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Showing 1-5 of 97 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-340-07

Date: 

April 1, 2020

Author(s):

Sary A. Malak and Neven Krstulovic-Opara

Publication:

Symposium Papers

Volume:

340

Abstract:

This paper provides an overview of simplified methods for dynamic blast analysis of structural members. The presented approach focuses on the use of a general simplified non-linear single degree of freedom dynamic model commonly used for typical flexural members such as slabs, beams or columns. The presented approach also allows modeling of members retrofitted against blast loading using fiber composites. The fiber composites considered in this paper include conventional Steel Fiber Reinforced Composites (FRC) as well as High Performance Fiber Composites (HPFRC). HPFRC’s include Short Steel Slurry Infiltrated Concrete (SIFCON), Long Continuous Slurry Infiltrated Steel Fibers Mat Concrete (SIMCON), and Fiber Reinforced Polymers (FRP). The model identifies different material parameters that affect the response of the structure. The effect of the material properties on the composite response is discussed within the framework of the existing blast-resistance guidelines and standards. Different retrofit techniques for existing concrete structures using fiber reinforced composites and the effect of varying the composite material properties on the response is presented. Final conclusions and recommendations are provided in terms of composite material’s properties, modeling performance and response. Specific limitations on their use is also discussed.


Document: 

SP-330-05

Date: 

September 26, 2018

Author(s):

Chengning Wu and Junqing Xin

Publication:

Symposium Papers

Volume:

330

Abstract:

In order to improve compressive strength and the durability of concrete, such as, alkali-aggregate reaction resistance, chloride ion permeation resistance, carbonation resistance, and freezing and thawing resistance, a new type of combined cementitious materials was used to make the concrete. One part of the cementitious materials was high early strength Portland cement (similar to ASTM type III Portland cement), which had more than 63 mass% C3S and hydrated quickly to generate calcium hydroxide to accelerate pozzolanic reaction. Another part of the cementitious materials was fine blast furnace slag powders which had more than 6000 cm2/g Blaine specific surface area to get faster hydration with the calcium hydroxide. And other part of the cementitious materials was fly ash which had high specific surface area and low ignition loss to get faster pozzolanic reaction. According to the results of tests in this research, it is clear that the compressive strength of the concrete made with the combined cementitious materials is near that of the concrete made with the high early strength Portland cement only. However, the alkali-aggregate reaction in the concrete made with the combined cementitious materials is much lower than that of the concrete made with the high early Portland cement, and/or mixed with the fine blast furnace slag powders or fly ash respectively. It is also confirmed that chloride ion permeation resistance, carbonation resistance, and freezing and thawing resistance of the concrete made with the combined cementitious materials are improved considerably.


Document: 

SP321-05

Date: 

September 29, 2017

Author(s):

Bradley Foust and Theodor Krauthammer

Publication:

Symposium Papers

Volume:

321

Abstract:

The boundary conditions at the supports of reinforced concrete slabs, specifically the amount of lateral and rotational restraint, dictate how they respond to particular loads. Membrane (in-plane) forces are present in slabs when their boundaries are sufficiently stiff, therefore restricting the slabs from lateral translations in addition to rotations. Increases in compressive strength and ductility in ultra-high-performance concrete (UHPC) introduce additional strength enhancement not present in Normal-Strength Concrete (NSC).

Ten reinforced concrete slabs were quasi-statically tested in a static water chamber that allowed hydrostatic forces to be utilized as a loading technique on the slab. Of the 10 slabs, 4 were simply supported, and the remaining 6 were rigidly restrained. The load-deformation responses of laterally restrained slabs were then compared to those of simply-supported slabs to determine the enhancement due to the boundary conditions (i.e., compression membrane action). The results of these experiments were then compared to the results of response calculations based on plastic theory.

Valuable data on rigidly-restrained UHPC slab response were obtained from the experiments. The experimental results were compared to the results of the associated numerical analyses. Existing plastic theory should be used with caution when calculating the ultimate resistance of UHPC slabs. The experimental and numerical results showed that UHPC slabs with sufficiently rigid boundary conditions have a static resistance two-and-a-half-times greater than the traditional yield-line theory resistance for UHPC slabs due to compressive membrane effects.


Document: 

SP-320_49

Date: 

August 1, 2017

Author(s):

Laurent Steger, Bernard Salesses, Cédric Patapy, Mohend Chaouche, Laurent Frouin, and Martin Cyr

Publication:

Symposium Papers

Volume:

320

Abstract:

Ordinary portland cement (OPC) substitution by high contents of ground granulated blast furnace slags (GGBS) reduces the early hydration kinetics, causing a slower development of mechanical properties. Chloride are well known for their accelerating effect on OPC but are mostly used for specific applications, such as non-reinforced concrete, due to their detrimental effects regarding steel bars corrosion. However, GGBS-based concretes are known for their ability to resist chloride ingress due to their capacity to fix more chlorides in hydrates, hence reducing the free chloride available for corrosion. This paper aims to present a link between strength development and in-situ formation of aluminate based hydrates at early age in the presence of chloride salts. Isothermal calorimetry is coupled with XRD investigations to gather insights on the accelerating mechanisms and on the potential impact of GGBS on durability. SEM-EDS observations were conducted to determine the spatial distribution of products formation and anhydrous grains dissolution in the presence of chlorides. The resistance to corrosion of chlorides/GGBS blends is then studied by electrochemical tests.


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