Timber at the edge: how far can engineered wood go against blasts and tornado winds

In structural engineering, buildings designed to withstand extreme events, such as explosions or severe wind loads, have traditionally relied on steel and reinforced concrete. These materials offer well-documented behaviour under high strain rates and dynamic loading conditions, making them the default choice for military, industrial, and other high-risk infrastructure. However, recent research is challenging this long-standing assumption. Engineered timber systems, including products such as CLT (Cross-Laminated Timber) and glulam, are now being investigated for their structural performance under dynamic loads. Their favourable high strength-to-weight ratio, combined with the ability to dissipate energy through mechanical connections, is opening new possibilities for protective design.

Research on blast loading consistently shows that material behaviour under high strain‑rate demands differs significantly from static conditions, often exhibiting increased apparent strength and stiffness.

Within this evolving context, Rothoblaas discussed the topic with Professor Ghasan Doudak from the University of Ottawa, a leading researcher on the behaviour of timber structures under blast loading and a featured speaker at the inaugural Timber Engineering Explained Workshop (TEEW), scheduled for October in Ottawa, Canada.

Let’s explore how timber behaves under extreme loading conditions, the critical role mechanical connections play, and how these insights can be extended beyond blast scenarios to other events such as tornadoes and earthquakes.

How did your research on blast-resistant timber structures begin?

The initial motivation came from collaborative research involving deployable timber buildings to be used by the military. At that time, timber was generally not considered a viable option for blast-resistant construction, particularly in strategic or defence‑related facilities. The central question was straightforward: could timber offer a viable alternative? Timber is lightweight, easy to transport, and fast to assemble. When combined with engineered systems such as CLT or glulam, it also demonstrates strong performance under lateral loading and even under ballistic impact. These characteristics make it particularly relevant for applications where speed of deployment and structural efficiency are critical.

Another important aspect is that blast resistance is not limited to military applications. The same principles can be applied to enhance the safety of civil buildings exposed to accidental explosions or other extreme events. The main challenge lies in the material behaviour: by its very nature, timber is not ductile, and achieving adequate performance requires an appropriate combination of greater mass, precision of engineered products, and connection systems capable of dissipating energy. At the same time, accurately modelling blast pressures is essential, as the intensity and duration of the load vary significantly with stand‑off distance, whether the explosion occurs in contact, in the near field, or in the far field.

You conducted full-scale explosion tests. What did these reveal about timber performance?

One of the most interesting findings was related to strain rate effects. This concept describes how a material’s mechanical properties, such as strength and stiffness, change when loads are applied very rapidly. Under very short-duration loading conditions, such as blast pressures, timber can exhibit higher resistance than it does under static or quasi-static conditions.

A key consequence is that timber elements may achieve higher-than-expected resistance during blast events, which must be properly captured in analysis and design to avoid overly conservative or misleading assessments of structural capacity.

*Images reproduced from the academic thesis “Effect of Realistic Boundary Conditions on the Behaviour of Cross-Laminated Timber Elements Subjected to Simulated Blast Loads” by Cote Dominic

Timber performs well under lateral loads such as wind and seismic actions. Does this translate to blast resistance?

There is a strong connection, but also a fundamental distinction. Both blasts and wind generate lateral forces on a structure, that exert pressures that are typically out-of-plane on wall and roof surfaces, while seismic actions primarily mobilize in‑plane response. Despite this difference in loading direction and structural engagement, one principle remains consistent: the overall response is governed by the integrated behaviour of the system, in which the role of the connections is critical.

In engineered timber systems, the structural strategy is to maintain the primary structural elements (such as columns and wall panels) relatively strong and stiff, while concentrating energy dissipation in the connections. Steel connectors can be designed and detailed to behave in a ductile manner, allowing them to absorb energy and prevent brittle failure of the timber elements.

This approach also offers an important advantage: following an extreme event, damaged connectors can be replaced, allowing partial recovery of the structure with limited intervention.

Can timber compete with steel or concrete in blast-resistant applications?

