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Ultrasonic Pulse Velocity in Concrete Using Direct and Indirect Transmission

This research investigated the relationship between velocities of ultrasonic stress waves transmitted along direct and indirect paths. Tests were conducted on plain concrete slabs of dimensions 1000 x 1500 mm, with thickness of 250 mm. Direct ultrasonic wave transmission tests were conducted between top and bottom surfaces of the slabs and indirect tests were conducted along the slab surface. A test procedure, used to determine indirect wave velocities, was refined by defining the number and spacing of transducers. Comparisons were made between direct and indirect wave velocity measurements using statistical analysis. The statistical analysis revealed that direct and indirect wave velocities could be used interchangeably to evaluate properties of the concrete. The minimum number of test points required for a reliable estimate of indirect wave velocity was studied, and recommendations are provided.

Abating Earthquake Effects on Buildings by Active Slip Brace Devices

A hybrid control system for reducing building vibration under a spectrum of earthquake load amplitudes is presented. The hybrid control is accomplished by an energy dissipation device called the active slip brace device (ASBD). The hybrid control system uses the ASBD to regulate the energy dissipation characteristics of the building during its response to earthquakes by utilizing active control principles. The ASBD consists of a Coulomb friction interface with a clamping mechanism on the interface. The clamping force on the friction interface is altered at short time intervals during building vibration. Computer simulations of building response with and without ASBD are compared.

Rationally Designed Staged Posttensioning to Abate Reflective Cracking on Side-by-Side Box-Beam Bridge Decks

Side-by-side box-beam bridges are often used at sites with tight under-clearance requirements and specified for accelerated construction. However, longitudinal reflective deck cracking is a recurring problem for these bridges and it raises concern for their durability and long-term safety. North American practices of the transverse connection design of this particular bridge are discussed in NCHRP Synthesis 393, and the Michigan design is presented as the preferred procedure. The most recent design in Michigan is an empirical procedure that incorporates the majority of the Synthesis 393 recommended best practices. Yet reflective deck cracking persists. A rational design procedure for which an analysis model was developed is presented here. In the rational design procedure, the analysis model is utilized to calculate the moment demand along the transverse joints. A two-stage transverse posttensioning procedure is recommended following AASHTO load and resistance factor design stipulations based on the moment demand calculated from the analysis model. The second stage of posttensioning precompresses the cast-in-place concrete deck, ensuring crack control. The objective of this study is to demonstrate the effectiveness of the two-stage posttensioning design and implementation procedure to mitigate reflective deck cracking. The effectiveness of the recommended design is demonstrated by utilizing a multistep finite element simulation of the construction process under construction and service loads. The cracking potential of the deck is evaluated under both current Michigan Department of Transportation and the proposed two-stage transverse posttensioning schemes. It is demonstrated that the two-stage posttensioning process can eliminate tensile stresses developed under gravity loading and reduce the temperature load effects to abate reflective deck cracking.

First Full-Depth Deck-Panel Accelerated Bridge Construction Project in Michigan: Constructability Challenges and Lessons Learned

AbstractAccelerated bridge construction (ABC) is gaining momentum as the bridge community is educated on the latest technologies and structural systems that can be implemented under the umbrella of ABC through workshops and demonstration projects. Further, ABC is promoted through various resources provided by the Federal Highway Administration (FHWA) and the Every Day Counts Initiative that recommends implementation of some form of acceleration into every bridge project. The ultimate goal is to make ABC a common practice. Hence, detailed documentation of challenges and lessons learned from previous ABC projects is vital for effective and efficient application of future ABC projects. This paper presents the first full-depth deck-panel ABC project in Michigan with details on the bridge configuration, strengths and limitations of the special provisions, observations during bridge construction, the project team’s timely decisions to overcome some of the constructability challenges, and lessons learned during ...

Capacity Evaluation of a Severely Distressed and Deteriorated 50-Year-Old Box Beam with Limited Data

Safety of adjacent box-beam bridges with distressed and deteriorated beams became a greater concern after the failure of a fascia beam of this bridge type in Pennsylvania, in 2005. As a proactive measure, eight box-beam bridges built in the 1950’s were inspected. Earlier routine inspection reports documented longitudinal cracking at the soffit of a fascia beam of Hawkins Road Bridge. Built in 1957 the bridge carries Hawkins Road over the I-94 freeway in Jackson County, Michigan. In 2006, following a repair decision for replacing the fascia, the beam with the distress was salvaged and the capacity was evaluated through load testing. Remaining prestress calculations showed 77% of the initial prestress that is 3% less than the final prestress used for the design according to the bridge specifications. Concrete modulus of elasticity was evaluated as 5,200ksi and the nominal compressive strength as 8,300 psi. Analysis of load test data indicated that a bridge with such a beam is safe to operate if the transverse connectivity is sufficient for load distribution as envisioned in the design. A major challenge however, is assessing the effectiveness of the load distribution through the transverse connectivity. Further, the importance of identifying concealed corrosion, and quantifying material properties and load distribution is highlighted.

