Geometrically non-linear stress and strain fields resulting from loads and prestressing are a specific property of box cross-sections. Their importance in the meaning of a calculation precision is evaluated in various ways by authors. Simultaneously, design of any structure – also of a box cross-section – is strictly connected with a correct evaluation of the stress level in materials, linearity of their behaviour and cracks appearance. This work is focused on the presentation of the existing theorical models describing the “shear lag” effect influence on the distribution of the local strain and stress in materials in box cross-section. The presentation is followed by their evaluation according to the agreements of their results with measurements results obtained on a real structure. PC bridge of a box cross-section, built as cantilever is the chosen example for comparison. Discussion of the scale of the effect influence completes the presentation of this work.

Geometrically non-linear stress and strain fields resulting from loads and prestressing are a specific property of box cross-sections. Their importance in the meaning of a calculation precision is evaluated in various ways by authors. Simultaneously, design of any structure – also of a box cross-section – is strictly connected with a correct evaluation of the stress level in materials, linearity of their behaviour and cracks appearance. This work is focused on the presentation of the existing theorical models describing the “shear lag” effect influence on the distribution of the local strain and stress in materials in box cross-section. The presentation is followed by their evaluation according to the agreements of their results with measurements results obtained on a real structure. PC bridge of a box cross-section, built as cantilever is the chosen example for comparison. Discussion of the scale of the effect influence completes the presentation of this work.