The Whittier Narrows, California Earthquake of October 1, 1987—Preliminary Evaluation of the Performance of Strengthened Unreinforced Masonry Buildings

1988 ◽  
Vol 4 (1) ◽  
pp. 197-212 ◽  
Author(s):  
T. A. Moore ◽  
J. H. Kobzeff ◽  
J. Diri ◽  
C. Arnold
Keyword(s):  
Los Angeles ◽  
Case Studies ◽  
Unreinforced Masonry ◽  
Preliminary Evaluation ◽  
Masonry Buildings ◽  
Plane Shear ◽  
Hazard Reduction ◽  
Out Of Plane ◽  
Shear Failures ◽  
Bending Failure

This report presents preliminary case studies of the performance of selected unreinforced masonry buildings during the Whittier Narrows Earthquakes. Attention is focused on buildings located in the downtown Los Angeles area which have been rehabilitated to conform with the Los Angeles hazard reduction Ordinance. There was no life loss or major injuries attributed to the response of unreinforced masonry buildings to the earthquakes. However, there was a significant number of both rehabilitated and non-strengthened buildings for which masonry peeled off upper story walls. This was mainly due to separation of the outer whythe of brick, or out-of-plane bending failure, and/or in-plane shear failures of wall piers, particularly at building corners. The falling bricks associated with these failures did present an injury hazard so it is important to investigate economical measures to minimize these hazards in future earthquakes.

Fragility Functions for Local Failure Mechanisms in Unreinforced Masonry Buildings

2021 ◽  
Author(s):  
Marco Nale ◽  
Fabio Minghini ◽  
Andrea Chiozzi ◽  
Antonio Tralli
Keyword(s):  
Failure Mechanisms ◽  
Regional Scale ◽  
Economic Loss ◽  
Unreinforced Masonry ◽  
Rigid Bodies ◽  
Local Failure ◽  
Masonry Buildings ◽  
Fragility Functions ◽  
Fragility Function ◽  
Out Of Plane

Abstract The unreinforced masonry buildings can be present frequent local failure mechanisms and represent a serious life-safety hazard as recent strong earthquakes have shown. Compared to new building, existing unreinforced masonry buildings prone to be more vulnerable, not only because they have been designed without seismic or limited loading requirements, but also because horizontal structures and connections amid the walls are not always suitable. Out-of-plane collapse can be caused by important slenderness of walls also when connections are effective. The purpose of this paper is to evaluate fragility functions for unreinforced masonry walls in the presence of local failure mechanisms considering the out-of-plane response. The wall response, very often, can be idealized as rigid bodies undergoing rocking motion. Depending on its configuration, a wall is assumed either as a rigid body undergoing simple one-sided rocking or an assembly of two coupled rigid bodies rocking along their common edge. A set of 44 ground motions from earthquake events occurred from 1972 to 2017 in Italy is used in this study. The likelihood of collapse is calculated via Multiple Stripe Analysis (MSA) from a given wall undergoing a specific ground motion. Later, the single fragility functions are suitably combined to define a typological fragility function for a class of buildings. The procedure is applied to a historical aggregate in the city center of Ferrara (Italy) as a case study. The fragility functions developed in this research can be a very helpful tool for estimating damage and economic loss for unreinforced masonry buildings and for a seismic assessment on a regional scale.

Performance of unreinforced and retrofitted masonry buildings during the 2010 Darfield earthquake

2010 ◽  
Vol 43 (4) ◽  
pp. 321-339 ◽  
Author(s):  
Dmytro Dizhur ◽  
Najif Ismail ◽  
Charlotte Knox ◽  
Ronald Lumantarna ◽  
Jason M. Ingham
Keyword(s):  
Case Studies ◽  
Unreinforced Masonry ◽  
Stone Masonry ◽  
Masonry Buildings ◽  
Failure Patterns ◽  
Reinforced Polymer ◽  
Moment Resisting ◽  
History Of ◽  
Fibre Reinforced Polymer ◽  
Building Characteristics

A brief history of Christchurch city is presented, including information on the introduction of unreinforced masonry as a popular building material and an estimate of the number of unreinforced masonry buildings in the Canterbury region currently. A general overview of the failure patterns that were observed in unreinforced clay brick and stone masonry buildings in the Christchurch area after the 2010 Darfield earthquake is provided. Case studies of the damage sustained to five unreinforced masonry (URM) buildings that were unretrofitted at the time of the earthquake, including photographic details, is documented. The performance of eight retrofitted URM buildings is then commented on, detailing the building characteristics and retrofit techniques. The case studies include the use of moment resisting frames, steel strong backs and strapping, diaphragm anchoring, surface bonded fibre reinforced polymer (FRP) sheets and cavity ties.

scholarly journals Some of the Latest Active Strengthening Techniques for Masonry Buildings: A Critical Analysis

