Marc J Veletzos

Experimental and Numerical Seismic Response of a 65 kW Wind Turbine

A full-scale shake table test is conducted to assess the seismic response characteristics of a 23 m high wind turbine. Details of the experimental setup and the recorded dynamic response are presented. Based on the test results, two calibrated beam-column finite element models are developed and their characteristics compared. The first model consists of a vertical column of elements with a lumped mass at the top that accounts for the nacelle and the rotor. Additional beam-column elements are included in the second model to explicitly represent the geometric configuration of the nacelle and the rotor. For the tested turbine, the experimental and numerical results show that the beam-column models provide useful insights. Using this approach, the effect of first-mode viscous damping on seismic response is studied, with observed experimental values in the range of 0.5–1.0% and widely varying literature counterparts of 0.5–5.0%. Depending on the employed base seismic excitation, damping may have a significant influence, reinforcing the importance of more accurate assessments of this parameter in future studies. The experimental and modeling results also support earlier observations related to the significance of higher modes, particularly for the current generation of taller turbines. Finally, based on the outcomes of this study, a number of additional experimental research directions are discussed.

Detection of Initial Yield and Onset of Failure in Bonded Posttensioned Concrete Beams

This paper discusses monitoring of bonded posttensioned (PT) concrete elements using the acoustic emission technique. In particular, a statistical pattern recognition technique based on a multivariate outlier analysis is presented to identify initial yielding and the onset of failure. Experimental tests on large-scale single-tendon bonded PT concrete beams, subjected to multiple load cycles, will be presented to validate the proposed monitoring system.

Modeling of Jointed Connections in Segmental Bridges

Precast segmental construction of bridges can accelerate construction and minimize the cost of medium span bridges in environmentally sensitive and difficult to access locations. Despite these benefits, the use of precast segmental bridges in seismic regions of the United States remains limited. A main obstacle to their use is concern regarding the seismic response of segment joints. Recent experimental research programs studied the seismic performance of segmental superstructures. However, an estimate of the seismic response of full-scale segmental bridges to real earthquake records remains unknown. This paper presents a segment joint modeling approach and is an important first step toward accurately estimating the seismic response of superstructure segment joints to input ground motions. The approach is a compromise between the detailed and computationally intensive continuum mechanics based finite element approach and a simple approach that models the joints with rotational springs. The approach considers the nonlinear tendon-grout slip response and was validated with data from large-scale experiments. Numerous modeling sensitivity studies were performed and recommendations for implementation in full-scale models are presented.

Equivalent Unbonded Length for Modeling of Multistrand Tendons in Precast Segmental Construction

Recently issued seismic design guidelines for precast segment construction require nonlinear modeling of segment-to-segment joints of important bridges. The response of segment joints is highly dependent on the length of debonding of the multistrand tendon. Neither the seismic design guidelines nor the literature provide sufficient guidance on how to determine the equivalent unbonded length of such tendons. This paper presents key results and conclusions of a large-scale experimental research program that investigated the debonding characteristics of multistrand tendons. Results indicate that tendon slip relative to the grout is small in comparison with slip between the duct and the surrounding concrete. An equation to evaluate the equivalent unbonded length of multistrand tendons was developed with direct application to modeling of the segment joint response.