Shelter Design Using Cold Formed Steel Section

ABSTARCT: Cold formed steel section are extensively used in industrial and many other non- Industrial constructions worldwide, it is relatively a new concept in India. These concepts were introduced to the Indian market lately in the 1990’s with the opening up o f the Indian economy and a number of multi-nationals setting up their green-field projects. Global Cold formed steel have established their presence in India by local marketing agents and certified builders. As the complete building package is supplied by a single vendor, compatibility of all the building components and accessories is assured. This is one of the major benefits of the Cold formed building system. When a building is no longer needed it can be disassembled, stored or moved to another location and re-erected because only bolted connections are used. There is no field riveting or welding & the rigid frame is strong. By using Cold formed system economy is achieved with completion of project in minimized time. In this project the detailed analysis of Industrial building with Cold formed concept is carried out. The Work is also extended by taking the parametric studies too. A comparative study has also been carried out between Hot Roll steel Industrial building and Cold formed Industrial building and a conclusion has been drawn.

1. GENERAL

INTRODUCTION

The design of industrial building is governed mainly by functional requirements and the need for economy of construction. In cross-sections these buildings will range from single or multibay structures of larger span when intended for use as warehouses or aircraft hangers to smaller span buildings as required for factories, assembly plants, maintenance facilities, packing plants etc. The main dimensions will nearly always be dictated by the particular operational activities involved, but the structural designer’s input on optimum spans and the selection of suitable cross-sections profile can have an important bearing on achieving overall economy. An aspect where the structural designer can make a more direct contribution is in lengthwise dimensions i.e. the bay lengths of the building. Here a balance must be struck between larger bays involving fewer, heavier main components such as columns, trusses, purlins, crane beams, etc. and smaller bays with a large number of these items at lower unit mass. An important consideration in this regard is the cost of foundations, since a reduction in number of columns will always result in lower foundation costs.

CLASSIFICATION

- 1. Hot-Rolled Steel Industrial building.
  2. Cold-Form Steel Industrial building.

HOT-ROLLED STEEL INDUSTRIAL BUILDING

The choice of cross-sections for a single storied Hot-Rolled Steel industrial building is very wide, but experience has shown that a limited number of shapes are the most practical and economical. Some of these cross-sections are shown in fig. The cross-sections used in Hot-Rolled Steel Industrial building have yield strength of 250Mpa. The following figure shows the cross section of Hot Rolled Steel Industrial Building.

Figure 1.1: Cross-sections used in Hot-Rolled Steel Industrial building

ORIGIN OF COLD-FORM STEEL CONCEPT

Cold-Form Steel buildings are a predetermined assembly of structural members that has proven over time to meet a wide range of structural and aesthetic requirements. Cold-Form Steel building concept originated during World War II in 1960’s in the United States and made available in India in late 90’s.

During World War II, best known Pre-fabricated building i.e. Which became a household word was mass produced by hundreds of thousands to meet a need for inexpensive and standardized shelter. Requiring no special skills, these structures are assembled with only hand tools and with no greater effort could be readily dismantled and moved and re-erected somewhere else. The scientific term Cold-Form Steel buildings came into being in the 1960’s. The buildings were “Cold- Form Steel” because like their ancestors, they relief upon standard engineering designs for a limited number of off the shelf configurations. As long as the purchaser standard designs the buildings could be properly called Cold-Form Steel.

COMPONENTS OF COLD-FORM STEEL BUILDING

Main frame
Secondary framing
Wind bracing
Exterior Cladding

Trapezoidal sheeting is used as exterior cladding. Cold formed Z or C Sections are used as Secondary framing. Main framing consists of built up I-Sections. Wind bracing consists of rods which are circular in cross section.

