Maximum Vertical Temperature Gradient Research Articles

A field study of temperature field distribution characteristics of flat steel box girder and its influential environmental factors

As one of the mainstream girder types of long-span bridges, the flat steel box girder (FSBG) under thermal action has been one primary concern for bridge engineers and researchers. This research presents a field study of the temperature field distribution characteristics of FSBG and its influential environmental factors. To achieve this, an acquisition equipment that comprises of thermometers and environmental sensors is applied to a prototype cable-stayed bridge under construction, in which the structural temperature field of FSBG and the surrounding environmental data are collected and analyzed thoroughly. The results indicate that the vertical temperature distribution (VTD) in certain time instants exhibits significant variations and the maximum vertical temperature gradient can reach up to 27.9 °C. Despite of this, it is found that the VTD of FSBG can be covered by several current standards such as AASHTO standard and New Zealand standard. As for the transverse temperature distribution (TTD), it is found that both the variation and temperature difference of TTD in certain time instants are considerable, especially at the deck surface, which far exceed those of the TTD prescribed in current standards. This indicates that the TTD of FSBG should be seriously considered during the bridge design phase. Furthermore, the field study reveals that the wind speed has negative effect on the structural temperature of FSBG (when the air temperature is less than that of FSBG), while the solar radiation exerts positive effect on the structural temperature of FSBG. The outcome of this study can provide valuable references for thermal design, monitoring and control of long-span bridges employing FSBGs as bridge main girder.

Influence of Reflective Coating on Temperature Field and Temperature Effect of CRTS III Slab Ballastless Tracks on Bridges.

To minimize the adverse effects of high temperatures on the service performance of track structures, research on the application of reflective coatings on track structures is urgently needed. Based on meteorological data and the characteristics of the multi-layer structure of the ballastless track, refined finite element models (FEMs) for the temperature field and temperature effect analysis of the CRTS III slab ballastless track structure on bridges were established. The temperature deformation characteristics and temperature stress distribution of the CRTS III slab ballastless track under natural environmental conditions were investigated. Similarly, the influence of a reflective coating on the structural temperature field and temperature effect was studied. The results showed that the temperature and vertical temperature gradient of the track slab were significantly reduced after the application of the reflective coating. Meanwhile, the thermal deformation and thermal stresses of the track slab and the self-compacting concrete (SCC) layer were minimized. Under high-temperature conditions in summer, the maximum temperature of the track slab decreased from 47.0 °C to 39.6 °C after the application of the reflective coating, and the maximum vertical temperature gradient of the track slab decreased from 61.5 °C/m to 39.1 °C/m after the application of the reflective coating. Under the maximum positive temperature gradient, the peak displacement of the upper arch in the middle of the slab and the peak displacement of the sinking in the slab corner decreased from 0.814 mm and 1.240 mm to 0.441 mm and 0.511 mm, respectively, and the maximum transverse tensile stresses of the track slab reduced from 2.7 MPa to 1.5 MPa as well. In addition, the reflective coating could also inhibit the failure of the interlayer interface effectively. The results of this study can provide a theoretical basis and reference for the application of reflective coatings on ballastless tracks on bridges.

Long-term temperature acceleration effect of solar radiation heating on chloride transport in the CRTS III multilayer structure

The service life of high-speed railway track structures located in coastal areas may be shortened by chloride erosion due to the marine environment. This study aims to simulate chloride transport within the track structure by boundary condition models based on high-precision climate data and structural damage. The established numerical models consider various factors, including structural damage, historical exposure data of air temperature and relative humidity, temporal resolutions, solar radiation history, and the deposition rate of atmospheric chloride. The main conclusions are as follows: The maximum vertical temperature gradient of the track slab is roughly 81K/m, and the daily average temperature differences between air and surface concrete in July and February are around 9.6°C and 4.8°C, respectively. The chloride flux boundary derived from the chloride deposit rate is nearly 1 × 10-9mol/(m2s) to 10 × 10-9mol/(m2s) under a marine atmospheric environment. Step functions of daily average and monthly average temperature can improve almost the same prediction accuracy of chloride diffusion, and increasing the monthly average temperature curve by 10°C can roughly estimate the upper limit of temperature acceleration.

