In this paper, a wear-out model, which is based on the concept ofdeterministic strength degradation and equal ranking between static and residualstrengths, is used to assess the fatigue behaviors of several different sandwich beams.The model requires only two parameters to describe the strength degradation infatigue. One parameter represents the rate of strength degradation and the othera relative fatigue life. A new approach is used to determine these parameters fromexperimental data. The model is shown to be able to describe rather well both thestatic strength distributions and the fatigue stress-life relations of the sandwichbeams. The residual strength distribution after 5000 cycles was predicted for theEglass–vinylester–D100 balsa wood sandwich at 60% maximum stress level with thef and s obtained through the fitting method developed in this paper. There is a goodagreement between prediction and experiment.
The
cracking resistance performance of an asphalt binder is a significant
factor affecting the durability of asphalt pavements, and wax-based
warm mix additives are devoted to improving the crack resistance of
asphalt pavements. However, different components of wax-based warm
mix additives (Fischer–Tropsch (F–T)-, fatty acid amide
(FAA)-, polyethylene (PE)-, and linear aliphatic hydrocarbon (LAH)-based
waxes) have different effects on the cracking resistance performance
of the asphalt binder. Therefore, the optimum component of additives
was determined by the combination of a microscopic method and a macroscopic
test. The average carbon numbers of four additives were determined
by a high-temperature gas chromatography (HTGC) test. The multiple
stress creep recovery (MSCR), double-edge-notched tension (DENT),
and extended bending beam rheological (ExBBR) tests were used to characterize
the macroscopic performance of a modified asphalt binder. The F–T
wax with long-chain molecules improved the high-temperature performance
and lowered the degree of acceleration of thermoreversible aging.
The FAA, PE, and LAH waxes with short-chain molecules enhanced the
ductile fracture resistance performance. Therefore, the average carbon
number as the optimum component of wax-based additives was recommended
as C40 to C60.
Test of two specimens (four different joints) of steel secondary beam embedded in reinforced concrete girder in frame structure and one specimen with steel cantilever beam embedded in reinforced concrete girder under static load were conducted. The steel beam up-flange was pulled out because of the concrete cracks caused by the moment, shear and torsion at the upper zone of the concrete beam near the steel beam end. Shear failure of the concrete beam and the top flange pullout failure are the most hazardous failure modes. Lacking restraint of concrete and the reinforcement of steel bar in the concrete slab and catenary action of restraint steel beam, the capacity of steel cantilever beam is much smaller than other beams. Load-slip curve of top flange of steel beam, load-rotation curve of the steel beam end are obtained through experiment. Primary calculation method of joints flexural capacity related to section size of composite steel beam, embedded depth of steel beam, flange width of steel beam embedded end, height of frame girder, is put up with. Analytical results of ABAQUS are shown as follows. Top flange pullout failure of steel beam is caused by the detachment of concrete and steel beam end, and the warp of the concrete slab near the support plays an unfavorable action on the performance of the steel beam. The end rotational angle of the steel beam with anchor bar is smaller than that without. The steel beam with shear connectors develops a smaller rotational angle and a higher load capacity.
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