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Mind your bolts

posted Jan 13, 2018, 4:42 PM by jeffery jim

1. Many structural engineers are not aware the importance of specifying the right way of treating bolt and nuts during rehabilitation works. I can count with my fingers if local engineers are aware of SSPC specifications although some drawings i came across did mentioned about surface treatment to SA2.5. Many did not know the difference between ST2 (using hand tool) and ST3 (using power tools). SA2.5 means near white blast by mean of SP10 using sandblasting.

2. SA2.5 is mainly for cleaning reinforcement bars (after performing to SP1 and SP2) which have yet to lost 10% of its diameter, in my case i usually prefer to take 8% since part of the surface might be lost when cleaning and removing the concrete which bonded to the reinforcement bar.

3. Bolt in the other hand should not be clean such manner without identifying the type and characteristic. This is important since the material used for cleaning may effect the slip coefficient of the bolt in use. Never ever use SP3 in cleaning bolts since this may reduced the bolt friction resistance by 25-30% overall due to polishing effect. Logically, surface which is too clean (to SA3) will have have less friction. Besides that, the reduction of thickness or change in dimension will result to change in area size of the bolt to cater stress area

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