• Journal of Korean Society of Steel Construction
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• v.12 no.2 s.45
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• pp.177-185
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• 2000

An experimental research to evaluate the slip coefficients of high-strength friction-type bolt connection of weathering steel plate has been performed in this paper. The test specimens with mill scale or shot blast had been exposed in open air during 3 and 6 months and cleaning of rust surface by hand brushing, power tool brushing and no cleaning was considered. The relaxation of bolt clamping force had also been measured during 600 hours. It was found that slip coefficients increased to the value over 0.6 with exposure except mill scale surface by power tool brushing. The relaxation of bolt tension force in exposed specimens also increased and maximum value reached to about 10%.

• Journal of Korean Society of Steel Construction
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• v.12 no.2 s.45
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• pp.167-175
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• 2000

An experimental research to evaluate the slip coefficient of high-strength slip-critical-type bolt connection of weathering steel plate has been performed in this paper. Experiments were performed with several surface conditions such as clean mill scale with hand or power brush cleaning, shot blast cleaned, inorganic zinc primer coated, and weather coated surfaces. Also, the relaxation of bolt clamping force was estimated during 500 hours. It was ascertained from the experiments that slip coefficients are greater than 0.40 in all faying surface conditions except mill scale surface with power brushing. The quantify of relaxation depended on the surface conditions and was $3{\sim}8%$, i.e., less than 10%.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.4A
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• pp.291-297
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• 2009

Relaxation of high strength bolts was investigated. Block type and splice type specimens were fabricated with different types of bolts and different clamping lengths. Bolts were tightened to the specified torque. Clamping forces were measured through strain gauges installed on the shafts of bolts, while specimens were kept in a constant temperature and humidity. In all cases, ratio of clamping force reduction is less than 10%. Test results of different types of specimens and bolts and different clamping lengths were compared each other by using a simple model, which is suggested in this study for the estimation of bolt relaxation. The suggested model shows reasonably good agreements with test results for all cases. No difference is found between F13T and F10T bolts, but Dacro coated bolts shows higher relaxation than black bolts by approx. 30%. And also the comparison of test results shows that ratios of bolt relaxation become larger as clamping lengths of bolt shorter and the number of faying surfaces greater.

• Journal of the Korean Society for Advanced Composite Structures
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• v.3 no.1
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• pp.8-15
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• 2012

The initial clamping forces of high strength bolts depending on different faying surface conditions drop within 1,000 hours regardless of loading, any other external force or loosening of the nut. This study is focused on an expectation model for relaxation of high strength bolt, which is confined to creep on coated faying surfaces after initial clamping. The range of this experiment is limited to estimate the relaxation of bolted joints coated by inorganic zinc primer. The candidate bolts were dacro-coated tension control bolts. The parameters of coated thickness for the faying surface were 96, 168,and $226{\mu}m$ respectively. From experiments, it exhibited that the logarithmic function for creep strain was derived due to the parameter of coating thickness. By using the creep strain, subsequently the quantitative model for estimating long term relaxation of high strength bolt can be taken with the elapsed time. The experimental results showed that the relaxation after the initial clamping of high strength bolt rose to a much higher range from 10% to 18% due to creep of the coating as the coating thickness was increased. This study showed that the clamping force reflecting relaxation after the elapse of constant time can be calculated from the initial clamping force of high strength bolt.

• Journal of Korean Society of Steel Construction
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• v.8 no.3 s.28
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• pp.151-160
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• 1996

The fatigue test under the constant amplitude repeated loading is performed to investigate the fatigue behavior of the Torque Shear type high tension bolted joint which is able to manage the axial force uniformly. From the test results, it's known that the reduction of the axial force of T/S bolt followed by the elasped time is similar to that of the high tension bolts. The difference of relaxation is not occurred according to the position of bolts, the size of the introduced axial force but the effect of the variation of temperature is large. In the reduction of the axial force followed by the cumulation of the fatigue load, the outer bolt is larger than the inner bolt. This result depends on the difference in the distribution of the non-slip zone. The variation of the surface roughness affects the slip and the reduction of the anal force.

