The aim of this study is to monitor the subsurface damage mechanisms of commercial cold-work tool steel by observing acoustic emissions generated in a spherical indentation test. Monotonic loads are applied in the elastic and plastic ranges to damage the specimen. Two types of damage prior to the occurrence of cracking are found: carbide breakage and plastic deformation. The phenomena are confirmed by microscopic images and the good agreement between the estimated carbide fracture strength and previous results. The two types of damage gives rise to different acoustic emission signals: a burst-type, high-amplitude signal for the breakage of carbides and a continuous-type, low-amplitude signal for plastic deformation. It is thus possible to detect and differentiate the incipient damage mechanisms on the subsurface in real time in a spherical indentation test.
The Alamillo Bridge is one of the long-span bridges crossing the Guadalquivir River. It was built on the occasion of Expo '92 in 1992 in Sevilla, Spain. The bridge is a cable-stayed structure spanning 200 m without any intermediate supports. Its originality is the lack of back stays and the balancing of the front stays through the backward inclination of a massive pylon. This paper shows the importance of experimental in situ techniques when applied to unconventional civil engineering structures and how—with the help of an important amount of accurate instrumentation, monitoring the most important experimental variables—it was possible to build the bridge correctly, safely, and on schedule.
This paper presents a methodology to assess the real longitudinal stiffness of a bridge including the foundation-soil interaction. The method is based on a dynamic test of the bridge complemented by structural identification. The experimentally obtained natural frequencies of the bridge in the horizontal and vertical planes are used to derive, via a parameter identification procedure and a dynamic model of the bridge, the most approximate values of the Winkler coefficients simulating the interaction of foundation with ground. The theoretical background of the procedure is first presented and then demonstrated on a prestressed concrete highway bridge with a total length of 2040 m (normal span length of 40 m). The bridge is located near the sea coast, and large variations in the soil properties were observed between the piers. As a consequence, it was not possible to assess in a reliable way the actual global stiffness of this bridge (due to the interaction of deck, piers, abutments and foundations) in front of horizontal forces (vehicle braking, earthquake, wind and so on) based on the results of the geotechnical survey. The dynamic excitation in the longitudinal direction was easily achieved by means of controlled vehicle braking at different points on the bridge. The results show the feasibility of using dynamic testing with vehicle braking as excitation to deduce the correct behavior of the bridge under the effect of horizontal loads.