Comparison of Seismic Performance of Solid and Hollow Reinforced Concrete members in RCC framed Building using ETABS Software

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1 Comparison of Seismic Performance of Solid and Hollow Reinforced Concrete members in RCC framed Building using ETABS Software Abhay B.Tech, Deptt. of Civil Engineering J.N.G.E.C. Sundernagar, India Abstract Hollow (Box-type) reinforced concrete beams and columns help in decreasing superstructure weight and hence seismic mass is minimized as compared to conventional solid reinforced concrete beams and columns. ETABS is commonly used to analyses: Skyscrapers, parking garages, steel & concrete structures, low and high rise buildings, and portal frame structures. The case study in this paper mainly emphasizes on structural behavior of R.C.C. framed building having hollow and solid reinforced concrete members. Modelling of 3-storey R.C.C. framed building is done on the ETABS software for analysis. Post analysis of the structure, maximum shear forces, bending moments, and maximum storey displacement are computed and then compared for all the analyzed cases. The results indicated that the drop in storey shear, overturning moment etc. in case of hollow members as compared to solid members in R.C.C. framed building. Keywords- Structural behaviour; Hollow (Box-type) reinforced concrete member; ETABS; Storey shear; Storey overturning moment. I. INTRODUCTION Hollow (Box-type) members are lighter in weight and help in decreasing superstructure weight and hence seismic mass is minimized as compare to conventional solid reinforced concrete beams and columns. The economical convenience in the use of hollow reinforced concrete member is due to the cost saving afforded by reduced section area (up to 70%). A. Kumar [6] proposed ferrocement box sections for beam-slab construction and flat slab construction. It is mentioned that the ferrocement box beam-slab construction is 15.6% cheaper than conventional beam and slab construction. T.C.Rao et al; [3] conducted an experimental investigation on ferrocement channel beams to study the cracking and ultimate strength in bending. This analysis mainly deals with the study of structural behaviour of Hollow (Box- type) and Solid reinforced concrete members in the RCC framed building under Seis mic load using ETABS software. A 12m x 12m RCC framed building having 4m x 4m bays is modelled using ETABS. The height of each storey is taken as 3.5m, making total height of the building 10.5m. Loads considered are taken in accordance with the IS-875(1987), IS-1893(2002) code and combinations are according to IS-875(Part5). Post analysis of the structure, storey shear, and maximum storey overturning moment, shear force and bending moments of beam and column, and maximum storey displacement are computed and then compared for all the analysed cases. II. RCC FRAMED BUILDING DETAILS An RCC framed building is basically an assembly of slabs, beams, columns and foundation inter-connected to each other as a unit. The load transfer mechanis m in these structures is from slabs to beams, from beams to columns, and then ultimately from columns to the foundation, which in turn passes the load to the soil. In this structural analysis study, we have adopted two cases by using Solid and Hollow (Box-type) members for the same structure, as explained below. 1. Solid reinforced concrete member 2. Hollow (Box- Type) reinforced concrete member An RCC framed building is 12m x 12m in plan with columns spaced at 4m from center to center. A floor to floor height of 3.5m is assumed. Plan of the building for both cases is shown in the following figure 1. Figure 1. Plan of the RCC framed building Print-ISSN: e-issn:

