Jun Teng

Exploratory study on water seepage monitoring of concrete structures using piezoceramic based smart aggregates

The technology of piezoceramic based smart aggregates (SAs) has demonstrated its potential in the comprehensive monitoring of concrete structures. However, its usage in the moisture monitoring of concrete structures has not yet been explored. In this research, SA transducers are used to detect the degree of water infiltration in concrete components and an active sensing method is proposed for moisture monitoring. For experimental study and verification, two short plain concrete columns, with embedded SAs, were fabricated, and an apparatus was developed to perform moisture monitoring of these two columns under different moisture conditions. Data were analyzed to study the relationship between the depth of water seepage and the sensing indicators of receiving signals. Experimental results show that the sensing indicators are very sensitive to the degree of water infiltration inside the column. These sensing indicators show a decreasing trend with increasing depth of water seepage, and this leads to the promising conclusion that these parameters can be used as evaluation indices for the water seepage monitoring of concrete structures.

Improving the damping ability by the addition of Nano SiO2 to the concrete materials

Damping in structures is commonly provided by viscoelastic nonstructural materials. Due to the large volume of structural materials in a structure, the contribution of a structural material to damping can be substantial. In this paper, the experimental investigation on damping ability of concrete materials and its members with Nana SiO2 was carried out by the method of 3-point bending beam damping measurement and cantilever beam free vibration respectively. The microstructure of concrete mix with Nano SiO2 was observed by XRD and SEM, then damping mechanism was discussed. The experimental results show that the damping reinforced effect achieved best with the 4% mixture ratio of Nana SiO2, but the optimal adulteration quantity of Nano SiO2 was 3% of cement weight by the comprehensive consideration of cost, workability, strength and dynamic properties. Nano materials as a mixture increase interfaces, and the non-uniform stress distribution under external force improves frictional damping energy consumption ability of concrete. The experimental results on the damping ratio and the loss tangent of the concrete materials with Nano materials are consistent.

Monitoring for Large Cross-Section CFSTs of a Super High-Rise Building with Piezoceramic Actuators and Sensors

As a typical composite structural type, concrete-Filled Steel Tubes (CFSTs) have been widely employed in civil engineering structures, especially in super high-rise buildings because of their enhanced load-carrying capacity and ductility. The uniformity and quality of the on-site cast concrete within the tube and the interface bonding performance between the steel tube and the concrete have received extensive attention. In this paper, Piezoelectric ceramic materials, such as Lead Zirconate Titanate (PZT) and a kind of functional smart aggregate (SA) based on PZT together are employed to evaluate the concrete quality and the bonding performance of CFST columns of a super high-rise building with a design height over 400 meters and with large cross-section CFST columns. Based on the wavelet packet analysis on the measurements of the PZT sensors, results show that no obvious damage and defect is detected and the concrete qualify and the interface of large cross-section CFST columns of this super high-rise building are in good condition. The proposed monitoring technology has great potential to be applied to practical engineering.

Seismic Performance Research of High-Rise Diagrid Tube-Core Tube Structures

Diagrid tube structure system has advantages on constructing high-rise buildings due to its great stiffness, however, its seismic performance analysis are limited. 10 CFST diagrid tube-concrete core tube structures are analyzed by Mode-Pushover method using Perform-3D program. The plasticity developing process and components yield order are summarized. The force distribution between diagrid and core tubes is researched and the force redistribution reason is explained from the change of diagrid tube forces. The structure lateral stiffness degradation is discussed based on the developing process of diagrid and core tubes lateral stiffness. The influences of main lateral stiffness related factors on the structure plasticity developing process, force distribution and stiffness change of the tubes are discussed at last.

Influence of Wind Pressure on the Carbonation of Concrete

Carbonation is one of the major deteriorations that accelerate steel corrosion in reinforced concrete structures. Many mathematical/numerical models of the carbonation process, primarily diffusion-reaction models, have been established to predict the carbonation depth. However, the mass transfer of carbon dioxide in porous concrete includes molecular diffusion and convection mass transfer. In particular, the convection mass transfer induced by pressure difference is called penetration mass transfer. This paper presents the influence of penetration mass transfer on the carbonation. A penetration-reaction carbonation model was constructed and validated by accelerated test results under high pressure. Then the characteristics of wind pressure on the carbonation were investigated through finite element analysis considering steady and fluctuating wind flows. The results indicate that the wind pressure on the surface of concrete buildings results in deeper carbonation depth than that just considering the diffusion of carbon dioxide. In addition, the influence of wind pressure on carbonation tends to increase significantly with carbonation depth.