Jointless Bridge Deck with Link Slabs: Design for Durability

Link slabs are used over the piers developing jointless decks while adjacent bridge spans remain simply supported. The Michigan Department of Transportation incorporates link slabs during deck replacements and deep resurfacing. Field performance assessment documented full-depth cracking of most of the link slabs. These cracks allow surface water infiltration, which leads to accelerated deterioration. This study was conducted to address link slab design and performance issues. The literature is inconsistent with the influence of design parameters on link slab performance. The objective was to document the link slab behavior of its design parameters, to propose a method to calculate the link slab moment and axial force, and to propose recommendations for updating current design details and construction procedures. Single-girder, two-span, finite element assemblage models under various types and levels of loads in conjunction with the link slab design parameters were used to evaluate the moments and axial forces developed in the link slab. Analysis showed that support conditions underneath the link slab greatly influence the link slab moment and axial force. Use of moment interaction diagram is recommended for the design. A detailed analysis and design example is presented incorporating live load, temperature gradient load, and the support configurations.

TEST METHOD FOR APPRAISING FUTURE DURABILITY OF NEW CONCRETE BRIDGE DECKS

The nondestructive test procedure for quantifying the future durability of bridge deck concrete is based on the fundamental relationship between ultrasonic pulse velocity (UPV) and the permeability of an elastic medium. An experimental study using standard concrete cylindrical specimens (ASTM C192) documented adequate sensitivity between UPV and permeability. The test procedure uses a parameter directly proportional to increase in-field concrete permeability called paste quality loss (PQL). The PQL is computed from UPV measurements on standard concrete specimens made from field concrete mixture (ASTM C31) and measurements on field concrete. Deck replacement projects on three National Highway System bridges were used as demonstration sites to implement the test procedure. The 56-day PQLs were calculated as 15%, 28%, and 9%, demonstrating a significant variability in the permeability of the three bridge decks. Field permeability tests were also conducted with Figg’s apparatus for comparison purposes. The PQL evaluation from postconstruction measurements is an effective and reliable method for testing the future durability of bridge decks.

SEISMIC SAFETY ASSESSMENT OF REINFORCED CONCRETE FRAME-WALL BUILDINGS

A method to evaluate the vulnerability of reinforced concrete strucutral walls to shear failure is presented. The method utilizes an experimentally developed shear stiffness model for distribution of shear stresses along reinforced concrete structural walls. Seven wall specimens tested by other investigators are analyzed to assess their shear strength supply and critical moment-to-shear ratios. The predicted shear strengths provide lower bounds to actual measured strengths.

Monitoring durability of new concrete bridge decks

The ND durability monitoring procedure, which measures the soundness of field concrete, is based on the fundamental relationship between ultrasonic pulse velocity (UPV) and permeability of an elastic medium. An experimental study documented adequate sensitivity between UPV and concrete permeability. The durability monitoring procedure is based on a parameter developed as part of this study and called paste quality loss (PQL) which is computed from the probability density function parameters of ultrasonic pulse velocity measurements taken from standard and field concrete. For PQL computation, measurements taken on standard concrete specimens, which are made from field concrete mixture, are compared to field measurements. The verification tests on 1000 mm x 1500 mm x 230 mm lab-deck specimens indicated that the PQL parameter computed from the UPV measurements as early as the 28th day is a good predictor of soundness. The UPV measurements made at increasing age of concrete very clearly document the rapid loss of soundness of improperly cured concrete decks. Deck replacement projects on three NHS bridges were used in the implementation of durability monitoring by PQL (paste quality loss) evaluation. The respective 56-day PQLs were calculated as 15%, 31% and 9% indicating a significant variability in the three bridges.

A hybrid energy-dissipation device for intelligent buildings

This paper describes the concept, design, development, and testing and evaluation of a hybrid energy-dissipation device, the active slip bracing device (ASBD). The device is a Coulomb-friction-based energy dissipater. It consists of multiple friction surfaces and an active clamping (normal) force mechanism. The ASBD is installed as part of the structural bracing in buildings. It will activate under low amplitude vibrations for assuring human comfort, and also under large amplitudes to avoid or reduce damage to the building, and to enhance the safety and comfort level of its occupants during high winds and earthquakes. The device was tested in a uniaxial testing frame. Experimental results reveal that the ASBD is a viable device with linear friction and energy-dissipation characteristics. The prototype device has proven to be reliable and durable.