Investigation on Effect of Reflective Coating on Temperature Field of CRTS Ⅱ Slab Ballastless Track under Sunlight

The internal temperature variation of ballastless track is very complicated under the effect of a sunlit environment, and there are serious transverse and vertical temperature gradients, which will cause cracking and deformation of the structure. In this paper, an ANSYS temperature effect analysis model for ballastless track, considering box girder structure, is established based on the environmental information of the bridge and the characteristics of the structural system. The model considers the influence of solar radiation intensity, wind speed, air temperature, geographical location, bridge orientation, material parameters, and other factors on the boundary conditions, and can meet the needs of the daylight temperature response analysis and calculation of any complex bridge structure. On this basis, the effect and applicability of a solar reflective coating on ballastless track cooling are studied. The results showed that the calculated results of the finite element model agree well with the measured results. Under the high-temperature conditions in summer, sunlight and ambient temperature mainly have significant effects on the temperature and temperature gradient of the track slab, and the maximum vertical temperature gradient reaches 74.48 °C/m. The reflective coating can significantly reduce the track slab’s temperature and vertical temperature gradient, with a maximum temperature gradient reduction of 34%. The transverse temperature gradient of the track slab can be reduced by up to 54% by further application of the side reflective coating. This study can promote the application of reflective coatings on high-speed railway track structures.

Experimental and numerical investigation on the temperature distribution of composite box‐girders with corrugated steel webs

Although composite box-girders with corrugated steel webs have been widely applied in practical bridge constructions, the nonuniform temperature field in the composite box-girders without sufficient study may lead to negative effects on the durability of bridge structures. Thus, this paper focuses on the temperature distribution characteristics of the composite box-girder with corrugated steel webs. The temperature data of a corrugated steel web box-girder specimen has been measured. An apparent nonuniform temperature distribution of the experimented specimen under solar radiation can be observed through the measured data. Then, the numerical simulation model of the corrugated steel web composite box-girder specimen has been established and validated by the measured temperature data. Based on the verified simulation model, the temperature distribution of an actual composite box-girder has been analyzed numerically. The results show that the difference between the vertical temperature gradients along the north and south sides of the girder can reach up to 11.9°C, and the maximum vertical temperature gradient can be more than 24.0°C in summer days. Moreover, parametric studies have been carried out to reveal the impacts of material parameters on the composite box-girder's temperature distribution and the thermal loading index. Both the concrete and steel surface absorptivity show significant influences on the temperature distribution and the thermal loading index through the parametric study. It hopes that the current investigation can provide some contributions for further applications of the composite box-girder with corrugated steel web, and other researches regarding temperature field of the structures.

Investigation of temperature gradients in composite girders in the southern region of the black sea

Based on an experimental composite concrete slab-steel beam girder and using a verified finite element thermal model, a case study analysis was performed to evaluate the temperature gradients in composite girders in the Black Sea’s Turkish city Samsun. The case study was conducted based on extreme data records of approximately 50 years. The extreme daily solar radiation and air temperature difference were utilized in finite element thermal analysis for six months that represent the different seasons of the year. The investigated months were the hot months (April, June, and July) and cold months (October, November, and December). The study focused on the vertical temperature gradients (along the vertical centerline of the girder) and the lateral temperature gradients (along the horizontal centerline of the topping concrete slab). The finite element results showed that the maximum vertical temperature gradient occurred in June and was 13.55 °C, while the maximum lateral temperature gradient occurred in December and was 10.11 °C. The results also showed that different behaviors of the positive vertical gradient were recorded for the cold months than those for the hot months. Similarly, the distributions of the positive lateral gradients were different for the two groups of months. These differences were attributed to the different sun movements and solar radiation striking angles in summer and winter.

