Materials and Structures/Mat6riaux et Constructions, Vol. 32, August-September 1999, pp 520-524 A new model for predicting crack width with different percentages of reinforcement and concrete strength classes G. Creazza and S. Russo Venice Institute University, Italy Paper received:December 16, 1998; Paper accepted:January 27, I999 A B S T R A C T R I~ S U M I~ This paper describes a new model for predicting crack width in presence of different percentages of rein- forcement and concrete strength classes that became from 30 to 80 MPa. The theoretical analysis is used to interpret the results of experimental trials on reinforced concrete ties submit- ted to tensile forces without inducing any yield in the bar. The purpose of the investigation was to study and predict the crack width using as base parameters the stress in the steel at crack and the mean distance between cracks. The calculation model is based also on a precise mechanical characterization of the concrete's effective tensile strength (i.e. in presence of reinforcement) and give a sufficiently user friendly procedure to determine crack width without taking into account the concrete and steel deformation, which are difficult to measure. Cet article prdsente un nouveau module de prdvision de l'amplitude des fissures en prdsence de diff&ents pourcentages d'armatures et de classe de rdsistance allant de 30 h 80 MPa. L'analyse th&rique est utilisde pour interprdter les rdsultats des essais exp&imentaux sur des traverses en bdton armd soumis desforces de traction sans rien ajouter h la barre. Le but de cette recherche dtait d'dtudier et de prdvoir la largeur des fissures, en utilisant comme paramOtres de base la contrainte clans l' acier et la distance moyenne entre les fissures. Le module de calcul est bas~ @lement sur une caract&isation micanique prdcise de la rdsistance h la traction du bdton, en prd- sence d'armature, et donne une mdthode facile pour ddterminer l'amplitude des fissures sans prendre en compte la ddformation de l'acier et du bdton, qui sont difficiles 21mesurer. 1. INTRODUCTION Studies on crack control concern aspects relating not only to the behavior of the IK.C. elements in serviceabil- ity conditions, but also to structural problems concerned with the overall durability of the construction. The use of high-strength concrete has recently been prompting further research in this sector and it now appears to have been confirmed that the use of said con- crete leads to a reduction in the mean width of cracks and an associated overall increase in the number of cracks [1]. This is a matter of fundamental importance for controlling the evolution of cracking phenomena, since it is common knowledge that any presence of cracks having a more than negligible amplitude can induce an excessive localization of strains and conse- quent severe structural damage. Moreover, controlling the cracking phenomenon has to do with aspects that cannot be correlated unequivo- call,/with the characteristics of the materials, but also with the steel-concrete interaction - and consequently with aspects relating to the bond - with the effect often- sion stiffening in the concrete under tension between cracks, and with the percentage of reinforcement used in each case [2, 3]. The present study proposes a theoretical model for calculating crack width using as base parameters the steel stress in the crack and the mean distance between the cracks once the cracking phase has become stable, with- out taking into account the concrete and steel deforma- tions, as proposed in other calculation methods [4, 5]. The model also proposes a detailed characterization of the effective tensile strength of concrete (i.e. in the pres- ence of reinforcement) , since nominal value - as we all know - is lower than the conventional one deducecl from the concrete's strength class. This is also caused by presence ofantogeneous stresses and by shrinkage phenomena. Numerous experimental findings available in the litera- 1359-5997/99 9 RILEM 520