Geoffrey W. Rodgers

Damage Avoidance Design Steel Beam-Column Moment Connection Using High-Force-to-Volume Dissipators

Existing welded steel moment frames are designed to tolerate substantial yielding and plastic rotation under earthquake loads. This sacrificial design approach can lead to permanent, and often irreparable damage when interstory drifts exceed 2%. The experimental seismic performance of a 50% full-scale damage avoidance designed structural steel beam-column connection is presented. The beam-column joint region consists of a top flange-hung beam connected to the column by an angle bracket. High-force-to-volume (HF2V) devices are attached from the column to the beam to provide joint rigidity and energy dissipation as the joint opens and closes. The HF2V devices are connected either below the beam flange or concealed above the beams lower flange. Reversed cyclic lateral load tests are conducted with drift amplitudes up to 4%. No damage is observed in the principal beam and column structural elements. The need for stiff device connections to achieve optimal device performance is demonstrated, and potential design solutions presented. Stable hysteresis and repeatable energy dissipation for a large number of cycles up to the 4% drift level is observed. It is concluded that superior and repeatable energy dissipation without damage can be achieved for every dynamic motion cycle, in contrast to conventional sacrificially designed welded moment frame connections.

High-Force-to-Volume Seismic Dissipators Embedded in a Jointed Precast Concrete Frame

An experimental and computational study of an 80-percent scale precast concrete 3D beam-column joint subassembly designed with high force-to-volume (HF2V) dampers and damage-protected rocking connections is presented. A prestress system is implemented using high-alloy high-strength unbonded thread-bars through the beams and columns. The thread-bars are posttensioned and supplemental energy dissipation is provided by internally mounted lead-extrusion dampers. A multilevel seismic performance assessment (MSPA) is conducted considering three performance objectives related to occupant protection and collapse prevention. First, bidirectional quasi-static cyclic tests characterise the specimen’s performance. Results are used in a 3D nonlinear incremental dynamic analysis (IDA), to select critical earthquakes for further bidirectional experimental tests. Thus, quasi-earthquake displacement tests are performed by using the computationally predicted seismic demands corresponding to these ground motions. Resulting ...

Experimental Studies on Cyclic Performance of Column Base Strong Axis–Aligned Asymmetric Friction Connections

AbstractThis paper describes experimental testing of an asymmetric friction connection (AFC) at the base of a steel column such as may be used in a moment-frame. Friction/sliding surfaces were parallel to the column-strong axis. In-plane, out-of-plane and 2D clover leaf–cyclic tests were conducted of columns both with and without applied axial force. Tests were conducted both with and without bolts passing through the plates to provide compression on the sliding/friction interface. It was found that this type of rocking base–friction connection can tolerate high levels of drift without significant strength degradation, although some stiffness degradation occurred, especially after the cycles in the weak-axis direction. A simple procedure proposed to estimate the moment resistance is verified. The friction-base connections, having similar cost to conventional connections and exhibiting low-damage performance, have the potential to become widely used in aseismic construction.

Physical Parameter Identification of Structural Systems with Hysteretic Pinching

This research investigates the physical parameter identification of a nonlinear hysteretic structure with pinching behavior for real-time or rapid structural health monitoring (SHM) after a major seismic event. The identification procedure is based on the overall least squares linear regression and hypothesis testing. It is applied to a general, nonlinear slip-lock (SL) pinching model. In particular, the hysteresis loop is reconstructed using data available from current sensor technologies. The path dependent hysteresis response is first divided into different loading and unloading subhalf cycles with a single valued function. These subhalf cycles are then assumed to be piecewise linear, and the number of segments for each subhalf cycle is identified using the sup F type test. The overall least squares linear regression is finally applied to the identified subhalf cycles to compute the regression coefficients and breakpoints that yield the elastic stiffness, plastic stiffness, and cumulative plastic deformation. The performance and robustness of the proposed method is illustrated using a single degree of freedom shear-type reinforced concrete structure with 10% added root mean square noise and variable pinching behavior. The proposed method is shown to be computationally efficient and accurate in identifying the damage parameters within 10% of true values. These results indicate that the system is able to capture nonlinear behavior and structural parameters, such as preyielding stiffness, postyielding stiffness and cumulative plastic deformation, directly relevant to damage and performance using a computationally efficient and simple method. Finally, the method requires no user input and could thus be automated and performed in real time for each half cycle, with results available effectively immediately after an event, as well as during an event, if required.

Nonlinear Regression Based Health Monitoring of Hysteretic Structures under Seismic Excitation

This paper presents a health monitoring method using measured hysteretic responses. Acceleration and infrequently measured displacement are integrated using a multirate Kalman filtering method to generate restoring force-displacement hysteresis loops. A linear/nonlinear regression analysis based two-step method is proposed to identify nonlinear system parameters. First, hysteresis loops are divided into loading/unloading half cycles. Multiple linear regression analysis is applied to separate linear and nonlinear half cycles. Preyielding stiffness and viscous damping coefficient are obtained in this step and used as known parameters in the second step. Then, nonlinear regression analysis is applied to identified nonlinear half cycles to yield nonlinear system parameters and two damage indicators: cumulative plastic deformation and residual deformation. These values are closely related to structural status and repair costs. The feasibility of the method is demonstrated using a simulated shear-type structure with different levels of added measurement noise and a suite of ground motions. The results show that the proposed SHM method effectively and accurately identifies physical system parameters with up to 10% RMS added noise. The resulting damage indicators can robustly and clearly indicate structural condition over different earthquake events.

