PDF superior A fatigue damage model for seismic response of RC structures

Among the different possi- bilities existing in the literature, it is very clear that models developed along the lines of continuum damage mechanics are more consistent with the definit[r]

This paper investigates the seismic performance of reinforced concrete (RC) moment resisting frame structures designed according to current codes and located in medium seismicity regions. To this end, a series of experimental and analytical studies are conducted on representative prototypes. First, several prototype buildings are designed and from one of them, a portion of the structure with one bay and a half, and one story and a half is selected. By applying scaling factors of 2/5, 1 and 1, for geometry, stress and acceleration, respectively, a test structure is defined. The test structure is constructed and tested with the 3x3m 2 shaking table of the Laboratory of Dynamics at the University of Granada. It is subjected to several seismic simulations of increasing intensity up to collapse. Results from these tests are used to validate/modify empirical equations proposed in the literature for predicting relevant aspects of the capacity of this type of structures such as the ultimate rotation of the plastic hinges. Second, several numerical models are developed and calibrated with the results from shake table tests. Third, nonlinear time history analysis are performed to evaluate the system seismic response. Finally, a probabilistic methodology is used that takes into account inherent uncertainties in the ground motion, computer models, and damage estimates. As a result of this research a quantitative and qualitative basis is provided for the assessment of the seismic performance under the design earthquake of a good deal of recent low-rise buildings constructed in Mediterranean countries in the last decade. Results serve to compute damage and loss analysis in the building components.

For low levels of seismic hazard, for which the structure is designed to perform basically in the elastic range (with minor damage), accidental eccentricity increases the lateral displ[r]

From the simplified model proposed by Flórez-López, it is the purpose of this paper to present a formulation that allows to take into account the degradation produced not only by the peak values but also by the cumulative effects such as the low cycle fatigue. For it, the classical damage dissipative potential based on the concept of damage energy release rate is modified using a fatigue function in order to include cumulative effects. The fatigue function is determined through parameters such as the cumulative rotation and the total rotation and the number of cycles to failure. Those parameters can be measured or identified physically through the characteristics of the RC. So the main advantage of the proposed model is the possibility of simulating the low cycle fatigue behavior without introducing parameters with no suitable physical meaning. The good performance of the proposed model is shown through a comparison between numerical and test results under cycling loading

Conventional seismic design codes allow for structures to be designed in such a way that the forces induced during strong earthquakes may exceed the elastic capacity of the building. This inelastic behavior is the mechanism through which typical constructions dissipate energy, and although it achieves the principal objective of avoiding collapse, it can ultimately lead to heavy structural damage that may be as expensive to repair as to replace a collapsed structure (Pall and Marsh, 1982). Two of the preferred lateral force resisting configurations for steel frames are the moment-resisting frames (MRF) and the braced moment-resisting (BMR) frames (Pall and Marsh, 1982). Damage observed in the 1994 Northridge earthquake (M w = 6.7), however, questioned the ability of these types of

approaches is limited due to the requirement for calibration at the structural scale. Approaches based on FKT where the fiber rotation and shear nonlinearity are carefully modeled provide an appealing alternative. Basu et al. (2006) formulated one such model using Schapery theory (Schapery, 1990) and tracking the misaligned fiber direction by integrating the increment in shear strain. Good agreement for strength as predicted by a 2-D model similar to that of Kyriakides et al. (1995) was achieved. Feld et al. (2012) proposed augmenting an existing CDM model with an additional term based on a rheological model to account for fiber kinking. Davidson and Waas (2017) used Hill’s anisotropic plasticity to model out-of-plane kinking. By introducing thin regions representing resin-rich layers between the plies, predictions with β > 0 were obtained. Bergan and Leone (2016) proposed a model based on fiber kinking theory that uses the deformation gradient decomposition (DGD) method to account for the coupling between longitudinal splitting and fiber kinking. The model predictions show that large rotations and shear nonlinearity dominate the response. Likewise, Gutkin and Pinho (2015), Gutkin et al. (2016) and Costa et al. (2017) introduced a model based on fiber kinking theory and a physically- based constitutive law for shear nonlinearity. The authors demonstrated that the model is capable of predicting the compression strength and residual stress. These methods are attractive since they are physically based on the mechanics of fiber kinking, while avoiding the complications of high order theories. The mesoscale model presented herein adopts this approach.

