Inte rnational Journal of Engineering Technology, Manage ment and Applied Sciences

www.ijetmas.com August 2015, Volume 3, Issue 8, ISSN 2349-4476

Comparative Study on Dynamic Analysis of Composite, RCC & Steel Structure Varsha Patil, Post Graduate Student in Structural Engineering, Saraswati College of Engineering, Kharghar Shilpa Kewate , Assistant Professor, Saraswati College of Engineering, Kharghar ABSTRACT Reinforced concrete and steel are the materials that are mostly used in the framing system for most of the building. Steel members have the advantages of high tensile strength and ductility, while concrete members have the advantages of high compressive strength and stiffness. Composite members combine steel and concrete, resulting in a member that has the beneficial qualities of both materials. The present study is based on structural behavior of Composite, RCC and Steel structure when subjected to earthquake. In the present work RCC, steel and composite materials are considered for comparative study of G+5 story commercial building which is situated in earthquake zone III, The provisions of IS:1893 (Part 1) is considered. A three dimensional modeling and analysis of the structure are carried out with the help of Etabs 2013 software. Equivalent static analysis and Response spectrum analysis are carried out on all three structures. The results are compared in terms of base shear, Lateral force distribution, maximum displacement, Time period and frequency, and found that composite structure gives better performance compare to RCC and steel.

Keywords Composite beam, Composite column, Deck slab, Base shear, displacement

1.INTRODUCTION In India reinforced concrete members are mostly used in the framing system for most of the buildings since this is the most convenient & economic system for low-rise buildings. However, for medium to high rise buildings this type of structure is no longer economic because of increased dead load, high stiffness, span restriction and hazardous formwork. Whereas in case of steel structures, steel has a high strength/weight ratio. Thus, the dead weight of steel structures is relatively small. This property makes steel a very attractive structural material for High-rise buildings ,long-span bridges, structures located in highly seismic areas where forces acting on the structure due to an earthquake are in general proportional to the weight of the structure. steel can undergo large plastic deformation before failure, thus providing a large reserve strength. This property is referred to as ductility. Properly designed steel structures can have high ductility, which is an important characteristic for resisting shock loading such as blasts or earthquakes. Steel in fact shows elastic behavior up to a relatively high and usually well-defined stress level. Also, in contrast to reinforced concrete, steel properties do not change considerably with time. But due to high strength/weight ratio, steel compression members are in general more slender and consequently more susceptible to buckling than, say, reinforced concrete compression members. Another disadvantage of steel is that, the strength of steel is reduced substantially when heated at temperatures commonly observed in building fires. Also, steel conducts and transmits heat from a burning portion of the building quite fast. Though these materials may have different properties and characteristics, they both seem to complement each other in many ways. steel has excellent resistance to tensile loading but lesser weight ratio so thin sections are used which may be prone to buckling phenomenon. On the other hand concrete is good in resistance to compressive force. Steel may be used to induce ductility an important criteria for tall building, while corrosion protection and thermal insulation can be done by concrete. Similarly buckling of steel can also be restrained by concrete. In order, to derive the optimum benefits from both materials composite construction is widely preferred. With the latest requirements in the market, it has become a necessity of time in India to reduce the construction time by adopting fast track construction methodologies as well as allowing parallel construction activities. The saving in construction time yields two fold benefits like reduction in investment in the form of interest and early return of the capital invested. Steel-concrete composite construction being a faster

