Pre-Engineered Buildings (PEB) is an emerging technology which is found more advantageous than the Conventional Steel building
In India, the steel structures are designed as PEB using the codal standards of conventional steel building. Also, the limits fixed to control sway and deflection is lesser. As a result, PEB is not completely effective despite its idea of sectional reduction. This study focuses on the design of an Industrial Gable building with crane using Indian and American code and to derive a comparison in the weight and effect of each load case on the building in terms of a quantitative data.
Pre-Engineered Buildings are pre-determined assemble of structural members that has proven over time to meet a wide range of structural requirements. PEB’s are factory made and are erected to the site. Complete shop fabrication results in superior quality and significant saving of construction time. PEB is designed to customer’s specification that varies from one to another.
Connection pattern and support arrangements are standardized and hundreds of pre-Engineered details are developed. These Pre-Engineered details are directly used in the buildings depending upon the exact requirements. This concept speeds up the design and detailing of the building thereby greatly reducing the cycle time
The Pre-Engineered Building comprises of three components they are
• Primary Component (Main Frame, Columns, Rafters, Bracings)
• Secondary Component (Purlins & Girls, Eave Struts, Tie rods & Angle Bracings and Washers)
• Roof and Wall Panels (Gable trim, Eave trim, Ridge trim and Panels/Sheeting)
The Pre-Engineered Building comprises of three components they are
The model of the Pre-Engineered Building is analyzed and designed using the StaadPro Software. The details of the Industrial Gable Building taken for the project are shown in
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Location |
Chennai, Tamil Nadu |
Building Length |
37.5 m |
Building Width |
30.0 m |
Eave Height |
8.50 m |
Bay Spacing |
7.50 m |
Roof Slope |
1 in 10 |
Material Yield Stress |
379.2 Mpa |
Concrete Grade |
M20 |
Max. spacing for Purlins & Girts |
1.525m (5’0”) |
Max. spacing for Flange Brace |
3.050m (10’-0”) |
The typical plan of the Pre-Engineered Building is presented below from
The Interior Main frames are rigid and tapered built up I section. The End Wall frames are continuous beam with turned interior columns. The Secondary Framing is of Cold Formed Z shaped section for Purlins and Girts and the Covering is a trapezoidal profile sheets for walls and roofs.
a. Structural Design and Drawing:
Wind Co-efficient, Design Parameters and Serviceability condition are considered as per the respective codes. Loads are calculated for the Interior & End frames; wall girts and roof purlins as per the codes.
The loads considered for the design are
• Dead Load
• Live Load
• Collateral Load
• Wind Load
• Seismic Load
• Brace Load
• Crane Load
Total Dead load comprises of Weight of Sheeting in addition to Purlin or Girt Weight. Collateral load includes Miscellaneous Support loading such as Lights, Sprinklers, Suspended Ceiling, Ducts/ Piping etc., Minimum Roof Live Load is taken from the ASCE 7-16 Table 4-1 Page no.186.
Reduced Roof Live load is calculated for end Frame as well as for Interior frames separately.
Reduced Live Load
Where
And
For a pitched roof, F = 0.12 x slope with slope expressed in percentage point.
Reduced Roof Live Load
The longitudinal and lateral loads such as Wind load and Seismic loads are resisted by the roof and wall bracing systems.
