Solve the problem described in the figure below for the joint action of Ε y, E x

Transcription

1 EXAMPLE 4 Correcting mistakes in SAP 2000 Solve the problem described in the figure below for the joint action of Ε y, E x Input data - Column EZ (both in 1 st and 2 nd floor) has dimensions 50/30 (X/Y) whereas the remaining columns have dimensions 20/40 (X/Y) - Beams have dimensions 20/60 (always the large dimensions refer to beam height) - The material will be concrete 5.0 m Ey=150KN 4.0 m B Z 3.0 m Ex=220KN A C E T z 4.0 m y x D H

2 EXAMPLE 4: Correcting mistakes in SAP Geometry mistakes 1.1) Unit mistakes If wrong units have been chosen during data input (e.g. kip-in instead of KN-m) then correcting is very difficult and the modelling should start from the beginning. 1.2) Wrong element dimensions The model is based on the Template models of SAP library according to the following figure: Figure 4.1. Determination of model geometry The resulting structure is depicted in Figure 4.2. Figure 4.2. Structural configuration

3 EXAMPLE 4: Correcting mistakes in SAP ) Errors The resulting structure already has 2 important errors. The first concerns the floor number which is 3 instead of 2 floors that were required from the problem statement. The second is the length of the bay along Χ being 4m instead of 5m ) Correction of errors a) We can always start again the model using the command File New model from Template β) We can delete the extra floor by deleting the corresponding elements. Moreover, we can correct the length error if we select all implicated joints having wrong coordinates (it doesn t matter if we also select the related Frame elements) and use the Move command to relocate them to the correct coordinates. In this specific structure, we can select all joints of the frame located at X=2 and request Move by 1m in the X direction. In order to make the frame selection easier we can work in the right window in 2D yz plane at coordinate X=2. Figure 4.3. Selection of frame at X=2 (yz view on the right) After the selection of the proper frame it is quite easy to select Move by 1m along the X axis. The previous correction resulted in moving the structure along with its center of gravity, which is not coinciding any more with the coordinate axes. In order to have

4 EXAMPLE 4: Correcting mistakes in SAP the centre of gravity at the X=0 and Y=0 coordinates we should select the whole structure and Move along Χ=-0.5m. Finally, we should also change the grid lines since the 2D views can only follow the existing grid lines which are not at the same location with the new configuration of our model. Grid lines of the X direction should be moved to +2.5 (from +2) and to -2.5 (from -2). It is obvious that correcting the model geometry is not always very easy, requiring numerous commands in order to achieve the correct configurations. Since we are still at the first stages of data input procedure, it might have been more convenient to start from the beginning at this point. Nevertheless, there are cases where the aforementioned modifications can not be avoided. 2. Errors in Frame section configuration 2.1) Errors in frame section dimensions The correct way to determine the frame section dimensions is to use the local axes configuration described in local axes appendix. If however something is wrong we can also use some other options to reveal any important errors. Let s suppose that frame sections are initially given according to Figure 4.4. Figure 4.4. Initial configuration of frame sections

5 EXAMPLE 4: Correcting mistakes in SAP Then each frame element is assigned with the corresponding frame section. In order to perform frame section assignment in a more efficient way we can work as follows: - Using the tool the whole structure is selected and assigned to COLUMN frame section - Then activating the right window in XZ plane (the one that includes EZ column), we select column ΕΖ (on both floors) and assign the COLEZ section - Finally activating the right window in XY plane we select all beams in both floors and assign them the BEAM section In the 3D model depiction (left window) we can use Set elements and Show Extrusions to obtain a nice visualization of the structure. Figure D structural view along with frame section dimensions

6 EXAMPLE 4: Correcting mistakes in SAP It is obvious that the beam section has been defined erroneously. Moreover, all columns (except EZ) have wrong orientation since their large dimension should have been along the Y axis. 2.2) Correcting the frame section dimensions From Define Frame Sections the correct dimensions are provided using the Modify/Show option. In the local axes notes the correct fields for each one of the related dimensions are explicitly provided. Figure 4.6. View of the structure after the corrections 3. Mistakes in load assignments First 2 load cases ΕΧ and ΕΥ are created. Also, a load combination is required to obtain the results for the action of both loads on the structure.

