Search

The cenozoic sediments cover of western central Atlantic oceanic floor was cored at about 5 000 m depth, close to the deformation front of the Barbados Accretionary Prism. Good preservation of sedimentary structures and high recovery rate allowed the recognition and study of hemipelagic calcareous or siliceous clays and muds, with or without interbedded airfall volcanic ash beds, and with or without interbedded coarser deposits coming from lateral inputs. The latters are either calcareous fine-grained turbidites coming from local shallower oceanic areas, or terrigenous and calcareous (more hypothetical) contourites (reworking turbidites) related to bottom currents running along the South-America margin. Fluid-escape veinstructures, related to dewatering process - upward, vertical to almost horizontal advection - were identified, especially in relation with the beginning of offscraping stress in early Miocene incipient décollementhorizon. Twenty-four color print photos of splitted cores are presented; the macroscopic features they show are commented and discussed. La couverture sédimentaire cénozoïque du plancher océanique de l'Atlantique Central occidental a été carottée à environ 5000 m de profondeur, à proximité du front de déformation du prisme d'accrétion de la Barbade. Une bonne préservation des structures sédimentaires et un taux de récupération élevé ont permis la reconnaissance et l'étude d'argilites et shales hémipélagiques, calcaires ou siliceuses, localement intercalées de lits de cendres volcaniques, et auxquelles s'ajoutent des niveaux plus grossiers attribués à des apports latéraux. Ces derniers consistent, soit en turbidites calcareuses à grain fin provenant de hauts-fonds océaniques proches, soit en (plus hypothétiques) contourites calcareuses et terrigènes (remaniant des turbidites) attribuées à l'activité de courants profonds longeant la marge sud-américaine. Des veinesd'échappement de fluides - advection verticale ascendante, à presque horizontale - ont été identifiées, particulièrement en relation avec la naissance des contraintes d' offscrapingau sein des sédiments Miocène inférieur, siège du futur décollement. Vingt-quatre photographies couleurs de carottes sont présentées; les structures macroscopiques qu'elles montrent sont commentées et discutées.

Low-rise buildings are typically designed with shear walls and horizontal diaphragms to resist lateral load during windstorms and earthquakes. Although seismic performance and lateral load resistance behavior are generally well-understood for light-frame wood construction, this is not true for log construction. Research is needed to characterize log shear wall behavior subject to racking loads, and to develop recommendations for designing log walls to resist lateral loads from seismic or wind events. Monotonic and reverse-cyclic tests were conducted on log shear walls with 1:1,2:1, and 4:1 aspect ratios. These walls showed higher resistance than conventional light-frame shear walls and similar hysteretic behavior to concrete and masonry shear walls. Log walls withstood large in-plane displacements without significant load reduction using lateral bracing typical of that used for light-frame wall testing; however, the test procedure would be improved by providing full-wall support to resist out-of-plane displacements of log shear walls. Design recommendations were developed based on the experiments reported herein. DOI: 10.1061/(ASCE)ST.1943-541X.0000035 CE Database subject headings: Shear walls; Seismic effects; Wood structures; Cyclic loads; Timber construction. Author keywords: Shear walls; Seismic performance; Log homes; Log walls; Cyclic loading.

The log building industry favors simple to install mechanical connections between log layers, also referred to as log courses, to facilitate fast and efficient construction. In active seismic regions, lag screws are commonly used: however, research is lacking on how these connections between log courses perform in monotonic and reverse-cyclic loading scenarios. For the current study, 406-ram-long logs were used to fabricate connection test specimens in a single-shear configuration to mimic a typical lag screw layout used in log shear wall construction. The intent of this study was to develop baseline data on these connections to relate log connection performance to full-scale log shear wall performance. A preliminary study of four commonly used lag screws of different sizes was conducted to assess the monotonic performance within log connections. Predictions of design capacities were calculated using the National Design Specification for Wood Construction which is based on derived equations from the European yield model. Predicted NDS design capacities were compared to experimental data. Design recommendations for deriving appropriate fastener spacing were provided along with fabrication parameters that were based on observed failure mechanisms. Tested connections exhibited high ductility, which is considered a positive attribute for seismic resistance, although reverse-cyclic tests revealed failures due to low-cycle fatigue of the lag screws, leading to prevalent cyclic stiffness degradation as displacements were increased. CE Database subject headings: Connections; Cyclic loads; Shear walls: Wood structures. Author keywords: Connections; Lag screw: Log structures; Wood structures. DOI: 10.1061/(ASCE)0899-1561 (2010)22:1(88)