AASHTO HB-17 pdf free download

AASHTO HB-17 pdf free download.Highway Bridges.
No lubrication shall be applied except that used for the whole lot of bearings. The bearing shall be loaded in compression with 100% of the full service dead plus live load, which shall be held constant for one hour prior to and throughout the duration of the sliding test. At least 12 cycles of sliding, each consisting of the smaller of the design displacement and ± 1 inch of movement. shall then be applied. The average sliding speed shall be 2.5 inches/minute. When the test is applied to curved sliding bearings. the design rotation shall be used in place of the displacement.
In flat sliding bearings, the breakaway friction coefficient shall be computed for each direction of each cycle, and its mean and standard deviation shall be computed for the sixth through twelfth cycles. Neither the friction coeffic lent for the first movement nor the mean plus two standard deviations for the sixth through twelfth cycles shall exceed the value used in design, and the mean value for the sixth through the tvelfth cycles shall not exceed two thirds of the value used in design.
In curved sliding surfaces, the moment corresponding to the design rotation shall be established at each peak movement (positive and negative) during the first and last six full cycles of testing. The corresponding load eccentricity shall be calculated by dividing the moment by the total compressive load acting. The eccentricity shall be small enough that the allowable stresses on the PTFE used in design are not violated.
18.7.2.8 Long-term Deterioration Test
The purpose of the test is to verify the long-term resistance of the materials to creep, wear and deterioration. The test shall be conducted on samples of the materials used in the bearings, or. at the option of the manufacturer, it may be conducted on a pair of bearings, placed back-to- back. The samples shall have an area not less than 7 in2. The test piece shall first be loaded in compression to a stress corresponding to 100% of the maximum dead plus live service load. Flat sliding systems shall then be displaced through at least 1000 cycles with an amplitude of at least ± 1 inch (2 inches peak to peak). Curved sliding systems and rotational systems that depend on deformation of an elastomcric element shall be subjected to displacements corresponding to 5000 cycles of rotation at ± the design amplitude. The sliding may take place at up to 10 inches/minute, except when readings are taken of the coefficient of friction, when the sliding speed shall be 2.5 inches/minute. The following shall be cause for rejection of the bearing:
(1) Damage visible to the naked eye on disassembly of the bearing, such as excessive wear, cracks or splits in the material.
18.7.2.9 Bearing Horizontal Force Capacity (Fixed or Cuided Bearings Only)
The purpose of the test is to verify that the bearing is stable and that the guide or restraint system has adequate strength under the most severe combination of horizontal and vertical loads.
One or more loading combinations, consisting of a horizontal and vertical service load which could exist simultaneously in the structure, shall be selected. The vertical load shall be applied first, at 1.0 times its nominal value. The horizontal load shall be applied in stages, up to 1.5 times its nominal value. Failure or excessive deflection of any of the components shall be cause for rejection.
18.7.3 Performance Criteria
It’ one hearing of the sample fails, all the bearings of that lot shall be rejected, unless the manufacturer elects to test each bearing of the lot at own expense. In lieu of this procedure, the Engineer may require every bearing of the lot to be tested.AASHTO HB-17 pdf download.