Damage and Implications for Seismic Design of RC Structural Wall Buildings

Abstract

In 1996, Chile adopted NCh433.Of96, which includes seismic design approaches similar to those used in ASCE 7-10 (2010) and a concrete code based on ACI 318-95 (1995). Since reinforced concrete buildings are the predominant form of construction in Chile for buildings over four stories, the 27 February 2010 earthquake provides an excellent opportunity to assess the performance of reinforced concrete buildings designed using modern codes similar to those used in the United States. A description of observed damage is provided and correlated with a number of factors, including relatively high levels of wall axial load, the lack of well-detailed wall boundaries, and the common usage of flanged walls. Based on a detailed assessment of these issues, potential updates to U.S. codes and recommendations are suggested related to design and detailing of special reinforced concrete shear walls.

Análisis del período y desplazamiento de edificios de hormigón armado considerando distintos grados de rigidez en sus elementos resistentes

“…Considerando que los daños ocurridos en los muros de hormigón armado, producto del terremoto del 27 de febrero de 2010 se localizaron en los muros esbeltos del primer subterráneo y primer piso (Wallace et al, 2012), es que se considera como muros agrietados aquellos muros esbeltos (relación de aspecto igual y mayor a 3) de los tres primeros niveles de pisos en todos los edificios estudiados, excepto el Pérez Zujovic, donde se considera cinco niveles de pisos de muros agrietados dado el mayor número de pisos respecto a los otros. Los muros restantes son considerados en condiciones no agrietados.…”

“…Estas fallas se originaron debido a grandes solicitaciones en las zonas más comprimidas de los muros sumadas a problemas en el detallamiento de elementos de borde y en la disposición del refuerzo transversal. Esto último no permitió proveer un confinamiento adecuado al hormigón ni restricción al pandeo de las barras longitudinales (Alfaro, 2013;Wallace et al, 2012).…”

Effect of axial compression on ductility design of RC walls

“…Higher axial compression tends to increase the shear strength of all types of RC walls, in particular squat RC walls, as shown in Figure 9(c). This is because axial compression can enhance not only the shear strength of walls but in some cases also the moment resistance (Kappos and Penelis, 1996;Wallace et al, 2012).…”

“…Modern complex structures and super-high-rise skyscrapers, both in Chile and in other parts of the developed world, are also often characterised by high compression forces in very slender members, as a consequence of architectural designs that maximise clear floor heights and usable floor areas. Recent studies (Su and Wong, 2006;Wallace et al, 2012) have indicated that structural walls in modern high-rise buildings would sustain an axial compression ratio (ACR) of 0·4 or above, which is much higher than the typical range of 0-0·2.…”

“…Hence the actual seismic responses of RC walls under a significant axial force can be complicated, given that interactions between different axial force effects and failure mechanisms further complicate the situation. Nonetheless, both research studies (Su and Wong, 2007;Zhang and Wang, 2000) and disastrous earthquakes (Adebar, 2013;Wallace et al, 2012) have repeatedly revealed that the adverse effect of axial compression on RC walls generally overwhelms the benefits introduced.…”