Seismic analysis of plan irregular multi-storied building using STAAD pro Sai pradeep.p* , Dr.S.Elavenil** School of Mechanical and Building Sciences, VIT University, Chennai, Tamilnadu, India Email:
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Abstract: This paper aims at studying description of different plan irregularities by analytical method during seismic events. The behaviour of building during earthquake depends critically on its overall shape, size and geometry building with simple geometry in plan have performed well during strong past earthquake but building with U,V,H,+ and octagonal structures shaped in plan have sustained significant damage. In recent past, several studies have been carried out to evaluate the response of irregular buildings work that has been already done pertaining to the seismic response of vertically irregular buildings frames. Buildings with plan irregularities are common in the affected area. Keywords: Plan irregularity, Seismic analysis, Modeling by S TAAD Pro, Moment resisting frames, Dynamic analysis
I. INT RODUCTION Buildings are the complex system and mult iple items have to be considered at the mo ment of designing them. Earthquake field investigations repeatedly confirm that irregular structures suffer mo re damage than regular counter parts .This is recognized in seismic design codes and restrictions on abrupt changes in mass and stiffness are imposed. Elevation irregularities have been observed to cause storey failu re due to non uniform d istribution of demand to ratios along the height. Plan irregularit ies, on non-uniform demand to capacity ratios amongst the columns within a single floor-by-floor basis have been used for many years in the form of storey-drift ratios that provide a simple nu mber that portrays the demand to supply picture along height of structure. Quantitatively, readily available and verified measures of demand to capacity ratios over the plan of structure subjected to bidirectional t ransit dynamic loading and responding in the inelastic range are still taking. II.LITERATURE REVIEW M.R.Wakchaure et al have analysed plan irregular mu lti storied building to estimate seis mic performance and effects of structural irregularity in stiffness, strength, Tsection and Oval shaped irregular p lan geo metric forms which are repeated in areas such as Mumbai in ETA BS 9.7v considering 35 and 39 storied build ings, to determine effect of p lan geometric form on seismic behaviour of structures with elastic analyses considering gust factor
using dual system for structural analysis. Shear wall positions are located in form of co re and colu mns are considered as gravity as well as lateral colu mns. Two types of models namely strength and serviceability models are developed. In strength model all the lateral systems (i.e. shear walls, bracings, coupling beams) are to be analysed. Raul Gon zalez et al have analysed damages caused by different plan irregularit ies during seismic events of different magnitudes ,the geometric forms that are repeated more in urban (squared,rectangular,U-sectionalsection) modelled in SAP2000 considering one, two and four levels to determine effect o f geo metry in seis mic behaviour of structures with elastic analysis . Rucha.S.Bangin war Et al have studied effects of p lan configurations on the seismic behavior of structure by response spectrum method by using Indian Standard Code (IS-code) of practice IS-1893(PartI: 2002) guidelines and methodology. The behavior of building during earthquake depends critically on its overall shape, size and geo metry. Bu ild ing with simp le geo metry in p lan have performed well during strong past earthquake but building with U, V, H& + shaped in plan have sustainable damage. In h is work .In his proposed work the effect of plan configurations on the behavior of structure of already constructed building located in the same area during earthquake which is analy zed by response spectrum method. S.K.Dubey and P.D.Sangamnerkar have analyzed the Behavior of asymmetric RC build ings. The main object ive of their study is to understand different irregularity and torsional response due to plan and vertical irregularity and to analyze T-shaped building while earthquake forces acts and to calculated additional shear due to torsion in the column. Additional shear due to torsional mo ments are considered because this increase in shear forces causes columns to collapse. So in design procedures additional shear is taken into account.
For this modelling height 3.0m, 32m Irregular in p lan is height of building
III.M ODELLING ,an 13-storey building with each storey in both X d irection and Y direction modelled as shown in fig2. The storey is constant including ground storey is
3.0m. The build ing are modelled using software STAAD Pro .The modelled G+13 mu lti storied build ing is provided with lateral load resisting systems such as mo ment resisting fames, bracings and shear wall in order to strengthen building against earthquake loads. Dead load and live load have been taken as IS 875 (part-I) and IS 875(part-II) respectively.
