Centrifuge modeling of rocking-isolated inelastic RC bridge piers

Experimental proof is provided of an unconventional seismic design concept, which is based on deliberately underdesigning shallow foundations to promote intense rocking oscillations and thereby to dramatically improve the seismic resilience of structures. Termed rocking isolation, this new seismic design philosophy is investigated through a series of dynamic centrifuge experiments on properly scaled models of a modern reinforced concrete (RC) bridge pier. The experimental method reproduces the nonlinear and inelastic response of both the soil-footing interface and the structure. To this end, a novel scale model RC (1:50 scale) that simulates reasonably well the elastic response and the failure of prototype RC elements is utilized, along with realistic representation of the soil behavior in a geotechnical centrifuge. A variety of seismic ground motions are considered as excitations. They result in consistent demonstrably beneficial performance of the rocking-isolated pier in comparison with the one designed conventionally. Seismic demand is reduced in terms of both inertial load and deck drift. Furthermore, foundation uplifting has a self-centering potential, whereas soil yielding is shown to provide a particularly effective energy dissipation mechanism, exhibiting significant resistance to cumulative damage. Thanks to such mechanisms, the rocking pier survived, with no signs of structural distress, a deleterious sequence of seismic motions that caused collapse of the conventionally designed pier. © 2014 The Authors Earthquake Engineering & Structural Dynamics Published by John Wiley & Sons Ltd

Dynamics and seismic performance of rocking bridges accounting for the abutment-backfill contribution

The present study explores analytically the concept of rocking isolation in bridges considering for the first time the influence of the abutment-backfill system. The dynamic response of rocking bridges with free-standing piers of same height and same section is examined assuming negligible deformation for the substructure and the superstructure. New relationships for the prediction of the bridge rocking motion are derived, including the equation of motion and the restitution coefficient at each impact at the rocking interfaces. The bridge structure is found to be susceptible to a failure mode related to the failure of the abutment-backfill system, which can occur prior to the well-known overturning of the rocking piers. Thus, a new failure spectrum is proposed called Failure Minimum Acceleration Spectrum (FMAS) which extends the overturning spectrum put forward in previous studies and it differs in principle from the latter. Parametric analyses are conducted with respect to the stiffness of the backfill, highlighting the importance of stiff profiles in rocking response of bridges. The comparison with the dynamic response of bridges modelled as rocking frames without abutments reveals that seat-type abutments and their backfill have a generally beneficial effect on the seismic performance of rocking pier bridges, but also that the simple frame model cannot capture all salient features of the rocking bridge response, as it misses potential failure modes, overestimating the rocking bridge’s safety when these modes are critical

Newly qualified physical education teachers’ experiences of developing subject knowledge prior to, during and after a Postgraduate Certificate in Education course

Office for Standards in Education (OFSTED) inspections of secondary Postgraduate Certificate in Education (PGCE) physical education courses in England between 1996 and 1998 (OFSTED, 1999) were critical of student teachers' subject knowledge. The purpose of this study was to investigate the development of subject knowledge and influences on the development of that subject knowledge in a sample of three newly qualified teachers (NQTs) who had completed a PGCE physical education course in England. The research comprised semi-structured interviews and analysis of documentation. Among these three NQTs there were some similarities, but more differences in terms of the development of subject knowledge as well as different influences on the development of subject knowledge. These results suggest that teacher educators may need to be flexible in how they approach and support the development of student teachers' subject knowledge. Results also suggest that teacher educators should work more closely with colleagues teaching sports-related undergraduate degree courses to support the development of subject knowledge for those students who wish to progress to a PGCE physical education course

A vector-valued ground motion intensity measure incorporating normalized spectral area

A vector-valued intensity measure is presented, which incorporates a relative measure represented by the normalized spectral area. The proposed intensity measure is intended to have high correlation with specific relative engineering demand parameters, which collectively can provide information regarding the damage state and collapse potential of the structure. Extensive dynamic analyses are carried out on a single-degree-of-freedom system with a modified Clough–Johnston hysteresis model, using a dataset of 40 ground motions, in order to investigate the proposed intensity measure characteristics. Response is expressed using the displacement ductility, and the normalized hysteretic energy, both of which are relative engineering demand parameters. Through regression analysis the correlation between the proposed intensity measure and the engineering demand parameters is evaluated. Its domain of applicability is investigated through parametric analysis, by varying the period and the strain-hardening stiffness. Desirable characteristics such as efficiency, sufficiency, and statistical independence are examined. The proposed intensity measure is contrasted to another one, with respect to its correlation to the engineering demand parameters. An approximate procedure for estimating the optimum normalized spectral area is also presented. It is demonstrated that the proposed intensity measure can be used in intensity-based assessments, and, with proper selection of ground motions, in scenario-based assessments

Shaking table tests and numerical analyses on a scaled dry-joint arch undergoing windowed sine pulses

