Can I use free software for professional structural design?

Yes, provided the software follows recognized design codes and produces auditable reports. Free doesn't mean amateur — what matters legally is that your analysis follows the applicable code (NBR 8800, AISC 360, Eurocode 3, IS 800, AS 4100, etc.) and that you, the responsible engineer, sign off on the design. CalcSteel implements the verification formulas directly from these codes and exports PDF reports with all the intermediate calculations, stress ratios and governing limit states. Many small offices, consulting engineers, and students use free tools daily for real projects. The professional liability is always with the engineer, not the software vendor.