Vertical Temperature Difference Research Articles

Fire Resistance Performance of Constrained H-Shaped Steel Columns with Uneven Vertical Temperature Distributions

Steel columns, which are widely used in building frameworks and spatial structures, are susceptible to capacity degradation during fires, potentially leading to the overall collapse of buildings. Existing research on the fire resistance of steel columns assumes that the temperature loads encountered by steel columns are evenly distributed vertically. However, real-world fire scenarios often feature significant vertical temperature differences. Therefore, this study comprehensively investigated these variations to derive a temperature curve that accurately represents real fire conditions. Subsequently, the fire resistance limits of steel columns were studied using this temperature curve, leading to a revised calculation formula for the critical fire resistance temperatures of steel columns. The following conclusions were drawn: (1) Nonuniform longitudinal temperature distributions are influenced by parameters such as the fire source distance, the heights of ventilation openings, and the distance between a vent and the temperature measurement point. Among them, the fire source distance has the greatest impact, with the maximum longitudinal temperature difference reaching over 500 °C. (2) Variations in the load ratio and longitudinal temperature differences alter the failure positions of steel columns, reducing their critical temperatures by up to 200 °C. (3) The revised critical fire resistance temperature formula is more accurate and safer compared with that outlined in the “Technical Code for Fire Protection of Steel Structures” (GB51249-2017). These findings offer valuable insights for the fire designs of steel columns.

Investigation of dynamic start-up and thermal airflow characteristics for air-carrying energy heating and cooling system: Sidewall, ceiling, and composite walls

The dynamic start-up process of the air-carrying energy radiant system (ACERS) is crucial for operation control. The dynamic heat transfer process of sidewall, ceiling, and composite walls for air-carrying energy heating and cooling systems was investigated using field experiments and numerical simulation. A new dynamic start-up model was proposed to rapidly predict the dynamic response time and heat transfer surface temperature for controlling indoor temperature. Six schemes with different thermal flow characteristics resulting from temperature difference and velocity uniformity were quantitatively studied through numerical simulation, which helps determine their rationality. The results show that the dynamic start-up model aligns well with experimental data, with an error of less than 3 %. The fast response time of the air medium heat transfer surface for heating/cooling is short (less than 0.5 h). The ceiling provides better adjustability compared to the sidewall. In the unstable state (Gc < 0), the Gc-related buoyancy has a vertical promotion effect, leading to increased convection and decreased vertical temperature difference in the room. Adding the sidewall heating to the ceiling heating reduces the indoor vertical temperature difference by 23 % for the composite walls heating compared to the ceiling heating. Convection accounts for 27 % of the sidewall heating, which is 2.7 times higher than that of ceiling heating (11 %). Combining the dynamic start-up model with numerical analysis enables rapid prediction and analysis of the thermal performance of ACERS, which can be applied to advanced control and optimization for energy-saving applications.

Reconfigurable flexible thermoelectric generators based on all‐inorganic MXene/Bi2Te3 composite films

AbstractFlexible thermoelectric generators (FTEGs) represent an excellent solution for energizing wearable electronics, capitalizing on their ability to transform body heat into electrical energy. Nevertheless, their use in the wearable industry is limited by the insufficient thermoelectric (TE) efficiency of materials and the minimal temperature variation among the devices. In this study, we have developed a Lego‐like reconfigurable FTEG by combining flexible TE chips, rheological liquid‐metal electrical wiring, and a stretchable substrate in a mechanical plug‐in configuration. The flexible TE chips are constructed from n‐type all‐inorganic MXene/Bi2Te3 composite films, which have their TE properties further enhanced through heat treatment. A demonstration of the FTEG illustrates its capability to convert heat into vertical temperature difference (ΔT), leading to a substantial ΔT at the cold end in contact with the environment, resulting in a power output of 7.1 μW with a ΔT of 45 K from only 5 TE chips. The reconfigurable FTEG presents significant potential for wearable devices to harness low‐grade heat.

