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Refinement of Strut-and-Tie Model for Reinforced Concrete Deep Beams.

Panjehpour M, Chai HK, Voo YL - PLoS ONE (2015)

Bottom Line: This study aims to refine STM through the strut effectiveness factor and increase result accuracy.The ultimate shear strength of deep beams obtained from non-linear finite element modeling and STM recommended by ACI 318-11 as well as AASHTO LRFD (2012) were compared with the experimental results.The equation of the strut effectiveness factor from AASHTTO LRFD was then modified through the aforementioned empirical equation.

View Article: PubMed Central - PubMed

Affiliation: Department of Civil Engineering, Faculty of Science, Engineering, Technology and Mathematics (FOSTEM), INTI International University, 71800, Nilai, Malaysia.

ABSTRACT
Deep beams are commonly used in tall buildings, offshore structures, and foundations. According to many codes and standards, strut-and-tie model (STM) is recommended as a rational approach for deep beam analyses. This research focuses on the STM recommended by ACI 318-11 and AASHTO LRFD and uses experimental results to modify the strut effectiveness factor in STM for reinforced concrete (RC) deep beams. This study aims to refine STM through the strut effectiveness factor and increase result accuracy. Six RC deep beams with different shear span to effective-depth ratios (a/d) of 0.75, 1.00, 1.25, 1.50, 1.75, and 2.00 were experimentally tested under a four-point bending set-up. The ultimate shear strength of deep beams obtained from non-linear finite element modeling and STM recommended by ACI 318-11 as well as AASHTO LRFD (2012) were compared with the experimental results. An empirical equation was proposed to modify the principal tensile strain value in the bottle-shaped strut of deep beams. The equation of the strut effectiveness factor from AASHTTO LRFD was then modified through the aforementioned empirical equation. An investigation on the failure mode and crack propagation in RC deep beams subjected to load was also conducted.

No MeSH data available.


Related in: MedlinePlus

Typical reinforcement details.
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pone.0130734.g003: Typical reinforcement details.

Mentions: The deep beams were identical in every aspect except for the position of the steel cages. Each beam had a length of 1840 mm with a rectangular cross-section as indicated in Fig 2. The flexural reinforcement consisted of 9T16 deformed steel bars, which were placed in three layers at the bottom of the beam cross-section. These steel bars were welded into 10 mm thick steel plates at both beam ends to provide adequate anchorage capacity. The anchorage steel plates that had a height of 120 mm fully covered the beam widths. An orthogonal steel mesh reinforcement with diameter of 6 mm and spacing of 100 mm was provided as the transverse reinforcement. This reinforcement provided the required minimum amount of web reinforcement that ACI 318–11 and AASHTO LRFD recommend [2, 3]. The additional reinforcements (steel cages) were provided under the load plates and on top of the support plates to prevent premature local bearing stress, as illustrated in Fig 3. The presence of steel cages and anchorage plates may change the formation of compression-compression-tension (CCT) node on top of the support plates. However, the formation of CCT node is not the concern of this research and does not affect strut performance. The beams were cast using a single supply of ready-mixed concrete. The maximum aggregate size in concrete was 10 mm. Two types of coarse (uncrushed granite) and fine (uncrushed sand) aggregates were used in the mix design. The water-to-cement ratio was 0.47. The concrete slump was 60 mm. The mix design for one cubic meter of concrete is shown in Table 1.


Refinement of Strut-and-Tie Model for Reinforced Concrete Deep Beams.

Panjehpour M, Chai HK, Voo YL - PLoS ONE (2015)

Typical reinforcement details.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4482495&req=5

pone.0130734.g003: Typical reinforcement details.
Mentions: The deep beams were identical in every aspect except for the position of the steel cages. Each beam had a length of 1840 mm with a rectangular cross-section as indicated in Fig 2. The flexural reinforcement consisted of 9T16 deformed steel bars, which were placed in three layers at the bottom of the beam cross-section. These steel bars were welded into 10 mm thick steel plates at both beam ends to provide adequate anchorage capacity. The anchorage steel plates that had a height of 120 mm fully covered the beam widths. An orthogonal steel mesh reinforcement with diameter of 6 mm and spacing of 100 mm was provided as the transverse reinforcement. This reinforcement provided the required minimum amount of web reinforcement that ACI 318–11 and AASHTO LRFD recommend [2, 3]. The additional reinforcements (steel cages) were provided under the load plates and on top of the support plates to prevent premature local bearing stress, as illustrated in Fig 3. The presence of steel cages and anchorage plates may change the formation of compression-compression-tension (CCT) node on top of the support plates. However, the formation of CCT node is not the concern of this research and does not affect strut performance. The beams were cast using a single supply of ready-mixed concrete. The maximum aggregate size in concrete was 10 mm. Two types of coarse (uncrushed granite) and fine (uncrushed sand) aggregates were used in the mix design. The water-to-cement ratio was 0.47. The concrete slump was 60 mm. The mix design for one cubic meter of concrete is shown in Table 1.

Bottom Line: This study aims to refine STM through the strut effectiveness factor and increase result accuracy.The ultimate shear strength of deep beams obtained from non-linear finite element modeling and STM recommended by ACI 318-11 as well as AASHTO LRFD (2012) were compared with the experimental results.The equation of the strut effectiveness factor from AASHTTO LRFD was then modified through the aforementioned empirical equation.

View Article: PubMed Central - PubMed

Affiliation: Department of Civil Engineering, Faculty of Science, Engineering, Technology and Mathematics (FOSTEM), INTI International University, 71800, Nilai, Malaysia.

ABSTRACT
Deep beams are commonly used in tall buildings, offshore structures, and foundations. According to many codes and standards, strut-and-tie model (STM) is recommended as a rational approach for deep beam analyses. This research focuses on the STM recommended by ACI 318-11 and AASHTO LRFD and uses experimental results to modify the strut effectiveness factor in STM for reinforced concrete (RC) deep beams. This study aims to refine STM through the strut effectiveness factor and increase result accuracy. Six RC deep beams with different shear span to effective-depth ratios (a/d) of 0.75, 1.00, 1.25, 1.50, 1.75, and 2.00 were experimentally tested under a four-point bending set-up. The ultimate shear strength of deep beams obtained from non-linear finite element modeling and STM recommended by ACI 318-11 as well as AASHTO LRFD (2012) were compared with the experimental results. An empirical equation was proposed to modify the principal tensile strain value in the bottle-shaped strut of deep beams. The equation of the strut effectiveness factor from AASHTTO LRFD was then modified through the aforementioned empirical equation. An investigation on the failure mode and crack propagation in RC deep beams subjected to load was also conducted.

No MeSH data available.


Related in: MedlinePlus