Good morning,
Yes, i spoke to a supplier yesterday. They recommended using 0.60fpu as a working effective prestress but recommended doing a more in depth analysis using AASHTO or PCI equations to calculate losses accurately. Apparently relaxation losses vary drastically between suppliers. I...
Hello,
Which design code is typically used to calculate prestress losses for PT rods? From what ive seen, AASHTO (5.9) provides equations to calculate prestress losses for prestressing strands. However, I am unsure if these equations can be used for PT rods?
Or do designers typically assume an...
What if the integral abutments are assumed to be infinitely rigid where they are restrained from any movement?
The axial force resisted by the girder would be extremely large.
Each abutment would resist this load? Or would the girder essentially buckle if not designed for?
Thank you guys for helping out.
It makes sense that the brg pad will deform before the brg pad slips. yes i agree BridgeSmith. The longitudinal force is the force required to deform the brg pad.
On another note, assume both ends of the girder are laterally restrained by a fixed connection. Do...
Could you please explain why the forces would be equal if each abutment has a different stiffness (one abutment considers the elastomeric brg pad stiffness while the other ignores it)?
I guess my confusion comes from the two scenarios. Not sure which assumption is valid:
1. To maintain...
Hello guys,
I am trying to calculate the temperature force for an abutment supporting steel girders (single span bridge). Elastomeric bearings (expansion) will be used at Abut 1. Fixed bearings will be used at Abut 2.
Questions:
How is the temperature force calculated at Abut 2 since the...
Rapt,
Thanks for responding. As suggested, I will calculate the cracked moment of inertia to calculate long term deflections. How is strain computed for both shrinkage and creep? Is there a reference you suggest looking into?
Thanks,
Does AASHTO specify criteria for reducing moment of inertia when calculating deflections (cracked section properties) for elastic or inelastic analysis?
I know ACI 318-14 Table 6.6.3.1.1(a) permits 0.70Ig for columns and 0.35Ig for beams but not sure about AASHTO.
Also, how do designers...
@retired13
Yes, I plan on doing hand calculations to determine the controlling live load case.
I also agree on the difference when designing the superstructure and substructure for live load (transversely). Believe it or not, that picture explains it in a simple manner. I guess the saying is...
Yes, it makes sense now.
I didn't know the 10' loaded width was the truck body attached to the 6' axles.
Originally I thought the 6' axles could move within the 10' loaded width, but i guess i was wrong.
Thank you for the clarification.
@retired13,
The sketch only shows one particular case. I'm interested in understanding how the design truck/tandem and lane load are positioned transversely for multiple cases (one lane, two lanes, etc).
The PDF I attached in the original post is how I think the design truck/tandem and lane...
Hello everyone,
I am trying to understand how a truck and lane load are positioned transversely along a bridge for one-lane loaded, two-lanes loaded, three, etc.
As per AASHTO, "Both the design lanes and the 10 ft loaded width in each lane shall be positioned to produce extreme force effects...
Thank you all for the responses.
Yes, originally I was going to use the deflection equations for a cantilever beam from AISC, but I realized the soil needs to be considered.
I will look into the CRSI manual for the deflection equations. Hopefully two separate equations are available (live...
Is there an equation (or any reference material) that determines the maximum lateral deflection at the top of a retaining wall (due live load surcharge and horizontal earth pressure)?
Not sure if I can use the deflection equations for a cantilever beam from AISC Table 3-23 due to the soil...
@HotRod10
Where would the boundaries be located to use the incremental approach?
Would it be similar to the new attached image?
Originally I was thinking the load would be determined half way along the girder (half the area goes to one girder and the other half goes to the other girder) to...
Hello everyone,
I am trying to create a spreadsheet that calculates DC loads for bridges. However, I do not know how software programs calculate the slab weight on flared girders. I have attached an image to see if anyone has a general idea of how to calculate the slab weight on the flared...