Annual and Seasonal Variation of the Ocean Thermal Resources off the Mexican Coast

A large amount of thermal energy is stored in the oceans between the tropics, available for conversion into electrical energy using OTEC technology. The aim of this study was to determine the annual and seasonal variability of the oceanic thermal resource in Mexico. Using the WOA18 database, we mapped surface temperature at a 10 m depth, deep cold water (&lt;5 °C), vertical temperature difference (18 and 20 °C), and temperature anomalies. From the results, four areas were analyzed as being suitable for the installation of OTEC technology: Pacific (A), Los Cabos (B), Caribbean (C), and Gulf of Mexico (G). The optimal thermal resource (≥20 °C) was found between a 400 and 1000 m depth in all seasons in A and C, in spring, summer, and autumn in G, and only in summer and autumn in B. The suboptimal thermal resource (between 18 and 20 °C) was present between 400 and 800 m in all seasons in A, C, and G, and in summer and autumn in B. These results provide new information of utmost importance for future location and design considerations of OTEC plants on Mexican coasts, and the methodology can be used in other areas where there is a lack of field data and the development of OTEC technology is being considered.

Temperature analysis and prediction for road-rail steel truss cable-stayed bridges based on the structural health monitoring

A growing number of road-rail steel truss bridges have been built worldwide in recent years. Due to the complex cross-sectional structure and increasing span length, these main girders are prone to developing uneven temperature fields and significant local thermal effects, which can lead to excessive temperature stresses and structural damage. An accurate assessment of the temperature distribution in road-rail steel truss girders is critical as it aids in the thermal response analysis of the bridge and the structural safety evaluation. The paper analyses the temperature distribution of the road-rail steel truss girder base on the light conditions and the structure of the main girder. A modified method for calculating the effective temperature (ET) and temperature difference (TD) is also proposed. Comparing with the conventional regional weighted averaging method, the modified method improves the accuracy of ET calculation by 20 %. A prediction method based on the long short-term memory (LSTM) network is proposed, which estimates ET and TD for road-rail steel truss girders based on the environment around the bridge. The deep learning-based method improves accuracy by 40 % compared with the conventional linear regression method for ET prediction. Meanwhile, the proposed method alleviates the current lack of prediction methods for TD of road-rail steel truss girders. A detailed analysis of the temperature of a road-rail steel truss bridge is also presented based on the structural health monitoring (SHM) system. A negative vertical temperature difference was observed in the fringe truss. The maximum transverse temperature difference (TTD) was much greater than the maximum vertical temperature difference (VTD). The above features deserve extra attention from bridge designers.

Temperature field characteristics of railway steel-concrete composite girger with different pavement layers

The temperature distribution in steel-concrete composite girders is complex, existing specifications and studies for temperature gradients in such girders are inadequate as they fail to fully account for the influence of track slabs and ballast. Therefore, this study takes into consideration the effects of laying track slabs and ballast and conducts temperature field experiments on steel-concrete composite girders. A finite element thermal analysis model was established and validated by the experimental data, and the effects of track slabs, ballast thickness, and wind velocities on the temperature field is analyzed. Results show that ballast and track slabs with a thickness of 40 mm exert similar effects on temperature field of girder. Compared to an uncovered composite girder, they change the temperature distribution of the concrete slab from a reverse "C" curve to a top-to-bottom decreasing trend under cooling and from a top-to-bottom decreasing trend to uniform distribution during heating, increasing vertical temperature difference in concrete slab by 4 °C when cooling 15 °C. Interestingly, the steel-concrete interface exhibits temperature differences during all test conditions. The temperature gradient curve observed in the steel-concrete composite girders with railway pavement layers in this study reveals substantial deviations from the temperature gradient curve stipulated by existing bridge design codes. Parameter analysis reveals that, as wind velocities increase, the maximum vertical temperature difference decreases, and the thickness variation of the railway pavement layer within the range of 30–50 mm was found to have no discernible effect on the temperature gradient of composite girder. This study provides reference for research on temperature gradients in railway steel-concrete composite girders.