Figure 1.2 (a): Standard Cold-Form Steel portal frames

Figure 1.2(b): Conventional frame

Figure 1.2(c): Cold form steel frame

A typical single-span frame of this design is shown in figure. It will be seen that the columns and rafters are tapered to match the general shape of the gravity bending moment diagram and the high moments at the column-rafter junction and at the apex can thus be accommodated by the deeper section. Uniform flange and web thicknesses can be used, resulting in a frame width. The higher fabrication cost of the tapered, welded construction is more than offset by the much reduced material content. The mass can be as little as 75 percent of a Hot-Rolled Steel rolled-steel portal frame of similar size. Web thicknesses are as small as 5mm and flange thicknesses 8mm.

Such thin-webbed sections require Non-Hot-Rolled Steel design fabrication procedures and the specialist fabricators use computer aided design and detailing routines and automated shop assembly methods.

MAJOR COMPONENTS OF COLD-FORM STEEL INDUSTRIAL BUILDING

Cold-Form Steel building uses three distinct product categories:

Built-up “I” section as primary structural framing members consisting of columns and rafters made up of hot rolled sections having yield strength of 345Mpa.
Cold formed “C” and “Z” shaped secondary members such as purlins, eave struts and side girts having yield strength of 345Mpa.
Profiled sheets for roof and wall cladding having yield strength of 345Mpa.

ADVANTAGES OF COLD FORMED SECTIONS OVER HOT ROLLED STEEL SECTIONS

No insect and fungal infection: The problems such as rotten and discomposed due to insect and fungal infection are eliminated.
Consistency and accuracy of profile: The nature and manufacturing of process Cold-rolling enables the desired profile maintained and repeated for as long as it is required, in a much closed tolerance. Moreover, the very little tool wears and the cold rolling process is ideally suited to computerized operation which assists to the maintenance of accuracy.
Versatility of profile shape: Almost any desired cross-sectional shape can be produced by cold-rolling, such as Z-section with lips and C-section with lips.
It could be pre-galvanized or pre-coated: The steel material may be galvanized or coated by plastic materials either to enhance its resistance to corrosion or as an attractive finish.
Best suited for site erection: The cold formed steel may be more advantageous than hot rolled steel since it can be cut and erected with very light machine and even only manpower.
Increase in yield strength due to cold-forming: The cold-forming process introduces local work hardening in the strip being formed in the vicinity of formed corners. This local work hardening may results an increment of ultimate yield strength about 25% from its virgin strength.
Minimization of material: Since the material used can be very thin in comparison to lower thickness limits of hot rolled sections, it allows the material usage for a given strength or stiffness requirements to be much less than that of the smallest hot rolled sections. The material thickness or even the cross- sectional geometry could be controlled to achieve the structural features with minimum material weight.

PLANNING OF COLD-FORM STEEL BUILDING FOR INDUSTRIAL PURPOSES

GENERAL

The planning of an Industrial building is based on functional requirements i.e. on the operations to be performed inside the building. In the planning of an Industrial building, due

Consideration should be given to factors such as wide area of primary frames, large height, large doors and openings, large span of primary frames , consistent to give minimum weight of primary frames, purlins, girts , eave struts etc. and lighting and sanitary arrangement. The site for a proposed plant is in general, pre-selected before it comes for design. But it is better to discuss with the designer the preliminary plans in advance. This gives the designer an opportunity to choose a suitable site giving due consideration to future developments. Some of the factors governing the site selection are as listed below:

- - The site should be located on an arterial road.
  - Facilities like water, electricity, telephone, etc.
  - Topography and water drainage.
  - Soil condition with reference to foundation design.
  - Sufficient space should be available for storage of raw materials and finished products.
  - Sufficient space should be available for transportation facilities to deliver raw materials and collect the finished products.
  - Water disposal facilities.

PRIMARY COLD-FROM STEEL FRAME

Assuming that a Cold-From Steel building system is selected for the project at hand, the next milestone is choosing among the available types of Cold-From Steel primary frame. Proper selection of the primary framing, the backbone of Cold-from Steel buildings, goes a long way toward a successful implementation of the design steps to follow. Some of the factors that influence the choice of main framing include:

- - Dimensions of the building: width, length, and height.
  - Roof slope.
  - Required column-free clear spans.
  - Occupancy of the building and acceptability of exposed steel columns.
  - Proposed roof and wall materials.

