Feng Xiong

An experimental study: Fiber Bragg grating–hydrothermal cycling integration system for seepage monitoring of rockfill dams

In order to make up defects liable for the conventional monitoring of rockfill dam seepage in spatial inconsequence and low efficiency, a new monitoring system is proposed based on the heating technique incorporated in the temperature tracer method, that is, the integrated system of fiber Bragg grating temperature sensing and hydrothermal cycling. The system has a boiler as its heating device, and heated water from boiler is admitted through redistributor and circular warm pipelines, in which fiber Bragg grating sensors are embedded in advance for measuring the water temperature, thereby the seepage behavior is identified from the correlative fields of temperature and seepage. A coefficient ζv, according to Newton’s law of cooling, is then fitted out by pipeline cooling curves and used as a new way to identify the seepage state. The temperature–time–travel curves for the cooling period have proved by calibration tests to be, in general, consistent with the mathematical model of temperature variations under Newton’s law of cooling, thereby to inverting the seepage velocity through the fitting formula of it with ζv. With the test model of concentrative leakage established in regard to the location, amount of leakage passages, and leakage rate, multi-condition tests have been conducted which conclude that the proposed method is capable of positioning leakage and quantifying seepage velocity; therefore, it is valid for seepage monitoring and identification.

An Experimental Study on Thermal Insulation Performance of Straw Wire Aircraft Sandwich Panel

Straw wire aircraft sandwich panel is a new type of composite slab which consist of straw insulation core lamped between two welded wire meshes. Diagonal shear connectors connect two wire meshes to form an integrated frame. The straw insulation core (also known as straw board) is prepared from cut straw agglutinated by magnesium oxychloride cement (MOC). In order to study thermal conductivity of straw board, multi-group models were quantitatively investigated by the CD－DR3030A thermal conductivity meter. Five parameters, including the water－cement ratio, cement content, straw gradation, straw length, wettability were considered in the test. The results show that the thermal conductivity of straw board samples is in the range of 0.08~0.12 w/m•k, which indicates that the straw board has a good thermal insulation property. And the water－cement ratio, cement content, straw gradation, straw length, wettability has remarkable effects on the thermal conductivity of straw board.

Calibration Experiment for Seepage Monitoring Using Fiber Bragg Grating Hydrothermal Cycling Integration System

Seepage monitoring is an important element in geotechnical engineering. This article proposed a new integrated system for seepage monitoring composed of a fiber Bragg grating (FBG) sensing system and a water-heating cycling system. The boiler is used as the heating equipment in the integrated system. The heated water is distributed to each heating pipeline for cyclic heating through the water separator and water collector. The FBG temperature sensors are preburied in the heating pipeline to monitor the water temperature in real time. Recognizing the correlation between the temperature field and the seepage field, we proposed to fit coefficient ξv according to the cooling curve and used it as an index to identify the seepage state. We conducted this numerical simulation to analyze the heat transfer process of the heat source in the porous media. We carried out the calibration experiments of seepage velocity using the FBG-sensing heating system in the porous medium with four different gradations. Our results showed that the temperature gradient decreased over time, indicating that the primary way the heat source was transferred was through the convective heat transfer caused by the seepage. Therefore, the coefficient ξv could be used as the seepage identification index. On the basis of our calibration experiments, we obtained the fitting formulas of ξv and the seepage velocity in four kinds of porous mediums. The formulas can be used for the inversion of seepage velocity. The experimental results proved that ξv was unrelated to the initial cooling temperature. This finding showed that the influence of an uneven temperature distribution along the heating pipeline on monitoring results could be ignored.

Shaking table test of dynamic interaction of soil – high-rise buildings

Two sets of shaking table tests for comparative analysis were first designed and conducted to investigate the laws of dynamic interaction between soil and multiple high-rise buildings. The first set involves only a single high-rise building, and the second set includes a building group. Numerical results of the finite element models, using the Davidenkov foundation model regarding the dynamic non-linearity of soil, are presented and compared with experimental records. Experimental results show that the acceleration responses of structures in the case of multiple high-rise buildings are less than the response in the case of a single structure. The effect of the dynamic interaction between soil and multiple structures on acceleration responses is more obvious for short-period structures than those with long periods under EL Centro excitation. However, the motions of the long period structures in the two tests are almost the same. Opposite phenomena occur under the Shanghai man-made wave excitation. Moreover, the influence on the superstructure displacement is more obvious for long-period structures. The structure displacement in the case of multiple structures is larger than that in the case of a single structure under small earthquake excitations, but it is the opposite under strong earthquake excitations.

