins areflexural members and are subjected to vertical loads due to dead and live loads andto loads normal to roof covering due to wind pressures. Purlins, thus, are subjectedto biaxial bending. The purlins are usually made of channel section or angle iron.
 channel section is best suited for a purlin.Purlins should be designed carefully as these constitute a large proportion of steeldead weight in the structure and therefore, the overall economy depends on thedesign of the purlins. Purlins can be designed as simple, continuous or cantilever  beams.

13. The spacing of purlins depends on the capacity of the roof sheets to carrywind or live load along with the dead load. The spacing is generally between 3m to6m. Theoretically, it is desirable to place purlins only at panel points becauseotherwise the principal rafter of the roof truss will be subjected to bending. But for large trusses, if the purlins are provided at panel points, their spacing will be large.Therefore, is such cases, purlins are provided at intermediate points and the principalrafter is designed for flexure and axial stresses,when the slope of roof is<30º,angle purlins with the following specified dimensions may be adopted:
Depth of purlin, D≥L/45
Width of purlin,B≥L/60
Maximum bending moment in the purlin= WL/10
Where L = Span of the purlin
W = Total distributed load on the purlin including wind load.It is to be noted that the bending moment about the minor axis may be neglected andthe angle purlin may be designed for a moment of WL/10 about the major axis
Loads on purlins:
1.Dead Load:Roof sheating: Corrugated steel sheets = 100 to 150 N/m2
Corrugated AC sheets = 170 to 200 N/m2
Purlin self weight = 100 to 120 N/m²

14. Upper chord slope,θ < 10º = 750 N/m2
2.Live load:
Upper chord slope,θ < 10º = 750 N/m2
Upper chord slope,θ < 10º = [750 – (θ – 10) N/m2
3.Wind load:
Design wind pressure, p = 0.6 ( k 1k 2k 3Vb)²
where k 1is the probability factor or risk coefficient. For all general buildingswith a mean probable design life of 50 years, the value of k 1is 1
 k2 is terrain, height and structure size factor.
K3 is topography factor and for level ground, with the upwind slope less than3°, its value is 1
Vb is the basic wind speed.
SAG RODS:
Purlins have a tendency to sag in the direction of sloping roof. Sag rods are provided between adjacent purlins to extend lateral support for the purlin in the weaker direction ad to take up the sag. These are round section rods that are fastened to theweb of the purlin. A sag rod is designed as a tension member to resist the tangentialcomponent of the resultant of the roof load and the purlin dead load. These are placed at a minimum gauge distance below the top. In general, a single line of sagrods at the centre of the purlins is sufficient for complete support. The sag rodshould not be terminated at the ridge because in such case, the ridge purline will besubjected to an excessive pull

15. Sag rod and tie rod
At the crown, sag rod provided is termed as tie rod.this resists the tangential components from the two side of roof truss.
The number of sag rods to support each purlin depends upon the length of the purlinand load to be supported. Generally a single line of sag rods at the centre of the purlin is sufficient

16. PRINCIPLE RAFTER :
Principle rafter is the primary compression member and is designed as a continuousstrut. Generally, a double angle section is preferred. It is because of two reasons.Firstly, it is desired to have the same radius of gyration about the main axes so as toachieve the same bending strength about the two axes. Secondly, the double anglesection provide an extra strength which is useful during erection when the trusses areunbraced
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 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.

17. Gantry girder and crane girder

18. Loads on gantry girder:
Gantry girders are laterally unsupported beam subjected to impact loads. They aresubjected to the following forces:
1.Vertical loads: These are the reactions from the crane girder which consist of self weight from the crane, crab and the crane capacity. The reaction will bemaximum when the crab is nearest to the gantry girder.
2.Lateral load: It is caused due to the sudden stopping or starting of the crab.
3. Longitudinal loads: It is caused due to the sudden stopping or starting of thecrane girders.The stresses produced in gantry girders due to these loads are more than those cause by the loads applied gradually. This is due to the forces set up by sudden application of brakes ,acceleration,retardation ,vibration etc. To account for this, suitable impact loads are introduced where necessary. According to IS: , additionalloads given in Table shall be considered when the structures are subjected toimpact loads in addition to live loads
Both the horizontal forces, lateral and longitudinal, are assumed not to act together with the vertical loads simultaneously. Only one of them is to be considered actingwith the vertical load at a time. Vertical load, of course, includes the additional loaddue to impact. Further, the permissible stress may be increased by 10% when theabove combination of vertical and horizontal load acts at a time. This increase is notin addition to that permitted on account of wind or earthquake forces

19. Impact and surge of crane
S.NO
Type of load
Additonal load 1
Vertical forces:
1.For electrically operated cranes.
2.Hand operated cranes.
25% of the max static loads .
10% of the max static wheel load. 2
Horizontal forces transverse to rails
1.For electrically operated cranes
2.For hand operated cranes
10% of the weight of crab&weight lifted by crane
5% of the weight of crab&weight lifted by crab 3
Horizontal forces along rails
5% of all static wheel loads

20. L=span of crane runway girder
Permissible deflections in gantry girder
S.NO
Type of crane
Allowable deflection 1
For manually operated cranes
L/500 2
Electrically opereted cranes upto 50t
L/750 3
Electrically operated cranes over 50t
L/1000 4
Other moving loads such as charging cars etc.
L/600
Where
L=span of crane runway girder

21.  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.

22. Project Reference Drawings / Documents
Bracing system
Project Reference Drawings / Documents
Indian Standard Codes 1
IS-456: 2000
Plain and Reinforced Concrete – Code of Practice. 2
IS 1893-Part - 1 & 4
Criteria for Earthquake Resistant Structures-Industrial structures including stack-like structures. 3
IS-875: 1987
Code of practice for design loads (other than earthquake loads) for buildings and structures 4
IS-800: 2007
Code of practice for general construction in steel