Experimental Evaluation of Seismically and Non-Seismically Detailed External RC Beam-Column Joints

An experimental investigation was undertaken to study the seismic performance of external reinforced concrete (RC) beam-column joints having representative details for mid-rise RC frame buildings in developing countries such as Iran that were designed and constructed prior to the 1970s. Three half-scale external RC beam-column joints were tested by applying lateral cyclic loading of increasing amplitudes. Tested specimens were comprised of one unit having seismic reinforcement detailing in accordance with the seismic requirements of ACI 318-11, and two units having non-seismic reinforcement detailing in accordance with the 1970s construction practice in many developing countries, such as Iran. Two typical defects were considered for the non-seismic units, being the absence of transverse steel hoops and insufficient bond capacity of beam bottom reinforcing bars in the joint region. Test results indicated that the non-seismically detailed specimens had a high rate of strength and stiffness degradation when compared to the seismically detailed specimen, which was attributed primarily to the joint shear failure or bond failure of the beam bottom bars. The non-seismically detailed specimens also showed a 30% reduction in both average strength and ductility and a 60% loss of energy dissipation capacity in comparison to the seismically detailed specimen.     

STRUCTURAL RESPONSE AND DAMAGE ASSESSMENT BY ENHANCED UNCOUPLED MODAL RESPONSE HISTORY ANALYSIS

The Uncoupled Modal Response History Analysis (UMRHA) method developed by Chopra et al. is modified in this paper to estimate damage to welded moment-resisting connections in a steel frame (MRSF) subjected to earthquake ground motions. The behaviour of these connections is modelled by a moment-rotation relationship that accounts for the cracking of the beam flange-to-column flange groove weld. The behaviour of the frame is approximated by a sequence of single-degree-of-freedom (SDOF) models for the first three modes to allow for the contribution of higher modes of vibration. The dynamic properties of these SDOF systems are determined by nonlinear static pushover analyses of the building frame. Because of the significant drop in connection strength caused by beam-to-column weld cracking, the pushover procedure uses a changing rather than invariant distribution of horizontal loads, while the structural responses are calculated from shapes that are based on the displaced shape of the frame after damage occurs. The accuracy of the method is demonstrated by a comparison with the results of a nonlinear time history analysis of the frame. This method can be used for rapid assessment of seismic damage or damage potential and to identify buildings requiring more detailed investigation.     

Displacement-Based Assessment of Non Ductile Exterior Wide Band Beam-Column Connections

Results from testing two half-scale exterior wide band beam-column sub-assemblages under cycles of lateral displacement are presented in this article. The first subassemblage represents the current level of detailing adopted in low to moderate seismic regions, such as Australia, for connections where seismic provisions are not normally a consideration in design. Minor (inexpensive) detailing changes in the reinforcement distribution and anchorage were introduced to the second test specimen. These changes significantly improved the connection performance in terms of increased displacement capacity and a reduction in strength deterioration. Using a displacement-based assessment approach to assess primary moment-resisting band beam frames of up to eight stories, it was found that the current level of detailing is adequate for the drift demands resulting from the expected Australian seismicity for a 500-year return period. However, for the displacement demands corresponding to a 2500-year return period, the frames sited on very soft soils and frames over four stories sited on intermediate soils would require improved detailing such as that used in the second sub-assemblage. A strength hierarchy of strong column-weak beam was assumed in this assessment.     

佛光寺彩画加固保护材料的选择实验研究

针对佛光寺无地仗彩画层所出现的颜料脱落、颜料褪变色、裂隙等突出病害,本研究利用正交实验对鱼胶和白芨胶两种传统保护材料进行了复配,得到适宜无地仗彩画加固保护的优选配方:以质量分数为3%的鱼胶复配以0.1%的白芨胶作为有效加固成分,再配以质量分数为0.5%的防霉剂(PTA)、0.1%的紫外吸收剂(BP-4)以及0.1%的抗静电剂。所得复配材料具有优良的加固性能及耐老化性能,可为佛光寺及其他地区无地仗彩画加固保护材料的选择提供参考。     

