Modelling and Analysis of a Multi-Storey Building using RFEM

Transcription

1 IJSTE - International Journal of Science Technology & Engineering Volume 3 Issue 09 March 2017 ISSN (online): X Modelling and Analysis of a Multi-Storey Building using RFEM Rohini. B Assistant Professor Department of Civil Engineering R.G.M.C.E.T, Nandyal, Andhra Pradesh, India Shanmukha Ch. B. Tech. Student Department of Civil Engineering R.G.M.C.E.T, Nandyal, Andhra Pradesh, India Abstract Rapid progress in population calls for the increase in necessity of structures for living. Under the changed circumstances, the vertical growth of buildings i.e. constructions of multi-storeyed buildings has become inevitable both for residential and as well as office purposes. In order to compete in the ever growing competent market it is very important for a structural engineer to save time. as a sequel to this an attempt is made to analyze and design a Multi-storeyed building by using a software package RFEM. Many leading software like STAAD-PRO, AUTOCAD, ETABS, RFEM, RX-TIMBER, etc. are available in the market used vividly for their project design purpose.with the objective to fulfil the above, the existing Mechanical block, RGMCET is chosen for the study. Only the superstructure is analysed neglecting the effect of seismic forces. The results obtained from RFEM agree with the results from Kani s method. Keywords: Multi-Storey Buildings, Softwares, Analyze, Design, RFEM, Kani s Method I. INTRODUCTION TO RFEM (R-FINITE ELEMENT METHOD) RFEM is a powerful 3D FEA program helping structural engineers to meet requirements in modern civil engineering. The RFEM program family is based on a modular system. Mainly RFEM is used to define structures, materials and loads for planar and spatial structural systems consisting of plates, walls, shells and members. It is also possible to create combined structures as well as modelling solid and contact elements. The modular approach allows you to combine all programs individually according to your needs. Upgrades at a later time are always possible. RFEM offers numerous interfaces representing as the perfect tool as smooth interaction between CAD and structural analysis in Building Information Modelling (BIM). Features of Graphical User Interface of RFEM Intuitive Graphical User Interface 1) The Start screen of RFEM resembles CAD environment. Fig. 1: RFEM start screen Multilingual Program Handling Saving User-Defined Configurations Photo-Realistic Visualization All rights reserved by 49

2 Display Control of Objects Global Unit Control Incremental Load Application Multi-Core Processor and 64-Bit Technology Comparison Study- Kani s Method and RFEM A simple frame shown in Fig. 2 is analyzed using Kani s method. The table 1 shows the comparison between the results obtained from Kani s method and RFEM. It is observed that the variation is approximately within 5%. Fig. 2: Frame considered for comparative study [1] Fig. 3: Model of frame in RFEM Table - 1 Comparative study Sl.no Members Bending Moments (in knm) Kani s method RFEM % error 1 AB BA BE BC CB CD DC DG EB EH GD GH All rights reserved by 50

3 13 HG HE HJ JH Modelling and Analysis of a Multi-Storey Building using RFEM II. PLAN OF BUILDING CONSIDERED FOR THE ANALYSIS The structure chosen to be analysed is G+3 institution building. The plan of the building is shown below. It is an existing building, Mechanical Block in RGMCET, Nandyal. Fig. 4: Plan of the building including dimensions of columns in mm. Structure Specifications 3 lecture halls in each floors (8.52 X 10.35)m Storeroom (2.44X10.35)m Stairs (6.7X3.75)m Staffroom (3.65X3.75)m Washroom (3.35X5.8)m Staffroom (3.35X5.8)m Lecture hall 1(8.23X18.65)m Lecture hall 2(14.6X5.38)m Corridor (41.60X2.3)m Dimensions are considered as per the centre line of the wall Location of Beams and Dimensions Fig. 5: Location of beams and all dimensions are in mm Calculation of Loads Dead loads: Self-weight All rights reserved by 51

