Wind and Seismic Analysis of Pre-Engineered Building

Abstract

With the development of science and technology in the field of structural engineering, it is possible to adopt pre- engineered buildings in both industrial and residential construction sectors. For important buildings it is more suitable to use pre engineered building as these are more safe and take less time in construction in comparison of RCC structures. In this paper, pre-engineered steel structure will be design and analyzed for wind and seismic analysis with different parameters using software Staadprov8i and analyzed with different loads on building i.e. dead load, live load, wind load, seismic load and load combinations on structure. The main objective of this work is to understand the concepts of PEB and find the least possible weight of structure and various displacement or significance of forces in each direction which will help the structure to be safe and stable. The pre-engineered construction concept involves pre-engineering and quality construction systems which will help to minimize the use of cost and time.

Introduction

I. INTRODUCTION

Steel Industry is growing rapidly all around the world. To meet the increasing demand of construction, alternative ways of construction are developing. Advances in technology have greatly improved over the years, contributing tremendously to improving living standards through various new products and services. A pre-engineered building (PEB) is one such revolution. They use a defined stock of raw materials that have been time tested to meet a wide range of structural and architectural design specifications. The majority of steel structures being built are only low-rise buildings, which are generally of one storey only. Industrial buildings, a subset of low-rise buildings are normally used for steel plants, automobile industries, light, utility and process industries, thermal power stations, warehouses, assembly plants, storage, garages, small scale industries, showrooms, offices etc. The application of pre-engineered building concepts to low rise buildings is very economical due to its light weight and economical construction. PEB systems are extensively used in industrial and much other non-residential construction world-wide. These buildings were pre-designed or 'pre-engineered' into standard sizes, spans, bays and heights, and use standard details for fixing cladding, roofing, gutters, flashing, windows, doors etc. taking advantage of industrial practices of mass production of components economically.

II. PRE ENGINNERED BUILDING

In structural engineering, a pre-engineered building (PEB) is designed by a manufacturer to fabricated using a pre-determined inventory of raw materials and manufacturing methods that can efficiently satisfy a wide range of structural and aesthetic design requirements. Pre-engineering building primary frame structure is an assembly of I-shaped structural members. The I-shaped beams are usually formed in the factory by welding steel plates together to form the I-sections. The I-section beams are then assembled on site with bolted connections to form the entire frame of the pre-engineered building. Tapered sections are also used to achieve varying depth. The concept of PEB is the frame geometry which matches the shape of the internal stress (bending moment) diagram thus optimizing material usage and reducing the total weight of the structure. The use of steel structures is not only economical but also eco-friendly at the time when there is a threat of global warming. Here, “economical” word is stated considering time and cost. Time being the most important aspect, steel structures (Pre- fabricated) is built in very short period and one such example is Pre Engineered Buildings (PEB). Pre-engineered building are steel building wherein the framing members and other components are fully fabricated in the factory after designing and brought to the site for assembly, mainly by nut-bolts, thereby resulting into a steel structure of high quality and precision. Steel is an expensive material as compared to the rest but when it comes to the cost-savings during the life span of the structure, steel proves to be a very affordable material . Steel can also be made rust proof by the application of special coated paints. Apart from that, steel is an insect and termite resistant material and the maintenance cost is lower during its life span as compared to other materials. PEB are generally low rise buildings however the maximum eave height can go up to 30 metres, Clear span upto 90 meter wide are possible.

III. WIND ANALYSIS

The force exerted by the horizontal component of wind is to be considered in the design of buildings, towers etc. The wind force depends upon the velocity of wind, shape, size & location of buildings. Wind analysis calculation given below according to IS code

875 part 3:1987 ;

Design wind speed Vz = Vb k1 k2 k3 Where,

Vz =Design wind speed at any height z in m/s,

Vb =Basic wind speed calculated from wind speed map of India, k1=Probability factor (risk coefficient clause 5.3.1),

k2=Terrain, height and structure size factor (clause 5.3.2) and k3=Topography factor(clause 5.3.3)