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Varsha Patil, Shilpa Kewate

Inte rnational Journal of Engineering Technology, Manage ment and Applied Sciences

www.ijetmas.com August 2015, Volume 3, Issue 8, ISSN 2349-4476 technology saves lot of time of construction and hence adoption of such methodology will help the planner to narrow the gap between demand and supply. It also provides more carpet areas that means more usable space. Hence ,steel-concrete composite construction is the answer of the future development in India. 1.1 Composite structure & it's elements A composite member is defined as consisting of a rolled or a built-up structural steel shape that is either filled with concrete, encased by reinforced concrete or structurally connected to a reinforced concrete slab. Composite members are constructed such that the structural steel shape and the concrete act together to resist axial compression and or bending. 1.1.1 Composite beam ISMB/ISWB steel section is made composite with the RCC slab or steel deck with the help of shear studs. The beams are considered effective as composite against sagging moment and the hogging moments are being resisted by the steel section alone. 1.1.2 Profiled Deck Composite floors using profiled sheet decking is use where the concrete floor has to be completed quickly and where medium level of fire protection to steel work is sufficient. In composite floors, the structural behavior is similar to a reinforced concrete slab, with the steel sheeting acting as the tension reinforcement. 1.1.3 Shear Connectors Shear connectors are steel elements such as studs, bars, spiral or another similar devices welded to the top flange of the steel section and intended to transmit the horizontal shear between the steel section and the cast in-situ concrete and also to prevent vertical separation at the interface.

Figure 1: Profiled Deck & Shear Connectors 1.1.4 Composite Column A steel-concrete composite column is conventionally a compression member in which the steel element is a structural steel section. There are three types of composite columns used in practice which are Concrete Encased, Concrete filled, Battered Section.

Figure 2: Composite Column

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Varsha Patil, Shilpa Kewate

Inte rnational Journal of Engineering Technology, Manage ment and Applied Sciences

www.ijetmas.com August 2015, Volume 3, Issue 8, ISSN 2349-4476 1.2 Advantages of composite structure  Most effective utilization of materials viz. concrete in compression and steel in tension.  Steel can be deformed in a ductile manner without premature failure and can withstand numerous loading cycles before fracture. Such high ductility of steel leads to better seismic resistance of the composite section.  Steel component has the ability to absorb the energy released due to seismic forces.  Ability to cover large column free area. This leads to more usable space. Area occupied by composite column is less than the area occupied by RCC column.  Quality of steel is assured since it is produced under controlled environment in the factory. Larger use of steel in composite construction compared to RCC option ensures better quality control for the major part of the structure.  Smaller structural steel sections are required compared to non-composite construction, therefore reduction in overall weight of the composite structure compared to the RCC construction results in less structural and foundation cost.  Faster construction by utilizing rolled and/or pre-fabricated components. Also speedy construction facilitates quicker return on the invested capital. 2. BUILDING DESCRIPTION The basic planning and the loading conditions are considered same for RCC, Steel and Steel-concrete, composite structure. In case of RCC structure, the structural members slab, beam and column are considered RCC and designed as per IS456:2000, in case of steel structure RCC slab, laterally supported steel beams and steel column have considered and designed as per IS800:2007 and in case of steel concrete composite structure the composite beams are designed with structural steel section anchored to the steel deck slab with the help of shear studs and columns are considered made of RCC having structural steel section in its core and reinforcement in the concrete outside and designed as per AISC360:10.The lateral loads are considered to be carried by the beam column frame as a moment resisting frame. For the analysis and design, the following design basis have considered:

Type of building Type of frame Total height of building Plan of the building Thickness of external walls Live load in office area Floor finish load Grade of Concrete Grade of reinforcing Steel Grade of structural steel Density of Concrete Density of brick masonry Zone Soil type Importance factor Seismic zone factor Damping ratio

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Varsha Patil, Shilpa Kewate

Table 1 : Design basis Office Moment Resisting Frame 25.5 m 30m × 18m 230m 4 kN/sq.m 1.5 kN/ sq.m M30 Fe415 Fu = 410 N/mm2 , Fy = 250 N/mm2 25 kN/m3 20 kN/m3 III Medium soil 1.5 0.16 for zone III 5% (For RCC structure) : 2% (For Steel and Composite structure)

Inte rnational Journal of Engineering Technology, Manage ment and Applied Sciences

www.ijetmas.com August 2015, Volume 3, Issue 8, ISSN 2349-4476 3.MODELING AND ANALYSIS