Response reduction factor= 5 Importance factor = 1 Damping= 5% Time period=0.84 sec Seis mic intensity = Moderate Zone factor = 0.16 Estimation fundamental t ime period T a using emp irical expressions given in the code IS: 1893:2002 Ta= 0.075 H0.75 for bare frame along each axis = 0.09h/sqt (d) for frame with substantial in fills Along X-axis = 0.09h/sqt (b) for frame with substantial in fills Along Z-axis Floor load= slab thickness x density 0.12 x 25 = 3 N/ mm2 Live load = 2.5 KN/ m2 as per IS 875 part (II)
Fig.1 T he plan of building model TABLE-1 MODELING DETAILS
No of stories Floor to floor height
G+13
Beam size
400 x 230 mm
Colu mn size
400 x 230 mm
3m
Thickness of Slab 120mm Grade of concrete M 20 Fe 415 Grade of steel S EIS MIC LOAD CALCULATION: Base Shear (Vb ) = A h x W A h = area of horizontal seismic coefficient W= seismic weight (dead load+ live load) A h = Z I Sa/ 2R g Z= zone factor I = importance factor R= response reduction factor Sa/g = Average response acceleration coefficient. Selection of Zone= III (Chennai) Type of Soil = med iu m
Fig2: Elevation of building with inclined bracings (G+13)
Fig: 4 Max displacements.
Fig3: Seismic loads on building in X+ve direction.
IV.RESULTS Analysis of G+13 storied building by using bracings as lateral load resisting systems TAB LE-2 Mode 1 2 3 4 5
Frequency 3.046 3.256 3.391 4.752 4.859
Period 0.32890 0.30717 0.29493 0.21045 0.20580
Accuracy 6.230E-16 9.510E-16 4.405E-13 3.888E-04 8.329E-03 Fig: 5 Bending moment diagram.
In the above table we have seen that time period, frequency and the accuracy where the seismic behaviour acts at different modes. Calculated frequency estimates which are of lower accuracy.
TABLE-3 Mode
Frequency
Ti me peri od
1
2.952
0.33897
2 3.017 0.33150 3 3.076 0.32511 Sum of modes=361.926
Modal mass proporti oning rati os XYRzTrans Trans rot 0 57.593 0 0 0
57.791 59.716
0 0
VI.CONCLUSION
V.GRAPHS
Fig:6 Bending moment diagram under action of Live load.
Fig: 7 Shear force diagram in Y direction.
The main purpose of this study is to analyse plan irregular high rise building by STAAD Dynamic analysis has been carried out to know time period, natural frequency, deformations, displacements and floor responses by using + shaped model. The analysis include part icipation of 90% of the building mass for every principal horizontal d irection of response as per IS 1893(Part-I)-2002 by comp lete Quadratic Co mbination (CQC). The time period for mode 1 is 0.3387 sec for mode 2 is 0.3315 sec for mode 3 is 0.3215sec and for mode 4 and 5 the time periods is 0.3173 sec and 0.2670 sec respectively. In the analysis high performance concrete with modern structural framings such as mo ment resisting frames are emp loyed. As per analysis plan irregularity rat ios for + shaped model is calculated by A/L ratio to be .34375 fro m the study of plan geometry The build ing is tested for distinct load combinations and weaker parts are found to be staircase and lift duct which are reinforced by providing mo ment resisting frames where ever necessary in order to ascertain and withstand seismic loads for zone III
VII. REFERENCES [1] Fig:8 Shear force diagram in X direction [2]
[3] [4] [5]
[6]
Fig:9 Variation of My and Mz in KN-M for every 0.5m increment in height of building
Fro m the graph we can see the variation on mo ment in Y direction with a slight change in time period and frequency for zone factor of 0.16 i.e., seismic analysis of plan irregular building in location of zone III.
Rucha.S.Banginwar,M.R.Vyawahare,P.O.Modani, “Effect of Plan Configurations on the Seismic Behavior of the structure By Response Spectrum Method” ,International Journal of Engineering Research and Applications(IJERA),Vol2,May-June2012 M.R.Wakchaure,Anantwad Shirish, Rohit Nikam, “ Study Of Plan Irregularity On High-Rise Structures”, International Journal of Innovative Research & Developement, Vol 1 Issue 8 October 2012. IS 4326:1993 Earthquake Resistant Design and Construction of Buildings - Code of practice IS 1893(Part 1):2002 `Criteria for Earthquake Resistant Design of Structures : Part 1 General provisions and Buildings’ Raul Gonzalez Herrera and Consuelo Gomez Soberon, “Influence Of Plan Irregularity Of Buildings”, 14 th World Conference on Earthquake Engineering October 12-17, 2008, Bejing, China. S.K.Dubey and P.D.Sangamnekar, “Seismic Behavior of Asymmetric RC Building”, International Journal of Advanced Engineering Technology, Vol II October-December 2011.
