SEISMIC PERFORMANCE OF HIGH-RISE BUILDING

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 3, March 2018, pp , Article ID: IJCIET_09_03_087 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed SEISMIC PERFORMANCE OF HIGH-RISE BUILDING Somil Khattar Student, School of Mechanical and Building Sciences, VIT University, Tamilnadu, Chennai, India Muthumani K Professor, School of Mechanical and Building Sciences, VIT University, Tamilnadu, Chennai, India ABSTRACT This work is aimed to study the seismic behavior of high-rise residential building (i.e. 72 m tall) located in Indore city of Madhya Pradesh, India. It is modelled in accordance with Indian Standard Codes. For high rise building, wind load is governing for most of the cases. The building is designed for design basis earthquake in accordance with IS 1893:2016 and its seismic performance is evaluated with maximum considered earthquake by response spectrum analyses using ETABS software. Same building is then modelled in accordance with American Code ASCE 7-16 and its structural stability parameters such as base shear, story drift and lateral displacement are compared with original building. On comparing the two, it is found that though both the code gives different time period value, base shear results with both the code are same. Also it is checked whether the moment demand of frame section is within the ultimate moment carrying capacity of frame at floors where reduction in plan area occurs. It is found that due to sudden reduction in plan area between two floors, stiffness in the building reduces suddenly. Hence stiffness has to be increased at the floor where plan reduces suddenly in order to avoid torsion in the building. Keywords: High-rise building, seismic performance, IS 1893:2016, ASCE 7-16, Forced Based Design, ETABS. Cite this Article: Somil Khattar and Muthumani K, Seismic Performance of High- Rise Building, International Journal of Civil Engineering and Technology, 9(3), 2018, pp INTRODUCTION High rise structures are constructed in metropolitan cities of India for residential and commercial building. Middle level cities like Ahmedabad, Pune, Indore, Bangalore, Hyderabad and many other cities in India are also growing at faster rate due to industrialization and modernization. Though, construction of high rise building in middle editor@iaeme.com

2 Somil Khattar and Muthumani K level cities will be same as that of metropolitan cities but to carry out as a mass scale; faster construction technique, innovative design, economical construction material and some better construction management technique needs to be evolved in view of environmental protection. Compared to gravity loads, earthquake load effects (i.e. forces and moment in column) are variable and it increases with increase in height. Earthquake resistant design of structure is a function of height and location of the structure, total mass and soil characteristics. It has been observed that structure can carry most of the earthquake load due to infill walls present in the structure. As the height of structure increases, then the requirement for adequate stability (i.e. resistance to overturning moment) and rigidity (i.e. resistance to lateral deflection) becomes important. There are two ways to overcome these requirements in a structure. One is to increase the size of the member beyond the strength requirement. However this approach is not feasible, as it becomes impractical and uneconomical to increase the size of member beyond its limit. Whereas, the second one is to change the form of the structure into more stiff and stable to increase stability and to overcome the deflection. For safety purpose, the design and analysis of buildings is very important. The forces and displacements are calculated for various load combination conforming to Indian Standard Design Code and each structural element will be designed for the critical one. Lateral forces due to earthquake loads increases rapidly for high-rise buildings. Shear wall is one of the best lateral load resisting structural systems, which is stiff as well as stable for building while designing for lateral loads. 2. BUILDING CONFIGURATION AND LOADING PARAMETERS Residential building located in Indore district of Madhya Pradesh, India is considered for the study. It consists of 3 basements, Ground Floor and 24 stories. It is located at Indore which lie in seismic zone III according to IS 1893:2016 (Part 1). From geotechnical report, medium soil is considered for designing purpose. Total height of the building (Ground floor plan to Terrace slab) is 72 m. Plan dimension in X and Y direction is and m respectively. Three basements are used for parking and service plant room. Ground Floor (GF), First Floor (FF), Second Floor (SF) and Third Floor (TF) Slab Level are used for parking purpose. Fourth floor slab is used for health club and swimming pool and above 20 stories are used for residential purpose. Floor height for two lower basement and upper basement is 3.3 m and 3.8 m, respectively. All floor above Ground floor level are 3 m in height. Conventional Flat slab with drop is provided at all the basement. At all typical level, conventional beam-slab with core walls and shear wall is provided to resist lateral loads imposed on the building. ETABS software is used for modelling of the building Materials Used The concrete strength adopted varies depending on element and floor level. Grade of concrete used for beams and slabs up to ground floor slab level is M35 and above ground floor slab, it is M25. Grade of concrete used for columns and core wall varies as: Up to 4 th floor roof slab level M50 Above 4 th floor slab up to 8 th floor roof slab level M45 Above 8 th floor slab up to 13 th floor roof slab level M40 Above 13 th floor slab up to 17 th floor roof slab level M35 Above 17 th floor roof slab level M editor@iaeme.com

