水硬石灰在花山岩画加固保护中的应用研究

水硬石灰兼具石灰和水泥的优点,低收缩、耐盐、适中的抗压和抗折强度、水溶盐含量低,同时与传统的砖石建筑兼容性好,是一种天然、无污染、耐老化的无机材料。本工作针对花山岩画的开裂特点制订出相应的力学参数要求,配制出两种不同的水硬石灰砂浆,并对这两种砂浆的力学性能进行了分析。同时探讨了不同养护条件对水硬石灰砂浆拉拔强度的影响。现场试验结果说明,填补粘结材料可以提供一定的粘结强度,并且具有使用方便,污染小的特点,可用于花山岩画开裂岩体应急保护加固处理。     

Material Characterization and Micro-Modeling of a Historic Brick Masonry Pillar

A masonry pillar composed of solid clay bricks, cement mortar and infill is extracted from a historical structure and tested in concentric compression. It is subjected to cyclic and monotonic loads up to compressive failure.

In parallel, samples are extracted from the pillar and are subjected to destructive tests. Non-destructive tests are performed on the pillar, as well. The properties of the constituent materials are critically examined and their role in the maximum load reached and the failure mode obtained are discussed.

Finally, a finite element micro-model of the pillar is used for the simulation of the pillar test. The influence of the existing damage on the pillar is investigated using the model, resulting in a fair approximation of the global Young’s modulus, maximum load and the failure mode.

Highlights

●?A brick masonry pillar extracted from a historical building is tested in compression.

●?Material samples extracted from the pillar are characterized by mechanical tests.

●?A finite element micro-model of the pillar is used for the simulation of the compressive test.

●?The effect of damage on the compressive strength of the pillar is numerically investigated.     

莫高窟壁画地仗试件物理力学性能分析

深入了解壁画地仗的物理力学性能,对以后开展壁画的保护工作具有非常重要的意义。为此,通过一系列的测试和试验研究,对莫高窟壁画地仗材料试块开展了物理力学性能分析。测试和试验项目包括块体密度测试、声波波速测试、单轴抗压试验、劈裂法抗拉试验和直剪试验等。通过测试,分别得到了粗泥层和细泥层的密度、纵波波速、横波波速、动泊松比、抗压强度、弹性模量、抗拉强度、粘聚力和内摩擦角等9种物理力学性能参数。本研究成果将为莫高窟壁画的后续保护和修复工程技术研究奠定基础。     

Experimental characterization of the constitutive materials composing an old masonry vaulted tunnel of the Paris subway system

A significant proportion of the Paris metro tunnels comprise a masonry vault built out of stone blocks and mortar joints, and sidewalls and slabs made of unreinforced concrete. In order to provide the necessary data for future structural evaluation, an extensive laboratory testing programme has been conducted to characterize the materials of the tunnel separately, i.e., mortar, stone, and concrete. The tests, carried out on specimens taken from cores extracted from a 1930s tunnel, enabled to determine the mechanical properties, including direct tensile, shear strength, and mode I fracture energy, as well as the properties of the stone-mortar interface. Results show that the masonry mortar joints could reach 10 cm in width, and that blocks of stone varied in composition and porosity, thus producing a wide range of mechanical properties. The concrete was composed of large-sized aggregates and showed low stiffness and strength. Based on these experimental results, ratios between mechanical characteristics are hereby proposed. Perspectives on the use of this experimental data in a finite element model are then discussed.     

贺兰口岩画附近典型危岩体稳定性分析

通过前期现场调查,分析了贺兰口岩画的主要病害,提出岩画附近的危岩体是其中威胁较大的一类地质病害。根据现场勘察将贺兰口岩画附近不同状态的危岩体分为坠落式、滑塌式和倾倒式三类失稳模式。经过室内试验得到了岩石矿物组成、密度、气孔率、吸水率、单轴抗压强度等物理性质,并且利用Hoek-Brown准则、贯通率法以及岩石表面回弹值估算了危岩体与主控结构面的强度参数,例如单轴抗拉和抗压强度、变形模量、内摩擦角和黏聚力,然后利用不同失稳模式的计算方法进行稳定性分析。结果表明部分危岩体处于不稳定状态中,需要进行加固。     

Experimental analysis of rubble stone masonry walls strengthened by transverse confinement under compression and compression-shear loadings

Stone masonry walls of ancient buildings have reasonable resistance to vertical loads but lower resistance to shear forces and reduced tensile strength. However, to achieve such compressive strength the masonry must not disaggregate when subjected to loading. This can be achieved if during the construction of the walls larger stones, usually referred as “through stones”, are used, spanning the thickness of the wall, making it possible to improve the transverse confinement of the masonry. For rehabilitation projects and structural reinforcement of such buildings, the transverse confinement can be achieved by fixing steel elements perpendicular to the wall. This confinement technique is often part of a more comprehensive rehabilitation solution, which includes the application of mortar or concrete reinforced layers applied to the wall surface.

