Study On The Moment Distribution Coefficient And The Effective Beam Width In The Calculation Of Beamless Floor

With the progress of construction industry,girderless floor has been widely used in public buildings such as warehouses,garages and shopping malls because of its large building space and flexible structure layout.However,due to its complex mechanical mechanism,relatively small lateral stiffness,poor seismic capacity and other defects,there is still no perfect unified design and calculation theory for beamless floor structure,leading to frequent accidents in engineering.Based on the mechanical garage of a restaurant building in Shenzhen,this paper studies several controversial problems in the design and calculation of beamless floor by combining theoretical analysis with numerical modeling.The main research contents and results are as follows:（1）Briefly introduce the existing calculation methods of beamless floor,and point out that there are disputes on the value of moment distribution coefficient and effective beam width coefficient of beamless floor under the existing methods.（2）Based on Midas/Gen,the numerical models of inner,side and outer slabs of beamless floor are established respectively.By comparing the calculated bending moments with those given by empirical coefficient method in Chinese and American codes,it is shown that the distribution ratio of bending moments for the inner span given by Chinese code is in good agreement with that of American ACI code and simulation calculation results,but for the side span,ACI code is more consistent with the actual calculation results,while Chinese code is more conservative.（3）Through Midas software,a total of five groups of 85 models are established for slab-column joints of beamless floor under different column section size,column spacing and slab thickness,and the relationship between the width coefficient of effective beam and each dimension parameter is analyzed.The results show that the value of the width coefficient ofeffective beam is basically linear with c₁/l₂,l₁/l₂,c₂/c₁ and the thickness of slab h,and the width coefficient of effective beam and each of effective beam are calculated by SPSS software.Through linear regression analysis,the expression of effective beam width coefficient is obtained as follows:（4）Using the modified effective beam method to redesign the structure,the effective beam value is higher than the code requirement,and less reinforcement will be used in the design of the slab according to the bending moment of the effective beam section;the seismic performance analysis of the redesigned structure under the elastic state can still meet the seismic fortification requirements under frequent earthquakes,which indicates that the recommended effective beam value given in the code is biased to preservation.However,this method is more economical on the basis of meeting the seismic requirements.