A conventionally reinforced slab may attain substantially larger deflections than those corresponding to 6 degrees support rotations. These increased deflections are possibleonly if the element has sufficient lateral restraint to develop in-plane tensile forces. Theresistance-deflection curve of Figure 4-4 illustrates the structural response of anelement having lateral restraint. Initially, the element behaves essentially as a flexuralmember. If the lateral restraint prevents small motions, in-plane compressive forces aredeveloped. Under flexural action, the capacity is constant with increasing deflection untilthe compression concrete crushes. As the deflection increases further and the loadcarried by the slab decreases, membrane action in the slab is developed. The slabcarries load by the reinforcement net acting as a plastic tensile membrane. The capacityof the element increases with increasing deflection until the reinforcement fails intension.