This paper reports the fact that an energy dissipation device (damage fuse) in its reinforced concrete (RC) frame can upgrade the ability to dissipate the energy created by earthquake excitations. When a damage fuse is applied to an RC frame, the fact that behavior such as cracking of attachment members and flexural yielding of reinforcing bars can reduce the effect of damage control should be taken into consideration, and the validity of performance evaluations of frames with a damage fuse and analysis models should be thoroughly examined in this light. Analysis models of RC frames with a damage fuse were found to effectively demonstrate the restoring force characteristics obtained from test results of horizontal loading. Several high-rise RC building projects have already chosen to use damage fuses to mini-mize serious damage to RC buildings subjected to strong earthquakes.
Major advances have been observed in the last decade in seismic engineering with further refinements of performance-based seismic design philosophies and definition of corresponding compliance criteria. Following the worldwide recognized expectation and ideal aim to provide a modern society with high seismic performance structures, able to sustain a design level earthquake with limited or negligible damage, emerging solutions have been developed for high-performance, still cost-effective, seismic resisting systems, based on adequate combination of traditional materials and available technology. In this paper, an overview of recent developments and on-going research on precast concrete buildings with jointed ductile connections, relying on the use of unbonded post-tensioned tendons with self-centering capabilities, is given. A critical discussion on the conceptual behavior, design criteria and modeling aspects is carried out along with an update on current trends in major international seismic code provisions to incorporate these emerging systems. Examples of existing on site applications based on a recently developed cable-stayed and suspended solution for frame systems are provided as further confirmation of the easy constructability and speed of erection of the overall system.
Non-linear time-history analyses on single-degree-of-freedom systems with load-displacement relations of prestressed and conventional reinforced concrete members are reported. The analytical results are used for investigating response characteristics of prestressed concrete systems and deriving substitute damping. The energy time-history of prestressed concrete systems is compared with that of reinforced concrete. The substitute damping obtained is compared with equivalent viscous damping derived directly from the load-displacement relationship of the systems. Referring to the substitute damping from the dynamic response analyses and the equivalent viscous damping from the stationary load-displacement curves, equivalent structural damping for concrete structures to be used in the capacity spectrum method is proposed.
This research is conducted to develop a model to predict the effective diffusion coefficients of substances (De) in concrete considering the spatial properties of composite materials. In this model, concrete is assumed to be composed of cement paste, an interfacial transition zone and aggregate, and the spatial properties of each material are considered with random arrangement of each material. De in concrete is calculated based on the calculation results for the cement paste and interfacial transition zone. The proposed model can appropriately evaluate De in concrete in previous research. The influence of the spatial properties of each composite material on the dispersion of De is analytically investigated. The influence of cement particle arrangement is larger than that of fine and coarse aggregate, and the lower W/C, the greater that influence. Moreover, the influence of the interfacial transition zone on chloride ion diffusivity in concrete is also analyzed. This influence was found to be quite large, so that the interfacial transition zone should be taken into account for simulating diffusion in cementitious materials. In this model, the pore structure of cement paste is very simplified. Thus, it is necessary to examine the correspondence of the modeled pore structure and the actual pore structure.
This paper aims to numerically simulate corrosion induced cracking, its propagation over sections of reinforced concrete members and the penetration of corrosive gel product into crack gaps. A coupled steel core and surrounding corrosion product are mechanically represented by a fictitious growing composite, with which the corrosive cracking initiation and subsequent propagation are simulated by 2D nonlinear crack analysis. The injection of corrosive gels into evolving cracks is substantiated in cases where corrosive cracks stably propagate such as large covers and/or comparatively small diameters of steel, and the coupled system of gel formation, migration and crack propagation is newly presented. The simulation scheme was verified through RC sections subjected to accelerated corrosion by electric current with regard to crack patterns and critical corrosion rates when cracks reach the outer surface of members.
