Y. H. Tu

Out-of-Plane Seismic Behavior of Unreinforced Masonry In-filled Walls

In Taiwan, un-reinforced masonry (URM) was a common type of construction for low-rise buildings due to their low cost and ease of construction. At 1970s and 1980s, an improved type known as “confined masonry” became the mainstream. Confined masonry consists of pre-laid URM brick walls and post-constructed reinforced concrete (RC) boundary beams and columns. It is believed that the RC boundary elements provide confinement to the walls because of shrinkage of concrete. Usually the URM walls in confined masonry are 1-brick thick (24cm), but a confined masonry building is not allowed to exceed 3 stories or 10m high by the Taiwan Building Code. So after 1990s, URM walls are mostly used as pot-laid partition walls for RC buildings. However, there are still many existing confined masonry buildings, include residence, school, and public buildings in Taiwan. Former researches have confirmed the in-plane seismic capacity of URM walls. But in typical school and street side buildings that only have walls in one direction, the out-of-plane direction of the walls becomes the weak direction and the walls fail in their out-of-plane direction before the in-plane strength can fully contributed. Therefore this paper presents an experimental investigation and an analytical approach for out-of-plane behavior and strength of URM walls in-filled in RC buildings subjected to lateral force. The experimental data comes from 2 in-site push over tests of typical school buildings by National Center for Research on Earthquake Engineering.

Seismic Damage Evaluation for Low-Rise RC School Buildings in Taiwan

Earthquake damage is not only a disaster, but also an examination for the present structure engineering technique and a lesson for the future one. By collecting and investigating damage data, the correlation between ground motion and damage can be established directly and applied to earthquake loss estimation and hazard mitigation. ATC-13 report presented a methodology that has been widely used for estimating damage/loss caused by earthquake and collateral hazards. The major procedure includes facility classification, selection of ground motion characterization, and damage estimates for different types of structures under specific ground shaking intensity. Mostly the motion-damage relationship developed by using investigated damage data during a past earthquake is in the form of vulnerability function, also termed fragility curve. It predicts the probability of reaching or exceeding specific damage state for a category of buildings with given earthquake intensity. The vulnerability functions are feasible for damage loss estimate in a large region, such as a city or a state, yet scatter caused by insufficiency of detail in structure classification exists generally. The applicability of the functions to regions outside the area where it is originally developed is unclear as well. Seismic evaluation that concerns about localized structural behavior and ground motion characteristics is utilized to establish the motion-damage relationship for individual buildings. While detailed information and complicated calculation are required, higher accuracy and applicability may be expected. Vulnerability functions can also be developed by performing seismic evaluation procedure on representative type of model buildings.

Damage databank and its application to seismic assessment for low-rise RC school buildings

This article introduces a databank of school buildings damaged in the Chi-Chi earthquake. Structural properties, damage records and ground motion intensity data were collected from over 150 buildings. The databank is expected to provide samples and information for seismic research, such as derivation of vulnerability functions and validation of seismic assessment methods. The buildings in the databank show great structural similarity and typical failure behaviour. A clear relationship was also found between the damage state and number of storeys. Therefore, a simple function for assessing the seismic capacity was derived using the databank. The seismic capacity can be estimated from the summation of lateral contribution of the base floor members multiplied by a proportional factor. The function was applied to school buildings from the databank and two street-side buildings for validation. The results were conservative but reasonable. A comparison between the function and detailed seismic analysis methods also showed a good correlation. The function may be suitable for preliminary and fast seismic assessment of similar types of school buildings facing the risk of an earthquake.