DEM Algorithm for Progressive Collapse Simulation of Single-Layer Reticulated Domes under Multi-Support Excitation

In this paper, the Member Discrete Element Method (MDEM) is modified and perfected for three aspects: the algorithm itself, loading and computational efficiency, and to accurately and quantitatively simulate the progressive collapse for large-span spatial steel structures. In addition, the corresponding computational programs are compiled. First, from the perspective of the method, a meshing principle for discrete element models is determined, a treatment for material nonlinearity and strain rate effect is proposed, and a damping model is established. Next, the Displacement Method is introduced to determine the multi-support excitation for the MDEM, and then motion equations of particles under multi-support excitation are derived. On this basis, the specific process of gravitational field loading is presented. Furthermore, parallel implementation strategies for the MDEM based on OpenMP are constructed. Finally, the collapse simulation of a 1/3.5-scaled single-layer reticulated dome shaking table test model under multi-support excitation is carried out. The comparison demonstrates that the ultimate load and failure mode as well as the complete collapse time of the numerical results are consistent with the experimentally measured responses, and the configuration variations from member buckling and local depression until collapse failure are fully captured. Moreover, the displacement time-history curves obtained using MDEM are almost identical to the experimental measurements, and there is a nuance only in the amplitude. It is verified that MDEM is capable of precisely addressing the collapse failure for large-span spatial steel structures. Additionally, the failure mechanism for structures of this type is naturally revealed.     

Plasters from Different Buildings of the Sacred Precinct of Tenochtitlan (Mexico City): Characterization And Provenance

In this work, we present the results of the characterization of 20 lime plaster samples taken from the Sacred Precinct of Tenochtitlan (Mexico City), the ancient capital of the Aztec empire. The samples come from different buildings of this precinct (A, B and D) and from the west façade of phase VI of the Templo Mayor pyramid. The objective of the work is to characterize the plaster samples, to understand the raw materials used, and to evaluate the presence of similarities and differences among the samples in the building techniques and raw materials employed. All the samples were studied with OM, SEM–EDS and LA–ICP–MS. The study provided evidence of the plastering and replastering practice in the same constructive phases. The results of the analyses showed the existence of important similarities and differences among buildings and constructive phases in the Sacred Precinct. In order to understand the provenance of the limestone used in the plasters, the lumps and the binder of the samples were analysed. The results were compared with those of the limestone outcrops located in central Mexico. The provenance study showed that all the limestone used in the construction of the analysed buildings of Tenochtitlan's Sacred Precinct comes from the Tula region.     

Archaeocyaths from Yorke Peninsula,South Australia and archaeocyathan Early Cambrian zonation

Zhuravlev, A. Yu., & Gravestock, D. I., 1994:03:28. Archaeayaths from Yorke Peninsula, South Australia and archaeocyathan Early Cambrian zonation. Alcheringa 18, 1–54. ISSN 0311-5518.

Two assemblages of archaeocyaths are documented from Lower Cambrian outcrops and drillholes on Yorke Peninsula. South Australia. The older assemblage (11 species) occurs in the uppermost Kulpara Formation and conformably overlying basal Parara Limestone, and is equivalent to Lower Faunal Assemblage II in the Flinders Ranges. The younger assemblage (28 species plus Acanthhcyathus and Rodiocyathus) occurs in the Koolywurtie Member near the top of the Parara Limestone. Equivalent taxa are widespread in the Flinders Ranges, western New South Wales and Antarctica. Archaeocyathan distribution is now sufficiently well known to propose three assemblage zones and two informal assemblages for regional correlation. No new taxa have been added, but Erugatocyathus scutatus (Hill) and Pycnoidocyathus latiloculatus (Hill), hitherto known only from Antarctica, are found in the upper assemblage on Yorke Peninsula. Irregular archaeocyathan systematics are discussed, the ontogeny of Archaeopharetra irregularis (Tylor) clarified, and Kruseicnema Debrenne. Gravestock & Zhuravlev, represented by K. gracilis (Gordon), is fully described.     

Lower Devonian ischnacanthid fish (Gnathostomata: Acanthodii) from the Taemas Limestone,Lake Burrinjuck,New South Wales

Dentigerous jawbones of ischnacanthid acanthodians from the Lower Devonian Currajong Limestone Member and the lower part of the Bloomfield Limestone Member of the Taemas Limestone (Murrumbidgee Group: early Emsian) in the Murrumbidgee valley at Good Hope, Taemas district, and the Goodradigbee valley at Wee Jasper are described. Three taxa of Taemasacanthus are recognized: T. sp. cf. erroli Long, 1986; T. narrengullenensis sp. nov. and T. cooradigbeensis sp. nov. Fragmentary fin spine remains and scales are also described.     

A study of limestone from the Longmen Grottoes of Henan province,China by neutron activation analysis

The Longmen Grottoes, also known as the Longmen Caves or Dragon's Gate Grottoes, are located near the city of Luoyang, Henan province, China. The grottoes were carved into the limestone cliffs during the period from 493 AD to 1130 AD. Limestone samples from different areas within the grottoes were analyzed by neutron activation analysis (NAA) to determine the concentrations of major, trace and rare-earth elements (REEs). Three compositional groups were identified corresponding to different areas within Longmen Grottoes. X-ray diffraction (XRD) was performed on a few samples to obtain information about the mineral structure. The results indicate that rocks in the northern area are comprised of dolomite, while rocks in the middle and southern areas are comprised of limestone. The NAA results provide information useful for identifying and relocating fragments from the grottoes that may have lost their identity. The compositional data also provides important clues regarding the geologic history of the limestone formation at Longmen.     

