Seismic performance of multi-storey rc Smrf and omrf

Journal of Structural Engineering Vol. 44, No. 6, February - March 2018 pp. 663-672

No. 44-65

Seismic performance of multi-storey rc smrf and omrf buildings A.K. Mapari*, and Y.M. Ghugal*  Email: [email protected]

*Applied Mechanics Department, Government College of Engineering, Karad - 415 124, India Received: 27 March 2017; Accepted: 24 August 2017

Reinforced concrete moment resisting frames are one of the widely used lateral load resisting systems. Special moment resisting frames (SMRFs) are known for its enhanced ductility capacity and used for the same in high seismic risk zones. In this study, performance assessment of multi-storey RC special moment resisting frames (SMRFs) and ordinary moment resisting frames (OMRFs) is presented to compare the base shear capacity and ductility of the buildings using SAP2000 software. The nonlinear static analysis i.e. pushover analysis is adopted for studying the behaviour of SMRFs and OMRFs. The effect of infill walls are also taken into account in terms of base shear and roof displacement. The buildings response reduction factors are obtained from the capacity curves obtained for each modelled building by studying its behaviour parameters such as overstrength factor and ductility reduction factor. The FEMA P695 methodology is used to calculate response reduction factors. Keywords: SMRF; OMRF; infill; pushover analysis; capacity curve; ductility; overstrength; response reduction factor.

In construction practices, among all the lateral load resisting systems, moment resisting frames are usually adopted over shear wall, bracings, etc. in reinforced concrete construction to provide the buildings architectural appeal and open spaces. Moment resisting frames are classified in two types such as Ordinary Moment Resisting Frames (OMRFs) and Special Moment Resisting Frames (SMRFs). SMRFs are the frames with special proportioning and detailing requirements lead to resist strong earthquake shaking without significant loss of stiffness or strength. These frames exhibit better performance in seismic events than OMRFs. When RC moment frames are selected for buildings, special moment resisting frames are assigned for the buildings in zones with high seismic risk, and the ordinary moment resisting frames are assigned to relatively low seismic risk zone. In moment resisting frames, special detailing promoting ductile failure modes lead to enhanced seismic performance. Generally, infill walls are not considered in analysis and design of RC frame buildings. They are assumed not to carry any vertical or lateral forces and alsoconsidered

not to transfer any forces between beams and columns that are generated in buildings during earthquake event, therefore known as non-structural elements. However, the brick infill walls in RC moment resisting frame buildings contribute significant strength and stiffness. It is noticed that the enhanced strength and stiffness of infill wall until they crack, alters the course of nonlinear response and also seen that infill walls reduce the maximum displacement and member ductility demand significantly1. It is explained that brick infill is responsible for withstanding strong seismic events in the past in case of many low-rise RC frame buildings without formal engineering design2. It is seen that the masonry infillscontribute significant lateral stiffness, strength, overall ductility and energy dissipation capacity. It is documented that average initial stiffness of infilled RC frame is about 4.3 times that of bare frame when masonry is unreinforced, and about 4 times that of bare frame when masonry is reinforced. On an average, unreinforced masonry infilled frames have about 70% higher strength than the bare frames; the value is about Journal of Structural Engineering Vol. 44, No. 6, February - March 2018

663

50% higher in case of reinforced masonry infilled frames. The average energy dissipation in unreinforced infill frames is about 22% higher than that in the reinforced infill frames3. Linear static or dynamic analysis does not accurately represent the actual behaviour of structures during strong seismic event as structures behave nonlinearly. So, the nonlinear analysis is important in obtaining accurate structural behaviour during strong seismic motion. Though the nonlinear analysis has become popular due to availability of ample number of analysis softwares with nonlinear capabilities such as SAP 20004, etc., the various non-linear static methods may lead to either significant overestimation or underestimation of the peak roof displacements5. It has been seen that buildings gave poor performances as height goes on increasing, though no collapse was noticed during non-linear analysis. It is concluded that it was due height-invarient or periodinvarient R factor assigned by the codes6. A profound knowledge of structural behaviour, geometric and material nonlinearities and also failure mechanisms is required to perform elaborate nonlinear analysis. Such elaborate and sophisticated analysis level for designing structures can’t be adopted in construction practices unless designing a special structure. To overcome this situation, use of moment resisting frames through lower design forces is encouraged by the design codes all over the world to gain more economical designs. For this, response reduction factors are used to arrive at economical and safe design accepting inelastic deformations and permanent damage to building. It has been seen that increasing the R factor from 4 to 5 reduces the design force and potentially the cost of building, up to about7 25%. On the other hand, restricting the R valuesis necessary to prevent excessive inelastic deformationsand loss of life, particularly in the event of a major earthquake. It has been shown that the buildings, which are properly designed and constructed as per the Indian standards for the gravity loads only, can generally survive a seismic excitation up to Maximum Considered Earthquake (MCE) of the zone IV without collapse. The buildings designed as OMRF or as SMRF, as per the Indian standards, satisfy the immediate occupancy performance level, even for maximum considered earthquake8. So, the actual value of response reduction 664