花山岩画岩体开裂机理统计分析

岩体开裂是危害花山岩画最严重的病害,会对岩画造成毁灭性的破坏。为制定有效的灌浆加固措施,在对岩体开裂成因及影响因素分析和现场调查的基础上,做了统计分析。结果表明:1)岩画区共有418处开裂病害,开裂岩体以风化开裂体为主,占69%,且构造开裂体的厚度大于风化开裂体;2)构造开裂体的钙质、钙质与泥质共同充填比例为78%,高于风化开裂体的52%;3)构造裂隙和风化裂隙的张开度均以小于6mm为主,可知当张开度大于6mm时,开裂体将发生剥离掉块;4)风化开裂体的危险性I级、Ⅱ级所占的比例为57%和22%,小于构造开裂体的64%和27%,但风化开裂体多发育于岩画存在部位,易出现开裂和掉块,破坏更大;5)构造开裂体的厚度较大、裂隙连通性好、危险等级高,而风化开裂体厚度较薄、裂隙贯通性差、危险等级较高。本研究结果可为开裂岩画岩体灌浆加固及后期修复提供理论依据。     

Development and Seismic Behavior of Precast Concrete Beam-to-Column Connections

A new precast concrete beam-to-column connection for moment-resisting frames was developed in this study. Both longitudinal bar anchoring and lap splicing were used to achieve beam reinforcement continuity. Three full-scale beam-to-column connections, including a reference monolithic specimen, were investigated under reversal cyclic loading. The difference between the two precast specimens was the consideration of additional lap-splicing bars in the calculation of moment-resisting strength. Seismic performance was evaluated based on hysteretic behavior, strength, ductility, stiffness, and energy dissipation. The plastic hinge length of the specimens is also discussed. The results show that the proposed precast system performs satisfactorily under reversal cyclic loading compared with the monolithic specimen, and the additional lap-splicing bars can be included in the strength calculation using the plane cross-section assumption. Furthermore, the plastic hinge length of the proposed precast beam-to-column connection can be estimated using the models for monolithic specimens.     

Seismic Retrofitting Techniques for Historic Adobe Buildings

This article presents a comprehensive overview of the techniques available for the seismic retrofitting of adobe buildings. It analyzes these techniques’ viability from a structural engineering standpoint and evaluates their suitability in the context of historic preservation. Analysis was based on an exhaustive review of studies addressing retrofitting techniques of earthen structures, as well as consultation with field experts. The guiding principles of conservation relating to the structural reinforcement of monuments were taken into account. Traditional techniques that enhance the stability of the building, such as wooden ring beams, wooden ties interconnecting parallel walls, corner keys, and the addition of buttresses were found to be effective solutions since they employ compatible and low-cost materials such as earth and wood. When these techniques prove insufficient, minimally invasive measures such as introducing a plywood diaphragm, horizontal steel rods, a geomesh covered with mud rendering or a strapping system can be appropriate.     

丙烯酸酯改性明胶古墨锭修补胶的试验研究

墨是中华民族的一颗瑰宝,然而随着时光的流逝,墨锭霉变、破损开裂、粉化酥解,而难以长久保存,刻不容缓需要保护。为此,采用反相乳液接枝的方法,用丙烯酸丁酯、丙烯腈对明胶接枝改性;分析了接枝改性的反应温度、反应时间、单体用量、预处理时间等对接枝反应的影响,并用FT-IR进行表征;分别进行干热加速老化试验前后的剪切强度、劈裂强度、抗弯强度等性能测试。经过模拟粘接和试验性修补结果表明,用丙烯酸丁酯、丙烯腈对明胶接枝改性胶的剪切强度0．44MPa、劈裂强度68N／m、抗弯强度69N／m,加速老化后仍分别保持0．37MPa、54N／m和44N／m。修复后的古墨锭,粘接强度高、防霉抗菌、耐老化、无损伤,对古墨锭的加固保护效果明显。     

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。     

Seismic Evaluation and Retrofit of Asymmetric Multi-Story Wood-Frame Building

The presented research focuses on large-scale seismic testing under multi-directional ground motion of a three-story high, wood-frame residential building representing late 1960's California construction. Earthquake lateral resistance is provided by plywood shear walls around the perimeter of the building with an open front in the first story for tuck-under parking. Accordingly, the as-built structural configuration is asymmetric in plan and discontinuous in elevation with tendency to twist about a vertical axis and to form a weak story mechanism. The test results confirm this tendency. They also reveal the sensitivity of the response to multi-direction ground motion. Asymmetric damage patterns are induced by the multi-component motions in the walls oriented perpendicular to the open front for the as-built test structure, with or without finish materials. However, the observed damage remained noncritical as far as structural integrity is concerned even for ground accelerations exceeding 120% of that recorded during Northridge earthquake. This is viewed as a consequence of the better construction of the test building compared to actual construction. Investigated retrofit includes adding a welded moment resisting steel frame around of the garage opening and strengthening the diaphragm to header beam connections. The study indicates that the retrofit significantly reduced the maximum story drift in the open front. Moreover, the finish material and the retrofit greatly reduce the maximum rotation of the building about the vertical axis.     

