seismic analysis of rcc, rcs and steel structures · seismic analysis of rcc, rcs and steel...

SEISMIC ANALYSIS OF RCC, RCS AND STEEL STRUCTURES

1Nikhil Chaudhari 2Bhakti Harne & 3 Rohan Choudhary

1PG student, M. Tech in Structural Engineering, Civil Engineering Department, Sandip school of Engineering and Technology, Sandip University, Nashik, Maharashtra, India.

2Assistant Professor, Department of Civil Engineering, Sandip school of Engineering and

Technology, Sandip University, Nashik, Maharashtra, India.

3Assistant Professor, Department of Civil Engineering, Sandip school of Engineering and Technology, Sandip University, Nashik, Maharashtra, India.

[email protected] [email protected]

[email protected]

Abstract: This topic presents an evaluation in construction method for multistory building. Gives

an alternative way of construction in high risk seismic zone made of combination of reinforced

concrete-steel (RCS). Past studies have shown these systems to be efficient in both design and

construction stages while able to maintain sufficient strength and ductility necessary in seismic

applications. This paper goals to enable the better receiving and use of merged RCS systems as a

viable alternative to lateral load resisting systems in assessment with the conventional RCC and

Steel frames. 12 models are considered to represent RCS, RCC and Steel (Four each) frames for

study. These Four Models are of height of 16m, 24m, 32m, 40m, respectively for representing each

frame. The provisions of IS 1893-2016 are adopted to obtain the seismic response of structures.

Seismic forces on structures are calculated for different heights and different parameters such as

time period, base shear, base moment and maximum roof displacement are presented. From this

study, I found that the RCS frame performs better or are well suited up to a height of 32m. A height

of 40m RCS structure becomes more vulnerable than RCC and Steel frames.

Keywords: Seismic, RCS, RCC, Steel, Seismic Response, Alternative.

1. INTRODUCTION

Tall building frames in India are mostly constructed using RCC material. This type of structure involves considerable dead weight and exhibits less ductility. In contrast, steel structure is most efficient type of structure as it is more ductile and involves very less dead weight. But as steel is costly material in India pure steel frames for high rise buildings are rarely seen. A combination of RCC and steel structural components is made in RCS frame. They provide excellent stiffness with RC columns and energy dissipation capacity through steel beams. As opposed to conventional steel or RC moment frames, the problems associated with connections are greatly reduced, and the RCS frames are generally more economical than purely steel or RC moment frames. In the United States, RCS moment frame construction was introduced during the late 1970’s and 1980’s as a variation of conventional steel frames in mid to high-rise buildings. These composite systems resemble conventional steel frame construction except that the steel columns are replaced by high strength reinforced concrete with the incentive to reduce material cost (Griffis

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1992). Innovative construction sequencing and connection detailing add to the attractiveness of RCS construction. In Japan, RCS frames developed as an alternative to conventional reinforced concrete construction for low- rise office and retail buildings (Yamanouchi et al. 1998). Here, steel beams are utilized to permit long span floor framing and to minimize field labor, while still achieving the material cost savings provided by reinforced concrete columns. Extensive collaborative research has been conducted in the United States and Japan to study the basic force transfer mechanisms in the connection region, as well as various joint details that could enhance the connection performance, especially under seismic excitations. Stanford University has undertaken this task and research is in process. India is the fastest growing country across the globe and need of shelter with higher land cost in developing cities like Chennai, Mumbai, Delhi, Bangalore where further horizontal expansion is not possible due to space shortage, the only option left with the vertical expansion. The reinforced concrete members are mostly used in the framing system for most of the building since this is the most convenient and economic system for low-rise buildings. Nevertheless, for average to tall rise building this type of structure is no longer economic because of enlarged dead load, fewer stiffness, span limit and unsafe formwork.

