Vulnerability of Progressive Collapse in Reinforced Concrete Flat-Plate Buildings

Progressive collapse is the spread of initial local failure, causing partial oreven total collapse of a building. Flat plate structure is widely used for office and residential buildings. There is a large inventory of older flat plate building without continuous slab bottom reinforcement through columns. Limited knowledge exists regarding the risk of disproportionate collapse inolder flat-plates under sudden column removal during abnormal events. Reliable mechanical model is needed for structural evaluation

Progressive Collapse Analysis of Older Reinforced Concrete Flat Plate Buildings Using Macro Model

Catastrophic progressive collapse of a building can be triggered by a sudden loss of a load-bearing element in an abnormal loading event. There is a large inventory of reinforced concrete flat plate buildings designed in accordance with older codes. Without using shear and integrity reinforcement in slabs, these older flat plates are vulnerable to progressive collapse. The overall goal of this research is to numerically examine the resilience of older flat plate buildings against progressive collapse due to instantaneous removal of an exterior or interior column. To achieve the research goal, a macro behavioral model of slab-column frame is created and applied to a prototype flat plate building designed following the ACI 318-71 code. The macro model employs both connector and shell elements. The shell elements are used to mainly simulate the flexural behavior of slab and the load redistribution over floor slabs. The connector elements are adopted to simulate bending moment, shear, and torsion transferred from slab to column, and to simulate connection punching shear failure. To ensure applicability of the proposed macro model, it is validated by 24 large-scale tests conducted on isolated slab-column connections under three different types of loading conditions. Both dynamic and static analyses are conducted on the prototype building under service live loads. The nonlinear dynamic analyses indicate that, following the sudden removal of a column, punching failure will occur in the neighboring slab-column connections and the failure will immediately propagate over the slab floors, leading to a collapse of the building. The dynamic analyses also reveal that neglecting strain rate effects on materials would lead to considerably overestimated global and local deformation demands on slabs. The nonlinear static analysis approach specified in the DoD progressive collapse design guideline is found inadequate in equivalently estimating the dynamic response of a flat plate system. The energy-based nonlinear static analysis procedure is therefore examined and proved to be an effective approach. To indirectly account for strain rate effects, parameters defining dynamic strengths of materials are suggested. To further examine the likelihood of progressive collapse, nonlinear dynamic and energy-based static analyses are applied to the prototype building under three gravity load levels and with varied properties of slabs

Synthesis, characterization and applications of new photocurable and biodegradable elastomers

Biodegradable elastomers have attracted a great deal of interest due to their potential applications in the biomedical field. Based on the advantages of the photocuring method, a new series of photocurable and biodegradable elastomers were designed. By using step growth polymerization, polyester liquids with different composition and molecular weights were synthesized. After endcapping with methacrylate groups, these liquids can be easily fabricated into completely amorphous elastomers by UV exposure for 1 min at room conditions. The prepared elastomers presented a wide range of mechanical properties (G equals 0.1-10 MPa) and a fast degradation rate (16 percent after 5 week incubation in PBS). The in vitro and in vivo biocompatibility studies of the elastomers indicated that these elastomers were good candidates as tissue engineering scaffolds. Meanwhile, the functionality of these photocurable elastomers was expanded by incorporation of amine containing monomers, and new elastomers were prepared to explore their potential as drug carrier systems. Monodispersed elastomeric particles were fabricated out of these amine containing materials by PRINTTM technology. These particles showed pH sensitive drug release of Doxorubicin (a hydrophobic drug model) and Minocycline chloride (a hydrophilic drug model), and the release profiles can be further tuned by the incorporation of a disulfide crosslinker

Depth determination of the Moho interface beneath the Tibetan plateau and other areas of China

We apply the adaptive moving window method of Sun et al. to the most recent catalog data and the data recorded by portable stations to construct the velocity structure of the crust and upper mantle, and to determine the depth of the Moho interface beneath the Tibetan plateau and other areas of China. We first select 2 600 locations in the study region with 1° intervals, then at each location invert for a five-layer 1-D P-wave velocity model from the surface down to the uppermost mantle by performing a Monte Carlo random search. The Moho depth at each location is then determined, and the Moho interface beneath the study region is obtained through proper interpolation with certain smoothing. Compared to depths obtained by previous studies, our results show more accurate Moho depths in the Tibetan plateau, Tianshan region and other areas of the study region.United States. Defense Threat Reduction Agency (Contract DTRA01-00-C-0024)Chinese Academy of Sciences (Fund KJCX2-EW-121