Analysis and Design of Structures Using Struds Software

Global J. of Engg. & Appl. Sciences, 2012: 2 (3) Research Paper: Suresh, 2012: Pp.275-277

ANALYSIS AND DESIGN OF STRUCTURES USING STRUDS SOFTWARE Suresh, B Dept. of Civil Engineering, Adama Science and Technology University, Ethiopia. ABSTRACT Currently there are several commercially available softwares in market for analysis and design of Civil Engineering structures like ETABS, STAAD Pro and STRUDS etc. Among these STRUDS is an ideal software solution for the usage of structural engineers for the analysis of 2D and 3D structures and design of different R.C.C and Steel components such as slabs, beams, columns, footings and trusses with design sketches. Struds has inbuilt graphical data generator to model the geometry of building structure. It performs analysis using stiffness matrix method and finite element method for maximum solution, accuracy and reliability. Struds performs the integrated design by limit state method of all R.C.C. components of the structure by directly reading the analysis results. If any component fails the program gives you warning messages and suggests you the possible alternative for design. Struds prepares graphical outputs in the form of drawings and diagrams. Design results in the text form of schedules, quantities and details are produced. The design process is highly interactive and extremely user friendly. It facilitates to change the design parameters anywhere in between the design process and redesign the structure. These changes are automatically reflected in graphical and numerical output form. Struds also enables to produce the working drawings in AUTOCAD. Keywords: Software, struds and structural engineer. INTRODUCTION User can idealize a building structure in the form of plane grid, plane frame or space frame. Plane grid is is a two dimensional structure having no horizontal (Global X, Y) movement of the structure. The degrees of freedom available are Fz, Mx, My. Columns are modeled as supports with only Fz restraint (Fig. 1). A Plane frame structure is bound by a global X-Z or Y-Z coordinate system with loads in the same plane. It has three degrees of freedom Fx, Fz and My in X-Z plane and Fy, fz and Mx in Y-Z plane (Fig. 2). Space frame is a three dimensional structure with loads applied in any plane and has six degrees of freedom Fx,Fy,Fz,Mx,My and Mz(Fig. 3) (Johansson and Veljkovic, 2001 and Karlstrom, 2004). And plane truss consists of truss members which have only axial member forces no bending. It has two degrees of freedom that is transitional in that plane (Fig. 4). In Struds user can start floor grid structure and he can transform the same as plane frame or space frame after attaching columns. View and space frame or any of the plane frame generated (Ng and Gardner, 2007 and Wu, 2011). Problem: Type: Plane Truss Analysis with Nodal Loads (Fan Truss) Purpose: Compare Theoretical results with STRUDS. Problem: Determine the Axial Forces in all the members of Plane Fan - Truss as shown in figure-5. Find also the reactions at support Modeling: For modeling open a new building file in the Preprocessor Preprocessor -> Building -> New 275

Plane Truss -> Create -> Predefined Truss -> Standard Truss -> Select Truss type -> Here we take Fan - Truss -> OK Geometrical Parameters Dialog Box appears. Set the properties as desired Let us set  Span of Truss = 10 m  Rise of Truss = 4 m -> OK Property -> -> Create -> Section -> create a section say sec1. -> Load -> Nodal Load -> we create two Nodal Loads N1 = 10 kN and N2 = 20 kN -> Attach -> material (steel) to all elements. -> Section to all elements. -> Load -> Nodal Load (N2 to Node 16 and N1 to Node 14 and 18). Support -> In predefined trusses supports are already there. If one wants to change he can. The default supports are hinged at Node 1 and Roller at Node 11. Save -> the truss (say fan.bld) Truss -> Analysis Files -> Current Truss -> save files in the same folder. Close the Truss and save the building (Fig 6). STRUDS Results: Axial force in the element:Element No:25 Distance 1 0.000 -20.000 4.000 -20.000 M factor 1.000 Elemental results(Axial,B.M)-Plane struss structure. Load combination: 1.0 D.L+1.0 L.L

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Global J. of Engg. & Appl. Sciences, 2012: 2 (3) El.No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

