An experimental program, investigating the potential of using multi-directional fibre-reinforced polymers (FRPs) as a strengthening option for glulam beams when subjected to blast loading, was undertaken. A total of ten different retrofit configurations were investigated and compared to the behaviour of unretrofitted glulam members. In general, the use of multi-directional GFRP contributed to significant performance enhancement, where ductility ratios in the range of 2.3{\textendash}3.6 were obtained. The use of bidirectional GFRP fabrics localized the damage in the wood section to a small area, and provided confinement which helped delay the failure of the retrofitted specimen. The FRP fabrics also contributed to an increase in wood ultimate tensile failure strain.
A two-step approach was proposed to predict the resistance function of the retrofitted specimens. The model predicted the peak resistance and deflection at peak resistance reasonably well. The approach was able to predict the ultimate failure deflection when the experimental ductility ratios were used. An approach for design using a lower-bound ductility ratio was proposed.
}, url = {https://www.sciencedirect.com/science/article/abs/pii/S0141029619319480}, author = {Daniel Lacroix and Ghasan Doudak} } @inbook {doi:10.1061/9780784482247.013, title = {Design and analysis of unretrofitted and retrofitted glulam beams and columns under blast loading}, booktitle = {Structures Congress 2019}, year = {2019}, pages = {137-146}, abstract = {The findings of a comprehensive study involving the static and dynamic investigation of seventy unretrofitted and FRP retrofitted glulam structural elements are presented in this paper. Key observations made in the experimental program regarding material properties, effect of combined axial and out-of-plane blast loading, and strengthening strategies using FRP are used as foundation for design recommendations. Based on the experimental results, unretrofitted glulam beams and columns were shown to have no significant post-peak resistance and thus it is recommended that such members be modeled using a linear flexural resistance curve with a ductility ratio of unity. A dynamic increase factor was found to only be present in beams with no continuous or closely aligned finger-joints. In cases where the finger-joint distribution is not known, a DIF of unity is recommended. Fibre-reinforced polymers (FRP) were shown to only provide significant post-peak resistance when bidirectional fabrics were used as confinement.}, doi = {10.1061/9780784482247.013}, url = {https://ascelibrary.org/doi/abs/10.1061/9780784482247.013}, author = {Daniel Lacroix and Ghasan Doudak} } @article {lacroix2018determining, title = {Determining the dynamic increase factor for glued-laminated timber beams}, journal = {Journal of Structural Engineering}, volume = {144}, number = {9}, year = {2018}, pages = {04018160}, publisher = {American Society of Civil Engineers}, abstract = {This paper presents the results from an experimental program that investigated the flexural behavior of glulam beams subjected to dynamic loading. A total of thirty-eight beams consisting of three different cross-sections were tested destructively under both static and dynamic loads. The analysis resulted in a dynamic increase factor (DIF) of 1.14 for strain-rates ranging between 0.14 and 0.51 s-1, however, the increase was only observed when the outer tension laminate did not include continuous finger-joints (single laminate width) or closely aligned finger-joints (multiple laminates width) in the high moment region causing a straight fracture across the width. No increase due to high strain-rate effects was found when a continuous failure across the width due to finger-joints (FJs) were present in the outer tension laminate, and thus if continuous laminates, uninterrupted by FJs cannot be guaranteed, a dynamic increase factor of unity is suggested for design. Since the beams exhibited little to no ductility, it is recommended that a linear-elastic resistance curve be used to generate the dynamic resistance curve. An equivalent single-degree-of-freedom (SDOF) model accounting for high strain-rate effects using the derived DIF, where appropriate, captured the displacement at failure, time to failure, and displaced shape with reasonable accuracy.