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Applications of Structural Plain Concrete

Wednesday, March 30, 2022  8:30 AM - 10:30 AM, Boca II

Since the original structural plain concrete code language (ACI 318-14 Chapter 14) was developed in the late 1960's the concrete industry has seen significant developments in materials and analysis methods. The session will focus on examples of the use of such approaches in structural ground supported slabs, walls and foundation elements.


Collaborative Casting with Robotics

Presented By: Ron Culver
Affiliation: Form Found Design
Description: Form Found Design co-founders, Joseph Sarafian, AIA and Ron Culver, AIA present their robotically adjustable fabric mold for concrete casting and illustrate how a new CAD-CAM process allowed them to build the first ever robotically cast concrete structure. When Amazon commissioned Form Found Design to build the MARS Pavilion, FFD harnessed a novel workflow that allowed for the casting of 70 unique concrete "wishbones" that bolt together within a 1mm tolerance to form a 15' tall compression structure. The team will discuss the robotics, material science, and software hurdles that they overcame to achieve this feat and will discuss present and future applications.


Three-Point Bending Tests of Notched Beam: A Suitable Test to Investigate Size Effect of Plain Concrete

Presented By: Christian Carloni
Affiliation: Case Western Reserve University
Description: This work presents the results of three-point bending (TPB) tests on the largest set of plain concrete notched beams ever tested. Five different sizes (depths), nominally 3 in., 6 in., 10 in., 20 in., and 40 in., were tested to evaluate size effect experimentally. The largest size was tested horizontally while floating on Plexiglas balls in order to remove the effect of the self-weight. In addition, for the second to largest size some specimens were tested horizontally and the others vertically in order to confirm that the different test set-up did not affect the results. Particular care was paid to obtain a set of specimens that were carefully cast from the same batch of concrete, cured under the same conditions, and tested at virtually the same age under the same environmental conditions. In quasibrittle materials like concrete, the fracture front is blunted by a zone of microcracking (that eventually coalesce into an actual crack) where nonlinear softening behavior occurs. This region is often called fracture process zone (FPZ). In a three-point bending (TPB) test of notched beams, the FPZ starts to develop before the peak load is attained. However, the FPZ continues to extend further after the peak is reached during the descending portion of the response. When the FPZ is fully developed, it may occupy a large portion or even the whole cross-section of the specimen. In small-size TPB specimens, the FPZ may not fully develop. In fact, as the FPZ continues to extend, it is contrasted by the presence of a compression zone on top due to the presence of bending moment in TPB tests. The size of the fully established FPZ is linked to the characteristics of the quasibrittle material investigated and can be used to predict to what extent notched beams and more in general structural elements (made of a given quasibrittle material) exhibit size effect that deviates from the one predicted by linear elastic fracture mechanics (LEFM). The load responses, the peak load Pmax.


Behavior of Lightly Reinforced Concrete Walls

Presented By: Laura Lowes
Affiliation: University of Washington
Description: The presentation summarizes the findings of a simulation-based investigation of the behavior and design of low-rise, lightly reinforced concrete walls, including lightly reinforced walls employing concrete with low steel fiber ratios. Lightly reinforced concrete walls, including insulated concrete formwork (ICF) walls, are used commonly for residential and low-rise construction. ICF construction can be particularly advantageous because the insulating formwork provides a substantially higher level of insulation than traditional construction. A primary cost of low-rise reinforced concrete construction is placement of reinforcing steel, and in regions of low to moderate seismicity, ACI 318 Code requirements for minimum reinforcement, rather than design loads, typically determine the volume of reinforcement that is required. The results of this study suggest that there is the potential for reducing reinforcement requirements and for using fiber reinforced concrete (FRC) with low reinforcement ratios for low rise walls, without impairing performance, in regions of low to moderate seismicity. The investigation comprised five phases: 1) a literature review which establish a study funded by PCA and conducted by Roller (1996) as the primary reference, 2) validation of a continuum-type finite element modeling approach using LS-Dyna for simulating the response of lightly reinforced concrete components, 3) a simulation-based investigation of the impact of reinforcement configuration, including the spacing of horizontal and vertical reinforcement as well as the use of two versus one layer of reinforcement, on the response of walls exhibiting flexure-controlled response to out-of-plane loading, 4) calibration of the LS-Dyna concrete constitutive model to simulate the behavior of FRC with low steel fiber ratios, and a 5) simulation-based investigation of the out-of-plane flexural response of FRC walls with low steel fiber ratios and low reinforcing steel ratios.

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