Compressive Membrane Capacity Estimates in Laterally Edge Restrained Reinforced Concrete One-Way Slabs

The load capacity of laterally restrained reinforced concrete one-way slabs is estimated in compressive membrane theory with use of a midspan deflection. However, the midspan deflection estimates exhibit large variability. The point of peak thrust leads to a more accurate index of the peak load capacity than midspan deflection. The calculation of the thrust within the compressive membrane theory is a maximum when the slab's axial shortening and the outward support movement are a maximum. The use of the peak thrust to select the peak capacity, when combined with a modification to Park and Gamble's (1980) compressive membrane theory, provides an improved overall correlation to the experimental data for a large range of span-to-thickness ratios (2.7 < Lih <28.3). In this study, peak midspan deflection estimates were developed to define the peak point of the load-deflection curve. The slab's axial concrete compressive strength and the peak concrete compressive strain are used within a curvature and geometrically based deflection equation, to predict the midspan deflection. The post-peak trough and ultimate points are related empirically to the tensile membrane curve, and the generated load-deflection curve compares well with the experimental data. A simple compressive membrane load capacity estimate for laterally restrained reinforced concrete one-way slabs is developed for field use. The estimate uses the axial force-moment interaction equations and a ratio for the peak thrust to the slab's axial capacity, and results in an accurate estimate of the peak compressive membrane capacity using yield line theory.U.S. Army.Department of Civil and Mechanical Engineering; U.S. Military Academy

Designing Artifacts for Systems of Information

Part 6: IS DesignInternational audienceThis paper reports an exploratory study of information systems (IS) design professionals that offers insight into the evolution of the systems concept in systems design practice. The analysis distinguishes the current object of this design effort as systems of information (SI). SI differs from IS in that SI seeks to maintain the necessary degree of integrated systematicity while retaining or acquiring the necessary technology. IS, in the past, had an implied capacity to build a complete system from the ground up. SI has an implied constraint that certain technological components must be “taken as given” and the design problem becomes one of maintaining an ideal socio-technical system as the various technologies evolve within and around the system

The age and origin of the Pacific islands: a geological overview

The Pacific Ocean evolved from the Panthalassic Ocean that was first formed ca 750 Ma with the rifting apart of Rodinia. By 160 Ma, the first ocean floor ascribed to the current Pacific plate was produced to the west of a spreading centre in the central Pacific, ultimately growing to become the largest oceanic plate on the Earth. The current Nazca, Cocos and Juan de Fuca (Gorda) plates were initially one plate, produced to the east of the original spreading centre before becoming split into three. The islands of the Pacific have originated as: linear chains of volcanic islands on the above plates either by mantle plume or propagating fracture origin, atolls, uplifted coralline reefs, fragments of continental crust, obducted portions of adjoining lithospheric plates and islands resulting from subduction along convergent plate margins. Out of the 11 linear volcanic chains identified, each is briefly described and its history summarized. The geology of 10 exemplar archipelagos (Japan, Izu-Bonin, Palau, Solomons, Fiji, New Caledonia, New Zealand, Society, Galápagos and Hawaii) is then discussed in detail