4 Masonry load Wall load=height of the wall X width X Density of masonry material For beam, B1 ( )X0.30X18.85X1=16.965kN/m 2 B2 ( )X0.28X18.85X1= kn/m 2 B3 ( )X0.30X18.85X1=17.813kN/m 2 B4 ( )X0.30X18.85X1= kN/m 2 On corridor beams, 1.17 X 0.23 X 18.85=5.10kN/m 2 Live Loads As per IS 875 part II Lecture halls 3kN/m 2 Corridor 4kN/m 2 Laboratory 3kN/m 2 Stairs 5kN/m 2 Staff room 2.5kN/m 2 Wash room 2kN/m 2 Wind loads Wind loads as per IS 875 part III Basic wind speed at the location of building: 39 m/s Design wind load (as per IS 875 part iii, Clause 5.3) V z = V b k 1 k 2 k 3 k 4, The wind pressure at any height above mean ground level shall be obtained by the following relationship between wind pressure and wind speed: P z= V z P z = wind pressure in N/m 2 at height z, and V z = design wind speed in m/s at height z. The design wind pressure p d can be obtained as, P d = K d. K a. K c. K Z Where K d = Wind directionality factor = 0.9\ K a = Area averaging factor = 0.9 K c = Combination factor = 1 P d= kn/m 2 This is multiplied with the area surrounding the joint that is exposed to the wind load. III. MODELLING OF STRUCTURE Importing Plan from AutoCAD to RFEM Open RFEM software, make sure that your line plan of building is pre drawn in AUTOCAD software. Click on File menu > Import, mark Autodesk AUTOCAD and then click OK. It is possible to change the coordinates of line plan while importing. Fig. 6: Plan imported from AUTOCAD All rights reserved by 52

5 Geometry and Material Now click on Node icon in the insert ribbon and place nodes where ever the columns need to be erected. Now click on New single member in the insert ribbon, select member type as beam or compression member based on model data In the new single member dialogue box select the member cross-section software aids for the creation of own cross-section or import from standard library cross-section data. Select the type of cross-section and click ok then enter the geometry of the member and click OK. Fig. 7: Importing cross section geometry data from library Fig. 8: Importing material data from material library Erecting Column in RFEM After click ok in the single member dialogue box you will get a column creation cursor Join the nodes to create column. Repeat the same procedure for all the required columns. All rights reserved by 53

6 Fig. 9: Erecting columns in RFEM Creation of the Beams Select single member in the insert ribbon > material type as beam > select import from cross sectional library > select beam > cross-section > give dimensions of the beam and then select material depending upon design requirements Then a beam cursor will appear on the screen join the nodes for creating the beam between the nodes. Fig. 10: Creation of beams Creating the Slabs Select the new rectangular surface in the insert ribbon > give material type > thickness and click OK. Surface creation cursor will appear join the nodes of the required surface. Surface will appear on the columns and beams. Fig. 11: Creating the slabs All rights reserved by 54

7 Giving supports to the column Modelling and Analysis of a Multi-Storey Building using RFEM Select new nodal support in the insert ribbon and select the type of support > place it where ever necessary in the project. Fig. 12: Giving supports to column IV. LOAD COMBINATION AND ASSIGNING OF LOADS Creation of loads Member Load Go to new member load in the insert ribbon and click on it Select load type Load distribution Load direction Enter the value of load parameter. Fig. 13: Assigning loads to members Surface Load New surface load in the insert ribbon Select load type Load distribution Load direction Enter the value of load parameter All rights reserved by 55

8 Fig. 14: Creation of new surface load Wind Load Wind load can be assigned as UDL over an exposed surface or nodal load assigned at the exposed node. In the current project nodal loads are assigned. New nodal load in the insert ribbon Select the node or enter node number Give the value of load Click OK. Assigning the Loads The different loads created are assigned respectively. Creation of Load Combinations Fig. 15: Wind forces acting in +X direction Load combination are created as per IS 875:2000 part 5 DL DL+IL DL+IL+ WL DL = dead load, IL = imposed load, WL = wind load Click on new loads and combinations > select new load combination > move the required load into the load combinations by entering the factors. All rights reserved by 56

