Mervyn J. Kowalsky

IMPROVED ANALYTICAL MODEL FOR SHEAR STRENGTH OF CIRCULAR REINFORCED CONCRETE COLUMNS IN SEISMIC REGIONS

Because of its brittle nature, shear is regarded as a mode of failure that should be avoided in reinforced concrete bridge column design. To provide a reinforced concrete bridge column with sufficient shear strength, it is imperative that the shear strength be predicted in an accurate and dependable manner. This paper discusses revisions to the three component model for seismic shear strength of circular columns developed at the University of California, San Diego (UCSD). The revisions suggested account for the effect of the concrete compression zone on the mobilization of the transverse steel, as well as the effect of aspect ratio and longitudinal steel ratio on the strength of the concrete shear resisting mechanism. The proposed model is compared with the previous UCSD model, as well as the design approaches of the Applied Technology Council (ATC) Report 32 and Caltrans Memo 20-4 through the use of an experimental database consisting of 47 circular reinforced concrete bridge columns. For comparative purposes, the proposed model is also compared with the ATC-40 assessment approach. Results are presented in the form of the ratio of experimentally recorded strength to design strength versus various key design parameters.

Behaviour of intrinsic polymer optical fibre sensor for large-strain applications

This paper derives the phase response of a single-mode polymer optical fibre for large-strain applications. The role of the finite deformation of the optical fibre and nonlinear strain optic effects are derived using a second order strain assumption and shown to be important at strain magnitudes as small as 1%. In addition, the role of the core radius change on the propagation constant is derived, but it is shown to be negligible as compared to the previous effects. It is shown that four mechanical and six opto-mechanical parameters must be calibrated to apply the sensor under arbitrary axial and transverse loading. The mechanical nonlinearity of a typical single-mode polymer optical fibre is experimentally measured in axial tension and is shown to be more significant than that of their silica counterpart. The mechanical parameters of the single-mode polymer optical fibre are also measured for a variety of strain rates, from which it is demonstrated that the strain rate has a strong influence on yield stress and strain. The calibrated constants themselves are less affected by strain rate.

Understanding Poor Seismic Performance of Concrete Walls and Design Implications

The 2010–2011 Canterbury earthquakes in New Zealand revealed (1) improved structural response resulting from historical design advancements, (2) poor structural performance due to previously identified shortcomings that had been insufficiently addressed in design practice, and (3) new deficiencies that were not previously recognized because of premature failure resulting from other design flaws. This paper summarizes damage to concrete walls observed in the February 2011 Christchurch earthquake, proposes links between the observed response and specific design concerns, and offers suggestions for improving seismic design of walls in the following areas: amount of longitudinal reinforcement in wall end regions, suitable wall thickness to minimize the potential for out-of-plane buckling, and minimum vertical reinforcement requirements.

INFLUENCE OF TENSION STRAIN ON BUCKLING OF REINFORCEMENT IN CONCRETE COLUMNS

This paper gives a hypothesis regarding the influence of tension strain on buckling in reinforced concrete columns primarily based on the kinematics of member deformation. A presentation of a series of 4 large-scale column tests aimed at investigating the proposed mechanism is next provided. The test columns are of identical proportions and reinforcement content, with the only variable being the applied load history. Based on the results, it is apparent that the amount of tension strain that reinforcing bars within concrete columns are subjected to directly affects the buckling phenomena upon reversal of loading.

Estimation of Frequency-Dependent Strong Motion Duration Via Wavelets and Its Influence on Nonlinear Seismic Response

In this paper, a procedure for estimation of frequency-dependent strong motion duration (FDSMD) is developed. The proposed procedure utilizes the continuous wavelet transform and is based on the decomposition of the earthquake record into a number of component time histories (termed pseudo-details) with frequency content in a selected range. The significant strong motion duration of each pseudo-detail is calculated based on the accumulation of the Arias intensity (AI). Lastly, the FDSMD of the earthquake record in different frequency ranges is defined as the strong motion duration of the corresponding pseudo-detail scaled by a weight factor that depends on the AI of each pseudo-detail. The efficiency of this new strong motion definition as an intensity measure is evaluated using incremental dynamic analysis. Results obtained show that the proposed FDSMD influence the peak response of short-period structures with stiffness and strength degradation.