Experimental Test and Validation of a Direction- and Displacement-Dependent Viscous Damper

AbstractSemiactive devices offer the opportunity to customize the device response, and thus to customize the overall structural hysteretic response. However, they are actively controlled and thus e...

Acoustic Emission Monitoring of Total Hip Arthroplasty Implants

Abstract Acoustic Emission (AE) monitoring of patients with Total Joint Replacement (TJR) implants uses an array of four passive ultrasonic receivers to undertake in-vivo monitoring of the acoustic events created by patients with TJR implants. This manuscript presents and compares the results of in-vivo and in-vitro measurements of the acoustic signature created by a range of Total Hip Replacement (THR) implants. A major focus of this investigation is in the characterization of squeaking of hard-on-hard bearing surface combinations. The presence of an audible squeak of the bearing surface can cause significant embarrassment and potential discomfort to patients. It has been identified that squeaking is primarily identified at the main bearing interface and the fundamental peak falls in the range of 2-5kHz, with multiple higher harmonics also observed. The frequency of the primary squeak is seen to vary based on bearing surface type of both the acetabular liner and femoral head (ceramic-on-ceramic, metal-on- metal bearing combinations) Comparison is also drawn between in-vivo and in-vitro testing through the use of implant components retrieved during revision surgery of patients previously subjected to in-vivo testing. In the trials presented within this manuscript, strong correlation was achieved between the two test methods. In-vivo signal magnitudes were substantially smaller than those recorded from bench tests directly on the implant. However, characteristic frequencies were very similar in both cases, indicating that tissue attenuation reduces signal magnitude, but the influence of any period shifting of signals through the soft tissue were minimal. These initial results provide an important base for future testing and provide useful insight into the underlying cause of audible squeaking of total hip replacement patients with hard-on-hard bearing surfaces.

Tissue Attenuation Characteristics of Acoustic Emission Signals for Wear and Degradation of Total Hip Arthroplasty Implants

Abstract Recent research has investigated the use of Acoustic Emission (AE) monitoring of patients with Total Joint Replacement (TJR) implants. This technique involves using a set of four passive ultrasonic receivers to monitor the acoustic events that are created when a TJR implant is articulated through a range of motion. Both in-vitro and in-vivo monitoring of implants is possible. The soft-tissue attenuation characteristics are a very important aspect of how these two signal types are related as the aim of AE monitoring is to provide in-vivo diagnosis of implant degradation. This manuscript presents the results of in-vivo monitoring of patients with Total Hip Replacement (THR) implants. The corresponding Bode plots are presented to approximate the soft tissue attenuation characteristics. Overall averages are taken across 45 patient data sets and each of the four sensors, located against the skin surface, from the greater trochanter to mid-femur. Each sensor set is also analysed individually to delineate different tissues attenuation at the different locations. These results of this research can be used to determine the maximum likely frequency of interest present on the skin surface during AE monitoring, even if higher frequencies may be observed in-vitro.

Christchurch Women's Hospital: Analysis of Measured Earthquake Data during the 2011–2012 Christchurch Earthquakes

A network of acceleration and displacement sensors installed in the Christchurch Womens Hospital (CWH) in July 2011 captured an extensive range of earthquake signals, allowing for a unique opportunity to analyze the performance of the New Zealand South Islands only base-isolated structure. Key characteristics of a range of earthquake signals, including frequency spectra and response patterns, are identified, with particular focus on the swarm of earthquakes on 23 December 2011, including four earthquake events greater than magnitude 5.0 on the Richter scale. The findings indicate that the response of the isolators and the superstructure was essentially elastic for the events analyzed during this period. Accelerations measured above and below the isolators were similar, indicating that the behavior of the devices resembled that of rigid blocks. No significant rocking or torsional motion of the building was observed.

Christchurch Women’s Hospital: Performance Analysis of the Base-Isolation System during the Series of Canterbury Earthquakes 2011–2012

AbstractLive monitoring data and simple dynamic reduced-order models of the Christchurch Women’s Hospital (CWH) help explain the performance of the base-isolation (BI) system of the hospital during the series of Canterbury earthquakes in 2011–2012. A Park-Wen-Ang hysteresis model is employed to simulate the performance of the BI system and results are compared to measured data recorded above the isolation layer and on the sixth story. Simplified single, two, and three degree-of-freedom models (SDOF, 2DOF, and 3DOF) show that the CWH structure did not behave as an isolated but as a fixed-base structure. Comparisons of accelerations and deflections between simulated and monitored data show a good match for isolation stiffness values of approximately two times of the value documented in the design specification and test protocol. Furthermore, an analysis of purely measured data revealed very little to no relative motion across the isolators for large events of moment magnitude scale (Mw) 5.8 and 6.0 that occ...