Bottle-shaped Struts Research Articles

Experimental Investigation on Compressive Behavior of Bottle-Shaped Struts

The goal of this investigation was the experimental verification of the dispersion of compression in bottle-shaped struts. Two typical bottle shapes were generated under load in compression concrete—both drilled and undrilled—and were reinforced concrete prismatic members with loading steel plate having a reduced area with respect to the entire cross section of the members. Axial load, and axial and lateral strains were recorded during the tests to evaluate the effects of key parameters. The comparative analysis of the experimental results showed that: 1) the presence of a hole produces a variation on the stress and strain distribution and a reduction in the load-carrying capacity; 2) the reduction in the dimension of the loading plate produces a reduction in the load-carrying capacity; and 3) the presence of transverse steel reduces this phenomenon, ensuring more ductile behavior. Finally, an analytical prediction of the load-carrying capacity was made and compared with the experimental results.

Minimum Reinforcement for Preventing Splitting Failure in Bottle-Shaped Struts

First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address

Effect of Detailing of Web Reinforcement on the Behavior of Bottle-shaped Struts

The effect of detailing of web reinforcement as per current design codes on the strength and serviceability behavior of bottle-shaped struts has been experimentally investigated, particularly in the context of codal minimum reinforcement requirements, by testing eleven scaled deep beams. The experimentally obtained efficiency factors of the bottle-shaped struts besides being significantly higher than the values given in the ACI 318-08 were also found to be sensitive to the amount of web reinforcement. The minimum web reinforcement requirements specified in current design codes were found to be adequate for controlling service load crack widths though the unreinforced bottle-shaped struts allowed in the ACI code were observed to violate the maximum crack width requirements. It has been shown that the transformation equation in the ACI code does not accurately represent the relationship between the strut efficiency factor and the amount of transverse reinforcement whereas a corrected version of the equation shows a clear dependence of the former on the latter.

An appraisal of the ACI strut efficiency factors

The strut-and-tie modelling recommendations of the American Concrete Institute (ACI) 318-08 Appendix A are widely followed for the design of disturbed regions in concrete structures. In this investigation, an experimental appraisal of the ACI 318-08-recommended efficiency factors for prismatic and bottle-shaped struts has been carried out and inconsistency in the recommendations for bottle-shaped struts highlighted. It has been demonstrated that a bottle-shaped strut is in no way inferior to a prismatic strut in terms of strength and, consequently, the efficiency factor of bottle-shaped struts needs to be revised. An error in the ACI 318-08-recommended formulation for minimum effective transverse reinforcement in reinforced bottle-shaped struts is identified and corrected.

Investigation of Dispersion of Compression in Bottle-Shaped Struts

First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address

Modeling of Direct Load Transmission in Lightweight-Concrete-Core Sandwich Beams

The direct load transmission behavior of hybrid sandwich beams consisting of a bottom fiber-reinforced polymer skin and a top concrete skin was investigated experimentally. The sandwich core consisted of lightweight concretes of different brittleness (sand lightweight aggregate concrete [SLWAC] and all lightweight aggregate concrete [ALWAC] mixtures). Cracking and ultimate load prediction using classical strut-and-tie models was inaccurate because these models do not take differences in material brittleness into account. A continuous direct load transmission model is proposed that consists of a diagonal bottle-shaped strut with an infinite number of transverse ties. The statically indeterminate system allows stress redistribution resulting from post-peak material softening after concrete cracking to be taken into account. This led to accurate modeling of the varying experimental responses due to different material brittleness. The arch rise of the bowed compression strut decreased after cracking due to the available width of the diagonal strut being reduced to the distance between initiating and propagating cracks parallel to the strut. The arch rise, furthermore, decreased with increasing material brittleness. © 2009, American Concrete Institute. All rights reserved.

Strength and deformation characteristics of bottle-shaped struts

Isolated strut tests were performed under monotonically increasing displacement controlled in-plane loading on thin plain, steel fibrous and reinforced concrete panels to determine the strength and deformation characteristics of bottle-shaped struts for use in strut-and-tie modelling. A total of 12 concrete panels were tested to failure. The results were used to evaluate the performance of reinforced struts and explore the possibility of using steel fibrous concrete in bottle-shaped struts. ACI 318–05 recommends a strut efficiency factor of 0·75 for an effective transverse reinforcement content greater than or equal to 0·3%. However, a recent study has indicated that the strut efficiency factor is insensitive to reinforcement in the strut. The results of this investigation reveal that reinforcement indeed has a significant influence on strut efficiency and the use of steel fibrous concrete in reinforced struts improves their toughness and post-peak response compared to that of non-fibrous-reinforced concrete struts.