This article presents results of an experimental research on material properties and mechanical characterisation of stone masonry specimens strengthened by two transverse confinement solutions (independent steel reinforcing rods and continuous steel ribbons wrapping the specimen). Specimens were tested under compression and compression and shear loadings.

This experimental work is part of a major research project to study the mechanical behavior of URM and strengthened walls, and the characteristics of the building materials of such specimens.     

Interaction Curves for In-Plane and Out-of-Plane Behaviors of Unreinforced Masonry Walls

Different types of macro-elements have been proposed to simulate the behavior of unreinforced masonry (URM) structures under seismic loads. In many of these, macro-elements URM walls are replaced with beam elements with different hysteretic behaviors. The effect of out-of-plane loading or change of gravity load due to the overturning moment is usually not considered in the behavior of these macro-elements. This article presents interaction curves for bidirectional loadings of unreinforced masonry walls to investigate the importance of these factors. Two parameters are systematically changed to derive the interaction curves for a wall with specific dimensions, including compressive traction atop the wall to represent gravity loading, and loading angle that represents a combination of in-plane and out-of-plane earthquake loadings. Interaction curves are developed considering various possible failure modes for bricks and mortar, including tension, crushing and a combination of shear and compression/tension failures. The proposed interaction curves show the initiation of failure of URM walls as a function of compressive traction and loading angle. Several examples are presented for URM walls with different aspect ratios to aid in understanding the effects of various parameters on the derived interaction curves. Finally, for a specific case, the derived interaction curve is compared with nonlinear finite element results and ASCE41. The results show that, as a simplified method, the derived interaction curves can be used for the preliminary evaluation of URM walls under bidirectional loadings.     

故宫灵沼轩的动力特性及抗震性能研究

故宫灵沼轩是我国最早建造的钢铁-砌体组合结构之一,具有重要的历史、艺术和科学价值。为了评估灵沼轩在地震作用下的结构安全状况,建立了灵沼轩结构的三维有限元模型,并对其进行了动力特性和地震时程分析,得出了其固有频率、模态振型、地震位移响应和地震应力响应。结果表明:灵沼轩整体结构布置对称性较高,扭转刚度较大,对抗震较为有利;在8度多遇地震、设防地震和罕遇地震作用下,灵沼轩的金属结构部分及砌体结构部分的顶点位移和层间位移角均符合现行规范要求,砌体结构部分的第三主应力响应均小于材料的抗压强度,不存在压溃风险。在8度多遇地震和设防地震作用下,砌体结构部分的第一主应力响应均小于材料的抗拉强度,结构不会发生拉裂。但在8度罕遇地震作用下,砌体结构的部分位置拉应力超过材料的抗拉强度,这些位置存在开裂危险。最后,综合动力特性和抗震性能分析的结果,提出了灵沼轩的抗震加固建议。     

THE RELATIONSHIP BETWEEN LITHOLOGY,FLAKING PROPERTIES AND ARTEFACT MANUFACTURE FOR AUSTRALIAN SILCRETES*

Mechanical properties of Australian silcrete strongly influenced raw material selection and artefact manufacture. Microcrystalline silcrete, with high compressive and tensile strength, is suitable for blade tools requiring fine retouch. Fine‐grained silcrete (high compressive strength but lower tensile strength) was often used for blade‐based implements, but is more susceptible to edge fracturing. Medium‐grained silcrete has poor flaking properties (low compressive and tensile strength) and was often used for flake manufacture. Thus material determinism can explain much of the variability in silcrete artefact morphology and assemblage composition. Silcrete compressive strength is positively correlated with percentage of microcrystalline matrix and negatively correlated with average grain size, so hand lens examination of a silcrete sample can give a good indication of its likely flaking quality.     

Mineralogical and Mechanical Properties of Masonry and Mortars of the Lucknow Monuments Circa the 18th Century

The Lucknow monuments of the 18th century are large masonry structures built using thin burnt-clay bricks (Lakhauri) and lime-crushed brick aggregate (surkhi) mortars. Investigations were carried out to characterize the engineering properties of old masonry materials and new mortars being used for renovation work. Mechanical properties of reclaimed Lakhauri bricks were found comparable to good quality contemporary bricks of the region. Moreover, X-ray diffraction (XRD) and scanning electron microscopy–energy dispersive X-ray spectrometry (SEM-EDS) analyses indicated that mineralogical composition is not too different, except for few minerals. The lime-surkhi mortar used in old masonry work was found to be lime-rich with binder to aggregate ratio of approximately 1:2 to 3 by volume. The renovation mortar had poor hydraulic property as compared to old mortars indicated by thermal gravimetric analysis–differential thermal analysis (TGA-DTA) analyses. The compressive behavior of multi-wythe recreated Lakhauri masonry prisms was characterized with low compressive strength, low modulus, and significant deformability which result in lower stress demands imposed on the structural assemblages by various environmental forces.     

