Rapture length defines material efficiency as strength / weight ratio:
R = F / λ
R = rupture length
F = breaking strength
λ = specific gravity (self weight)
Rupture length, is of particular importance for long-span structures. The depth of horizontal span members increases with span. Consequently the weight also increases with span. Therefore the capacity of material to span depends on both its strength and weight. This is why lightweight material, such as glass fiber fabrics are good for long- span structures. For some material, a thin line extends the rupture length to account for different material grades.
The graph data is partly based on a study of the Light weight Structures Institute, University Stuttgart, German.