A. K. M. Anwarul Islam

Effects of NSM CFRP Bars in Shear Strengthening of Concrete Members

This paper presents the results of an experimental study that investigated the shear strength contribution of carbon fiber reinforced polymer (CFRP) bars attached with concrete beams using near surface mounted (NSM) technique. In this research, four concrete beams were cast with regular steel reinforcement in flexure. The control beam had typical shear steel and the other three beams were strengthened in shear with CFRP bars. Strain gages were attached with the shear reinforcement of all four beams at various shear critical locations. Strains during loading to failure of the beams were recorded using a data acquisition system. Performance of NSM technique was found to be very effective with no occurrence of delamination, debonding or fracture of FRP. Effective strains in the NSM CFRP bars were determined through analyzing the collected strain data. A new formula to calculate the nominal shear strength provided by NSM CFRP bars has also been proposed.

Blast Capacity and Protection of AASHTO Girder Bridges

AASHTO has specified probability-based design methodology and load factors for designing bridge piers against ship impact and vehicular collision. Currently, no specific AASHTO design guideline exists for bridges against blast loading. Structural engineering methods to protect infrastructure systems from terrorist attacks are required. This study investigated the most common types of concrete bridges on the interstate highways and assessed the capacities of the critical elements. A 2-span 2-lane bridge with Type III AASHTO girders was used for modeling. AASHTO Load and Resistance Factor Design methods were used for bridge design. The girders, pier caps and columns were analyzed under blast loading to determine their capacities. This study determined the blast capacities of the AASHTO girders, pier caps and the columns, and the required standoff distance of explosion from the columns that may possibly protect the bridge from failure.

Structural Health Monitoring of Bridges Using Wireless Sensor Network

The objective of this research is to monitor the structural health of an urban bridge real-time in the City of Youngstown, OH, by applying new technologies involving acceleration sensors, wireless networks, internet web services, Java SunSPOTs and embedded systems. The research was aimed to assessing the current structural health and future performance of the bridge with any immediate repair or replacement needs. A total of 8 wireless accelerometer Java SunSPOT Sensors, developed by Sun Microsystems (now part of Oracle), were customized and deployed at structurally critical locations on the bridge. Acceleration data were collected via real-time wireless sensor network. Later the acceleration data were analyzed to assess the structural condition of the bridge.

Bridge Load Rating Using Dynamic Response

Proposed herein is a method for load rating of prestressed box beam (PSBB) bridges based on their dynamic response collected using wireless sensor networks (WSNs). The hypothesis states that the health of a bridge is associated with its vibration signatures. Two WSNs were deployed on a 25-year-old PSBB bridge, and trucks were run with variable loads and speeds for collecting its real-time dynamic response at current condition. Also performed were finite-element (FE) simulations of 3D bridge models under vehicular loads to acquire the representative dynamic response at its newest condition. The bridge model was validated by field testing and numerical analysis. The fast Fourier transform and peak-picking algorithms were used to find maximum peak amplitudes and their corresponding frequencies. The in-service stiffness of the bridge was calculated to determine its load rating, which resembles the actual load rating of the bridge. The application software developed from this research can instantly determine the load rating of a PSBB bridge by collecting its real-time dynamic response. The research outcome will help reduce bridge maintenance costs and increase public safety.

Monitoring Structural Health of a Bridge using Wireless Sensor Network

The objective of this research is to monitor the real-time structural health of an urban bridge in the City of Youngstown, OH, by applying new technologies involving acceleration sensors, wireless networks, internet web services, Java SunSPOTs and embedded systems. The research was aimed to assess the current structural health and future performance of the bridge with any immediate repair or replacement needs. A total of 8 wireless accelerometer Java SunSPOT Sensors, developed by Sun Microsystems, were customized and deployed at structurally critical locations on the bridge. Acceleration data were collected via a real-time wireless sensor network. Later the acceleration data were analyzed to assess the structural condition of the bridge.

