Douglas Nims

Testing of Passive Energy Dissipation Systems

Over the period 1986 to 1991, seven different passive energy dissipation systems were studied in experimental research programs at the Earthquake Engineering Research Center of the University of California at Berkeley. This paper presents an overview of these studies, describing the different types of devices, the results of the shake table experiments, and associated analytical work. Four of the systems studied are friction systems, and of these, three (Sumitomo, Pall, and Friction-Slip) are based on Coulomb friction. The fourth is the Fluor-Daniel Energy Dissipating Restraint, which is a device capable of providing self-centering friction resistance that is proportional to displacement. The three other systems all have different energy dissipation mechanisms: ADAS elements, which utilize the yielding of mild-steel X-plates; viscoelastic shear dampers using a 3M acrylic copolymer as the dissipative element; and Nickel-Titanium alloy shape-memory devices that take advantage of reversible, stress-induced phase changes in the alloy to dissipate energy. The effectiveness of the various systems is evaluated by comparing the response of the test structures without and with the energy dissipators. In some cases, where devices were studied using the same test structure, they are compared directly. All of the systems investigated exhibited characteristics beneficial to improved structural response to earthquake loading.

The Use of the Energy Dissipating Restraint for Seismic Hazard Mitigation

This paper describes the mechanical operation and presents parametric studies for the Energy Dissipating Restraint (EDR). The EDR is a strongly self-centering passive friction-based seismic energy dissipator with a wide range of hysteretic behaviors. In the behaviors of most interest in seismic design, the slip load is proportional to displacement. Typically the EDR would be installed in a building as part of the bracing system which resists seismically induced lateral forces.

A New Magnetic Sensor Concept for Nondestructive Evaluation of Deteriorated PreStressing Strand

This article describes proof-of-concept testing of a sensor based on magnetic field detection to estimate the remaining effective cross-sectional area in corroded prestressing strands inside prestressed concrete beams. The primary corrosion mode is rusting of the strand. The magnetic properties of rust are vastly different from those of steel, thus making a magnetic sensor theoretically feasible. An electromagnet system with Hall sensors has been designed. The electromagnet induces a magnetic field in the specimen by magnetizing it from one side, and at a particular distance from the electromagnets pole face. At near magnetic saturation, for various diameters and distances of up to 2 in from the magnet face, the induced magnetic field is reliably related to the effective cross-section of the steel bar. Experiments with steel rods and prestressing strands of different diameters conducted in a laboratory are presented. Initial results confirm that by using an appropriate electromagnet based on the magnetic-field technique, in-situ detection of remaining effective cross-sectional area is possible. Challenges in making this technique practical are discussed. If the follow-up research confirms the practicality of the proposed magnetic sensor, there is a potential to substantially improve the state-of-the-art in bridge inspection in terms of accuracy and convenience.

Field Test of Magnetic Methods for Corrosion Detection in Prestressing Strands in Adjacent Box-Beam Bridges

AbstractMagnetic methods are progressing in the detection of corrosion in prestressing strands in adjacent precast, prestressed concrete box-beam bridges. This study is the first field trial of magnetic strand defect detection systems on an adjacent box-beam bridge. A bridge in Fayette County, Ohio, that was scheduled for demolition was inspected. The prestressed box beams had significant strand corrosion. The corroded strands showed discontinuities and a reduced cross-sectional area. These changes are reflected in the magnetic signatures of the prestressing steel. Corrosion in the prestressing steel was detected using two magnetic methods; namely, the magnetic flux leakage method and the induced magnetic field method. The purpose of these tests was to demonstrate the ability of the magnetic methods to detect hidden corrosion in box beams in the field and tackle the logistic problem of inspecting box beams from the bottom. The inspections were validated by dissecting the bottom of the box beams after the ...