Journal of Structural Engineering Vol. 44, No. 6, February - March 2018

factor should be calculated for design of seismic resistant buildings. In this paper, a comparative study of seismic performance of SMRFs and OMRFs in terms of base shear and ductility demand is presented considering the effect of bare frame and masonry infilled wall frames by performing nonlinear static analysis i.e., pushover analysis. Response reduction factors are also evaluated for each building considered. EVALUATION OF SEISMIC RESPONSE REDUCTION FACTOR Response reduction factor, R also called as behaviour factor9, response modifacation factor10,11, etc. is a force reduction factor used to obtain the inelastic response reducing the linear elastic response of structure. FEMA P69512 describes the process for evaluating the performance of a proposed seismic-force-resisting system, assessing the acceptability of a trial value of the response modification coefficient, R and determining appropriate values of the system overstrength factor (Ω0), and the deflection amplification factor (Cd). Performance evaluation is based on the results of nonlinear static and dynamic analyses conducted. It requires judgment in interpreting analytical results, assessing uncertainty, and rounding of values for design. It has been seen that the ductility demand of structure increases as it pushed towards plastic range13. FEMA 36911 commentary gives elaborate procedure to derive the response reduction factor from bilinear elastic plastic capacity curve obtained from pushover analysis of structure. It should be noted that the structural overstreng this the result of the development of sequential plastic hinging in a properly designed, redundant structure. Several other sources also increase structural overstrength. First, material overstrength as actual material strengths is higher than the nominal material strengths specified in the design (e.g. yield strength of Fe415 is usually greater than 415 MPa). Second, designers themselves introduce additional overstrength by selecting sections or specifying reinforcing patterns that exceed those required by the design calculation. Similar situations occur when minimum requirements given in design codes control the design (i.e. minimum reinforcement ratios). Finally, the design of many flexible structural systems, such as moment resisting frames, are often controlled by

the drift rather than strength limitations as suggested by the codes with sections selected to control lateral deformations rather than providing the specified strength. Thus, structures typically have a much higher lateral resistance than specified as a minimum by the codes. As the structure begins to yield and deform inelastically, the effective period of response of the structure tends to lengthen, which for many structures, results in a reduction in strength demand. Furthermore, the inelastic action results in a significant amount of energy dissipation, also known as hysteretic damping, in addition to the viscous damping. The combined effect, which is also known as the ductility reduction, explains why a properly designed structure with a fully yielded strength (Vy, in Fig. 1) that is significantly lower than the elastic seismic force demand (VE in Fig. 1) can be capable of providing satisfactory performance under the design ground motion excitations. Base shear VE

Actual response

Vy

Idealised response

Vs O

∆s

∆y

∆max

Displacement

Fig. 1 Typical capacity curve for evaluating R factor

The response reduction factor depends on ductility and overstrength of structure and the response reduction factor (R) is obtained by taking product of structural overstrength factor (Ω0) and ductility reduction factor (Rd). Again, these structural overstrength factor and ductility reduction factors are gained from observing the bilinear elastic perfectly plastic capacity curve (Fig. 1) and using following formulae:

Ω0 =

Rd =

Vy

(1)

VE Vy

(2)

Vs

Vy VE VE = (3) Vs Vy Vs Thus, the response reduction factor, R represents the ratio of the base shear that would have developed in structure had it remained entirely linear and elastic throughout the seismic ground motion to the base shear at first significant yield point. The value of R is always greater than 1.

