High-strength concrete (HSC) walls having compressive strength of approximately 100 MPa (14,500 psi) were tested under cyclic lateral loading to investigate their shear behavior. The parameters included were height-to-length ratio of the walls, vertical and horizontal web reinforcement ratios, and the effects of boundary elements in the form of flanges. The experimental results show that shorter walls exhibit greater shear strength than taller walls. Both vertical and horizontal web reinforcements contribute significantly to increasing the shear strength of the walls, with the horizontal web reinforcement being more effective for walls having height-tolength ratio from 1.0 to 2.0. With increase in height-to-length ratio of walls, the concrete contribution to the shear strength decreases while the web reinforcement contribution increases. The presence of flanges also significantly increases the shear strength of HSC walls. Experimental wall shear strengths from this study as well as from literature were compared with predictions from the ACI Code and Eurocode provisions. It can be seen that both ACI and Eurocode do not give consistent safety factors. The ACI method can be unsafe for low-strength concrete walls, while the Eurocode is overly conservative in almost all cases.
The era of Construction 4.0 is characterized by technological advances used in the construction industry. One of the advancements is the use of 3D concrete printing in construction. However, until now, the development of 3D concrete printing in Indonesia is still minimal. The main challenge is to determine the composition of the material mixtures for making the mortar, having good extrudability but still has sufficient strength. The rapid initial setting time required was also different for the concrete for typical construction. Our previous mixture composition incorporating calcium oxide to accelerate the initial setting time was adequate. However, the extrusion process was still not satisfactory. In this study, the effect of cement to sand ratio, sand particle size, and the addition of synthetic micro-fiber was investigated on the main properties of 3D printing materials, i.e., initial setting time, flowability, extrudability, and compressive strength. It was found that using smaller maximum particle size sand increases the initial setting time. The addition of synthetic microfiber reduces the strength and the workability of the mortar. However, fiber inclusion has advantages as it reduces the possibility of cracking in the printed concrete. The extruded concrete specimens were shown to have significant strength reduction due to lack of compaction, and it was affected by the direction of printing showing orthotropic properties of the 3D printed concrete.
Numerous methods for calculating shear strengths of structural walls are available. However, due to the complexity of wall behaviors and possible loading combinations that they may be subjected to, it is quite challenging to derive a method that is reasonably simple but can accommodate various influencing parameters in order to acquire more accurate predictions of wall shear strengths. The authors had earlier tested a series of very-high-strength concrete wall specimens (f c ′ = 100 MPa [14,500 psi]) to investigate the influence on shear strength of several parameters, such as: height-to-length ratios, shear (web) reinforcement ratios in the vertical and horizontal directions, as well as the presence of flanges (boundary elements). The conclusions of the authors' experimental study in the light of other research results reported by other researchers will be summarized herein and will be used as a guide for deriving a proposed truss model. The proposed model is based on modern truss analogy principles (softened truss model, compression field theory) and it has been shown by comparing it with experimental results to be accurate and stable. The design and analysis procedure based on the proposed truss model will also represent an improvement over existing ACI and Eurocode design procedures.
Ten high-strength concrete slabs reinforced with a new type of steel fiber, double-hooked-end steel fibers, were tested under punching shear loads. The strength of the concrete f c ′ varied from 80 to 100 MPa (11,600 to 14,500 psi). The fiber content V f varied from 0 to 1.2%. Two different values of flexural reinforcement ratios ρ (= A s / bd) of 0.9% and 1.4% were chosen for this test program. The experimental results showed that the use of double-hooked-end steel fibers in concrete enhances slab performance significantly in many ways. As the fiber volume or fiber content V f increased, the flexural stiffness of the slab throughout loading history also increased, while both the deflections and crack widths decreased considerably. At the ultimate load stage, the punching shear strength increased by up to 156% compared to non-fibrous concrete slabs. The increase in punching shear strength is significantly higher than the increase introduced by conventional single hooked-end steel fibers. The ductility of the slabs was also significantly improved. Comparisons between design methods with experimental results show that the design method from The Concrete Society's TR-34 performs very well. Another method that was based on the yield line theory overestimates the strengths of the slabs. Model Code 2010 method also overestimates the punching shear strengths. Finally, some relevant design recommendations are given.
Three-dimensional (3D) printing for cementitious materials such as concrete has become increasingly popular. Numerous research efforts have been undertaken to fabricate structural elements, such as beams, using 3D-printed concrete. Because the behavior of 3D-printed reinforced concrete (RC) beams is not well understood, research in this area is still ongoing to investigate the behavior and compare it with conventional RC beams. In this paper, the results of an analytical study using finite element software on 3D-printed RC beams are presented. The main challenge was to determine a constitutive material model of the 3D-printed concrete for nonlinear analysis that was quite different from normal concrete. The developed model was validated using the results from several past experimental tests on 3D-printed RC beams. The results showed that the analytical model can accurately predict the maximum flexural strengths of the 3D-printed RC beams. However, the analytical model overestimated the initial stiffness of the beams. Furthermore, several local failures, such as shear failure of nodal points and bond failure between rebars and concrete, could not be well simulated by the analytical model. Thus, future research is needed to correctly define the constitutive material model for 3D-printed RC beams.
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