Abstract
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.
Abstract
Based on experimental records from a composite beam with a steel section and topping concrete flange, a finite element thermal analysis model was conducted and verified. The experimental ...beam was provided with 14 embedded and surface temperature sensors inside the concrete flange and on the steel section. The temperature records from the experimental beam were collected for two winter months. The finite element thermal model was conducted to simulate the thermal response of composite beams under the influence of open-field thermal conditions. The model solves for the conduction of heat in concrete and steel considering the different boundary conditions that include; solar radiation, reflected radiation, temperature of air and the speed of the ambient air. To verify the introduced thermal model, the predicted temperatures at the 14 thermocouples were compared with the experimental ones along the 24 hours of three days with different weather conditions. The comparisons showed that for the three days, the model could capture the temperature-time behavior accurately for all thermocouples with moderately low average absolute errors of 0.4 to 2.0 °C. Another notice was that the maximum errors in the steel section were higher than in concrete.
Abstract
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.
Abstract
Open field structures, like bridges, are loaded with the typical static, moving and dynamic loads in addition to the open-field thermal loads. These loads include the time-dependent changing ...of solar radiation and air temperature in addition to the speed of this air. Due to the importance of bridge structures and their high construction costs and long planned life spans, special focus are given to the thermal response of these structures in bridge design codes. With the advances of construction technologies and the use of new composite materials and configurations, updates in code specifications become required, which make the researches in this field of a vital and continuous need. An experimental concrete-steel composite beam with special configuration was cast and installed in an open field. Several temperature and strain sensors in addition to metrological sensors were used to observe its long-term thermal response. The presented experimental records can be helpful for a better understanding of the thermal behavior of such configuration of composite beams under open-field thermal loads. Along two-month cold-season measurements, a maximum temperature difference, within the beam body, of 13.3 °C was recorded, with maximum net tensile and compression thermal strains of 40 and 110 micro-strains
Asphalt concrete is a composite material that is extensively used in the construction of highways, airport runways and parking lots. Riding comfort, durability and water resistance are some of the ...driving mechanical characteristics making it the most preferred choice in the pavement industry. Multifunctional materials have the simultaneous ability to exhibit non-structural functions apart from their regular structural functions. Structural materials can be designed multifunctional by integrating electrical, magnetic, optical, and possibly other functionalities that exhibit advantages beyond the sum of the individual capabilities. Asphalt concrete has the potential of being used as a multifunctional material by controlling its electrical conductivity. Asphalt concrete, by nature, is a non-conductive composite material, but its conductivity can be improved by using conductive materials. The method of inclusion of a conductive filler within the asphalt concrete matrix and its percolation threshold are the factors of interest within this work. The study of the effect of inclusion of the conductive material on the mechanical properties of the hot-asphalt concrete mixtures is another goal of the present work. The results showed that the incorporation of carbon fibers (CFs) within the dense graded asphalt concrete mixtures can enhance their mechanical and electrical properties. The embedding of only 1.5% CFs by volume of mixture improved the stability, IDT and electrical resistivity by 72%, 20% and more than nine orders, respectively. Accordingly, 1.5% CFs represent the percolation threshold of all of the studied properties.
The mud is considered as one of the oldest construction materials in Iraq and is still used in the country regions for farmer’s houses or animal shelters. In Iraq, there are different types of mud ...constructions, including adobe, unfired bricks and cob. The presented study has focused on unfired clay brick where the clay is the main material. To ensure that the clay is pure and clean, it was excavated from the depth of 2 m below the natural ground level. Different types of unfired clay bricks produced by adding different materials to the clay to improve its properties and especially large deformation due to shrinkage. The added materials are classified into three concepts, the first additives are the natural fibers (straw, sawdust, and rice husk) and they are used to improve the tensile strength of brick and reduce the cracking due to shrinkage. The second additives included added the fine and coarse sand as a stabilizer to reduce the volumetric changes. The third additives are adding cement to increase the adhesive and cohesion of the mud matrix. The measurements included compressive strength of brick, mortar, and masonry and the flexural strength of bricks alone. The behaviour of unfired masonry prisms was also compared to the traditionally fired clay brick prisms. The results indicate that higher compressive strength of bricks was got for the mix that included clay, coarse sand and straw. The maximum flexural strength of bricks was got for the mix that included clay and sawdust, while for unfired masonry prism the higher compressive strength was obtained with a mix that included clay, coarse sand and straw. Finally, a proposed formula to obtain the compressive strength of unfired brick masonry from the compressive strength of brick and mortar is presented.