Urban highway bridge structure health assessments using wireless sensor network

This paper presents a wireless sensor network for assessing the structural health of urban highway bridges. Sensor data were collected on two pre-stressed box beam bridges (PSBB) with eight wireless sensor nodes. The wireless sensor was able to collect one hundred Accelerometer data samples per second without losing any wireless sensor data. Application software was developed to transform the sample data into frequency domain. Sensor data from all eight wireless sensor nodes have shown the similar peak frequencies with multiple trial runs on the same bridge. The peak frequency component was unique to each highway bridge. The signal to noise ratio in frequency domain is greater than seven to one. By comparing the actual wireless sensor data with the predictions from a finite element bridge model, a hypothesis of evaluating the structural health of the bridge was presented.

Bridge condition assessment from dynamic response collected using wireless sensor networks

We propose dynamic response based condition assessment of prestressed box beam (PSBB) bridges that will be more realistic and cost-efficient. The hypothesis includes that the dynamic response is a sensitive indicator of the physical integrity and condition of a structure. We deployed two wireless sensor networks for collecting the real-time dynamic response of a 25-year old PSBB bridge under trucks with variable loads and speeds. The dynamic response of the bridge at its newest condition was collected from FE simulations of its 3-D FE models mimicking field conditions. The FE model was validated using experimental and theoretical methods. We used Fast Fourier Transform and peak-picking method to determine peak amplitudes and their corresponding fundamental frequencies at its newest and current condition. The analyses interestingly indicate a 37% reduction in its fundamental frequency over a 25-year service life. This reduction has been correlated to its current visual inspection to develop application software for quick and efficient condition assessment of PSBB bridges. The research outcome will provide an efficient and cost-effective solution for bridge inspection and maintenance.

Bridge load rating from dynamic response collected using wireless sensor networks

We propose a method for load rating of prestressed box beam (PSBB) bridges based on their dynamic response collected using wireless sensor networks (WSNs). The hypothesis includes that the health of a bridge is associated with its vibration signatures. We deployed two WSNs on a 25-year old PSBB bridge, and ran trucks with variable loads and speeds for collecting its real-time dynamic response at current condition. We also performed FE simulations of 3-D bridge models under vehicular loads to acquire the representative dynamic response at its newest condition. We validated the bridge model by field testing and numerical analysis. We used Fast Fourier Transform and peak-picking algorithms to find maximum peak amplitudes and their corresponding frequencies. We calculated the in-service stiffness of the bridge to determine its load rating, which resembles the actual load rating of the bridge. The application software developed from this research can instantly determine the load rating of a PSBB bridge by collecting its real-time dynamic response. The research outcome will help reduce bridge maintenance costs and increase public safety.

Characterization of vibration transfer paths in nose gearboxes of an AH-64 Apache

Health monitoring of rotorcraft components, which is currently being performed by Health and Usage Monitoring Systems (HUMS) through analyzing vibration signatures of dynamic mechanical components, is very important for their safe and economic operation. Vibration diagnostic algorithms in HUMS analyze vibration signatures associated with faults and quantify them as condition indicators (CI) to predict component behavior. Vibration transfer paths (VTP) play important roles in CI response and are characterized by frequency response functions (FRF) derived from vibration signatures of dynamic mechanical components of a helicopter. With an objective to investigate the difference in VTP of a component in a helicopter and test stand, and to relate that to the CI response, VTP measurements were recorded from 0–50 kHz under similar conditions in the left and right nose gearboxes (NGBs) of an AH-64 Apache and an isolated left NGB in a test stand at NASA Glenn Research Center. The test fixture enabled the application of measured torques – common during an actual operation. Commercial and lab piezo shakers, and an impact hammer were used in both systems to collect the vibration response using two types of commercially available accelerometers under various test conditions. The FRFs of both systems were found to be consistent, and certain real-world installation and maintenance issues, such as sensor alignments, locations and installation torques, had minimal effect on the VTP. However, gear vibration transfer path dynamics appeared to be somewhat dependent on presence of oil, and the lightly-damped ring gear produced sharp and closer transfer path resonances.