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International Concrete Abstracts Portal

Showing 1-5 of 77 Abstracts search results

Document: 

SP-341-01

Date: 

June 30, 2020

Author(s):

Amer Hammoud and Hassan Aoude

Publication:

Symposium Papers

Volume:

341

Abstract:

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.


Document: 

SP-341-03

Date: 

June 30, 2020

Author(s):

Hyun-Oh Shin, Hassan Aoude and Denis Mitchell

Publication:

Symposium Papers

Volume:

341

Abstract:

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.


Document: 

SP-341-11

Date: 

June 30, 2020

Author(s):

Ahmed Ibrahim, Sabreena Nasrin, and Riyadh Hindi

Publication:

Symposium Papers

Volume:

341

Abstract:

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.


Document: 

SP-339_04

Date: 

March 1, 2020

Author(s):

Mark Sarkisian, Eric Long, and David Shook

Publication:

Symposium Papers

Volume:

339

Abstract:

Performance based seismic design (PBSD) has created new opportunities for enhanced performance, improved cost efficiencies, and increased reliability of tall buildings. More specifically, flexibility with initial design methods and the utilization of response history results for design, not just verification, have emerged. This paper explores four refined design methods made available by the employment PBSD to influence seismic performance and identify areas of importance. First is the initial proportioning of reinforcement to encourage plastic hinge behavior at specific locations. Second is the initial proportioning of wall thicknesses and reinforcements to encourage a capacity-based design approach for force-controlled actions. Third is the mapping of observed strain demands in shear walls to specific detailing types such as ordinary and special boundary zones. Fourth is an efficient envelope method for the design of foundations. Through these design methods, initial proportioning can be conducted in a more refined way and targeted detailing can result in cost savings. A case study of a recently designed high-rise residential building demonstrates that cost savings can be achieved with these methods.


Document: 

SP326-98

Date: 

August 10, 2018

Author(s):

Francesca Albani and Carlo Dusi

Publication:

Symposium Papers

Volume:

326

Abstract:

After World War II the research about the double curvature structures in reinforced concrete was a frontier in the field of typological, spatial and expressive innovation. Among the principal leading figures was the swiss engineer Heinz Isler with his methods called “form finding” based on the use of physical modeling to determine the form and subsequently investigate its stability. When a concrete shell is shaped using a hanging-membrane model, it assumes an ideal form using a minimum of materials, with minimal deformations and in compression only. This is only the first step in the process of finding the form. Then one has to do the exact structural analysis, the layout of the reinforcement and prestressing elements, and the detailing, to deal with construction problems, and finally to carefully observe the structure in use.

The need to protect the works of Heinz Isler has slowly been bearing fruit in recent years. This highlights in a very special way the crucial point of the debate on the protection of modern and contemporary architecture: the recognition of their architectural and cultural values, and consequently the difficulties of the institutions responsible for undertaking their preservation.

The paper intends to investigate the case of the Deitingen service station built in 1968-1969 which represents a fortunate phase in this process and shows how the factors linked to the durability of structures play a small role in the decision-making processes regarding the future of these works. The key role is played by the significance and values that acquires (or loses) over time.


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