Exploratory study on sulfate attack monitoring of concrete structures using piezoceramic based smart aggregates

Sulfate attack is one of the most frequent environmental attacks affecting concrete structures, which is manifested by expansive disruption and deterioration of cement paste. However, it is difficult to monitor the deterioration induced by sulfate attack as these attacks mainly occur in sulfate-bearing soils or ground waters. In this paper, the tentative experimental investigation on sulfate attack monitoring was carried out by using smart aggregate transducers and an active sensing method is proposed. A number of plain concrete columns with embedded smart aggregates were fabricated and then suffered to salt-fog exposure for several months. Active monitoring methods were performed to detect the deterioration of the specimens using smart aggregates. In addition, testing of the mechanical properties and water absorption ability of concrete specimens at different deterioration times was performed as well. Then the transmission mechanism of stress wave in concrete was discussed. The experimental results show that, with the growth of attacking time, the amplitude of the received signal decreased, and by calculating the damage index, the deterioration degree of concrete specimens was estimated. It is indicated that the proposed piezoceramic based SA monitoring method is valid in sulfate attack monitoring.

Seismic performance under environment corrosion for curved beam bridges with high piers

Dynamic response under rare earthquakes of the small radius curved beam bridges with high piers under environment corrosion are studied and compared with the cases without corrosion in this paper by time history analysis method based on an actual project. The influence of pier-height and the environment corrosion on the seismic performance of bridges during the service life are studied, and the cumulative damage of piers is discussed.

Research on Seismic Performance Objectives of High-Rise Diagrid Tube Structures

Diagrid tube structures have advantages on constructing high-rise buildings for its great lateral stiffness, but its seismic design methodology researches are limited. The two-stage design method in Chinese code is not specific enough for the seismic fortification objectives of this kind of structures. It is necessary to propose some specific seismic performance objectives for the key components. Typical CFST diagrid tube-concrete core tube structures are studied by dynamic elastic-plastic time-history analysis using Perform-3D program. The structure plasticity developing process is summarized and the distribution characteristics of seismic fortification lines between tubes are discussed. The influences of main structure lateral stiffness related factors on the plasticity developing process are researched. The key components of structure lateral stiffness and plastic energy dissipation are studied. The seismic performance objectives of the key components are proposed for the three-level seismic fortification objectives.

Probabilistic Characteristics of the Ductility Indices of Compression-Bending Reinforced Concrete Columns

The probabilistic characteristics of the seismic performance indices for the compression-bending reinforced concrete columns were studied, which is important for the Performance-Based Seismic Design (PBSD) and seismic performance evaluation of civil engineering structures. First, five damage states with four limit states were defined for the seismic performance level of ductile reinforced concrete components, along with the strain limit definition for each limit state. Then, based on the mechanical behavior and statistical characteristics of reinforcement and concrete, the deformation characteristics of circular reinforced concrete ductile component were analyzed probabilistically for each performance level. Hereby the probabilistic distribution characteristics of the performance indices for each performance level were obtained, and the regression formula as well as its probability distribution model for the performance index of each performance level was proposed, which can be used in the probabilistic analysis of seismic performance of civil engineering structures.

Ground Motion Synthesis Based on Power Spectrum Envelope

The paper proposes a new method, which is used for providing ground motion input for seismic design under rare earthquake action. The crucial step of this method is to use power spectrum envelop, obtained from natural earthquake records but not deriving from response spectrum, as target curve to synthesis ground motion. The result shows that power spectrum obtained from this method fits well with the target curve, and the produced ground motion can properly predict the response spectrum of acceleration. By importing the concept of energy envelope, this method reduces the randomness of the ground motion sampling and the variability of the result in dynamic finite element analysis.