Continuous LL (Truck only) Moment

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Continuous LL (Truck only) Moment

I am checking an existing bridge on TxDOT version of PgSuper 2.8.
The bridge has 3 spans made continuous for LL, 50'-60'-50' .

I have assigned ONLY The HS20-44 truck under the "Load" tab, no Lane, HL93,....
Cross section properties are the same for all 3 spans.

The results for "Design-HS-20_Truck" moment Per Lane is just over 600 k-ft in all spans, outer ones have slightly greater moments.

when I run a 3 span continuous with a 3 point loads of 8, 32, 32 , 14 feet apart in SAP2000 and STAAD, I get 509k-ft

I can understand a small difference but not 100 k-ft.... What Am I doing wrong??

I'd appreciate your help


Rick Brice
I'm not sure why you aren't

I'm not sure why you aren't getting good comparisons. I have compared the live load results for the attached PGSuper model with GTStrudl (output files attached) and have excellent agreement for both the simple span and continuous span cases.

Simple Span Analysis - Mid Span Moment
Span 1 & 3 - 620 k-ft (PGSuper) 620 k-ft (GTStrudl)
Span 2 - 800 k-ft (PGSuper) 800 k-ft (GTStrudl)

Continuous Span Analysis - Mid Span Moment
Span 1 & 3 - 490.43 k-ft (PGSuper) 490.54 k-ft (GTStrudl)
Span 2 - 495.45 k-ft (PGSuper) 495.08 k-ft (GTStrudl)

Continuous Span Analysis - Intermediate Pier Negative Moment
Pier 2 & 3 - 328.91 k-ft (PGSuper) 329.47 k-ft (GTStrudl)

For PGSuper, I made the dynamic load allowance for the truck to be 0%.

My guess is that you are comparing simple span analysis results to continuous span analysis results. Recall that PGSuper has three analysis modes. Simple span, continuous span, and envelope. Simple span treats all spans as simple regardless of boundary conditions. Continuous span models simple spans made continuous, taking the boundary conditions at each pier into account. Envelope mode uses the governing case of simple span and continuous span analysis modes.

Continuous LL Moment

I am using TxDOT version 2.8 to check an existing bridge. since the original design used a HS20 I assigned HS20-44 truck as live load from LOADS-->Live Load.. and chose the HS20-44 Truck but did not change the 30% impact to zero. once I changed it the results compared quite well.
I thought "Design-HS20_Truck" moment diagram did not include impact since there is also a "Design-LL+IM"" Option. My Mistake

Thanks very much for your time.

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