Limitations and Uncertainties in the Long-Term Deflection Calculation of Concrete Structures

Vakhshouri, Behnam; Nejadi, Shami

doi:10.1061/9780784413609.055

Cited by 9 publications

(4 citation statements)

References 15 publications

(8 reference statements)

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“…Although the above equations are simple to use, their predictions of long-term deflections have been controversial [24][25]. This study aims at presenting a simple formula to accurately estimate the long-term deflection of flexural RC members made from HSC but also applicable for NSC.…”

Section: Long-term Deflectionmentioning

confidence: 99%

Revised formula for predicting the long-term deflection multiplier of normal and high strength concrete

Muhaisin

Jawdhari

Ammash

2019

Rev. IBRACON Estrut. Mater.

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ResumoHigh strength concrete (HSC) has found many applications in civil engineering structures such as in high-rise buildings, and bridges. The mechanical properties of HSC are sometimes different than of normal strength concrete (NSC). In particular, HSC possess lower creep strains compared to NSC. As a result, members constructed using HSC have been found to deflect less under sustained long-term loads. However, formulas used by current codes of practice such as ACI (318) code and Australian standard (AS-3600) for predicting the long-term deflections don't account for effects of HSC. This study aims to present a theoretical formula to calculate the long-term deflections for reinforced concrete beams made from NSC and HSC, taking into account the influence of HSC. The formula was derived from curve fitting analysis of long-term deflections obtained from several experimental tests available in literature. The presented equation considers the effects of several factors, such as compressive strength of concrete, and reinforcement at compressive zone, found in the experiments to have a significant impact on long-term deflections. The results of the equation were compared with experimental results of other researchers, and a good agreement was obtained. Following a parametric study, the long-term deflections were found to decrease to about 50% when increasing the concrete's compressive strength from 20 to 100 MPa. The compressive steel reinforcement was found less effective in the case of HSC.El hormigón de alta resistencia (HSC) ha encontrado muchas aplicaciones en estructuras de ingeniería civil, como en edificios de gran altura y puentes. Las propiedades mecánicas de HSC son a veces diferentes de hormigón de fuerza normal (NSC). En particular, HSC posee cepas de fluencia más bajas en comparación con la NSC. Como resultado, los miembros construidos con HSC se han encontrado para desviar menos bajo cargas sostenidas a largo plazo. Sin embargo, las fórmulas utilizadas por los códigos de práctica actuales, como el código ACI (318) y el estándar australiano (AS-3600) para predecir las desviaciones a largo plazo, no tienen en cuenta los efectos de HSC. Este estudio tiene como objetivo presentar una fórmula teórica para calcular las deflexiones a largo plazo para vigas de hormigón armado hechas de NSC y HSC, teniendo en cuenta la influencia de HSC. La fórmula se derivó del análisis de ajuste de curvas de las deflexiones a largo plazo obtenidos de varias pruebas experimentales disponibles en la literatura. La ecuación presentada considera los efectos de varios factores, como la resistencia a la compresión del hormigón, y el refuerzo en la zona de compresión, que se encuentra en los experimentos para tener un impacto significativo en las deflexiones a largo plazo. Los resultados de la ecuación se compararon con los resultados experimentales de otros investigadores, y se obtuvo un buen acuerdo. Después de un estudio paramétrico, se descubrió que las deflexiones a largo plazo disminuían a aproximadamente 50% cuando aumentaba...

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Section: Long-term Deflectionmentioning

confidence: 99%

Revised formula for predicting the long-term deflection multiplier of normal and high strength concrete

Muhaisin

Jawdhari

Ammash

2019

Rev. IBRACON Estrut. Mater.

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“…7 shows cracked and uncracked sections of a simply supported one-way slab under sustained service loading. (1963) and Vakhshouri and Nejadi (2014) introduced the concept of the effective moment of inertia to predict the curvature and deflections directly from the elasticity theory. The concept was verified by different researchers mainly by implementing the idea of tension stiffening to apply for various types of structures, loading rates, fiber reinforced and FRP sheets, and bars included concrete members.…”

Section: Effective Moment Of Inertiamentioning

confidence: 99%

Instantaneous deflection of self-compacting and lightweight concrete slabs at early-age

Vakhshouri¹,

Nejadi²

2018

10.5267/j.esm

Self Cite

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This paper describes laboratory tests on twelve simply-supported one-way slabs including four lightweight concrete slabs in this study and previously conducted experiments on eight selfcompacting reinforced concrete slabs subjected to loading at the age of 14 days. All slab were identical by dimensions of 3.8 m long supported on 3.5 m span, 400 mm wide, and 161 mm deep with 4N12 bars at an effective depth of 136 mm providing a reinforcement ratio of 0.008. After seven days moist-curing, the specimens were removed from the formworks and subjected to different values of the uniformly distributed loading including the self-weight of slabs. The mid-span deflection of slabs was recorded immediately after putting the loading blocks on the slabs. Despite close values of the compressive strength of the mixtures, the obtained results validate the effect of the concrete type on the instantaneous deflection of slabs. A wide range of existing models of the effective stiffness of reinforced concrete section were investigated to predict the instantaneous deflection of slabs. Majority of the models are developed for conventional concrete. Comparing the predicted and experimental results of mid-span deflection confirmed that the existing models are inadequate for lightly reinforced specimens such as slabs. New models are proposed and verified to predict the effective moment of inertia in the slabs with and without fiber reinforcing concretes.

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“…This study evaluated and enhanced existing prediction models for deflection, considering factors such as material and geometric characteristics, construction factors, and cross-sectional properties for calculation. These enhancements result in more accurate predictions of long-term deflection in concrete beam bridges [7][8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

Research on the Method of Prestressing Tendon Layout for Large-Span Prestressed Components Continuous Rigid Frame Bridge Based on “Zero Bending Moment Dead Load Theory”

Liu,

Gu,

et al. 2024

Buildings

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Based on the theory of zero bending moment under constant load, various optimization methods exist for the top beam of large-span continuous rigid frame bridges. These include achieving zero bending moment at the root of the cantilever beam, at the control stage section, and through the zero deflection method. This study aims to explore the methods and effects of optimizing roof beam design using the constant load zero bending moment method and the “three group bundle method”. Using finite element modeling, the total number and eccentricity of prestressed tendons required for each suspended pouring block are determined. Additionally, the “three group beam matching method” is employed to adjust the steel beam, adhering to the design concept of “large cantilever beam matching and small cantilever beam matching”, to achieve a reasonable configuration of the top plate beam. Through specific engineering examples, the results demonstrate that utilizing the constant load zero moment method and the “three group bundle method” can significantly enhance the structural performance and economy of large-span continuous rigid frame bridges. Moreover, it offers practical operability, providing an important reference basis for similar project designs.

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Limitations and Uncertainties in the Long-Term Deflection Calculation of Concrete Structures

Cited by 9 publications

References 15 publications

Revised formula for predicting the long-term deflection multiplier of normal and high strength concrete

Revised formula for predicting the long-term deflection multiplier of normal and high strength concrete

Instantaneous deflection of self-compacting and lightweight concrete slabs at early-age

Research on the Method of Prestressing Tendon Layout for Large-Span Prestressed Components Continuous Rigid Frame Bridge Based on “Zero Bending Moment Dead Load Theory”

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