Samer H. Petro

Damage detection using scanning laser vibrometer

A damage detection algorithm based on the principle of curvature changes has been developed at CFC-WVU. However, the algorithm requires accurate mode shapes with adequate spatial density. Existing contact sensors can not provide adequate spatial density without adding excessive mass. Hence, non-contact scanning techniques, such as scanning laser vibrometer (SLV) has adequate sensitivity and accuracy is yet to be proven. The applicability of SLV on large structures is also questionable. To assess the suitability of using SLV for damage detection, a beam specimen has been tested using an existing system. The results confirm that damage detection using vibration measurements from SLV is successful. Due to more spatial density, the SLV data is shown to be more sensitive than the contact sensor test.

Fiber-Reinforced Polymer Composite Bridges in West Virginia

Fiber-reinforced polymer (FRP) composites have been used more often over the past decade than before in new construction as well as in repair of deteriorated bridges. Many of these bridges are on low-volume roads, where they receive very little attention. It is imperative that new bridge construction or repair be long lasting, nearly maintenance free, and as economical as possible. Relative to those factors, FRP composite bridges have been found to be structurally adequate and feasible because of their reduced maintenance cost and limited environmental impact (i.e., no harmful chemicals leaching into the atmosphere with longer service life). In West Virginia, 23 FRP composite bridges have been constructed, among which 18 are built on low-volume roads that have an average daily traffic (ADT) of less than 1,000, including 7 with ADT less than 400. General FRP composite bridge geometry and preliminary field responses are presented as are some of the preliminary construction specifications and cost data of FRP composite bridges built on low-volume roads in West Virginia

Ultrasonic instrumentation for measuring applied stress on bridges

The measurement of applied stress on bridges can provide valuable information on the condition of the structure. The conventional technique for measuring applied stress is with a strain gage. However, strain gages can be time consuming to install because first the surface must usually be prepared. On a bridge, paint removal will most likely be necessary as part of this surface preparation. When dealing with lead-based paints, which are considered hazardous waste, many time consuming removal procedures are required. Because of these factors, a device that measures applied stress without requiring paint removal could be useful. While a “clamp-on” strain gage can also be used to measure applied stress without requiring paint removal, this type of strain gage can not be used on some bridge details, such as webs of I-beams and tops of box girders. An ultrasonic technique using non-contact electromagnetic transducers provides a possible method for applied stress measurement which is not limited by the same factors as those with conventional strain gages. The transducers operate through nonconductive and conductive (lead-based) paint and work on rusted, pitted surfaces. Our previous research developed a technique for measuring applied stresses on bridges with EMATs and included many laboratory tests. This paper describes field applications of the technique on actual bridge structures, as well as additional system testing and instrument calibration in the laboratory.

CONSTRUCTION OF FIBER-REINFORCED PLASTIC MODULAR DECKS FOR HIGHWAY BRIDGES

Fiber-reinforced polymer (FRP) composite materials have shown great potential as alternative bridge construction materials to conventional materials such as steel and concrete. This is especially valid in the field of repair and rehabilitation of existing bridges as well as in new bridge construction. The acceptance of composites in the highway bridge industry is mainly due to their superior properties such as high strength, durability, corrosion resistance, and fatigue resistance. Moreover, FRPs are well suited for mass production of structural shapes because of their high strength-to-weight ratios, which has resulted in the rapid installation of FRP modular decks on highway bridges. Details related to the construction of FRP modular decks as replacements on existing highway bridge superstructures are provided. In addition, details on shipping, handling, erection, assembly, deck-to-deck connections, deck-to-stringer connections, joints, and wearing surfaces are discussed.

Progressive damage detection using noncontact measurements

This paper presents work in progress toward the development of a bridge condition assessment system. The system combines remote laser vibration sensing technology and a strain-energy- based damage detection algorithm. The results from vibration tests conducted on laboratory specimens with different degrees of damage are presented. The vibration signatures are acquired using Scanning Laser Vibrometers (SLV). The extracted mode shapes from these tests are then used in the damage detection algorithm. The preliminary results indicate that the strain energy differences are highly sensitive to damage, and can be used to locate and distinguish progressive damages. The combination of SLV technology and the damage detection algorithm makes remote sensing attractive for the monitoring and inspection of structures. Finite element simulation of a progressive damage at a single location is also presented to illustrate the sensitivity of the algorithm to increasing damages.

