Kenneth K. Walsh

Interfacial Properties of Ultrahigh-Performance Concrete and High-Strength Concrete Bridge Connections

AbstractRecently, ultra-high performance concrete (UHPC) has been utilized in highway bridge connections, where its superior strength and durability help to reduce joint cracking and enhance transverse load transfer. According to the load and resistance factor design (LRFD) bridge design procedure specified by AASHTO, the strength of the connections is dependent on the adhesion and friction between the connected materials. The objective of the present research is to identify the adhesion value between UHPC and high-strength concrete (HSC) with varying degrees of roughness. To this end, UHPC-HSC specimens were tested in direct tension according to ASTM protocols, and the maximum tensile stress at failure was obtained. Test results show that the average maximum tensile stress for the UHPC-HSC specimens with a smooth interface exceeds that determined from past research for any degree of roughness. Furthermore, the average maximum tensile stress increases with the degree of roughness. The results from the dir...

Modeling and Validation of a Passive Resettable Stiffness Damper

AbstractThe resetting semiactive stiffness damper (RSASD) has been shown to be effective at controlling vibrations in civil structures in the presence of near-field earthquakes. Although it has the advantages of being mechanically simple and relatively inexpensive, the RSASD requires a multicomponent feedback control system consisting of sensors, a microcontroller, a servo valve, and a battery to operate, rendering it less reliable during a seismic event. In the present work, the resetting passive stiffness damper (RPSD) is presented as an improvement to the RSASD, whereby the RSASD feedback control system is replaced by a novel mechanism to achieve resetting of the damper force. The results of laboratory studies on a small-scale RPSD demonstrate that the resetting mechanism performs as proposed. Results of numerical simulations performed for a five-story base-isolated building subject to four benchmark earthquakes indicate that the RPSD is capable of a similar control performance as the RSASD. Furthermor...

A resetting semi-passive stiffness damper for response mitigation of civil infrastructure

Earthquakes have the potential to cause large-scale destruction of civil infrastructure often leading to significant economic losses or even the loss of human life. Therefore, it is vital to protect civil infrastructure during these events. Structural vibration control provides a method for mitigating the damage to civil infrastructure during earthquakes by absorbing seismic energy from the structure. Semi-active control has emerged as an attractive form of structural control due to its effectiveness, inherent stability, and reliability. One semi-active control device particularly effective in reducing the response of civil structures subject to near-field earthquakes is the resetting semi-active stiffness damper (RSASD). Substantial research has been conducted to develop the RSASD and demonstrate its control performance. However, like other semi-active control technologies, the RSASD relies on a multi-component feedback control system that is subject to reliability issues. The purpose of the proposed research is to develop a novel resettable stiffness system that is capable of achieving a similar control performance to the RSASD, but with fewer feedback components. The resulting device, the resetting semi-passive stiffness damper (RSPSD), will offer increased reliability without compromising effectiveness. The objective of the present work is to present the concept for the RSPSD, develop a mathematical model describing its resetting, identify critical design parameters, and then evaluate its control performance for single-degree-of-freedom structures subject to an earthquake ground motion. Numerical results indicate that the RSPSD is capable of comparable control performance to the RSASD for the structures and earthquake ground motion considered.

Closed-Form Design Equations for Controlling Vibrations in Connected Structures

In this article, derivation of closed-form equations for solving the vibration control problem of two adjacent connected structures is presented. The closed-form solution is derived for a passive control method, where the structures are connected via a stiffness and damping element in parallel. The design of the connection elements is based on minimizing the absolute displacement transmissibility of the connected structures when ground acceleration is the input. The method is demonstrated for two connected multi-story buildings subject to the El Centro earthquake ground motion. Results show that the response of the connected buildings is reduced relative to the unconnected case.

