a b s t r a c tA general adaptive approach rooted in stratified sampling (SS) is proposed for sample-based uncertainty quantification (UQ). To motivate its use in this context the space-filling, orthogonality, and projective properties of SS are compared with simple random sampling and Latin hypercube sampling (LHS). SS is demonstrated to provide attractive properties for certain classes of problems. The proposed approach, Refined Stratified Sampling (RSS), capitalizes on these properties through an adaptive process that adds samples sequentially by dividing the existing subspaces of a stratified design. RSS is proven to reduce variance compared to traditional stratified sample extension methods while providing comparable or enhanced variance reduction when compared to sample size extension methods for LHS -which do not afford the same degree of flexibility to facilitate a truly adaptive UQ process. An initial investigation of optimal stratification is presented and motivates the potential for major advances in variance reduction through optimally designed RSS. Potential paths for extension of the method to high dimension are discussed. Two examples are provided. The first involves UQ for a low dimensional function where convergence is evaluated analytically. The second presents a study to asses the response variability of a floating structure to an underwater shock.

One dozen American Institute of Steel Construction (AISC) W14 steel columns were tested at the Energetic Materials Research and Testing Center (EMRTC), New Mexico Institute of Mining and Technology in Socorro, New Mexico with loading from typical size vehicle bomb threats at very close to moderately close standoffs. Pretest predictions of structural response were performed using standard SDOF methods and the Weidlinger Associates, Inc. (WAI) FLEX finite element code. Loads acting on the columns were determined from the U. S. Army developed CONWEP code using the Kingery-Bulmash equations for the pretest predictions. Seven tests included individual columns with axial loading and blast loading applied simulataneously. One test included 5 columns built into a frame with moment connections at the top of the columns and base plate connections at the base of the columns. The columns were instrumented with accelerometers and pressure transducers. The tests were designed to produce various levels of damage from mild to severe. This paper will compare the pretest and posttest predictions using both the SDOF and FLEX finite element methods with the actual test results. The comparison between actual loading and CONWEP loading will also be discussed. Conclusions will be drawn with regard to the use of CONWEP loading for this type of threat at various standoffs. Also, the use of SDOF and FLEX finite element methods to predict the response of AISC W14 steel columns will be compared.

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The threat of terrorist attack against civil infrastructure in the US and other countries has led to the need to better understand the response of structures and structural components to an impulsive air blast overpressure. One scenario that is present in many cities is delivery trucks entering basement or street level loading/unloading areas. A bomb present in one of these delivery trucks could cause considerable damage to the floor slab (and consequently the building) above the blast by causing a vertical uplift, a condition that the slab was not designed to resist. Traditional methods to retrofit floor slabs to resist an upwards blast pressure require that additional tension sustaining reinforcing bars (rebars) be placed near the slab upper surface. This reinforcing method is costly, difficult to produce, and adds additional weight to the overall structure in building retrofit situations. Another approach to reinforcing the slab is to bond light-weight, high strength fiber composite material to the slab upper surface as a means of resisting the tensile forces from the slab upward motion. This paper presents results from an effort to simulate the response of a reinforced concrete floor slab with a fiber composite retrofit subjected to a blast overpressure. The simulations were performed using the Weidlinger Associates’ FLEX [1] finite element code for structural response calculations. The MAZ [2] computational fluid dynamics code was used to generate blast pressure. This paper will discuss the modeling effort used to predict the response of fiber composite retrofitted slabs and compare the computational analysis to test results1.

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