The investigation of progressive collapse of buildings has been of special interests during the last decade. The aim of this study is to assess the influence of selected design parameters on the vulnerability of structures with flat plates or flat slabs to progressive collapse triggered by the severe damage or failure of a column as a result of accidental or maliciously intended terrorist activity. The variables of frames with two-way slab systems investigated include: the number of stories in buildings (low-, medium- and high-rise buildings), span ratio (the ratio of span lengths in two orthogonal directions), span length for square panels, as well as the effect of having flat plates compared to flat slabs detailed either as ordinary gravity load carrying systems or by following the seismic detailing requirements of the Canadian practice as per CSA A23.3-04. The linear-elastic static analysis method, outlined in the General Services Administration (GSA) guidelines of the US, was employed to conduct a parametric investigation to assess the significance of the design variables considered on progressive collapse potentials of buildings. This involved the computation of demand/capacity ratios (DCR) Higher DCRs were obtained for buildings with increased number of stories and span ratios, while the change in span lengths did not show a clear trend. Also, flat slabs were less vulnerable, and experienced smaller DCRs, than flat plates. Buildings detailed according to the seismic provisions of CSA A23.3-04 were less vulnerable than those detailed without these provisions. However, both slabs with non-seismic and seismic detailing required improvements in terms of the percentage of top and bottom reinforcement and bar lengths, depending on the slab type and the design parameters considered.

The investigation of progressive collapse of buildings has been of special interests during the last decade. The aim of this study is to assess the influence of selected design parameters on the vulnerability of structures with flat plates or flat slabs to progressive collapse triggered by the severe damage or failure of a column as a result of accidental or maliciously intended terrorist activity. The variables of frames with two-way slab systems investigated include: the number of stories in buildings (low-, medium- and high-rise buildings), span ratio (the ratio of span lengths in two orthogonal directions), span length for square panels, as well as the effect of having flat plates compared to flat slabs detailed either as ordinary gravity load carrying systems or by following the seismic detailing requirements of the Canadian practice as per CSA A23.3-04. The linear-elastic static analysis method, outlined in the General Services Administration (GSA) guidelines of the US, was employed to conduct a parametric investigation to assess the significance of the design variables considered on progressive collapse potentials of buildings. This involved the computation of demand/capacity ratios (DCR) Higher DCRs were obtained for buildings with increased number of stories and span ratios, while the change in span lengths did not show a clear trend. Also, flat slabs were less vulnerable, and experienced smaller DCRs, than flat plates. Buildings detailed according to the seismic provisions of CSA A23.3-04 were less vulnerable than those detailed without these provisions. However, both slabs with non-seismic and seismic detailing required improvements in terms of the percentage of top and bottom reinforcement and bar lengths, depending on the slab type and the design parameters considered.

The investigation of progressive collapse of buildings has been of special interests during the last decade. The aim of this study is to assess the influence of selected design parameters on the vulnerability of structures with flat plates or flat slabs to progressive collapse triggered by the severe damage or failure of a column as a result of accidental or maliciously intended terrorist activity. The variables of frames with two-way slab systems investigated include: the number of stories in buildings (low-, medium- and high-rise buildings), span ratio (the ratio of span lengths in two orthogonal directions), span length for square panels, as well as the effect of having flat plates compared to flat slabs detailed either as ordinary gravity load carrying systems or by following the seismic detailing requirements of the Canadian practice as per CSA A23.3-04. The linear-elastic static analysis method, outlined in the General Services Administration (GSA) guidelines of the US, was employed to conduct a parametric investigation to assess the significance of the design variables considered on progressive collapse potentials of buildings. This involved the computation of demand/capacity ratios (DCR) Higher DCRs were obtained for buildings with increased number of stories and span ratios, while the change in span lengths did not show a clear trend. Also, flat slabs were less vulnerable, and experienced smaller DCRs, than flat plates. Buildings detailed according to the seismic provisions of CSA A23.3-04 were less vulnerable than those detailed without these provisions. However, both slabs with non-seismic and seismic detailing required improvements in terms of the percentage of top and bottom reinforcement and bar lengths, depending on the slab type and the design parameters considered.