Damage Identification for Prestressed Adjacent Box-Beam Bridges

Structural health monitoring (SHM) has gained considerable attention as a tool for monitoring the health of civil infrastructure. For bridge infrastructure, previous methods have focused on the detection of localized damage through modal parameters extracted from the longitudinal direction of the structure. This paper investigates a new damage detection method based on the change in the first vertical mode extracted from the transverse direction of the bridge. The mode is determined through application of modal curve fitting to frequency response functions (FRFs) that are formed using vertical response data obtained in the direction perpendicular to the bridge’s longitudinal axis. Using this method, both local damage and global damage in the bridge reveal themselves as having a localized effect on the bridge response. Furthermore, damage is revealed in such a way that it enables differentiation of the damage types. To demonstrate the effectiveness of the method, modal parameters were extracted from acceleration data obtained from a finite element model of a full bridge. Analysis of the modal parameters showed that the proposed approach could not only detect both local and global bridge damage, but could also differentiate between damage types using only one mode shape. The proposed method was compared to a previously developed SHM method.

Development and testing of a newly proposed continuously variable stiffness/damping device for vibration control

Many variable stiffness and damping devices have been proposed to mitigate the unwanted effects of vibrations. Although the stiffness or damping of these devices may be varied in real-time, many are limited in range and speed. The objective of this study is to propose a new variable stiffness/damping device to improve upon these limitations. The continuously variable amplification device (CVAD) is comprised of a spherical continuously variable transmission (SCVT) augmented with rack-and-pinions and connected in series with a simple stiffness or damping element. The CVAD amplifies linear motion to the stiffness or damping element, and then amplifies the element force back through the system. The resulting CVAD force is increased by a factor equal to the amplification factor squared, relative to the stiffness or damping element alone. The amplification factor is determined by a single controllable parameter that can be adjusted rapidly in real-time. The resulting system is capable of producing a large, continuous, and instantaneous range of stiffness or damping. In the present work, the concept for the CVAD is proposed and equations are presented for the effective stiffness and damping of the CVAD connected in series with both linear and rotational elements. Then, corresponding mathematical models are developed based on the systems dynamics considering the motion of each component. Numerical simulations are performed for the CVAD connected to a linear and rotational stiffness element and subject to a harmonic input. The results indicate that the same wide range of effective stiffness can be achieved using both elements.

Benchmarking Project-Driven Production in Construction Using Productivity Function: Capacity and Cycle Time

AbstractDespite being inaccurate, linear models are often used by construction managers to describe production, which limits the development and application of a production theory. The objective of...

Early-Age Behavior of an Adjacent Prestressed Concrete Box-Beam Bridge Containing UHPC Shear Keys with Transverse Dowels

AbstractAdjacent precast prestressed concrete box-beam bridges have been used in the United States for many years and have performed well. However, the shear keys between adjacent box beams are sus...

Dynamics of Project-Driven Production Systems in Construction: Productivity Function

AbstractMathematical models have historically enabled a thorough understanding of production mechanisms in manufacturing supporting actions and laws to improve fabrication and building performance....

Field Study of Ohio’s Structural Support Inspection Program for Overhead Signs, Traffic Signals, and High-Mast Lights

The Ohio Department of Transportation (DOT) undertook a field study to evaluate its overall structural inspection programs for overhead sign supports (including those mounted on bridges), high-mast light supports, and traffic signal supports. This paper describes the Ohio DOT’s current support inspection program, the field study performed, and the recommendations that resulted from the field study. This research evaluated the adequacy and frequency of the current structural support inspection program for the studied supports. To assess the current program, a detailed, hands-on inspection was conducted on 202 supports. The results were then compared with the Ohio DOT’s current ground-based, visual inspection process. The hands-on inspection process found almost 87% more deficiencies; some deficiencies detected during the hands-on inspections could not have been observed from the ground. In addition, the different inspection procedures used by each district often produced inspection reports that varied in the amount of information and level of details collected during inspection. Recommendations were made to address the inventory process and inspection procedures for each type of support. A long-term goal should be to establish the current structural adequacy of every support in the Ohio DOT’s inventory at the time of inspection.