CONNECTIONS FOR PRECAST CONCRETE PANELS USED FOR HIGH RISE STRUCTURES
Precast load-bearing shear wall panels are used extensively for high-rise construction because of the ease and speed of assembly, and the high quality of the precast panels. The connections between panels are extremely important since they affect both the speed of erection and the overall integrity of the structure. This paper presents the results of a five-year research program conducted to investigate the behaviour and the capacity of nine connection configurations used for precast load-bearing shear wall panels subjected to monotonic shear loading. The paper also includes results of dry-packed connections subjected to reversed cyclic loads equivalent to earthquake loads. Connection configurations include two types of dry-packed multiple shear keys, dry-packed plain surface, dry-packed plain surface with continuity reinforcement, dry-packed with two types of mechanical shear connectors in addition to the continuity bars, dry-packed with post-tensioning, and connections which support hollow-core slab with and without post-tensioning. Three different levels of load normal to the connection were used to determine the effects of gravity load. Rational mathematical models were developed to predict the shear capacity of the connections at the maximum and ultimate limit states. These models were found to be in good agreement with the experimental results. The research findings of this investigation were implemented in the design and construction of three 32-stories apartment buildings in Winnipeg, Manitoba. The connections considered in this study provided significant savings in construction time and cost. 1 Professor, Civil Engineering Department, University of Manitoba 2 Graduate Student, Civil Engineering Department, University of Manitoba 3 Doctoral Candidate, Civil Engineering Department, University of Manitoba Rizkalla West Soudki, Connections for Precast Concrete Panels CONNECTIONS FOR PRECAST CONCRETE PANELS USED FOR HIGHRISE STRUCTURES S.H. Rizkalla, J. West and K.A. Soudk
Auxiliary Reinforcement in Concrete Connections
A simple but powerful method for the design of connections in precast concrete is introduced. The method is based on a physical model of behavior, rather than on curve-fitting to empirical data. It is thus suitable for a wide variety of connection problems, as well as for connection geometries not covered by previous tests. When properly used, this approach results in reliable, ductile connections which do not suffer from the various types of distress all too common in precast connections. The concrete is assumed to crack in an unfavorable location, in the region of the connection. The shear-friction hypothesis is then used to determine the amount of reinforcing which must cross the assumed cracks. Shearing stresses along an assumed crack are resisted by friction. The normal force required to mobilize friction is provided by reinforcing steel, placed normal to the assumed crack. Applications to composite beams, corbels, bearing shoes, tension splices, and confinement are discussed, and a practical design example is given.
Imposing Transboundary Conservation
SUMMARY Attempts to impose regional conservation strategies from the top down without local participation are doomed to failure. Even so, this does not negate the critical importance of promoting international transboundary conservation. This paper draws on a research project which examined transboundary cooperation in the 136 complexes of protected areas that adjoin across international boundaries, examples of internationally divided ecosystems. The results of an international survey demonstrate that such transboundary cooperation is already occurring in 82% of the cases, although most of it is at relatively low levels. Analysis reveals that numerous different variables correlate with cooperation but, not surprisingly, the most important ones are distinctly human variables relating to human relationships. This strengthens the proposal that sustainability of conservation projects depends on inclusion of all stakeholders and development of a supportive constituency. While international organizations play crucial roles in educating, equipping, and facilitating transboundary conservation, they cannot impose it. International contributions are instrumental, but ultimate sustained success depends on the day-to-day involvement and efforts of those on the local level who must do the interacting.