scholarly journals Effects of Variable Humidity on the Creep Behavior of Concrete and the Long-Term Deflection of RC Beams

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Pengfei Li ◽  
Shiqin He
Keyword(s):  
Experimental Data ◽  
Relative Humidity ◽  
Creep Strain ◽  
Analytical Models ◽  
Deformation Characteristics ◽  
Rc Beams ◽  
Test Results ◽  
Sustained Loads ◽  
Average Relative Humidity

The influences of variable humidity on the creep behaviors of concrete and the long-term deflections of RC beams are analyzed in this paper. A total of 6 prismatic specimens and 5 RC beams were subjected to sustained loads and 3 types of variable humidity conditions for 331 days. The creep strains of the prismatic specimens and the deflections of the RC beams were recorded to investigate the long-term deformation characteristics. The test results reveal that both the creep strain and the deflection of specimens under cyclic humidity conditions exhibit approximately linear tendencies that are obviously less than those of specimens exposed only to natural air. During certain wetting cycles, the deformation rate became slower and the creep strain even recovered with an increase in the humidity, especially for shorter wetting-drying cycles. Long-term deflections predicted using the CEB-FIP 90 and ACI 209R models were compared with the test results to evaluate the versatility of these current specifications. The findings included rather large errors between the predicted results and experimental data when the average relative humidity was adopted in the analytical models.

An Experimental Study on Residual Strength and Deformation Recovery of RC Beams Strengthened with FRP Plate

2015 ◽  
Vol 764-765 ◽  
pp. 1036-1040
Author(s):  
Kyoung Bong Han ◽  
Doo Yong Cho
Keyword(s):  
Residual Strength ◽  
Fiber Reinforced Polymer ◽  
Rc Beams ◽  
Fiber Reinforced ◽  
Reinforced Polymer ◽  
Cfrp Plate ◽  
Long Term Experiments ◽  
Sustained Loads ◽  
Deformation Recovery

In the recent construction industry, Fiber reinforced polymers (FRPs) have been considered to be an innovative material to repair and strengthen damaged structures. It is because FRPs have many beneficial characteristics, such as corrosion resistance, a high tensile strength-to-weight ratio, non-conductivity and design flexibility. As a demand of FRPs has increased, many researches on behavior of the structures which were externally strengthened with FRPs have been conducted. However, researches on time-dependant behavior of the structures have not been conducted yet. In order to provide improved serviceability to reinforced concrete (RC) members, the behavior of the RC members strengthened with FRPs under sustained loads should be investigated. This paper presents a series of long-term experiments and deformation-recovery experiments. For the long-term experiments, three RC beams were fabricated and two of the beams were strengthened with a carbon fiber reinforced polymer (CFRP) plate and a glass fiber reinforced polymer (GFRP) plate respectively. The beams were placed under sustained loads for about 550 days. After the 550 days, all of the beams were unloaded for the measurement of deformation recovery. The deflection and strains of rebar and FRP reinforcements were measures for about 60 days. As the result of long-terms experiment, the beams strengthened with CFRP plate showed a better performance in terms of deflection and strains of rebar and CFRP plate. Moreover, the beam with CFRP plate showed a higher deformation recovery and residual strength than the other beams.

scholarly journals Evaluating Flexural Strength of RC Beams Strengthened by CFRP using Different Analytical Models

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Riyam J. Abed ◽  
Mohammed A. Mashrei ◽  
Ali A. Sultan
Keyword(s):  
Flexural Strength ◽  
Prediction Models ◽  
Concrete Beams ◽  
Reinforced Concrete Beams ◽  
Analytical Models ◽  
Rc Beams ◽  
Test Results ◽  
Related Field ◽  
Cfrp Sheet ◽  
Externally Bonded

Abstract This paper deals with reinforced concrete beams strengthened by CFRP in flexure. The debonding between CFRP and the surface of the beam is the main problem. Many researchers around the world have made extensive efforts to study the phenomenon of debonding for efficient applications. Based on these efforts and different related field applications, code previsions and various models have been proposed for predicting debonding failure. Two code previsions and three typical models are presented in the current study. ACI-440.2R 17, CNR-DT 200 R1/2013, Said and Wu, Lu et al., and Teng et al. have been used to estimate the flexural strength of RC beams strengthened by CFRP with and without grooves. Test results of eleven flexural beams strengthened by CFRP sheet/laminate using externally bonded reinforcement (EBR) and externally bonded reinforcement on grooves (EBROG) methods were used in the current paper. The performance and accuracy of each model were evaluated based on these test results. Most of the prediction models that used in this study give a closer prediction of the flexural strength of beams strengthened by EBR compared to that of the beams strengthened by EBROG. Finally, the prediction results of CNR-DT 200 R1/2013 were the most accurate and approval with test results compared with other models in the current study

scholarly journals Long-term Deflections of Hybrid GFRP/Steel Reinforced Concrete Beams under Sustained Loads

