Failures of roof asphalt shingles under high winds have been reported to occur at wind speeds lower than the shingle performance classification. The understanding of the progressive failure mechanisms of shingles subjected to high-wind pressures has been hindered by difficulty in accurately quantifying uplifts and wind-induced pressures with high spatial resolution, especially for large-scale wind test setups that simulate realistic scenarios. This paper reports on an experimental study to assess the use of three-dimensional digital image correlation ('StereoDIC') to accurately measure full-field surface deformations of shingles installed on full-scale roof structures and subjected to realistic high winds. Deformation measurements were acquired on shingles installed on typical wood-frame roof panels and subjected to winds with speed up to 257 km/h (160 mph) using an outdoor wind tunnel. The specimens were designed to study the proposed test setup and StereoDIC measurement method for two different combinations of shingle surface coloration (and thus speckle pattern) and field of view. The experiments produced accurate local and full-field shingle deformation measurements. Different datasets were used to gain new insight into the influence of salient aspects of the wind test setup and deformation measurement method on the understanding of the temporal evolution of shingle uplift and failure mechanisms.

For the first time, the vision-based measurement method Stereo Digital Image Correlation (StereoDIC) is applied successfully to quantitatively assess the response of asphalt shingles installed in a model roofing system and subjected to hurricane velocity winds. By mounting a low profile asphalt-shingled plywood roof facsimile without building firmly to a rigid steel frame and supplying sustained winds of 67.1 m/s perpendicular to the leading edge region, StereoDIC measurements were obtained at 1 Hz to measure the full-field uplift displacements for shingles sealed using either single or double sealant strips. By varying the sealant activation process (time and temperature), the effect of installation in winter and summer seasons is also quantified throughout the wind loading process. Results indicate that with lower temperature sealant activation, both single and double sealant shingles sustained catastrophic failure within a short time when the wind speed reached 67.1 m/s, with the double sealant system lasting for about 500 s; visual inspection of the separation surfaces for the low temperature activation showed large specular reflecting regions, indicating either no bonding or minimal adherence. For a higher sealant activation temperature, (a) both single and double sealant shingles remained intact for more than 2 h in 67.1 m/s wind speeds, with no sealant separation observed and (b) displacements for the shingle with double sealant strips were significantly lower than for the single sealant system, confirming the efficacy of a double sealant strip system. As a general observation, StereoDIC measurements clearly show that shingle uplift displacement is not constant across the width of a shingle tab, with the edges of the shingle (tab cutout regions) having significantly larger uplift displacements that may serve as sealant separation initiation sites.

Since presentation of the 2013 Murray Lecture focusing on developments in digital image correlation (DIC), the methods have continued to expand internationally and their use has begun to grow in fields where there was less activity in the past. First, a brief history of digital image correlation methods is presented from the perspective of the first author, followed by a discussion of recent trends associated with the use of digital image correlation methods in academics, governmental laboratories and industrial settings. In the remainder of the article, new results are provided in three areas where DIC methods have seen rapid growth; application of StereoDIC or three-dimensional DIC (3D-DIC) to the study of wall structures in civil engineering; the use of Volumetric DIC or Digital Volume Correlation (DVC) to quantify the internal response of a specially-designed composite material and in the area of model validation for another application in civil engineering; transfer length measurements in pre-stressed concrete beams.

The authors regret that they have identified a miscalculation in the original article that required the authors to provide corrective additions that are listed below. Specifically the authors determined that the shingle uplift pressure, p1=12.5Pa, used in the original article (Croom et al., 2015) is associated with a 40km/h (25mph) wind velocity instead of 145km/h (90mph). A miscalculation of pressure values due to inaccurate unit conversion was the source of the misstatement. The corrected interior uplift pressure is p1=183Pa for a 145km/h (90mph) wind velocity and p1=507Pa for a 241km/h (150mph) wind velocity. Additional simulation results have been performed for the corrected pressures and the results are reported in this Corrigendum.

