Nonlinear Finite Element Analysis Of Two-way Reinforced Concrete Waffle Slab

As an important force-resistance structure, the capacity of reinforced concrete waffle slab is better than one-way slabs and two-way slab. Not only waffle slab exhibits higher rigidity, smaller deflections and behaves well under vertical loads but also the excellence of the structure made by waffle slab is lower structural height, lightweight and economic benefits and so on. But interior force of reinforced concrete waffle slab is difficult to be calculated because the distribution of interior force is complex under different loads and boundary. Moreover, inter- action of moment and tortuosity add the complex. At present the calculation method of waffle slabs focus on elastic phase. When concrete components cracked, bending stiffness and retortion stiffness descended, which is different from elastic stiffness. So in crack phase the computing outputs in using elastic stiffness will not be consistent with practice instance. Therefore, these results will mislead design. That is, some place will crack for lack of steel bars while in other place steel bars are too enough to yield.Therefore, finite element analysis is adopted in this paper, the character of waffle slab in elastic and plastic phase regarded. Interior forces and displacements in elastic and plastic phase are compared to get results that approach practical instance. Main works that have been done in this thesis including:1.After summed up all kinds of elastic methods of reinforce concrete waffle slab, cross beam method that moment, retortion, shearing force are considered is used in this paper. Finite element analysis based on cross beam method is applied to this phase of waffle structure in order to prove reliability of this method.2.Plastic finite element analysis program is compiled in this paper. Iterative calculation is applied to non-linear equations. After concrete elements crack, according to cracked bending stiffness provided by Reinforced Concrete Criterion and cracked retortion stiffness given by experiments, bending stiffness and retortion stiffness will be calculated again. Compared Interior forces in elastic states with those in plastic states,distribution of hypo- interior forces will be got.3. Distribution rule of deflection in plastic state is found. A formula is given to calculate cracked component of slabs in different boundaries.4.According to some factors that are not considered in my computer program, origin of error is put forward when using this program. Therefore, in order to improve computing precision, these factors should be modified. So these results can provide some ideas for designers.