Residential roofs are highly susceptible to wind loads. In most wood-frame buildings, the performance of roofs subjected to wind loads is highly dependent on roof-to-wall connections (RTWCs) and sheathing. These connections play a critical role in preventing roof failures if appropriately designed and constructed. However, the underperformances of roof structures are often observed that are widely associated with poor selection and applications of construction materials. For instance, toenails fasteners commonly used in RTWCs, especially in North America, have been associated with significant failures of roof structures. Therefore, the design of high fatigue performance RTWCs is highly desirable to ensure the integrity of residential buildings.
Recently, connection strengthening strategies such as construction adhesives and metal straps have been identified as promising solutions for enhancing the fatigue performance of wood-frame RTWCs. Particularly, adopting construction adhesives has proved effective for improving structural members’ performance, especially those subjected to natural detrimental loading conditions such as winds. Similarly, previous studies have demonstrated the capability of elastomeric adhesives to increase the uplift resistance of RTWCs. Collectively, adhesive materials provide an efficient, non-intrusive, and cost-effective solution for roof connections subjected to extreme wind loadings.
There are several ways of determining a connection’s wind load-bearing capacity over a long duration. They include cyclic fatigue experiments and the rainbow count methods commonly used to study the fatigue damage of metal roofs claddings. However, in low cycle fatigue, the damage accumulation mechanism for nailed connections in wood-framed structures is different from that of metal claddings. Therefore, a thorough understanding of whether fluctuating wind loadings for a prolonged period at lower amplitudes could induce fatigue failure is of great significance in evaluating the wind resistance performance of RTWCs. This is particularly relevant for non-hurricane regions exposed to winds with low to moderate speeds and where toenails are widely used in wood frame constructions.
On this account, Dr. Bilal Alhawamdeh and Professor Xiaoyun Shao from Western Michigan University investigated the fatigue performance of wood-frame RTWCs with elastomeric adhesives subjected to varying wind loading. The authors performed two fatigue experiments: varying and constant amplitude loading tests on three different RTWCs with and without the elastomeric adhesives. Their objectives were to understand better the wind-induced fatigue behavior at low to moderate wind speeds and to demonstrate the impact of elastomeric adhesives on the fatigue performance of RTWCs. Further, fatigue life prediction models were developed based on the constant loading test results. The work is currently published in the research journal Engineering Structures.
Dr. Alhawamdeh and Professor Shao showed that adding adhesives significantly increased the endurance limits of the RTWCs by 250 – 330%. Unlike connections with adhesives, toenailed connections failed in a less ductile fashion at fewer loading cycles and without warnings. Moreover, the authors also noted that buildings in non-hurricane areas are more susceptible to fatigue damage, especially at low mean wind speeds between 20 – 40 m/s, as it may result in loadings exceeding the endurance limit RTWCs. Furthermore, the proposed Miner’s cumulative fatigue damage model was successfully used to predict the fatigue life and load capacity of RTWCs, including when subjected to multi-amplitude wind loadings.
In summary, the wind fatigue performance of RTWCs was experimentally studied under both varying and constant amplitude loadings to establish the effects of elastomeric construction adhesive on fatigue behavior. Based on the test results, adding elastomeric construction adhesives to the toenailed connections exhibited superior fatigue performance than their toenailed counterparts without adhesives, consequently improving the fatigue and life-cycle performance of wood-framed buildings. The study results provided reliable data for analyzing the failure modes of RTWCs. In a statement to Advances in Engineering, Professor Xiaoyun Shao noted that the study insights would advance the application of construction adhesives in wood constructions to improve their fatigue performance under varying wind loads.
Alhawamdeh, B., & Shao, X. (2021). Fatigue performance of wood frame roof-to-wall connections with elastomeric adhesives under uplift cyclic loading. Engineering Structures, 229, 111602.