Hi, as you may know by now, nowadays SAP2000 lacks many of the tools it used to have for moving load analysis (due to a more recent software named CSiBridge), so if you have to stick with SAP2000:

Using a path and a moving load will assign your load over the previously defined frames (since SAP2000 no longer has a proper area distribution for moving loads), applying eccentricity will only produce torsional moments prior to the redistribution of forces and it may cause problems to your model depending on the deck's type, manually distributing axles loads of the vehicle would be the safest way but keep in mind that if you want the response along all the span you will have to make many load cases.

Using two paths each one as half of the vehicle to reduce torsional moments over the path's frames wouldn't be a good recomendation if you plan to use a "moving load case" because maximum and minimum envelope values not necessary occur at the same time, it would be preferable in that scenario to define a "moving load patterm" since it let you move at the same time both "half vehicles" and would require less effort than the node by node distribution.

If you also need to compute a load lane - that distributed (but not necessary continuous) load - (like the one used in conjunction with the HL-93 from AASHTO), then you have to take into account that: for a simply supported bridge you can assume that the lane load is a continuous load but for a continuous bridge not (since partially applying it can produce bigger solicitations), a "moving load pattern" doesn't take into account load lanes so if you decide to use the solution I wrote in the previous pharagraph you will need to apply in another (case or cases) the lane load and then make a linear combination with the moving load envelope.

One last advice: if you have to make many load cases, it would be better to use the SAP2000 API or at least the interactive database editing tool to get the job done efficiently

Giordano Avellaneda Thanks for your input. Can I model grillage analysis in CSI bridge? What about Staad Pro . Do i face torsional problems there as well?

yes u can analyse it in staad pro.

For compatibility torsion we can ignore the torsional moment (Mx- torsional moment in STAAD).

For equilibrium torsion we need to design the structure for equivalent moment and shear as per codal provision.

EQUILIBRIUM TORSION AND COMPATIBILITY TORSION

MOMENT:

The longitudinal flexural tension reinforcement shall be determined to

resist an equivalent bending moment Me1 as given below:

Me1 = Mu + Mt

where Mu = bending moment at the cross-section, and

Mt = (Tu/1.7) {1 + (D/b)}

where Tu = torsional moment,

D = overall depth of the beam, and

b = breadth of the beam.

SHEAR:

The equivalent shear, a function of the actual shear and torsional

moment is determined from the following impirical relation:

Ve = Vu + 1.6(Tu/b)

where Ve = equivalent shear,

Vu = actual shear,

Tu = actual torsional moment,

b = breadth of beam.

Note:

STAAD notations…

Mx - torsion

Mz and My major and miner axis moments.