The authors regret that they have identified a miscalculation in the original article that required the authors to provide corrective additions that are listed below. Specifically the authors determined that the shingle uplift pressure, p1 = 12.5 Pa, used in the original article (Croom et al., 2015) is associated with a 40 km/h (25 mph) wind velocity instead of 145 km/h (90 mph). A miscalculation of pressure values due to inaccurate unit conversion was the source of the misstatement. The corrected interior uplift pressure is p1 = 183 Pa for a 145 km/h (90 mph) wind velocity and p1 = 507 Pa for a 241 km/h (150 mph) wind velocity. Additional simulation results have been performed for the corrected pressures and the results are reported in this Corrigendum.

Understanding of deformations and the progressive failure mechanisms of asphalt shingles under wind loads is key to develop wind-resistant roofing systems, as well as standard test methods to characterize strength under representative wind loads. In fact, failure of shingles rated as resistant to winds up to 150 mph have been reported at speeds below 115 mph. Damage associated with failure of roof shingles continues to be a major source of insurance claims. Though pressure measurements can be taken at discrete points using pressure taps, no technology has been successfully deployed to measure full-field deformations on roof shingles subjected to wind loads. This paper reports on a feasibility study of three-dimensional digital image correlation (3D-DIC) as a non-contacting technique to measure full-field displacements of roof shingles under high wind loads. Feasibility is assessed based on evidence from load testing of three-tab shingles mounted on a full-scale roof panel specimen that was subjected to straight winds with speed up to 155 mph. Uplift displacements were measured on a target shingle tab. The natural color variations on the shingle exposed surface were used to provide a suitable speckle pattern for 3D-DIC measurements. It is shown that consistent 3D-DIC uplift displacement maps can be obtained up to failure. The evidence gained also highlights the importance of understanding the influence of time-dependent shingle material deformations, together with the progressive physical damage along the sealant strip.

An analytical model based on beam-on-elastic foundation (BOEF) principles is formulated and employed to simulate the structural response of a realistic asphalt shingle-sealant system under high wind loads. The system consists of individual three-tab shingles that are discretely bonded to the underlying shingles and subjected to differential out-of-plane pressures that are associated with high wind loads. Relevant mechanical properties for a typical modern asphalt shingle and sealant were determined experimentally and input in the proposed structural model. The model was then used to estimate the applied energy release rate, G, for the sealant strip as a function of length, location, and applied uplift pressures on the shingle. Results indicate that the G values are highly sensitive to sealant strip location and sealant length, where sealant length is defined to be along the perpendicular direction between the nail line and leading edge of the shingle, and that the sealant strip location in typical modern shingles is roughly optimized to ensure a balanced value of G at the inner and outer sealant strip edges. However, predictions also indicate that G could be further reduced by using longer sealant strips that are slightly shifted towards the leading edge of the shingle, thereby decreasing the potential for failure. Additional BOEF model simulations were performed using full-field shingle uplift displacements as input to determine the potential for estimating the average uplift pressures imparted on asphalt shingles under high wind loading. conditions. Promising results were obtained regarding the suitability of the proposed BOEF-based inverse analysis technique to estimate shingle uplift pressures. In addition, G values that are scaled for high pressures associated with extreme wind conditions, and resulting in sealant separation, are in qualitative agreement with an estimate of critical energy release rate, G(c), based on the results of standard direct tensile tests reported in the literature. (C) 2015 Elsevier Ltd. All rights reserved.

