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
Shear Transfer in Reinforced Concrete
Presents a study of shear transfer in reinforced concrete, that is, the transfer of shear across a plane, such as at the interface between a precast beam and a cast-in-place slab. Thirty-eight pushoff specimens were tested, some with, some without a pre-existing crack along the shear plane. The shear-friction theory was found to give a conservative estimate of the shear transfer strength of initially cracked concrete. A method is presented for the calculation of shear transfer strength in initially uncracked concrete, based on the Zia envelope to Mohr circles representing failure conditions for concrete.
HYPERGOLIC REACTION MECHANISMS OF CATALYTICALLY PROMOTED FUELS WITH ROCKET GRADE HYDROGEN PEROXIDE
Abstract The coupling of the physical and chemical processes controlling the ignition delays (τ ign ) of hypergolic propellants complicates the direct analysis of the transient ignition processes. The transport properties of both the propellants and the ambient gas, and the heat of vaporization and reaction affect τ ign and must be considered experimentally. Furthermore, since hypergolic ignition occurs, by definition, on contact, the mechanics of initial contact and subsequent mixing can affect τ ign and must also be considered. Experimental results from a study of the hypergolic ignition of a catalytically promoted fuel with rocket grade hydrogen peroxide (RGHP) are presented. Statistical analysis of the experimental data was conducted to evaluate the relative effects of RGHP concentration, initial ambient pressure, and the ambient gas on τ ign . At RGHP concentrations of less than 92% in water, stable ignition was difficult to achieve. At sufficiently high Lewis number, an oscillatory ignition process is observed. A phenomenological model comprising mixing, RGHP decomposition, fuel heating and vaporization, and auto-ignition is presented and compared to the experimental results.