Report About the Testing of an Anchor Section Reinforced With a TITAN 30/11 Hollow Bar as Tension Element

Transcription

1 Ischebeck Titan Injection Anchor System 1 Report About the Testing of an Anchor Section Reinforced With a TITAN 30/11 Hollow Bar as Tension Element This document contains the translation of report 1250/Mü/2800/523 of the University of Munich. Dr. Thomas Schmitz translated the report from German. CTS/TITAN IBO Hollow Bar Anchors 1 The system is called CTS/TITAN IBO Hollow bar system in North America (comment of the Translator) IA-11

2 Procedure The grout body of the Ischebeck TITAN Injection Anchor System1 is supposed to act as corrosion protection for the hollow steel anchor bar. To act as such, it is mandatory that the crack widths in the grout body stay within acceptable limits. The cracking behaviour of the grout body was to be determined experimentally. Investigations on anchor sections, which had been laboratory fabricated and had been tested as tension elements are described in report 1129/Mü/2800/523, dated April 29, To study the influence of the grout bodies shape on the crack width distribution, an excavated/exhumed anchor section was tested in the same way as the laboratory samples mentioned above. The test sample was delivered to us June 6, The order to perform the tests had been given to us verbally. Basics The testing of the laboratory-manufactured samples had shown that the average crack widths at the design load of 150 kn were between 0.04 and 0.1 mm. The 95% fractal* of crack widths, which is important for the classification of the corrosion protection capability, was between 0.23 mm and 0.37 mm. It had to be assumed that the crack formation of the lab samples would be different from the field samples because of the smoother more regular surface geometry of the former. To study the influence of geometry and surface roughness the present experiment with a field produced excavated anchor was performed. Materials & Methods The excavated anchor segment consisted of a TITAN 30/11 bar, galvanized and epoxy coated, which was covered with an irregular formed grout body on a length of 80 cm. The grout body is shown in figures 4 to 7 (pages 7 & 8). The grout body volume measurement showed an average cross section of 191 cm 2, which corresponds to an average diameter of 15.6 cm. The concrete cross-section however, was quite asymmetric in relation to the anchor bar so that it cannot simply be replaced by a circular cross section of equal area centred on the steel for the interpretation of the results. The material data of the bar can be taken from corresponding test results on TITAN 30/16 bars provided by the FMPA Stuttgart. According to these, the real steel cross-section deviates from the nominal value by 2.5%. The E-modulus of the steel is 191,000 N/mm2. Additional characteristic data are not required for the interpretation of the results communicated here. The influence of the galvanization and epoxy coating of the steel on the grout steel bond can be neglected for the presented study. The material data of the grout have not been determined. From experience a compressive strength of about 50N/mm2 can be assumed for the grout body. Experiments For the correct reading of the crack widths, the surface of the grout body was painted. The test sample was mounted into the tensile testing machine on the bare steel ends on both sides. The load was applied. in steps of 30kN each up to a maximum load of 300 kn, which is equal to twice the design load and to 1.15 times the yield load. At each load step, the crack picture was drawn and the crack widths measured at the respective locations with an accuracy of 0.01 mm. The reading locations were as close to the anchor steel as possible. Together with the load, the piston extension of the testing machine termed the machine extensions - was measured. Test Results The crack width pictures of the test samples are documented in images 8 to 11 on pages 9 & 10. The evaluations of the measurements were performed in the same way as for the laboratory produced samples. Image 3 (page 6) shows as a probability diagram the probability lines per load step. The horizontal cracks, which already formed at low loads as well as those formed later at higher loads at the ends of the gout body, were disregarded. Only vertical cracks were included into the evaluation. Since the permanent load is characteristic for the durability of the anchor steel in the ground, the diagram in figure 1 shows the comparison between the results derived from the laboratory samples and exhumed pile at the design load. The average spacing of the vertical cracks is shown in image 2. *Line denoting that 95% of all crack widths are below the indicated limit (comment of the Translator) CTS/TITAN IBO Hollow Bar Anchors IA-13

3 Interpretation of Results The exhumed anchor body displays a crack picture, which is similar to those of the laboratory samples. There are however the following differences, which can be attributed to the surface structure and the properties of the grout: At the design load of 150 kn, the crack widths of the exhumed pile were smaller than for the laboratory produced samples. Up to a load of 200 kn, the average spacing between cracks was higher for the exhumed anchor body than for the laboratory test bodies. The apparent contradiction that the exhumed anchor body on average exhibits larger crack distances and smaller crack widths can be attributed to its rough, irregular surface. This surface structure apparently leads to the development of micro cracks, which are not detectable by visual inspection. This in consequence corresponds to a higher elasticity of the grout body. For loads above 200 kn, the exhumed anchor behaves approximately as the laboratory sample with 300 mm grout body diameter. This means, the larger diameters of the irregular grout body of the exhumed pile govern the cracking behaviour. Summary The cracking behaviour of injection anchor grout bodies, reinforced with TITAN 30/11 hollow bar was investigated. In the first part of the experimental program, laboratory produced cylindrical test bodies had been tested in elongation/tension experiments. Now, a corresponding experiment was performed on the 1 m long segment of an exhumed anchor. The irregular cross section and the rough surface of the exhumed grout body result/cause for loads up to 125 % of design load in smaller crack widths as compared to the cylindrical and smooth laboratory grout bodies. The fact that, at the same time, the crack spacing is larger for the exhumed pile indicates a higher elasticity of the exhumed grout body. This is probably due to the formation of micro cracks, which are not visible to the naked eye because of their small width and the rough surface of the grout body. At the design load of the anchor bar of 150 kn, crack widths were 0.1 mm at maximum. Because of the short length of the exhumed segment, no statistical limits can be given. Longitudinal crack formation is lower in magnitude in the ground as is observed in the exhumed pile during the tension experiments. It is practically suppressed by the lateral forces of the ground on the grout body (and because the grout body is continuous, Comment of the Translator). Since longitudinal cracks weaken the bond between anchor steel and grout body, in the ground, because of the better bond of the anchor bar, smaller average crack spacing and consequently smaller crack widths are to be expected. IA-14

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