Expansion Gap Research Articles

Analysis of the influence of expansion gap on thermal stress and strain distribution of a hot blast stove

The hot blast stove is an important facility in the steel industry, which of the expansion gaps design has a significant buffering effect on the thermal stress with a high-temperature operating process. In this paper, a 3D numerical model of a hot blast stove was established to calculate the thermal stress distribution and analyze the remaining thickness of expansion gaps with different parts during the operating process. Young’s Modulus of the refractory linings was obtained by comparing with the experiment data and numerical data under the different temperatures and considering the influence of mortar. The result shows that Young’s Modulus of the refractory brick increased as the temperature, and the comparison of the experiment and simulation data of Young’s Modulus under three different temperatures displayed good agreement between the two sets of data. The first/third principle stress for the refractory linings can be reduced effectively by designing the expansion gap rationally, and the equivalent stresses of the shell are mainly concentrated at the joint and the neck. In addition, the expansion gaps are decreased under the thermal expansion and moved along a radial direction for the combustion/checker dome and the combustion/checker chamber.

Numerical Study and Structural Optimization of Water-Wall Temperature-Measurement Device for Ultra-Supercritical Boiler.

The temperature of the water wall in the furnace chamber is extremely important for the daily operation of a boiler. Considering the high temperature and dusty environment in the furnace, a temperature measurement device mainly composed of four parts (armored temperature sensor, in-furnace heat-collecting block, out-furnace fixing base, and protective cannula) was designed in this study, which could be used to directly obtain the temperature of the in-furnace water-wall. Numerical simulations of temperature measurement devices with different heat-collecting block structures were carried out using the computer fluid dynamics method. After comparing the measurement accuracy and considering the practical application scenarios, the optimized heat-collecting block structure with a specific expansion gap (0.5 mm wide and 4 mm deep) was selected for practical application. Such a temperature measurement device was then applied to a 1000 MW ultra-supercritical coal-fired boiler in China, and the tested in-furnace water-wall temperature data were in good agreement with relevant research. Compared with the conventional temperature measurement device arranged outside the furnace, the in-furnace water-wall temperature-measurement device adopted in this study has a more sensitive response characteristic and can directly reflect the temperature of the water wall inside the furnace. In addition, it can also reflect the local slag formation state of the water wall and has a long service life.

Shaking table experiment study of a multi-tower cable-stayed bridge with consideration of seismic pounding effect between the main bridge and approach bridge

In this study, a 1/100-scale shaking table experiment was designed and conducted for a multi-tower cable-stayed bridge in order to investigate its seismic response characteristics with consideration of seismic pounding between the main and approach bridges. The test parameters include the expansion gap size and period ratio between the main bridge and the approach bridge. Both the near-field and far-field ground motions were selected to excite the model. Test results indicate that the seismic response of multi-tower cable-stayed bridges is very sensitive to the gap size and a reasonable gap size of expansion joint can mitigate the pounding effect on structural response. In addition, a period ratio close to 2:1 resulted in the most significant pounding effect and should be avoided in the design stage to reduce the collision risk. Moreover, seismic pounding could significantly amplify the relative displacement between the pier and girder of the main bridge elevating the risk of girder unseating. The test results can provide a valuable reference for the seismic design of cable-stayed bridges with multi-tower.

Full-scale mud pumping test of ballastless trackbed under train loading

This paper presents a full-scale physical modeling investigation on the mud pumping in ballastless trackbed. The physical model was equipped with a rainfall device to simulate the in situ precipitation and various testing sensors were installed to monitor the dynamic response of the track-subgrade system. Results showed that the whipping of the track structure induced by high-speed train passages caused a separation between the track structure and the underlying roadbed, which allowed rainwater to intrude into the roadbed. The intruded rainwater infiltrated vertically and then permeated laterally from the bottom of the roadbed, eventually saturating the entire roadbed. Train moving loads partially promoted this rainwater infiltration. The excess pore water pressure (EPWP) was formed in the saturated roadbed caused by train moving loads, and it increased with train speeds and loading carriages. A noticeable upward EPWP gradient and a slight longitudinal EPWP gradient towards the expansion gap were also created in the saturated roadbed. Accordingly, both the vertical hydraulic gradient (HG) and longitudinal HG increased with train speeds and loading carriages, most of which, especially the vertical HG, exceeded the critical HG for particle migration with a diameter smaller than 7.1 mm. It caused severe upward particle migration and slight longitudinal particle migration towards the expansion gap. This spatial fine particle migration process, known as mud pumping, was driven by the HG-induced seepage force and further promoted by the EPWP amplification induced by high-speed train passages. Mud pumping resulted in a significant decrease in stiffness of the trackbed and a noticeable increase in vibration velocity of the track slab.

