This paper describes the results of an investigation on the use of high strength deformed bars for the reinforce concretes in harbour construction works and of the comparison tests on their properties such as yield point, elongation, tensile strength, bond strength with concrete, bending property and weldability.
　To expect economical and proper use of high strength deformed bars, improvements are considered necessary in many aspects of design and practice according to the results of the field investigation compiled from 68 cases of harbour construction works during the fiscal year 1965 under the direct control of Ministry of Transport.
　In most cases the allowable stresses were not higher than 1,800, 2,000 and 2,000 kg/cm2 for the deformed bars with guaranteed yield points of 3,000, 3,500 and 4,000 kg/cm2, respectively, and the nominal diameters of these bars were not more than 25 mm due to the structural requirements of harbour works with exceptional two cases where the bars of 32 mm were employed along with the allowable stress of 1,800 kg/cm2 for their guaranteed yield point of 3,500 kg/cm2. In all the cases investigated the allowable flexural compressive stresses of concrete were not higher than 84 kg/cm2, mnostly not higher than 70 kg/cm2 which was equivalent to 1/4 to 1/3 of the designed strengths, and the compressive strengths actually obtained in fields at 28 days were in general much higher than the designed strengths. The allowable bond stresses of concrete with deformed bars were not more than 1/10, mostly equal to 1/15, of the designed flexural compressive strengths. These all
owable stresses of reinforcing steel and concrete seem too conservative, since most of the reinforced concrete structures in harbour works are seldom subject to repeated loading nor to severe dynamic loading, the crack opening in concrete is estimated sufficiently small to affect the corrosion of steel bars under the circumstances, and the strenghts of concrete obtained in fields are generally much higher than required in design.
　Most of the splices were lapped splices with very few cases of gas welding under
pressure, while the anchorage of defomred bars with steel piles by arc welding
was commonly observed. In these cases of welding of defomred bars the field practice are not highly appreciated and in few cases the structural design of welding are regarded even improper.
　In most cases the conditions of storage of steel bars need to be improved,although the test results have proved the corrosion of steel bars suffered under the
conditions as observed is not so influential as to make any visual damage on their properties so far.
　The field practice of beding and rebending of deformed bars were observed much more severe than generally anticipated. This suggests the bending property of high strength defomred bars is to be evaluated through bend and rebend tests under the conditions as observed which is much more severe than required in Japanese Industrial Strandard G 3112-1964 Steel Bars for Reinforced Concrete.
　Based on the results of the filed investigation, laboratory tests were carried out on the representative high strength deformed bars of 15 varieties commericially available in Japan to compare their properties and to investigate the effects of deformations upon their properties.
　Among fifteen varieties of defomred bars two were found not comply with the JIS requirements as cited above and the other one differed considerably in its tensi
le properties and deformations depending upon the methods of sampling. The difference in yield point betweeen the guaranteed value and the measured one differed remarlkably according to the brand of deformed bars, that is, the latter was by 1 to 21% higher than the former, and the bars with the yield point extraordinarily
higher than required in JIS had naturally low elongation and poor bending property.
　The bond property of defomred bars with concrete was evaluated in this study by the bond strength obtained by the so-called pull-out test. The test results show
that the bond strength of concrete is approximately in linear proportion to the compressive strength of concrete within the range of 180 to 360 kg/cm2, provided
certain type of defomred bar is used. Also the bond strength was found to be affected principally by the pattern of deformations and the ratio of bond strength of deformed bars may be regarded approximately as 1.0, 0.9, 0.8 and 0.7 for the deformed bars of transverse, wave-like, modified wave-like and crosswise deformations, respectively, provided the deformations being complied with the JIS requirements.
　The bending property of defomred bars was evaluated in this investigation through the crack modulus which was introduced as an index expressed quantitatively the extent and tendency of crack formation on the surface of the deformed bars caused by bend and redend tests consisted of bend test of 90 deg. around. a pin 3.5d and 5.0d (d is a nominal diameter of defomred bars) in diameter and after that rebend test of 90 deg. at room temperatures. The test results show that the bending property of deformed bars are affected considerably by their ductility, pattern of defomrations the radius of the arc formed at the base of the deformation lateral to the bar axis, form of the cross section of bar and the direction of loading and that the bars with deformations which have the radius of arc about 2 times their height have excellent bending property.