Carlos E. Ventura

Dynamic recovery of critical infrastructures: real-time temporal coordination

This paper takes a systems engineering approach to the problem of operations coordination among multiple infrastructures to minimise the impact of large disasters on human lives. Temporal coordination is essential to avoid bottlenecks in the simultaneous recovery of multiple infrastructures systems. A solution framework is presented in terms of multiple-delay difference equations which bring out the temporal interdependencies among infrastructures. The present work is part of an effort by the Government of Canada, through the Natural Sciences and Engineering Research Council (NSERC) and Public Safety and Emergency Preparedness Canada (PSEPC) to fund research to develop innovative ways to mitigate large disaster situations.

Dynamic characteristics of a base isolated building from ambient vibration measurements and low level earthquake shaking

Ambient vibration tests were conducted on a base-isolated apartment building in Takamatsu, Japan, to determine the mode shapes and the associated natural frequencies and damping ratios at very low levels of excitation. The latest developments in signal analysis for modal decomposition are used to analyze the ambient response data. A finite element model of the building and isolators was calibrated and refined using the experimental results from the ambient vibration tests. This model was then used to simulate the recorded response of the building under excitation from a small earthquake. The finite element model, calibrated by ambient vibration data and the low level of earthquake shaking, provides the starting point for modelling the non-linear response of the building when subjected to strong shaking.

Analysis of ground motions at Treasure Island site during the 1989 Loma Prieta earthquake

Abstract Site response analyses and coherence studies were conducted at the Treasure Island site where surface motions were recorded during the Loma Prieta earthquake. The analyses were conducted using a nonlinear dynamic effective stress method which took into account the effects of the liquefaction that occured at the site. The rock motions recorded at nearby Yerba Buena Island were used as input motions. Computed and recorded ground motions transverse to the direction of wave propagation and associated response spectra were in good agreement. Agreement was also good in the radial direction, except in certain frequency bands higher than 1·25 Hz. Coherence studies showed that some of these discrepancies may be due to low coherence between the Treasure Island and Yerba Buena motions in these same frequency bands.

In-Plane Shake-Table Testing of GFRP- Strengthened Concrete Masonry Walls

In-plane shake-table tests were performed on eight full-scale unreinforced concrete block walls. Three of the walls were left as plain unreinforced masonry and five were strengthened using glass-fiber-reinforced plastic (GFRP) strips in four different configurations. All walls were first subjected to design-level earthquake records to determine the improvement obtained from the addition of the GFRP. The walls were then subjected to extreme-level earthquake records to examine the ultimate failure modes and the effects of the various GFRP configurations on the response of the walls. It was observed that all strengthened specimens performed well during the design-level shaking, and three of the four GFRP configurations also performed well during the extreme-level shaking. The tests showed that the use of vertical GFRP strips alone is able to improve the in-plane performance of URM walls. The strips were also able to control the failure modes, and prevent collapse after severe damage, improving significantly the life safety performance of URM walls.

Seismic Analysis of Base‐Isolated San Bernardino County Building

The authors investigate the seismic behavior of an existing base isolated building and interpret its recorded response to the 1990 Upland California earthquake. They formulate a linear-elastic model that accurately represents the building during the earthquake and infer its response behaviors. Additional analyses using severe earthquake excitations demonstrate the building behavior in major events and hypothetical seismic gap pounding situations. Key findings include the following: • The Upland earthquake resulted in relatively low intensity shaking at the site, and the building did not exhibit a classic soft story effect in the isolation system. • A linear-elastic model can accurately idealize the building during this event. • Under major earthquake excitation, base isolation can lead to peak story drifts, shears, overturning moments, and accelerations that are much smaller than those of nonisolated buildings. • Pounding at seismic gaps can produce large story drifts, shears and accelerations. These peak pounding responses can be greater than those from nonisolated buildings (i.e., having no pounding).