In the aftermath of the 2010 Haiti earthquake, households were often reluctant to reoccupy their dwellings due to concerns about the safety of damaged structures. If feasible, structural repair (to complement to temporary sheltering) is a realistic option for rapid reoccupancy as reconstruction poses greater barriers of cost and time. Considering the economic and technological limitations found in developing regions, this paper addresses the question of whether it is feasible to repair a severely damaged substandard CM wall in a context-sensitive fashion, that is, using: (a) materials that are locally available and commonly used and often substandard (e.g., low-strength concrete and mortar); and (b) construction and installation practices that are familiar to local workers, without the need for additional training. Two full-scale CM wall specimens were subjected to cyclic quasi-static in-plane load test till failure, and retested after repair by means of reinforced plaster made of low-strength mortar and steel welded wire mesh. Three-dimensional digital image correlation was used to provide full-field strain maps to describe the load-resistance mechanisms and damage evolution. It is shown that the failed CM walls can be transformed into walls with acceptable strength and deformability. In addition, it is shown that only the repaired specimens qualify as earthquake-resistant structures based the acceptance criteria set forth in Mexico City Building Code for Masonry Structures (NTCM 2004). It is concluded that it is feasible to repair a highly-damaged substandard CM wall in a context-sensitive fashion and make it safe, comparable to a CM wall built with acceptable materials and details.

The understanding of the load-resistance mechanisms and failure modes of large-scale concrete and masonry structures relies on accurate measurements of surface motions and deformations, and faithful crack maps. Measurements are typically taken using surface-mounted point-wise sensors (PWSs), and crack maps are hand-drawn based on visual inspection. It is impractical to obtain detailed displacement and deformation maps that describe the complex response of large structures based on PWS measurements. In addition, manual crack drawing is difficult, time-consuming, and prone to human errors, which makes it challenging to consistently produce faithful crack maps. This paper reports on a pilot study to test the use of three-dimensional digital image correlation (3D-DIC) as a non-contacting method to measure surface deformation fields on full-scale masonry walls, and produce detailed crack maps. Three confined masonry walls were tested under horizontal in-plane reverse-cycle loads. The specimens were designed to attain different levels of strength and deformability through different load-resistance mechanisms. Representative 3D-DIC measurements of drift, diagonal deformations, and interface slip between the reinforced concrete tie columns and the masonry infill were evaluated vis-à-vis benchmark PWS measurements, showing a comparable accuracy. Strain maps based on 3D-DIC measurements were enlisted to visualize the development of the fundamental strut-and-tie resisting mechanism in confined masonry walls subjected to horizontal in-plane loads, and illustrate practical structural analysis and design implications. More detailed crack maps compared with traditional hand-drawn maps were obtained based on 3D-DIC maximum principal strain contours.

The understanding of the load-resistance mechanisms and failure modes of large-scale concrete and masonry structures relies on accurate measurements of surface motions and deformations, and faithful crack maps. Measurements are typically taken using surface-mounted point-wise sensors (PWSs), and crack maps are hand-drawn based on visual inspection. It is impractical to obtain detailed displacement and deformation maps that describe the complex response of large structures based on PWS measurements. In addition, manual crack drawing is difficult, time-consuming, and prone to human errors, which makes it challenging to consistently produce faithful crack maps. This chapter reports on a pilot study to test the use of three-dimensional digital image correlation (3D-DIC) as a non-contacting method to measure surface deformation fields on full-scale masonry walls, and produce detailed crack maps. Three confined masonry walls were tested under horizontal in-plane reverse-cycle loads. The specimens were designed to attain different levels of strength and deformability through different load-resistance mechanisms. Representative 3D-DIC measurements of drift, diagonal deformations, and interface slip between the reinforced concrete tie columns and the masonry infill were evaluated vis-à-vis benchmark PWS measurements, showing a comparable

Confined masonry (CM) consists of unreinforced masonry walls confined with reinforced concrete tie columns and beams. Due to satisfactory performance during past earthquakes, CM has become the predominant construction style in several developing countries. However, poor construction practices and substandard materials may result in inadequate performance. This paper evaluates the feasibility and efficiency of an affordable and practical retrofit technology designed for CM constructions in developing areas. Corrosion-resistant aluminum strips are inserted into grooves and embedded in mortar along bed joints to enhance the in-plane shear resistance and deformability. Experimental evidence was obtained through in-plane cyclic load tests on full-scale CM walls. It is shown that a substandard CM wall can be transformed into a wall with acceptable strength and deformability, and the in-plane shear strength of a retrofitted wall can be estimated by means of a simple analytical model that accounts for the contribution of the horizontal reinforcement.