\ }, url = {https://www.scopus.com/record/display.uri?eid=2-s2.0-85046899598\&origin=inward\&txGid=e75bbaf642b3fed6499c093c8d4a0422}, author = {Lacroix, D and Doudak, G} } @article {lacroix2018effects, title = {Effects of high strain rates on the response of glulam beams and columns}, journal = {Journal of Structural Engineering}, volume = {144}, number = {5}, year = {2018}, pages = {04018029}, publisher = {American Society of Civil Engineers}, abstract = {A material predictive model that accounts for strain-rate effects and captures the effect of variable axial load on the dynamic response of glulam structural members subjected to combined lateral-blast and axial loading is developed and validated using experimental data for full-scale blast tests on beam and column specimens. Composite resistance curves, which capture the loss in axial load as the column displaces laterally, were shown to corroborate well with the measured axial-load time history and resistance curves. It was also found that the columns{\textquoteright} resistance can be obtained using an equivalent lateral-load approach when experimentally measured displacement, pressure, reaction, and axial-load time histories are considered. The model was also capable of predicting the maximum displacement and time to maximum displacement with reasonable accuracy.}, url = {https://www.scopus.com/record/display.uri?eid=2-s2.0-85043467537\&origin=inward\&txGid=f28f4cc17fb9a628b4503b3a9b1db920}, author = {Lacroix, D and Doudak, G} } @article {24845, title = {Experimental and Analytical Investigation of Cross-Laminated Timber Panels Subjected to Out-of-Plane Blast Loads}, journal = {Journal of Structural Engineering}, volume = {142}, year = {2018}, abstract = {Presented in this paper are the results of an experimental program investigating the out-of-plane behavior of CLT panels under static and blast loading. A total of 18 CLT panels, with panel thicknesses of 105 and 175\ mm corresponding to a 3-ply and 5-ply panel, respectively, were investigated with the aim to determine the dynamic increase factor (DIF). An average dynamic increase factor of 1.28 on the resistance and no apparent increase in stiffness from static to dynamic loading were observed. Two resistance material predictive models that account for high strain-rate effects and the experimentally observed post-peak residual behavior were developed. A single-degree-of-freedom model was validated using full-scale simulated blast load tests, and the predictions were found to match well with the experimental displacement-time histories.}, url = {https://ascelibrary.org/doi/abs/10.1061/\%28ASCE\%29ST.1943-541X.0001915}, author = {Mathieu Poulin and Christian Viau and Daniel Lacroix and Ghasan Doudak} } @article {lacroix2018experimental, title = {Experimental and analytical investigation of FRP retrofitted glued-laminated beams subjected to simulated blast loading}, journal = {Journal of Structural Engineering}, volume = {144}, number = {7}, year = {2018}, pages = {04018089}, publisher = {American Society of Civil Engineers}, abstract = {An experimental program investigating the potential of fiber-reinforced polymers (FRPs) as a strengthening option for glulam beams subjected to simulated blast loads was undertaken. A total of four different retrofit configurations were investigated along with a fifth alternative for restoring previously damaged beams. Increases in resistance and maximum deflection in the range of 1.35-1.66 and 1.3-1.62, respectively, were obtained when FRP tension laminates with and without confinement were used. Partial-length and full-length confinement prevented premature debonding and significantly altered the failure mode from simple tension failure to a combination of brash tension and compression failure while limiting the damage to a small region. The results also showed that the addition of FRP contributed to an increase of 1.17 in the tensile failure strain relative to the unretrofitted beams. A material predictive model that accounts for strain-rate effects was developed using experimental stress-strain relationships determined from coupon tests. The proposed model compared well with resistance curves obtained from full-scale testing of glulam beam elements subjected to simulated blast loading.