Aspect sensitivity of VHF scatterers in the troposphere and stratosphere from comparisons of powers in off-vertical beams

The aspect sensitivity of the radar backscatter power at 46.5 MHz has been examined for the troposphere and lower stratosphere. Use is made of the width of the effective backscatter polar diagram, assumed to be Gaussian, derived from the ratios of signal strength for different pairs of beam directions in order to distinguish between anisotropic and isotropic scattering. The results are used to examine the relative contributions of isotropic scatter, anisotropic scatter, and Fresnel reflection or scatter to the signal backscattered in the vertical direction. Furthermore, the change in the scattering characteristics during the passage of a warm front is examined.     

1940年桂林版《救亡日报》的保护修复

为了研究纸质文物的保存状况、原料成分、制作工艺及病害原因,特对1940年桂林版《救亡日报》进行科学的分析检测及保护修复。采用Nicolet 8700型傅里叶变换红外光谱仪分析纸张纤维的官能团结构,采用XWY-Ⅵ型纤维测量仪对纸张纤维进行观察,以鉴定其纤维的种类形态;采用VHX-1000E视频显微镜及场发射扫描电子显微镜(JSM-6700F型)对纸张样品的加工工艺及老化程度和污染物进行分析,以确定其是否加填或施胶处理。在此基础上,在修复中采用传统的装裱技术和丝网加固技术相结合,对此件文物进行保护性修复。修复后的文物解决了缺失部分的配补,皱褶部位得以平整舒展,病害得以清除,纸张的强度得以增强,恢复了文物的原貌,从而提高了文物的整体性、观赏性,为展出、研究提供了更好的史料。     

Formation of mesospheric VHF echoing layers due to a gravity wave motion

We present mesospheric backscattered VHF echo power and wind velocity data indicating the co-existence of a threefold strongly echoing layer and a wave motion, observed on 20 September 1985 with the MU radar at Shigaraki (34.9°N, 136.1°E), Japan. The echoing layers are clearly connected with the vertical and horizontal wind perturbations due to the wave. The analysis of the wind data have shown that the wave motion is due to an internal inertia-gravity wave with the vertical and horizontal wavelengths of 6 and 400 km, respectively, and period of 5.6 h. Evaluating the atmospheric stability in the wave field with the estimated wave parameters, the echoing layers are shown to be consistent with statically stable regions generated by the wave. It is suggested from our results that Fresnel scattering is a dominant echoing mechanism for a VHF radar beam in the mesosphere, as well as in the lower stratosphere.     

Influence of Masonry Strength and Openings on Infilled R/C Frames Under Cycling Loading

The influence of masonry infills with openings on the seismic performance of reinforced concrete (R/C) frames that were designed in accordance with modern codes provisions is investigated. Two types of masonry infills were considered that had different compressive strength but almost identical shear strength. Infills were designed so that the lateral cracking load of the solid infill is less than the available column shear resistance. Seven 1/3 – scale, single–story, single–bay frame specimens were tested under cyclic horizontal loading up to a drift level of 40%. The parameters investigated are the opening shape and the infill compressive strength. The assessment of the behavior of the frames is presented in terms of failure modes, strength, stiffness, ductility, energy dissipation capacity, and degradation from cycling. The experimental results indicate that infills with openings can significantly improve the performance of RC frames. Further, as expected, specimens with strong infills exhibited better performance than those with weak infills. For the prediction of the lateral resistance of the studied single-bay, single-story infilled frames with openings, a special plastic analysis method has been employed.     

硅酸乙酯类加固材料在潮湿环境土遗址加固保护中的应用研究

潮湿环境土遗址因含水率高、成分及所处环境复杂等特点,是文物保护工作中最难保护的文物之一,深入开展加固保护材料适用性及优化组合研究对于潮湿环境土遗址保护具有现实意义。以上海广富林文化遗址"F12房址"为对象,选取硅酸乙酯类加固材料Remmers SAE 300和SAE 300E,对其不同比例配合下的加固效果进行试验研究。通过表观形貌、渗透性、强度及抗水崩解性等指标分析,结果表明不同比例配合下的加固效果虽存在一定差异,但均能有效提高土体抗粉化能力和抑制霉菌生长,且当含水率较低时,加固作用将显著提高土体无侧向抗压强度和抗剪强度。研究结果对综合评定硅酸乙酯类加固材料在潮湿环境土遗址加固保护中的应用性有参考价值。     

