Eri Gavanski

Glass Breakage Tests under Fluctuating Wind Loads

The current North American design codes for wind loads have dealt with the unique characteristics of glass using the observed failure mechanism of static fatigue, which is based on the concept of damage accumulation as described by Brown’s integral. However, both the load resistance and the design loads have aspects that have not been fully validated because of available but limited experimental results, particularly with regard to fluctuating load patterns. With the recent development of a sophisticated pressure-loading device, precise, time-varying wind loads as well as conventional ramp loading were applied to annealed glass plates in this study. The measured results were consistent with Brown’s integral, confirming the conversion method from realistic wind-load time histories to equivalent static loads.

Effects of Pressure Equalization on the Performance of Residential Wall Systems under Extreme Wind Loads

AbstractDuring strong windstorms, sheathing and siding on residential, wood-framed, wall systems have commonly failed. In the current study, a clear difference is observed in the rate of failure occurrence for wall sheathing above or below the eaves. This observation can be explained from tests examining ultimate capacities and pressure equalization of both single- and multilayer residential, wood-framed, wall systems using realistic fluctuating loads. The results indicate that pressure equalization is a critical parameter in the performance of both the cladding and exterior sheathing. With interior sheathing included, significant pressure equalization was observed to occur across the exterior sheathing, because pressure equalization is observed to increase with load (and damage) levels. This substantially increases the ultimate capacity of these wall systems; however, the construction details of the various exterior layers play an important role in the levels of pressure equalization across each layer.

Uncertainties in the Estimation of Local Peak Pressures on Low-Rise Buildings by Using the Gumbel Distribution Fitting Approach

AbstractThe lack of a standard accepted method to estimate local peak pressure coefficients from wind tunnel data can lead to inconsistent definitions and interpretations, particularly because cost and time constraints associated with wind tunnel tests of low-rise buildings necessitate relatively short (equivalent full-scale) durations. This paper focuses on a Gumbel distribution fitting method widely used in practice. Because the sources of uncertainty regarding estimated peaks include the use of short-duration records (in practice) and the assumption that the observed peaks from wind tunnel pressure data are Gumbel-distributed, this is quantified in detail in terms of the parameters determining the required minimum record length. It is shown that 15 observed peaks can lead to local peak pressure estimates with adequate precision for many design scenarios. However, the conversion of peak coefficients from a short duration to those of a longer duration requires an increase in the number of observed peaks ...

Examination of Load Resistance in Window Glass Design

The glass failure prediction model has been used as a calculation method for the load resistance (LR) of glass specified in North American design codes. However, because of the technology available, this model has only been experimentally proven under ramp loading. The model also has several defects, which have been pointed out in recent years, some of which may originate from this insufficient experimental validation. Thanks to the newly developed technology at the University of Western Ontario, glass strength modeling was revisited with sufficient experimental results, including fluctuating wind loads of long time duration. In addition, the value of LR specified in the current North American design codes was examined in light of several assumed parameters used in its calculation.

Storm and Gust Duration Effects on Design Wind Loads for Glass

Duration effects on the design wind loads for glass are examined with respect to ASCE 7-10. Pressure time histories are created by combining variations of wind speed and wind direction from a “design cyclone” with pressure coefficients obtained from wind tunnel tests of low-rise buildings. The results indicate that the assumption of a 3-s gust duration in ASCE 7-10 may underestimate appropriate values for design loads for glass, with the degree of underestimation varying, depending primarily on the probability of exceedence of the peak pressures. On the basis of these results, modifications to the peak pressures specified in ASCE 7-10 are suggested that maintain the time duration of 3-s, consistent with current glass-design provisions.

Fragility Assessment of Roof-to-Wall Connection Failures for Wood-Frame Houses in High Winds

AbstractThe enhanced-Fujita scale (EF-scale) is used to identify tornado intensity. It uses several damage indicators (DIs), each of which has descriptions of the degrees-of-damage (DOD) along with...

Damage to residential construction from the tornadoes in Vaughan, Ontario on August 20, 2009

The results of a detailed damage investigation of the two tornadoes in Vaughan, Ontario, which were part of the 19 tornadoes in the outbreak of August 20, 2009, are presented. The bulk of the damage in both tornadoes consisted of structural roof failures categorized as F1 on the Fujita Scale and EF1 on the Enhanced Fujita Scale. However, multiple houses in both tornadoes suffered total roof failure, which is F2 (or EF2). It was observed that the total roof failures were all due to either internal pressurization and or weak (or non-existent) roof-to-wall connections. Since internal pressures are likely to be larger than external pressures for these single family residences, it is argued that the total roof failure occurred under wind speed conditions associated with a lower degree of damage, such that actual wind speeds are like those in EF1 in these particular tornadoes.

Wind Force Coefficients for Designing H.P.-Shaped Porous Canopy Roofs

Design wind force coefficients for H.P.-shaped porous canopy roofs have been investigated based on a series of wind tunnel experiments. Focus is on the column axial forces induced by wind loadings as the load effect, assuming that the roof is rigid and supported by four corner columns. The parameters under consideration are the rise/span ratio and porosity of the roof. The roof model is made of 1 mm thick perforated plastic plate with a number of small circular holes, the porosity of which is changed from 0 to 0.4. The overall aerodynamic forces and moments are measured by a force balance in a turbulent boundary layer. Based on the results, the design wind force coefficients are proposed. The validity of the proposed wind force coefficients is verified by a comparison of the load effects predicted by the proposed wind force coefficients with the maximum peak values obtained from time history analyses.