Two current projects face the same dilemma. The architects chose to use an HSS tubular steel section as a beam to support a stair landing. The project conditions dictate that the beams must be fireproofed for a 2-hour fire resistance rating. Because the beams are exposed to view, the fireproofing selection was an intumescent paint, for its appearance.
Now comes the challenge - finding a tested design assembly for tubular steel beams. None of the intumescent paint manufacturers have a tested assembly for tubular beams. The only available tests are for tubular columns.
Column designs cannot be substituted for beam designs. The fire exposure and protection requirements are entirely different.
Columns experience the greatest fire temperature only at the top of the column. Columns have no effective heat sink to help dissipate the heat. And columns are typically exposed to the fire on all sides.
Beams experience the greatest fire temperature along the full length of the member. Beams have the floor or roof deck they support as a heat sink to help mitigate the temperature effect on the beam. Beams are directly exposed to fires on only three sides.
The architects are searching for a solution. Unless the project conditions change, the only means to resolve the issue is for a fire protection engineer to issue an engineering judgment indicating an opinion that a selected fire proofing design will work for this particular condition. Then the last task is to convince the building official to accept the opinion without proof by test.
When fire-resistive assemblies are required by code, building officials expect to see tested assemblies shown on the drawings. Keep it simple. Be sure to search the available assemblies before completing the structural design. Then use the assembly as it was tested to avoid potential liability for unproven solutions.
David Stutzman