A Span Limit for Self-Supporting Brick Kiln Vaults: The Width a Catenary Arch of Fired Brick Can Cover Without Steel

This paper addresses kiln builders who want a permanent brick vault roof instead of a rebuilt temporary crown, but have no rule for how wide such a vault can safely span. It presents a vault span bound from catenary thrust and the sliding resistance of a standard two-brick abutment wall, derived entirely from stated assumptions and a computation whose code and full output accompany the paper. The sweep covers vault span from 1.5 to 5 m. The headline outcome is: largest span with standard abutment m 4; required abutment at 4m m 0.441; required abutment at 5m m 0.551; thrust at 4m kn per m 4.67. These figures identify a specific operating point or bound that a workshop can apply directly, and they also show how quickly performance deteriorates away from it. No kiln was built, no ware was fired, and nothing was measured for this study. SIMULATED, NOT MEASURED.