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Structural
- Oct 31, 2023
- 12
Hi Everyone,
I would appreciate any help in trying to understand how to tackle this problem I have with the design of steel bearings for a railroad bridge. I will start with the admission that my current understanding might be flawed. So, the question in topic is as follows, but first I will frame how I came across this problem.
Design is for railroad bridge (AREMA dictates). The fixed bearing assembly for this RR bridge consists of beveled rocker plates - pintles connecting the rocker plate to a base plate, base plate connected to masonry plate that rests on a 3/8" neoprene pad. There are 4 anchor bolts in the masonry plate connecting to the drilled shaft cap beam (see attached).
So, for the particular design of the bearing, I followed these steps: design for the min thickness of the rocker plate required for the vertical reaction bearing stress - check the shear capacity of the pintles for the horizontal shear from the superstructure (shear being the longitudinal / frictional reaction) - design the base and masonry plate for the min thickness required for vertical reaction bearing (followed ASIC min thickness base plate formula) - check the shear capacity of the 4 anchor bolts - check whether the anchors are subjected to net uplift due to the moment arm created from the shear acting at the pintle level. Next step is where I have been stumbling upon and have no clue how to solve or do an analysis.
The anchor bolts are 2 1/8" dia and the oversize required as per AISC is 3/8" larger. I am assuming that the horizontal shear is transferred to the substructure through the anchor bolts and as such due to the presence of this oversize, the bolts will be subjected to bending prior to being mobilized to transfer the shear. AISC Design Guide 1 (Base Plate and Anchor Rod Design) states that this is a particular check that needs to be performed if trying to transfer shear through anchors (they suggest to only consider half the anchor bolts if we want to bypass the bending check). unfortunately, the horizontal shear is too large, and 2 bolts is not sufficient. And, following the bending stress check, that fails for the anchor bolts as well. And this is where I am stuck. I am trying to figure out if this approach is sound, if not how to tackle this or is there anything else that can be done.
I know the post ended up being too long but felt it was necessary to explain. I have attached some of my calcs, the bearing detail for you all to look at.
Thanks.
I would appreciate any help in trying to understand how to tackle this problem I have with the design of steel bearings for a railroad bridge. I will start with the admission that my current understanding might be flawed. So, the question in topic is as follows, but first I will frame how I came across this problem.
Design is for railroad bridge (AREMA dictates). The fixed bearing assembly for this RR bridge consists of beveled rocker plates - pintles connecting the rocker plate to a base plate, base plate connected to masonry plate that rests on a 3/8" neoprene pad. There are 4 anchor bolts in the masonry plate connecting to the drilled shaft cap beam (see attached).
So, for the particular design of the bearing, I followed these steps: design for the min thickness of the rocker plate required for the vertical reaction bearing stress - check the shear capacity of the pintles for the horizontal shear from the superstructure (shear being the longitudinal / frictional reaction) - design the base and masonry plate for the min thickness required for vertical reaction bearing (followed ASIC min thickness base plate formula) - check the shear capacity of the 4 anchor bolts - check whether the anchors are subjected to net uplift due to the moment arm created from the shear acting at the pintle level. Next step is where I have been stumbling upon and have no clue how to solve or do an analysis.
The anchor bolts are 2 1/8" dia and the oversize required as per AISC is 3/8" larger. I am assuming that the horizontal shear is transferred to the substructure through the anchor bolts and as such due to the presence of this oversize, the bolts will be subjected to bending prior to being mobilized to transfer the shear. AISC Design Guide 1 (Base Plate and Anchor Rod Design) states that this is a particular check that needs to be performed if trying to transfer shear through anchors (they suggest to only consider half the anchor bolts if we want to bypass the bending check). unfortunately, the horizontal shear is too large, and 2 bolts is not sufficient. And, following the bending stress check, that fails for the anchor bolts as well. And this is where I am stuck. I am trying to figure out if this approach is sound, if not how to tackle this or is there anything else that can be done.
I know the post ended up being too long but felt it was necessary to explain. I have attached some of my calcs, the bearing detail for you all to look at.
Thanks.