Direct comparisons are difficult and highly dependent on the specific application. If we consider the strength-to-weight ratio, timber can present a viable alternative to both steel and concrete in certain scenarios. However, each material has a specific role and characteristics and as such it is important that they are used where required to optimize the overall performance of the structure.

Timber is particularly effective when lightweight, transportable, and rapid-assembly solutions are required. It also offers clear advantages when sustainability is a design priority. Concrete remains indispensable for underground or highly massive protective structures, while steel provides the ductility needed in applications where large inelastic deformations must be accommodated.

In practice, hybrid solutions often deliver the best performance. Timber structures rely on steel connections to achieve the ductility and energy‑dissipation capacity required under dynamic loading.

*Images reproduced from the academic thesis “Investigation and Optimization of Connections in Timber Assemblies Subjected to Blast Loading” by Viau Christian

Did you observe differences between CLT and traditional timber frame systems?

Yes, and the difference is significant. To effectively resist blast loads, engineered timber products such as CLT, GLT, or glulam are preferred, combined with properly designed connections. Traditional light timber frame systems do not provide the same level of resistance in these scenarios, but due to the abondance they also need to be assessed in case they are within the vicinity of a credible threat.

Engineered wood products offer a level of continuity, mass, and structural engagement that light‑frame systems simply cannot provide. They also create a reliable platform for incorporating mechanical connections with well‑defined ductile characteristics, enabling controlled energy dissipation. Achieving this type of predictable, replaceable, and energy‑absorbing connection behaviour is far more challenging in traditional light‑frame construction.

Is it possible to further improve timber performance under blasts?

Yes, several options exist. For example, reinforcing timber elements with self-tapping screws to prevent splitting or incorporating purpose‑designed energy-absorbing end connections can significantly enhance performance. These strategies improve the system’s ability to dissipate energy through controlled deformation of the boundary connectors rather than concentrating stresses in the timber elements.

Looking at events like tornadoes, where does the main vulnerability lie in timber buildings?

In most cases, the primary vulnerability is not in the timber elements themselves, but in the vertical load path. Failures often originate at points where the load path is discontinuous or where connections are not detailed to resist the uplift and reversal forces generated by extreme winds. Roof‑to‑wall and wall‑to‑foundation interfaces are particularly susceptible, as they are frequently designed for gravity loads only. Even straightforward improvements, such as replacing nails with fully threaded screws that provide reliable withdrawal resistance, can significantly strengthen the continuity of the vertical load path and improve overall performance under tornado‑level demands.

What are the key practical steps to improve resistance to extreme events?

The answer is consistent across all extreme‑event scenarios. A robust design approach for extreme events must be holistic, ensuring that the structural system behaves in a controlled and predictable manner. In timber construction, this means allowing connections to yield in a ductile fashion, but without permitting them to fail before the primary structural elements reach their own capacity. This concept, while well established in seismic design, is less familiar to many designers accustomed to steel or concrete systems and remains insufficiently understood in the context of blast‑resistant timber design. The challenge is to detail connections so they can deform, absorb energy, and protect the timber elements, while still maintaining the integrity of the overall load path.

*Images reproduced from the academic thesis “Effect of Realistic Boundary Conditions on the Behaviour of Cross-Laminated Timber Elements Subjected to Simulated Blast Loads” by Cote Dominic

From extreme events to everyday design decisions

The research presented by Prof. Doudak highlights a clear shift in how timber is evaluated in structural engineering. Timber is no longer limited to conventional, low‑risk applications. When combined with engineered products and properly designed and detailed connections, it can respond effectively to extreme loading scenarios, ranging from blasts to tornado‑level winds. For designers and engineers, the implication is direct: the performance of timber structures under extreme loads is not governed by the material alone, but by the interaction of the entire system, with the connection design playing a decisive role. Recognizing this system‑level interaction is essential when moving from standard design assumptions to scenarios involving elevated risk and dynamic demands.

Explore advanced connection design strategies and contemporary timber engineering principles in depth during the TEEW session and consult technical documentation on engineered connectors and fastening systems developed specifically for dynamic and extreme‑event loading.

*Images reproduced from the academic thesis “Investigation and Optimization of Connections in Timber Assemblies Subjected to Blast Loading” by Viau Christian