Poisson’s Ratio
As a concrete cylinder is subjected to compressive loads, it not only shortens in length but also
expands laterally. The ratio of this lateral expansion to the longitudinal shortening is referred
to as Poisson’s ratio. Its value varies from about 0.11 for the higher-strength concretes to as high as 0.21 for the weaker-grade concretes, with average values of about 0.16.
Reference: Design of Reinforced Concrete-Jack C. McCormac

برای بتن معمولی (غیر از بتن با مقاومت بالا) نسبت پواسون را بهتر است 0.2 وارد کرد. توجه شود که مبحث 9 چاپ 92 این مطلب را اشتباهی نوشته است و برعکس آنچه در بالا ذکر شد آورده است!!!