秦俑保护修复中陶体抗压抗折性能试验研究

在秦俑的保护修复中,对秦俑不同部位的陶体进行了抗压强度、抗折强度及粘接抗折强度的试验研究。选取有代表性的小残片作为样本,采用高压水射流方法加工小尺寸试件,分别进行了24组抗压强度、24组抗折强度和12组粘接抗折强度试验。结果表明:秦俑陶体整体平均抗压强度为29.65 MPa、抗折强度为12.65 MPa,不同部位的抗压强度差异相对较大、抗折强度差异相对较小;甲片部位的抗压强度和抗折强度均较高,而其他部位的抗压强度和抗折强度的相对大小有所差异;对于粘接修复后的陶体,抗折强度相比粘接前有所降低;腿部的各项力学性能都相对较低且位于秦俑受力的关键部位,因而有必要进行重点保护。     

Unstabilized and stabilized compressed earth blocks with partial incorporation of recycled aggregates

This article aims to characterize the physical, mechanical, and water-resistant behavior of unstabilized and stabilized compressed earth blocks (CEB) produced with partial incorporation of recycled fine aggregates from construction debris. The objective was to produce an alternative-earth construction material with lower embodied energy. To this end, different types of common CEB were covered, namely: unstabilized CEB; stabilized CEB with 8% cement; stabilized CEB with 4% cement and 4% lime. CEB were characterized in terms of density, thermal conductivity, compressive and tensile strength, water absorption, permeability, and resistance to water erosion from drip and spray tests. The influence of moisture content was also analyzed. Lime stabilization had little effect on the early age mechanical and durability behavior of CEB. Design coefficients are suggested for common cement-stabilized CEB under different environmental conditions. A minimum of 4% cement content was sufficient to produce water-resistant CEB with partial incorporation of recycled aggregates.     

贯入法原位测试夯土遗址表面强度的适用性和方法研究

表面强度是夯土遗址重要的测试指标和加固效果的评价依据。常规的强度测试方法受到取样和运输等因素的制约，不适用于作为夯土遗址如夯土补筑、表面加固等措施的效果评估方法。贯入法是成熟的砂浆强度检测方法，通过改装砂浆贯入仪降低了仪器量程；制作夯土样、室内试验验证了测试的较高精度；标定了夯土样贯入深度测量值与抗压强度的幂函数关系，确定了测强曲线。在夯土遗址现场开展原位测试，分析了布点密度对测试结果精度的影响，并利用测强曲线推算了测试区域的表面抗压强度。本研究提出了一套集“仪器改装-室内标定-现场高密度布点测试”为一体的夯土遗址表面强度评估方法，为土遗址加固效果的评价体系建设提供了参考价值。     

Assessment of material characteristics of ancient concretes,Grande Aula,Markets of Trajan,Rome

The Grande Aula, or Great Hall, of the Markets of Trajan (AD 96 to 115) is an intact example of the domed, concrete architecture of imperial Rome. Petrographic, x-ray diffraction, chemical, and SEM analyses demonstrate that wall mortars contain Pozzolane Rosse volcanic ash aggregate (harenae fossiciae) and strätlingite, a complex calcium aluminate cement hydrate (C₂ ASH₈) that gives modern cements good durability and compressive strength. Specific gravity tests and a new petrographic method for assessing bulk densities indicate unit weights of about 1750 kg/m³ for the wall mortars and 1430–1640 kg/m³ for the pumice bearing, vaulted ceiling mortars. Innovative point load source tests record the tensile strengths (f_t) of the aggregate and interfacial elements of the conglomeratic concrete fabric. These suggest f_t of about 2.7 MPa for brick, 1.2 MPa for Tufo Lionato tuff, and 0.9 MPa for Tufo Giallo della Via Tiberina tuff coarse aggregate (caementa), based on a tentative, approximate correlation with splitting (Brazilian) tests. The pozzolanic mortar and interfacial zones have lower f_t in the range of 0.8 MPa to 0.5 MPa. The relatively low mortar strength and its somewhat tenuous adhesion to the coarse aggregate suggests that the caementa may have arrested the propagation of tensile microcracks that formed in the mortar, thereby increasing the composite tensile strength of the concrete. Roman builders selected the complex aggregate mixes to optimize the performance of the wall and vault concretes.     

