Design Lane (Highway) [SIG]

Transverse Lane/Vehicle Placement:
Upon receiving roadway dimensions from the user, OpenBrIM seamlessly manages lane placement in the transverse direction for influence surface-based live load analysis. In a 50-foot roadway, for instance, it can accommodate 4, 3, 2, or 1 lane(s), with multiple presence factors of 1.2, 1, 0.85, and 0.65. OpenBrIM rapidly explores these alternatives, shifting lanes by one foot in the transverse direction and assessing billions of potential configurations within seconds, thanks to its efficient, multi-threaded GPU-based architecture.

Properties

Lane Width: The combined width of the vehicle (usually 6 ft) and its margin (1 or 2 feet) should not exceed the Lane Width, which is typically 12 ft.

Margin btw. Vehicle & Lane Edge : This is referring to the lateral distance from both sides of the lane where vehicles cannot be placed. The wheel load of any vehicle cannot be positioned in this specific location.

Vehicles

It is utilized to define a vehicle, vehicle's impact factor and direction within a single Design Lane in the longitudinal direction. Typically, AASHTO recommends placing one or two vehicles in the longitudinal direction within a single lane. Using the vehicle 1, vehicle 2, vehicle 3, and vehicle 4 parameters, OpenBrIM allows users to position up to four vehicles in the Design Lane's longitudinal direction. It should be noted that this does not apply to the placement of the Design Lane in the transverse direction, which is determined by the roadway width and design lane width.

Vehicle 1: The vehicles defined in the "Vehicles" section are assigned to the parameter that specifies the vehicle to be positioned within the Design Lane. This represents the first vehicle defined in the longitudinal direction.

Vehicle 1 Impact Factor: According to AASHTO Table 3.6.2.1.1, the dynamic allowance factor is indicated as 75% for Deck Joints - All Limit States, 15% for All Other Components, Fatigue and Fracture Limit State, and 33% for other limit states. In OpenBrIM, this information is used to specify the impact factor as 1.75, 1.15, and 1.33, respectively. This parameter increases the vehicle's wheel loads using the specified factors.

Vehicle 1 Left Wheel Factor: The left wheel impact factor is detailed in AREMA for rails; however, live loads can also include left wheel factor definitions tailored for specific needs. Since moving vehicles may experience various changes in load distribution due to movement, the loads applied by the wheels can vary in magnitude. For instance, in the case of a sharp turn, the left wheels may experience a 50% reduction in vertical loads. Such scenarios occur in real life, and these parameters can also be defined in OpenBrIM.

Wheel Impact Factors 1, 1.5 , 0.5

Section 1.3.5.d: Impact Load Due to Rocking Effect (RE)

The rocking effect is created by the transfer of load from the wheels on one side of a car or locomotive to the other side due to periodic lateral rocking of the equipment. The RE shall be calculated from loads applied as a vertical force couple, with each force being 20 percent of the wheel load (excluding impact). These forces act downward on one rail and upward on the opposite rail. This force couple shall be applied to each track in the direction that generates the greatest force in the member under consideration.

Vehicle 1 Direction[Both/Backward/Forward]: In the context of a vehicle, x=0 is considered to be the location of the front of the vehicle in vehicle definition. Moving in the forward direction means increasing alignment station values, while moving in the opposite direction is considered backward. If "both" is chosen, placement is carried out in both forward and backward directions, but only the critical placement is reported. According to AASHTO guidelines, using both directions is generally recommended, but for permit trucks with unique circumstances, it may be acceptable to use only one direction.

Vehicle 2:

Vehicle 2 Impact Factor:

Vehicle 2 Left Wheel Factor:

Vehicle 2 Direction:

Vehicle 3:

Vehicle 3 Impact Factor:

Vehicle 3 Left Wheel Factor:

Vehicle 3 Direction:

Vehicle 4:

Vehicle 4 Impact Factor:

Vehicle 4 Left Wheel Factor:

Vehicle 4 Direction:

Lane Load

Lane Load Magnitude: The design lane load, as defined in AASHTO LRFD, is typically 0.64 klf and expressed as force per unit length. It is used in conjunction with the design truck or tandem. OpenBrIM applies the lane load in both transverse and longitudinal directions on a design lane only if it increases the critical force effect. As indicated in the screenshot below, the red and yellow regions show the areas that can be loaded with the lane load for negative force effects, whereas the green and blue regions show the areas that can be loaded with the lane load for positive force effects.

