A Study On Improved Fictitious Beam Method And Its Application On Core Box Cast-in-Situ Concrete Hollow Floor

With modern people’s increasing demand of building functions, single floor system can’t meet the various requirements anymore. Many kinds of new floor form emerge at this time. Among them, Cast-in-situ reinforced concrete hollow floor system is one of the most widely used. As its light weight, saving in material, high stiffness, better economy, this floor system is particularly useful for large-span and high load building and because the cavity structure can reduce noise, insulate heat it is also a energy-saving structure. Among all the core form, box core is the most widely used because of its high hollow ratio and big rigidity. The Engineering design and calculation method of this floor system is usually elastic simplified method. This paper discusses Fictitious Beam Method introduced by 《Technical specification for cast-in-situ concrete hollow structure》and improves its accuracy which gives basis and advice for engineering design. The main content is divided into three subtasks as follows:1)Comparing all kinds of elastic simplified methods, evaluating their advantages and disadvantages, this thesis improves the widely used Fictitious Beam Method through following measures. For the great stress change part of the column strip, the improved Fictitious Beam Method lumps the first ribbed beam in one single cross beam and then lumps from the second ribbed beam to 1/4 close to the edge ribbed beam in one cross beam then lumps all the ribbed beam in the middle part in one single cross beam and finally takes some measures to reduce the torsional rigidity error influence. For the improved Fictitious Beam Method model, this thesis compares sap2000 finite element model with PKPM cross beams method model to verify its accuracy.2) Restricted by research conditions and theoretical level, the most study of hollow floor rests on elastic stage. The cognition of Failure Mechanism, failure mode and failure characteristics is still deficiency, so researchs on elastic-plastic stages are of great significance. However, hollow floor system don’t have primary and secondary beam, it produces plastic yield lines instead of plastic hinges which can be well simulated by most structural analysis software. So this paper adoptes simplified model based on improved Fictitious Beam Method to simulate non-beam hollow floor stress conditions on elastic-plastic stage. The result shows that the interlayer displacement angle conforms to the specification and the structure performs well in seismic-resistance and energy-dissipation.3) At last, according to the project of a group company’s research and exhibition center in kunshan which uses GBF honeycombed-core hollow floor with the thickness of 400 mm, this thesis replaces the slab to Core Box Cast-in-situ Concrete Hollow Floor with the thickness of 350 mm and adopts improved Fictitious Beam Method model to redesign and then calculate the stress.