Design wind pressure Pz=0.6 Vz2 Where,

Pz=Design wind pressure in N/m2 at height z and Vz =Design wind speed at any height z in m/s

Wind load on individual structural member such as roofs, walls and cladding given as:

F=(Cpe – Cpi) A Pz Where,

Cpe=External pressure coefficient, Cpi=Internal pressure coefficient,

A=Surface area of structural member or cladding unit and Pz=Design wind pressure in N/m2 at height z

IV. SEISMIC ANALYSIS

Earthquake is a natural procedure of shaking ground due to movement of tectonic plate. The force of earthquake is random so the design engineer need to care full predict of these force and analyze the structure under these random force. Earthquake loads are to be carefully modeled so as to assess the real behavior of structure with a clear understanding that damage is expected but it should be regulated.

Earthquake plays an influential role in analysis and design of structures. Seismic analysis is a branch of structural analysis that involves calculation of a building's (or non building's) earthquake response. Analysis is the process to determine the behavior of structure under specified load combinations.

A. Equivalent Static Lateral Force Method

This is a very simple method of analysis. The main assumptions in these method are that the lateral force is equivalent to actual loading.

In these method, the Base Shear which is total horizontal force on the structure is calculated on the basis of the structure mass and its fundamental time period of vibration. The total design lateral force or design seismic base shear (VB) along any principal direction shall be determined with the help of following expression:

VB = Ah W

Where,

Ah = Design horizontal acceleration spectrum using fundamental natural period Ta, W = seismic weight of all the Building

The Design horizontal Seismic Coefficient Ah for a Structure will be evaluated by expression:

Z = Zone Factor,

I = Importance Factor

Sa/g = Average response Spectrum Coefficient using soil type and fundamental time period R = Response reduction factor

Above the Value of W, Z, I, Sa/g, and R are dependent on the IS 1893 (Part 1): 2016

V. MODELING

In present study, single pitched roof industrial structure of portal frame type modeled. The steel structure of portal frame type analyzed using staadProV8i software.

IS codes we used for wind load calculation IS 875 (part 3) : 1987 and for seismic load calculation IS 1893 (part 1) : 2016.

The Behavior of industrial structure have been studied in terms of Displacement and unity check applied to achieve economical structure.

A. Structural Modeling

Table 1: Structural properties of model

B. Design Parameters

Table 2: Properties of Design Parameters

VI. RESULT AND DISCUSSION

Wind and seismic analysis are being carried out in accordance with Indian Codes. The result are displayed in terms of displacements in X, Y and Z direction and Unity Check for optimized structure. As the structure is considered for pinned support connections there will be zero bending moment in X, Y and Z direction.

A. Displacement

Displacement is taken from the software which have been further checked for permissible limits criteria (L/240) according to IS 800:2007 clause 5.6.1 table no. 6. The results in terms of maximum and minimum deflection for X,Y and Z direction shown below.

B. Unity Check

Unity check have been performed by optimizing structure several times to get stable and economical structure. Utilization ratio permissible limit is 0.95 and to avoid getting over safe structure we considered utilization ration between 0.5 and 0.95 which gives us stable and economical structure. The results for unity check taken from the software are shown below in table.

Conclusion

This study explains the behavior of modeled pre engineered building for two most important load factors wind load and seismic load, the conclusion are explained below based on the extracted results: 1) The analysis shows that the value of maximum and minimum deflection for X direction is 52.532 mm and -40.325 mm respectively. 2) The analysis shows that the value of maximum and minimum deflection for Y direction is 32.576 mm and -35.989 mm respectively. 3) The analysis shows that the value of maximum and minimum deflection for Y direction is 14.594 mm and -14.653 mm respectively. 4) On comparing the results we get that deflection is highest for X direction in comparison of Y and Z direction. X direction goes along width of the structure therefore width wise will attain highest deflection. 5) The Unity check results shows that the member properties are within limit between 0.5 and 0.95. Hence structure is stable and cost saving.

References

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Copyright

Copyright © 2022 Umang Jain, Dr. J. N. Vyas. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.