Toward a better understanding of the dynamic characteristics of single-storey braced steel frame buildings in Canada

Single-storey braced steel frame buildings (SSBSFs) are currently the most widely used commercial structures, which include strip malls, power centres, warehouses, small and medium-sized industrial plants. The lateral seismic or wind forces acting on such low-rise structures are usually transferred from a metal roof-deck diaphragm to a system of vertical bracing members. Because these flexible roof diaphragms have a considerable effect on the dynamic response of SSBSFs during an earthquake, they also play an important role in the evaluation of the fundamental vibration period, a key parameter in determining the magnitude of the design seismic forces. It is therefore of utmost importance to reliably predict the fundamental period of SSBSFs. This paper presents the results of a four-year field measurement research project on the dynamic behaviour of SSBSFs. The goal of the project was to create a reliable database for the dynamic characteristics of SSBSFs (periods, mode shapes, and damping) and to find a re...

Analysis and design of steel plate walls: analytical model

A simple rational model is developed in this paper to determine the structural behavior of steel plate wall (SPW) systems, and is referred to as the Modified Plate–Frame Interaction (M-PFI) model. The model considers bending and shear behavior, and the interaction of the two, for the SPW system. It is a modification of the Plate–Frame Interaction (PFI) model that only considers the shear response of the SPW system. The proposed M-PFI model can determine force and displacement values that correspond to the pre- and post-critical buckling state, the yield state, and the ultimate capacity of individual panels. In the end, design requirements for the beams and columns (also known as horizontal and vertical boundary elements) of the SPW are derived using the underlying theory of the M-PFI model.

Vibration frequencies of woodframe residential construction

Different methods of vibration measurement, such as ambient and forced vibration techniques, have been used in existing woodframe houses to determine fundamental frequency, but because of the highly nonlinear nature of this type of structural system, the reported results vary significantly. This paper discusses some of the differences of frequency values observed in various experimental studies, and identifies the source of these differences by relating the measured fundamental period to the level of shaking. The experimental results from different full-scale tests of woodframe houses and single wood shear walls are used in this paper to gain an improved understanding of the dynamic characteristics of this type of construction and to help explain the differences in results from ambient and forced vibration techniques. A simple equation to estimate forced vibration periods from ambient vibration periods is presented, and its possible application in engineering practice is discussed.

Seismic Evaluation of Existing Basement Walls

Current state of practice for seismic design of basement walls is using the Mononobe-Okabe (M-O) method that is based on the Peak Ground Acceleration (PGA). The National Building Code of Canada (NBCC) has considerably changed the seismic hazard level from 10 % in 50 years in NBCC1995 to 2 % in 50 years in NBCC2010, which leads to doubling the PGA in Vancouver from 0.24g to 0.46g. The current design PGA leads to very large seismic forces that make the resulting basement walls very expensive. Because there is a little evidence of any significant damage to basement walls during major earthquakes, the Structural Engineers Association of British Columbia (SEABC) initiated a task force to review current seismic design procedures for deep basement walls. Presented in this paper are some preliminary results of the work conducted by this committee. A series of dynamic numerical analyses have been carried out on a typical basement wall designed using the M-O earth pressures with the NBCC1995 PGA for Vancouver. This wall is then subjected to three ground motions spectrally matched to the Uniform Hazard Spectrum prescribed by the NBCC2010 and the seismic performance of the wall under this level of demand has been presented and discussed. Particular attention has been given to the resulting drift ratio in the walls.

Sensitivity Evaluation of Subspace-Based Damage Detection Method to Different Types of Damage

In this paper we investigate a damage detection technique based on the subspace method by applying it to an existing bridge structure model. A reference state of the structure is evaluated using this technique and subsequently its modal parameters are indirectly compared to the current state of the structure. There are no modal parameters estimated in this method. A subspace-based residual between the reference and possibly damaged states is defined independently from the input excitations employing a χ 2 test and then is compared to a threshold corresponding to the reference state. This technique is applied to a model of the bridge structure located in Reibersdorf, Austria. The structure is excited randomly with white noise at different locations and the output data is generated at typical locations instrumented and measured in a bridge. Various damages are simulated in different elements and the sensitivity of the method to each type and ratio of damages is assessed. This evaluation is performed by comparing the prediction of the damage state using this technique and the simulated damage of the structure. It can be inferred from the results that in general the statistical subspace-based damage detection technique recognizes most of the damage cases, except the ones with insignificant change in the global dynamic behaviour.