Introduction of structural aseismic research in China in recent four years

The paper mainly summarized the developments on structural aseismic theory, aseismic analysis and design of reinforced concrete structure, lifeline system, several another kinds of structures, site and structure foundation, structure mitigation and isolation of vibration in China in recent four years. This is the introduction of recent re-search results of Chinese professionals for international organizations and professionals. At the same time, it provides numerous abstract materials for colleagues to realize the trend of the structural aseismic theory and re-search range needing more study.

Earthquake simulator tests and associated study of an 1/6-scale nine-story RC model

Earthquake simulator tests of a 1/6-scale nine-story reinforced concrete frame-wall model are described in the paper. The test results and associated numerical simulation are summarized and discussed. Based on the test data, a relationship between maximum inter-story drift and damage state is established. Equations of variation of structural characteristics （natural frequency and equivalent stiffness） with overall drifts are derived by data fitting, which can be used to estimate structural damage state if structural characteristics can be measured. A comparison of the analytical and experimental results show that both the commonly used equivalent beam and fiber element models can simulate the nonlinear seismic response of structures very well. Finally, conclusions associated with seismic design and damage evaluation of RC structures are presented.

A Study on the Tensile Properties of the MWK Structures for Composite Reinforcement

In this paper, the tensile properties of the MWK structures produced with different basic stitches for composite reinforcement were experimentally studied. The results show that the MWK structures with the double loop pillar stitches have better mechanical properties.

Self-centering seismic retrofit scheme for reinforced concrete frame structures:SDOF system study

This paper presents the results of a parametric study of self-centering seismic retrofit schemes for reinforced concrete (RC) frame buildings. The self-centering retrofit system features flag-shaped hysteresis and minimal residual deformation. For comparison purpose,an alternate seismic retrofit scheme that uses a bilinear-hysteresis retrofit system such as buckling-restrained braces (BRB) is also considered in this paper. The parametric study was carried out in a single-degree-of-freedom (SDOF) system framework since a multi-story building structure may be idealized as an equivalent SDOF system and investigation of the performance of this equivalent SDOF system can provide insight into the seismic response of the multi-story building. A peak-oriented hysteresis model which can consider the strength and stiffness degradation is used to describe the hysteretic behavior of RC structures. The parametric study involves two key parameters -the strength ratio and elastic stiffness ratio between the seismic retrofit system and the original RC frame. An ensemble of 172 earthquake ground motion records scaled to the design basis earthquake in California with a probability of exceedance of 10% in 50 years was constructed for the simulation-based parametric study. The effectiveness of the two seismic retrofit schemes considered in this study is evaluated in terms of peak displacement ratio,peak acceleration ratio,energy dissipation demand ratio and residual displacement ratio between the SDOF systems with and without retrofit. It is found from this parametric study that RC structures retrofitted with the self-centering retrofit scheme (SCRS) can achieve a seismic performance level comparable to the bilinear-hysteresis retrofit scheme (BHRS) in terms of peak displacement and energy dissipation demand ratio while having negligible residual displacement after earthquake.

Quantitative approach for damage detection of reinforced concrete frames

The objective of this paper is to provide an analytical basis for the quantitative evaluation of damage to a reinforced concrete structure based on the vibration data obtained by using the damage detection technique. A partial reinforced concrete system of a weak beam/strong column moment frame is chosen as an example. A pushover analysis is carried out in order to numerically examine both the story shear-relative displacement characteristics and the associated damage level. In the analysis, a two dimensional nonlinear finite element analysis is employed considering several constitutive models. As a result, the degradation of the stiffness at the damaged story is characterized in association with the story relative displacement. It is also pointed out that the rotation angle of the column-base is highly correlated with the story relative displacement. Based on the analytical findings, quantitative approaches for a structural health monitoring system are suggested considering both the current sensor technologies and those available in the future. Keywords nonlinear FEM analysis - structural health monitoring - reinforced concrete structure - story stiffness - rotation angle of column-base Supported by: Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (Base Research (c) (1), Research No. 14550555)

Effect of temperature on the compressive behavior of carbon fiber composite pyramidal truss cores sandwich panels with reinforced frames

This paper focuses on the effect of temperature on the out-of-plane compressive properties and failure mechanism of carbon fiber/epoxy composite pyramidal truss cores sandwich panels （CF/CPTSP）. CFJCPTSP with novel reinforced frames are manufactured by the water jet cutting and interlocking assembly method in this paper. The theoretical analysis is presented to predict the out-of-plane compressive stiffness and strength of CFJCPTSP at different ambient temperatures. The tests of composite sandwich panels are per- formed throughout the temperature range from -90℃ to 180℃. Good agreement is found between theo- retical predictions and experimental measurements. Experimental results indicate that the low tempera- ture increases the compressive stiffness and strength of CF/CPTSP. However, the high temperature causes the degradation of the compressive stiffness and strength. Meanwhile, the effects of temperature on the failure mode of composite sandwich panels are also observed.