3 Seismic Performance of High-Rise Building 2.2. Loading Parameters Dead Load and Live Load Dead Load and Live Load are applied in the building as per IS 875(Part-1): (1987) and IS 875(Part-2) : 1987 [11], respectively Wind Load Wind Load is applied as per IS 875(Part-3): 1987 [11]. Basic wind speed (V b ) for Indore = 39 m/s. Design wind speed (V z ) = V b x K 1 x K 2 x K 3 Where, K 1 = Risk factor = 1 K 2 = Terrain and height factor (Category 4 and Building Class B) K 3 = Topography factor = 1 Figure 1 Residential plan and 3D view of the building 3. ANALYSIS OF BUILDING AS PER IS 1893:2016 [9] Building is designed as ductile shear wall with Ordinary moment resisting frame. As per IS 1893:2016 (Part 1), response reduction factor R is taken as 4.5. Time period is considered as per IS 1893:2016, considering infill time period formula: Ta = 0.09 x h / d - (1) Time period for x and y direction is found as and 1.25 sec, respectively Linear Static Analysis Static Analysis is carried out considering Infill Time period and only Earthquake force are considered for this analysis. Result for Static Analysis are as shown below editor@iaeme.com

4 Somil Khattar and Muthumani K Table 1 Linear Static Analysis as per IS 1893:2016 Load Cases Base Shear (kn) Max Storey Drift Max Displacement EQX mm EQY mm 3.2. Dynamic Analysis It is carried out with Response spectrum function and cases for spectrum are taken as SpecX and SpecY with basic scale factor. Sa/g value is taken from response spectrum function directly and hence scale factor for both the direction is taken as, = (I g) / (2 R) = (1 x 9810) / (2 x 4.5) = 1090 Let wind forces along x and y direction be GustX and GustY and are calculated as per IS part 3. Results for dynamic analysis are as shown below. Table 2 Response Spectrum Analysis as per IS 1893:2016 Load Cases Base Shear (kn) Max Storey Drift Max Displacement SpecX mm SpecY mm Gust X mm Gust Y mm It is found from the results that base shear for GustX is higher than SpecX and SpecY. Allowable storey drift in the building as per IS 1893: Cl is Maximum Storey Drift for all the cases is found to be within the limits Modified Dynamic Analysis As per IS 1893:2016 Cl ; when the base shear computed with response spectrum (V B ) is less than base shear computed with equivalent static method (Ṽ B ), than forces are to be scaled with the ratio of (Ṽ B /V B ). For Modified dynamic analysis, scale factor SpecX and SpecY are to be modified as, Scale factor for SpecX = 1090 x (6017/ 1760) = Scale factor for SpecY = 1090 x (5333/ 2238) = Results for Modified Dynamic Analysis are as shown below. Table 3 Modified Dynamic Analysis as per IS 1893:2016 Load cases Base shear (kn) Max Storey drift Max displacement SpecX mm SpecY mm Gust X mm Gust Y mm editor@iaeme.com