Group RAFTER RAFTER RAFTER RAFTER RAFTER RAFTER RAFTER RAFTER RAFTER RAFTER Main-Tie Main-Tie Main-Tie Main-Tie Main-Tie Main-Tie Main-Tie Main-Tie Main-Tie Main-Tie STRUTS STRUTS STRUTS STRUTS STRUTS STRUTS STRUTS

Node 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 1-12 12-13 13-14 14-15 15-16 16-17 17-18 18-19 19-20 20-11 2-12 3-13 4-14 5-15 6-16 7-17 8-18

Length 1.176 1.176 1.176 1.400 1.475 1.475 1.400 1.176 1.176 1.176 0.918 0.919 0.918 1.093 1.152 1.152 1.093 0.918 0.919 0.918 0.735 1.469 2.204 3.079 4.000 3.079 2.204

Axial 32.00 32.01 32.04 27.47 27.46 27.46 27.47 32.04 32.01 32.00 -24.98 -24.98 -25.00 -25.00 -19.39 -19.39 -25.00 -25.00 -24.98 -24.98 0.000 0.050 -10.00 -0.02 -20.00 -0.020 -10.00

B.M 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Theoretical results: The Fan - Truss taken is symmetrical in loading also, so we will analyze the half truss only. Total vertical load = 10 + 20 + 10 = 40 kN Reaction at both Node = 40 / 2 = 20 kN The inclined length = sqrt (4 * 4 + 5 * 5)= sqrt (41) = 6.4031 m The angle theta is given as: tan (theta) = 4 / 5; this gives theta = 38.6598 (degrees) cos (theta) = 5 / sqrt (41) sin (theta) = 4 / sqrt (41) At Node 1: For €V = 0, P1-2 = 20 / sin (theta) = 32.015 kN For €H = 0, P1-12 = P1-2 * cos (theta) = 25.000 kN At Node 12: For €V = 0, P2-12 = 0 (As there is no vertical force / load at Node 12) For €H = 0, P1-12 = P1-2 * cos (theta) = 25.000 kN At Node 2: Resolving perpendicular to the inclined element 2, P2-13 = 0 Resolving along the inclined element 2, P2-3 = P1-2 = 32.015 kN At Node 3: For €H = 0, P3-4 = P2-3 = 32.015 kN For €V = 0, P3-13 = 0 At Node 13: For €V = 0, P4-13 = 0 For €H = 0, P13-14 = P12-13 = 25.000 kN At Node 14: For €V = 0, 276

P4-14 = 10 (Applied Nodal Force at Node 14) For €H = 0, P14-15 = P13-14 = 25.000 kN At Node 4: At node 4 there are 5 elements Force in member 31, P4-13 = 0 Force in member 23, P4-14 = 10 kN Length of element 23, L4-14 = 2.204 m Length of element 14, L14-15 = 1.093 m Angle Ø is given as tan (Ø) = 1.093 / 2.204 => Ø = 26.3776 degrees For €V = 0, P4-15 * cos (Ø) + P3-4 * sin (theta) - P4-5 * sin (theta) = 10 --------(1) For €H = 0, P4-15 * sin (Ø) + P4-5 * cos (theta) - P3-4 * cos (theta) = 0 --------(2) On solving these two equations (1) and (2), we get P4-5 = 27.4687 kN P4-15 = 7.9916 kN At Node 5: Resolving along the inclined element 5, P5-6 = P4-5 = 27.4687 kN Resolving perpendicular to the inclined element 5, P5-15 = 0 At Node 15: At node 15 there are 5 elements Force in member 24, P5-15 = 0 Force in member 34, P4-15 = 7.9916 kN Length of element 25, L6-16 = 4 m Length of element 15, L15-16 = 1.152 m Angle Ø1 is given as tan (Ø1) = 1.152 / 4 => Ø1 = 16.0664 degrees For €V = 0, P6-15 = P4-15 * cos (Ø) / cos (Ø1) = 7.45057 kN For €H = 0, P15-16 = P14-15 - P4-15 * sin (Ø) - P6-15 * sin (Ø1) = 19.3875 kN At Node 16: For €V = 0, P6-16 = 20 (Applied Nodal Force at Node 16) For €H = 0, P16-17 = P15-16 = 19.3875 kN Comparison between theoretical and struds results: Axial Force in Element 1 and 10 2 and 9 3 and 8 4 and 7 5 and 6 11 and 20 12 and 19 13 and 18 14 and 17 15 and 16 21 and 29 22and28 23 and 27 24 and 26 25 30 and 36 31 and 37 34 and 32 35 and 33