7 EXAMPLE 4: Correcting mistakes in SAP A new node should be created at the center of the 1 st floor using the right window in XY plane view. The easiest way is to draw a new joint in a random location using the tool. Then after right clicking the joint, the proper coordinates (here X=0 and Y=0) can be provided. Figure 4.7. Relocation of the joint towards the center of the floor This joint is also created at the 2 nd floor using the Copy και Paste (Z=3) command. Afterwards the joint of the first floor is selected and a load in the ΕΥ load case is assigned (Υ=220) as in Figure 4.8. Obviously, this is a mistake that should be corrected.

8 EXAMPLE 4: Correcting mistakes in SAP Figure 4.8. Initial assignment of the load at the first floor The same joint is selected again and assigned a load in the ΕΧ loading case (Χ=220) using the option replace existing loads. After right-clicking on the joint, it is revealed that load exists for both loading cases ΕΧ (load parallel to Χ=220 being in the first field of Forces) and ΕΥ (load parallel to Υ=220 being the second field of Forces) Figure 4.9. Figure 4.9. Joint loads after the first correction effort Therefore it is clear that the option replace loads does not interfere with the other loading case (it only changes the loading properties of the specific loading case that it is used).

9 EXAMPLE 4: Correcting mistakes in SAP In order to finally erase the ΕΥ load of the first floor joint we should again assign loading in the ΕΥ load case, using zero (0) values for all fields and then use the option replace existing loads. After that the only load of the joint is going to be the one in the EX load case. 4. Mistakes in diaphragm assignment The horizontal loads are assigned at the additional joint at the center of each floor. In order to transfer this load to the rest of the structure it is very important to include this specific joint when determining the floor diaphragm. Note: If accidentally 2 diaphragms are given in a single joint then SAP 2000 will not be able to run the analysis and will come up with an error message (ANALYSIS INCOMPLETE). In this case, the diaphragm should be deleted and determined again in the correct way.

10 EXAMPLE 4: Correcting mistakes in SAP Quick model checking Materials Materials take place in the analysis when they are assigned in a specific frame section in Define Frame sections where the correct material should be given. The specific properties of each material can be viewed or changed in Define Materials. Geometry The dimensions of linear elements can be reviewed after right-clicking on each specific element. The length of the element can change using the Move command to relocate the Start or the End joint (or both). The joint location can be also reviewed or changed after right-clicking on each joint. Another way to relocate a joint is to use the Move command. Dimensions of the cross-sections can only change using the command Define Frame sections. A quick visual inspection can be performed using the Set Elements Show Extrusions ( ) where some errors are revealed if the dimensions of the cross-section differ substantially in the two directions (it is easy to distinguish if a 20/80 cross-section is oriented erroneously yet it is not that easy in the case of a 35/40 cross-section). In all cases the best way is to always check the Local axes when determining the cross-section properties. Degrees of freedom fixities (restraints) and constraints (diaphragms) From Analyze Set options we should check if all required degrees of freedom are available. (e.g. for a 3D structure all degrees of freedom should be available). Joint Restraints are revealed after right-clicking a joint. The number and location of the restrained field determines the type of fixity for each joint. The joint constraints (e.g. diaphragms) can be reviewed after right-clicking the joint. In the same way, we can see any mass properties (mass degrees of freedom) provided to a joint and the corresponding direction of movement.

11 EXAMPLE 4: Correcting mistakes in SAP Loading Joint loads are easy to review after right-clicking on the joint. All loads are presented in the corresponding loading case. It is also possible to review the loads from Display Show Loads Joint. Loading of linear elements (e.g. beams) can be made visible after selecting each load case from the command Display Show Loads Frame. Finally, all combinations should be checked to make sure they are correctly defined. Reviewing the results Deformed shape-joint displacements Display Show deformed shape (or ) and select the load case (or combination) for which the deformed shape is required. Reinstate the initial (undeformed) shape using the command Display Show Undeformed shape (or ). Moment and shear force diagrams Display Show element forces/stresses Frames (or ) and select the load case (or combination) for which the diagrams are required. The choice Fill diaphragm provides a colored diagram whereas the choice Show Values provides values on the diagram. In 3d problems it is better to review any diagrams in the 3d window. Support (fixities) reactions Display Show element forces/stresses Joints Reactions (or ) and select the load case (or combination) for which the support reactions are required.

12 EXAMPLE 4: Correcting mistakes in SAP