International Concrete Abstracts Portal

SP128 Leading world experts met in Hong Kong to participate in The ACI conference on Evaluation and Rehabilitation of Concrete Structures and Innovations and Design. The specific purpose of the Conference was to disseminate technical information on emerging concrete technology in the Pacific rim region. You can review the results of that timely event in a two volume document comprised of 90 technical papers. Volume I contains paper dealing with materials. Topics include: high elastic surface coatings, concrete deterioration on high chloride and sulfate environment, nondestructive testing, impact-echo technique, fiber reinforcement, injectable cementitious materials, and case studies. Volume II is comprised of papers pertaining to design aspects. Topics include: concrete for offshore structures, performance of structural repairs, design of high-strength and reinforced concrete structures, design of beams and columns, and case studies.order.

A major rehabilitation of the reinforced concrete approach viaduct to the Pattullo Bridge has been successfully completed over the last nine years. A condition inspection revealed that extensive cracking had taken place over the years,especially at the bridge girder ends due mainly to frozen bearings. A program of bearing replacement was carried out at all girder ends along with seismic improvements and general concrete repairs. An elaborate falsework system was designed which was easily adaptable to the varying geometry along the viaduct. Load transfer to the falsework to implement the rehabilitation was achieved using a hydraulic jacking system. The work was carried out in a series of six contracts and the project was completed without any bridge traffic closures during the assignment.

An intense fire in the antioxidant plant of a chemical factory near Bombay caused extensive damage to the reinforced concrete frame of the building as well as to the flooring, equipment, fixtures, and fittings. Consultants were appointed to investigate the damaged structure and later to design and supervise the rehabilitation work. After the preliminary investigation, the consultants decided that it was not necessary to demolish the structure, as long as it was possible to restore the structural members at a reasonable cost and within a short time span. In addition to visual inspection and sounding, extensive nondestructive tests were conducted to determine the extent of damage and the residual strength of the important load-carrying members of the structures. The findings of the investigations were analyzed and the restoration system was designed by the consultants. The paper outlines the considerations that led to restoration of the structure in preference to demolition, the details of investigations, the analysis of the findings, and the successful rehabilitation techniques that followed.

The crest of Kakabeka Falls, a major tourist attraction near Thunder Bay, Ontario, had changed rapidly within 15 years. Geotechnical evaluation had concluded that, due to the geometry of the rock formation, there was little continuous cap-rock beyond the crest of the falls. Undercutting by water and subsequent ice jacking and freeze-thaw action was eroding the remaining cap-rock. Without prompt remedial work, the falls would degenerate to rapids over 50 years. Rapid recession of the falls also threatened the foundations of two bridges. In 1988 and 1989, remedial works were undertaken to stabilize the erosion process and improve the appearance of the falls. Concrete mixes were designed using powdered color dyes to duplicate the color and appearance of the reddish brown cap-rock and black hales. The crest of the falls was reconstructed incorporating a weir which spread the water flow evenly across the width of the falls. Special formwork and hand-finishing techniques were used to texture the concrete surface to match the existing rock. Two years in planning and eight weeks in construction, the project successfully restored the falls to its former beauty.

The quality of in situ concrete construction in developing countries is affected by a number of factors. These factors may include absence of national standards and codes of practice, use of approximate methods of analysis and design, substandard materials, poor construction practices, and inadequate quality control and inspection procedures. Defects and failures may occur due to these factors that may affect the useful life of a structure. This paper evaluates the seismic behavior of reinforced concrete buildings designed and constructed by following the usual procedures in Saudi Arabia. Behavior of typical reinforced concrete frames is investigated by using nonlinear time-history analysis and Takeda hysteresis model. The factors considered in the study include compressive strength of concrete, detailing of reinforcement, and size and orientation of columns in the frame. The results show that while the frames remained elastic when subjected to an earthquake of low intensity (0.09), they developed inelastic behavior exceeding the ductility capacity at some point when subjected to an earthquake of moderate intensity (0.24). It has been also found that the orientation of columns, particularly the interior ones, has a substantial effect on the building resistance to earthquakes. The compressive strength of concrete, through it has a crucial effect on the overall behavior and durability of a building, did not significantly affect the primary moment-curvature relationships of under-reinforced member sections considered in the study when its specified value was lowered by 20 percent. A critical study of reinforcement detailing shows clearly an urgent need for implementing a national code of practice for concrete buildings in Saudi Arabia.