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This paper summarizes the results from a comprehensive experimental program in an effort to better understand the phenomenon of viscous heating of fluid dampers under small-stroke (wind loading) and large-stroke (earthquake loading) motions. Two dampers, one with 15-kip and one with 250-kip force output at peak design velocity, have been instrumented and tested under various amplitudes and frequencies. Temperature histories at different locations along the damper casing and within the silicon fluid that undergoes the shearing action have been recorded. Experimental data under small-stroke motions of the 250-kip damper showed that a single closed-form expression derived from first principles is capable of predicting the temperature rise at different locations of the damper with fidelity. The recorded data under long-stroke motions suggest a two-parameter law of cooling that allows the estimation of the internal temperature of the silicon oil once the external temperature on the damper casing is known. The presented cooling law is an extension of Newton's law of cooling. The study concludes that for both dampers, the same values of the model parameters provide a good approximation of the cooling behavior. The study presents a valuable formula that can be used in practice to estimate the internal fluid temperature of the damper given the external shell temperature. DOI: 10.1061/(ASCE)0733-9399(2007) 133:5(566) CE Database subject headings: Damping; Heating; Monitoring; Earthquake engineering; Parameters; Earthquake resistant structures.

In this paper, the inelastic response of rigid-plastic and elastic-plastic systems subjected to pulse-type excitations is revisited with dimensional analysis. Starting from Newmark's result on the maximum displacement of a sliding mass resting on a base that is subjected to a rectangular acceleration pulse, the paper introduces an energetic length scale of the excitation and the relevant dimension-less [PI]-products that govern the response of yielding structures. The introduction of Buckingham's [PI]-theorem reduces the number of variables that govern the response of the elastic-plastic system from five (5) to three (3). The proposed dimensionless [PI]-products are liberated from the associated elastic system response and are consistent with the incremental evolution from the rigid-plastic to the elastic-plastic system. When the response is presented in terms of the dimensionless [PI]-terms remarkable order emerges. It is shown that for a given value of dimensionless yield displacement the response curves (maximum relative dimensionless displacements) become self-similar and follow a single master curve. The self-similar solutions show clearly how the inelastic response amplifies as the normalized yield displacement increases and that an increase in strength may lead to an increase in inelastic displacements. The main advantage of the analysis presented in this paper is that it brings forward the concept of self-similarity--an invariance with respect to changes in scale or size--which is a decisive symmetry that shapes nonlinear behavior. CE Database subject headings: Seismic response; Earthquake engineering; Dimensional analysis; Nonlinear analysis; Bilinear analysis; Elastoplasticity.

In this paper the response of a bilinear oscillator subjected to pulse-type motions is revisited with dimensional analysis. Using Buckingham's [PI] theorem the number of variables in the response analysis is reduced from six (6) to four (4). When the response is presented in terms of dimensionless [PI] terms remarkable order emerges. It is shown that for a given value of dimensionless strength and dimensionless yield displacement, the response (relative dimensionless displacements and dimensionless base shears) is self-similar regardless of the intensity and duration of the pulse excitation. These self-similar solutions scale better with the peak pulse acceleration rather than with the peak pulse velocity, indicating that peak pulse acceleration is a superior intensity measure of the induced shaking. Most importantly, the paper demonstrates that for relatively small values of strength (larger values of ductility) the value of the normalized yield displacement is immaterial in the response, a finding that shows that the response of the bilinear single-degree-of-freedom oscillator exhibits a complete similarity (similarity of the first kind) in the normalized yield displacement. This finding implies that under a strong earthquake an isolated bridge will exhibit the same maximum displacement regardless if it is supported on lead-rubber bearings or friction pendulum bearings that exhibit the same strength and offer the same isolation period. CE Database subject headings: Seismic response; Earthquake engineering; Dimensional analysis; Nonlinear analysis; Bilinear analysis; Oscillations.

This paper investigates the 'goodness' of peak ground velocity as a dependable intensity measure for the earthquake shaking of civil structures. The paper stresses the importance of distinguishing between acceleration pulses and velocity pulses, and identifies two classes of near-source ground motions: those where the peak ground velocity is the integral of a distinguishable acceleration pulse and those where the peak ground velocity is the result of a succession of high-frequency, one-sided acceleration spikes. It is shown that the shaking induced by the former class is in general much more violent than the shaking induced by the latter class of motions even when motions that belong to the former class may be generated by significantly smaller-magnitude earthquakes. Building on the dimensional analysis introduced in the companion papers this paper shows that both linear and nonlinear structural responses from a variety of records which exhibit distinguishable pulses scale better with the peak pulse acceleration than with the peak pulse velocity, indicating that the peak pulse acceleration is a more representative intensity measure of the earthquake shaking. This conclusion is further supported from the response analysis of linear and bilinear single-degree-of-freedom oscillators subjected to selected records from the 1999 Chi-Chi Taiwan earthquake that exhibit unusually high and long period velocity pulses. The paper shows that these high velocity pulses alone do not impose unusual demands on most civil structures. What is more detrimental are local, distinguishable acceleration pulses that override the long period velocity pulses. CE Database subject headings: Velocity; Ground motion; Seismic response; Earthquake engineering; Dimensional analysis; Nonlinear analysis; Bilinear analysis.

This paper reports on the results from a comprehensive component testing program on a type of buckling-restrained brace known as the Unbonded Brace[TM] The experimental data are used to: (1) verify the results of theoretical predictions on the structural stability of the braces; (2) validate the inelasitc capacity of the braces under severe earthquake demands; and (3) calibrate a macroscopic hysteretic model that is found to predict, with fidelity, the brace force-displacement behavior. The study concludes that the unbonded brace is a reliable and practical alternative to conventional framing systems to enhance the earthquake resistance of new and existing structures; capable of providing both the rigidity needed to satisfy structural drift limits, while delivering a substantial and repeatable energy absorption capability. DOI: 10.1061/(ASCE)0733-9445(2004) 130:6(880) CE Database subject headings: Seismic tests; Buckling; Bracing; Experimental data