Experimental Investigation of Pounding Responses in Longer Structures at Expansion Gap

Experimental Investigation of Pounding Responses in Longer Structures at Expansion Gap

Experimental Investigation of Pounding Responses in Base-Isolated Frame Structures at Expansion Gap

Experimental simulation and parametric studies have been conducted to investigate the effect of pounding in base-isolated (BI) frame structures with expansion gaps. Earthquakes often result in extensive damage at expansion joints, which encouraged this experimental evaluation of pounding between BI frames. In the present research, the pounding effect in a series of combinations, such as adjacent flexible and stiffer BI frames of similar frequency and different frequency to adjacent frames, were experimentally analysed to find better combinations of adjacent structures with an expansion gap. In the experiments, the surfaces at the isolation and frame slab levels were free to impact in order to investigate direct pounding (DP) and mitigated pounding (MP) by inserting a neoprene rubber pad into the gap. The investigation was conducted by comparing BI structures with and without pounding responses as a result of the El Centro earthquake excitation. To demonstrate the extent of the pounding effect in adjacent structures, the horizontal and pounding force variations in each combination during DP and MP were evaluated. The experimental responses analysis results help in justifying a better variety of adjacent BI structures with an expansion gap. This experimental study shows that mitigating material in the gap is more efficient for nearer frequency combinations than for different frequency frame combinations.

Multi-objective optimization of thermal expansion and adjustable band gap for a chiral triangular lattice metamaterial

Multi-objective optimization of thermal expansion and adjustable band gap for a chiral triangular lattice metamaterial

Zero-point lattice expansion and band gap renormalization: Grüneisen approach versus free energy minimization

The zero-point lattice expansion (ZPLE) is a small variation of the lattice parameters induced by the presence of phonons in a material compared to the static lattice picture. It contributes significantly to the zero-point renormalization (ZPR) of the band gap energy, but its consequences have not been investigated as thoroughly as those stemming from electron-phonon interactions. In the usual first-principles approach, one evaluates the ZPLE by minimizing the $T=0$ K Helmholtz free energy. In this work, we show that the formalism based on the Gr\"uneisen parameters, which commonly neglects zero-point effects, can be efficiently used to compute the ZPLE for both isotropic and anisotropic materials at a much lower computational cost. We systematically test this formalism on 22 cubic and wurtzite materials, and we obtain excellent agreement with free energy minimization results for both the ZPLE and the resulting band gap ZPR. We use our results to validate an empirical expression estimating the ZPLE-induced ZPR, and we unveil its sensitivity to the temperature range involved in estimating the ZPLE from experimental data. Our findings finally reveal that the ZPLE contribution to the band gap ZPR can reach from 20% to more than 80% of the electron-phonon interaction contribution for heavier or more ionic materials, including materials containing light atoms. Considering both contributions on an equal footing is thus essential should one attempt to compare theoretical ZPR results with experimental data.