At present five basic types of Cold-From Steel frame are currently in the market:

- - Tapered beam.
  - Single-span rigid frame.
  - Multi-span rigid frame.
  - Lean-to frame.
  - Single span and continuous trusses.

“Frame width” is measured between the outside surfaces of girts and eave struts. “Clear span” is the distance between the inside faces of the columns. “Eave height” is measured between the bottom of the column base plate and eave strut. “Clear height” is the distance between the floor and the lowest point of the structure.

SECONDARY FRAMING

Secondary structural members span the distance between the primary building frames of the Cold-From Steel building systems. They play a complex role that extends beyond supporting roof and wall covering and carrying exterior loads to the main frame. Secondary structural, as these members are sometimes called, may serve as flange bracing for primary framing and may function as a part of the building’s lateral load- resisting system. Roof secondary members, known as purlins, often form an essential part of horizontal roof diaphragms; wall secondary members, known as girts are frequently found in wall bracing assemblies. A third type of secondary framing, known by the names of eave strut, eave purlin, or eave girt, acts as part purlin and part girt its top flange supports roof panels, its web, wall siding. Girts, purlins and eave struts exhibit similar structural behaviour.

Figure 2.1 (a): Secondary framing

Figure 2.1 (b): Overlapping of secondary members

CASE STUDY

COLD FORMED STEEL CONCEPT FOR INDUSTRIAL BUILDING

- 1. INTRODUCTION

In Cold-from steel Industrial building span range is kept between 10m-18m. The available profiles of slopes for Industrial building are 1:10, 1:12 & 1:20

PARAMETERS OF COLD-FORM STEEL INDUSTRIAL BUILDING

Location: Nagpur

Utility: Cement Godown

Building width; 15m

Building Length: 50m

Eave height: 5m

c/c of main frames : 6.25 m Maximum spacing of purlin: 1.5m Slope of Roof: 1:12

Aria Covered: 15 m × 50 m

Figure 3.1.1: Plan of CFS

1tan θ =

12𝜃 = tan⁻¹ 1 )

(12= 4.76

≅ 5°

Figure 3.1.2: Elevation of CFS

LOADING

IMPOSED LOAD

As per Table 2 of IS: 875(Part2)

UDL on roof measured on plan area for slope less than 10⁰ = 75 𝑘𝑔/𝑚²

WIND LOAD

According to value 5.3 of IS 875 (part3)

𝑣2 = 𝑣𝑏 𝑘1 𝑘2 𝑘3

Location assumed 𝑣𝑏 = Nagpur Basic wind speed (𝑣 ) = 44 𝑚/𝑠

𝑘₁ = 1 coefficient from table 1 of IS 875 (part3)

𝑘₂ = 0.88 from table 2 of IS 875 (part3)

𝑘₃ = 1 topography factor

Design wind speed 𝑣₂ 44 × 1 × 0.88 × 1

= 38.72 𝑚/𝑠

Design wind pressure 𝑝𝑧 = 0.6 𝑣𝑧 2

= 0.6 × 38.72²

= 900 𝑚/𝑠

- 1. Calculation Of External Pressure Coefficient “ Cpe ” Roof

Referring to Table 6 of IS: 875(Part3) Here h = 5m; w=15m

Roof Angle = 5⁰

Figure 3.1.3: Building Plan

Figure 3.1.4: Wind Across Length Of Building (Roof)

Figure 3.1.5: Wind Along Length Of Building (roof)Wall

Referring to Table 4 of IS: 875(Part3)

𝑕/𝑤 = 5/15 = 1/3 < 1/2

𝑙/𝑤 = 50/15 = 3.33 < 4

Figure 3.1.6: Wind across Length Of Building (Wall)