5 Seismic Performance of High-Rise Building 3.4. Modal Mass Participation Modal mass participation of the building with design stiffness modifier is as shown below. Table 4 Modal Mass Participation as per IS 1893:2016 Mode Time period(s) U x U y R z As per IS 1893:2016 Cl , total modal mass participation should exceed 90%. As far as this case is concerned, modal mass participation for 12 modes in x and y-direction is and respectively. It is found that modal mass participation along x-direction exceeds 90% and it falls short in y-direction. It is found from the results, that the first mode is governing in rotation. As per IS 1893:2016 Table 5 (i), fundamental torsional mode of oscillation shall not be governing in first two modes. Hence first mode in rotation is not accepted by IS Code. 4. ANALYSIS OF BUILDING AS PER ASCE 7-16 [13] As per ASCE 7-16 Table , building falls under category (F) i.e. Shear Wall Frame interactive system with Ordinary Reinforced Concrete Moment Frame and Ordinary Reinforced Concrete Shear Wall. Following parameters are considered from ASCE 7-02, Table (F): Response modification Co-efficient 4.5 Over strength Factor 2.5 Deflection Amplification Factor, Cd 4 Design acceleration co-efficient (Sa/g) for medium type soil is, 1.36/T = 1.36/1.25 = (as per IS 1893:2016) Zonal spectral acceleration for Indore, (Z x S a ) = 0.174g Seismic zonal map of United States is based on the ground acceleration. Zone 2A is limited to 0.15g and Zone 2B is limited to 0.20g. As the zonal spectral acceleration for Indore is 0.174g, it lies in Zone 2B. Hence, city named Bethel from Alaska is selected from United States that lies in Zone 2B and that has similar Ground Acceleration as Indore. Spectral Response acceleration parameters are considered in ETABS for zip-code (Bethel). Time period of the building as per ASCE7-16 Cl is given as: T a = C t h x - (2) As per ASCE 7-16, Table , for building with concrete moment-resisting frame; C t = and height of building from GF Level to Terrace Floor level, h = 72 m. Hence time period of building, T a = sec. Time period of the building as per ASCE 7-16 is almost double compared to time period as per IS 1893: editor@iaeme.com

6 Somil Khattar and Muthumani K 4.1. Linear Static Analysis Static Analysis is carried out considering Time period as per ASCE 7-16 and only Earthquake force are considered for this analysis. Table 5 Linear Static Analysis as per ASCE 7-16 Load Cases Base shear (kn) Max Storey Drift Max Displacement EQX mm EQY mm It is found from the results that though the time period as per ASCE 7-16 is almost double compared to IS 1893:2016; base shear value along x direction are found to be almost similar. Along y direction, base shear as per ASCE 7-16 is slightly higher as compared to IS 1893: Dynamic Analysis It is carried out with Response spectrum function similar to IS 1893:2016 and cases for spectrum are taken as SpecX and SpecY with basic scale factor. Scale factor along both the direction is similar to IS 1893:2016, i.e Results for dynamic analysis are as shown below. Table 6 Response Spectrum Analysis as per ASCE 7-16 Load cases Base shear (kn) Max Storey drift Max Displacement SpecX mm SpecY mm Gust X mm Gust Y mm As compared to IS 1893:2016, base shear for SpecX and SpecY are found to be doubled with ASCE Whereas, base shear value for GustX and GustY are almost similar in both the case Modified Dynamic Analysis For Modified dynamic analysis, base shear of SpecX and SpecY is matched with base shear of EQX and EQY respectively. And hence, scale factor is again modified. Scale factor for SpecX = 1090 x (6372/ 4205) = Scale factor for SpecY = 1090 x (6357/ 5728) = Results for modified dynamic analysis are as shown below. Table 7 Modified Dynamic Analysis as per ASCE 7-16 Load cases Base shear (kn) Max Storey drift Max Displacement SpecX mm SpecY mm Gust X mm Gust Y mm editor@iaeme.com

7 Seismic Performance of High-Rise Building 5. RESULTS AND DISCUSSION 5.1. Comparison of Results between IS 1893:2016 AND ASCE 7-16 Allowable displacement of the building as per IS 1893:2016 Cl is times height of building which is 288 mm and allowable displacement of the building as per ASCE 7-16 Table is times height of building which is 504 mm. Figure 2 Displacement Comparison between IS 1893:2016 and ASCE 7-16 along a) X direction and b) Y direction From Fig 2, it is found that as per IS 1893:2016, displacement is within the limits along both the direction. Maximum displacement as per ASCE 7-16 is found to be exceeding the allowable limit of IS 1893:2016 along x direction but as per ASCE 7-16 guidelines, it is within the limits. Hence displacements along both the directions are within the limits of their respective codal provision. As per IS 1893:2016 Cl , storey drift in any storey is limited to and as per ASCE 7-16 Table , allowable storey drift in any storey is limited to Figure 3 Storey drift Comparison between IS 1893:2016 and ASCE 7-16 along a) X direction and b) Y direction Allowable drift as per ASCE 7-16 is 0.007, but the results indicate that it is even within the limits of IS 1893:2016 guidelines. Hence storey drift results are found to be safe with both the codal provision editor@iaeme.com