潮湿环境模拟考古土遗址夯筑支顶加固效果评估

为研究潮湿环境土遗址加固效果评估方法,在杭州地区进行现场模拟探方加固实验,并对加固后坑壁的波速、含水率、相对水平位移进行监测,对加固的模拟探方稳定性做出评估,以望通过采用科学定量手段评价土遗址夯筑支顶加固效果,为土遗址夯筑支顶加固效果评估提供参考。试验结果表明:模拟探方坑壁表层含水率随深度的增加而升高,含水率变化量逐渐减小;加固后坑壁土体初始强度随深度的增加而提高,且后期硬化过程也较上部区域快,土体强度随时间在逐渐增加;夯筑后坑壁前四五天位移值逐渐增大,且位移值随深度的增加而升高,后期趋于稳定。研究表明,基于变形监测技术评估夯筑体整体稳定性科学合理,基于表层含水量和波速变化评估夯筑土体强度变化是较好的手段。评估结果可为其他潮湿地区土遗址夯筑加固效果评估方法提供参考。     

Effect of the joint type on the bearing capacity of a multi–drum column under static load

The results of an experimental study on the effect of the joints between the blocks on the ultimate bearing capacity of a multi-drum column loaded to centric vertical force and horizontal force in the middle of its height are shown. The column is approximately 2.5 m high, with one hinge at the top and another hinge at the bottom. Four types of joints between the blocks were considered: a dry joint (column C-DJ) and joints with stone powder (column C-SPJ), lead (column C-PBJ), and epoxy (column C-EPJ). The applied vertical and horizontal forces, horizontal displacement, vertical strains, and horizontal circumferential strains in the middle of the column height, as well as shortening of the column, were measured. Under axial compression, ratios between the ultimate load bearing capacities of tested columns were C-EPJ: C-DJ: C-SPJ: C-PBJ = 1: 0.68: 0.59: 0.51. The bearing capacity of the tested columns with regard to the horizontal force depended on the level of the applied centric compression force. Columns with soft joints (C-PBJ, C-SPJ) had the largest shortening and the largest horizontal displacements for the equal forces.     

故宫太和殿木构件现状分析及加固方法研究

为加强对古建筑的维修保护,故宫博物院对太和殿进行了勘查,发现如下木构件问题:西山挑檐檩跨中挠度过大;三次间正身顺梁及山面扶柁木榫头位置下沉10cm;明间藻井下垂13cm,井口爬梁已经开裂.通过运用结构力学相关方法,对这些构件的结构现状进行理论分析,研究了问题产生的原因,讨论了相应的加固方案,解决了这些问题.结果表明:西山挑檐檩虽然挠度较大,但强度满足要求,不需要加固;山面扶柁木榫头下沉的原因是局部受弯强度不足,但已通过支顶解决该问题;正身顺梁榫头下沉的可能原因是材料老化,局部受拉、弯、剪强度不足,通过采用钢木组合结构进行了加固;藻井下沉的原因是木材老化,井口爬梁抗弯及抗压承载力不足,通过采用扁钢箍加固的方法进行了加固.研究结果可为古建筑保护及修缮提供参考.     

Estimating the Seismic Performance of CFRP-Retrofitted RC Beam-Column Connections Using Fiber-Section Analysis

Over the past two decades, many experimental techniques have been developed to improve the efficiency of the externally-bonded fiber-reinforced polymers (FRPs) in order to improve the structural performance of reinforced concrete (RC) beam-column connections. Numerical analysis is also being used as a cost-effective tool to predict the experimental results and to further investigate the parameters that are beyond the scope and capacity of experimental tests. In this study, at first, a fiber-section modeling approach is developed for estimating the seismic behavior of RC beam-column connections before and after application of FRP retrofits. The accuracy of the analysis results were validated against a series of the available experimental data under both monotonic and cyclic loadings. It was pointed out that the proposed model can predict the strength and displacement of un-retrofitted and FRP-retrofitted RC beam-column connections up to the failure points. The verified model was then used to perform a parametric study pertaining to the effect of longitudinal reinforcement ratio on the efficiency of the adopted FRP retrofitting technique to improve the structural behavior of RC beam-column connections.     

水硬性石灰改性土修复加固材料性能研究

针对土遗址土体坍塌、残缺等病害,为选择更好的土遗址修复加固材料,通过遗址土中添加水硬性石灰进行改性,分析检测水硬性石灰改性土修复材料的性能,并与石灰改性土材料性能进行对比分析。研究结果表明,与石灰改性土性能相比,水硬性石灰改性土修复材料夯土收缩率小、水稳定性好、抗压强度大和强度增加快、耐冻融性好;其性能优于石灰改性土材料的性能,适合土遗址土体坍塌、残损病害的修补加固,其研究成果为土遗址的保护修复加固提供科学依据。