Soil-Underground Structure Dynamic Interaction Considering Soil Nonlinearity

Soil-underground structure dynamic interaction is a complex scientific problem, which reveals the seismic responses of underground structures when an earthquake occurs. Most of the research currently being conducted ignores the effect of soil nonlinearity on underground structures owing to its complexity. However since soil is typically a nonlinear media, its nonlinearity has an important effect on the seismic responses of an underground structure. This paper proposes an approach to consider soil nonlinearity in a numerical analysis of soil-underground structure interaction dynamics. By using ANSYS finite element analysis software, the underground structure and the surrounding soil are modeled, and soil nonlinearity realized through the Davidenkov soil model by using the restarting method and ANSYS Parameter Design Language (APDL). The mechanics parameter, i.e. the shear modulus is forced to change along a cover obtained from experiments in each step of the numerical analysis. Therefore the nonlinearity of soil material can be considered. In addition, an artificial boundary is established to simulate a radiation damping effect for the model and the Combin14 element is used as a viscoelastic boundary. The finite element analysis models of soil with and without an underground structure are respectively calculated under horizontal and vertical earthquake excitations. By comparing their results, The effect of underground structure on the free-field ground can be obtained. Finally the effect of different thicknesses of overlying soil on the underground structure seismic response is analyzed. Considering soil nonlinearity, this paper studies the seismic responses of soil-underground structure interaction under different seismic excitations and burial depths, derives a lot of conclusions from the theoretical analysis of the dynamic characteristics of soil-underground structure interaction and finally provides a theoretical basis for the engineering practice.

Soil-High-Rise Building Group Dynamic Interaction Considering Site Effect

This article reports a sub-domain method to analyze the dynamic interaction of soil-high-rise building group considering sit effect, which is the extension of the domain reduction method proposed by Bielak and his coworkers in the framework of the finite-element method, originally for building–soil–foundation interaction problems. The whole domain with high-rise building group is divided into two interrelated sub-domains, the external domain and the internal one. And the method contains two steps. In addition, the effect of the external domain to the internal domain is expressed by the equivalent forces which are put on the nodes of the interface between the two sub-domains in the second step. The formation of the equivalent force is attained according to the equation of motion. In the first step the free-field ground motion is calculated under the bedrock wave excitation, and all the nodal displacements are stored. Then the equivalent forces are calculated according the data in the first step, using the formulation of the equivalent force. In the second step a finite element analysis model of the sub-domain containing the internal domain and the high-rise building group is established, and the equivalent forces are put on the nodes of the interface. Later the seismic response of soil-high-rise building group can be calculated.

The Impact of Stairs on the Aseismic Properties of the Structure

The stair is a important structural component. In current design modeling, it is cut from the entire structure as a simple beam. But stairs show serious damages in some earthquake events. It implies that the seismic capacities of stair structures could be not enough when designed as current method. To investigate the seismic behavior and the effect on the structures for the stairs, a 5-story school building is selected as a case. Two structure models are established, including and without stair. First the reinforcement inside the stairs are compared. It shows the current simple method underestimate the loadings. Second the changes in the structure are investigated when adding the stair to the structural model. The stairs participation decreases the vibration period and storey drift, and increases the structural base shear and the internal forces of the members surrounding the stair. So, it is necessary to consider the stair in analyzing models.

Capacity and Stability Analysis for Construction Support System of the Upper Cantilevered Structure in a Performing Arts Center

The main structure of a performing arts center is in a bowl shape, formed by cantilever frames. When constructing, a temporary steel support system is designed to withstand the construction loads. The structural support system which is 30 meters high, is divided into five layers. In order to ensure the overall stability of the steel frame, scissors are set every three cross along the ring to the medial and lateral column. Since the loads are very big, bearing capacity and stability analysis of the support system are carried out. According to the site construction schedule, the loading processing is divided into 4 working conditions. Under each load condition, static and linear buckling analysis is conducted. For economic consideration, member sizes are optimized by pursuing the similar stress ratio based on the results of static and linear buckling. Structural software SAP2000 is employed as the analysis software. The results showed that: the working conditions 4 is the most dangerous working condition. The main stresses of beams and columns on the axis position are larger than other positions. The bucking analysis indicates that working conditions 1 to 4 the buckling factors of first-order buckling modes are greater than 1.0 under working conditions 1 to 4, which explaining that under the current loads, the steel support system is reached the required overall stability.

Analysis of Steel Trestle for Huge Crawler Cranes Based on ANSYS

In a performing art center project, the roof system uses steel trusses with large-span, which challenges the installation of trusses in construction. Two SCC400 hydraulic crawler cranes are arranged to lift roof trusses. Since it is impossible to sustain the huge cranes for structural slabs, an independent steel trestle will be constructed along the moving path of cranes. The steel trestle is a special frame system with three kinds of levels. Constrained by constructed basement structures, steel trestle has a complex shape and some long span members. It requires some members high capacity and stability. To investigate its mechanics properties, especially the whole stability, a set of analysis, including static and elastic buckling analysis, are carried out on this steel trestle by use of ANSYS software. According to the working conditions of crawler cranes, the loads caused by walking of cranes and hoisting trusses are considered. On the basis of the static analysis, the dangerous loading areas are determined to conduct eigenvalue buckling analysis. The results show that the loads in different positions have less impact on the force and deformation of the entire structure. The buckling characteristic value of the first four modes in both load conditions is larger than 1, which indicates that the system has enough stability.

Literature Review of Seismic Behavior of Composite Steel Plate Shear Wall

Composite steel plate shear wall (CSPSW), as a new lateral force resisting structure composed of steel plate and concrete slab, is introduced. CSPSWs can fully display the superiority of the steel plate and concrete. Ductility and energy dissipation capacity of the walls are increased and seismic behavior is improved. Recent seismic research around the word of two kinds of CSPSWs, namely, CSPSW with signal steel plate and CSPSW with double steel plates, is presented and discussed comprehensively. Some existing problems in current research of the walls are also reviewed in this paper.