0.6

Figure 3.1.7: Wind Along Length Of Building (Wall)

Considering openings to be < 5 % of Total Area Internal pressure coefficient = ± 0.2

PURLIN DESIGN

Dead Load:

Unit wt. /m of sheeting @ 0.06 𝑘𝑛/𝑚²

= 0.06 × 1.5

= 0.09 𝑘𝑛/𝑚

Unit 𝑤𝑡./𝑚 or Self 𝑤𝑡. of Purlin = 0.07 𝐾𝑁/𝑚

Total Dead Load per metre on each Purlin = 0.16 𝐾𝑁/𝑚

Imposed Load

Imposed Load intensity on Purlin = 0 . 7 5 𝐾 𝑁/𝑚²

Total Imposed Load per metre on each Purlin = 0.75 × 1.5 = 1.125𝐾𝑁/𝑚

Wind Load

Maximum Wind Load per metre on each Purlin= (1 + 0.2) × 1.161 × 1.5

= 1.62 𝑘𝑛/𝑚

Load Combination1- Dead Load + Imposed Load

= 0.16 + 1.125 = 1.285𝐾𝑁/𝑚

Load Combination2- Dead Load + Wind Load

= 0.16 − 1.62 = 1.46𝐾𝑁/𝑚

Choose z section

Figure 3.1.8: Z section Table 3.1.1: Property of the Z-section selected is as shown below

Area	Thickness	Wt/m	Ixx	Iyy	Zxx	Zyy
8.37sq .m	2.55mm	6.57kg /m	439cm⁴	58.4 cm⁴	46.21	10.01

END WALL COLUMN DESIGN

Figure 3.1.9: Column Elevation

Loadings:

C/C

Bending Moment on end wall Column due to Wind load from Gable end side Axial Compressive Load due to Self weight of side sheeting, girt etc. Consider End wall Column spacing 5m

Dead Load

Assume Self weight due to side sheeting and Girt = 0.16 KN/m.

Load at each node (junction with side Girt) on end wall Column 0.16×5 =0.8KN Axial Compressive Load on end wall column due to Side sheeting & Girt =0.8×3=2.4 KN. Where 3 is the number of Girts Assume Self Weight of Column = 1.5KN.

Maximum Length of End wall Column =5.84m. Total Axial Compressive Load

= 1.5+2.4=3.9KN.

Wind Load

Wind Load on End wall Column due to Wind influence area

= 5×5.84×0.9×0.9=23.65KN.

Consider End wall Column pinned at both the ends.

Max = 23.65 ×5.84

= 17.26 KN.m

Shear Force at ends (supports) due to Wind Load = 23.65 /2 = 11.83KN

Choose Cross Section

Figure 3.10: C section

3.1.2: properties of C section

𝐴𝑟𝑒𝑎	𝑈𝑛𝑖𝑡/𝑚	𝐼𝑥𝑥	𝐼𝑦𝑦	𝑍𝑥𝑥	𝑍𝑦𝑦	𝑅𝑥𝑥	𝑅𝑦𝑦
28.4𝑆𝑞 𝑀	22.4 𝑘𝑔/𝑚	1408𝑐𝑚²	432𝑐𝑚⁴	156.4𝑐𝑚³	54𝑚3	7.04𝑐𝑚	3.9𝑐𝑚

Dead Load

𝟑. 𝟏. 𝟕 𝐌𝐀𝐈𝐍 𝐅𝐑𝐀𝐌𝐄 𝐃𝐄𝐒𝐈𝐆𝐍 𝐋𝐎𝐀𝐃 𝐂𝐀𝐋𝐂𝐔𝐋𝐀𝐓𝐈𝐎𝐍 ∶ −

Dead weight (Roof Sheeting & Purlins) on frame is considered as 0. 1 7 2 kN/m²Hence, Loads on rafter as