Investigation of temperature effects on wide steel box girder of suspension bridge based on long-term monitoring data

The time-varying temperature distributions on bridge structures may remarkably change structural performance, which may result in differential strain/stress responses on structural members compared with the design conditions. Therefore, it is crucial to have a comprehensive understanding of temperature distributions and its effects on bridges. In this study, taking advantage of structural health monitoring technology, 1-year field monitoring data collected from a long-span suspension bridge were used to investigate the temperature distributions and their effects on the steel box girder. Specifically, the distributions and probability statistics of temperatures on the top and bottom plates were firstly analyzed. Based on which, the transverse and vertical temperature differences on the box girder were further examined, moreover, the representative values of temperature differences for various return periods were calculated by exceedance probability method. At end, a temperature prediction method was proposed to simulated the temperature field distributions during bridge life cycle, to provide substantial temperature data for estimating future operation condition. The results of this study were beneficial to structural evaluation of in-service bridges to ensure their serviceability and integrity in the life cycle.

Spatial and temporal indoor temperature differences at home and perceived coldness in winter: A cross-sectional analysis of the nationwide Smart Wellness Housing survey in Japan

Residents themselves are responsible for controlling their living environment, and their perception of coldness is important to protect their health. Although previous studies examined the association between perceived coldness and indoor temperature, they did not consider the spatial–temporal differences in indoor temperatures. This study, conducted in Japan, measured indoor temperatures in 1,553 houses across several rooms (living room, changing room, and bedroom) and heights (at 1 m above the floor and near the floor) over two weeks and obtained the perceived coldness from 2,793 participants during winter. Results showed substantial temperature differences between rooms (horizontal differences): 3.8 °C between living and changing rooms, and 4.1 °C between living rooms and bedrooms. The average vertical and diel (evening-morning) temperature differences in the living room were 3.1 °C and 3.0 °C, respectively. Regional analysis revealed that the Tohoku region experienced larger horizontal and diel indoor temperature differences, primarily due to its practice of intermittent and partial heating in living rooms only, in contrast to Hokkaido's approach of heating the entire house continuously. Despite Hokkaido's comprehensive heating system, it exhibited the largest vertical temperature difference of 5.1 °C in living rooms, highlighting the insufficiency of heating alone and the necessity for enhanced thermal insulation. The multivariate logistic regression analyses showed that average temperatures and vertical temperature differences were associated with perceived coldness, while horizontal and diel differences did not show a significant association, further emphasizing the importance of improved thermal insulation. Moreover, factors like individual attributes (age and gender), and lifestyle choices (meal quantity, exercise habits, alcohol consumption, and clothing amount) were significantly associated with coldness perception. Notably, older adults were less likely to perceive coldness but more vulnerable to the health impacts of low temperatures, underscoring the necessity of not solely relying on human perception for indoor temperature management to protect cold-related health problems.

PIV experimental study on natural convective flows at high Rayleigh numbers in industrial buildings

High heat loads in industrial buildings potentially form strong natural convective flows. These flows exhibit significant unsteadiness and anisotropy, which can profoundly impact indoor air distribution. To study the flow characteristics of thermal convective flows in large indoor spaces, we built a large-scale test bench with controllable thermal boundaries. Under three different heat source intensities represented by Rayleigh numbers (Ra = 3 × 1010, 6 × 1010, and 1 × 1011) that are typical in industrial buildings, we used 2-dimensional particle image velocimetry to capture the large-scale convective airflow by splicing nine subregions, each with 800 instantaneous flow fields sampled at a frequency of 3 Hz. The results show that the convective airflow exhibited large-scale circulation patterns. The velocity near the wall gradually increased with the increased Ra number, while the velocity at the center remained low. The turbulence intensity near the wall was less than 1, while that at the center was larger than 5 and fluctuated greatly. The dominant fluctuation frequency of the airflow under the high Ra was 0.1 Hz. Through proper orthogonal decomposition, it is found that even for horizontal flows, the main transient fluctuations still exhibit an up-and-down fluctuating flow structure. Additionally, the calculation of the velocity structure function revealed that the airflow near the wall is anisotropic, while the airflow at the center is isotropic. The Reynolds number of the flow generated by vertical temperature differences exhibits a power function relationship with the Rayleigh number. This study provides a basis for the optimization of air distribution design in industrial buildings.