R = Ω0 Rd =

BUILDING DETAILS A total 16 space frames are considered by varying height and type of frame i.e. special moment resisting frame and ordinary moment resisting frame. The detailed description of all selected frames is given in Table 1. The storey height is kept 3.5m and the bay width in both longitudinal as well as in transverse direction is kept 3m. The cross-section of beam is considered as 300mm × 500mm and the cross-section for column is considered as 400mm × 400mm. The response reduction factor for SMRF is 5 and for OMRF is 3 as per IS 1893 ( Part 1 ):200214. Plan for all models is kept same which is 18m × 12m with 6 bays in longitudinal direction and 4 bays in transverse direction (Fig. 2). Fixed supports are considered for all the models in study. For convenient result presentation, suitable designations are given to the frames. For example, 6S-SMRF-BF denotes six storey special moment resisting bare frame and 4S-OMRF-IF denotes four storey ordinary moment resisting frame with infill wall. Figures 3 and 4 shows typical elevation of 8 storey bare and infilled building in x and y direction respectively. Material properties and geometric parameters assumed in this study are given in Table 2. Also, the seismic design data assumed for the study are given in Table 3. MODELLING AND ANALYSIS The modelling of selected frames is done in SAP 20004. The building frames are first analyzed by response spectrum method i.e. linear dynamic analysis method and designed for it. For each analyzed frame, the design base shear (VB) obtained from response spectrum analysis is compared with the base shear (V’B) calculated using a fundamental time period Ta given in clause 7.6 IS 1893: 200214 for corresponding building modelled and the values of base shear obtained by response spectrum are then corrected by modified scale Journal of Structural Engineering Vol. 44, No. 6, February - March 2018

665

factor with the help of correction factor V’B/VB. Table 1 Details of building models

pushed until a collapse mechanism is developed. With the increase in the magnitude of loads, weak links and failure modes of the building are found. Table 3

Frame name

No. of storey

R

Frame

Type

Support conditions

4S-OMRF-BF

4

3

OMRF

Bare

Fixed

No.

6S-OMRF-BF

6

3

OMRF

Bare

Fixed

1

Seismic zone

8S-OMRF-BF

8

3

OMRF

Bare

Fixed

2

Zone factor

10S-OMRF-BF

10

3

OMRF

Bare

Fixed

3

Response reduction factor for SMRF

5

4S-SMRF-BF

4

5

SMRF

Bare

Fixed

4

Response reduction factor for OMRF

3

6S-SMRF-BF

6

5

SMRF

Bare

Fixed

5

Importance factor

1

8S-SMRF-BF

8

5

SMRF

Bare

Fixed

10S-SMRF-BF

10

5

SMRF

Bare

Fixed

6

Soil type

4S-OMRF-IF

4

3

OMRF

Infill

Fixed

6S-OMRF-IF

6

3

OMRF

Infill

Fixed

8S-OMRF-IF

8

3

OMRF

Infill

Fixed

10S-OMRF-IF

10

3

OMRF

Infill

Fixed

4S-SMRF-IF

4

5

SMRF

Infill

Fixed

6S-SMRF-IF

6

5

SMRF

Infill

Fixed

8S-SMRF-IF

8

5

SMRF

Infill

Fixed

10S-SMRF-IF

10

5

SMRF

Infill

Fixed

Table 2 Material properties and geometric parameters No.

Parameter

Value

1

Unit weight of concrete

25 kN/m3

2

Unit weight of masonry wall

18 kN/m3

3

Characteristic strength of concrete

25 MPa

4

Characteristic strength of steel

415 MPa

5

Damping ratio

5%

6

Slab thickness

150 mm

7

Wall thickness

230 mm

8

Modulus of elasticity of concrete

25000 MPa

9

Modulus of elasticity of infill wall

2482.2 MPa

Structures vibrating at fundamental modes, pushover analysis provides good estimates of global, as well as local inelastic, deformation demands15. Performance assessment of the designed frames is carried out using pushover analysis. Pushover analysis is a static nonlinear procedure to analyze a building where loading is incrementally increased with a certain predefined pattern (i.e., inverted triangular or uniform). Local non-linear effects are modelled and structure is 666


Design seismic data14 Parameter

Value V 0.36

Medium soil

Beams and columns are modelled as frame elements available in SAP20004, with lines joined at nodes. The floor slabs are assumed to act as diaphragms, which ensure integral action of all the vertical lateral loadresisting elements. The weight of slab and slab loads are distributed as triangular and trapezoidal load to surrounding beams as per IS 456: 200016. Auto hinge property of SAP20004 is used to introduce hinges in beams and columns to behave nonlinearly. Infill walls are modelled as equivalent diagonal strut10,17. Strut width by Mainstone17 or FEMA 35610 model is given as follows:

w = 0.175 ( λ1H )

