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Home > Publications > International Concrete Abstracts Portal
Showing 1-5 of 83 Abstracts search results
Document:
SP-353_04
Date:
July 1, 2022
Author(s):
Neil M. Hawkins and Carlos E. Ospina
Publication:
Symposium Papers
Volume:
353
Abstract:
The 2019 Edition of ACI 318 introduced several key changes to the one-way and two-way shear design of slabs. Chapter 22 introduced a size effect for the one-way and two-way shear strength of concrete for slabs either without or with shear reinforcement. ACI 318-19 also introduced a revised version of the Vc equation for one-way shear that included the effect of the member flexural reinforcement ratio. Chapter 8 of ACI 318-19 also introduced new minimum flexural reinforcement requirements to prevent premature punching failure of lightly-reinforced above grade two-way slabs and to promote instead a flexure-driven type of response. In ACI 318-19, recognition of the size effect is required for above grade slabs only and not for shallow footings or foundation mats. The Code is silent on whether the new Chapter 8 minimum flexural reinforcement requirements for slabs apply to spread footings. This paper examines the reasons for the differences in size effect requirements between slabs and footings. It also evaluates the applicability and the impact that the new Vc equation for one-way shear has on the shear strength of isolated or continuous footings and whether the new flexural reinforcement requirements of Chapter 8 can be extended to spread footings. It also suggests a design recommendation to acknowledge the beneficial effect that compact footing dimensions can have on punching strength.
The 2019 Edition of ACI 318 introduced several key changes to the one-way and two-way shear design of slabs. Chapter 22 introduced a size effect for the one-way and two-way shear strength of concrete for slabs either without or with shear reinforcement. ACI 318-19 also introduced a revised version of the Vc equation for one-way shear that included the effect of the member flexural reinforcement ratio. Chapter 8 of ACI 318-19 also introduced new minimum flexural reinforcement requirements to prevent premature punching failure of lightly-reinforced above grade two-way slabs and to promote instead a flexure-driven type of response. In ACI 318-19, recognition of the size effect is required for above grade slabs only and not for shallow footings or foundation mats. The Code is silent on whether the new Chapter 8 minimum flexural reinforcement requirements for slabs apply to spread footings.
This paper examines the reasons for the differences in size effect requirements between slabs and footings. It also evaluates the applicability and the impact that the new Vc equation for one-way shear has on the shear strength of isolated or continuous footings and whether the new flexural reinforcement requirements of Chapter 8 can be extended to spread footings. It also suggests a design recommendation to acknowledge the beneficial effect that compact footing dimensions can have on punching strength.
DOI:
10.14359/51737111
CI4401Mota
January 1, 2022
Mike Mota, Michael W. Hopper, Michael A. Russillo, and Ramon Gilsanz
Concrete International
44
Issue:
1
The article discusses technologies that allow flat-plate floor systems to economically achieve spans in the 45 to 50 ft (13.7 to 15.2 m) range. These technologies include using ASTM A615/A615M Grade 80 steel, concrete mixtures with design strengths of 8000 psi (55 MPa) and higher, voided slab formers, and post-tensioned slabs with tendons banded over the columns in both directions.
CI4208Huang
August 1, 2020
Cathy I-Chi Huang, David E. Hoy, Yun Jennifer Lan, Camille de Romémont, and Ramon E. Gilsanz
42
8
While the use of reinforcement with 80 or 100 ksi (550 to 690 MPa) yield strength enables a reduction in the amount of steel required, it may also result in greater slab deflections. However, the potential for increased deflection can be counteracted using high-strength concrete. This study compares designs with different strengths of reinforcing steel and concrete using slab prototype from an existing building.
SP-339_06
March 1, 2020
Drew A. Kirkpatrick, Leonard M. Joseph, J. Ola Johansson, and C. Kerem Gulec
339
The distribution of forces through floor diaphragms is critical to the overall behavior and performance of buildings during both wind and seismic events. Simplified methods commonly employed by design engineers establish approximate magnitudes and distributions of inertial and transfer forces within floor diaphragms. Such methods can be appropriate for regular low-rise buildings without significant transfer forces. However, for design of complex structures with large stiffness discontinuities in vertical or horizontal directions, a more detailed investigation and modeling of diaphragm behavior is usually required. Common situations in high-rise projects include a tower stack meeting a podium base with supplemental shear walls and a tower stack meeting a grade-level slab enclosed by basement walls. Large diaphragm transfer forces typically occur at these levels of abrupt stiffness changes. Using examples from recent projects and parametric studies following performance-based seismic design (PBSD) principles, this paper describes the use of strut-and-tie models in commercially available software (PERFORM-3D) to provide a better understanding of complex diaphragm behavior. Results can aid the designer in making decisions regarding floor thickness and reinforcing layout, including at chords and collectors. While the need for enhanced modeling techniques and understanding of diaphragm behavior has been highlighted by the increased use of PBSD, the findings presented in this paper may be applicable to projects based on traditional (code-based) approaches as well.
10.14359/51724694
CI4011Cepuritis
November 1, 2018
Rolands Cepurītis, Brad J. Pease, Jānis Kamars, and Jānis Ošlejs
40
11
Elevated ground slabs are an alternative for locations with poor and/or inconsistent subgrades. This article summarizes the basic slab-on-pile construction process and provides results from a load test conducted on a slab constructed using shrinkage-compensating steel fiber-reinforced concrete. Ancillary benefits of constructing such slabs are also summarized.
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