HLR Section 1 |
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Program Overview |
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CONTENTS | |
1.1
General Procedure for Performing a HL
Assessment |
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Other Links: | Main Index | Route Data | Vehicle Data | Analysis Options | | |
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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):
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1.2 Summary of the Analysis Process | |
Prior to beginning the analysis the program allows a number of options to be specified:
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. |
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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:
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 |
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1.3 Creating Nodes, Links and Routes | |
Creation of a heavy load route network should generally follow the steps given below:
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1.4 Entering and Editing Structure Data | |
Structure information is entered into the HLR database using the "Structure/Enter new bridge data"
menu options. Editing existing structure data is performed using "Structure/Load
structure data from database". Refer to Section 5 for detailed information
as to how this can be done. 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. |
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