Dongming Yan

Dynamic Properties of Plain Concrete in Triaxial Stress State

There was experimental investigation of plain concrete dynamic behavior at high strain rates using a custom-designed, triaxial, servo-hydraulic controlled testing machine with over 60 cubic specimens in this study. A gradually increasing force was used for axial loading of each specimen at a constant strain rate at 10 supra -5 second supra -1, 10 supra -4 second supra -1, or 10 supra -3 second supra -1 and laterally confined at a 0, 4, 8, 12, or 16 MPa (0, 0.58, 1.16, 1.74, or 2.32 ksi) constant pressure. At each strain rate, there was analysis and discussion of axial stress-strain curves under confining pressures. Test results indicated that there were significant increases according to confining pressure of both ultimate strength and its corresponding strain. There was development of empirical equations accounting for triaxial stress and strain rate effects. There is substantial ultimate strength increases under low confinement and moderate increases under high confinement with increasing strain rate.

Blast Test of Full-Size Wall Barriers Reinforced with Enamel-Coated Steel Rebar

A type of enamel coating that contain hydraulically reactive calcium silicates have been developed to improve the performance and service life of steel used as reinforcement in concrete structures. To demonstrate the effect of enamel coating on the mechanical performance of concrete structures subject to blast loading, two wall barriers with identical dimensions, which were often used to keep the terrorism attack (such as car bomb attack) away from critical buildings, were fabricated and tested in a military base. One of the wall barriers was reinforced with coated rebar and the other with regular rebar. Four equivalent TNT weights, 4 lbs, 10 lbs, 30 lbs and 45 lbs explosive were applied to observe the deformation, cracking and failure mode of the two barrier walls. Generally, the test results indicate that the barrier wall reinforced with enamel coated rebar has much better integrity than that with regular rebar: fewer cracks on the front and back faces of the wall, more stress transferred to the steel rebar, and mitigated catastrophic failure of the wall. The new coating can be of great value in increasing the performance and the service life of defense-critical infrastructure.

Condition Assessment of Bill Emerson Memorial Cable-Stayed Bridge Under Postulated Design Earthquake

In this study, a three-dimensional finite element model of the Bill Emerson Memorial cable-stayed bridge was developed and validated with the acceleration data recorded during the M4.1 earthquake of May 1, 2005, in Manila, Arkansas. The model took into account the geometric nonlinear properties associated with cable sagging and soil–foundation–structure interaction. The validated model was used to evaluate the performance of a seismic protective system, the behavior of cable-stayed spans, and the accuracy of two simplified bridge models that have been extensively used by the structural control community. The calculated natural frequencies and mode shapes correlated well with the measured data. Except that the hollow columns of two H-shaped towers were near yielding immediately above their capbeams, the cable-stayed spans behaved elastically as expected under the design earthquake that was scaled up from the recorded rock motions at the bridge site. The minimum factor of safety of all cables is 2.78, which is slightly greater than the design target.

Inspection, analysis and loading test of a slab bridge strengthened with FRP laminates

The advantages of FRP as a strengthening material have been widely recognized in recent years. Typical applications of FRP have extended from repairing of cracked columns, beams, bridge decks to enhancing the load capacity of critical structural components. As a demonstration of application of FRP laminates in concrete bridge decks with no transverse reinforcement, the Rolla Bridge in Missouri is selected for this study, which is a two-span simply supported reinforced concrete slab with no transverse steel reinforcement. The original construction combined with the presence of very rigid parapets caused the formation of a wide longitudinal crack which resulted in the slab to behave as two separate elements. The strengthening scheme was designed to avoid further cracking and such that the transverse flexural capacity be higher than the cracking moment. An initial load test, to evaluate the structural behavior, was performed prior the strengthening. The retrofitting of the structure was employed after the major cracks were injected to allow continuity in the cross section. Once the repair work was completed, another load test, identical in procedure to the previous one, was performed to evaluate the efficiency of the strengthening. No additional cracking was observed in the concrete decks as a result of the strengthening program.