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 explores both flexural and shear behavior of carbon fiber-reinforced polymer (CFRP) strengthened reinforced concrete (RC) beams. For flexural strengthening of RC beams, a total of ten large-scale beams were tested to failure under monotonic and cyclic loads. The beams were originally designed as wither under-reinforced or almost over-reinforced concrete beams. The present experimental results show that externally bonded CFRP strips to the tension face of the beam is an effective technique for repair and retrofit of RC beams under various loads. This study also shows that ductility of CFRP strengthened beams, in particular for a shorter beam, is adequate if the beam is properly designed and the CFRP strips are properly anchored. Five RC beams without shear reinforcement were also cast for studying shear strengthening of RC beams. Results of test demonstrate the feasibility of using externally applied, epoxy-bonded CFRP system to restore or increase the shear capacity of RC beams. The CFRP system can significantly increase the serviceability, ductility, and ultimate shear strength of a concrete beam, thus restoring beam shear strength using CFRP is also a highly effective technique. An analysis and design method for shear strengthening of externally bonded CFRP has been proposed as well.

During the last decade dozens of concrete bridges were raced in The Netherlands that had suffered from alkali-silica reaction (ASR). Since the bridge decks were not provided with vertical reinforcement, their shear capacity fully depends on the concrete tensile strength. To study the effect of ASR on the shear capacity, six beams sawn from two viaducts were loaded in bending till failure. Failure occurred at about 75% of the theorectical shear capacity of undamaged concrete. Contrary to what normally would be expected, failure was not attended with the development of inclined bending cracks, but with diagonal cracks that originated at mid-depth. Hence, the tensile strength reduction due to ASR resulted in a change of the failure mechanism from flexural shear into diagonal shear. To explain the observed crack development and shear strength, the influences of a longitudinal compressive stress due to the restraint of ASR-induced expansion and an orientation dependent tensile strength were taken into consideration.