PEC is currently working with the U.S. Department of State to develop novel energy absorbing connections (EACs) to protect the occupants in buildings subject to large blast loads, such as those from terrorist attacks. Structural components are typically designed to resist blast loads with rigid connections. An innovative approach for blast design is to support blast-loaded cladding components on a building with EACs, which deform as they resist the dynamic reaction force from the component. The EACs absorb energy from the applied blast load by ductile yielding with a controlled, nearly constant, resisting force out to a large deflection. The blast-loaded façade component supported by the EACs is also designed to yield in flexure and absorb energy, so that both the EACs and supported component work as a system to resist the blast by absorbing the energy applied by the blast load. Since the façade component does not need to resist all the applied blast energy, it can be designed with a lower strength than if it had traditional rigid connections. In addition, the EACs can be designed to transmit a lower maximum reaction force into the supporting structure than a rigid connection. This advantage of EACs can be most important when an existing building is retrofitted with a strengthened, blast resistant façade that could transmit very high reaction loads into the building’s lateral load resisting system if rigidly connected, requiring a cost-prohibitive upgrade of this system. A concept for installing EACs in a building is shown in Figure 1.
Based on the results from a literature search, two types of EACs have been identified as the best candidates: 1) deformable steel cross sections, and 2) thin gage aluminum sheets manufactured into a crushable, honeycomb pattern. Figures 2 and 3 show a steel EAC and aluminium honeycomb material with a steel EAC, respectively. Both types of EACs have been tested statically and dynamically using dropped weights. Figure 3 shows a combined EAC, where the aluminium honeycomb material is placed inside the steel EAC, so that both materials are part of the connection that absorb energy. The next step in the development is shock tube tests on precast concrete panels supported by EACs, which will be conducted this year.
For more information on this ongoing analysis, design and testing program, contact Chuck Oswald, PhD, PE.