Figure 1. Yishun Community Hospital Site, Singapore

2. METHODOLOGY

1) All the dimensions, loads and load combination are considered according to IS 456:2000. 2) Model calculations of equivalent static analysis are formulated on the MS-Excel sheet according to IS 1893(Part I):2002. 3) Different models are made with a square and irregular floor plan for all RCS, RCC and Steel structure. 4) Finite element software ETABS v17 is used to find the seismic performance of the models. 5) All models are be analyzed for seismic SMRF building with zone V. 6) Results are compared with all structures in terms of story drift, lateral displacement, base shear and time period. 7) Results are extract from ETABS and graphs will be plotted using MS Excel.

2.1 Model Description:

Total 12 frames are considered by varying height and type of frames i.e. RCC, RCS and Steel. Each frame has 4 models consisting of 16m, 24m, 32m, and 40m respectively. The detailed description of all selected frames is given in table-2.1A, 2.2B and 2.2C. The story height is kept as 4.0m and the bay width in both longitudinal as well as transverse direction is kept as 5.0m. Models will be analyzed for seismic SMRF building with seismic zone V and also live load reduction concept is adopted. Plan area for all models is kept same which is 25m X 25m with 6 bays in both longitudinal as well as transverse direction as shown in Fig-2.1. Supports are considered as fully restrained i.e. fixed for all models. Material properties assumed in this study are given in table-2.2. Also, the seismic design data assumed for the study are given in table -2.3. For convenient result presentation, suitable designations are given to the frames. For ex. EQ X &Y 16m denotes

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equivalent static base shear or moment in X & Y direction for the model of height 16m. Similarly, RS denotes response spectra and TH denotes time history. RCS-RCC denotes comparison between RCS and Reinforced Cement Concrete frames. RCS-Steel denotes comparison between RCS and Steel frames.

Figure 2.1 Plan

Table 2.1 Geometric Parameters (common for all models)

Table 2.2 Material properties and Geometric properties

SR. NO. PARAMETER VALUE

1 Unit weight of concrete 25 kN/m

2 Unit weight of masonry wall 18 kN/m

3 Characteristic strength of concrete 40MPa

4 Characteristic strength of steel 500 Mpa

5 Steel grade of rolled sections Fe360

Table 2.3 Column size of different heights of models

Sr. No. PARAMETER RCC STEEL RCS

1 Floor finish 1.5 kN/m2

2 Live Load on Floor 2.5 kN/m2

3 Roof live load 1.5 kN/m2

4 Slab (thk) 120 mm

5 Wall (thk) 230 mm

6 Beams 230X300 ISLB300 ISLB300

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In above table the steel column is made by using section design command and sections can be made by using 2-I sections (built-up) connected with two 10mm thick plates to flanges. As shown in Fig-2.2

Figure 2.2 Steel built-up section for column

Table 2.4 properties of Built-up column section

SECTION 2-ISWB300 2-ISWB350 2-ISWB400 2-ISWB450

Area, mm4 (x102) 160.7 223.6 280.3 340.2

Ixx, mm4 (x104) 32676.4 56747.4 111820.5 168808.5

Iyy, mm4 (x104) 19703.8 28064.7 34812.1 66025.1

Rxx, mm 142.6 159.3 199.7 222.8

Ryy, mm 110.7 112 111.4 139.3

Zxx, mm4 (x103) 2119.9 3412.3 5325.5 7213.2

Zyy, mm4 (x103) 1503.4 2235.5 2803.3 4252.2

Table 2.5 Seismic data used for analysis

Zone factor (Z) 0.36

Importance factor (I) 1

Response reduction factor (R) 2.5

Soil type Hard

Damping ratio 0.05

2.2 Analysis and calculations: Finite element software ETABS is used to find the seismic performance of the structures. Equivalent static analysis and Dynamic (Response spectra & Time history) analysis is carried out on above model. The Time History analysis is carried out by considering the plots of El-Centro 1940. As per the clause of IS code the live load is considered as 25% for less than and up to 3 KN/m2 and 50% for more than 3 KN/m2. Beams and columns are modelled as frame element and Slab is modelled as a membrane. The floor slabs are assumed to act as diaphragms which ensure

Height of

building PARAMETER RCC STEEL RCS

16M COLUMN 350X350 2-ISWB300 + 2-10mm plate 350X350




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that beams and slab is rigidly connected. The weight of slab and slab loads are distributed as triangular and trapezoidal on the beams. The brickwork load is distributed linearly on beam.