\ }, url = {https://www.scopus.com/record/display.uri?eid=2-s2.0-85046891561\&origin=inward\&txGid=4f6ba4b37b9a6f3a55dab942044e78d5}, author = {Lacroix, D and Doudak, G} } @article {24844, title = {Damage Level Assessment of Response Limits in Light-Frame Wood Stud Walls Subjected to Blast Loading}, journal = {Canadian Journal of Civil Engineering}, volume = {44}, year = {2017}, abstract = {Currently, no systematic approach exists for damage evaluation of light-frame wood structures subjected to blast loading. This paper presents a detailed assessment of the behaviour of 33 full-scale light-frame wood stud walls subjected to a total of 48 shots of simulated blast loading. Detailed documentation of the observed damage allowed for the development of an accurate evaluation strategy of the response limits. The observed response limits are compared to limits derived from single-degree-of-freedom modelling using scaled pressure{\textendash}impulse diagrams and to current code performance levels. It was concluded that the assumption made in contemporary blast design codes overestimates the ductility ratios for light-frame wood stud walls, and that using a maximum ductility of 2 is more appropriate and safer for blast design. Based on the observed damage levels obtained from the experimental study, the authors propose new ductility ratios corresponding to four damage regions.
}, url = {https://www.nrcresearchpress.com/doi/10.1139/cjce-2015-0418$\#$.Xv3z_ChKg2w}, author = {Christian Viau and Daniel Lacroix and Ghasan Doudak} } @proceedings {26876, title = {Behaviour of FRP retrofitted glued-laminated (glulam) beams subjected to simulated blast loads}, journal = {2016 World Conference on Timber Engineering, WCTE 2016; Vienna; Austria}, year = {2016}, abstract = {Preliminary results from an experimental program investigating the behaviour of retrofitted glulam beams subjected to static and dynamic loads are presented in this paper. The effect of glass fibre-reinforced-polymer (GFRP) laminates applied on the tension side was investigated under both static and dynamic loading as a potential retrofit on undamaged specimens. Furthermore, previously damaged beams were restored by applying GFRP confinement to the damaged region. The experimental results showed that the capacity of the retrofitted beams was improved significantly and the restored beams attained a significant level of their original dynamic capacity. Future work involves the development of a material predictive model that can account for the high-strain rate effects as well as investigating more retrofit options.}, url = {https://www.scopus.com/record/display.uri?eid=2-s2.0-85010931886\&origin=inward\&txGid=247562b269111a5945d3aaba6c53db89}, author = {Daniel Lacroix and Ghasan Doudak} } @proceedings {26875, title = {Behaviour of glued-laminated (glulam) beams and columns subjected to simulated blast loads}, journal = {2016 World Conference on Timber Engineering, WCTE 2016; Vienna; Austria}, year = {2016}, abstract = {This paper presents preliminary results from an experimental program investigating the dynamic behaviour of glulam beams and columns subjected to simulated blast loads. A total of eight glulam beams and columns were tested destructively under static and dynamic loads. Based on the dynamic tests conducted on the beams, an increase in strength under dynamic loading, relative to that measured under the static loading, was observed. A material predictive model that accounts for high strain-rate effects is developed. The experimental displacement-time histories were reasonably well predicted through a single-degree-of-freedom approach which used the proposed resistance model as input.}, url = {https://www.scopus.com/record/display.uri?eid=2-s2.0-85010987138\&origin=inward\&txGid=a7dde7600567dde6c93c7d79f86900f7}, author = {Daniel Lacroix and Ghasan Doudak} } @proceedings {26874, title = {Overview on the structural performance of timber structures under the effects of blast loading - Research and design considerations}, journal = {rd International Conference on Structures and Architecture, ICSA 2016; Guimaraes; Portugal}, year = {2016}, abstract = {Research on the performance of timber structures to the effect of blast loading is very limited and a holistic and systematic approach is needed. A comprehensive research program has therefore been developed at the University of Ottawa to investigate the performance of various structural timber systems when subjected to blast loads. This paper reports on some of the key findings from the experimental and analytical work since the beginning of this program. Significant results on the effect of strain rate on the material behaviour, failure modes, as well as various retrofit options are discussed. The assessment has paved the way to the development of code provisions that would allow the design of new, and retrofit of existing timber structures.