Marvin W. Halling

Unconstrained compression waves were measured using a newly developed, nondestructive, short impulse excitation device developed for long-term structural health monitoring. The measurements, using this innovative device, were used to determine the variation in the first longitudinal modal frequency as a function of loading magnitude and loading cycles to failure of various concrete mixes. Longitudinal frequency and cumulative energy variations were found to be a function of concrete compressive strength. These results imply that higher-strength concrete more easily absorbs energy and restricts the growth of microcracks. Based on the results, a new damage model is proposed that was shown to correlate with measured values to within 7%. This proposed model was found to have a closer correlation than Miner’s hypothesis and damage index models from other reviewed research.

Studies have shown that experimentally determined dynamic properties can be used to identify the characteristics of a structure. In this paper, a damage detection technique is developed and demonstrated using system identification, finite-element modeling, and a modal update process. The proposed approach, SFM, provides a rapid estimate of damage locations and magnitudes. The proposed methodology is applied to three case studies. The first is a numerical simulation using computer generated data. The second is an ASCE benchmark problem for structural health monitoring, where the results can be compared to other researchers. The third is a full-scale highway bridge that was field tested using a forced vibration shaking machine. In this case study, the bridge was shaken in several states of damage and the proposed methodology was utilized to detect and determine the location and extent of the damage. It was found that, using the collected data, the SFM approach was able to consistently predict the location of damage as well as estimate the magnitude of the damage.

This paper describes the measured behavior of a two span, live-load continuous bridge made with precast, prestressed, self-consolidated concrete girders. The lengths of each span are 27.2 m (89 ft 3 in.). The self consolidated concrete was considered high-performance, because of its high early compressive strength of 69.5 MPa (10.1 ksi) at release and 76.2 MPa (11.1 ksi) at 28 days. By using this high strength, self-consolidating concrete, the bridge designer is able to reduce the number of girder lines. These girders are among the first to be constructed in state of Utah using self-consolidating concrete. In order to monitor the behavior of the bridge, instrumentation was embedded in four of the twelve girders. Two interior girders in each span were chosen as representative girders. The instrumentation consists of vibrating wire strain gages with integral thermistors. The gages were placed at the centroid of the prestressing strands, girder centroid and composite girder centroid. Each of the gages has been monitored continuously since the time of casting. Data collected from each girder encompass the following phases: casting, de-stressing, curing, and deck placement. The measured changes in strain have been used to determine prestress loss values for each of the instrumented girders. These measured values are compared with predictive values using a newly proposed NCHRP method. The differences between the measured and predicted prestress losses are compared and recommendations for designers are provided.

A curved, three-span continuous, steel I-girder bridge in Salt Lake City was tested in order to determine its dynamic and static load carrying properties for three boundary condition states. For each of the three boundary condition states, two dynamic forced vibration methods were applied to the bridge as well as a static live-load test. The first forced vibration method used an eccentric mass shaker. The second method involved striking the side of the bridge with an impact hammer. The live-load test was performed by slowly driving a truck at a crawl speed across the bridge. Velocity transducers, accelerometers, and strain gauges were utilized to record the response of the bridge. The analysis and compilation of recorded dynamic response of the bridge enabled the preparation of mode shapes and natural frequencies for each boundary condition. This paper discusses the resulting changes in relevant dynamic properties and compares them with the changes in the static properties that were determined from the br...

In the field of nondestructive evaluation and damage detection, there is continued interest in the utilization of vibrational techniques. Structural damage will result in permanent changes in the distribution of structural stiffness. These changes may be detected through structural monitoring. Because of the direct relationship of stiffness, mass, and damping of a multi-degree-of-freedom system to the natural frequencies, mode shapes, and modal damping values, many studies have been directed at using these dynamic properties for the purpose of structural health monitoring. The use of vibrational monitoring is a developing field of structural analysis and is capable of assisting in both detecting and locating structural damage. Vibrational data have been shown to be most useful when used in conjunction with other monitoring systems if a remote and robust damage detection scheme is desired. This paper includes a literature review that summarizes the basic approaches to vibrational monitoring, suggested guid...

In the field of non-destructive evaluation and damage detection, there is continued interest in the utilization of vibrational techniques. Structural damage will result in permanent changes in structural stiffness, distribution of stiffness, and relevant material properties. These changes may be detected by monitoring dynamic behavior of the structure. Because of the direct relationship of mass, damping, and stiffness of a multi-degree-of-freedom system to the natural frequencies, mode shapes, and modal damping values, many studies have been directed at using these properties for the purpose of structural health monitoring. This paper compares the dynamic properties of a precast, prestressed concrete girder bridge determined from forced vibration testing with those of a three dimensional finite element model. The comparison showed that a finite-element model comprised of frame elements could accurately replicate the first seven modal frequencies to within an average difference of 6.5 percent.

In the field of non-destructive evaluation and damage detection, there is continued interest in the utilization of vibrational techniques. Structural damage will result in permanent changes in structural stiffness, distribution of stiffness, and relevant material properties. These changes may be detected by monitoring dynamic behavior of the structure. Because of the direct relationship of mass, damping, and stiffness of a multi-degree-of-freedom system to the natural frequencies, mode shapes, and modal damping values, many studies have been directed at using these properties for the purpose of structural health monitoring. The use of vibrational monitoring is very valuable in some cases, and is capable of assisting in both detecting and locating structural damage. Vibrational data is most useful when used in conjunction with other monitoring if a remote and robust damage detection scheme is desired. This paper includes a literature review and discussion of the basic approaches to vibrational monitoring, suggested guidelines for sensor selection and monitoring, and concludes with examples of two case studies.