DG-Design
Structural
- Jul 27, 2023
- 2
Hello.
I am currently reviewing the design of an existing top-running bridge crane. The owner would like to increase the capacity of the crane and wants to verify the existing runway beams can handle the increased load. The existing runway beam is a 24WF100 (structure was built in the 50s) with a C15x33.9 cap. The beam span is 18 ft between column centers.
When I perform my design checks, the interaction equation for biaxial bending yields a U.C. of 0.94. Bending about the X-X axis contributes 0.77 and bending about the Y-Y axis is 0.17 of said interaction equation. The owner would prefer that the U.C. be less than or equal to 85% of design capacity for extra safety.
I've researched several ways to reinforce the current beam, but I would like to see if there are some things I have not considered. Intermediate stiffeners are not the most effective for moving loads, have significant fatigue concerns, and AISC DG7 references Tech Report 13 which says these stiffener welds need to be full pen. I would not like to go that route. Since AISC DG7 mentions that a better practice is to thicken the web so that stiffeners are not required, my thought was to add a web plate to the beams to essentially double the current web (doubler plates). This would obviously increase the MoI and section modulus which would reduce the X-X axis bending moment contribution to the interaction equation.
With (4) end truck wheels on each side of the bridge, the max moment, according to my calcs, occurs at 9.27 ft along the beam span. I was thinking about adding a web plate to roughly 8 ft of the center of the beam since your bending moment decreases as you get closer to the supports. Does this seem reasonable to get my U.C. at or below 0.85? Also, I would greatly appreciate weld considerations if this is a viable option.
Thank you in advance.
I am currently reviewing the design of an existing top-running bridge crane. The owner would like to increase the capacity of the crane and wants to verify the existing runway beams can handle the increased load. The existing runway beam is a 24WF100 (structure was built in the 50s) with a C15x33.9 cap. The beam span is 18 ft between column centers.
When I perform my design checks, the interaction equation for biaxial bending yields a U.C. of 0.94. Bending about the X-X axis contributes 0.77 and bending about the Y-Y axis is 0.17 of said interaction equation. The owner would prefer that the U.C. be less than or equal to 85% of design capacity for extra safety.
I've researched several ways to reinforce the current beam, but I would like to see if there are some things I have not considered. Intermediate stiffeners are not the most effective for moving loads, have significant fatigue concerns, and AISC DG7 references Tech Report 13 which says these stiffener welds need to be full pen. I would not like to go that route. Since AISC DG7 mentions that a better practice is to thicken the web so that stiffeners are not required, my thought was to add a web plate to the beams to essentially double the current web (doubler plates). This would obviously increase the MoI and section modulus which would reduce the X-X axis bending moment contribution to the interaction equation.
With (4) end truck wheels on each side of the bridge, the max moment, according to my calcs, occurs at 9.27 ft along the beam span. I was thinking about adding a web plate to roughly 8 ft of the center of the beam since your bending moment decreases as you get closer to the supports. Does this seem reasonable to get my U.C. at or below 0.85? Also, I would greatly appreciate weld considerations if this is a viable option.
Thank you in advance.
