【作者】 王晓东；

【导师】 谢礼立； 张虎元；

【作者基本信息】 兰州大学 ， 地质工程， 2011， 博士

【摘要】 中国是世界上四大文明古国中唯一历史延绵不断的国家。在这漫长的历史长河中,中华民族的祖先在适应自然、改造自然的过程中留给我们大量的遗物、遗址、遗迹。古代夯土建筑就是众多历史遗存中比较璀璨的一类,其作为人类文明信息的一个实体数据库,包含丰富的历史文化信息,需要广大学者去保存和解读。古代夯土建筑主要分布在人口稀少、地震烈度高的干旱半干旱区,它们遭受着巨大的、潜在的地震毁灭威胁。本文进行了夯土建筑遗址动力效应方面的研究工作,主要有以下几方面。(1)楠竹加筋复合锚杆是土遗址特性及现代锚固技术相结合的产物,其由楠竹、粘结剂与钢绞线复合为一体,楠竹的内腔安放有钢绞线,楠竹与钢绞线之间充填内粘结剂。该锚杆较传统锚杆有较大的截面积,可以获得较大的锚固力,其防腐能力较高。另外竹木质材料能体现古代人民在建筑方面的首选木质材料的思想,其符合文物保护的特殊要求。本文自行设计复合锚杆室内静力学试验试件,分别进行了复合锚杆的压缩、拉拔和弯曲试验。压缩试验结果显示,楠竹加筋复合锚杆1：1和1：2试件抗压强度分别为72.08MPa和43.48MPa,弹性模量分别是5.29GPa和5.25GPa,径高比1：1试件抗压强度高于1：2试件,有箍筋试件强度高于无箍筋试件。箍筋的存在一定程度上限制了复合锚杆的横向变形,对内部材料的约束作用致使整体强度有所提高。锚杆形态特征不同,其压缩破坏特征有所差异,但均有完整的弹性、强化和软化三个阶段。锚杆的压缩破坏呈现腰折和灯笼装散裂两种模式。楠竹加筋复合锚杆钢绞线与内粘结剂的粘结滑移分为弹性强化阶段、软化下降阶段、残余应力阶段三个阶段。对钢绞线与内粘结剂界面粘结滑移特性描述的模型中,精确模型可以较准确地描述粘结滑移的全过程力学行为,简化模型则忽视了短暂的软化阶段。内粘结剂与钢绞线界面上的剪切应力分布存在明显的峰值,离加载段较近的地方应力值较大,随着荷载逐渐增大,应力峰逐渐向远离加载端的方向移动。内粘结剂与钢绞线界面上的最大平均剪切应力随锚杆长度的增加呈指数衰减规律。锚杆在正常工作时存在弯曲受力状态,根据锚杆的弯曲试验得其弯曲强度为40.05MPa,弯曲模量为1.38GPa。锚杆试件的着力点对应位置应变最小,远离着力点位置应变不断增大。同一试件在弯曲过程中,楠竹与内粘结剂界面上的应变比钢绞线与内粘结剂界面上的大。在试验中发现锚杆弯曲率大于2%时将发生内粘结剂开裂,因此在锚杆吊装时,易多点捆绑保持锚杆直线吊装,以免锚杆内部界面出现脱粘现象。(2)在室内制作能代表夯土建筑遗址的模型墙体进行模拟地震振动台试验,模型分为未锚固夯土墙体和木锚杆锚固夯土墙体。在振动台试验中,利用锤击法对墙体进行自振频率测定。随着加载过程,模型墙体的自振频率不断下降。由墙体加速度傅里叶谱可以看出,台面上输入的地震波卓越频率,经墙体介质传播后,发生了显著的变化,结构对地震波的高频段有放大现象,墙顶对地震波的傅里叶谱放大幅度较大。在模型结构临近破坏时,破坏的墙体加速度傅里叶谱值急剧升高,对两个模型墙体其破坏时最大谱值点均是出现在台面输入加速度的卓越频率段。模型墙体的加速度随着台面输入荷载的增大而增大,且沿着墙体高度方向被逐渐放大。在使用Taft波和EI centro波加载过程中,木锚杆锚固墙体的加速度始终大于未锚固墙体。输入荷载较小时,加速度放大系数随着台面加速度的增大而增大,随着输入地震波加速度的增大,损伤不断积累加深,结构刚度逐渐下降,自振频率减小,阻尼增大,模型动力放大系数也逐渐减小。木锚杆锚固墙体墙顶的加速度放大系数在上升段和下降段均大于未锚固墙体墙顶的加速度放大系数。在分别用两种波交替加载的过程中,锚固墙体墙顶对Taft波作用下加速度的放大最大达182.9%,而对EI centro波达到130.5%。随着台面输入加速度的增大,模型墙体的位移逐渐增大,且沿着高度方向被明显放大。在加载至467.81gal时,两面墙体在底部同时出现第一条裂缝,当荷载至563.52gal时,未锚固墙体的位移突增,而发生破坏。锚固墙体是当加载至688.40gal时,墙体顶部位移陡增,裂缝扩展而发生破坏。墙体顶部位移角总体趋势为未锚固墙体的位移角大于锚固墙体。两面墙体开裂位置基本相同,均出现在最低一层夯筑层间界面处。未锚固墙体在相对台面位移达到3.11mm后发生破坏,锚固墙体在7.75mm后发生破坏,其变形能力提高幅度达到149%。由两面墙体的破坏荷载来看,木锚杆锚固墙体的最大承载力至少比未锚固墙体提高22%,木锚杆锚固墙体延性和承载力要优于未锚固墙体。(3)利用有限元程序对现场模型建模并进行数值计算,通过改变锚固参数研究其动力特性。锚固与未锚固墙体各阶振动形态基本相同,锚杆的植入未大幅改变墙体的固有属性,模型主要振动形态为第一阶。简化模型的自振频率均大于考虑薄弱层模型的自振频率,植入木锚杆的墙体各阶自振频率大于未植木锚杆墙体,在墙体中木锚杆对墙体的面置换率越高,其自振频率也越高。同一荷载下,模型墙体的加速度沿着高度不断增大,在墙顶产生了明显的鞭梢效应。简化模型的正向加速度以线性方式均匀增加,负向峰值加速度的增长过程为三段式。在考虑薄弱层模型中,其正负向峰值加速度的增长为两段式。模型的峰值位移沿着高度逐渐增大,增大的速率沿着高度也是逐渐在增大,峰值位移的增大沿高度方向呈非线性变化,没有明显的分段,正向峰值位移的增长速率要大于负向位移的增长速率。通过应力云图分析,模型第一阶的最大应力区均出现在模型底部,且薄弱层部位应力也较大。对同一模型,剪应力在同一振型下小于拉应力,由此也可断定结构的破坏是弯曲而导致的薄弱面拉裂破坏。在锚固模型中,木锚杆上的应力最大。由位移云图来看,位移随着模型墙体高度升高而增大,相同高度产生的位移基本相同,模型下部小位移带较宽,而越向上位移梯度变化越快,梯度也越大。(4)对比振动台试验规律和数值模拟规律,模型在插入木锚杆后,模型的顶端峰值位移较未锚固模型会有一定程度的降低,而峰值加速度会有一定程度的升高。在数值计算中发现木锚杆对模型墙体面置换率越高,其位移降低的越多,加速度升高的幅度越大。更多还原

【Abstract】 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.更多还原