John Lynch's Activities

Conspan "Design Truck" vs "Double Truck"

John Lynch — Mon, 09 Nov 2015 17:37:54 GMT

I am having difficulty matching Conspan's "Double Truck" load. The user manual (and AASHTO) states that the negative design LL should be 90% of lane + 90% of two HL93s with non varying rear axles spaced no further than 50ft. I agree with this however when I produce my moment diagrams by hand, I do not match Conspan's Double Truck. When I open the live load library to investigate, I see the following note attached to the Double Truck: "NOTE: Internally CONSPAN automatically considers 80% of the truck load selected for analysis, applied simultaneously with this lane load". This does not match the AASHTO 3.6.1.3.1. Can you expand upon this live load case and where AASHTO talks about it?

In addition, I believe the "Design Truck" case is automatically recognizing a continuous span bridge and running the two HL93s spaced at 50ft+. The live load library gives no indication of this but my negative moment diagrams match it. Can you confirm my suspicions?

I should also note that I am running version V13.00.00.68. My company has had crashing issues on new computers with v14 and we are holding out to v15 in hopes that the problem goes away.

Thank you for the help in this negative moment issue.

Conspan Continuous span calculations of negative moment

John Lynch — Thu, 27 Aug 2015 22:00:20 GMT

I have modeled a two span continuous span bridge with bulb tee girders. However in design of the negative moment continuity steel, I noticed that at the pier Conspan has different negative moments coming from span 1 to span 2. I should also mention that this is occurring on only half the girder lines on the bridge. The other half of the bridge shows moment in equals moment out of the pier. How is this possible?

When I reproduce the moment curves for this bridge, it appears that Conspan jumped to taking the negative moment at the girder bearing instead of the center of the pier. This greatly underestimates the forces that this steel will experience. Again, this is only occurring on one span in half the girder lines.

Thank you

Conspan Vertical Shear: Beta and Theta calculation

John Lynch — Tue, 30 Jun 2015 20:13:22 GMT

I am trying to match Conspan's vertical shear output with some difficulty. I am following the AASHTO equations from section 5.8.3.4.2 with a negative longitudinal tensile strain. Since Conspan gives an output on just about every variable except for "Act", does anyone know how this value is calculated.

Also Conspan labels the strain as "esp_x", regardless of the method used. However it is clearly "esp_s" for this situation. I believe this is only a labeling error.

Thank you for any help given.