Full－range nonlinear analysis of fatigue behaviors of reinforced concrete structures by finite element method

The offshore reinforced concrete structures are always subject to cyclic load, such as wave load.In this paper a new finite element analysis model is developed to analyze the stress and strain state of reinforced concrete structures including offshore concrete structures, subject to any number of the cyclic load. On the basis of the anal ysis of the experimental data,this model simplifies the number of cycles-total cyclic strain curve of concrete as three straight line segments,and it is assumed that the stress-strain curves of different cycles in each segment are the same, thus the elastoplastic analysis is only needed for the first cycle of each segment, and the stress or strain corresponding to any number of cycles can be obtained by superposition of stress or strain obtained by the above e lastoplastic analysis based on the cyclic numbers in each segment.This model spends less computer time,and can obtain the stress and strain states of the structures after any number of cycles.The endochronic-damage and ideal offshore concrete platform subject to cyclic loading are experimented and analyzed by the finite element method based on the model proposed in this paper. The results between the experiment and the finite element analysis are in good agreement,which demonstrates the validity and accuracy of the proposed model.

Premature losses of leaf area in response to drought and insect herbivory through a leaf lifespan gradient

Implications of the differences in leaf life span are still subject to debate in the field of ecophysiology.Since leaf traits associated with these differences may be decisive for determining the distribution of tree species,this topic is particularly relevant in the context of climate change.This study analyzes the effects of the differences in leaf life span on premature losses of leaf area owing to insect herbivory and to abiotic stress.Loss of leaf area may be an important determinant of total leaf carbon assimilation.Seven Mediterranean tree species,distributed on four sites with different climates were studied.The species exhibited strong differences in leaf life span and in leaf traits,especially leaf mass per unit area.Premature leaf area losses were estimated in response to insect herbivory and summer drought over two years.The results revealed that,despite having older leaf cohorts with more damage,species with longer leaf duration had lower area lost to herbivores and less damage due to accelerated senescence during the summer drought.With respect to the predicted increase in water stress,deciduous species are at a disadvantage due to their high premature loss of leaf area and thus loss of photosynthetic capacity.

Material Properties and Tensile Behaviors of Polypropylene Geogrid and Geonet for Reinforcement of Soil Structures

The properties and tensile behaviors of polypropylene (PP) geogrids and geonets for reinforcement of soil structures are investigated.Mass per unit area of the geogrids and geonets was weighed using an electronic balance and aperture sizes of the geonets were exactly measured using a computer.Laboratory tests were performed using a small tensile machine capable of monitoring tensile force and displacement.Tensile failure behaviors were described,and tensile index properties such as tensile strength,maximum tensile strain,tensile forces corresponding to different strains in the geogrids and gronets were obtained.The characterization of these indexes is discussed.

Small-scale multi-axial hybrid simulation of a shear-critical reinforced concrete frame

This study presents a numerical multi-scale simulation framework which is extended to accommodate hybrid simulation （numerical-experimental integration）. The framework is enhanced with a standardized data exchange format and connected to a generalized controller interface program which facilitates communication with various types of laboratory equipment and testing configurations. A small-scale experimental program was conducted using a six degree-of-freedom hydraulic testing equipment to verify the proposed framework and provide additional data for small-scale testing of shear- critical reinforced concrete structures. The specimens were tested in a multi-axial hybrid simulation manner under a reversed cyclic loading condition simulating earthquake forces. The physical models were 1/3.23-scale representations of a beam and two columns. A mixed-type modelling technique was employed to analyze the remainder of the structures. The hybrid simulation results were compared against those obtained from a large-scale test and finite element analyses. The study found that if precautions are taken in preparing model materials and if the shear-related mechanisms are accurately considered in the numerical model, small-scale hybrid simulations can adequately simulate the behaviour of shear-critical structures. Although the findings of the study are promising, to draw general conclusions additional test data are required.

Advance in Researches on Bond Behavior for Steel-Corroded Concrete Members

The steel corrosion in concrete is widely reported over the last two to three decades. Much effort has been devoted to researching the causes and mechanisms of reinforcement corrosion and to the questions of durability for concrete structures, but relatively little attention has been devoted to the problem of assessing the effect of bond loss due to corrosion on the structural behavior of corroded elements. From the test results on corroded specimens, the mechanism of degradation in bond behavior between corroded bars and concrete, and the effects of bond loss on structural performances are summarized. Results show that corrosion level, cover depth-W-bar diameter ratio, surface condition of re/nforcement, stirrups, etc. can influence the bond behavior of corroded bars. In addition, the deterioration in bond due to corrosion may induce reduction in bearing capacity, degradation of serviceability, and the loss in ductility for steel-corroded concrete members.