U-series dating of soda straw stalactites from excavated deposits: method development and application to Blanche Cave, Naracoorte, South Australia

This study aimed to further test the method, reported by St Pierre et al. (2009), to develop robust chronologies of deposits in limestone caves through U/Th (Uranium/Thorium or U-Series) dating of soda straw stalactites. The chronology of fossil bearing deposits at Blanche Cave was further constrained with thermal ionisation mass spectrometry (TIMS) U/Th dating of 17 additional soda straw stalactite samples, and results were compared to recalibrated ¹⁴C ages of charcoal. The results support the assertion that soda straw stalactites can provide ages close to the time of sediment deposition and may be used as reliable chronological markers, particularly for periods reaching or beyond the radiocarbon dating limit. The application of an enhanced cleaning technique facilitated the reduction of detrital Th in samples, significantly increasing age accuracy and precision. Additionally U/Th age accuracy and precision was increased through the application of site-specific measured U/Th ratios to correct for the detrital ²³⁰Th component in samples.     

Early Cambrian endolithic algae

Phosphate fillings of the tunnels made by endolithic micro-organisms in the shells of Early Cambrian molluscs have been observed on phosphatic internal moulds at several sites. The best preserved examples are from the shells of the gastropod Yuwenia bentleyi from the Parara Limestone of South Australia. Three distinct types of borings are found in these shells: long unbranched tunnels that are either about 10 µm or 3 µm in diameter, and short vertical holes. The nature and distribution of the borings suggest that they were made by photosynthetic algae rather than fungi.     

Expanding the utility of Uranium-series dating of speleothems for archaeological and palaeontological applications

Uranium-series (U-series) dating of speleothems is frequently used for palaeoclimate studies but its archaeological and palaeontological applications are limited to stratigraphically significant speleothem formations, such as flowstones, to provide maximum and minimum temporal points. This study targeted soda straw stalactites for U-series dating. In contrast to other speleothem formations, soda straw stalactites are fragile, have typically short life spans (usually only years but rarely up to a few hundred years) and are frequently incorporated into cave deposits. Results of thermal ionisation mass spectrometry (TIMS) U-series dating of soda straw stalactites from palaeontological excavations at Blanche Cave, South Australia, show that small, dense, clean straws tend to yield ages closest to the time of stratigraphic deposition. A correlation between soda straw U-series ages and radiocarbon ages of charcoal from the site is shown. Multiple soda straw age determinations for a single stratigraphic unit are required in order to verify age concordance. In conjunction with other dating methods, U-series dating of soda straw stalactites may help to significantly constrain the age of stratigraphic units and associated archaeological and palaeontological deposits in order to provide more robust chronologies. Here we advocate the collection of soda straw stalactites at future excavations of limestone cave sites.     

Archaeological carved slabs of the Langobard art in churches of Peligna Valley and Spoleto (Italy): provenance of the stones

In this study we investigate the provenance of the limestone and marble used to made carved slabs today placed in three churches located in Raiano and Vittorito (Peligna Valley, Abruzzo, Italy) and in Spoleto (Umbria, Italy). The slabs, representative examples of the Langobard art (Middle Ages), are dated approximately from 8th to 9th centuries A.D. and have the same pattern in terms of decoration, suggesting a progressive expansion of Langobards in central and southern Italy, after the foundation of the Pavia Kingdom.     

Preliminary geochemical assessment of limestone resources and stone use at Maya sites in the Three Rivers Region,Belize

The carbonate bedrock of northwestern Belize is poorly understood from the standpoint of both geochemistry and the use of stone in prehispanic Maya sites for buildings and monuments. The friable nature of the rock in this topographically rugged area makes it especially difficult to distinguish monuments from bedrock spall, as little carving, if any, survives, and identification rests on location and positioning. The research presented here analyzed 63 limestone samples collected from two sites in the Three Rivers Region of Belize. ICP-MS and ICP-AES were used to characterize the major, minor, and trace element chemistry of the limestone bedrock of the region and determine the amount of geochemical variability. Another important objective was attempting to trace the movement of monument stone and determining whether it was imported from outside of the sites. Bedrock, quarries, and possible monuments were all sampled for these purposes. Bedrock proved to be similar across wide areas. However, at Chawak But'o'ob, along the flank of the Rio Bravo, changes downslope in Mg concentration suggest a leaching of the bedrock by meteoric waters based on differences in porosity. At Maax Na, a hilltop site, in contrast, such leaching is not as apparent. Many monuments at both sites were found to be composed of stone similar in chemistry to the local bedrock, including several of the identifiable stelae. However, our analyses also revealed that a few monuments at Maax Na were made of material with a different chemical composition, apparently from stone imported to the site. These results suggest that the Maya deliberately selected certain types of limestone for certain purposes, and may even have traded in non-local rock. Overall, the methods used in this pilot study indicate there is real potential in more intensive, regional assessments of the materials used at archaeological sites, even in areas where the local stone does not have a distinctive geochemical signature.