# [Possible Bug] Creep and Shrink Analysis is Successful for Solid Section but Unsuccessful for Hollow Section

I have 2 beams that only cross sections are different, one is solid section, the other one is hollow section. Both beams have steel parts (4 angles), concrete and tendon.

Solid section

Hollow section

The construction stages are as follows

CS NO TYPE T TITL
10 G_1 0 ‘Steel Angles’
20 G_1 0 ‘Concrete’
30 C 10 ‘C + S’
40 P 0 ‘Post-tensioning’

For solid section, the analysis is successful, but for hollow section, the analysis result will depend on the size of tendon duct.

The area of steel (4 angles) is about 24764mm2 according to Aqua. The equvalent diameter of the area is 0.25 x pi x dia^2 = 24764, dia = 177.6 mm

If tendon duct <= 177.6 mm, the analysis for hollow section is successful. If tendon duct > 177.6 mm (DO = 178), the analysis for hollow section is unsuccessful, it aborted at AQB CS 30 (Creep and Shrinkage),

+PROG Tendon
SYSP NOPS MAT ZV AZ LITZ MINR BETA MUE ECC SP DO
1 2 1822.8 1400 10 7 0.343774677 0.25 0 6 178

the error message are:

Start: Program AQB : creep step CS 30 C + S
+++++ error no. 70011 in program INIT_LOCATIO
Negative sectional area in cross section 2 CS 0 = 10
Please check construction stage numbers and if the ducts for tendons are defined to large

I have several questions:

1. I gusss the “Negative sectional area in cross section 2 CS 0 = 10” means: at CS 10,
24764mm^2 (area of 4 angles) - 0.25 x pi x (178mm)^2 (area of duct) = -120 mm^2
Why Sofistik consider tendon at CS 10, when only steel is activated? The tenon should be consider at CS 40.
2. Solid section has the same tendon as that of hollow section, but the analysis is always successful even if I use duct size = 500 mm for solid section.

The dat files are as follow. Plz put all dats in one folder.
Hollow - 177.dat is for hollow section with duct size = 177mm < 177.6mm, the analsis is successful;
Hollow - 178.dat is for hollow section with duct size = 178mm > 177.6mm, the analsis is unsuccessful;
Solid - 500.dat for solid section with duct size = 500mm >> 177.6mm, the analsis is successful
Aqua.dat (1.9 KB)
SofimshC - Hollow.dat (721 Bytes)
SofimshC - Solid.dat (721 Bytes)
Tendon - 177.dat (1.0 KB)
Tendon - 178.dat (1.0 KB)
Tendon - 500.dat (1.0 KB)