HLR Section 1
Program Overview
CONTENTS
| 1.1 General Procedure for Performing a HL Assessment 1.2 Summary of the Analysis Process 1.3 Creating Nodes, Links and Routes 1.4 Entering, viewing and editing Structure Data 1.5 Load Ratio Analysis 1.6 Problems, Bugs, Errors
| Other Links: | Main Index | Route Data | Vehicle Data | Analysis Options |
1.1 General Procedure for Performing a HL Assessment
| The normal procedure for assessing a standard heavy load application would typically involve the following steps (generally in the order given): Enter relevant job identification data (refer to Section 2) Enter vehicle data or select a vehicle from the data base (refer to Section 4) Select a standard heavy load route or create a new route (refer to Section 3) Alternatively, select only a number of specific structures for analysis (refer to Section 3) Select the required analysis and output control options (refer to Section 6.1) Perform the analysis (refer to the summary below or Section 6.2 for details) Review the results (refer to Section 7) Print any required reports (refer to Section 7) If required, save the HL application to the data base
1.2 Summary of the Analysis Process
| Prior to beginning the analysis the program allows a number of options to be specified: Parameters associated with structure-specific distribution factors The direction of travel along the route (in the forward, reverse or both directions) Whether reduced (width-modified) axle loads are to be used in the analysis or not The ultimate strength factor (LSf) to use for the specified heavy load vehicle when limit state capacities are available for structures The working stress factor (Fw) to use for structures with no limit state capacities (refer to the note below for a description as to how this factor is used and applied in HLR). A number of restriction flags that can be toggled on or off Since the ultimate strength factor is prescribed by the user prior to the analysis, scope exists to use a reduced factor for non-load carrying vehicles, (eg. cranes), where the possibility of overloading is reduced. Similarly, reduced ultimate strength load factors can be used when the field-weighing of load platforms accurately confirms axle loads. HLR allows the Working Stress Overload Factor to be varied in the range 100% - 140%. If the factor is left at the default value of 140% the program will simply use the full working stress overload capacity when performing the moment comparison. No further factoring is performed. If, however, the factor is changed to a value between 100% and 140%, HLR will linearly interpolate between the basic allowable capacity and the full overload capacity. If either of these two capacities do not exist, HLR will default to a simple ratio check, since it is unable to perform the interpolation. Refer to Section 6.2.8, Item 8, for a more detailed explanation. Note, however, that although the factors used in the analysis are the responsibility of the relevant infrastructure owner, they will never-the-less need to comply with the guidelines given in Section 7 of the Austroads Bridge Design Code.
| Basic Analytical Process The basic analytical process is relatively straight-forward (click here for a summary flowchart). Each structure along the specified route is first checked for height, width or other imposed restrictions. If no restrictions are found HLR will attempt to calculate the maximum moments induced by the heavy load vehicle and compare them with the working stress or ultimate live load moment capacities of the structure as stored on the structure database. In the case of a selected list of structures the program will check and report on both height-width restrictions as well as structural sufficiency. When checking each structure along the designated route for structural sufficiency, the maximum moments induced by the heavy load vehicle, Mhl, are compared to the moment capacity, Mc, of the structure as stored on the structure database. The comparison is done for three notional travel conditions: Unrestricted vehicle travel speed and location on the bridge deck Travel speed restricted but not the position of the vehicle on the bridge Both travel speed and vehicle position restricted Structures for which capacities do not exist are analysed using a modified moment-ratio method based on the original design vehicle. In the case of continuous structures, HLR will compare the moment envelopes produced by both the heavy load vehicle and the original design vehicle. For a detailed explanation of the assessment methodology refer to Section 6.2
1.3 Creating Nodes, Links and Routes
| Creation of a heavy load route network should generally follow the steps given below: Identify the heavy load route(s) on the road network and assign node numbers to key intersections. Ensure that node numbers consist of no more than 3 alpha-numeric characters (e.g. 40a). Create links between adjacent nodes (use Link / Create a new link from the menu) - refer to Section 3.2. Links are specified in terms of a Start and End node number that defines the notional forward direction of the link. Structure numbers can optionally be specified in the link data even though they may not have yet been entered into the database. The system will warn you of structures that have not yet been entered but it will allow you to save them if you wish to do so. Repeat this for all links along the route. Create a "standard route" by joining one or more links together (use Route / Create a standard route from the menu). HLR has two ways in which a standard route can be created - refer to Section 3.3 for details. Note that a standard route can consist of any number of links - either a single link (with or without structures along it) or multiple links joined together. Enter structure data as and when it becomes available (see also Section 1.4 below). During analysis structures that do not yet exist will be ignored. However, they will be listed in the detailed reports (but not in the Summary Report).
1.4 Entering, viewing and editing Structure Data
| Structure information can only be created and entered via BIS (Bridge Inventory System). It cannot be done from within HLR. However, structure data can be viewed using the Structure options in the main menu. It is recommended that links should always be created first, before entering data relating to structures lying on those links. The reason is that one of the structure data attributes refers to the node number associated with the notional forward direction of the link (the Start node number). If this number does not exist HLR will not allow you to save the structure data. Note, however, that structures with a blank (null) start node can be saved. In theory, therefore, it is possible to enter and save structure data first (with a blank start node) then return later and supply the node number after the link has been created.