Research On3D Strip Designing Method For Reinforced Concrete Beam Slab

To further explore and complete the designing method for RC floor considering beam-slab cooperative work, based on the study of literature [13],[14],[35],[36] and [37], the article adjusted, corrected and unified the membrane action coefficient and adjustment coefficient of "3D strip method" which proposed by literature [35] and [36] by nonlinear numerical analysis using FEM (Ansys), and let the internal force analyzed by "3D strip method" closer to which analyzed by nonlinearity simulation, and analyzed influence factors of the coefficients. In addition, analysis results showed that the negative moment of slab should be3-15times of positive moment, rather than1.5-2.5times known by "edge-supported slab" concept. And the article analyzed the difference of models’inner forces under vertical fully load distribution and vertical unfavorable live load distribution, and the change rule of moment-inflection-point, and gave a design proposal of the location of slab negative reinforcement cut-off.Analyzing model is a two-way unequal column3×3span RC frame of single floor model (full-scale model). Due to the computational analysis, slab dividing methods named3-strips and4-strips does not much affect the plasticity inner force, width of edge-strip can be1/4short-span or1/4its-span and it does not much affect the plasticity inner force too, so we can divide the slab to strips neatly according to particular case in engineering designing. In frame structure the influence of membrane action to plasticity inner force of beam-slab is very huge, and analysis shows that the main influencing factor of membrane action is the stiffness of column, so the article gave fixed values as membrane coefficients for engineering design. can In addition, the article analyzed models with bridging piece, outrigger and bridging piece with beam, the analysis result indicates that there is not membrane action in bridging piece and outrigger, and shows that the stiffness of column is the main source of membrane action again; because of the effect of slab, the plasticity inner force of beam in the bridging piece (align the beam and slab upper edges) reduce obviously. Analysis indicates that the main reason of the reduce of hogging moment of frame beam support (moment modulation) and the increase of hogging moment of frame slab support is that stress states of beam is eccentric compression and of slab is eccentric tension in this area.A large number of nonlinear numerical analysis indicates that,3D strip design method is a comparatively ideal and practical design method considering cooperative work of RC beam-slab.