Resilient Cities and Structures最新文献

Highly ductile cement-based materials have emerged as alternatives to conventional concrete materials to improve the seismic resistance of reinforced concrete (RC) structures. While experimental and numerical research on the behavior of individual components has provided significant knowledge on element-level response, relatively little is known about how ductile cement-based materials influence system-level behavior in seismic applications. This study uses recently developed lumped-plasticity models to simulate the unique failure characteristics and ductility of reinforced ductile-cement-based materials in beam hinges and applies them in the assessment of archetype frame structures. Numerous story heights (four, eight, and twelve), frame configurations (perimeter vs. space), materials (conventional vs. ductile concrete), and replacement mechanisms within the beam hinges are considered in the seismic analysis of the archetype structures. Results and comparisons are made in terms of the probability of collapse at 2% in 50-year ground motion, mean annual frequency of collapse, and adjusted collapse margin ratio (ACMR) across archetype structures. The results show that engineered HPFRCCs in beam plastic-hinge regions can improve the seismic safety of moment frame buildings with higher collapse margin ratios, lower probability of collapse, and the ability to withstand large deformations. Data is also reported on how ductile concrete materials can reduce concrete volume and longitudinal reinforcement tonnage across frame configurations and story heights while maintaining or improving seismic resistance of the structural system. Results demonstrate future research needs to assess life-cycle costs, predict column hinge behavior, and develop code-based design methods for structural systems using highly ductile concrete materials.

A 9 m high, near full scale three-storey configurable steel frame composite floor building incorporating friction-based connections is to be tested using two linked bi-directional shake tables at the International joint research Laboratory of Earthquake Engineering (ILEE) facilities, Shanghai, China, as part of the RObust BUilding SysTem (ROBUST) project. A total of nine structural configurations are designed and detailed. To have a better understanding of the expected system behaviour, as well as effects of other structural and non-structural elements (NSEs) on the overall system response, experimental testing at component level has been conducted prior to the shake table testing. This paper presents an introduction to the ROBUST project, followed by a numerical study on one of the nine configurations of the structure, having Moment Resisting Steel Frame (MRSF) in the longitudinal direction and Concentrically Braced Frame (CBF) in the transverse direction. Hysteretic properties employed in the numerical models are validated against component test results. The predictions of the building's seismic response under selected base excitations are presented indicating the likely low damage performance of the structure.

This paper proposes the novel concept of retrofitting damaged reinforced concrete frame with self-centering and energy-dissipating rocking wall. Parametric studies were carried out base on pushover and time-history analysis. In both pushover and time-history analysis, the soft-story mechanism was effectively mitigated through the rocking wall retrofit of the damaged structures. The results demonstrated that the stiffness and bearing capacity of the retrofitted system were improved compare to its intact state. Additionally, the seismic response of the damaged frame retrofitted using rocking wall in combination with post-tension and shear-type damper fell within the relevant design limits. Pushover analysis of the rocking wall indicated that there is a linear relationship between the wall thickness and the initial stiffness of the retrofitted system. The addition of post-tension tendon to the rocking wall system enables the wall to self-center and increases lateral stiffness and bearing capacity of the retrofitted system. When the shear-type damper was installed, the energy dissipation of the system was increased, and the stiffness and bearing capacity of the retrofitted system were also improved. In the time-history analysis, it was found that the thickness of the rocking wall is directly related to the maximum inter-story drift and the distribution patterns of inter-story drift of the frame. As the post-tension was added to the system, the maximum inter-story drift under rare earthquake excitation improved significantly. With the addition of shear-type dampers, the overall drift magnitude of the retrofitted system was fundamentally decreased.

Slender RC walls are used commonly in mid- and high-rise buildings to resist lateral loads arising from earthquakes and wind forces. To accommodate architectural constraints, facilitate construction, and maximize structural efficiency, the majority of these walls have complex configurations, comprising planar and non-planar wall elements that often include regular or irregular patterns of openings. To date most laboratory testing of slender RC walls has employed wall specimens with relatively simple configurations and without openings and coupling action which provides only limited understanding of the impact on performance of the variations in configuration and reinforcement detailing observed in real-world construction.

This study presents a 3D continuum modeling approach to improve understanding of the behavior of walls with complex configurations and support recommendations for design of these systems. Planar wall data were used to calibrate the continuum-type modeling approach; experimental data characterizing the response of non-planar walls and walls with openings are used to validate the model.

