Analisis De Estructuras Risa

TUTORIAL FOR RISA EDUCATIONAL
C.M. Uang and K.M. Leet 1. INTRODUCTION The educational version of the software RISA-2D, developed by RISA Technologies for the textbook Fundamentals of Structural Analysis, is an interactive computer program for the analysis of two-dimensional structures such as continuous beams, trusses, and frames. This program has been developed to make the definition, solutionand modification of 2-dimensional problem data as fast and easy as possible. RISA-2D Educational has full graphical modeling capability allowing you to draw and edit your model on the screen. The analysis results can also be displayed graphically. A help file is also provided for a more detailed description of the program features. The numbers of joints and members are respectively limited to 50in this educational version. The program solution is based on the widely accepted linear elastic direct stiffness method. First, the stiffness of each element of the structure is calculated. These stiffnesses are then combined to produce the model's global structure stiffness matrix. Next, the global matrix is solved for the applied loads to calculate joint deflections that are then used tocalculate the individual element forces and deflections. You need to download a self-extracting file containing both the RISA Educational software and this tutorial from http://www.mhhe.com//engcs/civil/leet/. We will use two examples−one truss and one frame−to demonstrate how to use RISA Educational to perform a structural analysis. 2. TRUSS ANALYSIS The 2-dimensional truss to be analyzed is shown inFigure 1. It is indeterminate to the first degree. Assume the area of each member is 1.2 in2 and the Young’s modulus is 29,000 ksi. A step-by-step analysis procedure is provided below.

Figure 1

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(1) Start the RISA-2D Educational program. Figure 2 shows that a manual bar will appear at the top of the window. In addition to a Data Entry toolbar, a global XY coordinate system and a set ofgrid lines in the Model View window will also appear.

manual bar

Figure 2 (2) If you have created an input file previously, click File from the manual bar and select Open to open the input file. Otherwise, you can go to the next step to create a new model. (3) Click Global from the manual bar and enter the information for Model Title and Designer in the Global Parameters window (see Figure 3).The program can provide internal forces (moment, shear, axial force) at a number of equally spaced sections along a member. The default number of sections is 5, which is useful when you analyze continuous beams or frames. For truss analysis, however, the only internal member force is axial load, and the axial load is constant along a truss member. Set the Number of Sections to 2 so that theinternal forces at both ends of the member will be provided. Click OK once you have completed the information.

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Figure 3 (4) Click Units from the manual bar. One option you can choose in the Units Selection window is Use CONSISTENT units. This is the method we usually use for hand calculations. That is, all the physical quantities like length, section properties (A and I), material properties(E), loads, reactions, member forces, and deformations are expressed in terms of consistent units (e.g., kips and inches). For practical applications, the program provides a more convenient way of handling unit conversions internally by allowing the designer to choose either the Standard Imperial or Standard Metric units. We choose Standard Imperial in this example. Clock OK once you have selectedthe units.

Figure 4

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(5) Click Modify from the manual bar and select Grid. A Define Drawing Grid window will show that the program assigns, by default, (0, 0) as the coordinates for the origin (see Figure 5). Furthermore, the program assigns 30 grids with a unit length (1 ft) as the increment in each direction (see Figure 2). Considering the overall dimensions of the structure in...