−0.4

Ldiag

(4)

In which 0.25

 E t sin 2θ  (5) λ1 =  m inf   4 Ec I col hinf  The modulus of elasticity of infill wall given by Kaushik, et al.18 is used in this study. It is calculated as follows:

Em = 550fm f m = 0.433 fb 0.64 f mo 0.36 �

(6) (7)

RESULTS AND DISCUSSIONS The capacity curves for the 4-storey, 6-storey, 8-storey and 10-storey buildings designed for both SMRF and OMRF in x-direction are shown in Figs. 2-5 respectively. Similar curves in y-direction are shown in Figs. 6-9 respectively. The figures describe the

8000 6000

4S OMRF BF

5000

4S SMRF BF

10000

0 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750

Roof displacement (mm)

Fig. 5 Capacity curve for 10 storey in x-direction

1000

7000 0 20 40 60 80 100 120140160 180 200 220 240 260

6000


Base shear (kN)

Fig. 2 Capacity curve for 4 storey in x-direction 9000 8000

6S OMRF BF 6S SMRF BF

6000

4S SMRF BF

4000

4S OMRF IF

2000

0

6S SMRF IF

4000

4S SMRF IF

3000

1000

6S OMRF IF

5000

4S OMRF BF

5000

3000


2000

Fig. 6 Capacity curve for 4 storey in y-direction

1000 0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480

Table 4 Performance Comparison of OMRF and SMRF Bare Frame Buildings in x direction Base shear (kN)

10000 9000 Base shear (kN)

8000

8S OMRF BF

7000

Storey

OMRF SMRF

8S SMRF BF

6000

8S OMRF IF

5000

8S SMRF IF

4000 3000 2000 1000 0

Displacement (mm)

OMRF SMRF

displacement in SMRF


% Increase in roof


% Decrease in base shear in smrf

Base shear (kN)

7000

0

10S SMRF IF

2000

2000 0

10S OMRF IF

4000

4S SMRF IF

3000

10S SMRF BF

6000

4S OMRF IF

4000

10S OMRF BF

8000

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280

Base shear (kN)

7000

12000

Base shear (kN)

nonlinear behaviour of buildings subjected to seismic force considering P-delta effect. Figures 2-9 show seismic behaviour of buildings considering the effect of bare frame and infill walls showing increased stiffness in case of infilled frames.

4

4348

2617

39.8

200

275

27.3

6

6132

3571

41.8

260

490

46.9

8

6670

3852

42.3

475

650

26.9

10

6678

3860

42.2

500

725

31.0

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700

The seismic response of special moment resisting bare frame buildings is compared to ordinary moment resisting bare frame buildings with fixed supports. Tables 4 and 5 shows the seismic performance comparison




667

8000 7000 Base shear (kN)

regarding the capacity of OMRF and SMRF bare frames to resist base shear and the maximum amount of roof displacement these can undergo in both x and y-directions. Similarly, Tables 6 and 7 describe seismic performance comparison between OMRF and SMRF infilled frames considering the base shear these can resist and roof displacement these can undergo. The tables also show the decrease in base shear and increase in displacements of SMRFs compared to OMRFs.

6000

8S OMRF BF

5000

8S SMRF BF 8S OMRF IF

4000

8S SMRF IF

3000 2000 0

Performance Comparison of OMRF and SMRF Bare Frame Buildings in y direction

4

4341

2596

40.2

230

285

19.3

6

5796

3343

42.3

330

580

43.1

8

5556

3198

42.4

475

750

36.7

10

5531

3133

43.3

525

700

25.0

OMRF

SMRF

SMRF

% Increase in roof displacement in SMRF

OMRF

Fig. 8 Capacity curve for 8 storey in y-direction

8000 7000 5000

10S SMRF BF

4000

10S OMRF IF 10S SMRF IF

3000 2000

8000

1000

7000

0 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750

6S OMRF BF

6000

6S SMRF BF

5000

6S OMRF IF

4000

6S SMRF IF

3000

Roof displacement (mm) Fig. 9 Capacity curve for 10 storey in y-direction Table 6

2000

Performance Comparison of OMRF and SMRF Infilled Frame Buildings in x direction

1000

Base shear (kN)