An experimental case study of natural ventilation effects on the residential thermal environment and predicted thermal comfort in Kunming

The use of natural ventilation for cooling in summer in mild climate areas can positively improve the indoor thermal environment and thermal comfort. In this paper, Kunming, China was chosen as a case to study experimentally the natural ventilation effects on the residential thermal environment and thermal comfort in mild climate rural areas. The effects of natural ventilation on the indoor thermal environment and thermal comfort under the typical hottest sunny days in summer in Kunming were investigated with seven different combinations of ventilation methods with the opening/closing of doors/windows. The results show that natural ventilation can considerably improve the indoor thermal environment. Furthermore, the uniformity of indoor thermal environments at different heights was assessed. Additionally, the vertical temperature difference between the head and foot areas around the human body remained below 3 °C. Moreover, the adaptive predicted mean vote (APMV) model was used to evaluate the thermal comfort under natural ventilation, and values of APMV ranged from −0.84 to 0.84 under six scenarios, considering an acceptable temperature range based on occupant satisfaction rates of over 80%. This study's outcomes offer valuable insights for the design of self-built housing in the extensive rural areas within mild climate zones in China.

Gender disparities in thermal responses under vertical air temperature differences

The effects of vertical temperature differences (VTD) on human thermal comfort have attracted growing attention from researchers when utilizing split air conditioners for winter heating. This study underscores the need to investigate the influences of gender disparities in the context of significant vertical temperature variations, a critical aspect that has not yet been comprehensively explored. Twenty gender-balanced subjects were exposed to a variety of stratified thermal environments created by a split air-conditioner. Their overall and local perceptual and physiological responses were measured at various operative temperatures and VTD. Results show that females have lower thermal sensation vote (TSV) and mean skin temperature under the same environments compared to males. Neutral operative temperatures of females and males are 23.7 ˚C and 20.8 ˚C, respectively. On the cold side, lower leg and foot thermal sensations are dominant whereas chest and back are dominant on the warm side. When females rated “slightly warm” (TSV equaled 1) or “warm” (TSV equaled 2), or males rated “slightly cool” (TSV equaled −1), increased VTD can lower thermal acceptability. The research findings have significant implications for the understanding of gender requirements of stratified heating environments and for maximizing the thermal comfort of the two genders.

The effect of baffles on vertical wall PCM to enhance natural convection

The objective of this study is to enhance convective heat transfer within phase change materials (PCM) using baffles on a vertical wall. PCMs have major drawbacks of low thermal conductivity, high viscosity, and limited natural convection. To address these issues, we investigated a passive approach to enhance natural convection with baffles. The new approach is to arrange multiple baffles with gaps on the opposite side of the heated vertical wall. This placement can minimize vertical temperature difference by blending upward-flowing hot liquid PCM with downward-flowing cold liquid PCM across the gaps and also increase circulating velocity by shortening path of circulation cell through sections divided by baffles. Visualization experiments of shadowgraphy and particle image velocimetry (PIV) were conducted to compare the case with baffle (WB) against the case without baffle (NB). The presence of the baffles lowered the average temperature difference in the horizontal direction by 40%. The WB case reduced the temperature difference in the vertical direction by 50%, compared with the NB case. Furthermore, comparison of the WB with NB showed that at the heat power levels of (4, 6, and 8) W, the convection coefficient increased by up to (28, 34, and 27)%, respectively. Therefore, by changing the internal flow pattern, the baffles on the vertical wall improved convective heat transfer performance.