Response Spectra Function is defined as per IS 1893-2016 Part I. 2.2.1 Analysis of frame using FEM software Etabs: Link Element: A link element connect two joints, i and j, separated by length L, such that specialized structural behavior may be modeled. Linear, Nonlinear and frequency-dependent properties may be allocated to each of six deformational degree of freedom (DOF) which are inner to link, counting axial, shear, torsion and pure bending. Internal deformation is then calculated from joint j displacement related to joint I, where it may be grounded to simulate a support point. Frame Element: Frame objects, used to model beams, columns, braces, and truss elements in planar and 3D systems, are straight lines which connect two nodes. Biaxial bending, torsion, axial deformation, and biaxial shear are all accounted for in the beam-column formulation which characterizes frame behavior. Numerous straight sections may be used to model curled members, and features are accessible for non-prismatic members.

3. RESULTS

3.1 Base Share (BS): For all models, the base shear and base moment in both the principle (longitudinal & transverse) directions are same i.e. for 16m, 24m, 32m, and 40m height respectively. This parameter is found to be minimum for RCS model and maximum for RCC model, except steel frame of height 40m.

Figure 3.1 base share (16m)

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The % variation of base shear, RCS frames compared with RCC and Steel frames are tabulated in table 3.1 as shown in figure 3.5 and 3.6.

Table 3.1 %variation in base shear

MODEL 16M (1) 24M (2) 32M (3) 40M (4)

EQ RCS-RCC 6.328 6.754 6.917 6.572

RS RCS-RCC 6.666 6.668 6.549 6.364

TH RCS-RCC 2.178 6.939 7.371 6.140

EQ RCS-STEEL 5.471 4.473 5.445 -6.564

RS RCS-STEEL 3.139 5.210 4.287 -0.261

TH RCS-STEEL 14.339 3.541 7.512 9.620 Note: The positive value in the table depicts that the value for other frames is more than that of the RCS frame and Vice-e- versa.

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Figure 3.5 % variation in Base shear of RCS and RCC frames

Figure 3.6 % variation in Base shear of RCS and Steel frames

3.2 Base Moment (BM):

The base moments of different models as shown in Fig- 3.7 to 3.10

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Figure 3.7 Base Moment (16m)




The % variation of base moment, RCS frames compared with RCC and Steel frames are

tabulated in table-4.2 and as shown in Fig- 3.11 and 3.12

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Table 3.2 % variation in Base Moment

MODEL 16M (1) 24M (2) 32M (3) 40M (4)

EQX RCS-RCC 7.077542 7.255847 7.293441 6.866671

RSX RCS-RCC 7.185972 7.423117 7.430709 7.005911

TH RCS-RCC 7.14268 8.519039 14.7721 6.356628

EQX RCS-STEEL 5.528768 4.489785 5.462399 -5.86144

RSX RCS-STEEL 4.68249 2.809407 4.040415 -6.97114

TH RCS-STEEL 12.35143 2.054483 6.570246 -6.34177

Note: The positive value in the table depicts that the value for other frames is more than that of the RCS frame and Vice-e- versa

Figure 3.11 %variation in Base Moment of RCS and RCC frames

Figure 3.12 %variation in Base Moment of RCS and Steel frames

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3.3 Model Time Period (MTP): The sum of modes to be used in the study earthquake quaking along a considered direction should

be such that the sum over-all of modal masses of all modes considered is at least 90 percent of the

total seismic mass and it is more vulnerable in the first three modes and so they are considered for

study purpose.

The three modal time periods are considered for study, mode 1, 2, and 3, in longitudinal, transverse

direction and torsional movement respectively. The graph shown below represents the values of

time periods for their respective modes that are obtained by the analysis of the structure. The MTP

found less in steel frames. From the comparison of RCS-RCC frames the MTP found less up to

height of 24m, equal for 32m and maximum in 40m model. Fig- 3.13 to 3.16 shows the time

periods of models.