Materials ◽  
2019 ◽  
Vol 12 (7) ◽  
pp. 1151 ◽  
Author(s):  
Elena Ferretti ◽  
Giovanni Pascale
Keyword(s):  
Stress Field ◽  
Static Analysis ◽  
Dynamic Load ◽  
Critical Analysis ◽  
Masonry Buildings ◽  
Load Bearing Capacity ◽  
Plane Shear ◽  
Out Of Plane ◽  
Active Confinement ◽  
Static Conditions

The present paper deals with the retrofitting of unreinforced masonry (URM) buildings, subjected to in-plane shear and out of-plane loading when struck by an earthquake. After an introductive comparison between some of the latest punctual and continuous active retrofitting methods, the authors focused on the two most effective active continuous techniques, the CAM (Active Confinement of Masonry) system and the Φ system, which also improve the box-type behavior of buildings. These two retrofitting systems allow increasing both the static and dynamic load-bearing capacity of masonry buildings. Nevertheless, information on how they actually modify the stress field in static conditions is lacking and sometimes questionable in the literature. Therefore, the authors performed a static analysis in the plane of Mohr/Coulomb, with the dual intent to clarify which of the two is preferable under static conditions and whether the models currently used to design the retrofitting systems are fully adequate.

scholarly journals Numerical Simulation of Unreinforced Masonry Buildings with Timber Diaphragms

Buildings ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 205
Author(s):  
Igor Tomić ◽  
Francesco Vanin ◽  
Ivana Božulić ◽  
Katrin Beyer
Keyword(s):  
Failure Modes ◽  
Unreinforced Masonry ◽  
Masonry Walls ◽  
Masonry Buildings ◽  
Seismic Behaviour ◽  
Plane Failure ◽  
Friction Resistance ◽  
Flexible Diaphragms ◽  
Out Of Plane ◽  
Equivalent Frame

Though flexible diaphragms play a role in the seismic behaviour of unreinforced masonry buildings, the effect of the connections between floors and walls is rarely discussed or explicitly modelled when simulating the response of such buildings. These flexible diaphragms are most commonly timber floors made of planks and beams, which are supported on recesses in the masonry walls and can slide when the friction resistance is reached. Using equivalent frame models, we capture the effects of both the diaphragm stiffness and the finite strength of wall-to-diaphragm connections on the seismic behaviour of unreinforced masonry buildings. To do this, we use a newly developed macro-element able to simulate both in-plane and out-of-plane behaviour of the masonry walls and non-linear springs to simulate wall-to-wall and wall-to-diaphragm connections. As an unretrofitted case study, we model a building on a shake table, which developed large in-plane and out-of-plane displacements. We then simulate three retrofit interventions: Retrofitted diaphragms, connections, and diaphragms and connections. We show that strengthening the diaphragm alone is ineffective when the friction capacity of the wall-to-diaphragm connection is exceeded. This also means that modelling an unstrengthened wall-to-diaphragm connection as having infinite stiffness and strength leads to unrealistic box-type behaviour. This is particularly important if the equivalent frame model should capture both global in-plane and local out-of-plane failure modes.

The Whittier Narrows, California Earthquake of October 1, 1987—Evaluation of Strengthened and Unstrengthened Unreinforced Masonry in Los Angeles City

1988 ◽  
Vol 4 (1) ◽  
pp. 157-180 ◽  
Author(s):  
K. Deppe
Keyword(s):  
Los Angeles ◽  
Unreinforced Masonry ◽  
Code Design ◽  
Masonry Buildings ◽  
Design Standards ◽  
Clear Cut ◽  
Low Probability ◽  
Observed Damage ◽  
Primary Basis ◽  
The City

On November 15, 1987, the City of Los Angeles' Earthquake Division, launched a study of the performance of its strengthened unreinforced masonry buildings during the Whittier Narrows Earthquake. The objective of the study was twofold: (1) To analyze the damage to unstrengthened as well as to strengthened and tension-anchored-only buildings, and from that analysis (2) to determine the most effective ways of improving the design standards for strengthening unreinforced masonry buildings. The initial part of that objective has been completed, and the findings of that study are the primary basis for this article. Observed damage demonstrated a clear-cut need to improve certain aspects of the Code design standards for strengthened buildings; more importantly, however, it sent out warning signals to owners of unstrengthened buildings and only to a slightly lesser extent to owners of tensioned-anchors-only buildings, of the very serious need to fully strengthen their buildings and to improve on the low probability of those buildings surviving a major earthquake. The second part of the study's objective will require additional work, and the combined effort of the City of Los Angeles and the SEAOSC.