8 Somil Khattar and Muthumani K 5.2. Force Based Design (FBD) Moment and Shear Force comparison for one exterior column and one interior column as shown in fig below is carried out. Comparison is carried out between two floors; i.e. at fourth floor and fifth floor plan level, where sudden change in plan occurs. Figure 4 Interior and Exterior Column considered for comparison at (a) Fourth Floor Slab and (b) Fifth Floor Slab The size of interior and exterior column at 4 th floor slab level is 375 x 900 mm and 375 x 1050 mm, which gets reduced to 300 x 900 mm and 300 x 1050 mm, respectively. M 3 and M 2 are bending moment along major and minor direction, respectively. Results for two critical load combinations is as shown below Moment Demand for Exterior Column Moment demand for governing load combination is as shown below. Table 8 BM and SF values for exterior column with load combination 1.5 (DL+EQX) Load Combination (DL+EQX) STOREY M 3 (kn.m) M 2 (kn.m) V 2 (kn) V 2 (kn) 5 th Floor Slab th Floor Slab Moment capacity of the exterior column is found to be kn.m and kn.m at 4 th floor slab and 5 th floor slab level, respectively with P u -M u curve from SP 16(1980). It is found that moment capacity of the column at 4 th floor slab level i.e kn.m is greater than moment demand i.e kn.m. Also it is found that moment capacity of the column at 5th floor slab level i.e kn.m is greater than moment demand i.e kn.m. Hence the column is safe at both the floors editor@iaeme.com

9 Seismic Performance of High-Rise Building Moment Demand for Interior Column Moment demand for governing load combination is as shown below: Table 9 BM and SF values for interior column with load combination 1.5 (DL+EQX) Load Combination (DL+EQX) STOREY M 3 (kn.m) M 2 (kn.m) V 2 (kn) V 2 (kn) 5 th Floor Slab th Floor Slab Moment capacity of the exterior column is found to be kn.m and kn.m at 4 th floor slab and 5 th floor slab level, respectively with P u -M u curve from SP 16(1980) [10]. It is found that moment capacity of the column at 4th floor slab level. i.e kn.m is greater than moment demand i.e kn.m. Also it is found that moment capacity of the column at 5th floor slab level i.e kn.m is greater than moment demand i.e kn.m. Hence interior column is safe at both the floors Displacement Limits As per IS 1893:2016 Table 5 (i), building is said to be irregular in torsion if the maximum deflection at one end of the floor is more than 1.5 times the minimum deflection at the far end of the same floor. There is sudden reduction in plan area from 4 th floor to 5 th floor slab level. Hence, results are found for Earthquake forces along both the direction at 4 th floor slab level and 5 th floor slab level. Figure 5 Nodes considered to find displacement for EQX at (a) Fourth Floor Slab and (b) Fifth Floor Slab Level editor@iaeme.com

10 Somil Khattar and Muthumani K Figure 6 Nodes considered to find displacement for EQY at (a) Fourth Floor Slab and (b) Fifth Floor Slab Level Let us consider the ratio of maximum horizontal displacement to minimum horizontal displacement at the far end of the same floor be m. Displacement result for 4 th Floor Slab Level are as shown below. Table 10 Displacement results at 4 th Floor Slab Level DISPLACEMENT (in mm) CASE PARAMETERS At Node 1 At Node 2 m Static EQX Dynamic SpecX Static EQY Dynamic SpecY At 4 th floor slab level, M value exceeds 1.5 for EQX and SpecX. Moreover, it is also found that m value for EQX is very high compared to the allowable limit. Hence this value has to be reduced. Displacement results for 5 th Floor Slab Level are as shown below. Table 11 Displacement results at 4 th Floor Slab Level DISPLACEMENT (in mm) CASE PARAMETERS At Node 1 At Node 2 m Static EQX Dynamic SpecX Static EQY Dynamic SpecY Similar to 4 th floor slab level, m value exceeds 1.5 for all EQX and SpecX at 5 th floor slab level. It is found that m value is slightly exceeding the allowable limit. Hence this value has to be reduced editor@iaeme.com