Design Temperatures for Composite Concrete-Steel Girders: B-Case Study

Long-term metrological records for Adana city, which is located in the Mediterranean region in Turkey, were facilitated in this study together with a verified finite element thermal model. The aim of this study is to investigate the sectional temperature gradients in concrete-steel composite bridge girders. Solar radiation and air temperature history of more than 50 years was used, and a practical-size typical composite bridge girder was modeled for six selected months that represent the conditions of the four seasons in Adana. The analysis showed that the behaviors of positive vertical and lateral temperature gradients in summer were completely different from those in winter, while the negative temperature gradients exhibited similar sectional distributions in all seasons. The results also showed that the maximum vertical temperature gradient occurred in summer, while the maximum lateral temperature gradient occurred in winter. The maximum positive vertical gradients occurred at the top concrete surface in summer and within the steel web in winter. For the investigated conditions, the recorded maximum positive vertical gradients in summer and winter were approximately 15.0 and 12.2 °C, respectively, while the maximum positive lateral temperature gradients in summer and winter were approximately 6.1 and 10.9 °C, respectively.

Heat Transport through Diurnal Warm Layers

AbstractPenetration of solar radiation in the upper few meters of the ocean creates a near-surface, stratified diurnal warm layer. Wind stress accelerates a diurnal jet in this layer. Turbulence generated at the diurnal thermocline, where the shear of the diurnal jet is concentrated, redistributes heat downward via mixing. New measurements of temperature and turbulence from fast thermistors on a surface-following platform depict the details of this sequence in both time and depth. Temporally, the sequence at a fixed depth follows a counterclockwise path in logϵ–logN parameter space. This path also captures the evolution of buoyancy Reynolds number (a proxy for the anisotropy of the turbulence) and Ozmidov scale (a proxy for the outer vertical length scale of turbulence in the absence of the free surface). Vertically, the solar heat flux always leads to heating of fluid parcels in the upper few meters, whereas the turbulent heat flux divergence changes sign across the depth of maximum vertical temperature gradient, cooling fluid parcels above and heating fluid parcels below. In general, our measurements of fluid parcel heating or cooling rates of order 0.1°C h−1 are consistent with our estimates of heat flux divergence. In weak winds (<2 m s−1), sea surface temperature (SST) is controlled by the depth-dependent absorption of solar radiation. In stronger winds, turbulent mixing controls SST.

Temperature Records in Concrete Box-Girder Segment Subjected to Solar Radiation and Air Temperature Changes

This paper presents the experimental results of a full-scale concrete box-girder segment subjected to ambient thermal loads. The experimental segment was instrumented with 62 thermocouples to measure the concrete temperatures in different locations and a weather station to measure air temperature, wind speed, and solar radiation. The records from the different sensors were collected for more than one year at time intervals of 30 minutes. The full one-year records showed that the maximum vertical temperature gradient was occurred in June and was approximately 20 °C, while the maximum lateral temperature gradient was occurred in December and was 19 °C. Finally, a vertical temperature gradient model, which composes of three multi-linear parts, was proposed. The resulted temperature distributions, stresses, and deflection from the proposed model were closer to those of the experimental gradient compared to the AASHTO’s and the NZ Bridge Manual’s gradient models.

Analysis of Sunshine Temperature Field of Steel Box Girder Based on Monitoring Data

In this study, based on the recorded meteorological data of the bridge site, a spatial‐temporal temperature model of a 3‐span steel box girder is developed through applying the thermal analysis software TAITHERM. Firstly, the rationality and dependability of the proposed spatial‐temporal temperature model are adequately verified by means of implementing the comparison with the measurement data. Then the temperature distribution of the steel box girder is analyzed and discussed in detail. The analytical results show that the time of the bottom of pavement reaching the daily maximum temperature lags behind the top of pavement by 2 or 3 hours due to the thermal insulation effect of pavement, and the maximum vertical temperature gradient of the structure exceeds the existing standards. Moreover, with the help of the analytical model, a parametric study of comprehensively meteorological factors is also performed. The results of the sensitivity analysis indicate that solar radiation is the most significant factor affecting the maximum vertical temperature gradient of the steel box girder, followed by air temperature and wind speed. After that, with the representative values of the extreme meteorological parameters during 100‐year return period in Wuhan City in China being considered as the thermal boundary conditions, the temperature distribution of the steel box girder is further studied for investigation purpose. The results demonstrate that the heat conduction process of the steel box girder has distinct “box‐room effect,” and it is of great necessity to consider both the actual weather conditions at the bridge site and the “box‐room effect” of steel box girder when calculating thermal behaviors of bridge structures. Finally, it is related that the particular method proposed in this paper possesses a satisfactory application prospect for temperature field analysis upon various types of bridges in different regions.