Enhancing quality control in transportation construction through nondestructive testing

This paper addresses the growing need for modern nondestructive evaluation (NDE) techniques for quality control during the construction/fabrication stages of transportation infrastructure. While the use of NDE techniques for in-service monitoring of infrastructure is increasing, very little effort is currently being made to use NDE for construction quality control. This paper proposes the use of modern NDE techniques for inspection of materials and quality control during construction of transportation infrastructure. The paper also discuses the use of conventional nondestructive and mildly destructive techniques. Examples of potential NDE applications for quality control in transportation construction have been presented. A short discussion on current impediments to NDE field use and possible solutions has been included.

Laser vibrometer application on bridge cable tension measurements

To ensure the safety and integrity of tied arch bridges, it is crucial that tension levels in cables do not exceed their design levels. Currently, visual inspection is required since there are no reliable techniques that can accurately determine the tension levels of these cables. A possible approach would be to correlate the vibration measurements with the tensions in these cables. However, due to their long length, access to these cables for mounting contact sensors is not easy. An attempt has been made to use a He/Ne laser vibrometer for non-contact cable vibration measurements on a tied arch bridge. The objectives of this test are to assess the quality of vibration measurements from the He/Ne laser under regular daylight environment and to determine the vibration signatures of these bridge cables under ambient condition. The results of study indicate that using non-contact measurements, a quick and easy prediction of tension levels in bridge cables can be made. This paper presents the results of the study and presents discussion on the advantages of non-contact measurements and possible testing difficulties.

Kings Covered Bridge Rehabilitation, Somerset County, PA

Kings Covered Bridge over Laurel Creek in Somerset County, Pennsylvania is approximately 114-foot clear span multiple Kingpost Truss with nail-laminated arches. This timber bridge is historically significant because it retains its original features of the 1860’s since the 1930s when it was spared from modernization by the construction of an adjacent steel highway bridge for vehicular traffic. Since that time Kings Bridge has a colorful history, including use as livestock barn and a proposed new use as a part of a “twin covered bridge” municipal park. Kings Bridge remains a museum-quality artifact. The bridge is currently supported by a temporary steel queenpost truss system pending full rehabilitation. The rehabilitation strategy for Kings Bridge is to minimize interventions, repair in-place, and to replace deteriorated members in-kind where possible. This paper documents the rehabilitation of Kings Bridge as of November 1, 2004. An updated presentation of the existing timber conditions; structural analysis; and final rehabilitation design will be presented at the ASCE Structures Congress in April 2005. Rehabilitation construction will begin fall 2005. The rehabilitation funding for Kings Bridge is 100% federal through the National Covered Bridge and the Transportation Enhancements programs.

Measurement of axial forces via natural frequency

This paper presents results from testing several suspender ropes of the Delaware Memorial Bridge using vibration measurements and a non-destructive evaluation (NDE) instrument called the Axial Load Monitor (ALM). The testing consisted of measuring the frequencies of suspender ropes and determining their tension levels. Results were compared to theoretical predictions. This paper presents the results of the testing and discusses the problems associated with vibration measurements on actual bridges.

Development and Field-Testing of a Hand-Held Ultrasonic Monitoring Device

The effective life of timber bridges is often shortened by decay of timber components and failure of timber connections. Consequently, periodic inspections must be carried out to identify potential problems. Reliable methods for in-situ assessment of the strength and degradation rate in terms of strength loss over a period of time are essential for maintenance and rehabilitation of wooden bridges. A nondestructive technique such as ultrasonic measurement and testing has been found to be more accurate than the conventional practice of visual inspection for assessing the condition of wooden members. Ultrasonic measurements have shown considerable promise in determining the stiffness and strength of wood members by identifying the presence of defects such as knots and decay [1,2,3]. Experimental results have shown significant differences between the velocities of ultrasonic signals in defect-free areas and areas with knots, decays, and other localized defects [4]. Halabe et al. [5,6] has shown that frequency domain signal amplitude and wave attenuation measurements, when used in conjunction with time domain velocity measurements, can be much more accurate and reliable than simply using velocity measurements in predicting stiffness and condition of wood. Use of simple parameters such as area under FFT amplitude plots or power spectral density plots can greatly simplify comparison of various signals in the field.