Wind load is calculated as per section 6.0 of ASCE7-16
The Wind Pressure is calculated by the formula,
Wind pressure,
Where 0.613 is constant, Kz is Velocity pressure exposure coefficient, Kzt is the Topographic factor, Kd is the Directionality factor, Ke is the Ground elevation factor, Vb is the basic wind speed and I is the Importance factor. Net Pressure Coefficient
where
Total Base shear shall not exceed
where Cv is the seismic coefficient, I is the importance factor, R is the response reduction factor, T is the structure period and W is the seismic load. When the Total base shear calculated exceeds the maximum value it is limited to the maximum value, hence Design Total Base Shear Cis the Base Shear
Dead load is calculated as per IS 875-2015 Part 1
The longitudinal and lateral loads such as Wind load and Seismic loads are resisted by the roof and wall bracing systems. Wind load is calculated from IS 875-2015 Part 3, the Wind Pressure is calculated by the formula,
Design Wind speed,
where k1 is the Risk coefficient From
The Design Wind Pressure
where
Design Horizontal Seismic Pressure
Wind Pressure Coefficient for various load cases are
Wind Perpendicular to Ridge W1 Right i.e., W1>
(Wind Right + Internal Pressure)
Wind Perpendicular to Ridge W1 Left i.e., W1<
(Wind Right + Internal Pressure)
Wind Perpendicular to Ridge W1 Right i.e., W2>
(Wind Right + Internal Suction)
Wind Perpendicular to Ridge W1 Left i.e., W2<
(Wind Right + Internal Suction)
Wind Parallel to Ridge WP
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Service Classification |
Heavy Service (Ware house) |
Crane Capacity |
100 kN |
Crane Weight |
38.55 kN |
Crab/Trolley Weight |
6.10 kN |
Wheel Base |
2.50 m |
Bridge Span |
13 m |
Number of wheels |
4 nos |
Number of wheels/sides |
2 nos |
The height of the gantry rail from the floor is of 6.3 meters. The site clearance for the runway beam of the crane is given as 300 mm on both the sides. A total of 2 cranes units are provided on both the axle. The distance of the roof bottom to the center of the hook is taken as 1.69 meters. The nearest hook approach on either side is around 1.1 meters. The minimum head room required as per Industrial standard for 10-ton single girder is 1.2 meters.
Wheel load is calculated by the formula, Wheel load WH = [(Rated Capacity of the crane + (Weight of the Hoist) + (0.5 x Weight of crane)]/ (Number of wheels at one side). Vertical Impact of a pendent operator crane is 10% of the wheel load.
The lateral force is calculated by the formula LatF = 20% [rated crane capacity + weight of the hoist] / 4. And the longitudinal force is calculated by LonF = 10% of the maximum wheel load x number of wheels per side. For runway beam that carries the crane, built-up section is used as per IS808-1989. Beam is of ISMB450 and then channel over it is ISMC300. The crane unit is fixed to the rail which is supported on the runway beam, thus the load from the runway beam is taken to the column through the brackets attached. To make the connection easier straight columns are provided.
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DL |
0 |
-791.22 |
0 |
0 |
-942.96 |
0 |
LL |
0 |
-661.78 |
0 |
0 |
-861.74 |
0 |
W1> |
426.83 |
598.23 |
0 |
419.68 |
783.90 |
0 |
W1< |
-426.83 |
598.23 |
0 |
-419.68 |
783.90 |
0 |
W2> |
426.79 |
1117.23 |
0 |
419.65 |
1449.24 |
0 |
W2< |
-426.79 |
1117.23 |
0 |
-419.65 |
1449.24 |
0 |
WP |
0 |
1362.36 |
0 |
0 |
1663.38 |
0 |
WB1> |
0 |
0 |
193.28 |
0 |
0 |
199.07 |
WB1< |
0 |
0 |
-193.28 |
0 |
0 |
-199.07 |
WB2> |
0 |
0 |
-18.38 |
0 |
0 |
22.13 |
WB2< |
0 |
0 |
18.38 |
0 |
0 |
-22.13 |
E> |
48.32 |
0 |
0 |
36.08 |
0 |
0 |
E< |
-43.56 |
0 |
-4.76 |
-32.55 |
0 |
3.54 |
EB> |
0 |
0 |
38.95 |
0 |
0 |
49.55 |
EB< |
0 |
0 |
-38.95 |
0 |
0 |
-49.55 |
CG |
0 |
-172.34 |
0 |
0 |
-172.34 |
0 |
CR |
-44.60 |
-1443.00 |
-26.78 |
-44.60 |
-1443.00 |
-26.78 |
A load combination results when more than one load type acts on the building. These combinations with the load factors for each load type is used to ensure the safety of the structure under maximum expected loading scenarios.
The basic load combination as per Indian code is as follows,
• DL + LL
• DL + CG + LL
• DL + CG + LL + WL
• DL + WL
• DL + CG + LL + E
• DL + CG + LL + CR
• DL + CG + LL + WL + CR
• DL + CG + LL + E + CR
• DL + E
Whereas for American code the basic load combinations are,
• DL + CG + LL
• DL + CG + WL
• DL + WL
• DL + CG + CR
• DL + CG + LL + WL
• DL + CG + WL + CR
• DL + CG + E
• DL + E
The load cases take different coefficients based on the combinations. Also, the load combinations multiply considering the direction, location and the position of the application of the load.