Assessment of vertical cooling performance of trees over different surface covers

Tree-induced cooling benefits are associated with various factors, such as canopy morphology, surface cover, and environmental configuration. However, limited studies have analyzed the sensitivity of tree-induced cooling effects to the combination of such factors. Most studies have focused on 1.5-m cooling performance, and few studies on the variability of the under-tree vertical cooling performance. Therefore, this study aims to investigate the vertical cooling performance of different combinations of trees and surface covers. The study was completed in Chongqing, China, with field experiments capturing vertical air temperature and wind speed at 0.5, 1.0, 1.5, 2.0 and 2.5 m under two typical combinations of “tree + grass” (ComA) and “tree + shrubs” (ComB), and capturing 1.5 m microclimatic environments of a control group with hard pavement without tree shade (REF). The results show that at an average ambient temperature of 33 °C, the maximum air-cooling temperatures for ComA and ComB were 2.46 °C and 1.78 °C, respectively. An increase in the ambient temperature corresponded to a decrease in the cooling effect difference between ComA and ComB. ComA had a maximum vertical temperature difference of 1.01 °C between H1.5m and H2.0m. Between H2.5m and H2.0m, the maximum vertical temperature difference for ComB was 1.64 °C. This study explored the changing patterns of under-tree vertical temperatures under different tree and surface cover combinations, conducive to clarifying the key elements affecting tree cooling performance. The results have implications for accurate thermal comfort assessments and provide a theoretical basis for fine-tuning the design of under-tree spaces.

Thermal sensation prediction model for high-speed train occupants based on skin temperatures and skin wettedness.

Passenger thermal comfort in high-speed train (HST) carriages presents unique challenges due to factors such as extensive operational areas, longer travel durations, larger spaces, and higher passenger capacities. This study aims to propose a new prediction model to better understand and address thermal comfort in HST carriages. The proposed prediction model incorporates skin wettedness, vertical skin temperature difference (ΔTd), and skin temperature as parameters to predict the thermal sensation vote (TSV) of HST passengers. The experiments were conducted with 65 subjects, evenly distributed throughout the HST compartment. Thermal environmental conditions and physiological signals were measured to capture the subjects' thermal responses. The study also investigated regional and overall thermal sensations experienced by the subjects. Results revealed significant regional differences in skin temperature between upper and lower body parts. By analyzing data from 45 subjects, We analyzed the effect of 25 variables on TSV by partial least squares (PLS), from which we singled out 3 key factors. And the optimal multiple regression equation was derived to predict the TSV of HST occupants. Validation with an additional 20 subjects demonstrated a strong linear correlation (0.965) between the actual TSV and the predicted values, confirming the feasibility and accuracy of the developed prediction model. By integrating skin wettedness and ΔTd with skin temperature, the model provides a comprehensive approach to predicting thermal comfort in HST environments. This research contributes to advancing thermal comfort analysis in HST and offers valuable insights for optimizing HST system design and operation to meet passengers' comfort requirements.

Analysis of factors influencing indoor thermal environment in passive houses in Plateau regions based on regression model

How to make full use of geographical advantage to improve the indoor thermal environment of passive buildings in plateau area has become a hot topic, which is of great significance for building energy conservation and thermal engineering design of passive buildings. This study took a residential house in Lhasa, Tibetas as the research object, obtained indoor air temperature distribution through field measurement. A multiple regression model was used to explore the influence of outdoor meteorological factors on indoor thermal environment. Results showed that the temperature near the south window was the highest mostly higher than 16 °C, and the vertical temperature gradient was higher than 7.5 °C with the solar radiation and outdoor temperature gradually raised during daytime. Besides, the vertical temperature difference is less than 3 °C as the distance from the south window increases, and the air temperature gradually goes down. The standardized regression coefficient (Beta) illustrated that solar radiation has the greatest influence on the indoor thermal environment compared with the outdoor temperature. Therefore, for direct gain passive buildings in Tibetan areas, the potential of reasonably setting transparent heat generation structures to improve the indoor thermal environment is far greater than that of improving the thermal insulation of non-transparent enclosures.