2020 ◽  
Vol 6 ◽  
pp. 1-11
Author(s):  
Phan Duy Nguyen ◽  
Vu Hiep Dang ◽  
Ngoc Anh Vu ◽  
Polikutin Aleksei Eduardovich
Keyword(s):  
Reinforced Concrete ◽  
Steel Reinforcement ◽  
Experimental Results ◽  
Reinforced Concrete Beams ◽  
Flexural Behavior ◽  
Rc Beams ◽  
Climate Conditions ◽  
Glass Fiber Reinforced ◽  
Sustained Loads

One of the solutions to improve the flexural behavior of Glass fiber reinforced polymer (GFRP) reinforced concrete (RC) beams is the addition of tensile longitudinal steel reinforcement. The numerous studies to date on hybrid GFRP/steel RC elements have mainly focused on the static and short-term responses, very little work has been done regarding the long-term performance. This paper presents experimental results of time-dependent deflections of cracked GFRP and hybrid GFRP/steel RC beams during a 330-day-period in natural climate conditions. Three hybrid GFRP/steel and one GFRP RC beams with dimensions 100×200×2000 mm were tested in four-point bending. Different steel reinforcement ratios were used to evaluate the effect of the steel reinforcement on the long-term behavior of the beams. Experimental results show that the immediate deflections are inversely proportional to the additional steel reinforcement. With the same initial instantaneous deflection, the total deflection increases when increasing the steel reinforcement ratio. Also, temperature (T) and relative humidity (RH) significantly affect the long-term deflection of the tested beams. The measured long-term deflections were found to be in good agreement with the theoretical values calculated from the proposed method. However, there was an overestimation when using ACI 440.1R-15 or CSA-S806-12 procedures.

scholarly journals Establishing material hygrothermal characteristics via long-term monitoring and best-fit numerical models

2020 ◽  
Vol 172 ◽  
pp. 17009
Author(s):  
Mihails Birjukovs ◽  
Inga Apine ◽  
Andris Jakovics
Keyword(s):  
Experimental Data ◽  
Relative Humidity ◽  
Initial Conditions ◽  
Numerical Models ◽  
Climate Data ◽  
Material Models ◽  
Long Term Monitoring ◽  
Best Fit ◽  
Term Monitoring

Numerical models of heat and moisture transfer for performance forecast of lightweight insulating assemblies require many inputs. These include exterior climate data (i.e. temperature, relative humidity, solar radiation), interior climate data or standard models, transfer coefficients, correct initial conditions, etc. Most importantly, one needs reliable material models. A material model includes porosity, density, heat capacity, but also non-constant properties, such as thermal conductivity, vapor/liquid water diffusivity, sorption curves. These are, in general, difficult to determine, and material database entries often are incomplete, or simply non-existent. However, if one performs long-term monitoring of temperature and relative humidity dynamics within building envelopes, there is a way to determine hygrothermal curves and properties of the underlying materials. This can be done by performing simulations and finding the set of optimal hygrothermal curves and coefficients such that the experimental data is matched sufficiently well. Despite the appeal, this best-fit model approach is fraught with perils due to many unknowns and must be used carefully. In this article, we demonstrate the application of this method to insulating assemblies for which 6+ years' worth of experimental data is available, and showcase our results obtained using WUFI Pro 6.3 and the derived and verified material models.

Residual Strength and Deformation Recovery of RC Beams Strengthened with FRPs Plates under the Sustained Load

2018 ◽  
Vol 26 (1) ◽  
pp. 119-126 ◽  
Author(s):  
Dooyong Cho ◽  
Hoseong Jeong ◽  
Kyoungbong Han
Keyword(s):  
Residual Strength ◽  
Fiber Reinforced Polymer ◽  
Fiber Reinforced Polymers ◽  
Rc Beams ◽  
Fiber Reinforced ◽  
Reinforced Polymer ◽  
Cfrp Plate ◽  
Sustained Loads ◽  
Deformation Recovery

In this paper, in order to estimate efficacy, creep recovery, and residual strength of Fiber Reinforced Polymers (FRPs) strengthened Reinforced Concrete (RC) beams, long-term flexural experiments and static flexural experiments were carried out. For the long-term experiments, the beams were strengthened with a Carbon Fiber Reinforced Polymer (CFRP) plate and a Glass Fiber Reinforced Polymer (GFRP) plate respectively. The beams were placed under sustained loads for about 550 days. After the 550 days, all of the beams were unloaded for the measurement of deformation recovery. The deflection and strains of rebars and FRPs reinforcements were measures for about 60 days. As the result of long-terms experiment, the beams strengthened with CFRP plate showed a better performance in terms of deflection and strains of rebars. And the strengthened RC beams were very effective in terms of deflection control. Furthermore, the strengthened beams have shown immediate deformation recovery. Through the static flexural experiments, it was shown that the CFRP strengthened beam had high residual strength. It seems that the sustained loads did not affect bond and residual strength of the beams.

