Structural Load And Parameter Identification For Condition Assessment Of Heritage Buildings

The heritage buildings in the world represent a fundamental resource and a sign of the national cultural background.With changing environments and time impacts,their structural resistance has been reduced.It has become crucial to monitor and protect these architectural heritage buildings.However,little information can be found to provide basic knowledge for maintenance and preservation regarding to a balance between the structural safety needs and the respect for their architectural and cultural value.Condition assessment of heritage buildings is increasingly becoming as a significant tool to achieve such a balance,through a proper combination of traditional and innovative techniques.Most components of heritage buildings are made of ancient timber constructions,which are characterized by a wide range of uncertainties mainly due to irregularity in the internal timber texture,the variability of structural load and joint stiffness,existent of cracks and the effects of undocumented damages and repairs.Based on its specific existing situation,it urgently needs to develop an effective approach for structural condition assessment of these heritage timber buildings.Firstly,the dynamic behaviour of the heritage building has been analysed using the field monitoring data.A fully understanding the dynamic behavior of the heritage building under in-service environments is the basis to assess the condition of the structure,especially its responses to earthquake,environmental and operational loading.The instrumentation,the field monitoring and the data analysis used for the dynamic behavior have been illustrated.Explanation of the sensing technology and data acquisition system selected for the research is also studied.This research conducted a dynamic monitoring system which has been installed in a heritage building for over three years and the large amounts of high quality data have been obtained.The relationship between the average acceleration amplitude and frequencies of the principle components and operational conditions has been discussed.One main contribution is to understand the health condition of complex heritage building based on large databases collected on the field.Secondly,an approach to continually identify both the external force and the environmental load from structure responses has been developed in this thesis.This approach has considered the operational conditions of heritage timber buildings that the environmental load is treated as the main external load.In this new computational strategy,the environmental load is modelled directly without the temperature information.The effectiveness of the proposed structural load identification approach is validated via numerical studies with a structure with or without noise in the measured data.The environment load in the structural components can be estimated accurately with the proposed strategy with less than 8%error when there is 10%noise in the measured responses of the structure.In this thesis,the external force and the environmental load on the heritage building was studied clearly.Thirdly,an approach has been developed to identify structural parameters and its external load simultaneously in operational environments.Regarding to the undergone alteration,deterioration and other changes of the heritage building,a novel method is proposed to identify the unknown structural parameters which combined the temperature-based sensitivity analysis and dual Kalman filter technique.This approach is utilized for direct correlation of the input(temperature)and output responses(strains)for finite element model calibration and parameter identification based on the field monitoring data.The structural parameter was identified using temperature-based sensitivity analysis,in which the friction slip of the interface,the shearing of the tenon and the gap between the tenon and the mortise of was taken into account.The connection of components is modeled as bilinear rotational springs.The temperature is treated as input of the structure and the environment load on the structure can be determined based on proposed method.The numerical results show the method is effective and reliable to identify both unknown boundary conditions and the connection stiffness accurately even with 10%noise in measurements.A long-term monitoring system has also been installed in a typical heritage building and the monitoring data are used to further verify the method.The experimental results show the identified stiffness by the proposed method is consistent with that by finite element model updating from ambient vibration measurements.It is also noted that the identified stiffness with bilinear connection stiffness model can get a better result than with linear one.Thus,the accurate structural parameter can be obtained based on proposed method which has shown substantial benefits for advancing our understanding of heritage building behavior.