【正文】 le stress between thecracks due to the transfer of forces from the tensile reinforcementto the concrete through bond. This contribution of the tensileconcrete is known as tension stiffening, and it affects the member’sstiffness after cracking and hence its deflection and thewidth of the cracks. With the advent of highstrength steel reinforcement, reinforcedconcrete slabs usually contain relatively small quantities oftensile reinforcement, often close to the minimum amount permittedby the relevant building code. For such members, the flexuralstiffness of a fully cracked cross section is many times smallerthan that of an uncracked cross section, and tension stiffeningcontributes greatly to the stiffness after cracking. In design, deflectionand crack control at serviceload levels are usually thegoverning considerations, and accurate modeling of the stiffnessafter cracking is required. The most monly used approach in deflection calculationsinvolves determining an average effective moment of inertia [Ie]for a cracked member. Several different empirical equations areavailable for Ie, including the wellknown equation developed byBranson [1965] and remended in ACI 318 [ACI 2021]. Othermodels for tension stiffening are included in Eurocode 2 [CEN1992] and the [British Standard BS 8110 1985]. Recently,Bischoff [2021] demonstrated that Branson’s equation grossly overestimates thtie average sffness of reinforced concrete memberscontaining small quantities of steel reinforcement, and heproposed an alternative equation for Ie, which is essentially patiblewith the Eurocode 2 approach. In this paper, the various approaches for including tensionstiffening in the design of concrete structures, including the ACI318, Eurocode 2, and BS8110 models, are evaluated critically andempirical predictions are pared with measured , remendations for modeling tension stiffening instructural design are included. Flexural Response after Cracking Consider the loaddeflection response of a simply supported, reinforcedconcrete slab shown in Fig. 1. At loads less than thecracking load, Pcr, the member is uncracked and behaves homogeneouslyand elastically, and the slope of the load deflection plotis proportional to the moment of inertia of the uncracked transformedsection, Iuncr. The member first cracks at Pcr when theextreme fiber tensile stress in the concrete at the section of maximum moment reaches the flexural tensile strength of the concrete or modulus of rupture, fr. There is a sudden change in the local stiffness at and immediately adjacent to this first crack. On the section containing the crack, the flexural stiffness drops significantly, but much of the beam remains uncracked. As load increases, more cracks form and the average flexural stiffness of the entire member decreases. If the tensile concrete in the cracked regions of the beam carried no stress, the loaddeflection relationship would follow the dashed line ACD in Fig. 1. If the average extreme fiber tensile stress in the concrete remained at fr after cracking, the loaddeflection relationship would follow the dashed the actual response lies between these two extremes and is shown in Fig. 1 as the solid line AB. The difference between the actual response and the zero tension response is the tension stiffening effect （ in Fig. 1） . As the load increases, the average tensile stress in the concrete reduces as more cracks develop and the actual response tends toward the zero tension response, at least until the crack pattern is fully developed and the number of cracks has stabilized. For slabscontaining small quantities of tensile reinforcement [typicallytension stiffening may be responsible for morethan 50% of the stiffness of the cracked member at service loads and remains significant up to and beyond the point where the steel yields and the ultimate load is approached]. The tension stiffening effect decreases with time under sustained loads, probably due to the bined effects of tensile creep, creep rupture, and shrinkage cracking, and this must be accounted for in longterm deflection calculations. Models for Tension Stiffening ACI 3182021 The instantaneous deflection of beam or slab at service loads may be cal