2 TABLE I. RCC framed Building Details Length x Width 12m x 12m No. of storeys 3 Storey height 3.5m Beam dimensions Column dimensions Slab thickness 100 mm Support conditions Fixed III. MEMBER DESCRIPTION TABLE II. Column Details Column in both the cases as it is light weight structure as fabricated walls are used to construct the rooms of building so they do not impart much load on the beams. Loads considered are as follows: 1. Dead load: Self-weight comprises of the weight of beams, columns and slab of the building. 2. Live load: Floor load: 3kN/m 2 (IS 875 (Part 2) acting on beams 3. Seis mic Load: Seis mic zone: V (Z=0.36), Soil type: II, Importance factor: 1, Response reduction factor: 5, Damping: 5%. IS 1893(Part -1):2002. Seismic load is considered along two directions EQX and EQY along x, y directions respectively. Thickness = 100mm VI. LOADING COMBINATION The structure has been analyzed for load combinations considering all the previous loads in proper ratio. Combination of dead load, live load and seismic load was taken into consideration according to IS-code 875(Part 5). TABLE V. Loading Combination IV. TABLE III. Beam Details Beam Thickness=100mm MATERIAL SPECIFICATIONS TABLE IV. Materials used in the RCC framed building Material Specifications Grade of Concrete,M30 f ck= 30N/mm 2 Grade of Steel f y = 415N/mm 2 Density of Concrete ϒ c = 25kN/m 3 V. LOADING Loads acting on the structure are dead load (DL), Live load and Earthquake load (EL). Here wall load is not considered Load Combinations Sr. No. Load Combination Name Load Case Factor 1 DCON1 DEAD DCON2 DEAD 1.5 LIVE DCON3 DEAD 1.2 EQX DCON4 DEAD 1.2 EQX DCON5 DEAD 1.2 EQY DCON6 DEAD 1.2 EQY DCON7 DEAD 1.5 EQX DCON8 DEAD 1.5 EQX DCON9 DEAD 1.5 EQY DCON10 DEAD 1.5 EQY DCON11 DEAD 0.9 EQX DCON12 DEAD 0.9 EQX DCON13 DEAD 0.9 EQY DCON14 DEAD 0.9 EQY -1.5 Print-ISSN: e-issn:

3 VII. MODELLING IN ETABS RCC framed building having solid concrete members have higher values of overturning moment as compared to hollow (Box-type) member. Hollow beams and columns help in reducing storey overturning moment as compared to solid beams and columns. There is 21.85% reduction for Base, 27% for 1 st storey and 26.4% for 2 nd storey in the storey overturning moment due to Hollow members. Behaviour of EQY load is same as that of EQX load as the building is symmetrical in plan. However the storey overturning moment decreases with increase in storey height for both cases. B. Comparison of Storey Shear for Solid and Hollow Structural members Figure 2. 3-D Model of RCC framed Building in ETABS Figure 3. Elevation View VIII. MODELLING RESULTS A. Storey Overturning Moments due to Seismic load Figure 5. Storey vs. Storey Shear due to EQY load As per above figure it has been concluded that the storey shear decreases with the increase in storey height. Storey shear is less in case of Hollow members than solid members in RCC framed building. It is observed that the storey shear for RCC framed building having hollow members is decreased by 27% as compared to solid members. C. Storey Drift for Hollow and s in RCC framed building Figure 4. Storey vs. Storey Overturning Moments due to EQX load Print-ISSN: e-issn: Figure 6. Storey vs. Storey Drift due to EQX load

4 From figure 6 it is observed that Hollow beams and columns in RCC framed building help in reducing storey drift as compared to solid beams and columns. There is 8-9.5% reduction in the storey drift due to Hollow members. D. Shear Force and B.M. of Column Column C5 of storey-1 of RCC of building is taken for comparison of maximum bending moment, axial force and shear force for both the cases. TABLE VII. Forces for C5 Column Forces Axial Force P kn kn Shear Force V kn kn Shear Force V kn kn Torsion T kn-m 0.23 kn-m Bending Moment M kn-m kn-m B.M. M3 (kn-m) B.M. M2(kN-m) B.M. M kn-m kn-m As per figure 8 it has been concluded that the maximum displacement increases with the storey height. There is 8-9.5% reduction in the maximum node displacement due to Hollow members in RCC framed building as compared to F. Max Stress (Smax) Range for RCC framed building TABLE VIII. Max Stress Range due to DCON5 and DCON10 Loading Combination DCON (DEAD EQY) DCON (DEAD+LIVE+ EQY) Storey (kn/m 2 ) (kn/m 2 ) to to to to to to to to to to to to As from above table it is observed that the maximum stress range is less in building having hollow member than the solid member for loading combination DCON5 and DCON10. Maximum stresses are higher at 1 st storey than the 3 rd storey for both cases. S.F. V3 (kn) Shear Force V2 (kn) Axial P (kn) Figure 7. Comparison of Column Forces using ETABS As it has been concluded that the Hollow member in RCC framed building help in reducing forces without failure which leads economical design of the building. E. Maximum Node Displacement Figure 9. Max Stress (S max) diagram for Solid framed Building due to 1.5(DEAD EQY) load Figure 8. Maximum Node Displacement of members Print-ISSN: e-issn: Figure 10. Max Stress (S max) diagram for Hollow framed Building due to 1.5(DEAD EQY) load

