Ian C. Hodgson

Application of state-of-the-art in measurement and data analysis techniques for vibration evaluation of a tall building

Recent advancements in sensing and data acquisition technology have made monitoring of structures and infrastructure more affordable and, at the same time, more comprehensive. Examples of such advancements are application of wireless technology for communication, the utilisation of fully automated systems for long-term monitoring and the remote control of the sensing system over Internet. Although each of these technologies has been used in different structural health monitoring projects in the recent years, inclusion of an all-in-one sensing system represents the state-of-the-art in measurement techniques. This paper presents the integration of all of the above-mentioned advanced monitoring approaches in one sensing system for forensic quantification of an in-service tall building. The inclusive measurement and monitoring system along with advanced data analysis techniques enabled extraction of detailed information about dynamic characteristics of the building structure and development of reliable conclusions regarding its performance. It is shown that the performance of the investigated structural components is satisfactory in terms of strength demand. However, the level of vibration in some portions of the structure does not meet the limits of human comfort. In addition, wind-speed spectrum, acceleration response spectrum and the modes of lateral vibration are extracted to assist with evaluation of the structures performance.

Forensic Examination of a Noncomposite Adjacent Precast Prestressed Concrete Box Beam Bridge

On the evening of December 27, 2005 the fascia beam supporting the east side parapet wall of the third span of the Lake View Drive Bridge failed under the action of dead load. To gain insight into the potential causes of the failure a series of forensic analyses were conducted on the beams decommissioned from the bridge. The study correlates external observations of surface condition with internal chloride profile, depth of carbonation, and existing corrosion. The forensic investigation indicated that strand cover was reduced due to the construction methods of the time. The chloride level in the concrete at the lower layer of strands was high enough that corrosion would be expected. Chloride attack was identified to have come from the leakage of water between beams from the bridge deck surface above. Based on the research findings recommendations are made for visual inspection, and guidelines are provided for condition rating of noncomposite prestressed concrete box beam bridges.

Localized Damage Detection Algorithm and Implementation on a Large-Scale Steel Beam-to-Column Moment Connection

Civil structures experience loading scenarios ranging from typical ambient excitations to extreme loads induced by natural events that, depending on their intensity, cause damage. It is important to detect damage before it propagates to become detrimental to integrity and functionality of the structure. Significant research efforts are focused on developing damage detection algorithms to diagnose damage from performance and response of the structure. A major challenge in many existing algorithms is in their validation and absence of real-scale implementation. This paper presents implementation of influence-based damage detection algorithm by implementation on a large-scale structural model (steel beam-to-column moment connection) which experiences progressive damage towards collapse of the system through increasing cyclic loading. IDDA utilizes statistical analysis of correlation functions between the structural responses at different locations. It is shown through this implementation that IDDA, accompanied by a statistical framework, can accurately identify structural changes and indicate the intensity of the damage.

Bilinear S-N Curves and Equivalent Stress Ranges for Fatigue Life Estimation

Abstract With the magnitude of some stress cycles in a live load stress range spectrum being higher than the constant amplitude fatigue limit (CAFL) of a structural detail, the development of a fatigue crack could be expected. The current procedure in the AASHTO specifications for fatigue life estimation utilizes an equivalent constant amplitude stress range with the direct extension of the S-N lines of slope −3 to below the CAFL. This approach is conservative; however, it often results in overprediction of fatigue damage and underestimation of the safe useful life of structural details. A set of bilinear S-N curves with the knee at the CAFL for the AASHTO fatigue strength categories and a slope of −4 below have been produced analytically for estimating fatigue life of existing structures subjected to variable live load stresses. This paper provides information regarding the development of the new equivalent constant amplitude stress ranges for the bilinear S-N curves. The results from a few examples are ...

Development of Flexural Strength Rating Procedures for Adjacent Prestressed Concrete Box Girder Bridges

An investigation was conducted on noncomposite prestressed precast concrete adjacent-box-beam bridges that suffered catastrophic failures resulting from the corrosion of the prestressing steel. These failures highlight the need to improve the methods used to detect corrosion damage and, subsequently, to load rate the damaged members. Currently, the inspection of concrete box girder sections relies on visual methods that correlate longitudinal and transverse cracking, spalling, and exposed strands with the rated level of performance of the member. To improve the current inspection techniques, visual assessment methods were examined through the destructive evaluation and material characterization of seven box-beam segments. The research results indicate that the fabrication techniques used for box-beam construction in the 1950–1960 time period allowed for large variations in construction tolerance. Half-cell methods were shown not to provide an accurate or reliable method of identifying the corrosion of prestressing strands. Longitudinal cracking was shown to be an accurate and reliable indicator of the underlying corrosion of prestressing strands. The probability of corrosion on strands adjacent to longitudinal cracks was determined and quantified. On the basis of the results, a new recommendation for determining the residual flexural strength of corroded prestressed beams is provided.

Fatigue Crack Formation and Repair Strategies for Steel Cantilever Bracket Tie Plates

AbstractA regular inspection of a bridge carrying U.S. Route 422 over the Schuylkill River in Berks County, Pennsylvania, revealed cracks in the floor beam–to–cantilever bracket tie plates. Similar fatigue damage of this type has been observed over two decades ago in other bridges. During this period, much advancement has taken place in structural evaluation through finite-element analysis. This paper presents a comprehensive procedure for the examination and retrofitting of tie plates using analysis and field measurement. A field and forensic investigation was conducted to examine the cause of the crack formation and the behavior of the bridge. The results of the field study and a fractographic examination confirmed that the cracks had occurred because of cyclic horizontal bending of the tie plates, which was generated by secondary out-of-plane bending of the top of the floor beam and cantilever bracket. Field measurements and evaluation indicated that some of the as-built tie plate details had exceeded ...

Influence of Flexibility on the Fatigue Performance of the Base Plate Connection in High-Mast Lighting Towers

This study investigates the effect of base connection geometry on base plate flexibility and the fatigue performance of multisided high-mast lighting towers. Three parametric studies investigating the effect of base plate thickness, tube wall thickness, and anchor rod configuration are discussed in this paper. The results of this study show that of the geometric parameters considered, base plate thickness has the largest influence on the stresses in the tube wall adjacent to the weld toe. By increasing the base plate thickness of the tower, significant improvement to the fatigue life is observed because the maximum stress, and hence stress range, at the base plate-to-tube wall thickness is reduced due to a reduction in local bending in the tube wall.