Dynamic Response And Earthquake-Resistant Conservation Of Historic Rammed Earth Construction

China is the only country in the Four Great Ancient Civilizations which continues its history and never breaks off. In the history, our ancestors bequeathed many hangovers, sites and relic while adapting and reforming natural environment. Historic rammed earth constructions, as one of more resplendent hangovers, records the information of human civilization and contains abundant history and culture message, so conservations and researches are required by scholars. Historic rammed earth constructions mostly locate in arid and semi-arid region that is sparse population and high seismic intensity, and are suffering from earthquake.The article carried out the following research on dynamic response and earthquake-resistant conservation of historic rammed earth constructions.(1) The bamboo-steel cable composite anchor (BSCC anchor) as the combination of earthen sites characteristic and modern anchorage technique is composed of bamboo, binder and steel strands, and the steel strand is put inside the bamboo with binder, a mixture of epoxy resin, fly ash and asbestos in certain proportion, filled in between. Compared with other traditional steel anchors, BSCC anchor has the advantages of higher anchorage strength due to larger cross-section, and stronger anticorrosion ability as extremely low moisture content of inner binder. Furthermore, the BSCC anchor has longer service expectancy as bamboo can better co-exist with soil, and the idea of wood as the primary construction material is well embodied in this anchorage material. The compression test, pull-out test and bending test were carried out in laboratory.Compressive strength of specimens with diameter-to-height ratios of 1:1 (72.08MPa) is higher than that of 1:2 (43.48MPa), and elastic modulus of two kind samples is 5.29GPa and 5.25GPa, respectively. The compressive strength of the specimens with hoop reinforcement is greater than that un-reinforcement, in that hoop reinforcement can restrict the horizontal deformation of specimens and then improving the strength and stiffness. There are three stages, elastic, strengthening and softening stage, for all specimen failure characters, in spite of the different in shapes.The bond-slip process between steel strand and inner binder was shown by three stages, which were, exponential-enhancing stage, softening-declining stage and residual stress stage. The bond-slip process could be described by an accurate model with exact description and a simplified model with ignoring the short softening-declining stage. The stress is not equally distributed at the interface between inner binder and steel strand of BSCC anchor, and there is obvious stress peak. It is found that shear stress is not uniform distributing between the interface of inner binder and steel strand, and it approaches a peak near the loading end, and the peak stress increases and shifts far further from the loading end when puling load is increased. The average shearing stress of the interface between steel strand and inner binder basically submitted exponential decay as the anchor length increased.Bending test indicated that the bending strength and modulus is 40.05MPa and 1.38GPa, respectively. The strain value of the strain gauges on both steel strand and bamboo improves as the load was increased, but the strain values of strain gauges on bamboo are bigger than those on the steel strand for the same specimen and load, owing to the strain gauges on bamboo are placed farther from the neutral axis of the specimens during loading process. The strain value is higher at the load point and lower at the ends, so slippage starts from two ends of the specimen. The BSCC anchor should be kept linear state by trussing multi-point on the basis of anchor length when hoisted for installation and the flexibility should be not greater than 2%.(2) Two models of rammed-earth wall, one anchored with wooden anchor and the other not, that could express basal characters of historic rammed earth construction, were built in the laboratory to test on seismic response by shaking table. The natural frequency, tested by impact testing, gradually reduces along with increasing of load. The Fourier spectrum of acceleration indicates that the frequency of acceleration input in shaking table is changed through spreading by model wall, the high frequency is magnified and the peak value of Fourier spectrum is highest at top of wall. The value of Fourier spectrum rapidly increases while the wall is destroyed, but the peak value of Fourier spectrum appears at the range of natural frequency of acceleration input in shaking table.The acceleration of wall increases along with the increasing of load, and is magnifying in the direction of height. The acceleration of wall anchored with wooden anchor is higher than that of the other wall un-anchored during loading with Taft wave and El centro wave. The amplifying coefficient of acceleration increases along with the increasing of load at the low level of load. During the increasing of load, the damnification of wall is gradually accumulated to bring on the fall of stiffness, natural frequency and amplifying coefficient. The amplifying coefficient of wall anchored with wooden anchor is higher than that of the other wall un-anchored, that the maximum is 282.9% to Taft wave and 230.5% to El centro wave.The displacement of wall increases with load, and is magnified along the height. As the load up to 467.81 gal, the first crack appeared at the bottom of two walls. While the load reached to 563.52gal, the displacement of wall un-anchored rapidly increased and the crack expanded, as a results, the wall was destroyed, but the case for the wall anchored with anchor happened until the load to 688.40gal. The displacement angle of wall un- anchored was more than that of the other wall anchored. The cracks of two walls appeared at first interface of two rammed layers at the bottom of walls.The wall un-anchored was destroyed while the relative displacement reached to 3.11 mm, and for the anchored wall, the relative displacement reached to 7.75mm, which was higher 149% than the wall un-anchored, in other words, the ductility of wall anchored with anchor is better than the other wall. Form the ultimate load, the bearing capacity improved by 22% at least with the help of anchoring.(3) The dynamic characteristic of model for field walls was simulated by finite element program. The vibration modes of walls are similar, and the main vibration mode is first order, this shows that the wooden anchor can not change the natural attribute of walls. The frequency of simplified models is higher than that of the models with dotty layers, and the frequency of models with anchor is higher than that of the models un-anchored. The frequency is high while the replacement ratio is great.In the same load condition, the acceleration of model walls increases with the height and produces the whipping effect on the top. The plus acceleration of simplified models increases linearly and the model of "syllogism" in the process of the minus acceleration. In view of dotty layers, the acceleration of the plus and minus models would present two stages, the peak displacement enhances gradually along with the height. The velocity of displacement increasing gradually improves along the height. Overall, the increasing velocity of plus peak displacement is more than of the minus.From the stress contour plot, the maximal stress region of the first order appeared at the bottom of models and the stress in dotty layers is also higher. It is justifiable to conclude that the failure of structure is rip failure of the dotty layers induced by bending according to that the shear stress is less than tensile stress in the same vibration mode. The stress of wooden anchor was the highest in the whole anchored models. It also can be seen from the displacement contour plot that the displacement improves along with the height and is close at the same height, the region of low displacement is wider at the bottom and then the displacement grads increases gradually and changes rapidly along the height.(4) From the rules between numerical simulation and shaking table test, the peak displacement at the top of models have a certain extent reduced by the way of being anchored but the acceleration increased simultaneously. It also concluded from numerical simulation that the more the replacement ratio was, the greater the raise would be.