BLAST HARDENING: RETROFIT CONCEPTS FOR EXISTING BUILDINGS

By Eamonn Ryan, derived from an ACI podcast

A March 2024 American Concrete Institute (ACI) podcast by Marlon Bazan, a principal at Protection Engineering Consultants, shared insights on effective blast hardening retrofit concepts covered in the ACI 370R report.  This is Part 1 of a three-part series.

The blast retrofits included strengthening of load-bearing and non-load bearing reinforced concrete elements and masonry walls using fiber-reinforced polymer (FRP), steel straps, corrugated metal panels, thickening of elements using shotcrete, as well as using spray-on elastomers and unbonded geotextile catch systems for unreinforced masonry walls, among others.

In recent years, the discussion surrounding structural engineering has increasingly focused on retrofitting existing buildings to enhance their resilience against blast loads and seismic events.

The presentation delved into the complexities of retrofitting building structures, emphasising the critical role of thorough structural analysis and practical experience in engineering. Bazan highlighted various methodologies that can be employed, ranging from traditional steel jackets and fibre-reinforced polymer (FRP) steel plates to more innovative approaches involving additional concrete and composite backing wall systems. Each method offers unique benefits and challenges, necessitating careful consideration in design and execution.

A fundamental aspect of blast retrofitting involves understanding the specific structural vulnerabilities that need addressing. Bazan stressed the importance of correctly identifying the primary reasons for retrofitting, whether to rectify flexural deficiencies, shear vulnerabilities, or to safeguard critical components within the building. This initial assessment informs the selection of appropriate retrofit options.

Moreover, the performance of each retrofit solution must be rigorously evaluated. While an analysis may indicate that a certain retrofit meets structural requirements, practical considerations such as construction feasibility and cost-effectiveness also play pivotal roles in decision-making. For instance, retrofitting that requires access to interior spaces may be impractical if those spaces are occupied or house sensitive equipment.

One of the significant challenges highlighted in Bazan’s presentation is the impact of retrofits on other structural elements within the building. Strengthening one component, such as increasing the flexural capacity of a beam or slab, can inadvertently affect the load distribution and behaviour of adjacent elements. This ripple effect necessitates a holistic approach to design, ensuring that the entire structural system remains cohesive and resilient under varying loads.

Furthermore, Bazan underscored the criticality of addressing shear capacities when implementing retrofit solutions. Many retrofit methods focus primarily on enhancing flexural strength, potentially overlooking increased shear demands that may result from strengthened components. Neglecting to account for these secondary effects can lead to unforeseen failure modes, compromising the overall effectiveness of the retrofit.

Continued in Part 2…