Structure and Property Changes in Sulfide Solid Electrolytes with Lithiation: A First-Principles Study

Sulfide-based lithium-ion conductors such as Li3PS4 (LPS) and Li10GeP2S12 (LGPS) have received considerable attention for use as solid electrolytes for rechargeable batteries because of their high ionic conductivity, wide electrochemical window, and appropriate mechanical properties. However, their wide application in all-solid-state lithium batteries is hindered by spontaneous decomposition and solid electrolyte interphase layer formation when in contact with Li metal. To better understand the structure and property changes of LPS and LGPS with lithiation, we have systematically analyzed lithiated LPS/LGPS with varying Li contents by calculating their structural, electronic, and mechanical properties with density functional theory. The variation of Li-ion conductivity in these materials with the lithiation degree is also evaluated using ab initio molecular dynamic simulations. Our results unequivocally show that Li incorporation leads to decomposition of PS4 3- and GeS4 4- tetrahedra, resulting in the formation of small P and GeP clusters, along with Li2S production. The P and GeP clusters are eventually converted to Li3P and Li15Ge4 when LPS and LGPS are fully lithiated. The structural evolution gives rise to volume expansion and band gap narrowing. Over-lithiated LPS/LGPS tends to show metallic character, which could be partly responsible for the electrolyte failure. Despite the significant structural changes, the Li ion diffusivity and conductivity in both LPS and LGPS remain at the same order of the magnitude. This work provides a better understanding of the reaction behavior of LPS and LGPS with Li metal and also insight into how to analyze the reaction at the Li metal/sulfide electrolyte interface leading to an inorganic interphase layer.

Literature review on education expansion and income gap in China

Since the reform and opening up, China's per capita years of education and college enrollment rate have been greatly improved. The impact of educational expansion on China's income gap has aroused widespread concern in the academic community. In this paper, the theoretical research and empirical analysis of education expansion and income gap are sorted out, and the related theoretical research at home and abroad are classified into three categories: education expansion has inhibition, promotion and comprehensive effects on income gap. In the empirical analysis, the paper summarizes the functional relationship between education expansion and income gap in China, and the heterogeneity analysis of income of different groups due to the expansion of different education levels.

Detection and Identification of Expansion Joint Gap of Road Bridges by Machine Learning Using Line-Scan Camera Images

Recently, the lack of expansion joint gaps on highway bridges in Korea has been increasing. In particular, with the increase in the number of days during the summer heatwave, the narrowing of the expansion joint gap causes symptoms such as expansion joint damage and pavement blow-up, which threaten traffic safety and structural safety. Therefore, in this study, we developed a machine vision (M/V)-technique-based inspection system that can monitor the expansion joint gap through image analysis while driving at high speed (100 km/h), replacing the current manual method that uses an inspector to inspect the expansion joint gap. To fix the error factors of image analysis that happened during the trial application, a machine learning method was used to improve the accuracy of measuring the gap between the expansion joint device. As a result, the expansion gap identification accuracy was improved by 27.5%, from 67.5% to 95.0%, and the use of the system reduces the survey time by more than 95%, from an average of approximately 1 h/bridge (existing manual inspection method) to approximately 3 min/bridge. We assume, in the future, maintenance practitioners can contribute to preventive maintenance that prepares countermeasures before problems occur.

Relaxation in non-Markovian models: From static to dynamic heterogeneity

Glass transition processes have often been explained in terms of wide distributions of relaxation times. By means of a simple stochastic model we here show how dynamic heterogeneity is the key to the emergence of the glass transition. A non-Markovian model representing a small open region of the amorphous material was previously shown to reproduce the time and thermal characteristic behavior of supercooled liquids and glasses. Due to the interaction of the open regions with their environment, the temperature dependence of the equilibrium relaxation times differs from the featureless behavior of the relaxation times of closed regions, whose static disorder does not lead to a glass transition, even with wider distributions of equilibrium relaxation times. The dynamic heterogeneity of the open region produces a glass transition between two different regimes: a faster-than-Arrhenius and non-diverging growth of the supercooled liquid relaxation times and an average Arrhenius behavior of the ideal glass. The Kovacs’ expansion gap was studied by evaluating the nonequilibrium distribution of relaxation times after the temperature quenches.