To obtain the geometrical parameters of the structure, we performed an exhaustive study of several TEM images using the ImageJ software [14] together with a statistical analysis. Each pixel in the TEM images can be assigned a dimensionless integer value in a gray scale from 0 (black) to 255 (white). Using the ImageJ software, the images were binarized, i.e., white or black colour was assigned to each pixel to identify and separate the air bubbles from the background. Then, we calculated the area and the position of the bubble regions in the analyzed images. In Fig. 3 a) we show an histogram of the air holes areas, from which the mean value of a single bubble area and its standard deviation results to be 23400 ± 7300 nm 2 .

In isolated buildings that are on soil type S3 and in seismic zone 4, maximum displacement values are obtained. This implies the use of flexible connections; in addition in some cases these displacements cause that there is a smaller usable area of the building. One alternative to reduce these displacements is the use of Supplementary Viscous Dampers in the base of isolated building which adds damping to isolation system. In this research, a mathematical model of a 5-story building with elastomeric isolators, located in seismic zone 4 and soil type S3 was evaluated. This model was then analyzed with Supplementary Viscous Dampers, considering 5 different conditions of critical damping ratio: 15%, 30%, 45%, 60% and 75%. For all analyzes, 7 time-history records compatible with Peruvian seismicity were used. Displacement reductions of isolated base were obtained up to 30% of its initial value. The variation of responses (Accelerations, Drifts, Shear Forces, and Dissipated Energy) was analyzed as a function of the damping increasing. It was verified that the Peruvian seismicity combination of isolators and dampers tends to increase the responses of the superstructure.

The standard finite element modelling is designed for continuous, singularity free problems; its application in fracture mechanics is limited due to the discontinuity introduced by the crack and the singularity in the crack tip. Some works tried to solve the problem with a special mesh distribution, where the discontinuity must align with the edge of the elements and a high mesh refinement must be performed in the zone near the discontinuity. It was proved that the problem can be solved for simple geometries and non complex load conditions [36]. In the standard finite element method, it is necessary to perform a remeshing every time the crack grows, causing high preprocessing times and computational requirements.

One of the most actives research centers in the world is the Riso National Laboratory. Lading et al. from this laboratory, have been working on FOS-based SHM systems for blades. By comparing the strains at several points gathered from FBGs the authors were able to detect some damages during laboratory tests and certification tests of some blades. Sorensen et al. also from this laboratory, pre- sented a very complete review of the fundamentals for remote structural health monitoring of wind turbine blades. Schroeder et al. reported that an FBG measurement system is currently monitoring a 53 m long rotor blade of a 4 . 5 MW wind turbine in a wind park at Wilhelmshaven, Germany. The strains are calculated for all the sensors and a complete strain spectra is obtained for the whole blade in real time. Data is transmitted to a ground station via bluethooth wireless interface. The purpose of the system is to monitor anomalies in the operation loads but not assess the damage oc- currence. Min and Hwang presented a methodology for the online strain measurement of rotating blades by using FBGs and a rotary coupler. The strains at five different locations in each one of the three blades of a small scale wind turbine were measured in real time. They probed the feasibility of the methodology proposed to measuring in real time the strains in a rotating blade. However, non damage detection or monitoring technique was presented in the related article. Kim et al. ex- perimentally validated the strain distribution in a wind turbine blade for evaluating stress levels by using FBGs and a rotating coupler. Strain distributions were obtained in terms of mean strain and strain amplitude. Measured strains were then directly compared with analytical ones. Park et al. reported the development of a wireless real-time monitoring system based on FBGs which have been tested in a 2 MW turbine since January of 2009 at Taebaek, South Korea. The system is based on modal analysis of the strain responses measured from the FBGs embedded in the blades. Only a FTT-based technique is reported for data processing (modal analysis).