An experimental study was carried out to investigate the behavior of high strength concrete short columns confined by circular spirals and square ties under monotonically increasing concentric compression. The test variables included volumetric ratio, spacing and yield strength of transverse reinforcement, longitudinal reinforcement ratio, lateral steel configuration, shape of cross section and concrete compressive strength. The effects of these variables on the uniaxial behavior of high strength concrete columns are presented and discussed The results indicate that more confinement is required in columns of high strength concrete than in columns of low strength concrete to achieve the desired post-peak deformability. The behavior of high strength concrete columns is characterized by the sudden spalling of concrete cover, leading to a loss of axial capacity. A comparative study of existing confinement models of high strength concrete columns was also conducted to assess their capabilities of predicting the actual test behavior. To this end, the stress-strain curves of the specimens tested in the present study were compared with the ones predicted by the various models. It is shown that Legeron & Paultre (2003) model estimates the actual experimental curves more closely as compared to the other models employed in the study.
A 3D FEM program was used to predict the punching shear failure mechanism and its strength for open sandwich slabs with studs. In the analysis, studs were modeled using link elements for shear transfer, whose constitutive model is derived from the authors' experimental studies, and truss elements for tension transfer. The results showed very good agreement between the analytical and experimental values. Punching shear failure phenomena were carefully examined in analysis observing predicted concrete cracking and concrete crushing. Based on analytical observation, a qualitative study on factors such as concrete strength, plate thickness, stud height, and stud spacing, was performed to develop an analytical expression for computing the punching shear strength of open sandwich slabs.
In this study, a model for the interface between a concrete slab and a steel plate in composite slabs with studs is developed through a bending test for composite beams. A smeared reinforcing stud model is also implemented to consider the shear-reinforcing effect of taller studs. 3D nonlinear finite element analysis using the model for the interface and the reinforcing stud model developed in this study is found to predict punching shear behavior of composite slabs.
Numerous analytical techniques, analytical theories, and analytical/design models have been proposed for the rational shear designs and shear behavior examinations of reinforced concrete beams. However, since shear design regulations in design codes are primarily based on experimental observations along with the elastic beam theory, the regulations may not accurately represent the true shear behavior of general reinforced concrete beams. Accordingly, much attention has been focused on the development of a general and consistent model or method. In this study, the strength and behavior of four reinforced concrete beams tested to shear failure were estimated using a nonlinear strut-tie model approach. Based on the strut-tie model analysis results, the validity of the nonlinear strut-tie model approach in the reasonable design of reinforced concrete beams and in the accurate examination of many shear-related failure phenomena was evaluated.
This paper reports the results of an experimental examination of the structural performance of steel structures employing a beam-column joint system with steel fiber reinforced cementitious composites. The beam-column joint was achieved by filling steel fiber reinforced cementitious composites into the gap between a U-section bracket and a middle beam. Tests consisting in the application of a cyclic shear load to simple beam specimens were performed, focusing on the effect of bracket length, the effect of fiber reinforcement and the influence of loading hysteresis. The experimental results show that the specimens with steel fiber reinforced cementitious composites offer sufficient strength and ductility without prominent damage compared with the specimens employing high strength mortar and conventional concrete.
High-rise buildings with a base isolation system have been realized by investigating the aspect of practical applicability through the identification and addressing of the difficulties involved in actual design applications. Among the base-isolated buildings we have designed so far, the Sendai MT Building is the first base-isolated building with a height exceeding 60 m in Japan, and the Thousand Tower was the tallest base-isolated residential Tower in Japan when completed. These examples show that the appropriate utilization of the base isolation system with high-strength materials and a long-span structure system makes it possible to endow high-rise buildings not only with strong seismic performance but also architectural design flexibility. This paper provides empirical evidence that the base isolation system can properly work for high-rise buildings. According to the seismic data obtained from the seismographs in the Sendai MT Building when the Off-Miyagi earthquake struck on May 26, 2003, the base isolation system of this high-rise building performed as effectively as designed.
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