Study On Reliability Of Formwork-Supporting System During Building Construction

The reliability of formwork-supporting system during building construction is one of the most important research areas on civil engineering which have a difficulty and challenge. In this paper, the reliability of formwork-supporting system during building construction was studied on the state of the art for formwork-supporting system, The research works included: slip and torsion capability of right-angle coupler, stability bearing capability of formwork-supporting system, system reliability during construction, human error rates and error magnitudes, and human reliability analysis and safety assessment. Aiming at the reliability analysis problems with implicit performance functions, a response surface method based on LS-SLM was presented. The major contents of this work can be summarized as follows.(1) Making full use of site investigation, human errors during construction of formwork-supporting system were summarized. On the basis of the data of site investigation, probabilistic models for geometric parameter and error rate of formwork-supporting system were established. The probabilistic models for slip bearing capability of right-angle couplers with different bolt tightening torque and torsional stiffness model were obtained through experimental study on right-angle coupler.(2) Considering the state of semi-rigid connection, a calculating model by 3D FEM was established to simulate the formwork support on the basis of experimental study on torsional stiffness of right-angle coupler. Linear and nonlinear buckling techniques were applied to analyze the stability of the formwork supports. Initial imperfection, plastic behavior and large deflection response of the formwork supports were taken into account in the nonlinear analytic model. Numerical results indicate that the linear buckling loads are higher than the nonlinear stability and so it is necessary to use the nonlinear stability solution. Nonlinear buckling analysis was used to calculate stability bearing capacity in the case of different design variables. The results of stability bearing capacity were transferred to effective length coefficients that were generally used in practice. The effect of initial imperfection, semi-rigid connection, bolt tightening torque and total height on stability bearing capacity was studied.(3) In view of the significant failure modes of formwork-supporting system and reinforced concrete member, the reliability of time-dependent system during the construction of typical multistory reinforced concrete buildings was developed by Monte Carlo simulation and interpolation technique. The influence of the number of levels of shoring/reshoring and liveload during construction of the building on system reliability was included in the analysis. It is found that the failure probability of structure during construction are far more than service period, and the failure states of formwork-supporting system are mainly caused by the slip failure of the right-angle coupler which connects the horizontal tube below the formwork with the upright tube.(4) According to numerous building failure investigations, failures due to human error are mainly during building construction. Construction processes are so complicated that it is not feasible to model all possible human errors. Naturally, there is a scarcity of statistical data associated with construction errors. It is important that the human reliability analysis (HRA) can consider the interaction of all error types. On the basis of the investigation on site, the experiment research and relative references, HRA method was applied to simulate the error rates and error magnitudes of the reinforced concrete members and the formwork-supporting system during building construction.(5) Probabilistic and human reliability models were developed in this paper to estimate the probability of structural failure during the construction of typical multistory reinforced -concrete buildings in the presence of human error. To measure the influence of the human error on system reliability, two cases for error-free case and error case were considered. Furthermore the check emphasis of formwork-supporting system was pointed during multistory building construction.(6) To study comprehensive evaluation problems in which criteria values and marks were fuzzy numbers, fuzzy numbers were introduced into grey relational comprehensive evaluation field. By combining the grey relational analysis with the fuzzy sets theory, a new multi-level and multi-attribute grey relational comprehensive evaluation method based on fuzzy numbers was proposed. Utilizing the new method, a standard of construction safety appraisal for formwork-supporting system was presented. This study shows the results obtained by the new approach combined with two distances between two fuzzy numbers, plane distance and lattice distance, are approximate to the result computed by traditional grey relational analysis method. This assessment framework was based on the new approach and a survey among project professionals in Zhejiang Province of China. This proposed framework provides a very useful decision support tool for project managers in assessing the construction safety of formwork-supporting system for their projects.(7) A response surface method based on LS-SLM was presented. Because of its high approximate capacity, LS-SVM was employed to approximate the implicit mapping between structural response variables and basic random variables. LS-SLM was learned by samplesgenerated from orthographic design method and the FEA programs, then validated by selected samples according to their probabilistic distributions. The learned LS-SVM was integrated with Monte-Carlo method to calculate the response variables and then failure probability. The new method can be used to solve the reliability problem in large complex structural engineering. The efficiency and accuracy of the proposed method were proved by typical engineering examples of structural reliability analysis.This paper is supported by research project for soft science of National Construction Ministry "Risk Analysis and its Control of Structure during Building Construction"(05-Rl-13) and research project of Construction Department of Zhejiang Province "Risk Analysis and its Application of Tubular Steel Bearing Scaffold with Coupler during Building Construction"([2003]No.226).