Tutorial 1: Direct Design of a Circular Pipe
- Becca Alford (Unlicensed)
Analytics
Problem Overview
A complete start-to-finish design using Eriksson Pipe will be demonstrated in this chapter. The job is a typical precast concrete pipe, which will be designed in accordance with the LRFD 4th Edition Specifications. Below are the input values for the problem.
Governing Specifications
AASHTO LRFD 4th Edition
Culvert Dimensions
Inside Diameter = 96 in
Wall Thickness = 9 in
Fill Depth = 14.0 ft
Reinforcement Covers
Exterior = 1 in
Interior = 1 in
Pipe Concrete
f’c = 4.0 ksi
wc = 0.150 kcf
Reinforcement
fy = 65 ksi
Dead Load
Soil Density = 0.12 kcf
Water Density = 0.0624 kcf
Live Load
HL-93 (LRFD)
Data Preparation
Most input fields in Eriksson Pipe’s interface were designed to minimize the preliminary work that must be done by the engineer prior to running the program.
Eriksson Pipe automatically computes the self-weight of the pipe.
Entering Data
To begin the tutorial, start Eriksson Pipe by accessing it though the Programs folder of the Start menu. Click the Start button in the lower left-hand corner of the screen, highlight the Programs folder, highlight the Eriksson Pipe icon, and click the icon. Note that due to differing versions of Windows, some of the following screen shots may look different on your system.
The startup screen will appear briefly, followed by the screen shown below.
When Eriksson Pipe is first started, you have two options. You can either begin a new design by clicking the New Project button, or you can open a previous job. Click the New Project button to begin.
Input your job information as shown above and select Next to go to the next screen. You can also press Cancel to abort the input process.
Eriksson Pipe has two input modes. When you start a new project the program will take you through a series of input screens (which are simply standard Windows dialog boxes) one by one. If you have already finished with the last input screen, or if you open an existing file, you can access any of the input screens individually. In this case, the input screens will have an OK and Cancel buttons. The OK button will save the input data and re-run the analysis. The Cancel button will discard any changes to the input.
The next available input screen are the Project Settings. Here you have options for Project Type and Project Units. For Project Type, you can select either Direct Design or Three Edge Bearing. For this tutorial, select Direct Design and press the Next button (the next tutorial will deal with a three edge bearing problem).
In the Pipe Properties dialog box, you will be able to select the pipe size and soil pressure distribution type, and modify the default materials properties. Note that many of the default input for new projects can be set in one of the three default Parameters dialog boxes. After we finish the input for this problem, we will take a look at the Parameters input.
For now, however, lets continue with the tutorial. For a pipe diameter, select 96 in the drop down list. Notice that the pipe wall thickness automatically changes to 9 inches. In the material properties section, change the design concrete strength to 4 ksi. Leave the soil pressure distribution at its default setting (Heger, or SIDD). Press Next to proceed to the next input screen.
Here you can select the design code and the installation conditions. Note that the available input in the installation conditions box is dependent on the soil pressure distribution type that we selected on the previous screen. For SIDD, we can can change the installation type and the depth of the earth fill above the crown of the pipe. Also, we can override the defaults for the vertical and horizontal arching factor.
For this problem, change the installation type to 2, and the height of the earth fill to 14. When you are finished, click the Next button.
In this dialog box, you specify loading data (soil, fluid and live). For live load, select HIGHWAY from the list. When the list closes, the HIGHWAY Live Load Parameter dialog box will automatically open (this DB can also be accesses by pressing the LLP button to the right of the list of live loads).
Here, accept the default parameters and just press ‘Close’. Back at Live Loads screen, press Next to continue.
The final input screen before the calculations are started is the Reinforcement screen. Here, the reinforcing diameter is already calculated for you, and is a percentage of the wall thickness (8%), or in this case 0.72 inches. Accept all of the defaults by pressing Finish at this point. This starts the calculation process and displays the text report.
Now that we have completed our first problem, an important resource of Eriksson Pipe’s to learn about is its help system. When any dialog box is open, you can press the F1 key on your keyboard to immediately get specific help about the current dialog box. Each dialog box’s help screen contains detailed information about the input required for that dialog box. Later, during the more complicated input areas, this will prove to be an invaluable reference.
Aside from the context-sensitive help, there are also help topics dealing with the general operation of the program and engineering theory as well. To access those areas, select Help|Topics from the menu bar. Do that now.
To view the contents of each major section, click the plus sign to the left of the the book icon next to the item of interest and one or more subtopics will appear. For example, under the Design and Analysis section, topics related to the underlying operation of the program are contained.
To close the Eriksson Pipe help system and return to the text report, click the “X” in the upper right-hand corner of the help window.
Before we look at the results of the design, note the area at the bottom of the screen. This is called the status bar. The three panes at the right side of the status bar contain information about the design. From left to right, they are defined as follows:
LRFD 4th Ed: Governing design specification.
Direct Design: Current type of design (Direct or Three-Edge Bearing).
US Customary Units: Selected units (US Customary or Metric).
All of the data input for this job has now been addressed. At this point, completion of the design consists of viewing the calculation results and and making refinements to the input data as necessary.
Getting Results
Eriksson Pipe incorporates an extremely fast and efficient calculation engine. On a typical PC, recalculation times are typically less than a few seconds. This results in the ability of the program to perform real-time calculations. That is, whenever a revision to the input data is made, calculations are automatically updated in the background, and the results are quickly made available to view in multiple formats. The practical result of Eriksson Pipe’s method of performing calculations is that after editing the input, you can immediately view the effects on the design.
This view of the results gives several pages of data. The text window shows the top of the detailed text report. This report can be several pages in length and so will not completely fit on the screen. Along the right-hand side of the screen there is a scroll bar that permits you to very easily and smoothly scroll and review the results. The rectangular-shaped button currently positioned at the top of the scroll bar is called the “thumb.” You can click and hold on the thumb and move your mouse toward you to fluidly scroll down the page.
You can vary the length of the text report, buy selecting File | Options. Do that now.
Here you can select how long of a text report you want. In the Reporting Options box, you can select up to four different lengths of reports, from a simple summary to the complete report that includes the computer modelling information.
Close the User Options DB to return to the text report. Now is a good time to obtain a printout. You can actually get a printout at anytime during the design. (Note, however, that until the job has been saved, it does not have a filename, so “tmp.pip’ will be shown as the filename at the top of each page of each report.) To bring up the Print dialog box, click the printer icon located on the left end of the toolbar.
The Print Dialog Box applies to the active window. In our case, the text view is the active one. You can also preview the report before you print by accessing Print Preview from the File menu.
The complete printout for the text report for both Tutorials are included in the Appendicies of this manual.
Saving Your Data
Saving your data permits you to recall the job at a future time for review and possible editing.
To save the data for our example, we will use the Save button or select the Save option on the File menu. Since we have not yet given this job a name, the Save As dialog box will appear.
Note that once a name has been entered, if you pick the Save option, the Save As dialog box will not appear again. So, if you desire to change the name of the job, you must actually pick the Save As option from the File menu.
Eriksson Pipe’s data files use the extension “.pip,” which Eriksson Pipe will supply for you. So enter “Tutorial1” as the job name and click the Save button.
To close the current job, select “Close Project” from the File menu.
At this point, you can start a new job, restore a previous job, or just close the application. To close the application either select Exit from the File menu or click the “X” in the upper right-hand corner of the screen. To exit the application, select Exit from the File menu.