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.     

Strength,Toughness and Thermal Shock Resistance of Ancient Ceramics,and Their Influence On Technological Choice

The basic underlying theory for the strength, toughness and thermal shock resistance of brittle multiphase clay ceramics, together with the measurement procedures to determine these parameters, are first outlined. Published experimental data obtained for test bars containing different types of temper and fired to a range of temperatures are then compared both with theoretical predictions and between themselves. The results confirm that to produce pottery with high strength requires high firing temperatures and low temper concentrations. Conversely, to produce pottery with high toughness and thermal shock resistance requires low firing temperatures and high temper concentrations, with platy or fibrous temper being most effective. There is no convincing published evidence that strength and toughness requirements were a significant factor in determining the technological choices (clay type, temper type and concentration, and firing temperature) in the production of pottery used as containers for transport and storage. In contrast, the routine use of high temper concentrations and low firing temperatures in the production of cooking pots suggests that the requirement for high thermal shock resistance was a factor that at least influenced technological choice in this case. In addition, there is some evidence that limestone and shell were, on occasions, deliberately chosen as temper in cooking pots. The need to take into account the crucial role that the full range of environmental, technological, economic, social, political and ideological factors have in influencing technological choice is also emphasized. This review highlights the fact that our current understanding of the factors determining strength, toughness and thermal shock resistance of clay ceramics is still far from complete. Further systematic measurements of these parameters, together with the establishment of a systematic database of the range of technological choices associated with the production of cooking pots, are therefore to be encouraged.     

Strength Hierarchy at Reinforced Concrete Beam-Column Joints and Global Capacity

Strength hierarchy assessment is a method that can be utilized to identify the weakest structural element at a reinforced concrete (RC) beam-column joint. The method was extensively used in various research activities at the University of Canterbury, which mainly involved beam-column joint subassembly tests. However, this method required improvements and refinements in order to be adopted in multi-story building applications. In this paper, the improvements made to the method are reported. In the improved method, capacity of the weakest element at every beam-column joint in an RC frame building can be related to the corresponding global base shear demand. The method has been illustrated via two example applications: an RC frame lacking joint shear reinforcement and a modern RC frame with adequate joint shear reinforcement. The case study examples confirmed the accuracy and the effectiveness of the method.     

Inelastic Displacement Demand of Strength-Degraded Structures

This article presents findings from parametric studies involving nonlinear time-history analyses of inelastic systems with and without strength degradation. Results showed that estimates based on the equal-displacement and equal-energy propositions can be exceeded significantly by the inelastic displacement demands in the acceleration and velocity-sensitive regions of the response spectrum. The displacement demand behaviour is sensitive to the strength degradation and the frequency properties of the ground shaking. With a modest strength reduction factor of 2, the inelastic displacement demand would typically be constrained by the Peak Displacement Demand as indicated on the elastic displacement response spectrum for 5% damping.     

Ductility of a Structural Wall with Spread Rebars Tested in Full Scale

The experimental work focuses on the ductility of the reinforced concrete (RC) seismic structural walls in buildings of mid-rise height. A full-scale five-story structural wall was tested to obtain results, still scarce in literature, without the influence of size effect. An unusual detailing with large diameter longitudinal rebars uniformly distributed in the wall length was adopted to prevent premature web rebar fracture and shear sliding. The plastic hinge length and deformations were evaluated in detail. The results show the high ductility of the wall that reached a total drift of 2.5%, larger than those usually required in design.     

Modification of Ductility Reduction Factor for Strength Eccentric Structures Subjected to Pulse-Like Ground Motions

This article investigates the ductility reduction factors for RC eccentric frame structures subjected to pulse-like ground motions. The structural models are with the strength eccentricities which are much disadvantageous than the stiffness eccentricities during the inelastic response range. A method to determine the ductility reduction factors of the strength eccentric structures is suggested by modifying those of reference symmetric structures through an eccentricity modification factor. The four factors of strength eccentricity ratio, ductility ratio, story number and velocity pulse of ground motions, are investigated to gain insight into this modification factor. It shows that the ductility reduction factors of the eccentric structures are clearly smaller than those of the symmetric structures. The eccentricity modification factor is mainly affected by the strength eccentricity and the ductility ratio, decreasing with the increment of the eccentricity or the decrement of the ductility ratio in a medium eccentricity range. The earthquake pulse-like effect and the eccentricity have coupling influence on the modification factor, while the effect of story number is not apparent. Based on the results of a comprehensive statistical study a simplified expression is suggested, which can estimate the eccentricity modification factors for both pulse-like and nonpulse-like ground motion cases.     

Design Principles for Minimum Torsional Response of Wall-Frame Concrete Structures

A seismic design procedure is described incorporating the well-accepted property that the stiffness of reinforced concrete elements is strength dependent and the requirement that the method of assigning strength to elements should be aiming at minimum torsional phenomena. Such a response allows a direct comparison with the findings of a static nonlinear analysis, which may provide the limits of story drifts and the induced plastic rotations in potential plastic hinges. The requirement of a practically translational response implies that the element strength assignment should be based on planar considerations and the initially elastic response should be of minimum torsion.     

Design of Passive Viscous Fluid Control Systems for Nonlinear Structures Based on Active Control

A practical procedure is developed for the design of passive control systems using viscous fluid dampers for nonlinear structures. The design methodology takes advantage of the modification of the damping, strength, and stiffness properties of the structure to achieve the desired relative displacement and absolute acceleration response. For this purpose, a study of poles in the complex plane is used to determine the required changes in the dynamic properties of nonlinear structures. Furthermore, a relatively simple relation between the ductility demands of highly damped single- and multiple-degree-of-freedom (SDF and MDF respectively) systems is established to reduce the computational burden of the proposed design method.     

土遗址裂隙注浆材料PS-(C+F)与SH-(C+F)性能对比研究

西北干旱、半干旱地区保存有大量的土遗址,裂隙、淘蚀、洞穴、冲沟、坍塌等一系列病害对遗址的破坏作用明显。就裂隙注浆材料而言,本研究基于PS-(C+F)的成功应用,为使注浆材料多元化,对比研究SH-(C+F)浆液作为注浆材料的适用性。通过室内对两种材料的力学性能、水理性质、抗冻性、抗老化性的比较以及现场对裂隙加固效果的检测,最终分析数据得出结论,SH-(C+F)与PS-(C+F)的力学性能相当,但SH-(C+F)的抗渗性、抗崩解性、抗冻性、抗老化性等略好一些。因此,SH-(C+F)浆液适宜作为注浆材料应用于土遗址裂隙加固中。试验结果对西北地区土遗址裂隙加固材料的多元化有重要的参考意义和指导作用。