Nondestructive investigations of expansion gap concrete roughness

This paper presents the results of non-destructive investigations of concrete roughness in expansion gaps in reinforced concrete structures. The goal of this paper is to contribute to surface roughness measurement techniques. Concrete specimens with differently prepared surfaces: 1) not rubbed down, 2) manually cleaned and 3) mechanically cleaned were examined. The spatial geometric structure of the specimen surfaces was investigated using a scanning optical profilometer. Surface geometry, profile and roughness were measured. Then surface features were analysed and presented in the form of histograms, Abbott-Firestone material ratio curves and surface micro asperity profiles. Moreover, area-related surface topography parameters, i.e. height, frequency and hybrid parameters as well as functions and associated parameters, were determined. Then morphometric measurements, geometric profile and roughness measurements as well as analyses of the surface undulations and the spatial locations of the parameters were carried out. The results obtained for the mechanically prepared surfaces were found to be the best. The results were compared and conclusions important for building practice were drawn.

Unseating of single-span bridges with skew angles out of the limit range for free rotation

Past researches have indicated that skewed bridges can rotate around the obtuse corners upon gap closure and the bridge deck can rotate freely when the skew angle is within a limit range. Beyond this range, the rotation of the bridge deck could be locked against the abutments. For these bridges, girder unseating can be avoided either by geometric constraint of the deck or by providing adequate support length to account for seismic demands. In this paper, the unseating of single-span bridges is studied for skew angles out of the limit range for free rotation. To begin, the skew angle limit range for free rotation was derived for bridges with and without expansion gaps. It was found that the expansion gap has a slight influence on the skew angle limit range for free rotation. The minimum support length (N) of skewed bridges to reach geometric constraint (when locked against the abutments) was then derived step-by-step based on geometry. It is found that the N to reach geometric constraint increases with skew angles approximately in an exponential manner. Finally, a parametric study was performed on prototype skewed bridges using a shake table experiment-validated nonlinear model to compute the support length demands during design-level earthquakes. Nonlinear analysis was performed under seven historical near-fault records scaled to the design-level earthquakes. Comparison was made between the support length to reach geometric constraint and those from numerical analysis. The results indicate that it is very likely that a single-span bridge of any skew angle could rotate freely during the design-level earthquakes even when its geometry could allow it to be blocked by the abutments. Therefore, the minimum support length of single-span bridges should be designed based on seismic demands rather than geometric constraint when the skew angles are out of the limit range. In addition, it was also found that the Japan Road Association (JRA) is unreasonable to assume zero skew effect on the minimum support length requirements and current codes and specifications underestimate the skew factor when the skew angles fall out of the limit range.

Shake table experimental study of curved bridges with consideration of girder-to-girder collision

It is well-known that curved bridges are vulnerable to girder unseating during strong earthquakes. This is mainly attributed to its irregular geometry and seismic pounding. In this paper, a shake table experiment was designed and conducted on a 1/25-scale model to investigate the influence of collision between adjacent girders on the seismic response of curved bridges. For this purpose, two curved bridges with an expansion joint in-between were taken as the engineering background. Three historical records including a near-fault pulse-like record, a non-pulse-like record and a far-field ground motion were used to excite the test model. The seismic responses of the tested curved bridges were discussed in detail. Impact forces were measured by three load cells installed at the expansion gap joint. To begin with, the model was excited by the near-field pulse-like record in a variety of input directions without seismic collision to identify the most unfavorable input angle of the ground motions. It was found that for the test model, the secant direction of the adjacent two piers of the single-span segment is the most unfavorable input angle for seismic excitations. It was also found that the collision frequently occurred at the corners of the girders and was non-uniform along the contact surface. In addition, the girder-to-girder collision could induce significantly large in-plane rotation of the adjacent bridges, which could substantially increase the global displacement demands of the bridges. Furthermore, the maximum total impact forces increased with the gap size from 1 mm to 2 mm and then decreased with the gap size from 2 mm to 4 mm. However, the maximum in-plane rotation decreased with the gap size from 1 mm to 4 mm regardless of the input motions. Compared with the non-pulse-like near-fault motions, the pulse-like near-fault motions can result in higher in-plane rotation and force demands due to their velocity pulses and hence are more detrimental to curved bridges.

Unraveling the Suppression of Oxygen Octahedra Rotations in A_{3}B_{2}O_{7} Ruddlesden-Popper Compounds: Engineering Multiferroicity and Beyond.