Experimental Study of Indoor Air Distribution and Thermal Environment in a Ceiling Cooling Room with Mixing Ventilation, Underfloor Air Distribution and Stratum Ventilation

A ceiling cooling system integrated with a mechanical ventilation system has been widely used in modern buildings with large sensible cooling loads due to the high thermal comfort level and large energy efficiency. However, there is a lack of systematic research on the influence factors such as ceiling surface temperature and cooling load on the indoor air distribution and thermal environment, and the impact of ventilation system type in the ceiling cooling room is still unclear. Therefore, this paper presented an experimental study of indoor air distribution and thermal environment in a ceiling cooling (CC) room with mixing ventilation (MV), underfloor air distribution (UFAD) and stratum ventilation (SV); the ceiling surface temperature was 17 °C–26 °C and the internal or external cooling load was 41.5 W/m2–69.5 W/m2. The results showed that the vertical air temperature difference and contaminant removal effectiveness were 0.2 °C–0.4 °C and 0.53–0.85 with CC + MV, 0 °C–1.2 °C and 0.68–1.25 with CC + UFAD and 0.3 °C–0.9 °C and 0.50–0.83 with CC + SV, and the corresponding heat removal effectiveness and air diffusion performance index were 0.96–1.11 and 96–100%, 0.9–1.5 and 57–100% and 1.11–1.34 and 71–100%, respectively. Moreover, the difference between mean radiant temperature and air temperature and the predicted mean vote of thermal sensation were from 0 °C to 0.9 °C and between 0 and 0.26 with CC + MV, from −0.1 °C to 2.2 °C and between −0.1 and 0.42 with CC + UFAD and from −0.1 °C to 0.9 °C and between −0.2 and 0.13 with CC + SV. Hence, the ventilation system type clearly affected the indoor air distribution and thermal environment in the ceiling cooling room, and the experimental results would be beneficial for the design and control of a ceiling cooling system combined with a mechanical ventilation system in practice.

Evaluation of heating performances of different ventilation methods in an office

In this study, 12 cases were investigated in an office-layout room using experiments and computational fluid dynamics (CFD) simulations. The heating performances of four ventilation methods (i.e. mixing ventilation (MV), stratum ventilation (SV), deflection ventilation (DeV) and impinging jet ventilation (IJV)) were comprehensively compared by various evaluation indexes (i.e. predicted mean vote (PMV), draught rate (DR), vertical air temperature difference (△T), air diffusion performance index (ADPI), energy utilization coefficient (EUC), air change efficiency (ACE) and contaminant removal efficiency (CRE)). Better thermal comfort was found in rooms heated by SV and DeV. The PMV, DR and △T under SV and DeV complied with Category B of ISO 7730:2005, and the ADPI was in full compliance with the stipulation of ANSI/ASHRAE 113-2022. For the energy-saving characteristic, the targeted-occupied-zone ventilation methods (i.e. SV, DeV and IJV) can effectively deliver warm air to the occupied zone, with the EUC values higher than unity and thus providing a good potential for energy saving. SV and IJV showed slightly higher ACEs in the breathing zone. The contaminant removal effectiveness of SV, DeV and IJV was comparable. Under the combined influence of occupant thermal plumes and locations of exhausts, MV showed a high CRE. However, the CRE under MV decreased significantly when the exhausts were not above occupants. In the case of supply air parameters in this study, the entropy-weight method indicated that DeV and SV had a better overall performance for winter heating, followed by IJV and then MV.