5 G. Weight of RCC framed building ETA BS software gives the total weight of structure. Data obtained is categorized into weight of beam, column and slab. TABLE IX. Weight of Members given by ETABS Section No. Total Length (m) Solid Member Weight (Ton) Hollow Member Weight (Ton) B450x C500x Slab S TOTAL From the table it is observed that there is reduction of total weight of the RCC framed building by using Hollow members Ton of M30 concrete is saved by using Hollow (Box-type) members % weight of the Structure is reduced by using Hollow members as compared to H. Axial Force (P) obtained from ETABS for columns of 1st storey TABLE X. Axial Forces for Columns of 1 st storey Axial Force P (kn) Column Maximum Minimum Maximum Minimum C C C C C C C C C C C C C C C C As from the above table is has been concluded that the axial force in solid columns of RCC framed building is higher as compared to hollow (Box-type) columns. IX. CONCLUSIONS On the basis of results obtained from structural analysis of R.C.C. framed building using ETABS the following conclusions can be drawn: (1) Maximum node displacement of hollow members given by ETABS is less as compared to solid members. There is 8-9.5% reduction in the maximum node displacement due to Hollow members in RCC framed building as compared to (2) There is 20% to 27% reduction in the storey overturning moment due to Hollow members in RCC framed building. However the storey overturning moment decreases with increase in storey height for both cases. (3) Storey shear for RCC framed building having hollow members is decreased by 27% as compared to solid members. Storey shear decreases with the increase in storey height. (4) There is 8-9 % reduction in the maximum node displacement and storey drift due to Hollow members in RCC framed building as compared to (5) Ton of M30 concrete is saved by using Hollow (Box-type) members in RCC framed building so it leads to economical design without the failure of the structure against seismic loads. REFERENCES [1] Thanuja H.P, E.Ramesh Babu and Dr N S Kumar, A Study on Behaviour of Circular Stiffened Hollow Steel Column Filled with Self Compacting Concrete Under Monotonic Loading, INDIAN JOURNAL OF APPLIED RESEARCH, Volume : 4, Issue : 8, August 2014, ISSN X. [2] Waleed AboEl-Wafa Mohamed, Seismic Capacity of RC hollow block slab building and retrofitting systems, Journal of Engineering Sciences, Assiut University, Faculty of Engineering, Vol.42, No. 3, May [3] Dr. T. ChandraSekharRao, Dr. T. D. GunneswaraRao, Dr. N. V. RamanaRao, Ch. Rambabu, An Experimental study on ferrocement box-beams under flexural loading, International Journal of Emerging Technology and Advanced Engineering, ISSN , Volume 2, Issue 9, September [4] Rao.T.C, Rao.T.D.G & Rao.B.P.R, Flexural Behaviour of Thin-webbed Ferrocement Channel Sections, International Journal of Applied Engineering Research, Vol.7, No.7 (2012), pp [5] Falah M. Wegian and Falah A. Almottiri, Experimental Studies on Reinforced Hollow- Block Concrete Sections, Jordan Journal of Civil Engineering, Volume 1, No. 4, [6] A. Kumar; Ferrocement Box sections-viable option for Floors and Roof of Multi-storied Buildings, Asian Journal of Civil Engineering (Building and Housing), Vol. 6, No. 6, 2005, pp. [7] Giulio Ranzo & M J N Priestley, Seismic performance of large reinforced concrete circular hollow columns, 12WCEE, [8] Bureau of Indian Standards: IS-875, part 1 (1987), Dead Loads on Buildings and Structures, New Delhi, India. [9] Bureau of Indian Standards: IS-875, part 2 (1987), Live Loads on Buildings and Structures, New Delhi, India. [10] Bureau of Indian Standards: IS-1893, part 1 (2002), Criteria for Earthquake Resistant Design of Structures: Part 1 General provisions and Buildings, New Delhi, India. Print-ISSN: e-issn: