Consider the $6$ m concrete column $($column $1)$ with a section of $500x300mm.$ Only half of the column is exposed to the environment with a relative humidity of $70\%.$ The column contains $10$ steel reinforcing bars with a diameter of $16$ mm each which is distributed symmetrical in the section. The concrete strength on $28$ days is $40$ MPa. Estimate the shortening of the column after $30$ years if it was loaded at $3$ days with a force of $900$ kN $.$ Assume that the concrete has achieved $50\%$ of the $28$ day strength at $3$ days. The E$-$modulus of the steel is $200$ GPa.