9 V. ANALYSIS OF THE STRUCTURE Steps involved in analysis of structure in RFEM In order to check the variation in bending moment, structure is analysed in RFEM as follows: Select calculations parameters in the results ribbon and enter all the required parameters in the dialogue box. Then click on calculate all icon in the results ribbon. The software package will analyse the structure and gives the results of the members and surfaces. In order to see the results right click on the member select Results diagram The results will appear in the dialogue box you can view all the loads and load combinations. Exporting Report Go to file > select export report > select the type of the file that to be exported and click ok. Fig. 16: Model of structure in RFEM VI. MANUAL ANALYSIS (KANI S METHOD) To elaborate this method we have considered Y5 frame to analyse. Sequence of steps to be followed Fig. 17: Frame Y5 showing members and joint notations Step 1: Rotation contributions Sum of the restrained moment of a joint and all rotation contributions of the far ends of members meeting at that joint is multiplied by respective rotation factors to get the required near end rotation contribution. For the first cycle when far end contributions are not known, they may be taken as zero (Ist approximation). By repeated application of this calculation procedure and proceeding from joint to joint in an arbitrary sequence but in a specific direction, all rotation contributions are known. The process is usually stopped when end moment values converge Table - 1 Calculation of rotation factors Joint Member Stiffness (k) Ʃk Rotation Factor A AB AC B BA BD All rights reserved by 57

10 CA C CD CE DB D DC DF EC E EF EG FD F FE FH GE G GH GI HF H HG HJ Table - 2 Calculation of distribution factors Storey Member Stiffness(k) Ʃk Distribution Factor I AC 1.11 BD II CE 1.11 FD III GE 1.11 HF IV IG 1.11 JH Step 2: Calculation of Fixed end moments Step 3: Calculation of Final End Moments Rules for the Calculation of final end moments (side sway cases) For beams, End moment = FEM + 2 near end contribution + Far end contributions. For columns, End moment. = FEM + 2 near end contribution + Far end contribution + linear displacement contribution of that column for the latest cycle. Table - 3 Final end moments. Member Fixed End Moment Near End Contribution Far End Contribution Final End Moment (in knm) (in knm) (in knm) (in knm) AB BA CD DC EF FE GH HG AC CA BD DB CE EC DF FD EG GE FH HF GI IG HJ JH All rights reserved by 58

11 VII. RESULTS AND DISCUSSIONS Results obtained from both manual analysis and RFEM are compared. The following tables show the comparison of results. Note: Sign convention in RFEM is different from manual analysis. Clockwise moments are taken as positive for Kani s method where as they were considered negative in RFEM.To avoid confusion, the final moments from Kani s method are expressed with the same sign convention as considered in RFEM. This is the frame considered initially for showing the calculation of Rotation factors and distribution factors. Fig. 20: Beam and Node numbers of Frame Y5 Table - 4 FEM of beams of Y5 frame Beams RFEM Kani's method Table - 5 FEM of columns of Y5 frame Columns REFM Kani's method VIII. CONCLUSIONS In this paper, analysis of a multi- storey building is done using RFEM and Kani s method and the results obtained from both methods have been compared and the results found to agree with each other. Using RFEM the analysis of the multi- storied building completed much quicker when compared to analysis using Kani s method. The variation is negligible for the members for less final end moments but was significant where final moments are higher. The end moments obtained from Kani s method are higher than those obtained from RFEM. Effective modelling can be done in RFEM when compared with STAAD-PRO. All rights reserved by 59

12 REFERENCES [1] Ramamrutham, Theory of structures,third edition [2] Indian codes referred: IS 875: Code of Practice for Design Loads (Other than Earthquake) for Building and Structures, IS 875: Part 1 Dead Loads Unit Weights of Building Materials and Stored Materials, Bureau of Indian Standards, Eighth Reprint Sept. 2003, 37 pages. IS 875: Part 2 Imposed Loads, Bureau of Indian Standards, Sixth Reprint June 1998, 18 pages [3] Dr. Prem Krishna Dr. Krishen Kumar Dr. N.M. Bhandari, IS 875: Part 3, Department of Civil Engineering Indian Institute of Technology Roorkee, 105 pages. [4] Website: All rights reserved by 60