Lane Load Width: According to AASHTO standards, the typical width for a lane load is 10 ft. Entered value is utilized convert lane load to the pressure per square foot. For instance, if the entered value for lane load magnitude is 0.64 klf and the lane load width is 10 feet, the pressure per square foot can be computed as follows:

0.64 klf ÷ 10 feet = 0.064 kips/ft

Thus, the pressure per square foot would be 0.064 kips/ft².

Afterwards, this value is multiplied by the areas (i.e., red and yellow regions, as shown in the screenshot below) that contribute to maximizing the lane load force for negative force effect.

Vehicle Placement Settings

Min. Vehicle Spacing (Back to Front): If there are multiple vehicles defined for the design lane, the spacing between them in the longitudinal direction cannot be less than the entered value. For example, in the case of two trucks for HL93, the typical value for this spacing is 50 ft per AASHTO.

Max Vehicle Spacing (Back to Front): If there are multiple vehicles defined for the design lane, the spacing between them in the longitudinal direction cannot exceed the entered value. Typically, a value larger than the length of the bridge is entered because AASHTO does not impose any limitation on this value. However, some DOT loading requirements may limit this distance as well.

Adjacent Span Placement:

Adjacent Span Placement[Yes/No]: The placement of the two-truck vehicle shown below is not compliant with AASHTO standards because both trucks are located on the same span. To prevent this type of placement, the user should select adjacent span placement as “Yes”.

Lane Placement Settings

This section can be used to define whether the design lanes will be generated according to the data provided previously or will be excluded from a specified region. To specify the region from which design lanes will not be generated, refer to the parameter descriptions and info box below.

Apply Lane Constraint[Yes/No]:

This feature allows users to restrict the placement of lanes within a specific region of the roadway, perpendicular to the direction of travel.

When 'YES' is selected: Lane placement restrictions can be set using the parameters listed below. These restrictions ensure that no lanes are placed within the specified region.
When 'NO' is selected: Lanes will be placed using the roadway data without applying any restricted areas. In this case, the parameters for Lane Transverse Offset Start and End will be labeled as Not Applicable (N/A).

Lane Transverse Offset Start: This parameter specifies the start of the transverse offset from the PGL and can only be defined if 'Apply Constraints' is set to 'YES', indicating where lane placement is restricted. The offset is measured relative to the PGL when looking upstation.

Positive values indicating the right side of the PGL.
Negative values indicating the left side of the PGL.

For example:

If vehicles should not pass starting at 28 feet to the left of the PGL, input -28.
If vehicles should not pass starting at 5 feet to the right of the PGL, input 5.

Lane Transverse Offset End: This parameter defines the end of the transverse offset from the PGL and can only be specified if 'Apply Constraints' is set to 'YES', marking the boundary where lane placement restrictions conclude. It follows the same logic:

Positive values represent the right side.
Negative values represent the left side.

For example:

If vehicles cannot pass within 10 feet on the right side of the PGL, input 10.
If vehicles cannot pass within 38 feet on the left side of the PGL, input -38.

These parameters define the areas where lanes cannot be placed, based on their transverse offset relative to the PGL.

Use Case: Median Between Lanes

In a roadway with a center median, lane placement must be restricted to prevent lanes from being placed over the median. Suppose the roadway has a total width of 36 feet, with a center median that is 2.5 feet wide, located at the centerline (PGL = 0). The median extends 1.25 feet to the left and 1.25 feet to the right.

In this scenario, to restrict vehicle placement over the median:

Lane Transverse Offset Start: Input 1.25 to mark the start of the restricted area on the right side.
Lane Transverse Offset End: Input -1.25 to mark the end of the restricted area on the left side.

This configuration means that lanes cannot be placed within the range of -1.25 to 1.25 feet, restricting placement over the median. Lanes will be placed outside this restricted area:

Left Side (negative values): Lanes can be placed starting from -1.25 feet and beyond toward the roadway's left edge (e.g., up to -18 feet).
Right Side (positive values): Lanes can be placed starting from 1.25 feet and beyond toward the roadway's right edge (e.g., up to 18 feet).

Live Load Analysis Consideration

For live load analysis, barriers in the middle of the roadway are often ignored for lane placement purposes, and vehicles are still placed in these regions to obtain critical loading conditions. This ensures that structural designs account for potential maximum force, stress, or deflection, even if the area is typically not used by traffic in real-world scenarios. One real-world scenario to consider is during rehabilitation projects, where medians can be removed, allowing traffic to move through the previously restricted area. Therefore, to be on the conservative side, lane constraints are typically not applied, even for median regions.

OpenBrIM