Effect of Load History on Performance Limit States of Circular Bridge Columns

In this paper, the importance of displacement history and its effects on performance limit states, the relationship between strain and displacement, and the spread of plasticity in RC structures is explored. An experimental study is underway to assess the performance of 30 circular, well-confined, bridge columns with varying lateral displacement history, transverse reinforcement detailing, axial load, aspect ratio, and longitudinal steel content. Eight of these columns, with similar geometry and detailing, were subjected to various unidirectional displacement histories including standardized laboratory reversed cyclic loading and re-creations of the displacement responses obtained from a nonlinear time-history analysis of multiple earthquakes with distinct characteristics. Longitudinal reinforcing bars were instrumented to obtain strain hysteresis, vertical strain profiles, cross section curvatures, curvature distributions, and fixed-end rotations attributable to strain penetration. Results have shown that the limit state of reinforcement bar buckling was influenced by load history, but the relationship between strain and displacement along the envelope curve was not. The main impact of load history on bar buckling is its influence on accumulated strains within the longitudinal reinforcement and transverse steel.

Calibration of a single-mode polymer optical fiber large-strain sensor

We calibrate the phase shift as a function of applied displacement in a polymethylmethacrylate (PMMA) single-mode optical fiber interferometer, operating at a wavelength of 632.8 nm. The phase sensitivity is measured up to 15.8% nominal strain in the fiber. The measured phase–displacement response is compared to a previous analytical formulation for the large deformation response of the polymer optical fiber strain sensor. The formulation includes both the finite deformation of the optical fiber and nonlinear strain-optic effects at large deformations. Using previously measured values for the linear and nonlinear mechanical response of the fiber, the nonlinear strain-optic effects are calibrated from the current experimental data. This calibration demonstrates that the nonlinearities in the strain-optic effect are of the same order of magnitude as those in the mechanical response of the PMMA optical fiber sensor.

Shaketable Testing of Rectangular Post-Tensioned Concrete Masonry Walls

This article reports on a study that investigated the in-plane seismic response of partially grouted post-tensioned concrete masonry (PCM) walls with unbonded tendons, by means of shaketable testing. The principal intent of this study was to validate use of this wall system for residential construction, before the first PCM house is built in New Zealand. The authors introduce and describe the testing program, then present their results from dynamic testing of four rectangular walls, of which one contained a shrinkage control joint. They discuss wall structural response in terms of flexural strength, displacement capacity, and tendon stress. The results of the shaketable tests showed the self-centering nature of post-tensioned masonry walls and their ability to achieve large displacements with minimal accumulation of damage. The authors conclude that the level of initial tendon prestressing has a significant effect on peak wall displacements.

Repair of Reinforced Concrete Bridge Columns Containing Buckled and Fractured Reinforcement by Plastic Hinge Relocation

AbstractThis paper describes a new repair technique that involves the use of plastic hinge relocation to restore strength and deformation capacity of RC bridge columns. Summarized is the overall repair concept and experimental results that include the reversed cyclic testing of three large-scale bridge columns that were previously damaged, repaired using the proposed methodology, and then subsequently retested. To date, two different repair alternatives were executed using unidirectional carbon fiber sheets in the hoop and longitudinal directions, the latter anchored into the RC footing with 30-mm-diameter carbon fiber anchors. A method for predicting the force-displacement responses of columns repaired in this manner was also developed and found to give reasonable results. Also included in this paper are design considerations, which are carried out in the steps needed to design a repair system to relocate the plastic hinge in a column containing buckled longitudinal reinforcement. The responses show that...

Seismic Performance Evaluation of Reinforced Concrete-Filled Steel Tube Pile/Column Bridge Bents

The seismic performance of reinforced concrete-filled steel tube (RCFST) pile/column bridge bents is examined based on the results of large-scale experimental tests, inelastic dynamic analyses, and parametric moment curvature analyses. It was found that when the pile/column is subjected to double curvature bending, the damage limit states are largely controlled by the tensile strain in the steel longitudinal bars at the top hinge. When the pile/column is subjected to single curvature bending, the limit states are controlled by the tensile strain in the steel tube at the below-ground hinge. However, for the single curvature bending case and relatively thick steel tubes it was also found that the pile/column is likely to remain elastic during a seismic event. Strain limit states are proposed and expressions to relate the strain limits with section curvatures are developed.