• Corrosion Science and Technology
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• v.11 no.2
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• pp.48-55
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• 2012

Clamping force of a high strength bolt is reduced by a certain period of time after the initial set-up. In case of special treatments on faying surfaces such as protective coating, clamping force is relaxed more severely. Tests for slip critical joints subject to various faying surface parameters were conducted. Five different surface treatments were tested including mill scale surface, blast surface, rust surface and coated surfaces. Each specimen was composed of F10T M20 of high strength bolts and steel plates. Based on the result of slip coefficient test, blast treatment surface showed 0.59, rust treatment surface showed 0.54 and inorganic zinc treatment surface exhibited 0.44. Clean mill treatment surface and red lead paint treatment surface were 0.23, 0.21 respectively. It is identified that the slip coefficient in Korean structural design guide should be determined for various surface conditions. Subsequently from long term relaxation test of ASTM A 490 high strength bolts, relaxation of no-coated surfaces such as blast, clean mill, rust treatment, the loss of initial clamping load was 10.5%, 13.6% and 7.9% for 1,000 hours, while the loss of initial clamping force was reached as 15.0%, 18.7% more than the required redundancy 10% in case of inorganic zinc and red lead painted treatment. It is required that the limit of relaxation on coated faying surface should be established separately for various surfaces.

• Steel and Composite Structures
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• v.16 no.6
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• pp.703-718
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• 2014

The initial clamping forces of high strength bolts subjected to different faying surface conditions drop within 500 hours regardless of loading, any other external force or loosening of the nut. This study develops a mathematical model for relaxation confined to creep on a coated faying surface after initial clamping. The quantitative model for estimating relaxation was derived from a regression analysis for the relation between the creep strain of the coated surface and the elapsed time for 744 hours. This study establishes an expected model for estimating the relaxation of bolted joints with diverse coated surfaces. The candidate bolts are dacro-coated tension control bolts, ASTM A490 bolt, and plain tension control bolts. The test parameters were coating thickness, species of coating. As for 96, 128, 168, and $226{\mu}m$ thick inorganic zinc, when the coating thickness was increased, relaxation after the initial clamping rose to a much higher range from 10% to 18% due to creep of the coating. The amount of relaxation up to 7 days exceeded 85% of the entire relaxation. From this result, the equation for creep strain can be derived from a statistical regression analysis. Based on the acquired creep behavior, it is expected that the clamping force reflecting relaxation after the elapse of constant time can be calculated from the initial clamping force. The manufacturer's recommendation of inorganic zinc on faying surface as $75{\mu}m$, appears to be reasonable.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.2
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• pp.136-143
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• 2011

The oversized and slotted holes are frequently required for the built-up in construction sites. The foreign provisions specify the reduction of the slip load subjected to the size of bolt holes and the direction of load. There are no domestic building codes and researches on the bolt holes. Therefore, it is necessary to evaluate a change of joint strength quantitatively according to the bolt-hole size and surface condition by means of experiment. This study was conducted to evaluate the slip load subjected to the size of bolt holes, and measured on a change of clamping force of high strength bolts during 168 and 800 hours to analyze the trend of relaxation after fastening bolts. Torque shear bolts defined on KS B 2819 was used for the specimen. Test results exhibit that the variation on the slip load of the others was below 10% by contrast with the standard hole and the highest rate of relaxation was 2.66% of the initial clamping force at the case of the long-slotted hole of 2.5D.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.2
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• pp.1-7
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• 2018

Suspension bridge cables made of high strength steel wires require periodical maintenance in accordance with the axial force of cable-band bolts, since the bolts in suspension bridges can undergo tension decrease due to creep of cable wires, bolt relaxation, load fluctuation, and cable re-arrangement, etc. Consequently, this study is aimed at investigating and subsequently evaluating the critical factors with respect to the bolt tension-decrease phenomenon in SR suspension bridge in Korea, based on field monitoring, theoretical studies, and field record management works. From the observation, it is interesting to note that the decrease in the bolt tension force is typically accompanied by plastic deformation of the zinc plating layers in the cable wires. In addition, a framework corresponding to generic methodologies to characterize the deformation in terms of the bolt tension-decrease and long-term history management has been developed in this exploratory study.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.4
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• pp.651-668
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• 2017

For initial stability of the tunnel, the primary support, Shotcrete and rockbolt shall be placed in the most appropriate time. This is because the role of such support plays a vital role in long-term and short-term tunnel stability. In this study, the rock bolt is an important supporting system that receives the external pressure generated by the stress relaxation during tunnel excavation as axial force and transmits it to the shotcrete on the tunnel excavation surface. Until now, most of the materials of rock bolts have been used in the field, but there have been many problems such as uncertain quality of Chinese materials entering the market, poor packing due to falling down of rock bolts when filled with mortar, and corrosion due to water. Therefore, in this study, we have developed a high strength steel pipe rock bolt using Autobeam material to solve and improve various problems of existing rock bolts. In order to evaluate the performance of the developed bolt, field tests were carried out and the existing mortar filler in order to improve the performance of the rock bolt, the design and construction criteria were studied and the results were included in this paper.