International Concrete Abstracts Portal

An innovative transverse reinforcement (TR) system for square reinforced concrete (RC) columns is proposed in this study. It consists of an interlocking pattern (SIP) formed by inclined ties for improving the confinement of the concrete core in the column. Specific improvements of the SIP system over the conventional ties (SC) include more uniform confinement along the axis of the column and better lateral restraint to longitudinal bars. The development and assembly of the SIP system are presented. The performance of short RC columns with an identical volumetric ratio of SC and SIP ties is investigated experimentally. Columns with the SIP tie system exhibit improvements in load capacity and ductility. In comparison with SC ties, higher deformations and larger strain energy are measured from the columns reinforced with SIP ties. The columns with SIP ties had significantly smaller visible damage when compared to the columns with SC ties. Experimentally measured axial strains in concrete and longitudinal reinforcing bars are also lower in the columns with SIP ties. A numerical evaluation indicates a higher average effective confinement pressure on concrete and lower damage in the cover for columns with the SIP system.

In durability design of concrete structures using performance-based framework, hydraulic sorptivity of concrete can be used as a key indicator. In this paper, a probabilistic methodology considering variability of hydraulic properties of concrete components, namely the mortar, aggregates, and interfacial transition zone (ITZ), is developed. Evaluation of the effective sorptivity of concrete is based on a rigorous nonlinear finite element (FE) analysis at the meso-scale level, which is verified using available experimental results. Using the response surface method (RSM), a conceptual model relating effective hydraulic sorptivity of concrete to aggregate volume fraction and hydraulic properties of mortar and the ITZ is derived. The proposed probabilistic methodology can be used for durability design of concrete structures. It is found that for high aggregate volume fractions the variability of hydraulic sorptivity is high due to increasing volume of ITZ.

This study aimed to develop a new method for proportioning self-consolidating concrete (SCC). This method is capable of proportioning SCC mixtures with specified compressive strength, contrary to previous SCC proportioning methods that emphasized the fulfillment of fresh properties requirements more than strength requirements. In addition, no previous method considered the grading of aggregate in SCC mixtures (fineness modulus of fine aggregate and maximum size of coarse aggregate) as in conventional concrete (CC) proportioning methods, making a need for numerous trial mixtures to adjust the fresh and hardened properties of SCC. Two well-known concrete mixture proportioning methods, the ACI 211.1 method for CC and the EFNARC method for SCC, were adopted to develop the new method. The requirements of these methods were combined with certain modifications and a new method was proposed. In this new method, the actual range of compressive strength of the ACI 211.1 method was widened from 15 to 40 MPa (2145 to 5800 psi) to cover a wider range of strength (15 to 75 MPa [2145 to 10,875 psi]), thus covering both normal- and high-strength SCC mixtures. Thirty mixtures were tested to examine the validity of the proposed method; all these mixtures satisfied the fresh SCC requirements. Concrete strength results were in good agreement with the nominal design strength except for mixtures with a strength of 75 MPa (10,875 psi); these mixtures required a slight adjustment in the water-cement ratio (w/c). A modification on the proposed compressive strength and w/c relationship were introduced depending on data from previous literature on SCC.

In this paper, a strut-and-tie-based method is presented for calculating the strength of reinforced concrete deep beams. The proposed method employs constitutive laws for cracked reinforced concrete, considers strain compatibility, and uses a secant stiffness formulation. This method accounts for the failure modes due to crushing of the nodal compression zone at the top of the diagonal strut, yielding of the longitudinal reinforcement, as well as that of strut crushing or splitting. This method is used to calculate the capacity of 214 normal- and high-strength concrete deep beams that have been tested in laboratories. This method is illustrated to provide more accurate estimates of capacity than the strut-and-tie provisions in either ACI 318-05 or the Canadian code. The comparison shows that the proposed method consistently predicts the strengths of deep beams with a wide range of horizontal and vertical web reinforcement ratios, concrete strengths, and shear span-to-depth ratios (a/d) well. The proposed approach provides valuable insight into the design and behavior of deep beams.

Disc. 102-S20/From the March-April 2005 ACI Structural Journal, p. 206 Stresses in External Tendons at Ultimate. (Paper by Carin L. Roberts-Wollmann, Michael E. Kreger, David M.Rogowsky, and John E. Breen). Discussion by Mohamed H. Harajli Disc. 102-S20/From the March-April 2005 ACI Structural Journal, p. 206 Stresses in External Tendons at Ultimate. (Paper by Carin L. Roberts-Wollmann, Michael E. Kreger, David M. Rogowsky, and John E. Breen). Discussion by Jinsheng Du, Wenliang Lu, and Wenyu Ji Disc. 102-S20/From the March-April 2005 ACI Structural Journal, p. 206 Stresses in External Tendons at Ultimate. Paper by Carin L. Roberts-Wollmann, Michael E. Kreger, David M. Rogowsky, and John E. Breen). Discussion by Antoine E. Naaman Disc. 102-S21/From the March-April 2005 ACI Structural Journal, p. 214 Ultimate Deflection Capacity of Lightly Reinforced Concrete Intake Towers. (Paper by Richard C. Dove and Enrique E. Matheu). Discussion by Ralph W. Strom