International Concrete Abstracts Portal

ACI Committees 441 – Reinforced Concrete Columns and 341A – Earthquake-Resistant Concrete Bridge Columns, Mohamed A. ElGawady Columns are crucial structural elements in buildings and bridges. This Special Publication of the American Concrete Institute Committees 441 (Reinforced Concrete Columns) and 341A (Earthquake-Resistant Concrete Bridge Columns) presents the state-of-the-art on the structural performance of innovative bridge columns. The performance of columns incorporating high-performance materials such as ultra-high-performance concrete (UHPC), engineered cementitious composite (ECC), high-strength concrete, high-strength steel, and shape memory alloys is presented in this document. These materials are used in combination with conventional or advanced construction systems, such as using grouted rebar couplers, multi-hinge, and cross spirals. Such a combination improves the resiliency of reinforced concrete columns against natural and man-made disasters such as earthquakes and blast.

The spiral reinforcement is a special detailing technique used for reinforcing columns in regions of high seismic activities because of its ability in energy absorption and ductility. In this paper, the results of the experimental testing on cross spiral confinement in reinforced concrete columns are presented. The experimental results were verified by nonlinear finite element analysis as well as an analytical model. The developed analytical model was based on the octahedral stress criterion and compared with other models available in the literature. In the Finite element model, the concrete damage plasticity and steel yielding criterion were used in the constitutive equations. The finite element showed very good prediction of the ultimate load and failure strain for various spiral reinforcement ratios. Analytical stress-strain models have been developed and compared to the experiment results in the literature and found work well in predicting the columns behavior under monotonic axial loads. The authors see that the proposed technique is a very good potential of industry implementation and provides a more seismic resiliency to structures.

Such detailing technique could be used as a mitigation system for columns in high seismic zones.

This paper presents the results from tests examining the performance of high-strength concrete (HSC) and normal-strength concrete (NSC) columns subjected to blast loading. As part of the study six columns built with varying concrete strengths were tested under simulated blast loads using a shock-tube. In addition to the effect of concrete strength, the effects of longitudinal steel ratio and transverse steel detailing were also investigated. The experimental results demonstrate that the HSC and NSC columns showed similar blast performance in terms of overall displacement response, blast capacity, damage and failure mode. However, when considering the results at equivalent blasts, doubling the concrete strength from 40 MPa to 80 MPa (6 to 12 ksi) resulted in 10%-20% reductions in maximum displacements. On the other hand, increasing the longitudinal steel ratio from ρ = 1.7% to 3.4% was found to increase blast capacity, while also reducing maximum displacements by 40-50%. The results also show that decreasing the tie spacing (from d/2 to d/4, where d is the section depth) improved blast performance by reducing peak displacements by 20-40% at equivalent blasts. The use of seismic ties also prevented bar buckling and reduced the extent of damage at failure. As part of the analytical study the response of the HSC columns was predicted using single-degree-of-freedom (SDOF) analysis. The resistance functions were developed using dynamic material properties, sectional analysis and a lumped inelasticity approach. The SDOF procedure was able to predict the blast response of HSC columns with reasonable accuracy, with an average error of 14%. A numerical parametric study examining the effects of concrete strength, steel ratio and tie spacing in larger-scale columns with 350 mm x 350 mm (14 in. x 14 in.) section was also conducted. The results of the numerical study confirm the conclusions from the experiments but indicate the need for further blast research on the effect of transverse steel detailing in larger-scale HSC columns.

This paper presents the results from tests examining the blast performance of columns constructed with ultra-high-performance concrete (UHPC) and high-performance reinforcement (high-strength steel or stainless steel). As part of the study six columns with square cross-sections were tested under simulated blast loads using a shock-tube at the University of Ottawa. Parameters investigated include the effects of concrete type, longitudinal reinforcement type and longitudinal reinforcement ratio. The results demonstrate that the use of UHPC increases the blast performance of reinforced concrete columns by increasing blast capacity and improving control of maximum and residual mid-span displacements by an average of 30% and 40%. Substitution of normal-strength bars with high-strength or stainless steel bars in the UHPC columns resulted in further reductions in displacements, which ranged between 18-43% for maximum deformations and 38-66% for residual deformations. The failure mode of all columns with low steel ratio of 1.24% (4 – No.3 bars) was tension bar rupture, regardless of steel type. Increasing the steel ratio from 1.24% to 1.84% (6 –No.3 bars) increased blast capacity and delayed failure. The use of increased amount of stainless steel bars was particularly effective, and transformed the failure mode from bar rupture to fiber pullout. The analytical study confirms that dynamic inelastic SDOF analysis can be used to reasonably predict the blast response of UHPC columns reinforced with varying steel types.

Ultra-high-performance concrete (UHPC) is an innovative material that exhibits high compressive and tensile strength as well as excellent durability. The provision of fibers in UHPC results in improved ductility and increased toughness when compared to conventional high-strength concrete. These properties make UHPC well-adapted for use in the columns of high-rise buildings and heavily-loaded bridges. This paper summarizes the results from a database of tests examining the effects of various design parameters on the axial load performance of UHPC columns. Experimental results illustrating the effects of concrete type (UHPC vs. high-strength and ultra-high-strength concrete), UHPC compressive strength and transverse reinforcement detailing are presented. The results show that the use of UHPC in columns resulted in increased load carrying capacity and post peak ductility when compared to conventional high-strength or ultra-high-strength concrete due to the ability of steel fibers to delay cover spalling. However, greater amounts of confinement reinforcement were required to achieve the same level of axial load performance as the UHPC compressive strength was increased from 150 to 180 MPa. The results also showed that the amount, spacing, and configuration of transverse reinforcement, as well as their interaction significantly affected the axial load response of UHPC columns. However, increasing the amount of transverse reinforcement had the most pronounced effect on post-peak behavior. The effect of the confinement provisions in current codes (CSA A23.3-14 and ACI-318-14) on the ductility of the UHPC columns was also investigated. Based on the results, an alternative confinement expression for achieving ductile behavior in UHPC columns was proposed.