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.

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.

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.

The use of unstressed Grade 1860 (MPa) seven-wire steel strands as longitudinal reinforcement in columns has the advantage of reducing the cost of steel as compared with conventional Grade 420 (MPa) deformed steel bars. A preliminary experimental study was conducted to investigate the performance of a column with unstressed seven-wire strands as longitudinal reinforcement. Large-scale column specimens were designed and tested using double-curvature lateral cyclic loading under a constant axial load. Test results showed that the column with strands as longitudinal reinforcement (RH1) showed less and wider cracks and less energy dissipation than the column with deformed bars as longitudinal reinforcement (ORH1). Despite this, RH1 showed a slightly higher drift capacity than ORH1 even when the strands used in RH1 had a much lower ultimate strain than the deformed bars used in ORH1.

Ultra-High Performance Concrete (UHPC) is a versatile building material as it is characterized by very high compressive strengths reaching 30 ksi [200 MPa], ductile tensile characteristics, and energy absorption. Currently, UHPC is commonly used in limited structural applications, such as joints and connections between precast structural elements. To extend the use of UHPC in full structural elements, a better understanding of the structural behavior and failure mechanism of such elements is needed. One potential application of UHPC for structural elements is columns, which is the focus of this study. This paper presents an experimental investigation of the behavior of UHPC column subjected to combined axial and lateral loading. A large-scale UHPC column is tested under axial and quasi-static cyclic lateral loading at the Earthquake Engineering Laboratory at the University of Nevada, Reno. To establish a comparison with conventional columns, a normal strength concrete (NSC) column with same dimensions and design as the tested UHPC column is analytically modeled and analyzed under similar loading protocol using OpenSEES. The experimental response of the UHPC column is evaluated and compared to the analytical response of the NSC column. Both global and local behavior are presented and discussed to include damage progression, failure type, peak moment strength, stiffness degradation, and displacement and curvature ductility.