0 40 80 120 160 200 240 280 320 360 400 440 480 520 560

0 Roof displacement (mm) Fig. 7 Capacity curve for 6 storey in y-direction

The seismic response comparison between bare frames and infilled frames is presented in Tables 8 to 11. A significant increase in base shear and decrease in roof displacement is noticed in infilled frames as compared to bare frames. It shows the increase in initial stiffness in infilled frames as compared to bare frames. 668


Storey

OMRF SMRF

Displacement (mm)

OMRF SMRF

% Increase in roof displacement in SMRF

Base shear (kN)

10S OMRF BF

6000

% Decrease in base shear in SMRF

Storey


Base shear (kN)

Displacement (mm)


Base shear (kN)

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750

1000 Table 5

4

7362

7209

2.1

80

90

11.1

6

8311

7147

14.0

110

130

15.4

8

8880

6704

24.5

160

190

15.8

10

9687

7821

19.3

230

270

14.8

Table 7

Table 10

Performance Comparison of OMRF and SMRF Infilled Frame Buildings in y direction

Performance Comparison of Ordinary Moment Resisting Bare Frames and Infilled Frames in x direction Displacement (mm)

Infilled

% Increase in base shear in infilled frame

Base shear (kN)

% Decrease in roof displacement in infilled frame

Displacement (mm) % Increase in roof displacement in SMRF

Storey


Base shear (kN)

Bare

4

6280

5703

9.2

90

100

10.0

6

6883

5968

13.3

120

160

25.0

4

4348

7362

40.9

200

80

60.0

8

6941

5314

23.4

170

210

19.0

6

6132

8311

26.2

260

110

57.7

10

7473

6031

19.3

270

300

10.0

8

6670

8880

24.9

475

160

66.3

10

6678

9687

31.1

500

230

54.0

OMRF

SMRF

OMRF

SMRF

Storey

Bare

Infilled

Table 8

4

2617

7209

63.7

275

90

67.3

6

3571

7147

50.0

490

130

73.5

8

3852

6704

42.5

650

190

70.8

10

3860

7821

50.6

725

270

62.8

Bare

Infilled

Infilled


Bare

Storey

Table 9 Performance Comparison of Special Moment Resisting Bare Frames and Infilled Frames in y direction

Bare

Infilled


Storey

Displacement (mm)


Base shear (kN)

54.5

285

100

64.9

5968

44.0

580

160

72.4

5314

39.8

750

210

72.0

6031

48.1

700

300

57.1

Bare

Infilled

4

2596

5703

6

3343

8

3198

10

3133

Base shear (kN)

Storey

Displacement (mm)

Bare

Infilled


Displacement (mm)


Base shear (kN)

Table 11 Performance Comparison of Ordinary Moment Resisting Bare Frames and Infilled Frames in y direction


Performance Comparison of Special Moment Resisting Bare Frames and Infilled Frames in x direction

30.9

230

90

60.9

6883

15.8

330

120

63.6

5556

6941

20.0

475

170

64.2

5531

7473

26.0

525

270

48.6

Bare

Infilled

4

4341

6280

6

5796

8 10

The behaviour factors of buildings such as overstrength factor and ductility reduction factor are obtained from the capacity curves of each buildings. From the overstrength and ductility reduction factors, the response reduction factor is calculated using FEMA 36911. The response reduction factors for each building are given in Tables12 and 13. The depending parameters are extracted from the corresponding pushover curve such as VE, VY, and VS and the overstrength factor (Ω0) and ductility reduction factor (Rd) are calculated with the help of Eqs. (1) and (2) respectively. The response reduction factor (R) is then calculated by using Eq. (3).