Comparison of the corrugated steel web composite box-girder and traditional girders regarding temperature field under solar radiation

The corrugated web composite box-girder (CWCB) is a novel structural form and has been widely adopted in bridge engineering due to its excellent mechanical properties and construction convenience. However, researches on the temperature field in CWCB is very limited, which may augment the risk of concrete cracking and steel web bucking and deteriorate the durability of bridge structures. This paper thereby experimentally investigates the time-varying and spatial temperature distribution features of CWCB based on a long-term temperature monitoring system. The experimental results indicate that the temperature field in CWCB is non-uniformly distributed and the vertical and horizontal temperature differences can reach up to 13.4 ℃ and 19.1 ℃, respectively. Meanwhile, the observed temperature distribution profile of the experimental CWCB is varying with seasons owing to the different exposure to solar radiation. Then, a refined numerical thermal simulation approach is developed and its reliability and accuracy have been validated by the experimental temperature data of three types of box-girders, i.e., CWCB, ordinary composite box-girder (OCB), and conventional concrete box-girder (CCB). Based on the validated numerical approach, the temperature fields of three full-sized box-girders are therewith compared and the results demonstrate that the temperature field in CWCB is much more complicated than the traditional box-girders. Besides, the obtained cross-sectional temperature differences of CWCB are significantly larger than that of the traditional box-girders. Finally, two temperature profiles have been proposed to characterize the thermal actions in CWCB, which are composed of parabolas and polylines. The outcome of this study can provide a useful tool for analyzing the temperature field and calculating the design thermal load of CWCB.

Determining the morphology of tornado-like vortices depending on thermal gradients: A numerical study

In this work, we study the role of the horizontal temperature differences on the top and bottom, their combined effect, and their relation to the vertical temperature difference in the development of traditional or reversed funnel-shaped vortices in a rotating cylinder inhomogeneously cooled on the top and heated at the bottom. These thermal inhomogeneities on upper and lower levels are observed in the formation of atmospheric vortices. Our numerical results show that if the thermal inhomogeneity is stronger on the top, an axisymmetric traditional funnel-shaped tornado-like vortex with an inner updraft of warmer air is developed. On the contrary, if the thermal inhomogeneity is stronger at lower levels, an axisymmetric reversed funnel-shaped vortex develops with an inner downdraft of cooler air. When thermal inhomogeneities are equal at both levels, it is the grade of localization of the heating (at the bottom) or the cooling (at the top), which determines the formation of a V-vortex or an inverted V-vortex, respectively. We perform a force balance analysis to give a physical insight into the phenomena. The results evidence the relevance of the thermal conditions on the vortical structures developed, and they may contribute to the understanding of the morphology of atmospheric vortices, such as tornadoes or cold air funnels.

Temperature behavior of cable-stayed bridges. Part I — Global 3D temperature distribution by integrating heat-transfer analysis and field monitoring data

Varying temperatures significantly affect long-span cable-stayed bridges. However, quantitative studies on their temperature behaviors are limited. Existing studies focus on 2D or 3D models of bridge segments only, exclude cables from heat-transfer analysis, and utilize inaccurate environmental conditions. For the first time, this study comprehensively and accurately investigates the global 3D temperature distribution of long-span cable-stayed bridges by integrating the heat-transfer analysis and field monitoring data. A navigation channel bridge of the Hong Kong‒Zhuhai‒Macao Bridge is used as the testbed. A global 3D refined finite element model of the entire bridge is established. The external thermal boundary conditions of the outer surfaces of the structure are carefully determined based on the real-time ambient temperature, wind, and solar radiation, which are tailored for each surface to reflect the influence of the geometric configuration. The internal thermal boundary conditions of the inner surfaces of the box girder and tower are dependent on the measured ambient temperature, considering the vertical temperature difference of the girder and the uniform temperature inside the tower. Then, the numerical heat-transfer analysis and field monitoring data are integrated to calculate the detailed temperature distribution of the entire bridge in different seasons. Results show that ambient temperature, wind, and solar radiation significantly affect the temperature distribution. For the girder, the vertical temperature difference is significant throughout the year, and the transverse temperature difference is nonnegligible in winter and summer, while the longitudinal temperature difference is trivial. The internal temperature of the tower remains stable owing to the insulation of the concrete. The temperatures of the cables vary from each other, which may cause stress redistribution within the structure. The calculated temperatures are in good agreement with their measured counterparts. The temperature results will be used to calculate the thermal-induced responses in the companion paper in a unified manner.