Preventing progressive collapse is a gravely important problem for society, particularly after the attacks on the Murrah Federal building in 1995 and the terrorist attacks on September 11, 2001. Such prevention requires knowledge of system-level behavior, but there is very little actual data because system-level tests are prohibitively expensive. Progressive collapse is by nature a system-level problem where the spread of an initial local failure from element to element eventually results in the collapse of an entire structure or a disproportionately large part of it (ASCE 7, 2002). Our understanding of collapse mechanisms and structural capacities under such conditions is limited because relevant experimental results on the behavior of elements and whole structures are scarce.
This proposal describes an exploratory research plan that obtains realistic and reliable data from a full-scale reinforced concrete (RC) structure scheduled to be imploded, in order to determine its capacity and potential progressive collapse mechanism after imposing preplanned damage scenarios. The data obtained form the building are realistic and reliable, because there is no need to impose any structural damage to RC beams and columns prior to the implosion other than making some small holes in exploding columns to place explosives. The nonstructural elements in the imploding stories will be removed for the ease of collapse. The removal of nonstructural elements will not considerably affect the collapse mechanism, yet makes it easier to examine the deformation capacity of structural elements without the complication introduced by nonstructural elements. The research program will serve as a first step to demonstrate the possibility of collection of such data, and the value of the data in developing reliable capacity models as well as procedures for reliable progressive collapse analysis.
GSA (2003) and DOD (2004) use scenarios with the removal of one column as the initial local failure to examine progressive collapse of structures. Prior to the main implosion of a building, some of the columns are exploded to evaluate the response of the building and proper implosion strategy. Based on an existing collaboration with the Controlled Demolition Inc, these columns will be chosen jointly with CDI experts. The building will be instrumented at two stages; one during the explosion tests and one during the main implosion. The first stage will provide invaluable information about the post-failure system response of the building, which will significantly help improve modeling techniques and estimation of demands following the removal of load bearing elements. The data collected from the second stage will be utilized to develop capacity models for collapse of RC structural elements due to the imposed large displacements and forces. The main objectives of the experiment are to: understand mechanisms of progressive collapse and failure modes; evaluate procedures for progressive collapse analysis currently used by engineers; determine effects of reinforcement details, joints and floor diaphragms on progressive collapse; identify deformation capacities of critical elements; and calibrate and verify advanced material and geometric nonlinear dynamic analysis of the structure.
Intellectual Merit: In this exploratory and innovative research, a full-scale system-level experimental program will be carried out to collect reliable responses from a RC structure with preplanned damage. Utilizing the data, the effects of reinforcement detailing on progressive collapse will be studied. The recorded data will be used to develop capacity models, which in turn can be used to more reliably estimate potential progressive collapse of structures. Furthermore, the data will be used to calibrate and verify advanced nonlinear dynamic analysis of progressive collapse.
Broader Impact: Development of reliable progressive collapse analysis leads to identifying structures that are potentially hazardous, which in turn results in better allocation of limited resources in rehabilitation of structures and development of cost-effective retrofit plans for existing structures. The outcomes of this project will also help quantify the effectiveness of structural integrity requirements in current codes for new structures. Furthermore, the outcomes can be used in examining collapse prevention performance of existing structures and their rehabilitation.
