Behavior and Efficiency of Bottle-Shaped Struts. Paper by Michael D. Brown, Cameron L. Sankovich, Oguzhan Bayrak, and James O. Jirsa

The authors have carried out a thorough and well-planned experimental study to determine the strength parameters of struts used in strut-and-tie modeling. The critical review of the provisions related to the strength of struts in ACI 318-05 and AASHTO-LRFD "Bridge Design Specifications" is informative. The following issues may need elaboration by the authors:

1. It is evident that in all the test panels, the authors have selected the panel dimensions in such a manner as to create a state of plane stress. But how exactly the dimensions, especially the thickness in relation to the panel size, have been selected is not clear.

2. The cylinder compressive strength of the concrete mixtures used by the authors in their study varies from 22 to 38 MPa. It is appreciated that it is impracticable to maintain exactly the same compressive strength of the concrete used in various test panels. One cannot overlook, however, the fact that the stress-strain characteristics of concrete will undergo a significant change as the strength increases from 22 to 38 MPa. This, in turn, is likely to influence the response of the test panels. The authors may like to clarify whether the aforementioned choice of concrete compressive strengths was deliberate or otherwise.

3. It appears that the steel reinforcing mat was placed at the mid-thickness of the specimens designated A through X. In almost all bottle-shaped struts encountered in practice, the crack control reinforcement is placed in two layers, one on each face of the member. In this context, the rationale of placing the reinforcement in the mid-thickness of the specimen is not clear.

4. The failure loads for the various tests have not been provided. In the presence of these loads, the reader would be able to better comprehend the performance of various test specimens.

5. The authors have reported that all the specimens have failed at the interface between the node and the strut, that is, failure has been caused by crushing of the concrete in the strut adjacent to the node. The reason for this mode of failure, however, has not been indicated. If the cause of this mode of failure in this weakest link of the system could be identified, then perhaps suitable remedial measures could be investigated to improve the performance of the system.

Discussion by Dipak Kumar Sahoo, Bhupinder Singh, and Pradeep Bhargava

Research Scholar, Department of Civil Engineering, Indian Institute of Technology, India; Assistant Professor, Department of Civil Engineering, Indian Institute of Technology; Professor, Department of Civil Engineering, Indian Institute of Technology

Copyright American Concrete Institute Mar/Apr 2007
Provided by ProQuest Information and Learning Company. All rights Reserved