The resilience index based on the integral of functionality/performance function within a time interval of interest has been widely used in the literature. However, it cannot fully reflect the sensitivity of the resilience of the object (e.g., structure or system) to the variation of functionality. In this paper, a generalized index is proposed to measure the resilience of structures and systems that is sensitive to the instantaneous functionality, as reflected by a generating function involved in the proposed resilience index. The mathematical properties of the proposed resilience model are discussed. It is proven that, the proposed index varies within [0,1], and is a monotone measure. If the generating function is a power function with $\alpha$ being the exponent (called $\alpha$-fairness function), the additivity property (i.e., superadditivity, additivity, and subadditivity) of the resilience index is dependent on the value of $\alpha$. It is also observed that the existing resilience index is a special case of the proposed one. A byproduct is that, with a properly selected generating function, the time-dependent reliability problem of an aging structure can also be described by the proposed resilience index. The applicability of the proposed resilience model is demonstrated through four examples.

Traditional retrofit methods often focus on increasing the structure's strength, stiffness, or both. This may increase seismic demand on the structure and could lead to irreparable damage during a seismic event. This paper presents a retrofit method, integrating concepts of selective weakening and self-centering (rocking) to achieve low seismic damage for non-code compliant reinforced concrete shear walls. The proposed method involves converting traditional cast-in-place concrete shear walls into rocking walls, which helps to lower the shear demand, while allowing re-centering. Two large-scale lateral load tests were performed to validate the retrofit concept on a concrete shear wall designed according to pre-1970s standards. The design parameters investigated were amount of energy dissipating reinforcements and confinement enhancement. Two different methods using Ultra High Performance Concrete (UHPC) were investigated to provide additional confinement to boundary elements of older shear walls. Observations from the tests showed minimized damage and enhanced recentering in the retrofitted wall specimens. Use of UHPC in the boundary elements of the retrofitted walls provided additional confinement and reduced damage in the rocking corners.

Use of indices that quantify the seismic residual capacity of buildings damaged in earthquakes is one way to draw judgements on the building's safety and possibility of future use. In Japanese damage assessment guidelines, several approximate calculation methods exist to evaluate the residual capacity of buildings based on visually observed damage and simplifying assumptions on the nature of the building's response mechanism and member capacities. While these methods provide a useful residual capacity ratio that enables a ‘relative’ comparison between buildings, the exact relationship to a physically meaningful residual capacity is unclear. The aim of this study is to benchmark the ‘approximations’ of residual capacity. To do so, a shake-table test was conducted on a ¼ scale 4-storey RC structure and a residual capacity evaluation was undertaken based on observed damage states. With the help of a numerical model, a benchmark residual capacity at each of the damage states is determined and compared to the approximate residual capacity calculation results via guidelines. It was found that approximate methods are generally accurate prior to yield but can become overly conservative post-yield. Simplifying assumptions of equal member deformation capacity used in the residual capacity ratio calculation was found to be suitable given constraints of rapid field evaluations.

This paper studies the behavior of a reinforced concrete (RC) structural frame employing a tessellated structural-architectural (TeSA) shear wall as the lateral-load resisting element. TeSA walls are made of interlocking modules (tiles) that provide easier repairability and replaceability. A nonlinear finite element model of a TeSA wall with tiles interlocking in one direction (1-D interlocking) is validated using test data. An RC frame from a building is modeled with a 1-D interlocking TeSA shear wall. The effects of varying rigidity of the wall-frame connections (rigid, hinged, slotted) on the lateral strength of the system and the axial load demands of the gravity-load resisting systems are evaluated. Finally, the effect of connection details on the damage of the TeSA wall is also studied. The study shows that the lateral strength of the system is the highest with a rigid connection between the wall and the system, followed by the system with hinged connections. Slotted connections, which provided no vertical coupling between the wall and the frame result in the lowest lateral strength. TeSA wall experienced “slight damage” up to a drift ratio of 2%. The system with rigid connections between the wall and the frame experienced the most damage, followed by system with hinged and slotted connections.

This paper presents a simple and practical structural connection able to develop predetermined discrete variable friction forces at target design displacement levels. The innovative connection is termed Modified Friction Device (Modified FD). Modified FDs are used to transfer the seismic induced horizontal forces from the floors to the core wall seismic force-resisting system of a building. The schematics of the physical embodiment of the Modified FD are presented. The components and the assembly of the Modified FD are discussed. The mechanics of the Modified FD are explained. Results from static structural analyses of two types of finite element models of the Modified FD are presented. The first model is developed using solid finite elements and it is used to assess the expected kinematics and the expected force-displacement response of the Modified FD. The second model is developed using a truss finite element and it can be used to efficiently simulate the force-displacement response of the Modified FD in numerical earthquake simulations of structural systems. The force-displacement response of the Modified FD computed using a numerical earthquake simulation of an eighteen-story reinforced concrete core wall building model is presented. The seismic response of the building model with Modified FDs is compared with the seismic response of the building model with monolithic connections and the seismic response of the building model with friction devices with constant friction forces. The results presented in this paper show that it is possible to develop a simple and practical structural connection with predetermined discrete variable force-displacement response to limit the seismic induced horizontal forces transferred between the floors of the flexible gravity load resisting system and the core wall piers in high-performance earthquake resilient buildings.