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Structural
- Oct 31, 2023
- 11
Hi Everyone,
I am having trouble on deciding the approach for designing the abutment cap beam for the bridge that I am working on.
Project Background - Single Span, 2 Through Plate Girder Railroad Bridge
Question and background: So, the plan for the bridge is already finalized. The abutment is supported by 3 - 5 feet dia Drilled shafts with a 7'-3" W x 4' - 6" D cap beam. The cover height from the bottom of the tie to the top of backwall is only 1 feet due to which the required rail load surcharge to be applied at the bottom of the cap is very high (approx 1650 psf). As per my understanding and working on DOT bridges, generally since the live load surcharge and lateral earth pressure is relatively small, the cap beams are analyzed for only the vertical loads and other force effects and you provide main reinforcement at top and bottom and, skin reinforcement on either side of the cap face (if greater than 3'). However, with the very high lateral pressure acting on the cap side face, how do I go about designing this element?
My current approach:
Step 1: Model the cap beam as line element in RISA.
Step 2: Analyze for only the vertical loads. Get the shear and moment.
Step 3: Analyze for only the lateral loads. Get the shear and moment and torsion.
(Please see attached the relevant plan and section, RISA analysis result).
So, this is where I am stuck at. After getting the results, what do I do? The beam is very deep (qualifies as Deep Beam?) How to approach this? Any reference?
Or can I use the conventional method of beam analysis and analyze the section at both the faces and provide reinforcement as per each face requirement?
I am having trouble on deciding the approach for designing the abutment cap beam for the bridge that I am working on.
Project Background - Single Span, 2 Through Plate Girder Railroad Bridge
Question and background: So, the plan for the bridge is already finalized. The abutment is supported by 3 - 5 feet dia Drilled shafts with a 7'-3" W x 4' - 6" D cap beam. The cover height from the bottom of the tie to the top of backwall is only 1 feet due to which the required rail load surcharge to be applied at the bottom of the cap is very high (approx 1650 psf). As per my understanding and working on DOT bridges, generally since the live load surcharge and lateral earth pressure is relatively small, the cap beams are analyzed for only the vertical loads and other force effects and you provide main reinforcement at top and bottom and, skin reinforcement on either side of the cap face (if greater than 3'). However, with the very high lateral pressure acting on the cap side face, how do I go about designing this element?
My current approach:
Step 1: Model the cap beam as line element in RISA.
Step 2: Analyze for only the vertical loads. Get the shear and moment.
Step 3: Analyze for only the lateral loads. Get the shear and moment and torsion.
(Please see attached the relevant plan and section, RISA analysis result).
So, this is where I am stuck at. After getting the results, what do I do? The beam is very deep (qualifies as Deep Beam?) How to approach this? Any reference?
Or can I use the conventional method of beam analysis and analyze the section at both the faces and provide reinforcement as per each face requirement?
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