Rocking Response Of Traditional Timber Structure Subjected To Horizontal Excitation

Ancient timber structures are cultural treasure of human beings,which have important historical significance and academic value.Timber structure is used as the core force-transmitting system in most ancient Chinese buildings.Scientifical protection of the timber structure has been increasingly recognized by modern society.Earthquake is one of the core factors affecting the survival of ancient buildings.The collapse of ancient timber structures under earthquakes is mostly caused by the overturning of timber frames.However,significant structural damage was rarely found in capsized timber frames.Reliable forecasts and proper treatment of ancient structures therefore represent a fundamental issue to be addressed when choosing the most appropriate strategies of structural protection.Related research is also an important component of preventive protection of ancient buildings,which has scientific significance and engineering guidance value.At present,most of the research related to the seismic performance and safety limit of timber structures is focused on the static and pseudo-static performance of joints or structures.However,due to the particularity of the timber structure,such studies can hardly reveal its seismic mechanism.Although the shaking table test research on timber structures has been carried out,the number of such studies is extremely small due to the high cost.Therefore,there are still problems of unclear disclosure on the dynamic response of timber structures.Theoretical analysis method was adopted in this paper to analyze the dynamic response of ancient timber columns under horizontal excitation.In addition,the field-measured method was used to study the statistical law of the gap between tenon-mortise joints.Rocking response analysis of the timber frame with joint gaps under horizontal excitation was carried out based on the above studies.Here below is the list of contents and main achievements of this study:(1)Based on the existing shaking table test and characteristics of ancient timber structures,the dynamic response analysis model of the timber column was simplified.Dynamic responses of timber column that may and may not be triggered under horizontal excitation was proposed.The critical conditions that cause different dynamic responses were described,and the governing equations for each dynamic response were established.The sensitivity analysis results of critical condition parameters for different dynamic responses show that the dynamic response of the timber column most likely tobe triggered under horizontal excitation is rocking.The change of the eccentricity of the Lu-dou can significantly affect the critical conditions of rocking of the timber column.The influence of trigger conditions and related parameters of different responses was analyzed by finite element method.The reliability of theoretical analysis results is verified.(2)The most easily triggered response of the timber column under horizontal excitation,rocking,was studied in depth.The different size relationships between the length of the bottom of the Lu-dou and the diameter of the column cross section were taken into account in the analysis model.The model of re-center energy dissipation for rocking timber columns with buckets was established based on the Housner’s model.According to the different sequence of the characteristic moments such as re-centering and termination of excitation,different rocking and overturning conditions were distinguished.The overturning critical conditions of the timber column under horizontal one-sine excitation was fully explained.Results show that when the length of the bottom of the Lu-dou is larger than the diameter of the column section and beyond the top of the column,the rocking stability of the timber column is the best.(3)The gaps of more than 1000 sets of tenon-mortise joints in an ancient building group were measured.The gap was divided into horizontal and vertical according to the position of it.Basic statistical information for the horizontal and vertical gaps was described.The Weibull distribution of horizontal and vertical gaps was fitted and tested through the maximum likelihood estimation method,probability plot correlation coefficient method,and Anderson-Darling method.The mechanical properties analysis of the tenon-mortise joint with horizontal and vertical gaps was carried out using the finite element method.Results show that the vertical gap at the top of the tenon has a more significant effect on the mechanical properties of the joint.(4)The analysis model of the horizontal timber frame of the East Hall of Foguang Temple was simplified according to the rocking response characteristics of the timber structure and original appearance of the timber frame.Critical conditions for timber frame uplift and limit rocking of tenon-mortise joints were derived.A re-centering energy dissipation model of the rocking timber frame was established.The model clarifies that the slenderness ratio of timber columns is a key factor that affects the energy dissipation.The overturning conditions of the timber frame under horizontal excitation were differentiated according to the sequence of occurrence of critical moments such as re-centering and termination of excitation.The possibility of a rockinglimit situation was also considered.The critical conditions for the overturning of the timber frame in different cases were proposed.The seismic performance of this type of timber frame was evaluated under the basic assumptions in this paper.The quasi-static and dynamic analysis of the timber frame were carried out using numerical simulation methods.The rationality and validity of the theoretical analysis and its basic assumptions were verified.