Figure 3.13 Time Period (16m)


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3.4 Roof or Maximum Top Story displacement (RSD):

The RSD increases as the height of the building increases. The Fig- 3.17 to 3.20 represents the displacement values for all models. As we know that steel is a ductile material, therefore the RSD is found to be less in steel frames and more in RCC frames. For RCS frames the RSD value found in between the value of RCC & Steel frames up to height of 32m and for the height of 40m it is found that RSD is more as compared to RCC & Steel frames.

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Figure 3.17 Top Story displacement (16m)



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The % variation of maximum roof displacement, RCS frames compared with RCC and Steel frames are tabulated in table- 3.3 and as shown in Fig- 3.21 and 3.22.

Table 3.3 %variation in roof displacement

Note: The positive value in the table depicts that the value for other frames is more than that of the RCS frame and Vice-e-versa.

Figure 3.21 %variation in roof displacement of RCS and RCC frames

MODEL 16M (1) 24M (2) 32M(

3) 40M (4)

EQ RCS-RCC 0.487 0.538 0.018 -1.223

RS RCS-RCC 0.442 0.133 0.471 -1.033

TH RCS-RCC 1.006 0.388 -0.560 -0.925

EQ RCS-STEEL -2.954 -1.434 -0.056 -7.849

RS RCS-STEEL -3.188 -1.286 -0.018 -3.308

TH RCS-STEEL 2.618 -2.270 -0.093 -2.816

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Figure 3.22 %variation in roof displacement of RCS and Steel frames

4. CONCLUSION

Up to certain height the performance of RCS frame is found to be better than RCC and Steel

frames. As we know that steel is a ductile material therefore, the time period and roof

displacement are found to be less in steel frames.

The MTP increases with successive increase in the height of structure. Successive

increment in models is adopted as 8m for study. For RCC frame, MTP increase in the range

of 25.98% to 52.91%, 25.98% to 52.91% and 24.5 to 51.83 for mode-1, 2 and 3

respectively. For Steel frame, MTP increase in the range of 23.36% to 57.86%, 28.14% to

54.01% and 25.13% to 54.83% for mode-1, 2 and 3 respectively. And for RCS frame, time

period increases in the range of 26.44% to 54.47%, 26.44% to 54.47% and 24.84% to

53.59% for mode-1, 2 and 3 respectively. The time period is found to be less for steel

frames because of its ductile nature.

The BS of RCS frames, found to be less as compared to RCC & Steel frames. The % of

variation is found to be 2.18% to 7.37% and 3.14% to 14.34% for RCC and Steel frames

respectively in X and Y direction, both static and dynamic analysis. Except steel frame of

height 40m, the BS is found more in RCS and the variation is found to be 0.26% to 6.56%

in static and response spectra analysis.

The BM of RCS frames, found to be less as compared to RCC & Steel frames. The % of

variation is found to be 6.36% to 14.77% and 2.81% to 12.35% for RCC and Steel frames

respectively in X and Y direction, both static and dynamic analysis. Except steel frame of

height 40m, the BM is found more and the variation is found to be 5.86% to 6.97% in static

and dynamic analysis.

The RSD for RCS as compared with RCC frames, the % of variation is found 0.02% to

1.01% less up to a height of 32m and for the height of 40m it is found 0.93% to 1.24%

more. And for RCS compared with Steel frames the % of variation is found to be 0.06% to

7.85% more, up to height of 40m in both static and dynamic analysis. Except for 16m

model the variation is found 2.62% less.

From this study, I conclude that the RCS frame performs better or are well suited up to a

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height of 32m. A height of 40m RCS structure becomes more vulnerable than RCC and

Steel frames.

5. ACKNOWLEDGEMENT

The authors wish to thank and acknowledge the support extended by the Sandip School of

engineering and technology, Nashik.

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