This study investigated the effectiveness of several types of adhesives used in post-installed rebar connections as a bonding agent between steel reinforcement bars and old concrete under pull out ...test. The experimental samples were; cylindrical samples of (150 mm dia. × 300 mm high) with anchors rebar of varying diameter (12 and 16 mm), different embedded length (100 and 150) mm with different holes’ diameters. The strategy of control were cast-in-place rebar concrete specimens while other samples are post-installed rebar concrete specimens of varied chemical adhesives as bonding agents, namely KUT EPOXY ANCHOR ‘NS’ and SIKAFLOOR169. The output showed that the different adhesives yielded closed pull-out load values. It is found that the pull-out capacity (bond strength) is increased by increasing the embedded length, the diameter of the rebar and slightly with the diameter of the hole. In addition, the failure mode of post-installed rebar concrete was governed by the embedded length and the area of contact with the adhesives. On the other hand, the larger diameter of rebar favors splitting or failure of concrete due to higher strength in binder-rebar interface compare to the binder-concrete interface. The results showed that the pull-out load was increased by (26 % and 32 %) as the rebar diameter increased from 12 mm to 16 mm for KUT “NS” and SIKAFLOOR respectively. The hole diameter had slightly effect of the pull out load where the average of increment was only 6 %. Finally, the bonding strength is considerably depended on the embedded length and less affected by the type of epoxy.
Many types of structures, or part of which, are directly under the exposure of the time-dependent variations of the temperature of air and solar radiation. Such thermal loads can vary the temperature ...of the different parts of the structural members causing undesired structural effects. In this research, an experimental study was conducted to investigate the influence of such thermal loads on composite beams. For this purpose, a concrete-encased-steel beam was instrumented with fifteen thermocouples and other sensors. The records were captured for a sunny winter day with moderately high daily air temperature difference of more than 18 oC and a solar radiation of more than 700 W/m2. The results showed that the hourly temperature variation and the sun movement in addition to the altitude angle of sun rays control the vertical and lateral temperature distributions of the beam. The maximum recorded difference between hourly maximum and minimum temperatures of the beam was 12.5 oC.
Summary
The structural performance of bridge structures is temporal and is mainly controlled by the types of the applied loads. To continuously observe the structural performance of bridges, ...structural health monitoring sensors that include among many temperature sensors are used. The impact of nonuniform temperature distributions in bridge girders due to the environment thermal loads has been recognized by former researchers and bridge design codes. To evaluate these and other effects on the structural behavior of bridge structures, many field and experimental structural health monitoring studies were carried out. However, more researches are required to investigate the temperature distributions in other girder configurations. This work is directed to investigate the impact of air temperature and solar radiation on temperature gradient distributions in concrete‐encased composite girders. For this purpose, an experimental concrete‐encased steel girder segment was instrumented with thermocouples and other sensors. The experimental data recording continued for 6 months during the hot and cold seasons. Furthermore, a thermal finite element (FE) parametric study was conducted to investigate the effect of the girder size. The test results showed that the vertical and lateral temperature gradient distributions and the variation of the temperature gradients with time are controlled by the amount and location of the received solar radiations. The FE analysis showed that the daily temperature variations are higher in smaller girders, whereas the temperature gradients are smaller than in larger girders. Moreover, the FE results showed that the thickness of the girder's concrete members has an important impact on temperature gradients and temperature distributions.
This article presents experimental results from a concrete-steel composite girder. The girder is composed of an I-shape steel beam that is topped by a reinforced concrete slab. The girder was ...constructed in an open environment so that it is freely subjected to the variation of the atmospheric thermal loads. These loads include the solar radiation, temperature of the surrounding air and speed of the wind. Therefore, a weather station that includes sensors to measure the three aforementioned thermal loads was installed beside the girder. The girder was instrumented with thermocouples that were either embedded in the concrete slab or attached to the steel beam. The thermocouples were distributed across the slab thickness, along its width and along the vertical centerline of the composite girder. The aim of this research is to provide experimental measurements that facilitate better understanding of temperature gradient distributions in composite bridge girders in winter. The test records were continued for approximately two months during the cold season. The test results showed that the negative vertical temperature gradient was higher than the corresponding positive one due to the low intensity of solar radiation. Similarly, the lateral positive temperature gradient along the width of the concrete slab was higher than the vertical positive temperature gradient due to the low altitude of solar radiations.
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