Figure 3: Building model plan and 3-D view 3.1 Structural member sizes Table 2: Structural member sizes Member

RCC

Steel

Composite

Secondary beam

200mm X400mm

ISWB350

ISWB 250

Main Beam (XDirection)

300mm X700mm

ISWB 500

ISWB 550

Main Beam (YDirection)

250mm X 600mm

ISWB450

ISWB450

Column

400mm X750mm

ISHB 400-2 with 40mm plate attached to both flanges

450mmX600mm with ISHB400 encased

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Varsha Patil, Shilpa Kewate

Inte rnational Journal of Engineering Technology, Manage ment and Applied Sciences

www.ijetmas.com August 2015, Volume 3, Issue 8, ISSN 2349-4476 The explained 3D building model is analyzed using Equivalent Static Method and response spectrum method a per IS 1893 (PART-1): 2002 . Different parameters such as Base shear, deflection, Time period and frequency are studied for the models. 4.RESULTS AND DISCUSSION A) Equivalent Static Analysis : Equivalent static analysis is performed on all three types of structures. Loads are calculated and distributed as per the code IS1893: 2002 and the results obtained are compared with respect to the following parameters.  Base shear

Figure 4: Comparison of base shear Base shear due to earthquake load ,for composite building is found to be 1185.68kN which is lower than RCC by 30%,while for steel by 2%.  Lateral forces acting on structure

Figure 5: Comparison of lateral forces From graph it is clear that the lateral forces acting on a RCC structure are much more than steel and composite structure, hence composite structure is less susceptible against seismic forces action on structure.

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Varsha Patil, Shilpa Kewate

Inte rnational Journal of Engineering Technology, Manage ment and Applied Sciences

www.ijetmas.com August 2015, Volume 3, Issue 8, ISSN 2349-4476 

Lateral displacement in X-direction

Figure 6: Comparison of maximum displacement due to Eqx From the graph of displacement v/s story, it is observed that composite structure has less displacement compared to RCC & steel building.Percentage reduction in top story displacement along longitudinal direction of composite building is 25% and 1.5% compared to RCC and steel building.  Lateral displacement in Y-direction

Figure 7: Comparison of maximum displacement due to Eqy Percentage reduction in top story displacement along transverse direction of composite building is 14% and 7.8% compared to RCC and steel building. B) Response spectrum analysis Response spectrum analysis is performed on all three type of structures and the results obtained are compared with respect to the following parameters:

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Varsha Patil, Shilpa Kewate

Inte rnational Journal of Engineering Technology, Manage ment and Applied Sciences

www.ijetmas.com August 2015, Volume 3, Issue 8, ISSN 2349-4476  Time period

Figure 8: Comparison of Time period  Modal Frequency

Figure 9: Comparison of frequency The increased stiffness of composite structure results in increased frequency and reduction in time period than RCC and steel structure. The frequency of composite structure is increased by 14% than RCC and 7% than steel structure. 5.CONCLUSION  In case of composite structure system, because of lesser magnitude of beam end forces and moments compared to RCC and steel structure system, one can use lighter sections in a composite structure. Thus it reduces the self weight of structure component.

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Varsha Patil, Shilpa Kewate

Inte rnational Journal of Engineering Technology, Manage ment and Applied Sciences

www.ijetmas.com August 2015, Volume 3, Issue 8, ISSN 2349-4476  Composite frames are light weight structure with good strength and stiffness. Due to this reason, composite structure is less susceptible against seismic forces action on the structure.  From graph ,it is clear that the maximum displacement at top in a composite structure, compare to RCC and steel are less which is due to higher stiffness of members in a composite structure compared to RCC and steel structure..  The increased stiffness of composite structure results in increased frequency and reduction in Time period than RCC and steel structure. REFERENCES [1] [2] [3] [4] [5] [6]

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