The goals of the research are to develop an innovative exterior wall system capable of providing anti-terrorism protection and energy efficiency while maintaining cost effectiveness. The research will mesh the techniques used in the precast concrete sandwich wall industry with recent developments in construction materials and reinforcement strategies to create a non-proprietary protection system that can be readily incorporated into domestic and international building construction applications. The system will be capable of resisting pressure demands generated from intentional and unintentional explosions, near contact detonations, and ballistic demands while still maintaining architectural features and thermal efficiency. To accomplish these objectives analytical parametric studies and experimental validation will be conducted through a collaborative research program at Lehigh and Auburn Universities. The parametric studies will evaluate novel materials and reinforcement strategies using both nonlinear dynamic finite element analysis methods and simplified mechanics based approaches. The experimental studies include static, blast, and ballistic evaluations and will be used to validate the models and demonstrate the capability and limitations of the system developed. The research will advance the science of insulated concrete sandwich wall design allowing economically advantageous protection measures to be integrated into the buildings we live and work in. This will directly provide a societal benefit by creating a system that will enhance our national defense. The research will expand ongoing studies on cement based insulated wall systems conducted by engineering organizations and government laboratories allowing current collaborations to be continued and strengthened. Broad dissemination of the research will be accomplished through partnership and involvement of industry representatives from the tilt-up concrete and prestressed concrete markets and participation of research groups from the U.S. Army and Air Force. The program will provide advanced training to undergraduate and graduate students and industry participants through newly developed courses. Underrepresented groups will be recruited for participation in the project.
Terrorist attacks have been carried out on our infrastructure at home and abroad at an alarming rate in the past decade. To protect our facilities and the people who work and reside in them from these threats, blast design criteria have become a standard structural requirement for U.S. government and military buildings. To meet these requirements traditional cast-in-place reinforced concrete construction methods are often utilized. While this type of construction has been proven against blast demands, the high economic cost, long construction timeline, and low energy efficiency makes it a reluctant choice for owners and designers. Insulated concrete sandwich wall panels have been used successfully in standard building construction for many years. These systems consist of an exterior façade an insulating foam layer and an interior structural concrete layer (Fig.1). These systems are often prefabricated allowing for a rapid construction schedule and is ideal for projects where short timelines are desired. The insulating properties of the panels provide a high thermal resistivity resulting in an energy efficient building with low winter heat loss and low summer cooling requirements. Most importantly these systems provide an effective means of protection against the blast pressures generated from an explosion. The high mass of the concrete wall coupled with the sandwich configuration of the panels provides an elevated resistance to the dynamic effects of blast demands. The research project identified that conventional wall systems have limited ability to resist large deformation without failing. The ability to deform without braking is one of the key characteristics needed to successfully resist explosive demands. An approach involving unbonded reinforcement and a new detail in which local mechanisms are installed were developed (Fig.2). The methods were tested at scale and using a water bladder to simulate uniform pressure loads. Analytical models were developed and verified for use in implementing the methods in practice. The behavior of insulated panels was found to be linked to the ability to successfully transfer forces between the interior and outer sections of concrete on the wall. To improve the transfer mechanism under blast loads an analytical model was developed which allows for designers compute the response of the system based on the type of shear ties used. The method was used to develop a new tie system for wall panels. To resist close-in detonations insulated panel systems were subjected to explosive detonations. The results of the experimental program were used to validate numerical models which can be used to model the effects of spall and breach of wall panels. The results indicate that the use of insulated wall panels provides an improved resistance to spall and breach over non-insulated concrete panels (Fig. 3). This advantage improves as the level of insulation increases. To comprehensively address ballistic threats such as those generated by small arms fire and mortar fragments a new probabilistic approach for quantifying the safety of precast concrete walls against fragment impact was developed. The approach allows for an enhanced ability to assess life safety of occupants based on the location of the facility, wall construction details, and the weapon type. A number of undergraduate and graduate students have participated in this research, gaining useful research experience and making significant contributions to the success of the project. We have also published the results in engineering journals and made numerous presentations to the professional engineering community to publicize the important findings from this project.