\ }, url = {https://www.scopus.com/record/display.uri?eid=2-s2.0-85015078212\&origin=inward\&txGid=8a9017c55480e8a17ee51fd9dc7b71e9}, author = {Daniel Lacroix and Christian Viau and C{\^o}t{\'e}, D and Mathieu Poulin and Lopez, A and Ghasan Doudak} } @article {24843, title = {Investigation of Dynamic Increase Factors in Light-Frame Wood Stud Walls Subjected to Out-of-Plane Blast Loading}, journal = {Journal of Structural Engineering}, volume = {146}, year = {2015}, abstract = {The results of an experimental program investigating the dynamic increase factors of light-frame wood stud walls under blast loading are presented in this paper. A total of 20 walls with two different sheathing types and thicknesses were tested to failure under static and dynamic loading. The study found that the observed failure mode for both static and dynamic loading was flexure; however, a difference in the type of flexural failure was observed. Average increase factors of 1.40 and 1.18 on the resistance and stiffness, respectively, were found. A detailed literature review combined with the test results from the current project yielded a strong correlation between the increase in strain rate and the relative increase in strength and an equation relating the dynamic increase factor (DIF) on the resistance to strain rate was proposed for strain rates in the ranges of 1.67{\textendash}1.65{\texttimes}103 s-11.65{\texttimes}103 s-1.}, url = {https://ascelibrary.org/doi/full/10.1061/\%28ASCE\%29ST.1943-541X.0001139}, author = {Daniel Lacroix and Ghasan Doudak} } @proceedings {26872, title = {Flexural response of glued laminated (glulam) beams subjected to blast loads}, journal = {World Conference on Timber Engineering: Renaissance of Timber Construction, WCTE 2014; Quebec City; Canada}, year = {2014}, abstract = {An extensive body of research is currently available on the behaviour of concrete and steel structures when subjected to blast threats, however, little to no details on how to address the design or retrofitting of wood structures are available. In this paper, preliminary results, both experimental and analytical, are presented on the flexural behaviour of glulam beams under high strain rates. A total of three 80 mm {\texttimes} 228 mm {\texttimes} 2,500 mm glulam beams with a clear span of 2,235 mm were subjected to simulated blast loads using a shock tube. The preliminary experimental results showed that a brash tension failure mode was observed on the tension laminate. It was also shown that a simplified SDOF model, using linear elastic resistance curves, was capable of predicting the failure displacement and level of damage with reasonable accuracy.}, url = {https://www.scopus.com/record/display.uri?eid=2-s2.0-84925003838\&origin=inward\&txGid=64a372fc810e3b30737c8e143aa54c6f}, author = {Daniel Lacroix and Ghasan Doudak} } @proceedings {26871, title = {Light-frame wood stud walls under blast loading - An assessment of the Canadian blast design standard provisions}, journal = {World Conference on Timber Engineering: Renaissance of Timber Construction, WCTE 2014; Quebec City; Canada}, year = {2014}, abstract = {Little details on how to address the design or retrofitting of wood structures subjected to a blast threat are available. Wood structures may be exposed to such loading due to their proximity to an intended target or they may be subjected to an accidental explosion. This paper presents an overview of the current information available on the behaviour of light-frame wood structures subjected to blast loading. A scaled P-I diagram was developed and used to predict damage to light-frame wood stud walls. The ductility ratios provided by the blast code were verified using experimental data. The comparison showed good agreement with the observed levels from experimental work in the superficial and moderate damage region. More work is currently underway to better establish the behaviour in the heavy to blowout ranges.