Building Should be Light

nisee


	*National Information Service for Earthquake Engineering* *University of California, Berkeley*


	It is of utmost importance that in seismic-resistant design the designer recognizes from the beginning that the dynamic forces in a structure can be controlled by proper selection of its structural system and by the amount and distribution of its reactive masses (masses that will react to the shaking of the building foundation). The smaller the reactive masses, the smaller the earthquake forces (inertia forces). The use of unnecessary masses should be avoided; any mass used in the building should have a seismic-resistant function. Damage due to the use of unnecessary masses are illustrated in Slides J59 and J60 for non-engineered buildings and in Slides J61-J64 for engineered buildings.


	J5 9. Damage to a wooden house due to a heavy roof supported on a flexible frame. 1971 San Fernando Earthquake.


	J60. Damage to the old portion of the Olive View Hospital in the 1971 San Fernando Earthquake. This building had a very heavy tile roof supported on unreinforced brick masonry and was neither designed nor detailed to resist seismic effects.


	All of these old buildings suffered significant damage and were subsequently demolished. The lessons from such damage are clearly to avoid the use of unnecessarily heavy roofs and unreinforced masonry.




		J61. Elevation of one of the wings of the Olive View Hospital Treatment and Care Building, illustrating the presence of unnecessary masses, 1971 San Fernando Earthquake.


	Note the heavy earthfill (0.46 m) requiring a heavy slab in Slide J61. This was located at a floor level where significant discontinuity in stiffness and strength existed in the lateral structural system [23]. As a consequence of this unnecessary mass and of the structural discontinuities, this wing of the building suffered the significant damage illustrated in Slides J62-J64.


	J62. Building of Slide J61, showing the collapse of the ground roof supporting the heavy earthfill for the garden. The collapse of the roof was due to shear failure in the columns supporting the roof. Note also that the shear failure of the supporting columns caused the precast concrete facade panels to fall from the spandrel girder on the sidewalk because of poor connections of the non-structural panels [23].


	J63. Building of Slide J62. Close-up of the failure of the roof supporting the garden. Note the heavy earthfill and roof slab with its watertight membrane that was needed to support the garden soil. Note also the distorted and disrupted (distressed) corner column, and how the pounding of the main building against the only stairtower that remained standing caused this tower to tilt [23].


	J64. Building of Slide J62. Close-up of the failure of the roof slab supporting the garden shown in Slides J61 and J62. Note the structurally unnecessary mass of the soil required for the garden, as well as the waterproof membrane. Note also at the top of the slide the distress in the beam-column joint at the floor above the garden roof [23].


	The University of California, Berkeley Copyright 1997, The Regents of the University of California. Structural Engineering Slide Library, W. G. Godden, Editor Set J: Earthquake Engineering, V. V. Bertero


	Site Design: Vivian Isaradharm, Oct. 97. Mail to: eerclibrary@berkeley.edu