International Concrete Abstracts Portal

Sliding failure of reinforced concrete shear walls was observed after the Chilean earthquakes in 1985 and 2010, during shaking table tests, and in many quasi-static cyclic shear walls tests. Sliding may occur along cold joints or flexural cracks that remain open due to permanent deformations induced during cyclic loading. If it occurs, sliding can significantly reduce the horizontal force resistance and change the deformation mechanism of reinforced concrete shear walls, and thereby markedly affect the seismic performance of shear wall buildings. This study provides the interaction diagrams intended to help reinforced concrete shear wall designers exclude the sliding failure mode. Regions where sliding, shear, and flexural failure modes are expected are delineated according to the shear wall shear span to length ratio, the axial force, the horizontal and vertical reinforcement ratios, and the concrete strength. These interaction diagrams are derived using a cyclic reinforced concrete wall response model that considers flexure, shear and sliding load-deformation relationships and the interaction between them. The inter-action diagram is used to develop design recommendations on how to avoid the sliding failure of reinforced concrete shear walls under earthquake loading.

This document presents research carried out in Chile for the study of the shrinkage behavior of Chilean concretes. The effect of the volume surface ratio, concrete slump, aggregate and cement type, nominal aggregate maximum size and admixture type were analyzed. A total of 82 different concrete mixtures with a mean cylinder compressive strength between 25 and 40 MPa at 28 days were studied, involving 492 test specimens. The evolution of the drying shrinkage strains was measured up to 1350 days of drying. The applicability of six different prediction models is discussed in the light of the measured shrinkage strains. The prediction of drying shrinkage with ACI-209, B3, CEB-MC90, GL2000 and Sakata 1993 and 2001 models were compared with measured results of Chilean concretes. The results showed that current shrinkage models were not adequate to predict the drying shrinkage of the tested Chilean concretes. However, it was found that for Chilean conditions the best result was obtained with the Sakata models having a coefficient of variation less than 30% when the testing data of all concretes was considered in the analysis. An appropriate methodology to carry out the updating of models was developed, based on the comparison of measured and predicted shrinkage values and the calibration of current proposed models. As a result an updated model to local conditions for use in design phase is proposed.

Following the strong earthquake in Chile on March 3, 1985, an intensive study was conducted to ascertain why the large inventory of moderate rise buildings in the coastal city of Vina del Mar performed so well during the earthquake. The major findings were that the vast majority of the buildings in this coastal city had a high wall area to total floor area ratio and that the reinforcement detailing in the boundaries of these walls were considerably less than required by U. S. codes. Analytical studies indicated that the high percentage of walls led to significantly lower drifts under severe seismic shaking, thus lowering the ductility demands on the walls. At lower levels of ductility demand, experimental results have demonstrated that wall boundaries did not need special detailing of transverse reinforcement. The findings from the series of research studies following the Chilean earthquake have led to modified U. S. design procedures that relate the need for special detailing in wall boundary elements to expected strain levels along the compression edge of the wall. The expected strain levels are determined based on the aspect ratio of the wall and the percentage of wall area to floor area used in the building.

The main characteristics of Chilean masonry construction are presented, including reinforced masonry and confined masonry. The seismic behavior of masonry is discussed, with special emphasis on the reasons for the poor performance of hollow clay brick reinforced masonry during the March 3, 1985 earthquake, compared with the rest of Chilean construction. The codes available for structural design are analyzed, including the development of the revised version of the seismic code to prevent damage in future earthquakes, and preparation of the draft for the design of confined masonry. Finally, the research done in Chile to develop the code provisions for the design of reinforced masonry structures is summarized.