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Yield Stress N/mm2 |
379.2 |
379.2 |
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Section |
3 Plate Section |
3 Plate Section |
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Stress Increase |
1.0 |
1.0 |
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Type of Loads |
Working load |
Factored load |
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Allowable Lateral Deflection |
Eave Height / 100 = 85 mm |
Eave Height / 200 = 42.5 mm |
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Allowable Vertical Deflection |
Span / 180 = 83.33 mm |
Span / 180 = 83.33 mm |
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Weight in Tons |
26.7101 |
37.0446 |
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Ratio (Weight) |
1.00 |
1.38 |
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End Frame |
Interior Frame |
End Frame |
Interior Frame |
Wind load |
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W1 Wall (kN) |
37.37 |
69.13 |
49.45 |
91.477 |
W1 Roof (kN) |
45.089 |
83.39 |
72.42 |
118.98 |
W2 Wall (kN) |
26.29 |
48.629 |
27.47 |
50.813 |
W2 Roof (kN) |
72.84 |
134.12 |
111.35 |
183.07 |
Seismic load |
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Wall |
0.323 |
0.595 |
0.238 |
0.442 |
Roof |
2.246 |
4.16 |
1.688 |
3.105 |
Vertical Clearance (m) |
7.634 |
7.750 |
7.684 |
7.434 |
Horizontal Clearance |
13.859 |
13.729 |
13.784 |
13.609 |
Maximum Vertical Deflection (mm) |
1.957 |
18.993 |
2.613 |
14.709 |
Maximum Lateral Deflection (mm) |
13.212 |
55.402 |
32.791 |
41.395 |
Coefficients (Min) |
Design |
Deflection |
Design |
Deflection |
Dead load |
0.6 |
- |
1.2 |
1.0 |
Live load |
0.75 |
1.0 |
1.05 |
0.8 |
Wind load |
0.225 |
0.42 |
0.6 |
0.8 |
Seismic load |
0.7 |
0.6 |
0.6 |
1.0 |
Crane load |
0.75 |
0.1 |
0.53 |
0.8 |
Based on the study the following conclusions are drawn,
The Steel consumption of this structure as per ASCE 7-2016 and IS 800 is in the ratio of 1: 1.38.
The Wind coefficient as per ASCE 7 -2016 code is least when compared to the Indian code. This results in a lesser wind load in American Design.
The Seismic load is slightly high in American code when compared to the IS code as the base shear seismic coefficient considered in the American Code is higher than the Indian Code.
The live load reduction is applicable based on the area of roof in American code, which is not taken in Indian Code when the slope is less than 100.
Serviceability condition (i.e., deflection) are very stringent in IS code and the advantage of wall covering is not explicitly mentioned.
In American code the allowable vertical deflection is span / 180 and for lateral deflection it is height / 100, whereas in Indian code the allowable vertical deflection is span / 180 and for lateral deflection it is height / 200.
The member design is governed by the strength criteria as per the American code and the serviceability is the main criteria as per the Indian Code.
Vertical and horizontal clearance are less as per Indian design due to the higher member depths.
The load combinations for the deflection as per the Indian code is the summation of two or more load cases where as in American code it is a single load case.
The study exhibits a tonnage difference of 38% higher in Indian code to American code. The revision of IS code will make it compatible with other international standards. In IS 800-2007 the serviceability limit is somewhat bought down but it has to be looked in detail with respect to American code. The sway and deflection limits are higher in American code which directly affects the section sizes. So, these limits can be revised based on Indian conditions. Separate codal provisions for Pre-Engineered buildings is important which helps to optimize the steel consumption and in overall cost reduction.
The limitation of the study is that it is caried out for a location in India and the design is done based on the prevailing Indian conditions using American code. Several considerations in American code are taken with respect to Indian topographical condition. The study is further aimed in a comparison of single slope building with other structures like multi gable, mono gable including various building components like mezzanine, monorail, pipe rack in both the codes.
We wish to express our sincere thanks to BlueScope Steel India Private Limited for providing the facilities to carry out this work. We are proudly obliged to render our immense gratitude to R.M.K. Engineering College for providing an excellent platform to connect with the industry.