The damages occurred during recent seismic events have emphasised the vulnerability of vaulted masonry structures, one of the most representative elements of worldwide cultural heritage. Although a certain consensus has been reached regarding the static behaviour of masonry arches, still more efforts are requested to investigate their dynamic behaviour. In this regard, the present paper aims to investigate the performance of a scaled dry-joint arch undergoing windowed sine pulses. A feature tracking based measuring technique was employed to evaluate the displacement of selected points, shading light on the failure mechanisms and gathering data for the calibration of the numerical model. This was built according to a micro-modelling approach of the finite element method, with voussoirs assumed very stiff and friction interface elements. Comparisons with existing literature are also stressed, together with comments about scale effects.This work was partly financed by FEDER funds through the Competitivity Factors Operational Programme-COMPETE and by national funds through FCT-Foundation for Science and Technology within the scope of the Project POCI-01-0145-FEDER-007633.info:eu-repo/semantics/publishedVersio

Generalized Dynamic Analysis of Structural Single Rocking Walls (SRWs)

The investigation of structural single rocking walls (SRWs) continues to gain interest as they produce self-centering lateral load responses with reduced structural damage. The Simple Rocking Model (SRM) with modifications has been shown to capture these responses accurately if the SRW and its underlying base are infinitely rigid. This paper advances previous rocking models by accounting for: 1) the inelastic actions at or near the base of the SRW; and 2) the flexural responses within the wall. Included in the proposed advancements are hysteretic and inherent viscous damping associated with these two deformation components so that the total dynamic responses of SRWs can be captured with good accuracy. A system of nonlinear equations of motion is developed, in which the rocking base is discretized into fibers using a zero-length element to locate the associated compressive deformations and damage. The flexural deformations of the rocking body are captured using an elastic term, while the impact events are modeled using impulse-momentum equations. Comparisons with experiments of structural precast concrete and masonry SRWs show that the proposed approach accurately estimates the dynamic responses of different SRWs with and without unbonded posttensioning, for various dynamic excitations and degrees of hysteretic action. Using the proposed approach, a numerical investigation employs different configurations of structural SRWs to quantify the various sources of energy loss, including hysteretic action and impact damping, during various horizontal ground motions

Pushover Analysis for Plan Irregular Building Structures

Nonlinear static procedures (NSPs), also known as "pushover methods", represent the most used tool in the professional practice for assessment of seismic performance of building structures. Most of the methods subscribed by major seismic codes for seismic analysis of new or existing buildings have been originally defined for simple regular structures

A smart pipe energy harvester excited by fluid flow and base excitation

This paper presents an electromechanical dynamic modelling of the partially smart pipe structure subject to the vibration responses from fluid flow and input base excitation for generating the electrical energy. We believe that this work shows the first attempt to formulate a unified analytical approach of flow-induced vibrational smart pipe energy harvester in application to the smart sensor-based structural health monitoring systems including those to detect flutter instability. The arbitrary topology of the thin electrode segments located at the surface of the circumference region of the smart pipe has been used so that the electric charge cancellation can be avoided. The analytical techniques of the smart pipe conveying fluid with discontinuous piezoelectric segments and proof mass offset, connected with the standard AC–DC circuit interface, have been developed using the extended charge-type Hamiltonian mechanics. The coupled field equations reduced from the Ritz method-based weak form analytical approach have been further developed to formulate the orthonormalised dynamic equations. The reduced equations show combinations of the mechanical system of the elastic pipe and fluid flow, electromechanical system of the piezoelectric component, and electrical system of the circuit interface. The electromechanical multi-mode frequency and time signal waveform response equations have also been formulated to demonstrate the power harvesting behaviours. Initially, the optimal power output due to optimal load resistance without the fluid effect is discussed to compare with previous studies. For potential application, further parametric analytical studies of varying partially piezoelectric pipe segments have been explored to analyse the dynamic stability/instability of the smart pipe energy harvester due to the effect of fluid and input base excitation. Further proof between case studies also includes the effect of variable flow velocity for optimal power output, 3-D frequency response, the dynamic evolution of the smart pipe system based on the absolute velocity-time waveform signals, and DC power output-time waveform signals

Displacement‐based analysis and design of rocking structures

Rocking can be used as a seismic isolation strategy for bridges and buildings. Letting a structure uplift works as a mechanical fuse and limits the design forces of both the foundation and the superstructure. Interestingly, there is no correlation between the rocking oscillator and the elastic one. Therefore, there is not any “equivalent linear system” and the elastic spectra are useless when it comes to rocking. Thus, there is no simplified design procedure that a practicing engineer could use. In order to create design rocking spectra, the rocking oscillator should be described with the simplest possible way and the least necessary parameters. Since Housner’s seminal paper in 1963 the traditional DOF chosen to describe the motion of a rocking block has been its tilt angle. This description uncovers that out of two blocks with the same slenderness ratio, the larger one is more stable. This tilt-based description is mathematically correct, but not optimal. This paper shows that the top displacement is a better descriptor of the rocking oscillator, because it uncovers a fundamental property useful for design: As long as the blocks are not close to overturning, the top displacements of a large and a small block of the same slenderness are going to be roughly equal. This property is proven for both analytical pulses and for recorded ground motions. In mathematical terms, the displacement demand on a rocking block is a unary function of its slenderness angle. In practical terms, this means that the displacement demand of any block can be computed by the displacement of a block of the same slenderness, yet very large size – likewise the displacement demand of a yielding oscillator can be computed based on the displacement of an equivalent linear system. Thus, the rocking-related seismic hazard can be computed by much simpler rocking spectra. As an example, the proposed method is applied for the preliminary design of a rocking frame having the dimensions of a typical overpass bridge