scholarly journals Long-Term Behavior of RC Beams Strengthened with Hybrid Composite Beam

2019 ◽  
Vol 9 (9) ◽  
pp. 1734
Author(s):  
IL-Heon Kim ◽  
Hyung-Joo Lee ◽  
Joo-Won Kang ◽  
Yeol Choi
Keyword(s):  
Hybrid Composite ◽  
Composite Beam ◽  
American Concrete Institute ◽  
Time Dependent ◽  
Rc Beams ◽  
Experimental Conditions ◽  
Sustained Loads ◽  
Long Term Behavior ◽  
Hybrid Composite Beam

This paper describes the results of long-term tests on reinforced concrete (RC) beams strengthened with hybrid composite beam (HCB) under two different sustained loads. Test specimens were fabricated to reflect the most common RC beam size used in school buildings in South Korea. The specimens had dimensions of 400 mm (width) × 600 mm (depth) × 6000 mm (length), and were tested with or without external strengthening by a hybrid composite beam (HCB). Test results showed that strengthening the RC beams with HCB not only reduced the instantaneous deflection but was also effective in decreasing long-term deflection. In this study, time-dependent factors were investigated using a modified version of the American Concrete Institute (ACI) equation. Time-dependent factors of HCB-strengthened RC beams found in the present work differed from those of other investigations due to various experimental conditions. In the present study, we found that the ACI equation may not provide a reasonable estimation of the long-term behavior of HCB-strengthened RC beams.

Analysis of Long-Term Stress of Steel-Concrete Composite Beams

2010 ◽  
Vol 163-167 ◽  
pp. 2037-2040
Author(s):  
Min Ding ◽  
Jin San Ju ◽  
Xiu Gen Jiang
Keyword(s):  
Relative Humidity ◽  
Concrete Slab ◽  
Concrete Strength ◽  
Composite Beams ◽  
Reinforcement Ratio ◽  
Longitudinal Reinforcement ◽  
Slab Width ◽  
Yearly Average ◽  
Average Relative Humidity

The theoretical model to compute long-term stress of steel-concrete composite beam was deduced. On this basis, the effects of factors such as concrete age to loading, longitudinal reinforcement ratio in concrete slab, concrete slab width, environmental yearly average relative humidity and concrete strength on long-term stress of composite beams are discussed. The results show that additional stress at the top of concrete slab is tensile stress and that at the bottom of steel beam is compressive stress. Concrete slab width, as well as longitudinal reinforcement ratio can not be ignored. Concrete strength and concrete age to loading have relatively bigger effect as well. But environmental yearly average relative humidity has less impact.

scholarly journals Moisture Performance of Façade Elements Made of Thermally Modified Norway Spruce Wood

Forests ◽  
2020 ◽  
Vol 11 (3) ◽  
pp. 348 ◽  
Author(s):  
Miha Humar ◽  
Boštjan Lesar ◽  
Davor Kržišnik
Keyword(s):  
Relative Humidity ◽  
Moisture Content ◽  
Norway Spruce ◽  
Spruce Wood ◽  
Moisture Performance ◽  
Average Relative Humidity ◽  
Thermally Modified Wood ◽  
Moisture Content Measurement ◽  
Modified Wood

Wooden façades are gaining in importance. Thermally modified wood is becoming one of the preferred materials for claddings. In spite of the fact that façades made of thermally modified wood have been in use for more than two decades, reports about long-term monitoring have been sparse. The results of three-year monitoring of a façade made of thermally modified wood in Ljubljana are reported. Moisture content measurements of thermally modified façades were taken at 22 locations and compared to the moisture content of untreated Norway spruce wood. Temperature and relative humidity were recorded in parallel. The moisture content of the wood was compared to the average relative humidity before the measurements. The results confirm the lower moisture content of thermally modified wood in comparison to reference Norway spruce. The moisture content of the wooden façade could be best correlated with the average relative humidity and temperature 48 h before the wood moisture content measurement was taken.

Parents' long-term adjustment to the genetic test results of minors at risk for Long QT Syndrome

2004 ◽  
Author(s):  
K. S. W. H. Hendriks ◽  
F. J. M. Grosfeld ◽  
A. A. M. Wilde ◽  
J. van den Bout ◽  
I. M. van Langen ◽  
...  
Keyword(s):  
At Risk ◽  
Long Qt Syndrome ◽  
Genetic Test ◽  
Test Results ◽  
Long Qt ◽  
Genetic Test Results ◽  
Qt Syndrome
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