11 Seismic Performance of High-Rise Building 6. CONCLUSIONS It can be concluded that though the time period value as per ASCE 7-16 is almost double compared to IS 1893:2016, forces are found to be almost similar for both the cases. The building was found safe as per Forced Based Design but due to irregularity in the plan and sudden reduction of plan area between two floors, ratio of maximum displacement at one end to the minimum displacement at the farther end exceeded the ratio of 1.5 which violates the codal provision as per IS 1893(Part-1):2016 Table 5 (i). Also torsion was found to be prevalent in the first mode. There is sudden reduction in plan area from 4th Floor slab to 5th Floor slab which results in sudden reduction of stiffness from 4th Floor slab to 5th Floor slab. To overcome this problem, cross-bracings must be provided in the periphery of the building along x direction as shown in Fig. 7 starting from 5 th Floor Slab to 9 th Floor slab level. Figure 7 Provision of bracing By providing bracings from 5 th Floor slab to 9 th Floor slab level, it is found that torsional mode of oscillation in third mode is greater than first two modes. Results for modal mass participation of the building after provision of bracings are as mentioned in Table 12. Table 12 Modal mass participation of building after addition of bracing Mode Time period(s) U x U y R z Hence torsional irregularity in the building is overcome by providing bracings above certain storey where sudden reduction in plan area is found. Displacement result for 4 th Floor Slab Level and 5 th Floor slab level after provision of bracings from 5 th Floor slab level to 9 th Floor slab level are as shown in Table 13 and Table 14, respectively. Table 13 Displacement results at 4 th Floor Slab Level after provision of bracings DISPLACEMENT (in mm) CASE PARAMETERS At Node 1 At Node 2 m Static EQX Dynamic SpecX Static EQY Dynamic SpecY editor@iaeme.com

12 Somil Khattar and Muthumani K Table 14 Displacement results at 5 th Floor Slab Level after provision of bracings DISPLACEMENT (in mm) CASE PARAMETERS At Node 1 At Node 2 m Static EQX Dynamic SpecX Static EQY Dynamic SpecY As per IS 1893:2016, Fig. 3A, m value should not exceed 1.5. From results, it is observed that m value at both the floor is found to be within the limits. m value for EQX at 4th Floor slab level is 1.5, but still it is within the limits. Stiffness reduces gradually between two floors where plan reduces. Hence by providing cross-bracings up to few floors above the level where plan reduces suddenly, torsion was brought to third mode as recommended by IS 1893(Part-1):2016 and also the ratio of maximum displacement at one end to minimum displacement at far end was brought within the limit of 1.5. REFERENCES [1] Dennis Poon et al. (2010), Performance Based Design and Analysis of TIAPINGQIAO LOT 126/127, American Society of Civil Engineers, 2010, [2] M. Sarkisian et al (2013), Performance-Based Engineering of Core Wall Tall Buildings, American Society of Civil Engineers, 2013, [3] Ali Ruzi Ozuygur (2015), Performance based seismic design of an irregular tall building A case study, Institution of Structural Engineers, February 2016 (5), [4] Sameh A. El-Betar (2015), Seismic performance of existing R.C. Framed Building, Housing and Building Research Centre Journal (2017) 13, [5] Roberta Apostolska et al. (2016), Seismic performance of R.C. High Rise Building Case study of 44-storey structure in Skopje, Tehničkivjesnik Journal 23, 4(2016), [6] M J N Priestley (2007), Displacement Based Seismic Design of Structures, IUSS Press, New Zealand. [7] Tall Building Initiative, 2010, Guidelines for Performance-Based Seismic Design of Tall Buildings, Version 1, Report No.2010/5, Pacific Earthquake Engineering Research Center, Berkeley, CA [8] IS 456 (2000): Plain and Reinforced Concrete Code of Practice, Bureau of Indian Standards, New Delhi, July, [9] IS 1893 (Part 1): 2016 Criteria for Earthquake Resistant Design of Structures, Bureau of Indian Standards, New Delhi, June [10] SP 16 (1980) : Design Aids For Reinforced Concrete To Is 456(1978), Bureau of Indian Standards, New Delhi, March, [11] IS 875 (1987) : Code of Practice for design loads for buildings and structures, Bureau of Indian Standards, New Delhi, [12] CED 38(10639) Criteria for structural safety of Tall Buildings, Bureau of Indian Standards, New Delhi, August, [13] ASCE/SEI 7-16 Minimum Design Loads and Associated Criteria for Buildings and Other Structure, [14] Anjana R K Unnithan and Dr. S. Karthiyaini, Design and Analysis of High Rise Building with Steel Plate Shear Wall. International Journal of Civil Engineering and Technology, 8(4), 2017, pp editor@iaeme.com