Research on the performance of sidewall perforated plate air supply system that suitable for prefabricated buildings

Taking the rural prefabricated residential building as research object, prefabricated sidewall partitioned perforated plate air supply model and traditional jet air supply model were established respectively. Then, CFD commercial software was used to simulate the temperature field, velocity field, formaldehyde concentration of indoor air-flow distribution of the two air supply model that mentioned above. Simulation results show that in the indoor breathing zone, the valuation index of prefabricated sidewall partitioned perforated plate air supply system, such as the velocity non-uniformity coefficient, air diffusion performance index, ventilation efficiency are entirely superior to the traditional jet air supply system. Moreover, the maximum vertical temperature gradient and maximum horizontal temperature gradient of the prefabricated sidewall partition perforated plate air supply system were also small which means the new air supply system could satisfy the indoor air quality and human thermal comfort requirements.

Experimental analysis of temperature gradients in concrete box-girders

This paper describes the construction and instrumentation of an experimental box-girder segment, aiming to analyze the temperature distributions in concrete bridges under the fluctuation of air temperature and solar radiation thermal loads. The instrumentation included air temperature, solar radiation, and wind speed sensors in addition to 62 thermocouples, while data acquisition continued for more than one year. The maximum vertical temperature gradient was recorded in June, while the maximum lateral gradient was recorded in December. Empirical formulas were proposed to predict the maximum vertical and lateral temperature gradients, in addition to the daily maximum and minimum mean temperatures of the bridge.

Improving Understanding of Microclimate Heterogeneity within a Contemporary Plant Growth Facility to Advance Climate Control and Plant Productivity

Greenhouse crop production is maximized by maintaining optimal growing conditions. Accurate management of climate conditioning equipment based on measurements of the internal greenhouse microclimate is necessary to optimize crop production. Traditionally, greenhouse microclimate is monitored by a single suite of sensors located at a fixed (often central) location that is considered representative of the entire greenhouse climate. To advance greenhouse crop production additional sensors may better represent greenhouse microclimate heterogeneity and improve performance of climate conditioning equipment. However, elucidating the proper number and distribution of additional sensors requires investigation. Distributed high resolution air temperature (n = 63), relative humidity (n=63), and incoming solar radiation data were collected between May 9th, 2012 and September 5th, 2012 to test the efficacy of conventional centrally located sensors to characterize the spatial and temporal climate variability inside three contemporary greenhouse facilities. Results indicate substantial microclimate heterogeneity with mean horizontal temperature gradients of as much as 5.0°C/m, and mean horizontal VPD gradients of 1.5 kPa/m. Most substantially, the maximum vertical temperature gradient was 11.65°C/m. Results indicate that as few as five properly deployed sensor assemblages (e.g. temperature, humidity, solar radiation) may be necessary to more accurately monitor horizontal and vertical microclimate heterogeneity in a typical greenhouse room. This would improve climate conditioning accuracy and improve the homogeneity of the internal greenhouse climate, which may result in increased productivity and profits for greenhouse managers.

The annual cycle of vertical mixing and restratification in the Northern Gulf of Eilat/Aqaba (Red Sea) based on high temporal and vertical resolution observations

The stratification in the Northern Gulf of Eilat/Aqaba follows a well-known annual cycle of well-mixed conditions in winter, surface warming in spring and summer, maximum vertical temperature gradient in late summer, and erosion of stratification in fall. The strength and structure of the stratification influences the diverse coral reef ecosystem and also affects the strength of the semi-diurnal tidal currents. Long-term (13 months) moored thermistor data, combined with high temporal and vertical resolution density profiles in deep water, show that transitions from summer to fall and winter to spring/summer occur in unpredictable, pulses and are not slow and gradual, as previously deduced from monthly hydrographic measurements and numerical simulations forced by monthly climatologies. The cooling and deepening of the surface layer in fall is marked by a transition to large amplitude, semi-diurnal isotherm displacements in the stratified intermediate layer. Stratification is rebuilt in spring and summer by intermittent pulses of warm, buoyant water that can increase the upper 100–150m by 2°C that force surface waters down 100–150m over a matter of days. The stratification also varies in response to short-lived eddies and diurnal motions during winter. Thus, the variability in the stratification exhibits strong depth and seasonal dependence and occurs over range of timescales: from tidal to seasonal. We show that monthly or weekly single-cast hydrographic data under-samples the variability of the stratification in the Gulf and we estimate the error associated with single-cast assessments of the stratification.