The competition between polar distortions and BO_{6} octahedra rotations is well known to be critical in explaining the ground state of various ABO_{3} perovskites. Here, we show from first-principles calculations that a similar competition between interlayer rumpling and rotations is playing a key role in layered Ruddlesden-Popper (RP) perovskites. This competition explains the suppression of oxygen octahedra rotations and hybrid improper ferroelectricity in A_{3}B_{2}O_{7} compounds with rare-earth ions in the rocksalt layer and also appears relevant to other phenomena like negative thermal expansion and the dimensionality determined band gap in RP systems. Moreover, we highlight that RP perovskites offer more flexibility than ABO_{3} perovskites in controlling such a competition and four distinct strategies are proposed to tune it. These strategies are shown to be promising for designing new multiferroics. They are generic and might also be exploited for tuning negative thermal expansion and band gap.

Response of Multistorey Structure with and Without of Expansion Gap for Wind Loading and Dynamic Analysis

Response of Multistorey Structure with and Without of Expansion Gap for Wind Loading and Dynamic Analysis

Requirement of expansion joint for temperature load for RCC structures

Concrete is the most commonly used material in building construction. Concrete structures are subjected to seasonal and daily temperature changes due to their interaction with the surrounding environment, in addition to live and dead loads. Significant change of temperature can impose large amount of stress in a structure. These thermal stress values can even exceed the stress values induced by the live and dead loading in case of no or little thermal insulation and could lead to severe damages if not considered during the design. One way of minimizing the temperature stress is to limit lengths of building. In Bangladesh National Building Code and many other national codes, there is no specific guideline for length limits or provision for considering stresses due to temperature load. This paper is aimed to determine the maximum permissible length of a structure without providing an expansion joint so that temperature changes do not create undue stresses. Parametric study involving thermal effect on RCC structures was performed for varying dimensions, conditions and story levels. If temperature effect for structures with significant length is considered, it has been found that top deflection and rebar percentage exceeds limiting values. The finding could become useful in guiding to set the permissible building length without expansion gap.

Spatial Heterogeneities in Structural Temperature Cause Kovacs' Expansion Gap Paradox in Aging of Glasses.

Volume and enthalpy relaxation of glasses after a sudden temperature change has been extensively studied since Kovacs' seminal work. One observes an asymmetric approach to equilibrium upon cooling versus heating and, more counterintuitively, the expansion gap paradox, i.e., a dependence on the initial temperature of the effective relaxation time even close to equilibrium when heating. Here, we show that a distinguishable-particle lattice model can capture both the asymmetry and the paradox. We quantitatively characterize the energetic states of the particle configurations using a physical realization of the fictive temperature called the structural temperature, which, in the heating case, displays a strong spatial heterogeneity. The system relaxes by nucleation and expansion of warmer mobile domains having attained the final temperature, against cooler immobile domains maintained at the initial temperature. A small population of these cooler regions persists close to equilibrium, thus explaining the paradox.

Experimental Studies on Seismic Response of Skew Bridges with Seat-Type Abutments. II: Results

This paper investigates the seismic response of skewed bridges using the comprehensive data set obtained from a family of shake table experiments. To begin, the influence of friction along the abutment on the in-plane rotation of skewed bridges is evaluated. Then the influence of expansion gap size, type of ground motion (near field and far field), and input direction on seismic response is described. It is shown that once impact occurs between the bridge and abutment back wall, significant forces can be generated normal to the back wall due to impact and in the plane of the back wall through friction. These forces cause in-plane rotation of otherwise symmetrical skewed bridges. Both impact and friction should therefore be included in numerical models used to compute in-plane displacements of the superstructure. Moreover, it is shown that bridges with very small or very large gaps experience lower response. It is also shown that numerical models that do not include the gap could give nonconservative results, especially for moderate-sized gaps. Furthermore, skew bridges are more vulnerable to near-field ground motions than far-field motions. Finally, if the major component of the ground motion is applied in the transverse direction alone, comparable maximum displacements and in-plane rotations are obtained for biaxial excitations, but it produces significantly smaller impact forces than for biaxial input due to the contribution of the minor component in the longitudinal direction.