International Concrete Abstracts Portal

The island of Guam is located in the Mariana Islands chain in the Pacific, approximately 3800 miles west of Hawaii. This small island played an important role in World War II, when it was occupied by the Japanese and recaptured by American forces. In 1978, the war in the Pacific National Historical Park was established to commemorate those involved in the assault and defense of the island as well as Guam's residents during the war. Approximately 100 extant military structures are located within park boundaries. As part of a National Park Service program to preserve the site and its features as an historic park, a survey was made of 12 structures including four pillboxes, four gun emplacements, two bridges, one masonry wall, and one partially submerged latrine foundation. The surveyed structures are all partially or totally constructed of concrete. Some local materials were used in construction, including coral sand, seawater, coconut logs for formwork, and chain link fence for reinforcing in some structures. An on-site investigation conducted in February, 1990, included documentation and assessment of existing conditions, preparation of measure drawings, and removal of samples for laboratory analysis. Observed deterioration included cracks, water leakage, surface erosion, corrosion of embedded steel, spalls, growth of vegetation, soil subsidence, war damage, and adverse effects from visitors. Based on the results of visual inspection and testing, the structures were evaluated and categorized in terms of deterioration and level of required intervention. This information is being used to develop recommendations for repair, stabilization, and restoration.

A six-story reinforced concrete military school building in Ankara, Turkey was severely damaged as a result of a steam boiler explosion in the basement. Damage was localized to the first and second stories. Upper floors survived the explosion with minor cracks even though three basement- and two first-floor columns, together with the connecting beams and slabs, were totally demolished. The building was repaired in 1988 in accordance with the procedure and specifications prepared by the two senior authors. The most critical decision was to allow workers into the damaged building to clear the debris and to set up temporary shoring for final repair. Extensive analyses revealed that nonload-bearing partition walls prevented the collapse of the structure by acting as compression struts and thus providing the reserve strength. The rehabilitation of the building was done at a minimum cost by making intermittent openings in existing partition walls to provide continuity in the slabs that had to be recast and by the utilization of the existing reinforcement.

Strengthening of concrete structures in situ by bonding steel plates to concrete surfaces through epoxy-resin adhesives is now recognized as an effective and convenient method of improving their performance under service loads and increasing their ultimate strength. This paper presents a critical review of the structural behavior of the plated beams with emphasis on the effects of plating on serviceability and ultimate limit states. Problems of premature bond failure are described, and methods of overcoming such failures and insuring full flexural capacity, ductility, and composite action are reported. Resistance to fire hazards and other relevant design considerations are discussed.

When, what, and how should existing concrete structures be inspected? How should their real safety and serviceability, as well as their remaining service life be evaluated? When and how should they be repaired, rehabilitated, and reconstructed? When should the existing structure or some of its members be replaced with new ones? Those are essential and timely questions of both technical and economical nature to which scientists and experts all over the world search for the right answers. The purpose of rehabilitation of deteriorated structures is to reestablish their capability to accept, with the sufficient safety and the desired durability, all the effects, and to respond to all functional requirements that have been anticipated by the original design. Reconstruction has the purpose of making the existing structures, which need not be deteriorated, capable of accepting higher effects and responding to higher functional requirements compared to those anticipated by the original design. Strengthening of the existing concrete members, to be done within the reconstruction, can be realized by the decrease of the load effects (decrease of the dead load, the decrease of span, the change of the structural system), by the increase of the resistance of the members (the increase of the cross section, additional reinforcement, additional steel plates) and by the change of the state of stress (additional prestressing).

A general introduction is followed by justification of the need for and benefits of evaluation of service life of structures. It is argued that, since decisions on the part of promoters and designers are made in the environment of uncertainty, deterministic approaches are misleading. A probabilistic approach, in the form of a combination of Monte Carlo simulation and microcomputers, is recommended for its ability to address the challenge adequately and conveniently. Case studies are used to illustrate the value of the methodology through its ability to evaluate service life and costs, thereby acting as an efficient tool for aiding selection of the efficient alternative from available alternative designs and maintenance policies. The sensitivity analysis, which is an integral part of the methodology and can be applied at both the modelling and the input parameter stages, serves to point out the critical factors or issues involved and should be valuable to practitioners and researchers. An interactive and tolerant program, VENTURER is available, which places the expertise of the probabilistic analysis at the fingertips of the professionals, even if they are not familiar with statistics.