Assessing the Ageing Impact on Fatigue-Life of Asphalt Concrete

The fatigue-life of asphalt concrete is often related to environmental condition,loading condition,ageing,material composition and properties.This work investigates the influence of short and long term ageing of laboratory beam specimens,asphalt percent,and testing temperature on fatigue life of asphalt concrete wearing course.Slab samples of(30 × 40 × 6)cm have been prepared,beam specimens of(40 × 5 × 6)cm were extracted from the asphalt concrete slab samples and tested for fatigue-life under the impact of three levels of micro strain(250,400,and[3]750)at(5,20,and 30)℃ before and after practicing long-term aging.It was observed that the fatigue-life decreased by(85 and 97)%,(87.5 and 97.4)%,(71.4 and 95.2)%after increasing the applied microstrain from(250 to 400 and 750)μƐfor control mixture and for mixtures subjected to shortand long-term ageing processes respectively.The fatigue-life increased by(142.8 and 257.1)%,(34.4 and 57.8)%and(10 and 30)%when the asphalt content increased from(4.4 to 4.9 and 5.4)%for specimens practicing the applied microstrain of(250,400 and 750)μƐrespectively.It can be concluded that the fatigue life increases by a range of(two to fifteen)folds when the testing temperature increases from(5 to 20 and 30)℃ respectively.

Plate reinforced square hollow section X-joints subjected to in-plane moment

The static test of 13 square hollow section(SHS) X-joints with different β and different types of plate reinforcement under in-plane moment in brace was carried out. Experimental test schemes, failure modes of specimens, moment-vertical displacement curves, moment-deformation of the chord, and strain strength distribution curves were presented. The effect of β and plate reinforcement types on in-plane flexural property of SHS X-joints was studied. Results show that punching shear of chord face disappears, brace material fracture appears and concave and convex deformation of chord decrease when either collar plates or doubler plates were welded on chord face. Moment-vertical displacement curves of all specimens have obvious elastic, elastic-plastic and plastic stages. As β increases, the in-plane flexural ultimate capacity and initial stiffness of joints of the same plate reinforcement type increase, but ductility of joints decreases. With the same β, the in-plane flexural initial stiffness and ultimate capacity of doubler plate reinforced joints, collar plate reinforced joints, and unreinforced joints decrease progressively. Thickness of reinforcement plate has no obvious effect on in-plane flexural initial stiffness and ultimate capacity of joints. As thickness of reinforcement plate increases, the ductility of reinforced X-joints decreases. The concave and convex deformation of every specimen has good symmetry;as β increases, the yield and ultimate deformation of chord decrease.

Analysis of stiffness and flexural strength of a reinforced concrete beam using an invented reinforcement system

In this study,we conducted experimental tests on two specimens of reinforced concrete beams using a three-point bending test to optimize the flexure and stiffness designs.The first specimen is a reinforced concrete beam with an ordinary reinforcement,and the second specimen has an invented reinforcement system that consists of an ordinary reinforcement in addition to three additional bracings using steel bars and steel plates.The results of the flexure test were collected and analyzed,and the flexural strength,the rate of damage during bending,and the stiffness were determined.Finite element modeling was applied for both specimens using the LS-DYNA program,and the simulation results of the flexure test for the same outputs were determined.The results of the experimental tests showed that the flexural strength of the invented reinforcement system was significantly enhanced by 15.5%compared to the ordinary system.Moreover,the flexural cracks decreased to a significant extent,manifesting extremely small and narrow cracks in the flexure spread along the bottom face of the concrete.In addition,the maximum deflection for the invented reinforced concrete beam decreased to 1/3 compared to that of an ordinary reinforced concrete beam.The results were verified through numerical simulations,which demonstrated excellent similarities between the flexural failure and the stiffness of the beam.The invented reinforcement system exhibited a high capability in boosting the flexure design and stiffness.