populations. First, climate change is causing and will continue to cause changes in rainfall patterns across the world such as a global decrease of precipitations and desertification. These changes are predicted for both mountain and valley areas and a consequent increase of seasonal droughts in these environments is expected (IPCC, 2012). On the other hand, several human- driven changes, such as biological invasions, fragmentation and habitat loss will cause a decrease in pollinator populations as well as a decoupling of distribution ranges and phenology between pollinators and plants, all of which causes a decrease in pollinator availability on plant habitats (Leimu et al., 2010; Eckert et al., 2010). The combination of these two threats implies that, in many self-compatible species, selfing frequency will increase (Hauser & Loeschcke, 1996; Reed et al., 2012), and the consequences of this change may alter the balance between positive and negative effect of inbreeding in the face of new climatic extremes such as increasing aridity. In this context, to assess the interplay between these two different threats imposed by global change in plant populations might allow better understanding how animal pollinated plants will respond to future environmental changes.

Figure 7 displays a comparison of acceleration time histories obtained applying both loadings at the same sensor location (number 8), together with a portion of the one recorded during the test. In this test there were 30 jumpers and the main jumping frequency was set to 2 Hz. As expected, predictions based on SCI P354 become periodic after a few seconds, while Sim's load model leads to a variable pattern, which is closer to the experimental record. It is also interesting to point out that neither load model is able to reproduce the highest amplitude spikes in the experimental record, since the latter are associated to high frequency pulses acting during very short time intervals.

The micromechanical model, developed by Gurson-Tvergaard-Needleman (GTN) has been used, because it allows the different stages of ductile fracture, namely (nucleation, growth and coalescence of microvoids) to be recorded and distinguished by means of different damage constitutive parameters. The original Gurson model [8,9] considered a damaged material as a continuum medium with a different constitutive equation that includes a damage parameter called porosity f , which may vary from zero for undamaged material to one for completely damaged material.

In this research, as shown in Figure 2, we consider applying the dynamic pulley damper system to a high- rise condominium consisting of a surrounding frame (housing part) and a core part (parking tower). The surrounding frame and the core part are connected by a wire through pulleys and a damper device is installed at the top of the core. The movable pulleys amplify the relative displacement of two structures, and the damper moves largely to dissipate energy to reduce the vibration of the surrounding frame.

This paper summarizes the work developed in order to establish a framework for seismic retrofitting of bridges. In this context, the first objetive is to find a numerical model to evaluate the damage induced in a structure, under seismic action, as an index of its vulnerability. The model used has the advantage that is based on concepts of fracture mechanics and concentrated plasticity. As a result, the work is based on basic principles. The performance of this model is being evaluated. Some results of the computer program developed for this pourpose are shown.

The level of damage expected in RC frames with wide beams subjected to the recent Lorca earthquake (Spain) on May 11th, 2011, was investigated numerically using an energy-based seismic[r]

Keywords: Fracture mechanics; Damage mechanics; Reinforced concrete building; Damage index; Seismic damage analysis; Lumped plasticity models1. Introduction.[r]

In general, the results shown the good behavior of this type of structures against an earth- quake both by its own design and by thickness adopted for the constructive elements. This ques- tion is clearly demonstrated by its survival today even having been exposed to high-intensity earthquakes that have affected them throughout its history. Even so, a good maintenance pro- gram and the adoption of specific reinforcement measures on futures intervention processes is revealed as crucial to eliminate the punctual weaknesses the typology has shown during the analysis process.

HONDA: Fatigue Damage of Metals Under Varying Stress. Amplitude[r]

Biomarkers are useful tools for assessing and monito- ring health, training status and performance. As there is some controversy in the literature, depending on the pro- cess to be monitored, a combination of biomarkers could be useful. However, controversy exists regarding which parameters are most relevant for monitoring fatigue. The most researched and applied to muscle fatigue are cor- tisol, lactate and IL-6. Also gaining increasingly more importance is the measurement of ammonia, leukocytes and oxidative stress parameters. The biomarkers of muscle fatigue could be a prognostic tool to identifying subjects who are at increased risk of poor adaptation to training. Exercise, in particular, has a major influence on the most widely used inflammatory biomarkers, inclu- ding C-reactive protein and interleukin-6. Additionally to biochemical biomarkers, the measurement of physi- cal fitness components should be included in order to monitor progress and adaptation to training, as fitness is considered one of the most important markers of health.