U.D.L = 0.17 x 6.25 = 1.0625 KN/m Loads on Column = 0.17 x 1.5 x 6.25 = 1.59 KN

Total Load transferred by Girt & Sheeting on Column = 1.59 x 3 = 4.78 KN

Service Load

Service Load on the Rafter is considered as 0.1 kn/m² Hence, Loads on rafter as U.D.L = 0.1 x 6.25 = 0.625 KN/m Imposed Load

As Ø < 10⁰ Live Load = 0.75 2

Hence, Loads on rafter as U.D.L = 0.75 x 6.25 = 4.6875 KN/m

Wind Load:

Wind load on the frame due to wind

= 9× 6.25×0.9× (1.2+0.2)

=70.875 KN

Figure 3.1.11 The Frame With Configuration Of All Four Members Table 3.1.3: properties of member of the frame

Member No	Defth at start node	Depth at end Node	Width of flange	Thickness of Flange	Thick ness of web
1	250mm	400mm	200mm	10mm	6mm
2	400mm	400mm	200mm	10mm	6mm
3	400mm	400mm	200mm	10mm	6mm
4	400mm	250mm	200mm	10mm	6mm

Figure 3.1.12: 3D view of CFS

Check for Deflaction

𝑀ax^m permissible Defⁿ due to wind load only for frame = h/ 60 to h/100 ( horizontal)

= 5000 / 60 = 83.33mm

𝑀aximum permissible Vertical Deflection due to live load on frame

= span = 15000/240

=62.5mm

The frame was checked for horizontal at node 2 & 4 for wind load &was found to be safe. The frame was checked for vertical deflection at node for 3 & was found safe.

The Weight of Cold Formed Industrial Building

The total weight of Cold Formed Steel Industrial Building having area 15×500 m. & eave height 5 m. was found to be 15.92 Ton & cost of building is estimated 11.14 Lakh. The cost of cold formed steel is 70Rs/Kg

ANALYSIS & DESIGNS OF HOT ROLL STEEL INDUSTRIAL BUILDING USING SOFTWARE

- 1. PARAMETERS OF HOT ROLLED INDUSTRIAL BUILDING



Building Width	: 15m
Building Length	: 50 m
Eave Height	: 5m
C/C of Main frames	: 6.25 m
Maximum spacing of purlin	: 1.5 m
Slope of Roof	: 1:12
Structural material yield stress	: 250Mpa

Figure 3.2.1: Elevation of HRS

Figure 3.2.2: Plan of HRS

Figure 3.2.3: 3D View of HRS Table 3.2.1 Result of Conventional Industrial Building

Sr. No.	Member description	Section	Total wt (TN)
1	Rafter	ISMB-400	7.7
2	Purlins	ISJC-175	10.30
3	Main columns Main columns	ISMB-400 ISMB-350	3.8 1.59
4	Gable end wind column	ISMB-350	0.71
5	Tie runners	ISMB-250	0.821
	Total weight		25.159

The total weight of Conventional Industrial Building having area of 15×50 m & eave height 5m was found to be

RESULT AND CONCLUSION

1. RESULT Case1:

With the analysis and design of section, it has been observed that by using cold formed steel building instead of hot rolled steel building the material is saved by using cold formed steel was 9.239 T. The spacing of c/c main frame is 7.14m.

Case2:

With the analysis and design of section, it has been observed that by using cold formed steel building

instead of hot rolled steel building the material is saved by using cold formed steel was 13.92 T. The spacing of c/c main frame is 6.67m.

CONCLUSION

In Industrial building the material & cost of the building is minimized in case of cold formed steel while in case of conventional building it was be higher both in two cases. The saving in material and cost is about 25 %.

FUTURE SCOPE

Analysis and Design of Cold Formed Steel done for multi-storey building by considering various sectional properties of cold formed steel. Also design different parts such as eave strut, bracing system, sag rod and foundation can be done for different consideration of section.

Engineering Concepts

Design of Cold-Formed Steel Structures as Per IS 801