中国古代砖砌体力学性能研究综述

古代砖砌体建筑由于材料劣化、环境影响,材料特性及力学性能均受到不同程度的影响和损伤,为了保护历史文化的载体,结合古建筑材料获取原始且必要的数据,系统总结了古砖、传统灰浆的制备工艺和材料性能,简要归纳了古砖、传统灰浆和古砖砌体基本力学性能及其测试方法,对比分析了单砖和砌体抗压强度的差异以及古建筑砌体材料力学性能研究现状。并对今后古砌体如弹性模量等力学性能、古砌体材料及结构的损伤机理等的研究提出了展望或建议,可为砖石古建筑的修缮保护提供参考依据。     

Determination of Shear Strength of Masonry Panels Through Different Tests

This study addresses the problem of evaluation of strength of masonry walls. In-plane behavior of masonry panels has been studied under monotonic diagonal-compression and shear-compression loading in quasi-static test facility. The results of 35 laboratory and in situ tests are analyzed to show that in the case of the diagonal compression test results are lower than the strength of masonry walls evaluated trough the shear-compression test, highlighting the problem of choosing the test which best simulates to the real behavior of the masonry when stressed by lateral loads. A presentation is also given of the results of a F.E. investigation for shear strength evaluation of masonry walls. F.E. modeling non-linear procedure was used for the representation of masonry panels. The numerical simulations are compared with experimental results and the reliability of the different finite element models is discussed, thus confirming the different shear strength values measured in the experimental campaign.     

Characterization of Hydraulic Lime Mortar Containing Opuntia ficus-indica as a Bio-Admixture for Restoration Applications

Many successful and long lasting structures that contain lime mortars are hydraulic in nature. Organic admixtures are added to lime mortar mix to modify their fresh and hardened state properties. The present work proposes plant extract as bio-admixture for repair mortar towards the protection of heritage structures. The effect of cactus extract on the properties of hydraulic lime mortar is studied. Mortar´s composition is selected with respect to the composition of historic mortars and modern restoration practice. Cactus extract was added to the lime sand mixture with varying concentrations (25%, 50%, 75%, and 100%) and with different fermentation periods of 0, 1, and 2 days The consistency and workability of modified mortar, mechanical behavior, water absorption, porosity, and water/salt absorption through capillary rise, salt crystallization have been studied. Micro structural properties of the resulting mortar have been evaluated by XRD and FT-IR to identify their mineralogical composition and morphology by SEM-EDX. It is observed that addition of 75% cactus extract with 1-day fermentation produces maximum positive effect on the strength and durability properties of lime mortar. It improves the mechanical characteristics, limits water and salt absorption by capillarity into mortar and also show resistance to salt crystallization cycles.     

圆明园如园延清堂遗址局部勘探所获建筑材料的评价及其保护建议

圆明园位于北京西郊海淀,是清朝帝王在150余年间创建和经营的一座大型皇家宫苑,在世界园林史上有着非常重要的地位。本研究以如园延清堂基址为示范点,逐步探索如何对圆明园进行保护而做的一些基础工作。此次调查布置人工探查点4个,具体揭露延清堂基址的部分基础形式,并对揭露的三合土地基进行单轴抗压试验,提供三合土地基的天然单轴抗压强度及饱和单轴抗压强度,最后对不同深度的单轴抗压强度对比分析,结果表明大理岩条石作为文物有灭失的可能,应当重点进行保护;三合土地基上部及下部单轴抗压强度较低,中部单轴抗压强度较高,暴露于地表的三合土也急需保护。     

A CAPACITY PREDICTION PROCEDURE FOR CONCRETE-FILLED STEEL COLUMNS

A seismic design procedure for partially concrete-filled box-shaped steel columns is presented in this paper. To determine the ultimate state of such columns, concrete and steel segments are modelled using beam-column elements and a pushover analysis procedure is adopted. This is done by means of a new failure criterion based on the average strain of concrete and steel at critical regions. The proposed procedure is applicable to columns having thin- and thick-walled sections, which are longitudinally stiffened or not. An uniaxial constitutive relation recently developed is employed for concrete filled in the thick-walled unstiffened section columns. Modifications are introduced to this model for other types of columns. Subsequently, the strength and ductility predictions obtained using the present and previous procedures are compared with the corresponding experimental results. Comparisons show that the present procedure yields better predictions. It is revealed that the inclusion of the confinement effects and softening behaviour of concrete is important in the present kind of prediction procedures. Furthermore, an extensive parametric study is carried out to examine the effects of procedures and geometrical and material properties on capacity predictions.