International Concrete Abstracts Portal

A total of 25 papers are included in this Symposium Publication on HPC. The general topics include HPC bridges, HPC structural lightweight concrete, material science of HPC, and structural safety of HPC. 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. SP189

The shear stress detrmined using ACI 318-95 is limited to the stress determined for 10,000 psi (69 MPa) concrete. This limit has been set because it was considred that there was not enou data to justify the extension of existing equations to higher strengths. Modification are suggested which adapt the ACI equations so thy apply to the full range of concrete strengths. The proposed equations predict the shear strength of beams more accurately than the current ACI equations. For the beams investigated, the coefficient of variation is only 2/3 of that obtained using the ACI equations. The proposed equations apply to concrte stengths as high as 18,000 psi (124 MPa). Aoart frin tgeur simplicity, the proposed equations have a number of other advantages. Unlike ACI equations 11-1 to 11-3, they correctly predict the increased strength of beams with small shear-span to depth ratios. Because the proposed equations assume the most pessimistic location of cracks, the maximum stirrup spacing requirements are satisfied sirectly so that adtitional spacing limitations appear to be extraeous. To illustrate the improvement that can be obtained using the proposed equation, published test results are compared with predicted values.

ACI Code-95 recommendations for column design are based mostly on test results on concretes with strengths up to 42 MPa. Due to differences between high-strength concrete (HSC) and normal-strength concrete (NSC) material and structural behavior, using these recommendations for HSC columns does not mean that the same level of safety as for NSC is obtained. As a consequence, the reliability that the same level of safety as for NSC is obtained. As a consequence, the reliability of HSC columns must be assessed. Since most of the variables involved in column design (material properties, geometric characteristics, loads, etc.) are random, a basic step in the reliability assessment of HSC columns is the modeling of uncertainties associated with both column strength, as well as, load effects is presented. Regarding the computation of the statistics of the HSC column strength, many issues have to be resolved: (a) the scarcity of information on the variability of the compressive strength of HSC; (b) the unavailability of a closed form solution to express column strength; and © the compatibility with the assumed failure criterion. Regarding the computation of the load effect statistics, special attention given to the case of slender HSC columns.

The influence of the type of placing of concrete (free fall or compacted layers) in vertical elements on the mean value of the compressive strength, as well as its variability is investigated in the present work, with comparisons of normal (NSC) and high-performance (HPC) concretes. The experimental program consists of the fabrication of NSC and HPC columns with steel reinforcement placed under two extreme conditions, and the extraction and testing of cores from different heights. From these results, the corresponding strength reduction factor to be applied to concrete is obtained for NSC and HPC with the condition that the same safety level is to be obtained in both cases. The study covers the range of target reliability indices from 3.5 to 5. The extreme values of the sensitivity factor of the random variable concrete strength are also considered. The main conclusion that can be drawn is that the reduction factors used in design codes or normal concretes do not apply to HPC since its final strength is more sensitive to the placing conditions. However, due to the limited number of tests performed, further and more extensive results are necessary to calibrate a value of the strength reduction factor for the design codes.

The AASHTO “Task Force on Strategic Highway Research Program (SHRP) Implementation” developed and instituted the Lead State Program in 1996. The mission of the Task Force was to optimize ways in which SHRP technologies could be implemented at the state level. The Task Force understood the benefits of mutual cooperation in sharing resources, working as teams, and collectively implementing the technologies. In order to achieve their mission the Task Force developed the concept of “Lead States Teams”. A “Lead States Team” is a group of states that are willing to take the lead and assist in the implementation of specific, targeted SHRP technologies in which they have interest and have gained some practical experience.