Theoretical Results 32.015 32.015 32.015 27.469 27.469 25 25 25 25 19.388 0 0 10 0 20 7.451 0 7.992 0

STRUDS Results 32.00 32.01 32.04 27.47 27.46 24.98 24.98 25 25 19.39 0 0.05 10 0.02 20 7.44 0.03 8.00 0.04

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% Deviation 0.04 0.01 0.07 0.00 0.00 0.08 0.08 Nil Nil 0.01 Nil Negligible Nil Negligible Nil 0.15 Negligible 0.10 Negligible

Global J. of Engg. & Appl. Sciences, 2012: 2 (3) Other advantages: Though it is not possible to consider secondary moments due to eccentric seating beams .And no stress concentration effect consideration due to cut outs in slabs. But It is possible to analyze beams of irregular sections that is concrete I beams and beams having hexagonal section. It is possible to design beams of inclined in plan. Beam design is done for worst of all load combinations including pattern loads, Earth quake loads and wind loads. In beam design parameters user defined detailing option is given. In user defined detailing one option to decide maximum bar length is given which will be helpful in deciding laps in detailing. And also Floating columns can be considered in Struds. The user can account for the soft story effect in Struds for seismic analysis. However the storey which is to be decided as a soft storey needs to be defined explicitily by the user. Modeling and analyzing buildings which may be located on sloping hill sides is possible. Which provides an unique feature to modify the footing level. The effect of shear walls can be taken into account by STRUDS by using Master-slave concept. Facility to view shear wall detail for selected floors by selecting default levels for that particular floor is given. Along these triangular slabs , trapezoidal slabs and flat slabs also can be designed. User can specify drawing parameters for slabs, beams, columns, shear walls and footings.Use of Fe 550 grade steel in design of slabs, beams ,columns, shear walls and footings is implemented. Stress contours to visualize the behavior of structure including principal and von mises stresses is possible. Struds analyze a truss supported by Reinforced concrete columns. And in steel trusses it is possible to create compound sections from the basic sections such as equal and unequal angles,

channels, I and tubular sections. In relation to other soft wares ETABS file and it’s analysis file can be imported the same in STRUDS and also export STRUDS file in ETABS. Also possible to import geometry from AUTOCAD to STRUDS (Gardner and Nethercot, 2004 and 2006). CONCLUSION The analysis and design by using STRUDS software is given results with negligible difference with manual calculations. Thus the software is good for using analysis and design of structures, simple and also user friendly. And also providing other advantages to the users as specified. REFERENCES Gardner, L and D.A. Nethercot. 2004. Numerical modelling of stainless steel structural components — A consistent approach. Journal of Structural engineering, ASCE, 130(10):1586– 601. Gardner, L and N.R. Baddoo. 2006. Fire testing and design of stainless steel structures. Journal of Constructional Steel Research, 62:532–43. Johansson, B and M. Veljkovic. 2001. Steel plated structures. Progress in Structural Engineering and Materials, 3(1):13–27. Karlström, P. 2004. Thin-walled steel studs in fire: Analysis and design recommendations, Licentiat Thesis, Luleå University of Technology, Sweden. Pp. 73. Ng, KT and L. Gardner. 2007. Buckling of stainless steel columns and beams in fire. Engineering Structures, 29(7):717–30. Wu, C. 2011. ”Special Issue on Protection of Structures against Blast Loading.” J. Perform. Constr. Facil. 25: 358–359.

Fig. 1. Fz restraint model

Fig. 2. Three degree freedom model

Fig. 3. Three dimensional structure model

Fig. 4. Transitional plane

Fig. 5. Plane Fan - Truss

Fig. 5. Analysis File - Truss

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