}, url = {https://www.scopus.com/record/display.uri?eid=2-s2.0-84924955574\&origin=inward\&txGid=4864234802b1dbae9962a2648f379219}, author = {Daniel Lacroix and Ghasan Doudak} } @article {26863, title = {Retrofit Options for Light-Frame Wood Stud Walls Subjected to Blast Loading}, journal = {Journal of Structural Engineering}, volume = {140}, year = {2014}, abstract = {This paper presents the results of an experimental program, where a total of eight retrofitted walls were subjected to blast loading, simulated by shock waves using the University of Ottawa{\textquoteright}s shock tube. Four different external retrofit options were considered and their behavior in terms of failure mode, stiffness, and strength were documented. Nonlinear single-degree-of-freedom (SDOF) modeling was performed using material models developed specifically for each retrofit. In general, good agreement was found between the predicted level of damage and calculated displacement using the model and the measured behavior. The study shows that a significant increase in stiffness and strength can be achieved.}, url = {https://ascelibrary.org/doi/10.1061/\%28ASCE\%29ST.1943-541X.0000885}, author = {Daniel Lacroix and Ghasan Doudak and Khaled El-Domiaty} } @proceedings {26870, title = {Behaviour of light-frame wood stud walls under high strain rates}, journal = {CSCE Annual Conference: 3rd Specialty Conference on Material Engineering \& Applied Mechanics, Montreal; Canada.}, volume = {5}, year = {2013}, pages = {3922-3929}, abstract = {This paper presents the methodology and preliminary results of an experimental program, where the behaviour of light-frame wood walls systems under blast loading was investigated. The walls were tested both statically and dynamically and material properties, such as the dynamic increase factor (DIF), were determined. Two different types and thicknesses of sheathing elements, namely OSB and plywood were studied. Preliminary results indicate that there is a significant increase in capacity when the walls were loaded under dynamic loading relative to their static capacity.}, url = {https://www.scopus.com/record/display.uri?eid=2-s2.0-84938343630\&origin=inward\&txGid=2e14cc2162cb3df51ca435f9e8d271e0}, author = {Daniel Lacroix and Ghasan Doudak} } @proceedings {26869, title = {Modelling the behaviour of light-frame wood stud walls subjected to blast loading}, journal = {CSCE Annual Conference: 3rd Specialty Conference on Material Engineering \& Applied Mechanics, Montreal; Canada}, volume = {5}, year = {2013}, pages = {3930-3938}, abstract = {This paper presents analysis using a non-linear material predictive model considering partial composite action for wood light-frame stud walls subjected to blast loading. The proposed model was verified against data from an experimental program, where walls were tested statically and dynamically. The validity of the current provisions of the Canadian blast standard is evaluated and discussed. The modeling results show a tendency for increased capacity and stiffness under high strain rates. The results also demonstrate that neglecting partial composite action yields predictive capacity values that are too conservative.}, url = {https://www.scopus.com/record/display.uri?eid=2-s2.0-84938363634\&origin=inward\&txGid=31e02f79b70e2691c3b1871f6c9f2d96$\#$}, author = {Daniel Lacroix and Ghasan Doudak} } @proceedings {26868, title = {Behaviour of Typical Light-Frame Wood Stud Walls Subjected to Blast Loading}, journal = {World Conference on Timber Engineering 2012, Auckland, New Zealand}, volume = {2}, year = {2012}, pages = {561-569}, address = {WCTE: Extreme Events, Session 30, Engineering Case Studies 2, Auckland, New Zealand}, abstract = {In the past few decades, the effects of accidental explosions and risks associated with terrorist attacks on structures have become a topic of interest for civil engineers and researchers. Although intensive research on the behaviour of concrete, steel and masonry subjected to blast loads was conducted, information on the behaviour of timber structures is still limited to mostly research on impact loads. The objective of this paper is to establish blast response limits for light-frame wood stud walls for different damage levels under blast-induced shock waves. Following analysis using the single-degree-of-freedom modelling approach and experimental testing, it was found that a shock tube can effectively be used to assess the damage levels for wood stud walls. The experimental data agreed with the predicted responses using SDOF models with appropriate combined material models for studs and sheathing.}, url = {https://www.scopus.com/record/display.uri?eid=2-s2.0-84871952943\&origin=inward\&txGid=7464328856732e98592a5d29f2bb3b9c}, author = {Daniel Lacroix and Ghasan Doudak} }