Stiffness Reduction Factors for Prestressed Beams

[Vshah97]

For general concrete beam design we use 0.35Ig as our stiffness modification factor for the analysis, what is the stiffness reduction factor we have to use per Code for Prestressed Beam analysis, I know 0.35 is ok to use and conservative, but if I want to push it, what does the codes say for this?

 

[HTURKAK]

Refer to ACI 318-19 Table A.8.4

Effective stiffness values For prestressed beams ;

Axial= 1.0EcAg ; Bending = 1.0EcIg ; Shear =0.4EcAg









Don't underestimate a nail. A nail saves a horseshoe, a horseshoe saves a horse, a horse saves a commander, a commander saves an army, an army saves a whole country.. GENGHIS KHAN

 

[wrantler]

may I ask when you would use the shear effective stiffness value.

 

[rapt]

Are those values for gravity loading or sway analysis?

For gravity loading it is normal to use full stuffness. And then allow for cracking in areas where it is required, eg deflections.

A blanket use of low values can be unconservative, eg with punching shear.