Flexure Fixtures are designed for center and third point loading of concrete beams. A lower support channel rests on the machine lower platen, it has a series of locating holes to permit adjustment of the span of the support blocks in 3 inch increments. A flexible upper bearing block is used to apply the vertical force using either a single loading nose for center-point loading, or with dual loading noses when doing three-point loading. The upper bearing block allows adjustment of the loading noses in 1 inch increments.
Both types of fixtures are suitable for determining the flexural strength of concrete beams. The capacity of the fixture is dependent on the portion of the lower channel that is supported by the machine table.
Principle of Operation
Two lower support blocks consisting of hardened bearing blocks will support a specimen centered across both blocks. The bearing surfaces are half cylinders that pivot on rollers. The lower support blocks are adjustable within the lower channel to provide several different spans in fixed increments. The entire assembly is held in place using pins that bear against the front and back of the machine table.
The upper bearing block is similar in construction in that the same pivoting half cylinder bearing surfaces are used. However, the upper assembly includes an additional pivot on the mounting block. This pivoting action enables the entire upper block to move in order to maintain contact with the specimen during failure. The upper assembly can be used as either a 3-point bend fixture or a 4-point bend fixture.