Practical assessment of magnetic methods for corrosion detection in an adjacent precast, prestressed concrete box-beam bridge

Magnetic methods are progressing in the detection of corrosion in prestressing strands in adjacent precast, prestressed concrete box-beam bridges. This study is the first field trial of magnetic strand defect detection systems on an adjacent box-beam bridge. A bridge in Fayette County, Ohio, which was scheduled for demolition, was inspected. Damage to prestressed box-beams is often due to corrosion of the prestressing strands. The corroded strands show discontinuities and a reduced cross-sectional area. These changes, due to corrosion, are reflected in the magnetic signatures of the prestressing steel. Corrosion in the prestressing steel was detected using two magnetic methods, namely the ‘magnetic flux leakage’ (MFL) and the ‘induced magnetic field’. The purpose of these tests was to demonstrate the ability of the magnetic methods to detect hidden corrosion in box-beams in the field and tackle the logistic problem of inspecting box-beams from the bottom. The inspections were validated by dissecting the bottom of the box-beams after the inspections. The results showed that the MFL method can detect hidden corrosion and strand breaks. Both magnetic field methods were also able to estimate corrosion by detecting the effective cross-sectional area of the strand in sections of the beams. Thus, it was shown that the magnetic methods can be used to predict hidden corrosion in prestressing strands of box-beams.

Measuring Displacement of Tall Concrete Columns During Construction

Multiple-span, segmental concrete bridges built by balanced cantilever construction demand precise geometric control so that adjoining tips align at the time the closure segment is cast. When this type of bridge superstructure is cast monolithically on tall piers, moment redistribution, as well as creep, shrinkage, and temperature effects, can cause excessive demand on the exterior end spans and piers of the structure. To compensate, designers often use horizontal forces (jacking) to induce a counteractive moment in the pier columns. However, designers often do not make the effort to ensure that the intended displacement is realized at the needed structural elements. A methodology for measuring deflections of tall pier elements with tiltmeters during construction is presented in this paper for the Jeremiah Morrow Replacement Bridge, Interstate 71, Lebanon, Ohio. Fast-sampling data collection systems and postprocessing algorithms, including thermal effect removal, are detailed. In addition to the deflections from unbalanced cantilever moment during the casting cycle, fast-sampling data for the first horizontal jacking event are discussed and compared with the data collected through traditional laser survey techniques. The data were valuable information. They allowed the designer to fine-tune the geometry setup during the segment casting cycles, and they provided real-time displacement readings that permitted field decisions about the final force application during the jacking event.

Automated Ice Inference and Monitoring on the Veterans’ Glass City Skyway Bridge

AbstractUnder certain weather conditions, the Veterans’ Glass City Skyway (VGCS) Bridge in Toledo, Ohio, accumulates ice on the stay sheaths in such a way that has led to large fragments falling into traffic lanes. To aid the Ohio Department of Transportation (ODOT) in their response to this, an automatic inference and monitoring system was implemented. This system utilizes existing weather station measurement data to infer possible events, alerting officials and providing tools to further assess the situation. The development of the decision, the algorithm, and implementation process are presented. The system was implemented in January 2011, and it warned of and monitored an icing event that occurred February 20–24, 2011. Ice fell shortly after the system indicated conditions were met for icefall. ODOT personnel used the ice inference system to assist them in managing the response to the icing event.

Experimental Study of Mechanical Pipe Snubber Seismic Behavior

A series of seismic tests of mechanical snubbers on a full-scale model piping system provided a unique opportunity for detailed scrutiny of snubber seismic behavior on an actual piping system. The observed snubber behavior is a complicated pattern of braking and releasing, drag and drift, and the dynamic characteristics of the snubber, as well as the input motion, play a role in the response of the snubber. The snubbers were effective in limiting pipe displacements. Relative accelerations across the snubber were larger than expected. Snubber hysteretic behavior was irregular. Results from this testing are important in understanding snubber behavior, evaluating snubber performance, and in assessing alternatives to snubbers.

Linear-friction dissipators for truss structures

This paper is concerned with the dynamic response of truss structures containing linear- friction dampers. This type of passive energy dissipator shows different stiffness in loading and unloading, leading to triangular hysteresis loops under cyclic loading. The free and forced vibration responses of simple truss structures incorporating linear-friction dampers are analyzed. The harmonic linearization technique is used in combination with the modal strain energy method to estimate the response of truss structures with linear-friction dampers. The accuracy of this linearization technique is assessed in the context of truss structures in this paper. It is demonstrated that excellent accuracy is achieved using this linearization method.

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.