Revisiting the Thermocline Depth in the Equatorial Pacific*

Abstract The thermocline depth is defined as the depth of the maximum vertical temperature gradient. In the equatorial Pacific, the depth of 20°C isotherm is widely used to represent the thermocline depth. This work proposes that under the circumstance of a significant mean climate shift, it is better to use the original definition of the thermocline depth in studying the long-term changes in mean climate and tropical coupled climate variabilities. For instance, during the transient period of global warming, the tropical thermocline is usually enhanced because the surface layer warms more and faster than the lower layers. The depth of maximum vertical temperature gradient shoals, which is consistent with the enhanced thermocline. However, the 20°C isotherm depth deepens, which suggests a weakened thermocline. This discrepancy exists in both the observations and the future climate simulations of coupled models.

An explicit solution of the linear thermocline equations

A simple analytic solution of the linear thermocline equations is obtained for the case where the forcing is purely by Ekman pumping, and the results are displayed graphically. The motivation was purely to find a very simple solution to use as a departure point for discussion of the ocean circulation and its associated temperature. However, the calculated temperature field turns out to display a surprising degree of reality in that (i) isotherms slope up toward the east in the subtropical gyre (but down in the subpolar gyre), (ii) the surface temperature increases towards the west in the subtropical gyre (but decreases in the subpolar gyre), (iii) the maximum vertical temperature gradient is subsurface in the subtropical gyre (the gradient is greatly reduced in the subpolar gyre), (iv) the surface temperature decreases towards the poles, except at low latitudes. (v) the meridional surface temperature gradient is largest in the subpolar gyre, and (vi) surface isotherms spread out longitudinally near the eastern boundary. The surprising result is that all these features are produced by wind forcing alone, and thus raise the question as to what extent the same is true of the actual temperature field of the ocean. DOI: 10.1111/j.1600-0870.1985.tb00427.x

Diurnal temperature gradients in shallow water produced by populations of artificial aquatic macrophytes

Three artificial populations, with leaf area indices (L) of 4.4, 1.5, and 0.54 were submerged in identical tubs of 1-m3 capacity. Experiments showed that the maximum vertical temperature gradient of the water varied and was dependent on the ratio of solar radiation to wind speed, the leaf area index, and the arrangement of the leaves in the population. The time of day of the maximum temperature gradient was also dependent on L and leaf arrangement. The interception of the light energy by the leaf surface heated the water locally, while the shadow beneath caused the temperature to remain low. With fewer plants, water evaporation was slightly greater. Evaporation resulted in a marl deposit which was confined to the upper surface of the leaves.

Thermal behavior of shipping casks under fire conditions

To provide basic information for more reliable prediction of temperatutes in a shipping cask under external fire conditions, a 15-ton lead-shielded cask was subjected to a large, open-air petroleum fire for 1 hr. Experimental results were correlated by electrical analog computation, using various assumed values for important parameters. The radiant absorptivity (α) of the cask was found both by analog computations and by hand calculations to be about 0.6. Although the cask was externally finned, α was calculated from the area of the outer shell excluding the fins, which contribute little to radiant heat transfer. Convection of molten lead in the walls was found to be such that the horizontal temperature gradient in the molten lead was negligible. On the other hand, the maximum vertical temperature gradient was about 8°F per inch of height. Hand-calculation methods are presented for predicting the extent of melting as a function of time for lead-shielded casks of rectangular or cylindrical shape, for any selected fire conditions. Methods are also suggested for estimating the maximum cavity temperature in casks with either lead or non-melting shielding.