In-situ and Design Strength for Concrete in Offshore Platforms


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Title: In-situ and Design Strength for Concrete in Offshore Platforms

Author(s): Atle K. Haug and Bernt Jakobsen

Publication: Special Publication

Volume: 121


Appears on pages(s): 369-398

Keywords: building codes; compressive strength; concrete cores; cubes; evaluation; high-strength concretes; offshore structures; tests; statistical analysis; Materials Research

Date: 11/1/1990

Presents a summary of the results from a systematic in situ testing program on the concrete compressive strength in three Norwegian offshore platforms representing 460,000 m3 of high-strength concrete. The goal of the testing program was to document that the in-situ strength in these platforms is higher than assumed in relevant design codes and thus substantiates a higher utilization of the compressive design strength. The specified concrete quality for these projects has been in the range of C55 to C70. In a systematic manner, approximately one thousand 75 mm concrete cores have been tested and evaluated. Comparison has been made to the results of 100 mm cube specimens as reference. The main factor influencing the in situ strength proved to be the effective compaction applied to the fresh concrete. Thus, slipformed concrete shows systematically higher strength than conventionally placed concrete in stationary formwork. The in situ strength was significantly higher than presumed in relevant design codes. The results further indicate that the increase with time of the in situ strength was slightly higher than for the laboratory-cured reference specimens. For concrete platforms that are subjected to rigorous quality control programs and stringent working procedures, like the Condeep platforms, it is suggested that an increase in the compressive design strength should be allowed with 5 to 10 percent for slipformed concrete compared to the actual values given in the recently revised Norwegian design code.