Rating Parameters dialog

The Rating Parameters dialog is available in both Standard Specifications (LFD) and LRFD mode.

In Precast/Prestressed Girder the rating parameters are common to all beams, and once a selection has been made in this screen, they are automatically applicable to all beams in the bridge. The general process is to select and add the live loads for each category, i.e. inventory and operating in Standard mode, and Design, Legal and Permit for the LRFD mode, and select the parameters that you wish to rate for (i.e. Moment, vertical shear, compression etc.) and click OK to close this screen. When you go back to the Beam tab and click on Rating Results, the program will automatically perform the live load analysis and calculate the rating factors for the selected beam, and display them in the rating output window.

In the LFD mode, click Rating to view and edit the Rating Parameters screen. Select from the Inventory Rating and the Operating Rating columns using the arrow buttons (>>) to move one or more items to the Selected column.

Figure 1 Rating Parameters in Standard Specification (LFD) mode

Allowable Stress Factors (LFD mode)

• Concrete:

  These are the default concrete allowable stress factors for inventory and operating as specified in the equations in section 6.6.3.3 of AASHTO Manual for Condition Evaluation of Bridges.

• Prestressing Tendons:

  These are the default prestressing tendon allowable factors for inventory and operating as specified in the equations in section 6.6.3.3 of AASHTO Manual for Condition Evaluation of Bridges.

• Cracked Section Analysis:

  The option for cracked section analysis for computing tension in prestressing tendons at the bottom of the beam can be activated using the check box. The cracked section option is only applied to the prestress tendon tension calculations under Operating Rating.

Rating Parameters Screen Terms (LFD mode)

• Inventory Rating Selected Trucks:

  Select the trucks from the list of available trucks that you wish to use for Inventory Rating on the girders by simply checking the checkbox in front of the vehicle you wish to include. You can define your own rating vehicles in the Live Load library, and they will show up in the list titled Available.

• Operating Rating Selected Trucks:

  Select the trucks from the list of available trucks that you wish to use for Inventory Rating on the girders.

• Rating Options:

  You can select the individual components that you wish to consider for rating. By default the program will select the option for "All", but based on your agency requirements, you may chose to activate only specific criteria.

• Load Rating in the LRFD mode:

  Precast/Prestressed Girder performs Load Rating according to section 6.4 of the Manual for Condition Evaluation and Load and Resistance Factor Rating (LRFR) of highway Bridges. Click on Rating to view the Rating Parameters.

Figure 2 Rating Parameters in LRFD mode:

Select and add the live loads to be considered for each of the rating levels (i.e. Design, Legal and Permit). Multiple vehicles can be selected for each rating level. The program will compute the detailed rating factors for individual trucks at all tenth points along the bridge, as well as provide a summary rating report listing the most critical rating factors from amongst all the locations for each vehicle. If a vehicle is not part of the list of available vehicles, add the particular vehicle to the LRFD load library using the appropriate category (i.e. for design rating, add under truck type; for legal rating, add under legal loads; for permit rating, add under permit loads). The HL93 design load is a program specific notional load that cannot be edited by the user and includes the effects of the lane, truck and tandem taken in the manner specified by LRFD. For continuous spans, a check box to consider double truck in the negative moment zone is available to the user.

The next step is to select the rating options, such as moment, shear, prestress tendon stress, concrete stress, etc., that you wish to compute load rating factors for. Set the common factors such as system and condition factors, ADTT factor, Dynamic Load factor and DW factor that will be applicable to all rating levels. Click the Limiting Stresses button and specify the limiting values to be used in the rating equation.

Figure 3 Limiting Stresses for Rating in LRFD mode:

Then, for each rating level, set the appropriate factors based on LRFR Table 6.1, or your state specifications. For Permit Vehicles, the permit factor which is computed based on user selections for Permit Type, Load conditions and Frequency can be selected for each rating vehicle added to the list of selected vehicles for permit rating. The Copy to All Permit vehicles copies the factors (including the permit vehicle factor) for the selected permit vehicle to the remaining permit vehicles.

Select the type of report (current choices are Basic Report and Florida DOT style report which represents an additional summary report as required by FDOT), and then click OK to close the Rating Parameters window. The rating parameters have now been specified, and clicking on the Rating results button initiates the rating analysis and the results are presented to the user in the enhanced report format.