Design of Deep Beams Using Strut-and-Tie Models--Part II: Design Recommendations

The findings of the first part of this study showed that the use of current strut-and-tie modeling provisions of both ACI 318-05 and AASHTO Load and Resistance Factor Design (LRFD) can lead to an unconservative calculation of nominal capacities for some test specimens, with neither producing levels of safety that meet a 5% exclusion rule. This paper develops new provisions based on the lower bound to a database of 596 published test results. These new provisions incorporate the effects of strut inclination, concrete strength, geometry of a bottle-shaped strut, and shear reinforcement while increasing levels of conservatism relative to ACI 318 and AASHTO LRFD provisions. The equilibrium of the bottle-shaped strut was considered to determine the amount of required reinforcement. Struts were separated into two classes: those with sufficient reinforcement and those without sufficient reinforcement. Lower bounds were determined to the data compiled from tests of both sets of struts. When calculating the normal capacities of the specimens in the database with the new design provisions, 96% of the specimens had measured loads in excess of the nominal capacities. The new provisions satisfy the 5% exclusion rule.

Minimum Transverse Reinforcement for Bottle-Shaped Struts

This paper investigates the amount of transverse reinforcement needed to resist the tension developed in a bottle-shaped strut. Bottle-shaped struts are wider at their midpoint than at either end. As the struts widen near the midpoint, tensile stresses transverse to the direction of compression are developed. Reinforcement must be placed within the strut to carry this transverse tension. An expression for the required transverse reinforcement was developed and a database of 476 test specimens was used to evaluate these equilibrium-based equations along with a series of three tests of deep beams. The strut efficiency factors presented in Appendix A of ACI 318-05 were used in this evaluation. The shortcomings of current ACI 318-05 provisions that allow the design of a deep beam without any shear reinforcement are discussed. The amount of transverse reinforcement required to maintain equilibrium in a bottle-shaped strut is proportional to the force applied to the strut and inversely proportional to the slope of the angle of dispersion. These findings suggest that additional research regarding the serviceability of structures designed using strut-and-tie provisions is needed.

Strength of Struts in Deep Concrete Members Designed Using Strut-and-Tie Method

Results from an experimental investigation aimed at evaluating the adequacy of the strength factors for concrete struts in strut-and-tie models given in Appendix A of the 2002 ACI Building Code are presented. The main design variables considered were: the angle between primary strut-and-tie axes, amount of reinforcement crossing the strut, and concrete strength. A total of 12 deep beams were tested, eight with normal strength concrete and four with high-strength concrete. The ratio between experimentally obtained failure loads and the strengths predicted using the strut strength factors given in Appendix A of the ACI Code ranged between 1.00 and 1.22, and between 0.91 and 1.02 for normal and high-strength concrete beams, respectively. Inconsistencies were found in the provisions for minimum reinforcement crossing a strut in Sections A.3.3 and A.3.3.1 when applied to the test specimens, with the former leading to substantially larger reinforcement ratios. The use of a strut strength factor β s = 0.60 in high-strength concrete bottle-shaped struts without web reinforcement led to strength predictions approximately 10% higher than the experimental failure loads. The limited test results suggest that, as a minimum, an effective reinforcement ratio of 0.01, calculated according to ACI Code, Section A.3.3.1, should be provided in high-strength concrete members when a strength factor β S = 0.60 is used. Additional test data, however, are required before a definite recommendation can be made in this regard.

Behavior and Efficiency of Bottle-Shaped Struts

This paper attempts to determine the strength of compressed struts to be used in strut-and-tie modeling. The strength of the struts were evaluated for safety and accuracy as provided by the American Concrete Institute (ACI) and the American Association of State Highway and Transportation Officials (AASHTO) provision guidelines. In the experiment, 26 concrete panels were tested to failure. The investigation examined various effects, including: reinforcement crossing strut axis, angle between reinforcing steel and strut axis, specimen width, specimen thickness, three-dimensional stress state, bundled versus distributed reinforcement, compression reinforcement and boundary conditions on tests. It appears that the ACI’s specifications demonstrated erratic, but conservative results when compared with the test data, while the AASHTO’s standards were less conservative and more consistent.