الفهرس 
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Abstract
This investigation aims to study the effect of core sample extraction from concrete columns on the ultimate load capacity. It has been reported that the ultimate load capacity of hollow concrete column is less than that of solid concrete column due to the extraction of core sample which decreases the column cross section and increases the stress on concrete. This research was carried out to investigate the effect of core test orientation on the ultimate load capacity of concrete columns. The rehabilitation of tested concrete columns was studied using many repair techniques.
Manual filling of core hole with concrete in the traditional repair method is used.
Normal concrete and grout was used in filling of core hole in the tested concrete columns. The use ofP.L.S and gravel was considered on the concrete that was filled the core hole in the tested concrete column.
For core test precautions; the ultimate load capacity and hollow/solid load ratio of tested concrete columns were studied according to the reduction on columns cross section. The diameter of core test knifes were 1, 3, 4, and 6 inch. The tested columns were in dimensions 200x3S0, 200xSOO, and 200x600 mm. Arching phenomenon of load was studied in columns with different knifes diameters. The tested columns were drilled in two orientations; longitudinal and transverse directions. Depth of core test was considered in two values; all length of the column and 12 cm depth.
For columns rehabilitation; 7 techniques were used in repair of hollow columns.
Atmospheric pressure was used in compaction of filling concrete in several techniques, while the hand filling was used in another one. 2 bar pressure was used in concrete compaction in one technique. Normal concrete and grout were used in the filling of core hole. Adhesion bonding agent was used in the bonding of old and new concrete in several techniques. The core hole was strengthened by steel tube with 5 mm thickness. The ultimate load capacity and repaired/solid load ratio of tested concrete columns were studied according to the type of repair techniques.
from the test results of ultimate load capacity of columns, core sample extraction from the tested concrete columns generally decreases the ultimate load capacity at the different column cross section reduction. Also, the deterioration increases as column cross section reduction increases. The ultimate load capacity and hollow/solid load ratio of tested