No description available.

Nonlinear response of a structure to progressive loading may originate from two different sources viz, geometric nonlinearity and material nonlinear behaviour. For a rationally proportioned concrete structure, the material nonlinear responses are believed to contribute the major part of its total nonlinear behaviour. Geometric nonlinearities, become significant only when the structure is relatively slender. It is the material nonlinearities of reinforced concrete structures that are of interest in this investigation. Two plate bending finite elements have been generalised to include coupling of inplane actions with the bending effects. This was achieved through layering concept. One of these elements had been employed by some previous researchers. But the present formulation is different from theirs in that a numerical integration scheme is introduced to evaluate the stiffnesses and internal equivalent forces. A number of schemes for solving the nonlinear equations have been included in the present formulation. Suitability and effectiveness of these schemes in tracing the material nonlinear responses of concrete slabs have been examined. The numerical material model behaviour is based on the experimental observation reported by various authors. Readily available material characteristic properties are used in the description of the model. The overall response of reinforced concrete slabs is found to be significantly influenced by the cracking and post cracking treatment of concrete. Some form of tension stiffening scheme seems necessary to represent the structural response realistically. A number of conventional tension stiffening schemes have been incorporated, including a simple alternative formulation. The effect of different tension stiffening schemes and some other numerical parameters on the numerical solution of concrete structures have been investigated. Laboratory tests were carried out on a number of square and rectangular model slabs. The supporting arrangement and the applied loading systems were the main variables. These experimental records were later compared with the numerical predictions. Some other test results from literature have been included also.

No description available.

A tear in the subducting Nazca slab is located between the end of the Pampean flat slab and normally subducting oceanic lithosphere. Tomographic studies suggest mantle material flows through this opening. The best way to probe this hypothesis is through observations of seismic anisotropy, such as shear wave splitting. We examine patterns of shear wave splitting using data from two seismic deployments in Argentina that lay updip of the slab tear. We observe a simple pattern of plate-motion-parallel fast splitting directions, indicative of plate-motion-parallel mantle flow, beneath the majority of the stations. Our observed splitting contrasts previous observations to the north and south of the flat slab region. Since plate-motion-parallel splitting occurs only coincidentally with the slab tear, we propose mantle material flows through the opening resulting in Nazca plate-motion-parallel flow in both the subslab mantle and mantle wedge.

No description available.

No description available.

No / Gas chromatography-mass spectrometry (GC-MS) and bulk carbon isotope determinations have been performed on samples ('cemented organic residues', charcoal, sediment and fire-cracked rock) excavated from twelve slab-lined pits from various locations in Arctic Norway to test the premise that these archaeological features were used for the extraction of oil from the blubber of marine mammals, such as seal, whale and walrus. A wide range of lipid compound classes were detected especially in the cemented organic residues and in the charcoal samples. The presence of long-chain unsaturated and isoprenoid fatty acids together with oxidation and thermal alteration products of unsaturated acids such as dicarboxylic acids, dihydroxyfatty acids and ω-(o-alkylphenyl)alkanoic acids suggests that these features were used for marine oil extraction at elevated temperatures. Notably the location of the hydroxyl groups in the dihydroxyfatty acids provides a record of the positional isomer of the precursor fatty acid and allows confirmation that 11-docosenoic (cetoleic) acid, the most abundant C22:1 isomer in marine oil, was a major component of the original lipid. Further information was provided by the presence of long-chain fatty acyl moieties in surviving triacylglycerols and the presence of cholesterol. A fungal metabolite, mycose (trehalose), was found in all samples apart from a fire-cracked rock and points to microbiological activity in the pits. Bulk isotope analysis conducted on the 'cemented organic residues' is consistent with modern reference samples of blubber and oil from seal and whale. These data provide clear analytical evidence of the function of slab-lined pits in the archaeological record and suggest widespread exploitation of marine mammals for producing oil for heating, lighting and myriad other uses in the past.