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International Concrete Abstracts Portal

Showing 1-5 of 16 Abstracts search results

Document: 

SP175-11

Date: 

December 1, 1998

Author(s):

David Z. Yankelevsky and Itzhak Avnon

Publication:

Symposium Papers

Volume:

175

Abstract:

This paper is concerned with the description and explanation of Hardened Cement Paste (HCP) response to dynamic (explosive) loading. An experimental testing technique had been developed to study the dynamic cracking of HCP samples, using cylindrical explosive microcharges. Following the initiation of the microcharge, radial cracks propagate and measurements of their growth may be conducted. Procedures to predefine the crack path have been investigated, like preparation of linear grooves along the sample. Predefining the crack path enabled relatively simple measurements of its propagation velocity. The dynamic crack propagation velocity was found to be relatively low, within the range of 70-200 m/sec. (about an order of magnitude lower than the theoretical value). The dynamic HCP failure process was found to be usually of multicrack type. Studies of michrocharge initiation near a samples boundary provided insight into the development of scabbing cracks and of their interaction with the radial cracks propagating towards the boundary. It has been found that that crack interaction is strongly dependent on the relationship between the stress wave velocity and the crack propagation velocity.

DOI:

10.14359/5923


Document: 

SP175-10

Date: 

December 1, 1998

Author(s):

Cheng Yan and Sidney Mindess

Publication:

Symposium Papers

Volume:

175

Abstract:

The bond between deformed reinforcing bars and concrete under pull-out and push-in loading was studied under dynamic loading for plain concrete, polypropylene fibre reinforced concrete, and steel fibre reinforced concrete. A universal testing machine and an instrumented drop weight impact machine were used to generate static, medium rate, and impact loading, which covered a bond stress rate ranging from 0.5 x 1 O-8 to 0.5x 10-2 MPa/s. The stress distributions in both the steel and the concrete, the bond stresses and slips, the bond stress-slip relationships, and the fracture energy in bond failure were investigated. It was found that loading rates had a significant influence on these parameters.

DOI:

10.14359/5922


Document: 

SP175-12

Date: 

December 1, 1998

Author(s):

Jaap Weerheijm

Publication:

Symposium Papers

Volume:

175

Abstract:

The mechanical behaviour of concrete is based on the extension of present internal damage, the fracture process. To understand and predict the rate effect on material behaviour, the influence of dynamics on this fracture process should be considered. This idea was followed in the model developed at the TNO Prins Maurits Laboratory (TNO-PML). The damage extension in the real material was represented as crack extension in a fictitious fracture plane using the basic principles of Linear Elastic Fracture Mechanics (LEFM). This resulted in a good model prediction of the dynamic tensile strength, including the steep strength increase at high loading rates. The model clearly shows that inertia effects govern the mechanism of this steep increase. In this paper the various steps in the modeling process are described, specially focusing on the representation of the characteristic internal damage into a fictitious fracture plane. To illustrate the applicability of the approach it is presented in comparison to results of tensile tests with and without lateral compression.

DOI:

10.14359/5924


Document: 

SP175-13

Date: 

December 1, 1998

Author(s):

Peter H. Bischoff

Publication:

Symposium Papers

Volume:

175

Abstract:

Reliable analitical methods are needed to aid the analysis and design of concrete structures under impact and blast loading. Calculated results from such an analysis are often compared and fitted with physical test results to validate the method of analysis employed. Material models used in the analysis must, account for strain-rate sensitive behavior, and these material models are also based on results from experiments. Hence, reliable development of material models and analytical techniques is contingent upon correct, observation of experimental results. This paper focuses on effects which could alter the test results and influence their subsequent interpretation, such as testing machine characteristics, inertia, time delays in measured signals caused be analogue filters, and vibrational energy. All of these effects can lead to incorrect, measurement of a test response under high strain-rate loading. Examples are given of incorrect measurement, of the compressive stress-strain response of concrete at strain-rates in the order of 0.1 s -1 , where results from such tests have been obtained with hydraulic testing machines. Failure to account. for inadequacies in the testing technique affected conclusions about changes in deformation behavior (such as stiffness and axial strain at peak stress). and also led to an apparent loss of ductility. Results from impact tests on a flexural member demonstrate how vibrational effects from a falling mass can lead to incorrect conclusions about the measured contact. load.

DOI:

10.14359/5925


Document: 

SP175

Date: 

December 1, 1998

Author(s):

Editor: William Bounds / Sponsored by: ACI Committee 370

Publication:

Symposium Papers

Volume:

175

Abstract:

The 15 papers in this Symposium Publication describe a range of applications for this seemingly narrow area of structural engineering: design to resist or discourage terrorism against civilian and governmental buildings, design to eliminate or minimize destruction from industrial accidents, and design to protect military facilities. To assist the reader in focusing on a particular level of interest, the papers have been grouped into three sections. Section One, Design Aspects, relates directly to the design process. Section Two, Current Procedures and Recent Developments, provides an overall viewpoint. Section Three, Theoretical Developments, focuses on research issues. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP175

DOI:

10.14359/14216


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