Retrofitting Effect of Unreinforced Masonry Walls Using FRPs

2010 ◽  
Vol 452-453 ◽  
pp. 765-768 ◽  
Author(s):  
B.I. Bae ◽  
B.K. Park ◽  
Hyun Ki Choi ◽  
Chang Sik Choi
Keyword(s):  
Evaluation Method ◽  
Shear Walls ◽  
Shear Wall ◽  
Shear Behavior ◽  
Unreinforced Masonry ◽  
Seismic Retrofitting ◽  
Fiber Reinforced Polymers ◽  
Masonry Buildings ◽  
Plane Shear ◽  
Masonry Shear Wall

Unreinforced masonry buildings have significant portion of existing and historical buildings around the world. Recent earthquakes have shown the needs of seismic retrofitting for these types of buildings. There are many types of retrofitting materials for URM(unreinforced masonry buildings) such as shotcrete, ECC and FRPs. Many engineers use many types of fiber reinforced polymers because these types of material enhance the shear strength of wall without expansion of wall sectional area and additional weight of total structure. However, the complexity of mechanical behavior of masonry shear wall and the lack of experimental data of masonry wall which was retrofitted by FRPs may cause the problem that engineers hard to determine the retrofitting level. Determining and providing the information for retrofitting effect of FRPs for masonry shear wall, this paper investigate in-plane shear behavior of URM and retrofitted masonry shear walls using two types of different FRP materials. Specimens were designed to idealize the wall of low rise apartment which was built in 1970s Korea with no seismic reinforcements and have 1 aspect ratio. Retrofitting materials were carbon FRP and Hybrid sheet which have different elastic modulus and ultimate strain. Consequently, this study will evaluate the structural capacity of masonry shear wall and retrofitting effect of FRP sheet for in plane shear behavior comparing with evaluation method for reinforced concrete beam which was retrofitted by FRPs.

scholarly journals Some of the Latest Active Strengthening Techniques for Masonry Buildings: A Critical Analysis

2019 ◽  
Author(s):  
Elena Ferretti ◽  
Giovanni Pascale
Keyword(s):  
Stress Field ◽  
Bearing Capacity ◽  
Static Analysis ◽  
Dynamic Load ◽  
Critical Analysis ◽  
Masonry Buildings ◽  
Load Bearing Capacity ◽  
Plane Shear ◽  
Out Of Plane ◽  
Static Conditions

The present paper deals with the retrofitting of unreinforced masonry (URM) buildings, subjected to in-plane shear and out of-plane loading when struck by an earthquake. After an introductive comparison between some of the latest punctual and continuous active retrofitting methods, the authors focused on the two most effective active continuous techniques, the CAM system and the Φ system, which also improve the box-type behavior of buildings. These two retrofitting systems allow us to increase both the static and dynamic load-bearing capacity of masonry buildings. Nevertheless, information on how they actually modify the stress field in static conditions is lacking and sometimes questionable, in the literature. Therefore, we performed a static analysis in the plane of Mohr/Coulomb, with the dual intent to clarify which of the two is preferable under static conditions and whether the models currently used to design the retrofitting systems are fully adequate.

Performance of masonry structures during the 1994 Northridge (Los Angeles) earthquake

1995 ◽  
Vol 22 (2) ◽  
pp. 378-402 ◽  
Author(s):  
Michel Bruneau
Keyword(s):  
Los Angeles ◽  
Unreinforced Masonry ◽  
Masonry Building ◽  
Masonry Buildings ◽  
Masonry Structures ◽  
Northridge Earthquake ◽  
Seismic Evaluation ◽  
Masonry Construction ◽  
Reinforced Masonry ◽  
The Impact

The surface magnitude 6.8 Northridge earthquake which struck the Los Angeles area on January 17, 1994, damaged a large number of engineered buildings, of nearly all construction types. As earthquakes of at least similar strength are expected to occur in most of eastern and western Canada, the study of the effects of this earthquake is of particular significance to Canada. This paper, as part of a concerted multi-paper reporting effort, concentrates on the damage suffered by masonry buildings during this earthquake, and explains why the various types of observed failures occurred. The seismic performance of all masonry construction similar to that commonly found in Canada is reviewed, but a particular emphasis is placed on providing an overview of damage to unreinforced masonry structures which had been rehabilitated before this earthquake. To provide a better appreciation of the impact of this earthquake on masonry buildings, and a better assessment of the engineering significance of their damage in a Canadian perspective, this paper first reviews the evolution of building code requirements for unreinforced masonry buildings up to the seismic retrofit ordinances enacted prior to this earthquake. Examples of various damage types, as observed by the author during his reconnaissance visit to the stricken area, are then presented, along with technically substantiated descriptions of the causes for this damage, and cross-references to relevant clauses from Canadian standards and codes, as well as the recently published Canadian Guidelines for the Seismic Evaluation of Existing Buildings, whenever appropriate. Key words: earthquake, unreinforced masonry, seismic rehabilitation, retrofit, retrofitted masonry building, reinforced masonry, buildings, failure, collapse, heritage buildings.

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