669

CONCLUSIONS

Table 12 Response reduction factors (R) of buildings in x direction Rd

Ωo

R, calculated

R (IS 1893: 2000)14

4S-OMRF-BF

5.1

1.1

5.4

3

6S-OMRF-BF

3.1

1.0

3.3

3

8S-OMRF-BF

3.8

1.0

3.9

3

10S-OMRF-BF

3.1

1.1

3.2

3

4S-SMRF-BF

11.0

1.1

12.2

5

6S-SMRF-BF

9.4

1.0

9.8

5

8S-SMRF-BF

9.5

1.0

9.9

5

10S-SMRF-BF

7.6

1.1

8.0

5

4S-OMRF-IF

3.2

1.3

4.2

3

6S-OMRF-IF

2.5

1.4

3.4

3

8S-OMRF-IF

2.4

1.7

4.0

3

10S-OMRF-IF

2.4

1.6

3.7

3

4S-SMRF-IF

4.1

1.6

6.3

5

6S-SMRF-IF

4.3

1.5

6.4

5

8S-SMRF-IF

3.9

1.4

5.7

5

10S-SMRF-IF

3.6

1.5

5.4

5

Building details

Table 13 Response reduction factors (R) of buildings in y direction Rd

Ωo

R, calculated

R (IS 1893: 2000)14

4S-OMRF-BF

4.5

1.1

4.8

3

6S-OMRF-BF

4.1

1.0

4.2

3

8S-OMRF-BF

4.3

1.0

4.5

3

10S-OMRF-BF

3.8

1.0

3.9

3

4S-SMRF-BF

11.1

1.1

12.2

5

6S-SMRF-BF

11.4

1.0

11.9

5

8S-SMRF-BF

11.3

1.0

11.7

5

10S-SMRF-BF

8.6

1.0

9.0

5

4S-OMRF-IF

3.3

1.2

4.1

3

6S-OMRF-IF

2.4

1.1

2.7

3

8S-OMRF-IF

2.4

1.3

3.2

3

10S-OMRF-IF

2.5

1.6

3.9

3

4S-SMRF-IF

4.7

1.6

7.3

5

6S-SMRF-IF

3.9

1.4

5.5

5

8S-SMRF-IF

4.8

1.4

6.9

5

10S-SMRF-IF

4.5

1.3

5.8

5

Building details

670


The performance assessment of buildings with varying storey heights and designed for SMRF and OMRF is presented in this study. The buildings are designed and modelled using SAP20004. The response of these buildings is noticed by performing nonlinear static analysis. A capacity curve with base shear and roof displacement is plotted for each building. From this study following observations are noted: • It has been seen that SMRF buildings attracts 39% to 43% less base shear than OMRF buildings in x direction, where as in y-directions SMRF buildings attracts 40% to 44% less base shear than OMRF buildings. In case of infilled frames, SMRF buildings attracts 2% to 25% and 9% to 24% less base shear than OMRF buildings in x and y directions respectively. • It has also been seen that SMRF buildings in both x and y direction are more ductile than OMRF buildings. The SMRF buildings comprises almost 26% to 47% more ductility in x-direction and 19% to 44% more ductility in y-direction than OMRF buildings. Similarly, in case of infilled frames, roof displacements of SMRF buildings are 11% to 16% and 10% to 25% more than OMRF buildings in x and y directions respectively. Thus, increased ductility of SMRF buildings is observed. • It is noticed that initial stiffness of SMRF frames with infill walls increased drastically than SMRF bare frames as these frames attract much more base shear. It is noted that specially moment resisting infilled frames attract 50% to 64% and 39% to 55% more base shear and undergo 62% to 74% and 57% to 73% less roof displacements than bare frames in x and y directions, respectively. • In case of OMRFs, infilled frames attract 24% to 41% and 20% to 31% more base shear and undergo 54% to 67% and 48% to 65% less roof displacements than bare frames in x and y directions, respectively. • The response reduction factors calculated for SMRF bare frame buildings are found to be much higher than the response reduction factor offered by IS 1893: 200214 which is 5. However, in case of OMRF bare frames buildings these factors are slightly higher than that is offered by IS 1893: 200214 which is 3.

•

In case of infilled frames, the response reduction factors of each building calculated are slightly higher than that is given by IS 1893: 200214 for both the SMRF and OMRF buildings.

It should be noted that there is always variation to some extent in seismic demand prediction acquired by pushover analysis, though it gives a good insight about nonlinear behaviour during the seismic event. For more accurate analysis, the nonlinear dynamic analysis or nonlinear time-history analysis should be adopted. NOTATIONS Em Ec Icol Ldiag VE

VS VY fm fb fmo hcol hinf tinf w

- Elastic modulus of the infill wall (MPa) - Elastic modulus of the frame material (MPa) - Moment of inertia of the section of the column of surrounding frame (mm4) - Length of the diagonal strut (mm) - ultimate base shear that would have developed in the seismic force-resisting system had it remained entirely linear and elastic throughout the seismic event - base shear that is developed in the lateral system at the “first significant-yield point.” - fully yielded inelastic base shear. - Compressive prism strength of masonry (MPa) - Compressive strength of clay brick (MPa) - Compressive strength of mortar (1:6) (MPa) - Height of the column of surrounding frame (mm) - Height of the infill wall panel (mm) - Thickness of the infill wall (mm) - Equivalent diagonal strut width (mm)

REFERENCES 1.

2.

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