Analysis On Dynamic Characteristics And Dynamic Stability Of Fastener-style Tubular Formwork Support

Fastener-style tubular formwork support system has been widely used in the buildingconstruction for a long time. In china，this type of support system accounts for about70%oftotal formwork used, in the dominant position. The security and stability of formwork systemis the basic guarantee for the construction to be carried out smoothly. However, as atemporary structure, its importance is often overlooked. Template support system instabilityand collapse usully occurred during the period of pouring concrete. Load calculation errors,overlength of the pole that stretched out of horizontal bar, insufficient integral stiffness offormwork support system are all causes of its instability. Live load changes greatly duringconcrete pouring phase, and different process of pouring concrete make load effect different.Accumulation of local materials and apparatus for construction, with vibration of concretewill make supporting formwork system bear uneven loads. Local load concentrated in beamand the impact effect of concrete both have amplifiction effect to load. All these factorsshould be considered carefully to aviod potential hazard of instability. Overall instabilitycritical load, displacement curves and failure modes of formwork support system still needsfurther research.Basing on the prophase research result of our research team, this paper do some analysisand numerical simulation on dynamic characteristics of formwork support system, dymamicchange of it’s natural frequency, harmonic response, dynamic stability. The computationalanalysis mainly include following aspects:1. Prestressed modal analysis to get dynamic characteristics of different quality load. Useblock lanczos method to extract characteristic parameters, analysis the trends of naturalfrequency.2. Harmonic response analysis under harmonic load at the top of formwork support system.Get the nodal displacement variation with frequency, load frequency that have asignificant influence on model structure, the effect of load amplitude.3. Static nonlinear analysis to determine the static nonlinear stability critical load PScrbyjudging the positive definiteness of structure stiffness tangential matrix.4. Dynamic stability analysis of formwork support system under the step load. According tothe static analysis results gradually apply the load value, get dynamic stability criticalload PDcr, and compare it with static analysis result.5. Apply horizontal load which is a certain percentage of the vertical step load, do nonlinear time history analysis, get static and dynamic stability critical load value of the modelstructure under different laod levels.6. After the eigenvalue bucking analysis, extract the lowest order bucking mode componentnode displacement to simulate the initial geometric imperfections distribution of modelstructure, analyze the effect of initial defects on the stability of the dynamic stability.By all the analysis, this paper mainly get the following conclusions:1. Pulse harmonic load of pumping concrete have impact on the performance of formworkstructure stability. With the construction of the concrete casting, the dynamiccharacteristics change of the formwork supporting system is regular, the vibrationfrequency decrease with quality load increasing, while displacement and deformationcharacteristics change. Tracking observation to the deformation and displacement of thesupport system can keep abreast of its dynamic characteristics and judge its stability.2. Static and dynamic stability of formwork supporting frame structure are affected by theload forms and additional horizontal load and initial defect. Dynamic stability bearingcapacity of formwork support systerm is far less than the bearing capacity of staticstability. So, dynamic function templates support system instability is one of theimportant reasons for the collapse.