Influence of the column-to-beam flexural strength ratio on the failure mode of beam-column connections in RC frames

The column-to-beam flexural strength ratio(CBFSR)has been used in many seismic codes to achieve the strong column-weak beam(SCWB)failure mode in reinforced concrete(RC)frames,in which plastic hinges appear earlier in beams than in columns.However,seismic investigations show that the required limit of CBFSR in seismic codes usually cannot achieve the SCWB failure mode under strong earthquakes.This study investigates the failure modes of RC frames with different CBFSRs.Nine typical three-story RC frame models with different CBFSRs are designed in accordance with Chinese seismic codes.The seismic responses and failure modes of the frames are investigated through time-history analyses using 100 ground motion records.The results show that the required limit of the CBFSR that guarantees the SCWB failure mode depends on the beam-column connection type and the seismic intensity,and different types of beam-column connections exhibit different failure modes even though they are designed with the same CBFSR.Recommended CBFSRs are proposed for achieving the designed SCWB failure mode for different types of connections in RC frames under different seismic intensities.These results may provide some reference for further revisions of the SCWB design criterion in Chinese seismic codes.

Evaluation of ground motion parameters and seismic response of reinforced concrete buildings from the Mw 6.9,2011 Sikkim earthquake

The continuous collision of the Eurasian plate and the Indian plate has resulted in several earthquakes in the Himalayan region.The 6.9 Mw 2011 Sikkim earthquake,which caused immense damage to the built environment in Sikkim,was triggered by an intraplate source on the overriding Eurasian plate.Strong ground motions from the earthquake were recorded at stations established by IIT Roorkee as part of the PESMOS program.In this paper,near-field and far-field ground motions from this earthquake were analyzed to evaluate their key characteristics and examine their time-frequency features by employing Fast Fourier Transforms(FFTs)and Continuous Wavelet Transforms(CWTs).A comparison between the ground motion parameters of near-field and far-field seismic waves highlights the distinct characteristics of near-field ground motions.Additionally,the impact of near-field and far-field ground motions on the seismic response of a code-compliant RC building is investigated.The results from the non-linear time history analyses indicate that the roof displacements,drift ratio and strain induced in the frame elements are less than the code-prescribed maximum limits.Further,the demand and capacity levels for the RC frame elements were evaluated to compute the performance ratios.The results indicate that the extensive damage to reinforced concrete buildings in the 2011 Sikkim quake was primarily due to the nonengineered nature of the structures and also due to the non-compliance of the built structures to the seismic design code provisions.

Fe_(2)O_(3)-MWNTs Composite with Reinforced Concrete Structure as High-performance Anode Material for Lithium-ion Batteries

A Fe_(2)O_(3)-MWNTs(multi-walled carbon nanotubes)composite with a reinforced concrete structure was fabricated employing a two-step method which involves a sol-gel process followed by high-temperature in situ sintering.This Fe_(2)O_(3)-MWNTs composite,intended to be used as an anode material for lithium-ion batteries,maintained a reversible capacity as high as 896.3 mA·h/g after 100 cycles at a current density of 100 mA/g and the initial coulombic efficiency reached 75.5%.The rate capabilities of the Fe_(2)O_(3)-MWNTs composite,evaluated using the ratios of capacity at 100,200,500,1000,2000 and 100 mA/g after every 10 cycles,were determined to be 904.7,852.1,759.0,653.8,566.8 and 866.3 mA·h/g,respectively.Such a superior electrochemical performance of the Fe_(2)O_(3)-MWNTs composite is mainly attributed to the reinforced concrete construction,in which the MWNTs function as the skeleton and conductive network.Such a structure contributes to shortening the transport pathways for both Li+and electrons,enhancing conductivity and accommodating volume expansion during prolonged cycling.This Fe_(2)O_(3)-MWNTs composite with the designed structure is a promising anode material for high-performance lithium-ion batteries.

Effects of Temperature Variations on Safety of Reinforced Concrete Structures During Construction

Since 1960s, many research works on the reinforced concrete structure have been published and some concise and practical calculation methods for safety control during construction have been achieved. The reinforced concrete structure during construction is a time-dependent structure which consists of a partly completed structure and a formwork-shore system. Experience shows that the most critical condition of the time-dependent structure may happen when the formwork-shore system is partly removed or reset and accidents may occur. In the present paper, effect of ambient temperature variation between day and night is considered, new structural models for reinforced concrete frames, slab-column systems and shear wall structures are proposed, and a new software named Safety Analysis During Construction Considering Temperature(SACT) is also introduced. Compared with on-site measurements, the software SACT is validated for application on construction site.