International Concrete Abstracts Portal

This Symposiuml Publication includes 48 papers from the ACI Fifth International Confrence on Innovation in Design with Emphasis on Seismic, Wind, and Environmental Loading, Quality Control, and Innovation in Materials/ Hot-Weather Concreting, held in December 2002 in Cancun, Mexico. Topics include the behavior of flared-column bents under seismic loading, marine exposure of high-strength light-weight concrete, and seismic strengthening of a nonductile concrete frame building. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP209

The behavior of liquid containing structures (LCS) subjected to seismic excitations is reviewed. The major parameters affecting the response of concrete circular tanks for LCS are discussed. Existing codes aud standards related to seismic design of LCS are reviewed. With the aid of a design example, results of the various design standards are compared. The effects of earthquake load on the behavior of reinforced concrete (RC) tanks are also investigated through a detailed example.

Cast-in-place deep foundations such as drilled shafts and piers are often subjected to two sources of problems. First, the integrity and uniformity of the cross-sectional area of these structural elements cannot be assured using normal concrete because of limited accessibility and visibility during construction. Cavities and soil encroachments leading to soil pockets can jeopardize their load-bearing capacity. Second, corrosion problems of steel reinforcement in deep foundations have been costly, requiring annual repair costs of more than $2 billion in the US alone. To address these two challenges, a novel technology for the construction of drilled shaft concrete piles is proposed in this study. Self-consolidating concrete, a material that compacts under its self-wight without vibration and without bleeding or segregation, is used to assure the structural integrity and uniformity of the cross-sectional area of deep foundations. The self-consolidating concrete is cast into FRP envelopes, which provide corrosion-resistant reinforcement. This paper presents results of a laboratory investigation on the mechanical performance of these novel piles including the effect of using expansive cement and shrinkage-reducing admixtures to enhance the FRP tube-concrete interfacial bond.

The objective of this research was to verify the feasibility of reducing the drying shrinkage of concrete made with portland pozzolan cement. Major variables included slump, shrinkage-reducing admixture brand, admixture dosages and specimen dimensions. Tests were carried out on 132 prism specimens and shrinkage strain8 were measured up to 360 days of drying. Also compressive strength, splitting strength and static modulus of elasticity were determined. Based on the results obtained, it was concluded that dl of the five brand admixtures evaluated reduce drying shrinkage. One Qf the experimental admix- tures exhibited the best behavior and reduced up,k, 45% of the average free shrinkage of concrete at 360 days of drying. Results were compared with drying strain predictions of ACI, CEB, B3, GL, Sakab and Sakata 2001 models. It was conduded that in general a l l the ana- lyzed shrinkage models do not adequately represent the observed shrinkage behavior of concretes made with portland pozzolan cement and shrinkage-reducing admixtures. Therefore, two prediction models to estimate drying shrinkage strains were developed based on the ACI drying-time function and Sakata’s ultimate shrinkage strain. One of these models is for use at a design level when no information about a particular shrinkage reducing admixture is known, and the other is applicable to concrete made with a particular admixture brand.

The current ACI Building Code (ACI 318-99) procedure for the shear design of pile caps is the same approach used for two-way slabs. The procedure involves determining a section thickness such that the concrete shear stress (@,) is greater than the applied shear stress (vu) on the critical section. For footings supported on piles, the ACI Code recognizes that these general provisions are not applicable as the depth of the footing increases and some of the pile loads fall within the critical section. In deep pile caps, the critical section may even be located outside the footing, making it impossible to investigate shear at d or dn. For these situations, the ACI Commentary states that the designer should examine shear strength at the face of the column and it refers to procedures outlined in the CRSI Handbook (1996). ACI has recently published proposed revisions for the ACI 318-02 Code, which promotes the use of strut-and-tie models as an alternative to the existing ACI and CRSI procedures. The design methodology involves limiting the concrete stresses in the compression struts and nodal zones to insure that the tension tie (longitudinal reinforcement) yields before significant diagonal cracking develops in the compression struts or crushing in the nodal zones. This paper explains the existing ACI and CRSI procedures and the proposed ACI provisions for strut-and-tie design.