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.
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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 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 Direction:
Vehicle 3:
Vehicle 3 Impact Factor:
Vehicle 3 Direction:
Vehicle 4:
Vehicle 4 Impact 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
Apply Lane Constraint[Yes/No]: Lane placement constraints are implemented to prevent the placement of lanes in a specific section of the roadway perpendicular to the direction of travel. If the lane transverse offset left and right parameters are entered and "yes" is selected, lane placement will be restricted to that particular region.
Lane Transverse Offset Left(+Y) - Right(-Y): Specify the starting and ending transverse station range along the roadway where you want to place the lanes. Suppose a roadway has a width of 48 feet, and the PGL location is assumed to be 0. The left width is 38 feet, and the right width is 10 feet when looking upstation from the alignment. In this case, the lane placement will occur within the range of -38 to 10 feet in the transverse direction. If there are restrictions on lane placement between 5 and 10 feet, as well as between -38 and -28 feet in the transverse direction, the lanes will only be placed between -28 and 5 feet in the transverse direction. Thus, typically, the user would input a value of -28 for the left lane transverse offset and a value of 5 for the right lane transverse offset. However, since the design lane is a core object rather than a library object, this time the user should input 28 instead of -28 for the left value and -5 instead of 5 for the right value. Our core coordinate system considers the right side as the negative -Y direction when looking up station (-X to +X) from the alignment, while the left side is represented by the positive +Y direction.
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