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@Engr. Muhammad Salman share your model to check for the issue...

I also did not face this issue. While defining the load case, do you have the option of choosing the initial conditions of the load case for your version of ETABS? If yes, try playing with it to see if results change.

Check the initial conditions your load case. There might be issue there

This is what i found in "Structural Concrete theory and Design by Nadeem Hussen" Here it also reports the same thing that we should design for torsion for atleast φ4λ Sqrt(fc ′) A2cp / Pcp Which is also specified by ACI that we can reduce our torsion upto phi.Tcr i.e. cracking torsion and not below this. Even if we neglect the remaining torsion for compatibility, we should atleast perform design for phi.Tcr or should at least provide minimum longitudinal and transverse reinforcemet for torsion. This is to control crack width to satisfy servicability. ACI, Nilson and Nadeem hussen all quote the same thing. Hence reducing the modifier upto such a little value is not good at start. At start we should go for a value of 1, 0.3 or any other suitable value which user think is small enough to release majority of compatibility torsion and will sustain only smaler torsional moments. After designing, if still some indeterminate beams are being failed, then for the specific beams we can reduce value unless we get Tu equall to phi.Tcr or a bit larger than that. Because putting Torsional modifier to 0.001 would not report any torsional reinforcement and hence adding no torsional reinforcement at all would cause excessive crack widths affecting serviceability of the structure.

I am confused regarding this approach of reducing torsional modifier to such great extent. According to ACI 11.5.2.2 In a statically indeterminate structure where reduction of the torsional moment in a member can occur due to redistribution of internal forces upon cracking, the maximum Tu shall be permitted to be reduced to the values given in (a), (b), or (c), as applicable: (a) For nonprestressed members, at the sections described in 11.5.2.4 φ4λ Sqrt(fc ′) A2cp / Pcp It says that we can reduce torsional moment upto a specified limit. Not to zero or 0.001. In its commentary it says, For this condition, illustrated in Fig. R11.5.2.2, the torsional stiffness before cracking corresponds to that of the uncracked section according to St. Venant’s theory. At torsional cracking, however, a large twist occurs under an essentially constant torque, resulting in a large redistribution of forces in the structure.11.34,11.35 The cracking torque under combined shear, flexure, and torsion corresponds to a principal tensile stress somewhat less than the quoted in R11.5.1. When the torsional moment exceeds the cracking torque, a maximum factored torsional moment equal to the cracking torque may be assumed to occur at the critical sections near the faces of the supports. This limit has been established to control the width of torsional cracks. Also according to Nislon, this distribution is only possible after extensive cracking as highlighted in below pic. So I doubt the approach used to neglect torsion upto 0.001 level What i got from the 2nd attachement of Zain Saeed the author is dividing Tcr with Tu to find how much reduction in Tu is needed to reduce torsion upto Tcr which is, as mentioned above, is necessary to keep torsional crack widths in control. and hence using the modifier for each section defined for beam. It might be a bit lengthy task to evaluate for each type of section ( most loaded members of a type of beam may be checked only), but the approach seems more realistic. Kindly comment as I think if even we reduce to 0.001, still this redistribution in torsion is not possible without large twisting which is not possible without excessive cracking. So reucing upto such a low value does not seem good.

Dear Zain, I don't know the origin of document,you have uploaded for calculating torsional constant,but the methodology given therein is incorrect.As "Tcr" and "Tu" given therein are indeed threshold torsional strength and ultimate torsional stresses respectively, and are both design properties not analysis properties. (See ACI 318-11 section 11.5.1). Whereas the torsional constant, ETABS asks in "analysis property modification factors" is simply the torsional moment of inertia (J) used to determine torsional stiffness of a member (JG/L) i.e something else. As long as its value is concerned,then in building structures it is a general practice to use a negligible value like .001 to nullify beam's torsional stiffness.In this way, the torsional stresses (if arising due to compatibility of deformation i.e compatibility torsion ) are transferred via alternate load path (i.e redistribution of torsional moments occurred), considering that beam is unable to provide torsional restraint and in other condition if torsional stresses in beam is required to satisfy equilibrium of structure (where redistribution is not possible) then torsional stresses in beams remains independent of whatever value of "J" you have selected as equilibrium equations are necessarily satisfied independent of stiffness as "Compatibility is optional and equilibrium is essential". This approach of minimization of "J" economize beam sizes that arise from stringent combined shear and torsion requirement of building codes,but consequently beam sections designed in this way will start developing internal horizontal cracks (hairline cracks not affecting functionality of structure) due to torsional stresses and their torsional strength will continuously degrade till the design condition is achieved i.e negligible torsional strength of beam.But as the structure is designed to be stable without torsional stiffness of beam so it remain stable after this condition is achieved.However, the beam member itself cracks that doesn't affect the functionality of structure in any way. A very descriptive and clarifying description is available in "Reinforced concrete design by Arthur Nilson". As long as authentication of this approach is concerned then it is allowed by building codes as, 1, ACI-318-11 section 11.5.2.1 & 11.5.2.2. 2, UBC97 section 1911.6.2.1 & 1911.6.2.2 3, BS 8110-1 1997 section 3.4.5.13 Keeping in view above mentioned, it is a general practice to nullify torsional constant of beams in building structures and it is not required to use any iterative process to derive torsional constant of each beam section that is indeed not practical as there will be thousands of beam span in large structures.