International Concrete Abstracts Portal

ACI 437 provides requirements for the performance of large scale structural load tests. These include mapping and monitoring cracks, shoring, and actual application of the load in a minimum of four separate increments. Any walls or other improvements that might provide support to the element being evaluated must be cut free. Deflection is to be monitored and load deflection curves prepared for each increment, and the full load is to remain in place for a minimum of 24 hours. Straightforward as these requirements appear, they can present a daunting task for those actually conducting the test. Where reaction is available for simple tests such as for beams and girders, either hydraulic jacks or pneumatic bags can be used to supply the load. Where large horizontal areas such as floors are involved, such simplicity is often not possible and some form of physical mass must be used. In areas that are open, the load can be applied with a crane, but on the interior of structures it must often be applied by hand or with the aid of small handling equipment, which severely limits the choice of load media. Whereas load tests are usually designed by structural engineers, the actual application is performed by construction workers. In order to assure optimal performance, it is imperative that both work together during the design as well as the application. The schedule and logistics of the loading operation must be well thought out prior to the actual work. Obviously, safety of the overall operation must be assured. Consideration must be given to not only the potential failure of the element being evaluated, but damage to other portions of the structure as well. This can include overloading of other elements during movement and handling of the load media, or damage by flooding where water is used. The logistics of load tests are discussed in detail, including preloading surveys and documentation, provision of shoring and other required preparation of the test area, selection of the load media and its application, and the required monitoring and control.

A unique test set-up is described which facilitates the testing of full scale continuous reinforced concrete flat slabs with spans up to 6 m under vertical loading. In the past, tests were done either on full scale isolated slab-column connections or on reduced scale slab systems. Both test methods are not ideal to establish the shear behaviour of flat slabs. The test set-up which was designed and built at the University of Calgary avoids the major sources of error by providing realistic boundary conditions along lines of zero shear of part of a slab centered about an exterior column and the adjacent interior column. The boundary conditions are created by boundary frames which allow vertical displacement but no rotation along the lines of zero shear. By using this set-up the effect of moment redistribution as well as membrane action can be determined. In this paper the boundary frames and their effects on the behaviour of the tested slab were evalutated experimentally and theoretically by finite element analysis. Based on the results, modifications to the original boundary frames were made.

The construction of submerged or partially submerged pile caps often requires the use of a cast-in-place unreinforced slab referred to as a seal slab. This slab is cast underwater around piling and inside sheet pile walls to form the bottom of a cofferdam and withstand upward hydrostatic pressure. As the seal slab is only used for a relatively short period of time during placement of the reinforcing steel and concreting, its design has received little attention in refinement tending toward conservatism. Therein, the magnitude of available bond strength between the seal slab and piling to resist the uplift pressure has been poorly quantified and largely underutilized. This paper presents experimental results from 32 full-scale tests conducted to define the interface bond between cast-in-place concrete seal slabs and piling (sixteen 356 mm square prestressed concrete piles and sixteen 356 mm deep steel H-piles). Three different concrete placement environments--dry, fresh water, and bentonite slurry--were evaluated using the dry environment (where no fluid had to be displaced by the concrete) as the control. The effective seal slab thickness was varied between 0.5d and 2d, where d was either the width or depth of the pile section. Both "soil-caked" and normal, clean pile surfaces were investigated. Additionally, four of the sixteen concrete piles were cast with embedded gages located at the top, middle and bottom of the interface region to define the shear distribution. The study showed that: (1) significant bond stresses developed even for the worst placement environment, and (2) the entire embedded surface area should not be used in calculating the pile-to-seal slab bond capacity. Current design values in the Florida Department of Transportation specifications reflect the findings of this study.

This paper presents the results of an investigation on the fatigue performance of two full-size pre-cracked prestressed concrete bridge girders. One AASHTO Type III girder and one AASHTO Type V girder were tested under 1,000,000 cycles of repeated service load intermingled with 2,500 cycles of repeated overload. The behavior of the girders was monitored after each 200,000 cycles of service load as well as each 500 cycles of overload. At the end of the fatigue tests, the girders were tested to failure to determine their ultimate strengths. The test results demonstrated that the fatigue loadings had virtually no effect on the girder behavior. The girders showed no degradation in stiffness or strength after 1,002,500 cycles of fatigue loading. Both girders showed considerable ductility, and their ultimate loads and maximum deflections exceeded the predicted values.

The structural behavior of reinforced concrete framed shear walls subjected to reversed cyclic lateral loading were studied by testing ten large-scale specimens, including high-, middle-, and low-rise shear walls. An analytical model was also proposed to predict the behavior of the tested specimens. The parameters of concrete strength and vertical stell ratio of walls were investigated. The predicted maximum load and corresponding displacement, and load-displacement curves satisfactorily agreed with the experimental results. In addition, the experimental results showed that the failure mode of high-rise shear walls was flexural; their ductility factors were greater than those of low-rise shear walls; their displacements were also greater. The mid-rise shear walls failed by a combination of both flexure and shear. The experimental results also showed that the maximum loads were greater for specimens with higher concrete strength or higher verical stell ratio. The vertical stell ratio of walls has more significant effect on flexure-predominant walls. However, it is insensitive to shear-critical walls. It was found that the simple model develped from previous small-scale tests could not closely reflect the experimental results of all specimens. This suggests that the size effect needs to be taken into account in the analytical model.